FR2502444A1 - PROCESS FOR PRODUCING PRINTED CIRCUITS - Google Patents

Abstract

PROCESS FOR THE PRODUCTION OF PRINTED COPPER CIRCUITS WITH PARTIALLY COPPER AND TILE PADS AND HOLES. THE PRINTED WIRING TRACE IS OBTAINED BY BITTING THE PLATE 2, 3 OF AN INSULATING SUPPORT 1. THE AUXILIARY SUPPLY CONDUCTORS 8, 9 ARE CONSTITUTED BY THE DEPOSIT OF A COPPER LAYER. THE PELLETS AND HOLES 4, 5 ARE COPPER AND TILED USING RESERVES. COPPER SUPPLY CONDUCTORS ARE ELIMINATED BY DIFFERENTIAL BITE AFTER MASK REMOVAL. THE PRINTED COPPER 2, 3 WIRING IS EQUIPPED WITH A 14 CORROSION PROTECTION LAYER.

Description

The present invention relates to a process for the production of

  copper printed circuits with pellets and partial holes

coppered and tinned.

  The further miniaturization of discrete components and the increasing degree of integration of integrated circuits are placing new demands on their wiring units in the form of printed circuits. The current means no longer make it possible to satisfy these

  requirements, despite the development of the subtractive technique.

  Trials to control geometries greater than or equal to

  50 pm in mass production, by an additive technique, half

  additive, PDR or photoadditive, have not been successful

  than now. External influences are the cause: dust, air humidity, temperature, properties of the specific materials of the insulating support and spare films, scum, reserve spikes, galvanic influences, etc. The use of multilayer systems is imitated for economic reasons and because these systems are not

practically not repairable.

  The subject of the invention is a process which makes it possible to satisfy the most stringent requirements and consequently economically and without limitation conductor strips having a width of 50 μm or more of a thickness of 15 μm or of 70 to 175 μm. , and with a spacing of pm or more. According to an essential characteristic of the invention, the layout of the printed wiring is obtained by biting the veneer of an insulating support; the auxiliary power supply conductors are constituted

  by depositing a layer of copper; the pellets and holes are

  partly coppered and tinned with reserves; the drivers

  Auxiliary copper feeders are removed by different bite.

  after the removal of the mask; and printed copper wiring

  has a protective layer against corrosion. The pro-

  tector is advantageously constituted by a photo-epoxy resin

  polymer. The first phase of the process according to the invention is thus the

  engraving of the printed wiring layout in the veneer of the insulating support.

  The influence of dust is very low when it is advantageous to use

  a positive liquid reserve with a resolving power of about 1 μm. The thickness of the conductive strips is fixed by the

  choice of the thickness of the copper layer plating the

  lant. The troublesome influences of subtractive and semi

  additive disappear, because there is no galvanic deposition on the conductive strips. Auxiliary power conductors are required to partially copper and tin the beaches and holes. They are

  deposited on the entire surface and simultaneously constitute the premetition

  holes. Auxiliary power supply conductors

  only about 2 kgf / inch of adhesion on the etched insulating support, but this is not a problem because they are

  then eliminated by bite. Auxiliary power drivers

  are removed by a differential bite after copper plating

  partial fraction of 30 μm and the partial tinning of 8 & 20 vm according to the technique.

  In order to reduce the action of the differential bite, the first mas-

  that etching is advantageously maintained on the conductive strips of copper and simply copper. Partial coppering and tinning obviously require a second photomask or screen mask, which is however not critical as a result of the relative geometries.

coarse pellets and holes.

  In a preferred embodiment of the invention, the copper conductive strips are protected against corrosion and mechanical damage. Since the tolerances of conventional screen printing processes with binary varnishes are approximately 0.2 mm, a photopolymer epoxy resin is used which, after exposure and development,

  is hardened thermally at 135 0C by its hardener additive. The tolerances

  The costs of this process are 30 um. The adhesion force on copper

is good.

  The procedure of the process according to the invention is presented by

example as follows.

  1. Cutting the insulating support with the corresponding thickness of the

veneer layer.

  2. Drilling holes on a numerically controlled drill

freezer.

3. Deburring and fine brushing.

  4. Deposition of the positive liquid reserve by casting a layer having

a thickness of about 8 μm.

  5. Insolation and development of printed wiring.

  6. Engraving the printed wiring layout, preferably with a solu--

  Bite bite with CuCl or alkaline.

  7. Second sunstroke and development of pellets and holes.

  8. Deposit of auxiliary supply conductors and premetallisa-

  holes by chemical and galvanic deposition of copper.

  9. Fine brushing of the premetallization.

  10. Deposit of the second mask by photography or silkscreen.

  11. Copper (30 μm) and tinning (8 to 20 μm) partial.

  12. Removal in methylene chloride.

  13. Alkaline differential bite with optical brightener

in the case of tin-lead.

  14. Removal of the first photomask in methylene chloride.

15. Fusion of the eta-n-lead.

  16. Polishing copper surfaces by fine brushing and drying.

  17. Casting of a photopolymer epoxy resin.

  18. Insolation and development using a mask film.

19. Hardening at 1350, 1 hour.

20. Contour cutting.

21. Final check.

  Other features and advantages of the invention will be better

  understood using the detailed description below of an example

  embodiment and the accompanying drawings in which:

  FIG. 1 represents an insulating support whose two faces present

  a copper plating; Figure 2 shows the insulating support double-sided plated and provided with two holes; Figure 3 shows the double-sided plated insulating support and pierced after depositing a reserve on both sides; FIG. 4 represents a reserve mask with the desired layout of the conductors; Figure 5 shows the result obtained by the bite of the copper layers at the places not protected by the reserve; FIG. 6 represents the result obtained by eliminating the reserve layer in the vicinity of the holes by a new path; Figure 7 shows the device according to Figure 6 after the deposition of a copper layer on both sides; Figure 8 shows the device according to Figure 7 after the deposition of a second mask layer on both sides; Figure 9 shows the device after the copper plating and tinning pellets and holes; Fig. 10 shows the device after the removal of the second mask and auxiliary power conductors; and the figure it represents the printed circuit after protection of the bands

  copper conductors against corrosion.

  The production of a printed circuit according to the invention is made from an insulating plate 1, the two faces of which are according to FIG. 1 plated with copper, one face carrying the copper layer 2 and the opposite face the copper layer. 3. In order to establish a connection

  between specific points on one side and specific points

  mined on the other side, holes are drilled between the two faces of

the plate or insulating support 1.

  According to the geometry and the dimensions of the insulating support, the holes are made either at the beginning of the manufacturing process, or during

  at a later stage. In the case of an insulating plate of small geo-

  metie, the holes are produced before depositing the resist layer.

  This example is illustrated in FIG. 2, in which the insulating plate

  lante l two-sided plated is provided with two holes (4, 5). FIG. 2 obviously only represents a part of the complete insulating support;

  in practice, there are naturally many more than two holes in general

  ral. A resist layer (6, 7) is according to FIG.

  two plated faces of the insulating plate 1 provided with holes. For

  From the printed wiring, the resist layers 6 and 7 are insolated and then developed, thus producing a reserve mask with the desired pattern of conductors according to Figure 4. The copper layers (2, 3)

  are then eliminated by bite, with the exception of the parts

  green by the reserve. This stage is represented in FIG. 5, in which the insulating plate 1 comprises only the printed targeting 2, 3 with a cover layer (6, 7) in reserve, as well as the holes

(4, 5).

  Certain determined zones of the conductive strips, namely the pellets and the holes, must according to the invention be reinforced metallically. To do this, the remaining parts of the positive reserve layers are plotted a second time. Figure 6 shows the resist layers (6, 7) after the new trace, which removes them in the vicinity of the holes (4, 5). Since a power supply is required for the next galvanic deposition, intended to reinforce the pellets and to metallize the holes, a copper layer (8, 9) is deposited on both sides and simultaneously serves as a pre-metallization layer for the holes and pellets, such as the shows Figure 7. The thickness of these

  copper layers (8, 9) is preferably less than 10 Vm.

  In order to limit the copper layers (8, 9) to those parts where a copper coating is required, a second masking layer

  (10, 11) is deposited according to FIG. 8 on the printed circuit, and then

  in the desired way by insolation and development. The reinforcement

  Galvanic is then performed, with deposition of copper (12) and tin (13) through the holes of the masking layers (10, 11) according to Figure 9, on the loose pellets and in the holes. The deposited layer (12, 13) consists of a copper layer 12 with a thickness of about 30 μm and a layer of tin 13, with a thickness of less than 30 μm.

  The second mask (10, 11) and the auxiliary power conductors

  Then, the second mask (10, 11) is peeled off and the feed conductors (8, 9) are eliminated by a differential bite. The first mask (6, 7) covering the conductive strips (2, 3) is

then peeled also.

  Tinning is done with bright tin or an alloy

  tin-lead. In the latter case, the alloy is preferably melted.

  When the fusion oxidizes the copper conductive strips, the copper oxide layer thus produced is removed by polishing, for example. In order to protect the copper conductive strips (2, 3) against corrosion, the latter are advantageously embedded in a layer 14 of plastic material according to FIG. 11. The layer 14 is advantageously constituted by a photopolymer epoxy resin, which is eliminated in the region of the holes and pellets to allow subsequent welding. After drawing the layer 14 of plastic material, the epoxy resin is thermally cured in the form of

  binary system. The insulating plate 1 is then cut and

  trolled. Of course, various modifications may be made by those skilled in the art to the principle and to the devices which have just been described as non-limiting examples, without

depart from the scope of the invention.

Claims (10)

claims   A process for the production of copper printed circuits with pellets and partially copper-plated and tin-plated holes, and characterized   in that the layout of the printed wiring is obtained by biting the   cage of an insulating support; the auxiliary supply conductors consist of the deposition of a layer of copper; the pellets and holes are partially coppered and tinned with reserves; the auxiliary copper supply conductors are eliminated by differential bite after removal of the mask; and the wiring   printed copper is provided with a protective layer against   erosion ,. 2. Method according to claim 1, characterized in that the printed wiring copper is protected against corrosion by a resin photopolymer epoxy.   3. Method according to claims 1 or 2, characterized in that the   Holes are machined after engraving the layout of the printed wiring in the case of coarse geometries and before in the case of fine geometries.   4. Process according to any one of claims I and 3, characterized   in that a first photopolymer mask, preferably of the type   positive and can be insolated and developed several times, is   for engraving the layout of the printed wiring.   5. Process according to any one of claims 1 to 4, characterized   the fact that after engraving the layout of the printed wiring,   holes and holes are released by a second partial sunstroke and   a development of the reserve, while the first mask   polymer is kept on copper conductor strips as   stop layer for the differential bite.   6. Process according to any one of claims 1 to 5, characterized   characterized in that the auxiliary copper supply conductors are chemically or galvanically deposited; and the first photopolymer mask is covered on the copper conductive strips, and   the pellets and holes are precooked.   7. A process according to any one of claims 1 to 6, characterized   in that a second photopolymer mask or mask produced by   silkscreen is used by reserve for copper plating and tinning pellet and holes.   8. A process according to any one of claims 1 to 7, characterized   After the partial copper and tin-plating, the second mask is removed and the auxiliary copper-supply conductors are eliminated by differential bite, the first photopolymer mask on the copper conductive strips and the tin-plating. pellets and holes prohibiting an attack of these surfaces, so   that the initial accuracy of the plot is preserved.   9. Process according to any one of claims 1 to 8, characterized   in that for the protection of the copper conductive strips, a photopolymer epoxy resin is deposited by casting and then insolated   using a film, and the pellets and holes are hardened thermal- after development.   10. Process according to any one of claims 1 to 9, characterized   in that the partial tinning is carried out with bright tin,   a tin-lead alloy or a molten tin-lead alloy. l