GB2223385A

GB2223385A - Vitreous substrate bearing electric circuit components and method of manufacturing same

Info

Publication number: GB2223385A
Application number: GB8814823A
Authority: GB
Inventors: Jean-Marie Bertieaux
Original assignee: AGC Automotive Belgium SA
Current assignee: AGC Automotive Belgium SA
Priority date: 1988-06-22
Filing date: 1988-06-22
Publication date: 1990-04-04
Anticipated expiration: 2008-06-22
Also published as: FR2638934B1; DE3919974C2; DE3919974A1; FR2638934A1; IT1234803B; GB8814823D0; IT8967463A0; GB2223385B; BE1004164A3

Description

1988-15 METALLAC 757 304G 1 VITREOUS SUBSTRATE BEARING ELECTRIC CIRCUIT

COMPONENTS AND METHOD OF MANUFACTURING SAME J 3 The invention relates to an article comprising a vitreous substrate bearing electric circuit means which is formed at least in part from, or is in contact with, a deposit or deposits of vitreous enamel. The invention incLudes a method of manufacturing such an article.

Such articles can be formed to various configurations for various purposes. One example is the incorporation of a radio antenna in a vehicle window. A second example is the incorporation of part of a burglar alarm circuit across a window, for example a shop window or a window of a bank teller cage, so that on interruption or modification of the circuit due to damage to the window an alarm signal is given off. A third example, perhaps the most important commercially, is the incorporation of art electric resistance heater in a window, for example the rear window of a vehicle.

In such articles, it is clearly necessary to draw electricity from the circuit means of the article, or supply electricity to it, and thi may be done via a current collector deposited on the substrate. It is presently a common practice for such a collector to be formed by a deposit of conductive enamel. In many instances, such conductive enamel is deposited on top of a non-conductive enamel which serves as a mask, for example such a non- conductive enamel deposit may lead around the entir( periphery of th( artic-!( to give its margins a uniform appearanco whfj, viewed from one side. In many case.- also, it is a requiement to us( quite sub;tirit ial quantities of the conductive enamel. For exampl(-, th(most common type of vehicle rear window lieatei comprise-,; line- of conductive enamel' connected in parallel between collector strips al- the 2 margins of the window. In order to ensure a proper distribution of heat dissipation over the area of the window, it is necessary that the collector strips should have low electrical resistance, and they are therefore very much wider than the heating lines and may also be thicker, and it is not unknown for more than half the total enamel used to be concentrated in the collector strips. This adds considerably to manufacturing costs, because such conductive enamels typically contain between 45 and '75% by weight of silver.

It is a principal object of this invention to provide a vitreous substrate bearing electric circuit means in which there is a reduced requirement for expensive conductive enamel, and which accordingly allows a reduction in manufacturing costs.

According to the present invention, there is provided an article comprising a vitreous substrate bearing electric circuit means which is formed at least in part from, or is in contact with, a deposit or deposits of vitreous enamel, characterised in that the circuit means includes at least one current collector which consists of or includes a metal deposit in contact with the or a said enamel deposit.

The metal deposit included in, or constituting, the collector will itself be conductive, so for a given total resistance of the collector, that collector can contain a reduced amount of conductive enamel. Such a deposit can be applied simply and economically, and the invention accordingly allows a reduction in manufacturing costs of such articles.

The vitreous substrate may take any desired form, and it may be opaque or transparent. it is envisaged that the greatest demand will be for such articles wherein the substrate is a transparent vitreous sheet, and in the remainder of the description which forms part of this specification, it will be assumed that the substrate is indeed a transparent vitreous sheet. Such a sheet may be a simple flat sheet of glass, or it may be bent to a desired curvature, and/or tempered, and/or laminated, for example to a sheet of plastics material or to another sheet of glass.

The electric circuit means may consist of any desired circuit elements carried by the substrate. it may for example comprise a patterned or continuous transparent conductive coating, for example of doped stannic oxide, which is pyrolytically applied to the vitreou!:substrate, but in the embodiments of the invention which are presently most preferred, said electric circuit means consists of or includes at 1 3 least one deposit of a conductive vitreous enamel. Such conductive vitreous enamel may for example be deposited as a plurality of lines extending in parallel between a pair of collectors. Such articles are particularly useful as heatable windows for vehicles.

Advantageously, elongate current collectors are provided deposited on said substrate and said electric circuit means includes at least one conductive element adherent to the substrate and extending between such collectors. The use of elongate collectors is particularly beneficial for achieving a good distribution of current to a conductive element consisting of a uniform conductive coating, or to a plurality of elements extending between the collectors, for example for forming a heating panel.

In the most preferred embodiments of the invention, the or at least one said elongate current collector consists of or includes an elongate metal deposit. such an elongate metal deposit facilitates the conduction of current along the collector.

Advantageously, the or at least one said current collector is wholly or mainly formed by a said metal deposit. The adoption of this feature ensures the elimination of most or all of the conductive enamel which would have been used for forming such a collector prior to this invention, and accordingly gives correspondingly greater savings in manufacturing costs. Also, it further reduces, and may enable the avoidance of, overheating, for exaniple lcw.-al overheating, of the collector during use, due to a to(- high resistance of that collector or of part of it.

In order to simplify cc)nnexion of the electric circuit means carried by the substrate to other electric circuit components, it is prefeired that a terminal is soldered to the or each current collector.

In fact, we have found that the soldering of terminals to conductive enamel on a vitreous substrate is not an easy operation to perform, especially when that conductive enamel has been deposited over another layer of ceramic material. It is very difficult to achieve a strong bond between the conductive enamel and the terminal with the result that the terminal can easily be broken off accidentally. In the case of a heatable vehicle window, this can mean that it is necessary to replace the entire window. Furthermore, the soldering operation car, easily affect the appearance of any subjacent portion of vitreous enamel, so that it becomes of a non-uniform appearance. This can mar- the aesthetic appearance of the window and can be an important commercial disadvantage. In the most preferred embodiments of the invention therefore, such terminal is 4 soldered to the or a said metal deposit. A strong solder bond can be formed between a terminal and a metal deposit very much more easily than it can be between such a terminal and a conductive enamel. This leads to further savings in manufacturing costs, and has the important additional advantage of involving less risk of marring the appearance of a subjacent enamel deposit. The reason why there is a reduced risk of marring a subjacent enamel deposit is not clear, and having particular regard to certain preferred methods of forming such a metal deposit, it is quite surprising. A further advantage afforded by the provision of a said metal deposit for solder attachment of a terminal is that it allows a greater choice among possible solder alloys. When soldering a terminal to a conductive enamel which contains, as almost all do, a high proportion of silver as conductor, it is commonly regarded as necessary to use a solder alloy which itself contains a high proportion of silver. Silver-solder alloys tend to be expensive, and they very often require a considerably higher soldering temperature than many other alloys used as solders. It will be appreciated that the advantages given above relating to soldering a terminal to such a metal deposit are afforded quite independently of any saving in amounts of conductive enamel used for forming the collector.

Preferably, the or a said metal deposit has been formed at a temperature above 1200C. This can facilitate rapid deposition of the metal. we also believe that the temperature at which the metal deposit is formed may have an influence on the strength of the bond between that deposit and the subjacent surface. of course the temperature of deposition must not be so high that there is serious risk of damaging the substrate and any elements borne thereby when such deposition is effected. Deposition of the metal at elevated temperatures can promote bonding, whether direct or not, between the metal and the substrate. This is important for achieving a secure fixing of a terminal. We have found that by deposition of the metal at elevated temperature it is very simple to achieve a very strong solder bond of a terminal to the substrate via a layer of such deposited metal. Solder can easily form a strong bond to such a metal deposit and the deposit can itself easily be formed so that it is strongly bonded to the substrate. In fact the bond between the solder and the metal deposit, and the bond between the metal deposit and the substrate, can each easily be made stronger than a direct bond between solder and conductive enamel.

There are various techniques which could be used for forming a metal deposit at an elevated temperature. Advantageously, the or a said metal deposit is a flame-sprayed deposit. Such deposits are very simple and inexpensive to make, and they are particularly well adapted for rapid series production on a large scale. Flame-spraying can result in the formation of a film of metal which is well bonded to the substrate. Furthermore, we have found that such a Elame-sprayed metal deposit can be formed without marring the appearance of a subjacent enamel deposit through the vitreous sheet. From the commercial point of view, this is an important aesthetic advantage. It is very surprising that the appearance of such enamel is not marred: enamels commonly used are fired at temperatures of up to about 700'C, and the melting points of many metals which may be used for forming such a deposit are significantly higher than that.

The metal deposit is preferably formed after a said enamel deposit, and in such manner that the or a said metal deposit overlies subjacent vitreous ena.mel. Thii assures good electrical connexion if the enamel is conductive, and allows at least partial masking of the metal deposit whether the enamel is conductive or not. It is prefer-red that such metal deposit overlies a subjacenL deposit of non-conducting vitreous enamel.

Advantageously, such metal deposit overlies a discontinuous subjacent deposit of vitreous enamel whereby part of such metal deposit is in direct contact with the vitreous substrate. This promotes bonding of the metal deposit to the substrate.

Various metals may be used for forming a said metal deposit. It is preferred that said metal deposit is formed from: copper, or nickel, or an alloy of copper and nickel, or of nickel and chromium, or of copper and titanium, optionally containing zinc and/or aluminium. The use of such metals gives a good compromise between electrical conductivity, cost and resistance to atmospheric corrosion.

Articles according to this invention are especially suitable for use as heatable windows, for example rear windows, of vehicles.

In some preferred embodiments of the invention, the substrate bears a marginal deposit of non-conducting opaque enamel extending around its entire periphery. Such non-conducting opaque enamel may be the sole enamel deposit on the substrate, or there may be one or more further enamel deposits, for example of conductive enamel. An article having such a marginal enamel deposit is especially suitable for use as a window of a vehicle. it is now becoming common practice in the automobile industry to 6 secure windows, for example rear windows, into motor vehicles by adhesively bonding the window directly to the vehicle bodywork. This allows the window to be set flush with the body and so reduces drag. Such an opaque marginal strip of enamel can serve to mask the line of adhesive leading around the periphery of such a window, and thus protect it from the effects of ultra-violet radiation. The invention includes embodiments wherein such a window is bonded to the body of a vehicle by adhesive material which is masked from the exterior of the vehicle by such marginal deposit of opaque enamel.

Such opaque enamel may contain pigment, for example black pigment, to provide it with an aesthetically advantageous appearance. In some preferred embodiments of the invention, such marginal deposit of enamel contains pigment to match its colour to that of the vehicle.

The invention extends to a method of manufacturing an article comprising a vitreous substrate bearing electric circuit means which is formed at least in part from, or is in contact with, a deposit or deposits of vitreous enamel, characterised in that the circuit is formed with at least one current collector which consists of or includes a layer of metal deposited in contact with the or a said enamel deposit.

This is a very simple and cost effective way of manufacturing such an article.

In the embodiments of the invention which are presently most preferred, said circuit means is formed by a process including the step of depositing at least one body of conductive vitreous enamel on said substraLe. Such conductive vitreous enamel may for example be deposited as a plurality of lines connected in parallel between a pair of collectors. such articles are particularly useful as heatable windows for vehicles.

Advantageously, said circuit means is formed by a process including the steps of depositing on said substrate a paii of elongate current collectors and at least one conductive element adherent to the substrate and extending between such collectors. The formation of elongate collectors is particularly beneficial for achieving a good distribution of current to a conductive element consisLing of a uniform conductive coating, or to a plurality of elements extending between the collectors, for example for Eorming a heating panel.

In the most preferred embodiments of the invention, the formation of at least one said elonqate current collector consists of or includes the 7 step of depositing a said layer of metal as an elongate strip. Such an elongate metal deposit facilitates the conduction of current along the collector, at low additional cost. Given that it is necessary to form a deposit of metal at all, equipment and production time must clearly be set aside for that purpose, and this implies certain production costs. The only necessary additional cost incurred by extending the area over which the metal is deposited is the cost of the additional deposited metal, which can be small in comparison, together with a possible minor increase in production time.

Advantageously, the or at least one said current collector is formed in such manner that at least the greater part by weight of the conductive material deposited in such collector is contained in said layer of metal. The adoption of this feature ensures the elimination of most or all of the conductive enamel which would have been used for forming such a collector prior to this invention, and accordingly gives correspondingly greater savings ir, manuEacturing costs. It is also especially advantageous where a collectcr of particularly low resistance is required. There is a limit to the thickness of conductiye enamel which can be applied in a single serigraphic step, and this in turn imports a limit to the conductivity of the collector. If it is required to deposit an enamel collector of higher conductivity, further enamel must be deposited in a second serigraphic step, and this process of itself adds considerably to manufacturing costs. Such higher conductivity can readily be imparted to a collector- by forming such a metal deposit.

in order to simplify connexion of the electric circuit means.carried by the substrate to other electric circuit components, it is preferred that a terminal is soldered to the or each current collector. This is a convenient way of attaching a terminal in conductive contact with a collector.

in fact, we have found that the soldering of terminals to conductiv(enamel on a vitreous substrate is not an easy operation to perform. It is very difficult to achieve a strong bond between the conductive enamel and the terminal with the result that the terminal can easily be broken off accidentally. In the case of a heaLable vehicle window, this can mean that it is necessary to replace the entire window. Furthermore, the soldering operation can easily affect the appearance of any subjacent portion of vitreous enamel, so that such enamel becomes of a non-unifoint appearance. "This can mar the aesthetic appearance of the window and can 8 be an important commercial disadvantage. In the most preferred embodiments of the invention therefore, such terminal is soldered to the or a said metal deposit. A strong solder bond can be formed between a terminal and a metal deposit very much more easily than it can be between such a terminal and a conductive enamel. This leads to further savings in manufacturing costs, and has the important additional advantage of involving less risk of marring the appearance of a subjacent enamel deposit. The reason why there is a reduced risk of marring a subjacent enamel deposit is not clear, and having particular regard to certain preferred methods of forming such a metal deposit, it is quite surprising. A further advantage afforded by the provision of a said metal deposit for solder attachment of a terminal is that it allows a greater choice among possible solder alloys. when soldering a terminal to a conductive enamel which contains, as almost all do, a high proportion of silver as conductor, it is commonly regarded as necessary to use a solder alloy which itself contains a high proportion of silver. Silver-solder alloys tend to be expensive, and they very often require a considerably higher soldering temperature than many other alloys used as solders. It will be appreciated that the advantages given above relating to soldering a terminal to such a metal deposit are afforded quite independently of any saving in amounts of conductive enamel used for forming the collector.

PreEerably, the or a said metal deposit is formed at a temperature above 120'C. This can facilitate rapid deposition of the metal. We also believe that the temperature at which the metal deposit is formed may have an influence on the strength of the bond between that deposit and the subjacent surface. of course the temperature of deposition must riot b(-so high that there is serious risk of damaging the substrate and any elements borne thereby when such deposition is effected. Deposition of the metal at elevated temperatures can promote bonding, whether direct or not, between the metal and the substrate. This is important for achieving a secure fixing of a terminal. we have found that by deposition of the metal at elevated temperature it is very simple to achieve a very stron,,, solder bond of a terminal to the substrate. Solder can easily form a strong bond to such a metal deposit and the deposit can itself ea!ily bu formed so that it is strongly bonded to the substrate. in fact the bond between the solder and the metal deposit, and the bond between the metal deposit and the substrate, can each easily be made stronger than a direct bond between solder and conductive enamel.

-1 1 j 9 There are various techniques which could be used for forming a metal deposit at an elevated temperature, for example a plasma torch or an electric welding torch could be used. Advantageously. the or a said metal deposit is formed by flame-spraying. This is a very simple and inexpensive way of forming the required deposit, and it is particularly well adapted for rapid series production on a large scale. Also. if it is desired to make a collector of particularly low resistivity, it is very simple to build up the deposit to a required thickness by making a desired number of passes of a spray gun used for forming the deposit. Furthermore, we have found that such a flame-sprayed metal deposit can be formed without marring the appearance of a subjacent enamel deposit through the vitreous sheet. From the commercial point of view. this is an important aesthetic advantage.

It is very surprising that the appearance of such enamel is not marred: enamels commonly used are fired at temperatures of up tc, about 700'C, and the melting points of many metalss which may h-e used [o., forming such a deposit by flame-spraying are significantly higher than that.

various techniques for flame-spraying metal onto a vitreous substrate may be used. In one such technique, the substrate is preheated, a wire of the required metal composition is progressively fed to the flame of an oxyacetylene torch (the gas feed rates being adjusted so that the flame is a reducing flame) and the flame is played over the area of the substrate onto which it is desired to form the metal deposit. This technique results in the formation of a filip of metal which is well bonded to the substrate. It is desirable to enFire that the flame is a reducing flame so that the metal layer deposited has a low content of oxide in order to facilitate a subsequent soldering step.

The or a said metal layer may be formed before a said enamel deposit, but it is preferably deposited on top of at least one subjacent deposit of vitreous enamel. This assures good electrical connexion if the enamel is conductive, and allows at least partial masking of the metal deposit whether the enamel is conductive or not. it is prefer-red that the or a said metal layer is deposited on top of at least one subjacent deposit of non-conducting vitreous enamel.

Advantageously, such metal layer is dep(-sited on top of a discontinuous subjacent deposit of vitreous enamE-l whereby part of such metal layer is in direct contact with the vitreous substrate. This promotes bonding of the metal deposit to the substrate.

Various preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which:

Figure 1 is an elevation of part of a first embodiment of the invention constituted as a heatable vehicle window, Figure 2 is an elevation of a detail of a second embodiment of the invention, Figure 3 is a sectional view of an embodiment of the invention, Figures 4 and 5 are respectively sectional views of two further embodiments of the invention, and Figures 6 and 7 are elevations of details of yet other embodiments of the invention.

In Figure 1, a glass sheet 1 is cut to size and shape to serve as a vehicle rear window. A deposit of opaque non-conductive enamel 2 is applied serigraphically in a manner known per se around the entire periphery of the sheet 1, and a conductive grid 3 composed of lines 4 of electrically conductive enamel is also applied to the sheet by a serigraphic technique, so that those lines extend between the side margins of the sh(.et 1, their ends overlying the opaque enamel 2 at those margins. The enamel deposits are then baked in a single step to fire them. Firing of the enamel conveniently takes place during heating of the glass sheet prior to bending it to a desired curvature. Alternatively, such firing may take place during heating of the glass sheet prior- to a thermal tempering treatment.

A metal strip 5 is flame-sprayed along substantially the full length of each side margin of the sheet I so that it is in direct contact with the ends of the grid lines 4 at that mat-gin of the sheet. At least tht. side margins of the sheet I may be preheated if desired. in order to deposit that metal strip, metal wire is progressively fed to the flame of an oxyacetylene torch, and that flame is played along the margin of the sheet. In a particularly convenient method, an oxy-acetylene torch is provided with means for proqressively feedinq wire into the torch burnor b.

so that it is surrounded by the gases feeding the flame. The burner is located above the sheet and directed obliquely outwardly towards the margin of the sheet. A shield of a suitably refractory material, for example of sheet stainless steel, is located between the burner and the sheet to prevent material emitted from the burner from Impacting against the sheet at any location other than the desired marginal strip, and the burner is arranged so that the central portion of the cone of material emitted from the burner will impact against that marginal region. If the metal strip being deposited extends right to the edge of the sheet, some waste material may be collected after it has passed the sheet. The sheet may be provided with such a flame-sprayed metal layer during its conveyance past a spraying station, or alternatively, the sheet may be held still while the burner is passed along the margin of the sheet, depending on what is found most convenient. The gas feed rates to the flame are adjusted so that the flame is a reducing flame to result in the deposition of a metal strip which is low in oxide and which adheres well to the previously deposited opaque enamel. The deposition of metal is confined to the area occupied by the opaque enamel 2 so that it is wholly masked from the opposite face of the sheet 1. in this manner it is very simple to make a substantially unif(yrm deposit of metal having a thickness of about 10 micrometres. if it is desired to make a metal collector strip 5 of lower resistivity, it is a very simple matter to increase the thickness of the collector by making one or more additional passes of the flame spraying apparatuE.

A ceiitral portion of each metal strip 5 is then tinned and a terminal 6 is soldered thereto.

The terminals 6 are found to be securely attached to the sheet 1. and the metal strips 5 serve as current collectors for the heatable grid 3.

if desired, the sheet 1 may be allowed to cool after firing of the enamel deposits so that the opaque enamel 2 on the side margins of the sheets may be dressed, for example using steel'wool, to provide a key so that the deposited metal film is more strongly adherent thereto.

The strip 5 of metal is conveniently formed from: copper, or nickel, or an alloy of copper and nickel, or of nickel and chromium, or of coppex and titanium, optionally containing zinc and/or aluminium.

Figure 2 shows a detail of another panel comprising a glass sheet 1 bearing a marginal deposit of opaque enamel 2. in this embodiment. conductive enamel grid lines 4 are applied to the sheet I at the same time 12 as current collectors 7 of the same conductive enamel. Those current collectors 7 are confined to marginal regions of the sheet so that they are masked from the opposite face of the sheet 1 by the opaque enamel 2. A localised deposit 8 of metal is formed within the area of each current collector 7 in the manner described with reference to Figure 1. the metal is tinned and a terminal 6 is soldered thereto. In a variant, the metal is deposited as a current collector such as the strip 5 shown in Figure 1. This allows a reduction in the amount of conductive enamel applied to form the current collector 7.

Figure 3 may be considered as a sectional view of the embodiment of Figure 1, or of the embodiment of Figure 2, and it shows a layer of solder 9 securing the terminal 6 to the metal deposit 5 or 8 as appropriate. If the metal deposit is a localised deposit such as 8, then there must be presenta current collector of conductive enamel 7 overlying the opaque enamel layer 2- lf on the other hand, the metal deposit is an elongate current collectoi such aE 5, then the conductive enamel overlying the opaque enamel 2 may be constituted either by the ends of the conductive lines 4 alone Figure 4 a continuous stannic oxide margin of the or by a current collector such as 7. shows one marginal region of a vitreous sheet 1 which bears transparent conductive coating 10 for example of doped - A conductive enamel current collector 7 is applied to a sheet 1, and a localised deposit 8 of metal is formed thereon. A terminal 6 is secured to the deposit 8 of metal by means of a layer of solder 9. In a variant, the metal is deposited on the enamel -1 as an additional current collector in the form of a strip such as the strip 5 shown in Figure 1.

Figure 5 shows in section a detail of an embodiment which is in effect the embodiment of Figure 2 but without the marginal deposit 2 of opaque enamel. The vitreous sheet 1 bears a conductive grid of enamel lines 4 connected to current collectors such as 7 also of conductive enamel. A metal deposit 8 is formed on the enamel current collector and a terminal 6 is secured thereto by the solder layer 9.

Figure 6 show a detail of another panel comprising a glass sheet 1 bearing conductive enamel lines 4 forming a heating grid 3 which (xteridbetween current collectors -1 of the same conductive enamel. Those current collectors 7 extend down the side marginal regions of the sheet arid part way along the bottom margin. An elongate deposit 11 of metal is formed within the area of each current collector 7 in the manner described with 13 reference to Figure 1, in order to facilitate current flow along the collectors. In this embodiment, a terminal 6 is soldered to an end region of the collector 7 which is not overcoated with the metal deposit 11. in a variant, the metal is deposited over a greater area of the current collector, for example coextensively with it. This allows a reduction in the amount of conductive enamel applied to form the current collector 7. for example by permitting a reduction in the width to which the collector is deposited.

Figure 7 shows a detail of yet another panel comprising a glass sheet 1 bearing conductive enamel lines 4 forming a heating grid which extends across the sheet. A deposit of opaque non-conductive enamel 2 is applied serigraphically in a manner known per se around the entire periphery of the sheet 1, and a conductive grid composed of lines 4 of electrically conductive enamel is also applied to the sheet by a serigraphic technique, so that those lines extend between the side margins of the sheet 1, their ends overlying the opaque enamel 2 at those margins. The opaque enamel deposit 2 includes a discontinuous strip 12 formed by spot deposits of enamel located inwardly of a peripheral continuous deposit of that enamel.

A metal strip 5 is flame-sprayed along substantially the full length of each side margin so that it is in direct contact with the ends of the grid lines 4 at that margin of the sheet. The metal strip 5 extends over the discontinuous strip 12 of opaque enamel so that parts of it are directly bonded to the glass sheet 1. A central portion of each metal strip 5 is then tinned and a terminal 6 is secured to it with solder 9.

14

Claims

1. An article comprising a vitreous substrate bearing electric circuit means which is formed at least in part from, or is in contact with, a deposit or deposits of vitreous enamel, characterised in that the circuit means includes at least one current collector which consists of or includes a metal deposit in contact with the or a said enamel deposit.

2. An article according to claim 1. wherein said electric circuit means consists of or includes at least one deposit of a conductive vitreous enamel.

3. An article according to claim 1 or 2, wherein elongate current collectors are provided deposited on said substrate and said electric circuit means includes at least one conductive element adherent to the substrate and extending between such collectors.

4. An article according to claim 3, wherein the or at least one said elongate current collector consists of or includes an elongate metal deposit.

5. An article according to any preceding claim, wherein the or at least one said current collector is wholly or mainly formed by a said metal deposit.

6. An article according to any preceding claim, wherein a terminal is soldered to the or each current collector.

7. An article according to claim 6, wherein such terminal is soldered to the or a said metal deposit.

8. An article according to any preceding claim, wherein the or a said metal deposit has been formed at a temperature above 120C.

9. An article according to claim 8, wherein the or a said metal deposit is a flame-sprayed deposit.

10. An article according to any preceding claim, wherein the or a said metal deposit overlies subjacent vitreous enamel.

11. An article according to claim 10, wherein such metal deposit overlies a subjacent deposit of non-conducting vitreous enamel.

12. An article according to claim 10 or 11, wherein such metal deposit overlies a discontinuous subjacent deposit of vitreous endlitel whereby part of such metal deposit is in direct contact with the ViLr(!OU-substrate.

1 1 1 I.

13. An article according to any preceding claim, wherein said metal deposit is formed Erom: copper, or nickel, or an alloy of copper and nickel, or of nickel and chromium, or of copper and titanium, optionally containing zinc and/or aluminium.

14. An article according to any preceding claim constituted as a heatable window of a vehicle.

15. An article according to any preceding claim, wherein the substrate bears a marginal deposit of non-conducting opaque enamel extending around its entire periphery.

16. An article according to claims 14 and 15, wherein such window is bonded to the body of a vehicle by adhesive material which is masked from the exterior of the vehicle by such marginal deposit of opaque enamel.

17. An article according to claim 16, wherein such marginal deposit of enamell contains pigment to match its colour to that of the vehicle.

18. A method of manufacturing an article comprising a vitreous subtrate bearing electric circuit means which is formed at least in part from, ot is in contact with, a deposit or deposits of vitreous enamel, which method is characterised by providing a current collector of said circuit means whose formation includes the step of depositing a layer of metal so that in the finished article such layer is in contact with the or a said enamel deposit.

19. A method according to claim 18, wherein said circuit means is formed by a process including the step of depositing at least one body of conductive vitreouf; enamel on said substratc.

20. A rno-thod according to claim 18 _)i 19, wherein said circuit means is formed by a process including the steps of depositing on said substrate a pair of elongate current collectors and at least one conductive element adherent to the substrate and extending between such collectors.

21. A method according to claim 20, wherein the formation of at least one said elongate current collector consists of or includes the step of depositing a said layer of metal as an elongate strip.

22. A method according to any of claims 18 to 21, wherein the or at least one said current collector is formed in such manner that at least the greater part by weight of thc c(-.)nductive matterial deposited in such collector is contairiod in said layer of metal.

2?. A mtthod acc-(-.)rdi-ng to any of claim,- 18 to 22, whfreirj a termindl is soldered to the or each current collector.

16 24. A method according to claim 23, wherein such terminal is soldered to the or a said metal layer.

25. A method according to any of claims 18 to 24. wherein the or a said metal deposit is formed at a temperature above 120'C.

26. A method according to claim 24, wherein the or a said metal deposit is formed by flame-spraying.

27. A method according to any preceding claim, wherein the or a said metal layer is deposited on top of at least one subjacent deposit of vitreous enamel.

28. A method according to claim 27, wherein the or a said metal layer is deposited on top of at least one subjacent deposit of non-conducting vitreous enamel.

29. A method according to claim 27 or 28, wherein such metal layer is deposited on top of a discontinuous subjacent deposit of vitreous enamel whereby part of such metal layer is in direct contact with the vitreous subf,trite.

30. A methodi according to any of claims 18 to 29, wherein said metal deposit is formed Erom: copper, or nickel, or an alloy of copper and nickel, or of nickel and chromium, or of copper and titanium, optionally containing zinc and/or aluminium.

o 0 o - Ilubhshedl990a:,-The Patent O:ffice.Stateeliouse.66 71 High HoIborn. LondonWClR4TP_Further copies maybe obtained from The Patent Office Sales Branch. St Ma::; Cray. Orpington. Kent BR5 3RD Printed by Multiplex teclimques Itd. St Mary Cray. Kent- Con 1 87 f 1 1