FR2487152A1 - Printed circuit substrate and component support mfr. - uses mask applied over substrate over which conductive layer is deposited and from which unwanted parts of layer are removed - Google Patents

Abstract

The substrate is produced from a plastics injection moulding or by machining a ceramic or glass base or other insulating material, with the holes for the component leads. A protective mask is placed on one face of the substrate and a conductive layer deposited over it, the mask is then removed. Alternatively the conductive tracks are embossed on the face of the substrate and formed by fusion of metal powder or vacuum deposition. The mask may be a thin foil of stainless steel, or an anti-adhesion layer. The unwanted conductive layer may be rubbed away by a brush or an abrasive or ultrasonic cleaning or by milling. The components, may be mounted on the substrate before the conductive layer is deposited and the substrate and component leads cleaned by brushing or sanding after the components have been mounted. The substrate has particular application in the production of analogue electronic watches. The processes consist of a reduced number of simple stages which lend themselves to automation.

Description

METHODS OF MANUFACTURING A SUBSTRATE AND A MODULE
INCLUDING THIS SUBSTRATE
The present invention relates to methods of manufacturing a substrate comprising an insulating support of determined shape having a first and a second face and at least one conductive surface disposed on a part of said first face, for a module comprising at least one electronic component. .

 It also relates to a method of manufacturing a module comprising, on the one hand, a substrate comprising an insulating support of determined shape having a first and a second face and at least one conductive surface disposed on a part of said first face, and , on the other hand, at least one electronic component having at least one connection element electrically connected to said conductive surface.

 Such modules are used in almost all devices including electronic components, such as transistors, diodes or integrated circuits and / or electrical components such as resistors or capacitors.

They generally comprise a substrate constituted by a printed circuit ensuring both the mechanical support of the components and their electrical connection. Where appropriate, the printed circuit includes terminals allowing the electrical connection of the module with other modules or with external elements such as push-buttons, display devices or electro-mechanical elements (motors, transducers, etc. .)
The printed circuit is made from insulating supports cut to the desired shape and dimensions from plates or films previously covered on one or both sides with a conductive layer generally made of copper. If necessary, holes are drilled in the support and in the conductive layer.

 The conductive surfaces, or tracks, necessary for the electrical connection of the various components to each other or to the input or output terminals are then obtained by etching this copper layer by a photolithographic process and, where appropriate, the holes are metallized by an electro-chemical process.

 The electrical or electronic components are then mounted on the printed circuit. Their connection wires are placed in the holes, metallized or not, and bent so that they are held mechanically before the welding operation. The latter is carried out for example on each wire individually using a soldering iron, or simultaneously for all the wires in a so-called wave soldering operation.

 Various auxiliary operations must be planned during the course of this manufacture. In general, one or more protective layers, of tin or even gold, must be deposited on the printed circuit to avoid corrosion of the copper and / or improve the welding conditions. A lacquer layer is still sometimes deposited on the printed circuit, after soldering the components, again to avoid corrosion problems.

 Other modules use as a substrate of the printed circuit a ceramic plate on which conductive tracks are attached, for example by screen printing. The assembly and soldering of the components are carried out by processes very similar to those used with conventional printed circuits.

 The above description, even if very brief, shows that the manufacture of substrates and electronic modules requires a series of numerous and relatively complex operations. As a result, electronic modules are expensive components, despite all the progress that has been made and continues to be made in their manufacture.

 In addition, in the total cost price of a module, the share coming from the price of the printed circuit and the cost of assembly and soldering of the components tends to increase. The components are indeed very standardized, which makes it possible to manufacture them in very large series and therefore to reduce their price. The printed circuits, on the other hand, are different for each type of device, which prevents their manufacture in very large series. The mounting and welding of the components must also be adapted from case to case, which does not make it possible to reduce the cost of the modules to the desired extent.

 This problem is not very acute in devices such as computers or machine controls where the modules include a large number of components mounted on a single printed circuit. In devices such as electronic watches, where the modules contain only a few components mounted on a printed circuit, this problem becomes significant.

 An object of the present invention is to propose manufacturing methods making it possible to reduce the price of the substrate of an electronic module.

 This object is achieved by the process consisting in providing an insulating support having the shape and the dimensions of the substrate and manufactured, for example, by injection of a plastic material in a suitable mold, in applying a protective mask on a first face of the support leaving uncovered the part of this first face intended to receive a conductive surface, to deposit on this first face provided with this mask a conductive layer, for example, by spraying a molten metal, and finally to eliminate the part of this conductive layer which is deposited on the mask, the rest of this conductive layer then constituting the conductive surface.

 This object is also achieved by a process close to the previous one, consisting in providing an insulating support having the shape and the dimensions of the substrate and the part of its first face intended to receive the conductive surface situated in withdrawal with respect to the rest of this first face. , and manufactured by injecting a plastic material into a suitable mold, depositing a conductive layer on the whole of this first face, for example by spraying a molten metal, and removing the surface layer of the first face, for example by milling, without touching its recessed part, which eliminates the part of the conductive layer deposited on this surface layer, the rest of this conductive layer then constituting the conductive surface.

 Another object of the present invention is to propose a manufacturing method making it possible to reduce the price of an electronic module.

 This object is achieved by the method consisting in manufacturing a substrate according to one of the preceding methods, in mounting the components on the support before the conductive layer has been deposited, by placing the connection wires of these components at the locations of the support intended receiving the conductive surfaces, and depositing the conductive layer also on these connection wires.

 Other characteristics and advantages of the invention will appear on reading the following description of particular modes of the methods given solely by way of examples, with reference to the appended drawing in which - FIG. 1 is a partial view of a module electronic; - Figures 2a to 2e are sections along the axis A-A of Figure I and illustrate a first method of manufacturing this module according to the invention; - Figure 3 illustrates a possibility of fixing a component on the module substrate; - Figure 4 illustrates a possibility of electrical connection of a component with a conductive track of the substrate; - Figures Sa to 5d are also sections along the axis A-A of Figure 1 and illustrate a variant of the first method; - Figures 6a to 6c are also sections along the axis A-A of the module of Figure 1 and illustrate a second method of manufacturing the module of fig. 1 according to the invention; and - Figure 7 is a section along the line Vil-Vil of Figure 6a.

 FIG. 1 represents a portion of one of the faces of an electronic module. This module comprises a substrate formed by an insulating support 1 pierced with holes such as 2 and by conductive surfaces, or tracks, such as 3, disposed on this support.

 Electrical or electronic components are placed on the face of the substrate not visible in this figure 1. One of the connection wires, designated by 4, of one of these components, is placed in the hole 2. It is electrically connected to the track conductive 3 by a drop of solder which has not been shown so as not to interfere with the understanding of the drawing.

 The substrate 1 provided with its holes such as 2 can be manufactured with its shape and its final dimensions, for example, by a well known method of injecting a plastic material into a mold of suitable shape. It can also be manufactured by machining a ceramic or glass plate, or any other insulating material. The methods used for this machining will not be described in more detail here, since they depend on the material chosen and are, in any case, well known.

 In a first method of manufacturing the substrate according to the invention, this support 1 is substantially flat (FIG. 2a). One of its faces, la is covered, after its manufacture, with a protective mask 5 (fig. 2b). This mask 5 has a shape such that it covers the entire face 1a of the support 1, with the exception of the areas where the conductive tracks 3 will be formed in a later stage of the process.

This mask 5 can be mechanical, that is to say formed by a thin sheet, or film, of a metal such as, for example, brass or stainless steel, or a plastic such as, for example , Teflon or Kapton (registered trademarks of the Dupont house of
Nemours). It naturally includes in this case, openings having the shape of the desired conductive tracks.

 This mask 5 can also be formed by a layer of a non-stick material such as that which is sold under the name of "Anti-bond" by the house of Metco Suisse SA in Glatbrugg (Switzerland).

This layer is then deposited in the desired places, by screen printing for example.

 In the next step of the method, a conductive layer is deposited on the entire surface of the support 2 which remains uncovered and on the mask 5. The part deposited directly on the support 1 forms the conductive tracks or surfaces such as 3. The part 6 deposited on mask 5 (fig. 2c) will be eliminated in the next step.

 This conductive layer can be deposited by any known method. The vacuum metallization technique, for example, has been used successfully. A particularly simple process, which has also been used with success, consists in spraying the support 1 and the mask 5 with a molten metal. Manual or automatic installations that allow almost any metal to be sprayed are often used in the manufacture of mechanical parts. The metal thus deposited serves to reinforce these parts or to protect them against wear or corrosion. These installations can be adapted without difficulty to the present process.

It is obvious that ceramic and glass, which withstand high temperatures without damage, are perfectly suitable as a support material when the conductive layer is deposited by this method of spraying a molten metal. However, tests have shown that even plastics whose melting temperature is lower than the melting temperature of the metal used, such as Ryton (registered trademark of the house
Phillips Petroleum Company), can be used successfully.

 The thickness of the conductive layer naturally depends on the duration of the deposition operation. If this thickness is small, the rise in temperature of the support during deposition is minimal and remains localized in its surface layer.

 If the thickness of the desired conductive layer is large, it suffices to make the deposit by several successive short-term sprays, separated by sufficient intervals so that the support can cool. Any deformation of the support is thus avoided.

 Attempts to spray metals such as tin alloys commonly used as low temperature solder or zinc have given good results. Other metals can of course be used. Their choice depends on the process chosen for the deposit, the nature of the support, etc.

 The next step, illustrated by FIG. 2d, consists in eliminating the parts 6 of the conductive layer which are on the mask 5, therefore outside of the conductive surfaces such as 3.

 This elimination is done simply by removing the mask 5 if the latter is a mechanical mask. If the mask 5 consists of a layer of non-stick material, this elimination can be done by rubbing the substrate using a brush or an abrasive such as sandpaper or emery paper. It is also possible to remove this part 6 from the metal layer by an ultrasonic cleaning process. In such a well-known method, the support is immersed in a liquid and subjected, via the liquid, to ultrasonic vibrations. These vibrations cause the elimination of the non-stick layer 5 and of the conductive layer 6.

 The substrate thus obtained is finished, and it can be used as a conventional printed circuit, for the manufacture of an electronic module. In a known method of manufacturing such a module, the electrical or electronic components such as the component 7 shown partially in FIG. 2e are mounted at their location on the face of the substrate opposite to that carrying the conductive tracks. Their connection wires such as 4 are bent to the desired shape and placed in the holes such as 2. The components are fixed in their location by bending their connection wires, by gluing or by pushing back part of the material of the support as illustrated in figure 3.

 This FIG. 3 is a section through the support 1 and a cylindrical component 8, a resistor for example. This component 8 is placed in a housing 9 formed in the support 1. It is held in this housing by two bulges 1 of the material of the support 1. This material has been driven back by the action of ultrasound transmitted by a tool of adequate shape, supported with sufficient force in 11.

 The method of fixing the components illustrated in this FIG. 3 is obviously applicable only if the support is made of plastic.

 After the components such as 7 or 8 have been put in place and fixed in one way or another, their connection wires are electrically connected to the conductive tracks 3, for example by a drop of solder 12 (fig. 2nd). This drop of solder can be deposited by means of a soldering iron or by a technique known as wave soldering or by any other process. The module as shown in Figure 2e is then finished.

 If the conductive tracks 3 are constituted by a meltable material at relatively low temperature, such as a tin alloy, it is also possible to bond the wires 4 with the tracks 3 by a so-called reflow process. In such a process, the material of the tracks is heated to a temperature such that it begins to melt. This material flows and comes into contact with the connection wires 4. After cooling, an electrical connection is thus established between the tracks 3 and the wires 4.

 It should be noted that the components such as 7 are not necessarily required to be mounted on the face of the support 1 opposite the face carrying it the conductive tracks 3.

 These components could just as easily be mounted on the side of these conductive tracks. Likewise, and especially in the latter case, the connection wires 4 do not necessarily have to be put in holes such as 2. They can just as easily be applied against the conductive tracks 3.

 The latter technique obviously applies to the case of the electrical connection of the terminals of a component having no actual connection wires. This case is illustrated by FIG. 4 which shows in partial section a module comprising # ant a substrate formed by a support 1 and conductive tracks 3, obtained by the method described above. The module comprises an integrated circuit 13 provided not with connection wires but with terminals 14, which are inaccessible for conventional welding by adding solder. In such a case, the method using the reflow of the material of the conductive tracks 3 applies particularly well.

 Figures Sa and 5d illustrate a method of manufacturing a module according to the invention.

 In this method, the support 1 is manufactured as described with the aid of FIG. 2a.

 The next step is illustrated in FIG. Sa. It consists in placing the components such as 7, in fixing them on the support, as described above, and in placing their connection wires in the places provided for the conductive tracks.

 The protective mask 5 is then applied (fig. 5b), and the conductive layer deposited (fig. 5c) as has also been described above.

 As the connection wires 4 of the components 7 are already in place, the conductive layer is also deposited on them. The electrical connection of these wires 4 with the tracks 3 is therefore directly carried out during this deposition, and the soldering step described above is eliminated.

 To ensure good electrical contact and good adhesion of the conductive layer on the connection wires, it is desirable to remove from them the oxide layer which generally covers them, and to make them slightly rough.

 This can be done by brushing or sanding the substrate after the components have been put in place and before applying the protective mask.

 The last step of this process again consists in eliminating the part 6 of the metallic layer which is deposited on the mask 5. This elimination can be done as described above. The module as shown in Figure 5d is then finished.

 This process is particularly advantageous because it makes it possible to reduce the price of the module by eliminating the step of soldering the connection elements.

 Another method of manufacturing a substrate according to the invention is illustrated by FIGS. 6 and 7. In this method the support 1 is manufactured so as to present surfaces located set back from its outer surface. These surfaces are constituted by the bottom of grooves designated by 15 in Figures 6a and 7. This Figure 7 is a section of the support 1 by a plane perpendicular to the plane of Figure 6a and cutting the latter along the line Vil-Vil.

 The shape of these grooves, in a plan view of the substrate, is identical to the shape of the conductive surfaces such as the track 3 in FIG. 1.

 In this process, the support 1 is advantageously made by injecting plastic material into a mold. It is indeed the easiest way to form the grooves 15. It is however not excluded to manufacture the substrate with its grooves 15 by machining a ceramic or glass plate.

 The next step of this process consists in depositing over the entire surface of this support 1 a conductive layer, again by any of the processes described above.

 Part of this conductive layer designated by 6 in FIG. 6b is deposited on the external surface of the support 1. Another part, designated by 3, is deposited at the bottom of the grooves 15.

 In the next step of this process, the surface of the support 1 is machined, for example by milling, so as to remove the surface layer of material located above the line 16 drawn in phantom in Figure 6b.

 Figure 6c shows the substrate finished after this machining.

Parts 6 of the conductive layer have been removed, while parts 3, which form the conductive tracks, have not been touched.

 The process which has just been described has the advantage over the previous one of not having a step of depositing a protective mask. On the other hand, it has the drawback of requiring a more complex mold for the manufacture of the support.

 The support provided with grooves used in the latter method can also be used in a variant of the first method of manufacturing the substrate described above. In this variant, the substrate support is provided with its grooves. The protective mask 5 is deposited on the external surface of the support, between the edges of the grooves. The part of the conductive layer which is deposited, in the following step, on this mask, is then removed by one of the means described, without removing material from the surface of the support. A possible deformation of the support caused by the release of internal stresses during the machining of the surface layer can thus be avoided.

 This possible deformation can also be avoided even in the process where the surface layer of the support is removed by machining, to separate the conductive tracks from each other. To do this, it suffices to provide very wide grooves, occupying practically the entire surface of the support, separated by thin walls. The amount of material removed by this machining is then low enough so that there is no longer any risk of deformation of the support.

 Whatever the manufacturing process for this substrate provided with grooves, the module using this substrate can be manufactured according to one of the processes described above. The second of these methods, which consists in placing the components before depositing the conductive layer, is particularly advantageous in this case.

 The methods described above are not limited to the manufacture of substrates carrying conductive surfaces on only one of their faces. It is obvious that they are easily applied to the manufacture of substrates carrying conductive surfaces on their two faces.

 For this, it suffices to subject the second face of the support to the same operations as those which have been described. Almost all of these operations can be done at the same time on both sides.

 In the case of such a substrate carrying conductive tracks on the two faces, electrical connections must often be established between conductive tracks located on different faces. Such a connection can for example be carried out by a connection wire of an element placed in a hole passing through the substrate. This wire is soldered on each side of the substrate to the corresponding track.

 It is also possible to use for this purpose a small piece of conductive wire also placed in a hole in the substrate and welded at its two ends to the desired conductive tracks. It is finally possible to make metallized holes during the operation of depositing the conductive layer.

 It is obvious that the module manufactured according to one of the methods described above can also serve as a support for mechanical or electro-mechanical elements. This possibility is particularly advantageous when the module is intended to be used in an electronic watch comprising needles and an electric motor driving these needles by means of a gear train. In such a case, it is possible to provide in the support housings intended to receive at least part of the mechanical elements such as the gear wheels or their bearings.

 In summary, the methods according to the invention comprise a reduced series of simple steps which lend themselves well to advanced automation. They therefore make it possible to significantly reduce the cost of manufacturing substrates and / or electronic modules compared to conventional methods.

Claims (24)

 1. A method of manufacturing a substrate, comprising an insulating support of determined shape and dimensions having a first and a second face and at least one conductive surface disposed on a part of said first face, for a module comprising at least one component electric or electronic, characterized in that it consists of - providing said support with said shape and said dimensions; - applying a protective mask on said first face outside said part of the first face; - depositing a conductive layer on said part of the first face and on said mask; and - removing the part of said conductive layer then constituting said conductive surface.  2. Method according to claim 1, characterized in that it consists in providing said support with, in addition, said part of the first face set back from the rest of said first face.  3. Method according to claim 1, characterized in that it consists in providing said support with, in addition, a housing for said component.  4. Method according to claims 1, 2 or 3, characterized in that it consists in depositing said conductive layer by spraying a molten metal.  5. Method according to claims 1, 2 or 3, characterized in that it consists in depositing said conductive layer by vacuum evaporation of a metal.  6. Method according to claims 1, 2 or 3, characterized in that it consists in applying said mask by depositing a non-stick material.  7. Method according to claim 6, characterized in that it consists in eliminating said part of the conductive layer by rubbing said first face by means of a brush or an abrasive.  8. Method according to claim 6, characterized in that it consists in eliminating said part of the conductive layer by ultrasonic cleaning of said substrate.  9. Method according to claims 1, 2 or 3, characterized in that said mask is a mechanical mask and in that it consists in eliminating said part of the conductive layer by removing said mask.  10. Method according to claim 9, characterized in that said mask is cut from a metallic film.  11. Method according to claim 9, characterized in that said mask is cut from a plastic film.  12. Method according to claims 1, 2 or 3, characterized in that said support is provided by a method comprising the injection of a plastic material into a mold.  13. Method according to claims 1, 2 or 3, characterized in that said support is provided by a method comprising the machining of a ceramic plate.  14. Method according to claims 1, 2 or 3, characterized in that said support is provided by a method comprising the machining of a glass plate.  15. Method according to claims 1, 2 or 3, characterized in that it consists - of applying in addition to said second face a second mask leaving uncovered part of said second face and protecting the rest of said second face; - further depositing a conductive layer on said exposed portion of the second face and on said second mask; and - removing the part of said conductive layer deposited on said second mask, the remainder of said conductive layer, deposited on said exposed part of the second face, then constituting a conductive surface carried by said second face.  16. Method for manufacturing a substrate comprising an insulating support of determined shape and dimensions having a first and a second face and at least one conductive surface disposed on a part of said first face, for a module comprising at least one electrical component or electronic, characterized by the fact that it consists of - providing said support with said shape and said dimensions and with said part of the first face set back from the rest of said first face by injecting a plastic material into a mold; - depositing a conductive layer on the whole of said first face; and - removing the surface layer from said remainder of the first face to eliminate the part of said conductive layer deposited on said rest of the first face, the remainder of said conductive layer then constituting said conductive surface.  17. The method of claim 16, characterized in that it consists in providing said support with, in addition, a housing for said component.  18. The method of claims 16 or 17, characterized in that it consists in depositing said conductive layer by spraying a molten metal.  19. Method according to claims 16 or 17, characterized in that it consists in depositing said conductive layer by vacuum evaporation of a metal.  20. Method according to claims 16 or 17, characterized in that it consists in removing said surface layer by milling of said first face.  21. Method according to claims 16 or 17, characterized in that it consists in removing said surface layer by friction of said first face by means of an abrasive.  22. Method according to claims 16 or 17, characterized in that it consists in providing said support with, in addition, a part of said second face located behind the rest of said second face, to deposit, in addition, a second conductive layer on the entirety of said second face and removing the surface layer of said remainder of the second face to remove the part of said second conductive layer deposited on said remainder of the second face, the remainder of said second conductive layer then constituting a second conductive surface disposed on said second face.  23. A method of manufacturing a module comprising, on the one hand, a substrate comprising an insulating support of determined shape and dimensions having a first and a second face and at least one conductive surface disposed on a part of said first face, and, on the other hand, at least one electrical or electronic component having at least one connection element electrically connected to said conductive surface, characterized in that it consists in - manufacturing a substrate according to the method of any one of claims 1 to 22; - mounting said component on said support before said conductive layer has been deposited, by placing said connection element on said part of the first face; and - additionally depositing said conductive layer on said connection element.  24. The method of claim 23, characterized in that it consists in brushing or sanding said support and said connection element after said component has been mounted.