l|||||||||l|||||||||l|||||||l||||||||||||l||||||||||||||||||l||||||||||l|||
`U8006188391B1
`
`(12) United States Patent
`
`US 6,188,391 B1
`(10) Patent N0.:
`
`(45) Date of Patent: Feb. 13, 2001
`Seely et al.
`
`(54)
`
`(75)
`
`TWO-LAYER CAPACITIVE TOUCHPAD AND
`METHOD OF MAKING SAME
`
`Inventors: Joel Seely, Milpitas; Robert Leonard
`Malak, San Jose; Timothy Peter Allen,
`Santa Cruz; Richard Robert Schediwy,
`Union City; William Andrew
`Cesarotti, San Francisco, all of CA
`(US)
`
`(73)
`
`Assignee: Synaptics, Inc., San Jose, CA (US)
`
`5,757,368
`5,767,457
`5,869,790 *
`5,926,171 "
`
`.
`5/1998 Gerpheide et al.
`.
`6/1998 Gcrpheide ct al.
`................... 345/174
`2/1999 Shigetaka etal.
`.................. 345/174
`7/1999 Matsufusa etal.
`OTHER PUBLICATIONS
`
`http://www.safecomputing.com/alpspad.htrn,
`Website,
`“Cursor Controls—ALPS Numeric Pad & TrackPad”, Aug.
`6, 1998, p. 1.
`Website, http://www.safecomputing.com/cirque_cats.htm,
`“Altemative Keyboards/Adapters—Cirque GlidePoint—
`Easycat, Powercat, Smartcat”, Aug. 6, 1998, pp. 1—2.
`
`( * )
`
`Notice:
`
`Under 35 U.S.C. 154(b), the term of this
`patent shall be extended for 0 days.
`
`* cited by examiner
`
`(21)
`
`(22)
`
`(51)
`IFn\
`(52)
`K35)
`
`(56)
`
`Appl. N0.: 09/112,097
`
`Filed:
`
`Jul. 9, 1998
`
`Int. Cl.7 ....................................................... G09G 5/00
`US Cl.
`. 345/173; 178/1803
`
`Field of Search.
`....... 345/173,174—179;
`..
`178/1806,18.01, 18.03; 341/22, 34, 33
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,305,017
`5,349,303
`5,543,590
`5,565,658
`
`4/1994 Gerpheide .
`9/1994 Gerpheide.
`8/1996 Gillespie et al. .
`10/1996 Gcrpheidc ct al.
`
`.
`
`Primary Examiner—Regina Liang
`(74) Attorney, Agent, or Firm—Malcolm B. Wittenberg
`
`(57)
`
`ABSTRACT
`
`By suitable use of screen-printed carbon ink patterning,
`combined with patterning of the solder-mask layer on the top
`(finger) surface, a compact capacitie touchpad pointing
`device has been realized using only a two--layer board as a
`substrate, The first layer, on the topside of the printed circuit
`board, combines both the horizontal and vertical sensor
`electrode traces. The second layer, located on the underside
`of the printed circuit board, is formed in the conventional
`manner by attaching the controller chip and/or related cir-
`cuitry.
`
`22 Claims, 7 Drawing Sheets
`
`62
`
`16804 "..l'I'I'..'......'.".'.".
`
`7"...“
`
`7'...
`
`101
`
`Page 1
`
`of16
`
`Wintek Exhibit 1022
`Wintek v. TPK
`
`lPR2013-00567
`
`lPR2014-00541
`
`IPR2014-00568
`
`Page 1 of 16
`
`

`

`US. Patent
`
`Feb. 13, 2001
`
`Sheet 1 of 7
`
`US 6,188,391 B1
`
`30 30 30 30 3O 30 30 30 30 30 30 30 30 30 30
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`00000000000000
`
`000000000000000
`
`10000000000000
`
`FIG. 1A
`
`(PRIOR ART)
`
`28
`
`34
`
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`00000000000000
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`00000000000000
`
`26
`26
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`26
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`26
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`26
`
`/
`
`24
`
`24
`
`L0
`
`22/
`
`FIG.
`
`13
`
`(PRIOR ART)
`
`Page 2 of 16
`
`Page 2 of 16
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`

`

`US. Patent
`
`Feb. 13, 2001
`
`Sheet 2 0f 7
`
`US 6,188,391 B1
`
`30
`
`34
`
`«xxx: xxxx :o’cxx
`oxxxxxxxxxxxxxx
`oxxxoa’sx xxXxxokxx
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`
`FIG. 1C
`
`(PRIOR ART)
`
`19
`
`22f
`
`FIG. 1D
`
`(PRIOR ART)
`
`36
`
`,
`
`26
`
`32
`
`3O
`
`Page 3 of 16
`
`Page 3 of 16
`
`

`

`US. Patent
`
`Feb. 13, 2001
`
`Sheet 3 0f 7
`
`US 6,188,391 B1
`
`47
`
`
`
`
`44
`
`
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`
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`
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`
`
`
`
`
`CONTROLLER
`
`
`
`48
`
`FIG. 2
`
`(PRIOR ART)
`
`
`
`FIG. 3
`
`(PRIOR ART)
`
`(2‘3
`
`Page 4 of 16
`
`Page 4 of 16
`
`

`

`US. Patent
`
`Feb. 13, 2001
`
`Sheet 4 0f 7
`
`US 6,188,391 B1
`
`_
`.—
`
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`
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`
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`
`Page 5 of 16
`
`Page 5 of 16
`
`

`

`US. Patent
`
`Feb. 13, 2001
`
`Sheet 5 0f 7
`
`US 6,188,391 B1
`
`
`
`84
`
`84
`
`86
`
`FIG. 5
`
`(PRIOR ART)
`
`FIG. 6
`
`Page 6 of 16
`
`Page 6 of 16
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`

`

`US. Patent
`
`Feb. 13, 2001
`
`Sheet 6 of 7
`
`US 6,188,391 B1
`
`OIIIIIIIIIIIIIIIC
`000000000000
`
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`
`Page 7 of 16
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`Page 7 of 16
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`
`
`
`
`

`

`US. Patent
`
`Feb.13,2001
`
`Sheet7 0f7
`
`US 6,188,391 B1
`
`m.6."—
`
`
`
` EEEEEEEEEE@o
`
`
`Page 8 of 16
`
`Page 8 of 16
`
`

`

`US 6,188,391 B1
`
`1
`TWO-LAYER CAPACITIVE TOUCHPAD AND
`METHOD OF MAKING SAME
`
`BACKGROUND OF THE INVENTION
`
`1. Technical Field
`
`invention relates to touchpad pointing
`The present
`devices, and in particular to a touchpad pointing device
`which is less expensive to fabricate.
`2. Summary of the Prior Art
`Over the last several years, capacitive touchpad pointing
`devices have been used extensively in personal computers.
`When used in conjunction with a computer, a touchpad
`allows the user to manipulate a graphics cursor on a CRT
`display. The touchpad comprises a sensitive planar surface
`and means for detecting the position of an object, such as a
`finger or a stylus, near or in contact with, the sensitive planar
`surface. The touchpad continuously communicates this posi-
`tion information to the electronic apparatus, typically at a
`rate of from 40 to 100 Hz.
`
`10
`
`15
`
`Presently, approximately 70% of all new notebook com-
`puters include a touchpad as the primary pointing device. In
`this competitive touchpad market, price has become an
`increasingly important factor. A touchpad design that
`is
`intrinsically less expensive to make has significant commer-
`cial advantage.
`For reasons to be disclosed below, most existing capaci-
`tive touchpad designs are built using a four-layer printed
`circuit board as the basic structural substrate. The circuit
`traces on the “top” two (finger-side) layers of the board serve
`as the capacitive sensing matrix, and the traces on the
`“bottom", or underside (component-side) layer provide elec-
`trical interconnections for the components mounted thereon.
`The remaining buried layer, the fourth layer, is generally
`used as a ground plane though it could, in theory, be put to
`some other use.
`
`While fourvlayer printed circuit boards are widely avail—
`able from many manufacturers, it is well-known that they
`are substantially more expensive than two-layer printed
`circuit boards of the same size. In large quantities, in excess
`of 200,000 units per month, a four-layer touchpad-sized
`printed circuit board with dimensions of, for example, 65
`mm by 49 mm might typically cost $0.80 per unit, with the
`exact figure depending on many factors. Atwo-layer circuit
`board of the same size might cost as little as approximately
`$0.40. This savings is substantial when compared to the
`overall cost of the entire touchpad device. The ability to use
`a two-layer instead of four-layer circuit board would tend to
`give a strong competitive advantage to a manufacturer
`capable of producing such a device.
`Two-layer touchpads have been constructed for limited
`applications. As will be described in greater detail below,
`these two-layer touchpads require that the controller chip be
`remotely located on the same circuit board away from the
`touch sensitive area. Thus, such two-layer touchpads do not
`perform an equivalent function as do present four-layer
`touchpads.
`
`SUMMARY OF THE INVENTION
`
`The subject patent application relates to a capacitive
`touchpad using a two-layer printed circuit board and method
`of fabricating it. In particular, an improved touchpad for use
`in a system for moving a cursor on a display screen is
`described which includes a printed circuit board having a top
`and under side, a first layer formed on the top side of the
`printed circuit board which includes both a plurality of
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`horizontal sensor electrodes and a plurality of vertical sensor
`electrodes, and a second layer formed on the underside of
`the printed circuit board which includes the standard elec-
`trical components associated with the touchpad, such as the
`controller chip and associated interconnect wiring.
`In the preferred embodiment the horizontal, or X elec-
`trodes are metal traces made by conventional printed circuit
`fabrication, and are, typically copper. The vertical electrodes
`are made of conductive ink, such as carbon ink. An insulator
`is provided at each intersection of a metal
`trace and a
`conductive ink trace. This insulator may be a solder mask
`insulator. An additional protective layer of mylar is provided
`on top of the first layer.
`By suitable use of screen-printed carbon ink patterning,
`combined with patterning of the solder-mask layer on the top
`(finger) surface, a compact capacitive touchpad pointing
`device has been realized using only a 2-1ayer board as a
`substrate. The first layer is a single composite layer for both
`the horizontal and vertical sensor electrode traces; and the
`second layer, on the underside of the printed circuit board,
`includes the controller chip, sensor circuitry and/or related
`circuitry. The present invention is advantageous because it
`significantly reduces the cost of touchpad devices without
`adversely affecting their functionality.
`
`A BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIGS. lA—lD illustrate a conventional four—layer touch-
`pad.
`FIG. 2 is a block, schematic diagram of a prior art
`two-layer touchpad device.
`FIG. 3 is a perspective view of a prior art four-layer
`touchpad device.
`FIG. 4 shows the layout of the top conductive (horizontal)
`traces for a standard four-layer printed circuit board.
`FIG. 5 shows the layout of the second layer with vertical
`conductive traces.
`FIG. 6 shows the vertical carbon ink traces which are
`applied to the horizontal trace layout, in accordance with the
`present invention.
`FIG. 7 shows the pattern for providing isolation between
`the horizontal traces and the vertical carbon ink traces, in
`accordance with the invention.
`
`FIG. 8A is a plan view and
`FIG. 8B a cross-sectional view showing details of a
`composite, two—layer sensor touchpad in accordance with
`the present invention.
`FIG. 9 is a view of the actual underside of a two-layer
`touchpad showing components attached thereto.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`All four-layer technologies share an important common
`feature: the finger is detected by a plurality of horizontally-
`aligned sensor electrodes disposed on a first layer which is
`separated by an insulator from a plurality of vertically-
`aligned sensor electrodes disposed on a second layer. Such
`sensor electrodes are usually formed as standard copper PC
`board traces. Thus, the sensitive area of the touchpad con-
`sists of a 2-layer structure: one layer with horizontally-
`running electrode traces, and another layer with vertically-
`running electrode traces.
`An example sensor electrode arrangement for a four-layer
`touchpad is shown in FIGS. 1A—1D. More details of this
`structure is described in US. Pat. No. 5,543,590 entitled
`
`Page 9 of 16
`
`Page 9 of 16
`
`

`

`US 6,188,391 B1
`
`3
`“Object Position Detector with Edge Motion Feature”,
`assigned to the same assignee as the present invention, and
`incorporated herein by reference. Top, bottom, composite
`and cross-sectional views, respectively, are shown, of a
`capacitive touchpad 10 which includes a sensor array 22.
`The surface of touchpad 10 is designed to maximize the
`capacitive coupling to a finger or other conductive object.
`The touch sensor array 22 includes a first set of conduc-
`tive wires or traces 26 disposed on a bottom layer 28 thereof
`and run in a first direction to comprise horizontal positions
`of the touch sensor array 22. A second set of conductive
`wires or traces 30 are disposed on a top layer 32 thereof and
`run in a second direction preferably orthogonally to the first
`direction to form the vertical positions of the touch sensor
`array 22.
`The first and second sets of conductive traces 26 and 30
`are alternately in contact with periodic sense pads 34 com-
`prising enlarged areas, shown as diamonds in FIGS. lA—lC.
`While sense pads 34 are shown as diamonds in FIGS.
`lA—IC, any shape, such as circles, which allows them to be
`closely packed may be used. As an arbitrary convention, the
`first set of conductive traces 26 will be referred to as being
`oriented in the “X” or “horizontal” direction and can also be
`referred to as “X lines" or “horizontal sensor electrodes”.
`The second set of conductive traces 30 will be referred to as
`being oriented in the “Y" or “vertical” direction and can also
`be referred to as “Y lines” or “vertical sensor electrodes". It
`should be understood that the use of the terms “horizontal”
`and “vertical" are not to be limited to a specific orientation
`of a touchpad with respect to the computer or device with
`which it is used. In other words, a user may in fact, rotate the
`touchpad such that what are defined as “vertical” traces end
`up horizontally with respect to the user.
`Every other sense pad 34 in each direction in the pad
`pattern is connected to first and second sets of conductive
`traces 26 and 30 on the top and bottom surfaces 28 and 32,
`respectively of substrate 24. Substrate 24 may be a printed
`circuit board made using standard industry techniques. An
`insulating layer 36, typically of mylar, is disposed over the
`sense pads 34 on the top of the horizontal electrodes. A
`further description of the operation of touchpad 10, as well
`as a capacitive position sensing system in which a touchpad
`is incorporated, is provided in the above—referenced US.
`Pat. No. 5,543,590.
`The X and Y sensor electrodes are connected to measure-
`ment and control electronics, as is well known. In commer~
`cial applications, these electronics reside on a nearby mixed-
`signal ASIC, the controller chip. Each of the horizontal and
`vertical sensor electrodes is connected to a separate pin on
`the controller chip. Thus only two conductive layers are
`actually required for the detection and location of the user’s
`finger: one layer for the horizontal electrodes, and one layer
`for the vertical electrodes.
`
`As noted above, two—layer touchpads have already been
`constructed for a restricted set of applications where the
`controller chip is located on the same circuit board remotely
`from the sensitive area. FIG. 2 is a block, schematic diagram
`of such a two—layer touchpad device 40. A two-layer touch-
`sensitive array 42 includes a plurality of horizontal sensor
`electrodes 44 and a plurality of vertical sensor electrodes 46
`on printed circuit board 47. The vertical and horizontal
`sensors are connected to the controller chip 48, as is well
`known in the art. Notice that the controller chip 48 and the
`sensor electrodes 44 and 46 are disposed on two non-
`overlapping regions of the same circuit board 47. Circuit
`board 47 must be substantially larger than the “sensitive
`
`4
`area”, e.g., the touch—sensitive array 42, in order to provide
`room for mounting the controller Chip 48, associated
`circuitry, and the interconnections between the controller
`chip 48 and the sensor electrodes 44 and 46.
`Two-layer touchpads constructed in the manner shown in
`FIG. 2 are suitable for applications where the physical size
`of the device is not tightly constrained, i.e., applications
`where a large touchpad circuit board with inactive (non-
`touch-sensitive)
`regions does not pose a packaging or
`mounting problem. Since the principal commercial applica-
`tion of touchpads is in notebook computers, where physical
`space is at an extreme premium, this geometrical configu-
`ration is not favored because it is not compact.
`If the touchpad is created on a four~layer circuit board, the
`controller chip 46 and associated circuitry 49 can be dis-
`posed on the underside 50 of the board as shown in FIG. 3.
`The horizontal and vertical sensor electrodes 44 and 46 are
`disposed on the top two layers 52 of the circuit board 10.
`Strictly speaking, a three-layer circuit board would be suf—
`ficient
`to achieve this same over—under geometry. As a
`practical matter, three-layer printed-circuit boards, however,
`are not significantly less expensive than four-layer circuit
`boards and are not commercially available. The remaining
`buried layer is usually employed as a ground plane. The
`presence of a ground plane may be beneficial to the touch-
`pad’s operation for a variety of secondary reasons such as
`improved immunity to electrostatic discharge. However, it
`has been found that a ground plane is not essential, and in
`accordance with the present invention, it is one of the layers
`that has been eliminated.
`In summary,
`the conventional
`four-layer circuit board has four layers: the first and second
`layers, respectively, are for the horizontal and vertical sensor
`electrodes; the third is the ground plane; and the fourth is the
`components and associated circuitry mounted on the under-
`side of the printed circuit board.
`The four—layer touchpad shown in FIGS. 1 and 3 has one
`principal advantage over the two-layer pad shown in FIG. 2
`and that is one of compactness. The touchpad printed circuit
`board if! of the four-layer design of FIGS. 1 and 3 is no
`larger than the required sensitive area, so no space is wasted.
`This is a critical design feature for use in a notebook
`computer application. The industry has accepted a standard
`PC board size which is only slightly larger than the sensitive
`area 42. For use in such standard applications, the 2-1ayer
`configuration shown in FIG. 2 is not suitable at all.
`The present
`invention allows the components to be
`mounted on the back side of a 2—layer printed circuit board,
`with both the horizontal and vertical electrodes disposed on
`the top layer without interference. This permits a two-layer
`touchpad to fit
`in the standard compact size particularly
`suited for laptop computers and similar application.
`FIG. 4 shows an actual layout 60 of the top conductive
`traces for a standard four-layer touchpad as shown in FIGS.
`lA—lD, which are on the finger-side of the printed circuit
`board 62. There is a rectangular ring 64 around the perimeter
`of the board 62, which is connected to the ground plane (not
`shown) through vias 66 at each corner. A via is a conductive
`through-hole that allows a connection to pass from one side
`to the other of board 62. The ground ring is not an opera—
`tional part of the sensing electronics, and is not directly
`related to the present invention.
`The bulk of the surface area is covered with an array of
`diamond-shaped conductors 68. Half of these diamonds 68
`are connected together horizontally by twelve wires (traces)
`69 that run the width of the pad. The interconnection
`between the diamonds occurs where they would have nearly
`
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`PagetOof16
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`Page 10 of 16
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`US 6,188,391 B1
`
`5
`touched at the corners 70, and is not readily apparent without
`close inspection. These horizontal wires terminate in vias 72
`at the left and right edges of the board 62 shown by the
`semicircular lumps on the half-diamonds at the edges of
`board 62. Vias 72 connect to traces on the opposite side of
`the circuit board 62 then to the controller chip 48 as shown
`in FIG. 3. This leaves the other half of the diamonds 68
`“floating”, i.e., without electrical connections to any other
`device.
`
`The “floating diamonds” 68 are not an essential part of the
`sensing scheme, but they do serve two purposes. First, the
`floating diamonds on the top (exposed) layer tend to increase
`capacitive coupling between the finger and the vertical
`sensor electrodes, which lie immediately underneath. This
`effect is generally believed to be small. Second, the floating
`diamonds create an even surface texture. If these diamonds
`were removed, the interleaved presence or absence of con-
`ductive diamonds on the top surface of the circuit board
`would create a visible and tangible texture. The surface is
`protected by a thin adhesive label, but the texture showing
`through the label would be cosmetically objectionable. One
`could look at
`the top—layer
`trace pattern as 12 (rather
`oddly-shaped) horizontal electrodes which,
`incidentally,
`share the top surface with a plurality of floating metal
`diamonds.
`
`PIG. 5 shows the actual layout 80 of the second (hidden)
`layer conductive traces on printed circuit board 62. In a
`standard four-layer Synaptics touchpad, this layer is sepa-
`rated from the surface layer 60, shown in FIG. 4, by a thin
`3-mil core layer of standard FR4 PC board laminate. Con-
`ductors deposited on this layer are close enough to the
`surface of the touchpad 10 to be subject
`to significant
`capacitive coupling from objects on the surface like, for
`example, a finger.
`Lay—out 50 is half-covered with an array of diamond-
`shaped conductors 82. Diamonds 82 are connected together
`vertically by 15 wires or traces 84 that run the height of the
`layout 80. These vertical wires 84 terminate in vias at the top
`and bottom edges of the board, shown by the semicircular
`lumps 86 on the half-diamonds at the edges. These vias 86
`connect to signal traces on the bottom (component) layer of
`the circuit board, and ultimately to the controller chip 48.
`The diamond-shaped conductors shown in FIG. 4 lie directly
`under the floating diamonds on the top layer, described
`above.
`'lhe second-layer trace pattern define 15 (rather
`oddly—shaped) vertical electrodes.
`invention the second
`In accordance with the present
`(hidden) layer is eliminated and the horizontal and vertical
`traces are consolidated in one layer. More particularly, the
`top trace layout 60, shown in FIG. 4, serves to locate both
`the horizontal and the vertical sensor electrodes by connect-
`ing the “floating" diamonds 68 together vertically. This
`cannot be accomplished by merely connecting them together
`with ordinary metal circuit board traces since those traces
`would be “blocked” by the traces 69 running horizontally. To
`overcome this problem another means for interconnection is
`utilized, namely, the use of screen~printed conductive ink to
`provided the vertical traces.
`Screen-printed carbon ink is a standard, inexpensive pro-
`cess step used in high-volume circuit board manufacturing.
`Carbon ink is the most commonly-used variety of conduc-
`tive ink, though any alternate type of conductive ink or paste
`such as silver ink would serve equally well for the purposes
`herein disclosed. Conductive inks compatible with printed
`circuit board screening processes can be obtained from a
`variety of vendors,
`including the Electra Polymers and
`
`6
`Chemicals, America Corp. of Orange, Calif. An example
`actually used goes by the product name of Electrador
`ED-SSOO series carbon conductor paste. While in the pre—
`ferred embodiment,
`the conductive ink is screen printed,
`other methods of applying the conductive ink may be used.
`The metal conductive traces on a circuit board are gen-
`erally covered by a protective insulating layer known as
`solder mask. This protective layer keeps the metal from
`oxidizing and corroding over time. Often, it is desirable to
`have exposed conductive regions on the circuit board. These
`exposed conductive regions might be used, for example, as
`switch contacts, or for interconnection to other devices.
`There are several well-known techniques used to keep
`exposed metal from corroding. A subsequent gold-plating
`step, for example, aflords substantial resistance to corrosion,
`but is comparatively expensive. A lower—cost alternative to
`gold-plating is screen-printed carbon ink.
`Typically, exposed metal
`traces are “painted” with a
`selectively-applied (screen-printed) layer of ink loaded with
`graphite. The ink is somewhat conductive, so alfords elec-
`trical connection. The ink is non—metallic, so it resists
`oxidation and corrosion. For example, carbon-ink printing is
`commonly used to form inexpensive arrays of switch con-
`tacts on printed circuit boards used in TV remote controls.
`Carbon and other types of conductive inks are also widely
`used in the PC board industry to provide a supplemental
`layer of interconnection, thus eliminating the need for jump-
`ers and other supplemental interconnect devices. This is the
`same purpose for which the conductive ink is used in the
`present invention.
`The present invention uses a screen-printed carbon ink
`step to connect vertically the “floating diamonds” 68 on the
`top layer. The carbon ink is applied in the form of 15 vertical
`“wires” which make contact with the exposed floating
`diamonds. Apattern 90, formed of a plurality of carbon ink
`lines 92,
`is shown in FIG. 6. Since the carbon ink is a
`conductor,
`the floating diamonds will now be connected
`together to form 15, rather oddly shaped vertical electrodes
`on layout 60 (FIG. 4). Thus, the single upper layer exactly
`duplicates the function of the 15 vertical electrodes on the
`second, hidden layer 80 (FIG. 5).
`The conductive carbon ink must cross the horizontal wires
`or traces 69 on the top layer 60 without forming an electrical
`connection. This is accomplished by selective patterning of
`the insulating solder-mask layer covering the top surface.
`Solder-mask is a standard part of the printed circuit board
`process, and can be patterned without adding any additional
`cost. FIG. 7 shows a suitable pattern for the solder mask.
`Breaks in the solder mask under the vertical carbon ink lines
`allow the exposure of the “floating diamonds” 68; solder
`mask serves to insulate the horizontal wires or traces 69
`underneath the vertically-running carbon ink traces shown in
`FIG. 6.
`
`This arrangement removes the need for the layer 80
`entirely, and therefore allows the sensor electrodes to be
`formed on a single PC board layer with the addition of a
`carbon-ink screening step, which is a comparatively inex-
`pensive step. With thc horizontal and vertical sensor clec~
`trodes all on one layer, the touchpad can now be constructed
`on a 2-layer printed circuit board, with the reverse or under
`side used for components and routing.
`FIG. 8A is a plan view and FIG. SE a cross-sectional view
`showing details of a composite, two-layer sensor touchpad
`100 in accordance with the present invention. Printed circuit
`board 62 is covered with copper 101 to form conductive
`regions along the edge 102 of the printed circuit board 62,
`
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`15
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`US 6,188,391 B1
`
`7
`as well its sides and bottom, and to form the horizontal traces
`and diamonds 68. The vertical carbon ink traces or wires 104
`are shown overlaying the floating diamonds 68 and hori-
`zontal conductors 69.
`Solder mask insulation 103 is provided to separate the
`carbon ink traces from the horizontal copper traces 69 while
`allowing contact between the carbon ink traces and the
`diamonds 68, as shown in FIG. 8B. As is conventional, a
`mylar layer is provided over
`the top of the two-layer
`touchpad 100, but which is omitted from FIGS. 8A and 8B.
`Via 66, described above, is also shown in FIG. 8B.
`FIG. 9 is a view of the actual underside 110 of a two-layer
`touchpad showing components attached thereto in the well
`known manner by soldering. Such components include the
`sensing circuitry, controller, interconnect wiring, or what-
`ever conventional circuitry is associated with touehpad 10.
`By suitable use of screen-printed carbon ink patterning,
`combined with patterning of the solder—mask layer on the top
`(finger) surface, a compact capacitive touchpad pointing
`device has been constructed using only a two—layer printed
`circuit board as a substrate with one layer on one side of the
`board defining both the horizontal and vertical traces and a
`second layer on the underside of the printed circuit board,
`formed in the conventional manner, by the controller chip
`and/or related touchpad circuitry.
`Although the present
`invention has been shown and
`described with respect to preferred embodiments, various
`changes and modifications are deemed to lie within the spirit
`and scope of the invention as claimed. The corresponding
`structures, materials, acts, and equivalents of all means or
`step plus function elements in the claims which follow are
`intended to include any structure, material, or acts for
`performing the functions in combination with other claimed
`elements as specifically claimed.
`What is claimed is:
`1, A touchpad pointing device comprising:
`a printed circuit board having a top and under side,
`a first layer on the top side of the printed circuit board
`which includes a plurality of metal sense pads,
`and a first plurality of conductive traces disposed in a first
`direction connecting some of said sense pads forming
`sensor electrodes in said first direction,
`and a second plurality of conductive traces disposed in a
`substantially orthogonal direction connecting others of
`said sense pads forming sensor electrodes in said
`second direction said first and second plurality of
`conductive traces are on the same surface of the first
`layer,
`and a second layer formed on the underside of the printed
`circuit board which includes conductors for the inter—
`connection of electrical components associated with
`the touchpad.
`2. The sensor of claim 1 wherein said first plurality of
`conductive traces is metal and where said second plurality of
`conductive traces is conductive ink.
`3. A touchpad as in claim 2 where an insulator is provided
`at each intersection of a metal trace and conductive ink trace.
`4. A touchpad as in claim 3 wherein said first plurality of
`metal traces is copper and wherein said plurality of conduc-
`tive ink traces is carbon ink.
`
`5. A touchpad as in claim 3 wherein the insulator is solder
`mask insulator.
`6. A touchpad as in claim 3 where the sense pads are in
`the shape of diamonds.
`7. A touchpad as in claim 3 including an additional
`protective layer of Mylar over the first layer.
`
`8
`8. A touchpad as in claim 2 wherein said first plurality of
`metal traces is formed in copper and wherein said second
`plurality of conductive ink traces is carbon ink.
`9, A touchpad as in claim 2 where the sense pads are in
`the shape of diamonds.
`10. A touchpad as in claim 2 including an additional
`protective layer of Mylar over the first layer.
`11. A method of fabricating two-layer touchpad for use in
`a system for moving a cursor on a display screen
`compnsmg,
`forming a first layer on the top side of the printed circuit
`board which includes a plurality of metal sense pads,
`and a first plurality of conductive traces disposed in a first
`direction connecting some of said sense pads forming
`sensory electrodes in said first direction,
`and a second plurality of conductive traces disposed in a
`substantially orthogonal direction connecting others of
`said sense pads forming sensor electrodes in said
`second direction; said first and second plurality of
`conductive traces are on the same surface of the first
`layer,
`and forming a second layer formed on the underside of the
`printed circuit board which includes conductors for the
`interconnection of electrical components associated
`with the touchpad.
`12. A method as in claim 11 wherein the step of forming
`said first plurality of conductive traces in metal is accom-
`plished using conventional printed circuit board fabrication
`techniques and wherein the step of forming said second
`plurality of conductive traces is done as conductive ink
`traces.
`13, Amethod as in claim 12 including the step of forming
`an insulator at each intersection of a metal trace and con—
`ductive ink trace.
`14. A method as in claim 13 wherein the step of forming
`the first plurality of metal traces comprises forming them of
`copper and the step of forming said second plurality of
`conductive ink traces comprises forming them of carbon ink.
`15. A method as in claim 13 wherein the step of forming
`an insulator comprises the step of forming a solder mask
`insulator.
`16. A method as in claim 13 wherein the step of forming
`the sense pads comprises the step of forming them in the
`shape of diamonds.
`17. Amethod as in claim 13 including the additional step
`of forming a protective layer of Mylar over the first layer.
`18. Amethod as in claim 12 wherein the s