The present invention relates to keyboards for electronic apparatuses
such as hand held calculators, electronic learning aids and hand held electronic
games. Construction of apparatuses of this type was disclosed in U.S. Patent No.
3,819,921 "Miniature Electronic Calculator" issued to Jack S. Kilby, Jerry D.
Merryman and James H. Van Tassel on June 25, 1974. This patent discloses a hand
held calculator including a keyboard input means, a visual display device and an
integrated semiconductor circuit array located in substantially one plane including
memory for storing entered digits, an arithmetic unit for performing calculations
and a control unit controlling the transfer of data from the memory to the arithmetic
unit and back to the memory.
Since the innovation described in U.S. Patent No. 3,819,921 major
improvements in the computational ability and reductions in the cost of such apparatuses
have been achieved. Heretofore such advances in the art of manufacture of miniature
electronic apparatuses have come about due to improvements in the semiconductor
art, specifically improvements in the complexity and reductions in the cost of
integrated circuit semiconductor devices which form the primary electrical component
of such apparatuses. Such innovations are exemplified by U.S. Patent No. 4,074,351
"Variable Function Programmed Calculator" issued to Gary W. Boone and Michael J.
Cochran on February 14, 1978, which discloses an improved integrated circuit such
as employed in apparatuses of this type. U.S. Patent No. 4,326,265 "Variable Function
Programmed Calculator" issued to Gary W. Boone on April 20, 1982 dis closes an
electronic system which advantageously employs the integrated circuit taught in
U.S. Patent No. 4,074,351.
The improvements in the semiconductor integrated circuit exemplified
by the above cited patents have resulted in revolutionary improvements in apparatuses
of this type. However, further improvements in semiconductor electronic technology
presently yield decreasing benefits in the complexity and cost of such apparatuses,
particularly in the field of low cost apparatuses. As a result, further decreases
in cost will now become more dependent upon improvements in the manufacture of
these apparatuses. This is because improvements in integrated circuit technology
have proceeded at such a rapid pace that this area of the apparatus assumes a
decreasing proportion of the total cost of manufacture. Thus improvements in the
manufacture of such apparatuses assume a corresponding increasing importance in
the total cost of such an electronic apparatus.
In the article entitled "Subassembly with parts, interconnects shaves
cost of hand-held calculators", published in Electronics July 7, 1977 pages 42
and 44, there is described a hand-held calculator in which the interconnection
wiring, the resistors and the keyboard contacts are printed on a flexible insulating
substrate and the terminals of a calculator integrated circuit are connected to
the wiring elements by pressure applied by clamping so that soldering is not required.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a keyboard for
an electronic apparatus, the keyboard including few piece parts and being specifically
adapted for substantially automated assembly.
According to the present invention there is provided a keyboard structure
for an electronic apparatus comprising:
BRIEF DESCRIPTION OF THE DRAWINGS
a body of non-conductive material providing a keyboard surface;
an electrically conductive contact provided at a plurality of key switch positions
on said body of non-conductivity material;
a keyboard sheet of non-conductive material having opposing first and second surfaces,
said first surface being disposed adjacent to and substantially covering said
an interconnection pattern including a plurality of electrical conductors disposed
on said first surface of said keyboard sheet facing said keyboard surface and
arranged to provide a pair of electrical conductors in proximity at each of said
key switch positions and said keyboard sheet including a plurality of keys respectively
corresponding to a pair of electrical conductors on said interconnection pattern
in proximity at each of said key switch positions such that actuation of a particular
key on said keyboard sheet causes a respective pair of electrical conductors corresponding
to a particular key switch position to be moved into engagement with said electrically
conductive contact on said non-conductive keyboard surface to provide an electrical
connection between said respective pair of conductors via said conductive contact
at the selected key switch position; provided with a plurality of spaced depressions
formed therein to extend partially through the thickness thereof, said spaced
depressions opening onto said keyboard surface and respectively located at corresponding
key switch positions;
each of said electrically conductive contacts being disposed at the bottom of respective
depressions within said body of non-conductive material;
said keyboard sheet comprising a flexible membrane of non-conductive material;
said flexible membrane flexing in a direction toward said keyboard surface of said
body to move a respective pair of electrical conductors corresponding to a particular
key switch position into engagement with said conductive contact disposed at the
bottom of the depression located at the respective key switch position in response
to pressure on said second surface of said flexible membrane selectively applied
at said particular key switch position in providing the electrical connection between
said respective pair of conductors via said conductive contact at the selected
key switch position.
The present invention will be better understood from the following
description of embodiments of the electronic apparatus taken in conjunction with
the drawings in which:
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
- FIGURE 1 is an exploded view of the major components of one embodiment of the
- FIGURE 2 illustrates a preferred embodiment of a first conductive pattern;
- FIGURE 3 illustrates the insulative pattern corresponding to the first conductive
pattern illustrated in FIGURE 1;
- FIGURE 4 illustrates the second conductive pattern or jumper pattern used in
conjunction with the embodiments illustrated in FIGURES 2 and 3;
- FIGURE 5 illustrates a preferred embodiment of the manner in which an integrated
circuit is coupled to the interconnection pattern;
- FIGURE 6 illustrates a preferred embodiment of the placement of the conductive
adhesive on the connector portion of the interconnection pattern;
- FIGURE 7 illustrates an alternative embodiment for connection of an integrated
circuit to the interconnection pattern;
- FIGURE 8 illustrates the preferred embodiment for connection of a liquid crystal
display device to the interconnection pattern;
- FIGURE 9 illustrates an alternative embodiment of the connection of an integrated
circuit to the interconnection pattern employing a conductive elastomeric interface;
- FIGURE 10 illustrates a preferred embodiment of the manner in which a pair
of batteries are coupled to the interconnection pattern;
- FIGURE 11 illustrates the detail of a spring employed for connection of batteries
to the interconnection pattern;
- FIGURE 12 illustrates a preferred embodiment of a key in the nondepressed or
- FIGURE 13 illustrates the preferred embodiment of a key in the depressed or
- FIGURE 14 illustrates an electronic schematic diagram of a preferred embodiment
of the apparatus;
- FIGURE 15 illustrates an alternative embodiment for connection of an integrated
circuit to the connector portion of the interconnection pattern;
- FIGURE 16 illustrates the connection of a photovoltaic to the interconnection
- FIGURE 17 illustrates an embodiment of the first interconnection pattern disposed
on the first surface of the flexible membrane
- FIGURE 18 illustrates the pattern of insulated layers disposed on first side
of the flexible sheet;
- FIGURE 19 illustrates the pattern of the second or jumper interconnection pattern
disposed on the first surface of the flexible sheet;
- FIGURE 20 illustrates an embodiment of the front portion of the exterior case
of an electronic apparatus;
- FIGURE 21 illustrates a cross-section of the single sheet membrane keyboard.
FIGURE 1 is an exploded view of the major components of an electronic
apparatus. The electronic apparatus 10 includes bottom case 11, having a conductive
interconnection pattern 12 imprinted thereon, a top case 13 and a battery door
Major electrical components of the electronic apparatus are attached
to bottom case 11. These electrical components include integrated circuit 15, display
device 16 and a power source comprising a pair of batteries 17. These major components
are interconnected in the proper manner via the interconnection pattern 12 printed
on the bottom case 11.
The last major component of the electronic apparatus is keyboard
18. Keyboard 18 comprises a keyboard sheet having a plurality of keys. These keys
are disposed in substantial alignment with key switch portions of inter-connection
pattern 12 (further disclosed below) and also in registration with key holes disposed
within top case 13.
Construction of the electronic apparatus 10 is achieved via a few
simple steps. Bottom case 11 is formed including the conductive interconnection
pattern. 12. The major components, including an integrated circuit, a display
device and batteries, are attached to the bottom case. Keyboard sheet 18 is sandwiched
between the proper key switch areas within conductive interconnection pattern
12 and the key holes of top case 13 as bottom case 11 and top case 13 are joined
together. Battery door 14 is inserted within top case 13 thereby properly aligning
and connecting batteries 17.
FIGURE 2 illustrates a preferred embodiment of a first conductive
pattern. The interconnection pattern 12 imprinted on bottom case 11 includes a
plurality of crossover portions. In this embodiment bottom case 11 must be constructed
of nonconducting material. Each of these crossover portions requires one conductor
to cross without electrically joining another conductor. In order to achieve such
a crossover, it is necessary to provide two conductive patterns and one insulative
pattern within the interconnection pattern 12. FIGURE 2 illustrates the first
conductive pattern in such a system.
FIGURE 2 illustrates the first conductive pattern of interconnection
pattern 12. This first conductive pattern includes substantially all of the primary
interconnections with the exception of a number of jumpers in crossover positions
within the interconnection pattern 12. Interconnection pattern 12 includes sets
of connection conductors 21, 22 and 23 which are especially adapted for connect
ion to major components of the electronic apparatus. Connection conductors 21,
which are illustrated as including 28 conductors disposed in two rows of 14, are
especially adapted for connection to an integrated circuit semiconductor device.
Connection conductors 21 are disposed in a position for registration with the
external leads of a 28 pin dual in line package integrated circuit. FIGURE 2 also
illustrates connect ion conductors 22, which are especially adapted for connection
to the display device. For example, the display device may comprise an eight digit
liquid crystal display having seven segments for each digit as well as a decimal
point. In addition a memory input indicator and a negative sign indicator may
also be provided, making a total of 66 display segments. If these are accessed
via a one third duty cycle drive method using 3 common lines and 26 select lines
then a total of 29 connections is required. Connection conductors 22 illustrated
in FIGURE 2 include 29 conductors disposed along one edge of the position for the
display device. Lastly, interconnection pattern 12 includes connection conductors
23 which are specifically adapted for connection to the terminals of a pair of
batteries employed as the power source of the apparatus.
Interconnection 12 illustrated in FIGURE 2 includes a plurality of
kew switch positions 24. These key switch positions 24 are disposed in a matrix
having six rows and four columns. Each key switch position 24 has a pair of conductors
25 and 26. The conductor 25 of each key switch position 24 is connected to a row
conductor. The conductor 26 of each key switch position 24 is connected to a column
conductor. These conductors 25 and 26 are disposed in an interleaved comb pattern
whose purpose will be further described below.
In addition to the ordinary key switch positions 24 illustrated in
FIGURE 2, FIGURE 2 further illustrates two special key switch positions 27 and
28. In accordance with the teachings of U.S. Patent No. 4,115,705 "Electronic
Calculator with Push-Button On-Off System" issued to David J. McElroy September
19, 1978, the preferred embodiment of the electronic apparatus of the present
invention includes momentary contact on and off switches. In accordance with the
teachings of the above cited patent, key switch portions 27 and 28 (together with
the other key switches 24 in the left most column) have one of the conductors
connected to one terminal of the power supply, that is one of the two connection
conductors 23 provided for connection to the pair of batteries. The other conductor
of key switch portions 27 and 28 are connected to the column conductors in the
manner of the other key switch positions 24. In accordance with the teachings
of the above cited patent, the integrated circuit of the present apparatus is provided
with a latch circuit having two stable conditions. Actuation of the key corresponding
to key switch position 27 insures that the latch places the integrated circuit
in the on condition. Actuation of the key corresponding to key switch positin
28 insures that the latch places the integrated circuit in the off state.
FIGURE 2 further illustrates concentric alignment patterns 32. Concentric
alignment patterns 32 are employed in conjunction with similar concentric alignment
patterns illustrated in FIGURES 3 and 4 as alignment gauges for the completed
pattern. When the three layer interconnection pattern is complete concentric alignment
patterns 32, 33 (illustrated in FIGURE 3) and 34 (illustrated in FIGURE 4) form
a set of concentric circles, if the three printed layers were properly aligned.
Because of the concentric circle pattern, it is very easy to distinguish misaligned
patterns and reject a part having such a misaligned pattern.
FIGURE 3 illustrates the insulative pattern; The insulative pattern
includes a plurality of insulators 35 which are disposed at predetermined crossover
positions on the bottom case 11. Each of the insulators 35 is disposed to overlie
and cover a small portion of the first conductive pattern illustrated in FIGURE
2. The insulative pattern also includes concentric alignment patterns 33.
FIGURE 4 illustrates the second conductive pattern or jumper pattern.
The second conductive pattern includes a plurality of conductors 40. Each of these
conductors 40 is disposed in a position to over lie the previously transferred
insulators 35 illustrated in FIGURE 3. In addition, each of these conductors 40
extends beyond the ends of its corresponding insulator 35 to contact selected
portions of the first conductive pattern illustrated in FIGURE 2. Using this technique
the conductor 40 electrically connects to separate conductors of the first conductive
pattern illustrated in FIGURE 2 while being insulated from a crossing conductor
by virtue of the insulator 35. Thus this technique enables the contruction of
an interconnection pattern 12 which is more complex than would be possible if such
crossovers were not permitted. The second conductive pattern also includes concentric
alignment pattern 34.
The three patterns illustrated in FIGURES 2, 3 and 4 are preferrably
formed on the bottom case 11 via a pad transfer printing process. Initially the
image to be transferred is etched into a steel cliche plate. Thus for example
the image of the first conductive pattern illustrated in FIGURE 2 would be etched
into a first cliche plate. This cliche plate is preferrably made of milled and
hardened steel to permit long life. The depth of this etch is directly proportional
to the amount of ink to be transferred from the cliche plate to the work piece,
which is bottom case 11 in the preferred embodiment.
Once the cliche plates have been formed for the desired printed images,
these cliche plates are placed upon an automatic printing apparatus which carries
out the printing process. An ink reservoir is placed along one end of the cliche
plate in a cliche holder assembly. This ink reservoir stores the particular ink
to be employed in image of that particular plate. Firstly, a spatula blade is
withdrawn from the ink reservoir and carries a thick layer of ink over the cliche
plate. As the arm carrying the spatula is returned a thinner doctor blade wipes
the cliche plate clean of ink except for the ink now stored within the etched
portion of the plate. This etched portion of the plate has the image desired to
be transferred to the work piece.
Next a soft silicon rubber transfer pad is pressed down and compressed
over the cliche plate in the vicinity of the image etch. As the pad is withdrawn
substantially all of the ink previously stored in the etched image of the cliche
plate now adheres to the surface of the pad. Lastly, the pad is moved to the position
of the work piece and is pressed down and compresses over the work piece. When
the pad is withdrawn from the work piece substantially all of the ink previously
held by the pad is now transferred to the surface of the work piece.
The ability to control the transfer of ink from the cliche plate
to the pad to the work piece depends upon the relative adhesion of the ink to these
surfaces. A steel cliche plate is ordinarily employed to insure that substantially
all of the ink is removed from the etched image during the initial step. The particular
composition of the silicon rubber pad is then selected in order to insure substantial
removal of the ink from the etched image and also substantial transfer of this
ink to the work piece.
In a typical practical machine which performs this printing process
a single arm is employed for both the spatula and wiper blade and the transfer
pad. Thus as the pad is withdrawn from the cliche plate and transferred to the
site of the work piece, this arm also causes the spatula to transfer the ink to
the cliche plate for the next printing. Upon removal of the pad from the work
piece and withdrawal to the image on the cliche plate, the doctor blade also passes
across the surface of the cliche plate to clean all of the ink except that stored
within the etched portion. Thus the cliche plate is then ready for transfer of
the next image. In addition, a practical printing machine of the type described
will most often also include some form of automated work piece movement, so that
a new work piece is presented at the printing site each time the pad is prepared
for transfer of ink.
As will be clearly understood from a study of the above description
in relation to FIGURES 2, 3 and 4, each bottom case 11 must undergo three separate
printing processes as described above. The first conductive pattern illustrated
in FIGURE 2 is transferred to the bottom case 11 followed by transfer of the insulative
pattern illustrated in FIGURE 3 and lastly the second conductive illustrated in
FIGURE 4 is transferred. The transfer printing process described above can be readily
adapted to such a three step transfer printing process. This is easily achieved
by providing three separate cliche plates with separate etches for each of the
three patterns or one single cliche plate with three separate etched areas each
corresponding to one of the patterns. Each separate cliche plate or etched area
would employ its own ink reservoir having the proper ink for that particular pattern.
The apparatus would be provided with three separate arms each having a spatula
and doctor blade for properly applying the ink to the corresponding etched pattern
and each having its own silicon rubber transfer pad for transfer of the ink of
that particular pattern.
In a preferred embodiment, three separate work pieces would be employed
simultaneously, one for each of the three separate patterns. A conductive ink would
be transferred on to a first work piece according to the pattern illustrated in
FIGURE 2, an insulative ink would be transferred on to a separate work piece in
accordance with the pattern illustrated in FIGURE 3 and conductive ink would be
transferred on to a third work piece in accordance with the pattern illustrated
in FIGURE 4.
Upon withdrawal of the printing arms the work pieces would be transferred
one station. This would place a new work piece at the station for receiving the
first conductive pattern. In addition the work piece previously receiving the
first conductive pattern would be placed in the center station to receive the insulative
pattern. Lastly, the work piece which had just received the insulative pattern
would be placed in the third work station in order to receive the second conductive
pattern. The work piece which had previously received the second conductive pattern
would be transferred out of the printing area as this work piece is complete.
As noted above the preferred embodiment for forming the interconnection
pattern involves a pad transfer printing process. This process is advantageous
in that it can readily accomodate surface irregularities in the work piece. For
example, as noted below, the integrated circuit may be mounted in a depression
29 in bottom case 11 and the above described pad transfer printing process would
enable easy formation of conductors between connection conductors 21 as shown in
FIGURE 2 despite the presence of depression 29. However, if accomodation to surface
irregularities is not required the patterns illustrated in FIGURES 2, 3 and 4 may
be produced by other known methods such as silk-screening.
The ink employed in this interconnection pattern manufacture technique
are of two types, solvent inks and ultraviolent light cured inks. In the case of
solvent inks a preferred conductive ink is Dupont 4198. Dupont 4198 uses silver
as its primary conductor and comprises approximately 70% silver suspended in butyl
cellusolve acetate. After transfer of the ink to the work piece, the ink would
cure by evaporation leaving the silver conductor behind. This solvent conductive
ink could be employed for both the first conductive pattern and the second conductive
pattern. A preferrable insulative ink is solder mask type LA from Weiderhold.
This insulative ink is also of the solvent cure type.
Solvent inks of the type described above are constantly deteriorating
due to premature curing prior to application to the work piece. The solvent in
subsequent layers of solvent ink causes previously formed layers, even if fully
cured, to deteriorate. Thus solvent inks are less desirable from a reliability
standpoint than ultraviolent light cured inks. Ultraviolent light cured inks are
formed of monomer molecules. Upon exposure to ultraviolent light of a proper wave
length, intensity and duration, these monomers are formed into polymers which
substantially fixes the ink pattern on to the work piece. A preferrable ultraviolent
light conductor ink is Methode 6065E. Two preferrable insulator inks are Unimask
2000 and SPR-WE-7, both available from W. R. Grace. A preferrable manufacturing
method when ultraviolent inks are employed would include an ultraviolent light
source to cure the transferred patterns during the period while the work pieces
are advanced to the next work station.
After the three layer interconnection pattern is formed as described
above, it is preferrable that the pattern be tested to determine if they are properly
formed. A visual test employing concentric interconnection patterns 32, 33 and
34 has been detailed above. It is preferrable that an electrical test also be
performed. This may be achieved as an additional step following the three step
printing process. An electrical probe is lowered to the completed bottom case having
multiple probe tips contacting the conductive pattern at predetermined locations.
It is possible using such an apparatus to rapidly test each crossover for proper
electrical conduction through each of the jumpers illustrated in FIGURE 4 and
for proper insulation by each of the insulators illustrated in FIGURE 3. This automated
electrical test preferrably includes some technique for separating out the rejected
bottom case automatically so that only properly constructed bottom cases are employed
in the final assembly process.
FIGURE 5 illustrates a preferred embodiment for attachment of the
integrated circuit 15 to the bottom case 11. Integrated circuit 15 forms the major
electrical component of the electronic apparatus of the present invention. As
illustrated in FIGURE 2, the interconnection pattern printed on bottom case 11
includes a first set of connection conductors 21 for attachment to the leads of
the integrated circuit 15. This connection is shown in cross section in FIGURE
FIGURE 5 illustrates the details of the attachment of integrated
circuit 15 to the first set of connector conductors 21 of the interconnection pattern.
FIGURE 5 illustrates depression 29 within bottom case 11. Depression 29 is formed
to substantially conform to the shape of integrated circuit 15. FIGURE 5 illustrates
a cross sectional view of one side of a particular integrated circuit in a dual
in line plastic package. Integrated circuit 15 includes leads 51 which protrude
from the ends of the plastic package. Most dual in line integrated circuits are
sold with the leads bent for easier insertion into a printed circuit board, however
FIGURE 5 illustrates that lead 51 of integrated circuit 15 is straight and unbent.
By careful matching of the known dimensions of the plastic case of integrated circuit
15 with the dimensions of depression 29 a small gap of known dimensions between
lead 51 of integrated circuit 15 and conductor 21 printed upon bottom case 11 is
formed. This small gap is filled by a conductive adhesive 52, which is illustrated
in FIGURE 5 as adhering to both lead 51 and conductor 21. In addition, in a preferred
embodiment, the plastic case of integrated 15 is attached to the bottom of depression
29 by some other type of adhesive which serves as the major mechanical connection
between integrated circuit 15 and bottom case 11. Many commercially available
adhesives are suitable for this purpose and will not be described further.
FIGURE 6 illustrates the manner in which the conductive adhesive
52 is placed between the conductors of the integrated circuit and the interconnection
pattern. FIGURE 6 illustrates a portion of bottom case 11 near depression 29,
which is especially adapted for holding the integrated circuit 15. Along the edge
of depression 29 are a plurality of conductors 21. Each of these conductors 21
forms a part of the interconnection pattern printed on bottom case 11. A small
portion of conductive adhesive 52 is shown as placed at a predetermined spot on
each of the conductors 21 near the edge of depression 29. These small portions
of conductive adhesive 52 may be properly placed by a silk screen process or a
mask printing technique. By properly placing a carefully controlled amount of
conductive adhesive on conductors 21, it is possible to substantially fill the
predetermined gap between connectors 21 and lead 51 while minimizing the possibility
of shorts between adjacent connectors 21.
The above described embodiment for connecting integrated circuit
15 to the interconnection pattern 12 substantially reduces alignment problems.
By proper correspondence of depression 29 to the known dimensions of the plastic
case of integrated circuit 15 it is possible to constrain the possible positions
of leads 51 so that they invaribly correspond to the proper conductors 21. Thus
integrated circuit 15 could be hand placed within depression 28 of bottom case
11 or could be placed via automated machinery without requiring extremely close
tolerances in the placement of the integrated circuit.
FIGURE 7 illustrates a cross sectional view of an alternative embodiment
for attachment of integrated circuit 15 to the conductors 21. In accordance with
the more normal practice, FIGURE 7 illustrates integrated circuit 15 having a
bent lead 51. FIGURE 7 illustrates that integrated circuit 15 is placed upon bottom
case 11 in a position so that leads 51 are substantially aligned with the corresponding
connection portion 21. As illustrated in FIGURE 5, FIGURE 7 shows conductive adhesive
52 placed between lead 51 and conductor 21. As described above in conjunction with
FIGURE 5, it is preferrable to include some form of mechanical adhesive between
the plastic case of integrated circuit 15 and back case 11 to provide the major
mechanical hold between these components. As an alternative, the major mechanical
hold upon the integrated circuit may be achieved via a pressure fit between bottom
case 11 and top case 13, perhaps employing a post such as post 94 illustrated in
FIGURE 14. Therefore, the major task performed by conductive adhesive 52 is electrical
connection between the integrated circuit and the interconnection pattern.
FIGURE 8 illustrates a cross sectional view of a preferred embodiment
for attachment of a display device to interconnection pattern 12. Display device
16 is preferrably a liquid crystal display device. Display device 16 includes
front glass plate 61 and back glass plate 62. Sandwiched between these two glass
plates is a cavity 63 which includes the major components of the liquid crystal
display including the electrodes and the liquid crystal chambers. In the cross
section illustrated in FIGURE 8, electrode 64 is shown as adhering to one surface
of glass plate 61 and emerging from chamber 63. It should also be noted that the
upper glass plate 61 extends beyond the edge of the lower glass plate 62.
Bottom case 11 includes depression 30 constructed in order to accommodate
the display device 16. Depression 30 is constructed of a depth compared to the
known dimensions of display device 16 so that, when display device 16 is placed
within depression 30, there is a predetermined gap between electrode 64 and conductor
22 deposited on bottom case 11. As described above in conjunction with the attachment
of integrated circuit 15 to bottom case 11, a conductive adhesive 65 is disposed
between the electrode 64 of the display device 16 and the conductor 22 disposed
on bottom case 11. The conductive adhesive 65 may be initially placed on conductor
22 in the same manner as illustrated in FIGURE 6 and described above. In addition,
in the manner described above in conjunction with attachment of integrated circuit
15, it is preferrable that another adhesive is employed to attach back plate 62
of display device 16 to the bottom of depression 30. By this manner, the major
mechanical stress is taken by this mechanical adhesive and the major task fulfilled
by conductive adhesive 65 is electrical connection of display device 16 to the
interconnection pattern 12. As noted above in relation to mechanical support of
the integrated circuit, as an alternative major mechanical support of display
device may be provided by a press fit between bottom case 11 and top case 13.
In an alternative embodiment, the conductive adhesive employed for
electrical connection of the integrated circuit or the display device may be replaced
by a conductive elastomeric interface. A conductive elastomeric interface is made
of alternating conductive and nonconductive layers of a flexible, elastic material.
The integrated circuit or display device may be coupled to the corresponding connection
conductors using such a conductive elastomeric interface having vertical layers.
These vertical layers have a size which is less than the minimum spacing between
the connection conductors or the leads of the electrical component. Preferrably
the layers are sized so that a plurality of the conductive layers can be fitted
into the width of one connection conductor or component lead.
FIGURE 9 illustrated the positioning of such a conductive elastomeric
interface 70 between leads 51 and connection conductors 21 mounted on bottom case
11. Conductive elastomeric interface 70 includes conductive layers 71A, 71B, 71C,
71D and 71E sandwiched between insulative layers 72A, 72B, 72C, 72D and 72E. The
leftmost lead 51 is electrically connected to the leftmost connection conductor
21 via conductive layers 71A and 71B. Similarly the rightmost lead 51 and the rightmost
connection conductor 21 are electrically connected via conductive layers 71D and
71E. These connections are insulated from one another by insulative layers 72B
and 72C. Because the distance between adjacent leads 51 and connection conductors
21 is greater than the width of a conductive layer, there is no possibility of
shorting adjacent connections. The layer width has been selected relative to the
width of leads 51 and connection conductors 21 so that at least one and often two
conductive layers will make the electrical connection. So long as leads 51 and
connection conductors 21 are substantially aligned, proper connections are formed
no matter what the alignment of conductive elastomeric interface 70. Conductive
elastomeric interface 70 is held in place by mechanical force provided by the mechanical
adhesive or the pressure fit used to secure the electrical component.
FIGURE 10 illustrates a cross sectional view of the manner of attachment
of batteries 17 to the apparatus. FIGURE 10 illustrates bottom case 11, top case
13, battery door 14 and a pair of battery cells 17. Each of the battery cells
17 is disposed on and placed in electrical contact with one of the conductor 23
(see FIGURE 2). Conductors 23 serve as the means for connecting the power source
represented by battery 17 to the circuit of the electronic apparatus.
Battery door 14 preferrably includes a post 91 disposed on the interior
surface thereof. A steel spring 92 is preferrably disposed on the interior surface
of battery door 14 in contact with post 91. Post 91 serves as a tie point for
securing spring 92 to the interior surface of battery door 14. As illustrated in
FIGURE 10, spring 92 preferrably contacts one end of each of the batteries 17.
Spring 92 thus performs two functions. Firstly, it provides electrical connection
between one terminal of each of the batteries 17, thereby connecting these batteries
in series across the two conductors 23. In addition, steel spring 92 is preferrably
constructed in order to provide some mechanical force pressing battery 17 into
the conductors 23. This mechanical force is advantageous in assuring proper electrical
contact of the batteries 17 in series across conductors 23. Additionally, steel
springs 95 may be disposed between each battery 17 and its corresponding connection
conductor 23. Steel springs 95 supply additional mechanical force for retaining
batteries 17, and further supply some mechanical compliance enabling batteries
17 to move during mechanical shock and recover with proper electrical connection.
Steel springs 95 are preferrably formed of stamped sheet metal as illustrated in
FIGURE 11 and are connected to connection conductors 23 via conductive adhesive.
Alternately, if addition shock absorption capacity is not required, batteries 17
may be directly connected to connection conductors via conductive adhesive.
In the preferred embodiment battery door 14 has lips which slide
in grooves within top case 13 in order to secure battery door 14 in top case 13.
Spring 92 and 95 preferrably are compressed during this operation, thereby generating
the above described force and also tending to hold battery door 14 in place.
FIGURE 10 illustrates additional features which tend to secure batteries
17 from lateral motion. Firstly, the right most battery 17 is prevented from extreme
motion to the right via the end portion of top case 13 which forms the side of
the electronic apparatus. In addition, the left most battery 17 is restrained from
movement to the left via post 93 formed in top case 13. Post 93 is illustrated
as extending from top case 13 and resting within depression 31 within bottom case
11. Bottom case 11 has a plurality of depressions 31 which are disposed in position
corresponding to post 93 of top case 13. This combination of post 93 and depression
31 enables substantial mechanical contact between bottom case 11 and top case
13. This substantial mechanical contact greatly facilitates the mechanical connection
of bottom case 11 to top case 13. One or more post 93 with corresponding depressions
31 may be disposed in positions adjacent to the positions of batteries 17 in order
to restrain lateral movement of batteries 17.
FIGURES 12 and 13 illustrate the operation of one key of the keyboard
sheet 18. FIGURE 12 illustrates the key in the nondepressed, inactuated state and
FIGURE 13 illustrates the key in the depressed, actuated state.
Keyboard sheet 18 includes a plurality of key tops 101 which are
disposed within the interior of the electronic apparatus and extend through key
apertures within top case 13. Each key top 101 has a corresponding major plate
102 which lies beneath the aperture through top case 13 and substantially restrains
additional vertical movement through the aperture. Each key includes a flexible
portion 103 around the periphery of major plate 102 for attachment of the particular
key to keyboard sheet 18. Flexible portion 103 includes a reduced cross sectional
dimension which permits substantial flexure in the vertical direction when pressure
is applied to the top of key top 101. At the bottom of major plate 102 is a conductive
portion 104 which is constructed of a conductive material and which is disposed
in alignment with each of the key switch areas 24, 27 and 28 illustrated in FIGURE
The ordinary operation of each key is as follows. The flexible portion
103 urges the major plate 102 upward toward the aperture within top case 13. This
causes key top 101 to be fully extended and more importantly prevents conductive
portion 104 from contact with the particular key switch position below. Upon application
of vertical pressure to key top 101, flexible portion 103 is strained until it
undergoes a folding state as illustrated in FIGURE 13. Upon achievement of the
folding state, key top 101 as well as major plate 102 and conductive portion 104
are forced downward until conductive portion 104 contacts the pair of conductors
25 and 26 of the corresponding key switch position 24, 27 or 28. This contact causes
electrical conduction between conductors 25 and 26. Note that conductors 25 and
26 are formed in an interleaved comb pattern in order to assure a greater reliability
in switch closure by creating a longer periphery where conductors 25 and 26 are
adjacent. This electrical conduction is sensed by integrated circuit 15 as a key
switch closure. In accordance with the construction of integrated circuit 15,
this key switch closure is interpreted as entry of data or commands.
During this time the flexible portion 103 is under considerable stress
and resists this stress with upward pressure upon major plate 102. Release of the
vertical pressure on key top 101 causes flexible portion 103 to urge major plate
102 upward towards its rest position. As a result, conductive portion 104 is no
longer placed in contact with the pair of conductors 25 and 26, thereby breaking
the electrical connection.
The sudden switch between the substantially flat state of flexible
portion 103 illustrated in FIGURE 12 to the folded or warped state illustrated
in FIGURE 13, generates a substantial positive feel to the finger employed for
depression of key top 101. This keyboard feel enables feedback to the operator
that the key switch has been depressed.
FIGURE 14 illustrates an electrical schematic diagram of a preferred
embodiment of the electronic apparatus constructed in accordance with the present
invention. Note that the schematic diagram illustrated in FIGURE 14 is embodied
in the three patterns forming the interconnection pattern illustrated in FIGURES
2, 3 and 4.
FIGURE 14 illustrates electronic apparatus 10. Electronic apparatus
10 includes integrated circuit 15, display device 16, power supply 17 and a keyboard
110 including keys 24, 27 and 28. Integrated circuit 15 is illustrated as including
28 pins. In accordance with the teachings of U. S. Patent No. 4,242,657 "Display
and Keyboard Scanning for Electronic Calculator or the Like" issued to Gary W.
Boone and Michael J. Cochran on December 30, 1980, integrated circuit 15 includes
a combined display and keyboard scan. One set of pins from integrated circuit
15 are attached directly to display device 16. Display device 16 is illustrated
as including eight seven-segment digits with decimal points with the addition
of a memory indicator and a negative sign indicator. FIGURE 14 illustrates another
set of terminals from integrated circuit 15 are applied to the column conductors
of the keyboard 110. A third set of terminals from integrated circuit 15 are applied
in parallel to terminals of display device 16 and to the row conductors of keyboard
110. This circuit permits integrated circuit 15 to generate combined keyboard and
display scan signals on the common lines for application to both keyboard 110
and display device 116. Actuation of any key from keyboard 110 is recognized by
sensing the voltage on the keyboard column conductors. The lines from integrated
circuit 15 which are applied directly to display device 16 provide display information
in conjunction with the scan signals for generating the desired visual display.
The combined system illustrated in FIGURE 14 is constructed in accordance with
the teachings of U. S. Patent 4,326,265 "Variable Function Programed Calculator"
issued to Gary W. Boone on April 20, 1982.
In some cases it is necessary to depart from the circuit illustrated
in FIGURE 14 by provision of one or more discrete components external to integrated
circuit 15. For example, it may desirable to substitute a photovoltaic cell power
supply for the batteries 17 illustrated in FIGURE 14. In such a case it is easy
to provide a photovoltaic cell sufficiently large to generate the average power
required by the integrated circuit. However, in some instances the peak power
required by the integrated circuit will exceed the power which can be generated
by a reasonably sized photovoltaic cell. In such a case it is desirable to provide
a capacitor external to the integrated circuit to store charge and thereby smooth
out the power requirements of the system and permit it to be powered by a photovoltaic
cell. In such a case it is necessary to provide a means for attachment of this
discrete component external to the integrated circuit device.
FIGURE 15 illustrates a preferred embodiment of the manner of connecting
an integrated circuit and an external discrete component to the interconnection
pattern 12 printed on bottom case 11. This technique includes the use of a small
printed circuit board 58 to hold both the integrated circuit 15 and the discrete
FIGURE 15 illustrates an embodiment of integrated circuit 15 formed
in a flat pack case. The cross sectional view of FIGURE 15 shows lead 51 emerging
from one end of integrated circuit 15 which passes through an aperture in printed
circuit board 58. The lower surface of printed circuit board 58 includes a conductive
printed pattern 53 constructed in a conventional manner. Integrated circuit lead
51 is electrically coupled to interconnection pattern 53 via solder 57 in accordance
with known techniques.
FIGURE 15 also illustrates external component 56, which may be a
disk capacitor, mounted on printed circuit board 58. Capacitor 56 includes leads
54 which pass through apertures within the printed circuit board 58. These leads
54 are coupled to portions of interconnection pattern 53 via solder 57 in the same
manner as attachment of the intergrated circuit leads 51. Although capacitor 56
is illustrated as mounted on the reverse side of printed circuit board 58 from
the integrated circuit 15, these components may be mounted on the same side depending
upon the clearance afforded by depression 29.
FIGURE 15 illustrates bottom case 11 having depression 29 for mounting
the combined structure attached to printed circuit board 58. Depression 29 has
a depth so that integrated circuit 15 may be adhered to the bottom of depression
15 while providing a predetermined gap between interconnection pattern 53 mounted
on the bottom side of printed circuit board 58 and conductor 22 of interconnection
pattern 12 mounted on the top surface of bottom case 11. As in the case of mounting
the dual in line package integrated circuit 15, a suitable mechanical adhesive
is employed to attach integrated circuit 15 to an appropriate position in depression
24. A small amount of conductive adhesive 52, deposited in the same manner as
illustrated in FIGURE 6, serves to electrically couple the predetermined lines
of interconnection pattern 53 and conductors 22. As noted above with respect to
other components, the printed circuit board 58 may be secured via a pressure fit
and connected via a conductive elastomeric interface as alternative embodiments.
FIGURE 16 illustrates a preferred embodiment of the manner of mounting
a photovoltaic cell within the electronic apparatus. FIGURE 16 illustrates bottom
case 11, top case 13 and photovoltaic cell 19.
Photovoltaic cell 19 includes a photovoltaic layer 111 which includes
the electrical power generation circuit. This photovoltaic layer 111 is mounted
on a back plate 112 which provides major mechanical support for the photovoltaic
cell 19. Note that back plate 112 is disclosed as extending beyond the edge of
photovoltaic layer 111. In the preferred embodiment an aperture is disposed within
top case 13 sufficient to permit external ambient light to fall on photovoltaic
layer 111. At the same time, the ends of back plate 112 extend beyond the dimensions
of the aperture and enable mounting of the photovoltaic cell 19. FIGURE 16 further
illustrates electrical lead 113 disposed upon the lower surface of back plate
FIGURE 16 illustrates top case 13 which includes posts 93 and 94.
In accordance with the matter illustrated in FIGURE 10, post 93 is disposed in
and received by depression 31 within bottom case 11. As taught in conjunction
with the matter illustrated in FIGURE 10, post 93 may be disposed in this position
to limit the lateral motion of photovoltaic cell 19. Post 94 is disposed in a
position which substantially opposes a depression 32 within bottom case 11. Post
94 has a height selected to engage the end of back plate 112 and substantially
limit the vertical motion of photovoltaic cell 19.
The major electrical connection between photovoltaic cell 19 and
interconnection pattern 12 is illustrated in FIGURE 16. Interconnection pattern
12 disposed on bottom case 11 includes conductor 23 for connection to the voltage
source. Disposed between conductor 23 and electrical terminal 113 of photovoltaic
cell 19 is a mushroom shaped connector 114. This mushroom shaped connector 114
has a stem which extends into the depression 32 within bottom case 11. Connector
114 includes a crown portion whose bottom is placed in substantial contact with
conductor 23 and whose top is placed in substantial contact with electrical lead
113. Connector 114 is preferably constructed of a conductive silicon rubber which
is highly elastic.
The combination illustrated in FIGURE 16 is assembled as follows.
Firstly, the stem portion of connector 114 is disposed in the corresponding depression
32 within bottom case 11. Next photovoltaic cell 10 is placed on top of the connector
114 so that lead 113 is in substantial contact with the top of connector 114.
Lastly, top case 13 is aligned and connected to bottom case 11. This preferably
causes post 94 to press back plate 112 to slightly compress connector 114. This
compression causes connector 114 to exert a force on both conductor 23 and lead
113, thereby electrically connecting these structures. It should be understood
that FIGURE 16 illustrates only one of at least two required connections for photovoltic
cell 19. Another connection of substantially the same type is preferably provided
between photovoltaic cell 19 and the interconnection pattern 12 in order to provide
a complete circuit.
FIGURES 17, 18 and 19 illustrate the patterns necessary to construct
a twenty four key matrix keyboard on a single sheet. FIGURE 17 illustrates a first
conductive pattern. FIGURE 18 illustrates an insulative pattern. FIGURE 19 illustrates
a second conductive pattern or jumper pattern.
FIGURE 17 illustrates the first conductive pattern on the flexible
sheet 120. Flexible sheet 120 includes a tail portion 121 and has an interconnection
pattern disposed thereon including a plurality of conductors 172. The first conductive
pattern on flexible membrane 120 includes a plurality of key switch positions 124.
Each key switch position 124 has a pair of conductors arranged in an interleaved
The first conductive pattern illustrated in FIGURE 17 includes conductor
123 which is disposed around the periphery of the first surface of flexible membrane
120. This conductor 123 is connected to one of the pair of conductors of key switches
125 and 126. Conductor 123 is preferrably connected to one terminal of the power
supply and provides a ground plane for the keyboard. This ground plane is necessary
to minimize the buildup of static charge which is particularly troublesome if the
electronic apparatus includes one or more metal oxide semiconductor devices which
are sensitive to static charge.
In accordance with the teachings of U.S. Patent No. 4,115,705 "Electronic
Calculator with Push-Button On-Off System" issued September 19, 1978 to David J.
McElroy, the keyboard illustrated in FIGURE 17 includes key switch 125 and key
switch 126, each having one of their two conductors connected to the fixed potential
of conductor 123. In accordance with the teachings of the above cited patent,
key switches 125 and 126 may then be employed as momentary contact on and off switches.
The other key switches 124 illustrated in FIGURE 17 are disposed
in a matrix form, that is each key switch has one of its pair of conductors connected
in a column and the other of its pair of conductors connected in a row. Tail portion
121 includes conductors 122 and conductor 123. Together these conductors available
at tail 121 include all of the lines necessary to sense the closure of any of
key switches 124, 125 or 126.
Flexible membrane 120 is preferably manufactured of a single sheet
of flexible material. This single sheet may be constructed of vinyl, Mylar (registered
trade mark) or polycarbonate. As will be further explained below, a vinyl sheet
is preferable because this enables easier application of graphics to the second
surface of the sheet.
The first conductive pattern illustrated in FIGURE 17 is preferably
transfer printed onto the first surface of flexible membrane 120. A conductive
ink formed of approximately 50% silver ink and 50% graphite ink may be employed
for this conductive pattern. Other types of conductive ink could be employed instead.
This is preferably applied to flexible sheet 120 by a silk screening or lithographic
process. In addition, a conductive ink of the pure solvent type or of the ultraviolent
light cure type may also be employed.
FIGURE 18 illustrates the insulative pattern applied to the first
surface of flexible membrane 120 after the application of the first conductive
pattern. This insulative pattern includes a plurality of small insulators 130.
Each of the small insulators 130 is disposed on the previously deposited first
conductive pattern at one of the crossover points 127 (illustrated in FIGURE 17).
The insulative pattern is preferrably formed of an insulative ink transfer printed
on the surface of flexible membrane 120 over the first interconnection pattern
in a manner similar to the deposition of the first insulative pattern.
FIGURE 19 illustrates the second conductive pattern or jumper pattern.
The second conductive pattern includes a plurality of conductors 140, each of which
is disposed at a position corresponding to one of the crossovers 127 illustrated
in FIGURE 17. The second conductive pattern is preferrably deposited on the first
surface of the flexible membrane 120 over the combination of the first conductive
pattern and the insulative pattern. This second conductive pattern may be applied
in the same manner as the first conductive pattern. Application of insulators
130 and jumpers 140 to the crossover points 127 enables construction of one or
more conductor crossing patterns on the surface of flexible membrane 120. This
provision for a crossover pattern enables more complicated interconnection patterns
to be formed on the flexible membrane 120 than would he possible without such crossing
patterns. This enables construction of more complicated keyboards than would otherwise
FIGURE 20 illustrates a view of the front case of an electronic apparatus
employing the single sheet membrane keyboard of the present invention. FIGURE 20
illustrates front case 150. Front case 150 has a keyboard area 151. This keyboard
area 151 has the same outline as the flexible membrane 120, with the exception
of the tail portion 121. The keyboard portion 151 is preferrably substantially
flat with the exception of a plurality of depressions 152. Each depression 152
is disposed at a location within keyboard surface 151 corresponding to one of
the key switches 124, 125, or 126. In a preferred embodiment, front case 150 is
constructed of an injection molded plastic. Because front case 150 is formed of
plastic, keyboard surface 151 is nonconducting. Of course front case 150 may be
formed in a different manner and from different material as long as keyboard surface
151 is nonconducting. Proper construction of the mold for front case 150 permits
construction of a substantially flat keyboard surface 151 which has depressions
152 as described. The bottom of each depression 152 includes a conductive layer
153 disposed at the bottom thereof. This conductive layer 153 preferrably comprises
a layer of conductive ink transferred printed into the bottom of the depressions
152. This transfer ink may be of the same type as employed in manufacture of the
first and second conductive patterns placed upon flexible membrane 120.
Front case 150 contains a pair of apertures 154 and 155. Aperture
154 is preferrably a slot opening disposed within keyboard surface 151 at a position
corresponding to tail portion 121 of flexible membrane 120. During assembly the
tail portion 121 of the single sheet keyboard is inserted into slot 154 and the
first surface including the interconnection pattern of flexible membrane 120 is
glued on to keyboard surface 151. This assembly provides registration of each
of the key switches 124, 125 and 126 with a corresponding depression 152 and conductive
Also included within front case 150 is a display opening 155. In
the preferred embodiment, a visual display such as a liquid crystal display, a
light emitting diode display or a vacuum florescent display is placed within the
case of the electronic apparatus so that it may be viewed through display aperture
155 within top case 150. This display is employed to communicate to the operator
of the apparatus the results and the operational state of the apparatus. Other
forms of communication between the apparatus and the operator are possible. As
an example, an electromagnetic or piezoelectric transducer could be employed to
enable musical tone or synthesized speech output. In such a case front case 150
must be constructed to accomodate the transducer rather than a visual display.
FIGURE 21 illustrates a cross sectional view of the membrane keyboard
of the present invention. FIGURE 21 includes a view of a typical crossover portion
127 and typical key switch position 163.
Flexible membrane 120 is disposed substantially over the surface
of top case 150. On the upper surface of flexible membrane 120, away from top case
150, is disposed a graphics layer 161 and a protective layer 162. Graphics layer
161 preferably includes characters, words, names and colors which properly identify
each key switch position of the membrane keyboard. This graphics layer 161 enables
proper operator identification of the various key switch positions of the membrane
keyboard, thereby permitting the operator to properly select the desired key closures
for the desired machine operation. Graphics layer 161 is preferably printed upon
the top surface of flexible membrane 120 by an ordinary printing process. As noted
above, it is preferable to employ a vinyl sheet for flexible membrane 120 because
such vinyl material more easily accepts the printed graphic layer 161. Also placed
upon the upper surface of the membrane keyboard is a protective layer 162 which
may be composed of a transparent mylar layer. This protective layer preferably
is employed to minimize wear and rub off of the graphics layer, thereby extending
the useful life of the membrane keyboard.
On the other surface of flexible membrane 120, that is the surface
which faces top case 150 of the apparatus, the first conductive pattern, the insulative
pattern and the second conductive pattern are disposed. FIGURE 21 illustrates
conductors 122a, 122b, 122c and 122d, each of which is formed as a part of the
first conductive pattern. Conductor 122a is illustrated in cross section and passes
approximately perpendicular to the cross sectional view illustrated in FIGURE
21. Conductors 122b, 122c and 122d preferably extend substantially in parallel
to the cross sectional view illustrated in FIGURE 11. The region between conductors
122a, 122b and 122c forms a crossover area 127. As explained above, an insulative
pattern is disposed upon the first surface of flexible membrane 120 at positions
corresponding to the crossover portion 127. As illustrated in FIGURE 21, insulator
130 is disposed on top of conductor 122B and between conductors 122b and 122c.
The second conductive pattern includes a jumper 140 which is disposed over the
insulator 130 and is placed in contact with both conductors 122b and 122c of the
first conductive pattern. As a result of this construction, a continuous electrical
path from conductor 122b, through jumper 140 to conductor 122c is constructed.
This continuous electrical path is insulated from the crossing electrical path
of conductor 122a via insulative layer 130.
Also illustrated in FIGURE 21 is the operation of key 124 at key
switch position 163. Key 124 includes a pair of conductors, 122c and 122d, which
are disposed upon the surface of flexible membrane 120 in registration with a
corresponding depression 152 in top case 150. This area of the keyboard is a key
switch position 163. Pressure upon the external face of the membrane keyboard in
the area of key switch position 163 causes membrane 120 to flex until both conductors
122c and 122d are in contact with conductive layer 153 placed at the bottom of
depression 152. This simultaneous contact causes a continuous electrical path
from conductor 122c through conductive layer 153 to conductor 122d. As explained
above, this may be detected by proper sensing upon the conductors 122 appearing
at the ends of tail portion 121 as a closed key switch. Removal of the pressure
on the exterior of key switch position 163 causes flexible membrane 120 to regain
its original position, thereby disconnecting the electrical path between conductors
122c and 122d. This disconnection of the electrical path is sensed as an open