GB2207815A - Process for producing a programmed matrix - Google Patents

Abstract

A programmed matrix device is produced by forming a first layer (1) of conductive tracks on an insulating substrate (2). A dielectric second layer (3) of organic photoresist material is applied over the first layer (1), and dots (5) of a material opaque to actinic radiation are applied to the dielectric layer (3) to overlie selected tracks of the first layer (1). After exposure to actinic radiation, the dot-providing material and the unexposed material of the second layer underlying the dots (5) are removed with a solvent, leaving apertures through the second layer accessing the selected tracks of the first layer. A third layer (7) of tracks of electrically conductive polymer material is provided over the second layer (3) and non-parallel to the tracks of the first layer (1), such that the track material of the third layer (7) passes through the apertures in the second layer (3) to interconnect selected tracks of the first and third layers and define a selected code or bit pattern. <IMAGE>

Description

TITLE: PROCESS FOR PRODUCTION OF A PROGRAMMED MATRIX This invention relates to a process for making a programmed matrix device of the type in which one or more first electrically conductive coplanar tracks, supported and arranged on a substrate, is or are traversed by one or more second electrically conductive tracks such that one or more first tracks are electrically connected to one or more selected second tracks at chosen regions of traversal, through one or more apertures in a dielectric layer provided between the first and second tracks, while being electrically insulated by the dielectric layer from the other second tracks.Such programmed matrix devices function as memory devices and large numbers can be manufactured each with a different, unique identity code permanently stored therein which is determined by appropriate choice of a pattern of interconnecting links formed between the first and second conductive tracks, at regions of their traversal, during the manufacturing process. Appropriate interrogating circuits are arranged to address the matrix device via the first and second conductive tracKs and read the code stored in the device. Matrix devices of this nature can be incorporated in transponders for use in identification systems, the transponders being suitably embodied in the form of tags for attachment to animals, persons, vehicles, or other objects to be identified.Remote interrogation systems can be provided to communicate with the transponders by a suitable means such as inductive loop, infra-red or radio-frequency transmission.

A matrix device of this type and a process for its manufacture is described in published British Patent Application number GB 2167621A. In the process described in that Application, a plurality of parallel first conductive tracks is provided by screen printing, on & insulating substrate. A film of a dielectric material is likewise provided over the first conductive tracks and a programmed laser is then used to form apertures through the dielectric at selected locations to expose certain underlying first conductive tracks. One or more second conductive tracks is or are screen printed over the dielectric film to traverse the first conductive tracks and make electrical contact with selected first tracks through the apertures provided by the laser in the dielectric film.The device is therefore programmed during manufacture according to the pattern of apertures produced in the dielectric film. This is a very advantageous process since it allows a very large number of devices, each with its own unique code, to be readily produced by simple programming of the laser. It also enables information relating to the codes to be stored in the laser programmer so that replacement devices of any particular code can be readily produced.

There are, however, requirements for producing programmed matrix devices without involving expensive and sophisticated laser equipment, particularly where a relatively small number of coded devices is required. One process with this objective is described in British Patent Application No 8624309. It is an object of the present invention to provide an alternative process for making a programmed matrix device which does not require the use of a laser.

The present invention provides a process for the production of a programmed matrix device comprising: providing an electrically insulating substrate; forming on a major face of said substrate a first layer comprising one or more electrically conductive film tracks; forming a second layer which is a film of dielectric material overlying the first layer and comprising an organic photoresist material which is hardenable or curable by exposure to actinic radiation; applying overlying the second layer a material which is adapted and arranged to provide dots which are opaque to actinic radiation and which overlie one or more selected tracks of the first layer; exposing the second layer to actinic radiation; removing the dot-providing material; removing, by means of a solvent, material of the second layer underlying the dots and which was not exposed to the actinic radiation, to form a plurality of apertures through the second layer accessing the one or more selected tracks of the first layer; and forming a third layer comprising one or more electrically conductive film tracks of electrically conductive polymer material arranged in a direction non-parallel to the one or more tracks of the first layer and overlying the second layer such that film track material of the third layer passes through the apertures in the second layer to interconnect tracks of the first and third layers and define a selected code or bit pattern.

Any required code or bit pattern can be selected during manufacture by appropriate application of the dots of material in locations where it is required for apertures to be formed and electrical interconnection to be subsequently effected between tracks of the first and third layers.

The substrate may comprise any of the well-known materials used in electrical circuit manufacture, such as glass, ceramic, enamelled metal, or rigid or flexible organic plastics materials.

The first layer may comprise any electrically conductive material which is compatible with the substrate material and capable of being provided in the form of film tracks. Examples of materials which may be selected for the first layer are: (a) thick film elecrically conductive cermet materials, applied as an ink or paste, by screen printing and then fired; (b) thick film electrically conductive polymer materials, applied as an ink or paste by screen printing and then heated to effect polymerisation or curing thereof; (c) printed circuit board track material, particularly copper, bonded to the substrate, the substrate being suitably of a type employed in rigid or flexible printed circuit board manufacture.

The third layer may comprise any electrically conductive polymer thick film material which is compatible with the photoresist material of the second layer and capable of being provided in the form of film tracks.

It is suitably applied as an ink or paste by screen printing and then heated to effect polymerisation or curing thereof.

The second layer may comprise any of the photoresist materials which are well-known in the art of printed circuit and thin film circuit manufacture. Such materials are available to be applied in liquid or dry-film form. Photoresist materials such as those commonly used as solder masks, are particularly suitable. The solvent, often referred to as a developer or developing solution is selected according to the photoresist material being used. Such solvents, for removing the unexposed photoresist material, are well-known and commercially available and are specified by the supplier of the photoresist material selected. The material providing the dots suitably comprises an ink or paint which is opaque to actinic radiation. Black ink or paint is particularly suitable.The dots may be applied either directly to the second layer or to a sheet of a material which is transparent to actinic radiation and which is temporarily located overlying the second layer and either in contact with or just out of contact with the second layer. After carrying out the exposure to actinic radiation, the sheet of material with the dots thereon is removed. Such a sheet with dots thereon may conveniently be in the form of a photomask.

The dots, in the form of ink or paint, may conveniently be applied using a pen or stylus arrangement. A felt or fibre-tipped pen is suitable for this purpose.

Alternatively, a suitably controlled jet of ink or paint may be used to form the dots.

The dots may be applied manually or using automatic equipment. When manual techniques are used, suitably involving a pen held by an operator, assistance in identifying the precise locations to apply the dots may additionally be provided. Such assistance may be in the form of a suitable instruction chart or a suitable overlay carrying a printed pattern showing the locations for the dots.

Automatic techniques may also be used for applying the dots of ink or paint. For example, a computer-controlled flat-bed plotter equipped with a suitable pen or stylus for applying ink or paint is suitable for this purpose. Alternatively, a numerically controlled machine of the type used for drilling holes in printed circuit boards may be utilised, with a pen or stylus for applying ink or paint substituted for a drill which is commonly provided therein. Furthermore, available forms of automatic printing equipment, including ink-jet and dot matrix printers, could be readily adapted to provide the necessary precisely-located dots of ink or paint.

The actinic radiation is suitably provided by an ultra-violet light source. Such light sources are commercially available for this purpose and well-known in the art.

The invention is now described by way of example with reference to the accompanying drawing which represents an exploded perspective view of an embodiment of a programmed matrix device produced according to the process of the invention.

A first layer comprising a plurality of first electrically conductive film tracks 1 is provided on a major face of a substrate 2. The film tracks are conveniently of copper, etched from a sheet of copper bonded to the substrate 2 which suitably comprises a printed circuit board base material of rigid or flexible form, such as epoxy-glass or polyimide.

Copper clad printed circuit board base materials of this type are well known as are the techniques of etching used to produce the tracks 1 which are arranged substantially parallel with one another. A second layer 3 of a dielectric material is provided on the substrate 2 on top of the tracks 1. This dielectric second layer 3 comprises a photoresist material which is curable or hardenable by exposure to actinic radiation, such as ultraviolet radiation. A suitable photoresist material, which is used in the present example, is Finedel (Trade Mark) type DSR-2200 supplied by Hoechst UK Ltd. This material is normally used as a solder mask for printed circuits and is applied as a film by well-known screen printing techniques.Other photoresist materials, including dry film types such as Vacrel (Trade Mark), manufactured by E I DuPont de Nemours, and dry film solder mask materials manufactured by Thiokol Chemicals Ltd, are also suitable for forming the second layer 3. The substrate 2, provided with the screen printed layer 3 of photoresist material, is heated in an oven to dry the layer 3. In the case of the Finedel type DSR-2200 material, a drying time of 15 to 30 minutes at a temperature in 0 the range of 70 to 80 C, is used.It is required to provide apertures 5 through the second layer 3 at predetermined locations such that a third layer, comprising one or more second electrically conductive tracks 7, can be subsequently provided on top of the second layer 3 such that one or more of the second conductive tracks 7 electrically contacts certain selected first conductive tracks 1 through the apertures 5, as indicated by the dotted lines 9. This selected interconnection of the first and second conductive tracks will serve to programme the resulting matrix device with a particular permanent binary or hexadecimal code during manufacture. Accordingly, to produce a range of devices each with a different code permanently programmed into it during manufacture, it is necessary to arrange for different combinations of first and second tracks 1 and 7 to be interconnected during manufacture.This is achieved as follows. Dots of ink or paint which is opaque to actinic radiation are applied to the surface of the second layer 3 of photoresist material at each location 5 where it is required to provide an aperture through the layer- 3 to produce a device progammed with one particular code.

These dots, which are suitably black in colour, can be applied manually using a pen which is suitably of a felt-tipped or fibre-tipped variety.

Alternatively, the dots can be applied automatically. One convenient arrangement for this purpose involves locating the substrate 2, provided with the tracks 1 and photoresist layer 3, on a computer-controlled flat bed plotter (not shown) such as a Hewlett-Packard type HP 7225 A, and providing the plotter with a suitable pen or stylus supplied with ink or paint. The plotter is then programmed to move the pen sequentially to each location 5 and provide a dot of ink or paint at these locations. By changing the programming of the plotter, different combinations of dots are provided which will result in devices with different codes. This is only one example of an automatic technique which can be used to provide precisely-located dots of a material which is opaque to actinic radiation.Another technique which can be employed involves the use of a numerically-controlled machine of the type used to drill holes through printed circuit boards, but in which the usual drill is replaced by a pen. After applying the dots of ink or paint at each required location 5, the second layer 3 is exposed to actinic radiation to cure the exposed regions of the second layer 3. For materials such as the Finedel DSR-2200, used for the second layer 3, exposure to ultra-violet radiation is carried out, suitably by employing a high pressure mercury or metal halide lamp. After exposure, the dots of ink or paint are removed with a suitable solvent and the second layer 3 treated with a solvent which dissolves regions of the material of the second layer 3 which were previously protected from exposure to the actinic radiation by the dots of ink or paint.Apertures are thereby formed through the second layer 3 at each location 5 and portions 6 of selected conductive film tracks 1 are exposed through the apertures. The solvent used to selectively remove the material of the second layer 3 at the locations 5 is often referred to as a developer or developing solution. In the case of a second layer 3 comprising Finedel DSR-2200, an aqueous developing solution comprising 0.6% to 1.0% of sodium carbonate, heated to about 0 35 C, is suitably applied for about one minute, eg by a spraying technique. Some materials used for the second layer 3 then require a final thermal curing treatment to be given. For example, in the case of the Finedel DSR-2200, this suitably comprises a treatment at 1700C for 10 minutes in an infra-red oven.

The third layer, comprising electrically conductive tracks 7 is then applied on top of the dielectric second layer 3 such that, for one or more of the tracks 7, material of these tracks enters the apertures at the locations 5 in the second layer 3 and contacts the portions 6 of the underlying first tracks 1. The tracks 7 are conveniently provided by screen-printing, using an electrically conductive polymer thick film material, which is subsequently heat treated to effect polymerisation and/or hardening thereof. Such conductive polymer thick film materials are well known and commercially available. Examples of suitable materials are Polymer Silver 4422 and Polymer Nickel 2548 manufactured by the Electro Materials Corporation of America (EMCA), but many others are available. The programmed matrix device is thereby completed. Terminal regions 4 and 8 on the first and second tracks 1 and 7 respectively are used to connect the device with appropriate external circuitry, the terminal regions 4 being arranged to be uncovered by the second layer 3.

Instead of dots of ink or paint being applied to the surface of the second layer 3 at the locations 5, a sheet of material (not shown) transparent to actinic radiation and having the dots appropriately provided thereon, could be temporarily precisely located overlying but, not necessarily in contact with, the second layer 3 and the layer 3 then exposed to actinic radiation.

Although in the accompanying drawing the first and third layers are shown to each comprise a plurality of first and second tracks 1 and 7, if required only a single track could be provided for either the first or the third layer and a plurality of tracks provided for the other. This arrangement could be used to provide a programmed matrix device which functions as a pre-programmed bit set or binary coded array. If required also, electrical resistors, preferably of film form, may be provided connected to the first or second conductive tracks 1 or 7. Such resistors can operate in well-known manner as pull-up resistors to maintain a steady state electrical condition on the conductive tracks with which they are associated.

The progammed matrix device produced by the present invention operates in the same way as the device described in Applicants' published Patent Application No GB 2167621A and finds similar application.

Claims (18)

1A process for the production of a programmed matrix device comprising: providing an electrically insulating substrate; forming on a major face of said substrate a first layer comprising one or more electrically conductive film tracks; forming a second layer which is a film of dielectric material overlying the first layer and comprising an organic photoresist material which is hardenable or curable by exposure to actinic radiation; applying overlying the second layer a material which is adapted and arranged to provide dots which are opaque to actinic radiation and which overlie one or more selected tracks of the first layer; exposing the second layer to actinic radiation; removing the dot-providing material; removing, by means of a solvent, material of the second layer underlying the dots and which was not exposed to the actinic radiation, to form a plurality of apertures through the second layer accessing the one or more selected tracks of the first layer; and forming a third layer comprising one or more electrically conductive film tracks of electrically conductive polymer material arranged in a direction non-parallel to the one or more tracks of the first layer and overlying the second layer such that film track material of the third layer passes through the apertures in the second layer to interconnect tracks of the first and third layers and define a selected code or bit pattern.

2 A process according to Claim 1 in which a required code or bit pattern can be selected during manufacture by appropriate application of the dots of material in locations where it is required for apertures to be formed and electrical interconnection to be subsequently effected between tracks of the first and third layers.

3 A process according to Claim 1 or 2 in which the substrate comprises any of the well-known materials used in electrical circuit manufacture, such as glass, ceramic, enamelled metal, or rigid or flexible organic plastics materials.

4 A process according to Claim l, 2 or 3 in which the first layer comprises an electrically conductive material selected from: (a) thick film electrically conductive cermet materials, applied as an ink or paste by screen printing and then fired; (b) thick film electrically conductive polymer materials, applied as an ink or paste by screen printing and then heated to effect polymerisation or curing thereof; (c) printed circuit board track material, bonded to the substrate, the substrate being of a type employed in rigid or flexible printed circuit board manufacture.

5 A process according to any preceding Claim in which the third layer comprises a composition which is applied as an ink or paste by screen printing and then heated to effect polymerisation or curing thereof.

6 A process according to any preceding Claim in which the second layer comprises a photoresist material of the type used in printed circuit and thin film circuit manufacture and which is applied in liquid or dry film form.

7 A process according to any preceding Claim in which the material providing the dots comprises an ink or paint which is opaque to actinic radiation.

8 A process according to Claim 7 in which the dots in the form of ink or paint are applied using a pen or stylus arrangement.

9 A process according to Claim 8 in which assistance in identifying precise locations to apply the dots is provided in the form of an instruction chart or an overlay carrying a printed pattern showing the locations for the dots.

10 A process according to Claim 8 in which a computer-controlled flat-bed plotter equipped with a pen or stylus is used for applying the dots.

11 A process according to Claim 8 in which a numerically controlled machine of the type used for drilling holes in printed circuit boards is utilised for applying the dots, a pen or stylus being substituted for a drill which is commonly provided therein.

12 A process according to Claim 7 in which a suitably controlled jet of ink or paint is used to form the dots.

13 A process according to any preceding Claim in which the dots are applied directly to the second layer.

14 A process according to any of Claims 1 to 12 in which the dots are applied to a sheet of material which is transparent to actinic radiation and which is temporarily located overlying the second layer and either in contact with or just out of contact with the second layer, the sheet of material with the dots thereon being removed after carrying out the exposure to actinic radiation.

15 A process according to Claim 14 in which the sheet with dots thereon is provided in the form of a photomask.

16 A process according to any preceding Claim in which the actinic radiation is provided by an ultra-violet light source.

17 A process for the production of a programmed matrix device substantially as hereinbefore described with reference to the accompanying drawing.

18 A programmed matrix whenever produced by the process of any preceding Claim.