DE4311266A1 - Electroless solder plated circuit board mfg. process - avoids copper@ layer attack by solder plating soln. - Google Patents

Abstract

Prodn. of a circuit board, having an electroless solder plated wiring pattern (1), involves (a) forming a wiring pattern (1) on a circuit board substrate (4); (b) covering a first portion (1, 2), requiring a solder coating, with an insulating mask (5); (c) electrolessly depositing a metal, which is not attacked by the solder plating soln., onto an exposed second portion (3) to form a metal mask (6); (d) removing the insulating mask (5); and (e) electrolessly plating solder alloy from an immersion bath onto the first portion (1, 2). Also claimed are (i) a circuit board having a relatively thin electrolessly plated solder alloy layer in the vias (3) and a relatively thick electrolessly plated solder alloy layer on fine contacts (1); (ii) a method of producing the above circuit board; (iii) a circuit board mfg. process in which a wiring pattern (1) and solder coatings are formed on the substrate (4), electroless copper plating is carried out on copper base contacting patterns and vias (3) of the wiring pattern and solder alloy is electrolessly plated onto the copper; and (iv) a circuit board mfg. process in which the circuit board substrate is stationary or is continuously or intermittently reciprocated in an electroless solder plating soln. ADVANTAGE - The processes avoid redn. of copper layer thickness of the wiring pattern and in the vias and improve circuit board reliability.

Description

The present invention relates to a method of manufacture development of a printed circuit board according to the preamble of claim 1. In particular, the invention relates to a method for manufacturing position of a printed circuit board with a solder alloy Wiring patterns of the circuit board is deposited by an electroless solder coating on the wiring patterns, without the copper coating thickness of a through hole decrease, is carried out.

Fig. 8 is a flowchart showing a flow of a method of manufacturing a circuit board according to the prior art, which is disclosed in JP 321183/1990. In a conventional circuit board according to the prior art, after a wiring pattern or wiring pattern has been formed on the circuit board and a solder cover has been applied or varnished, the circuit board is immersed in a coating solution of an electroless solder coating, whereby an accessible copper metal part with tin ions and lead ions react in the coating solution and a solder alloy with tin and lead as main components is deposited on the copper patterns.

The electroless solder coating is used as the coating solution a solution with tin, lead, an organic sulfonic acid and Thiocarbamide used as main components, such as as is known from JP 290774/1989. The coating solution of an electroless solder coating can be a solder alloy, whose main components are tin and lead, on the copper mine deposit tall as mentioned above. With such coating solutions of electroless solder coatings becomes a solder alloying with tin / lead-io reacting with the copper metal in the coating solution according to the following different exercise reaction deposited.

0.74 Sn ²⁺ + 0.26Pb ²⁺ + 2Cu → Sn-Pb (74 at% Sn) + 2Cu⁺.

In the above reaction formula, 2 moles of copper in the Coating solution dissolved when 1 mol of the solder alloy (74 at% Sn) is deposited. This corresponds to a thickness the solder alloy layer (74 at% Sn) of 1 µm in thickness loosened copper layer of 0.85 µm. The copper continues layer thickness in a copper etching step and the like that precedes the electroless solder coating step. This means that the Ab exceeds the above decrease quantity increase in the copper layer thickness actually caused.

Since the electroless solder coating according to the conventional Ver drive to manufacture a baffle as mentioned above the quantity of decrease is considerable, if a thick solder alloy layer with a thickness of not less than 10 µm should be deposited. Example wise foot contact pattern for attaching an IC package ses, in particular an IC package with fine connecting lines  like a TCP (tape carrier pack), require one high dimensional accuracy. However, if the pattern size by Performing an electroless solder coating is reduced, it becomes difficult to make these IC packages with high accuracy assemble.

It is also known that a through hole of the circuit board has a low thermal fatigue resistance if the copper layer thickness is not equal to or greater than at least 25 microns. FIG. 9B is a diagram illustrating a cross section of a through hole 31 of a circuit board under thermal stress in comparison with that of FIG. 9A in the normal situation. If the thermal load acts on a through hole 31 with a thin coating thickness, a crack 34 is caused at the central, coated part, since the coated part cannot withstand a load caused by different thermal expansion coefficients of a resin part 32 and a copper metal 33 becomes. In the case of a small through hole with a diameter of 0.3 to 0.6 mm, it is difficult to carry out the copper coating to a layer thickness which takes into account a decrease in the copper layer thickness which is reduced by the current-less solder coating.

As described above, is in a conventional method for the production of a printed circuit board by a currentless solder stratification pattern accuracy poor, and reliability Liquidity is reduced as no countermeasure is taken with regard to the decrease in the pattern size and the copper thickness of the through passage holes is provided.

The object of the present invention is to achieve the above-mentioned. Problems to solve and a method of manufacturing a circuit board to create that is able to decrease the To reliability due to the decrease in the copper layer thickness prevent which is caused when an electroless solder layering is performed on wiring patterns.  

According to a first aspect of the present invention, a method for producing a printed circuit board is shown, the wiring pattern part of which has a solder alloy layer by an electroless solder alloy method, wherein
Wiring patterns are formed on a substrate for the circuit board;
a first part, which requires a solder alloy layer, is covered with an insulation mask;
electroless plating with a metal that is not attacked by an electroless solder alloy solution is performed on a second part that is not covered with the insulation mask, thereby forming a metal mask on the second part;
the isolation mask is removed;
the substrate for the circuit board is immersed in the electroless soldering coating solution, whereby the solder alloy is deposited on the first part that is not covered with the metal mask.

According to a second aspect of the present invention a circuit board shown, the wiring pattern part with a solder alloy layer through an electroless solder coating is coated, a first thickness of a first solder alloy layer, which abge on through holes is less than a second thickness of a second Solder alloy layer that abge on fine contacts is divorced.

According to a third aspect of the present invention, there is shown a method of manufacturing a printed circuit board according to the second aspect, the wiring pattern part of which is provided with a solder alloy layer by an electroless solder coating method, wherein
Wiring patterns are formed on a substrate for the circuit board;
the fine contacts are covered with a first mask;
performing a first electroless solder coating on the accessible through holes, thereby forming a first solder alloy layer;
the first mask is peeled off;
the through holes covered with second masking who;
a second electroless solder coating is performed on the fine contacts, thereby creating a second solder alloy layer on the fine contacts, a first thickness of the first solder alloy layer deposited on the through holes being smaller than the second layer of a second solder alloy layer, which was deposited on the fine contacts;
and the second mask are removed.

According to a fourth aspect of the present invention, there is shown a method of manufacturing a circuit board whose wiring pattern part is solder-coated by a solder alloy coating method, wherein wiring patterns and solder covers are formed on a substrate for a circuit board;
electroless copper plating on copper foot contact patterns and through holes on the wiring patterns; and
a solder alloy is deposited on the copper foot contact pattern and the through holes by an electroless solder coating.

According to a fifth aspect of the present invention a method for producing a printed circuit board shown, de Ren wiring pattern part with a solder alloy layer is coated by an electroless solder coating process, wherein the electroless solder coating is performed while a substrate for the circuit board is at rest or constantly moving back and forth in a coating solution becomes.  

According to the method of manufacturing a printed circuit board The first aspect of this invention is the through hole previously covered with a metal that does not through the coating solution of the electroless solder coating is attacked. So even if the ladder plate in a coating solution of the electroless solder coating device is immersed, no electroless solder coating craze tion triggered on the through hole part, and the copper The layer thickness of the through holes is not reduced.

In the circuit board according to the second and third aspects This invention will decrease the copper layer thickness Through holes limited because of a thinner solder alloy layer on the through holes and the contact for attaching parts of the wiring pattern the first electroless solder coating is provided, and the Solder alloy layer that is thicker than the solder alloy layer that is deposited on the through hole deposited on the fine contacts as these are fine Contact with the first mask when soldering for the first time coating step covered and the through hole and the contacts for attaching parts to the second Mask mask covered in the second solder coating step are.

According to the method of manufacturing a printed circuit board The fourth aspect of the present invention is the current loose copper coating on the copper foot contact parts and the through hole parts previously up to one Thickness performed by the electroless solder reduced copper layer thickness. So that can the removal of the copper layer on the copper base contact parts and the through-hole parts prevented if only the coating thickness of the currentless Copper coating corresponding shift reaction is carried out.  

According to the method of manufacturing a printed circuit board the fifth aspect of the present invention becomes a thick one Solder alloy layer formed on the surface pattern part, and a thin solder part is placed on the through hole part formed because the coating in the electroless solder coating tion is performed while a substrate for the conductor plate is motionless or is constantly being moved back and forth. This means that the decrease in the copper layer thickness of the inner wall of the through hole can be kept smaller than that of the surface pattern.

The invention based on the description before embodiments with reference to the accompanying Drawings explained in more detail. Here show:

FIG. 1 is a flow chart showing the flow of the process for producing a circuit board according to a first embodiment of this invention;

Fig. 2A-2D are schematic sectional views showing the states of a circuit board in the respective steps of FIG. 1;

Fig. 3 is a graph showing the relationship between the solder thickness and the coating time for the case in which a solder alloy deposited on the copper patterns by the method of manufacturing circuit board of FIG. 1;

Fig. 4 is a flowchart illustrating a procedure of the method for manufacturing a circuit board according to a second embodiment of this invention;

Fig. 5A-5E are schematic sectional views illustrating the states of a circuit board in the respective steps of Fig. 4;

Fig. 6 is a graph showing the relationship between the copper thickness decrease and the coating time for the case where no treatment on a part that does not require solder coating, Runaway and was on the processing takes place at power-Lötbeschich leads;

FIG. 7A-7C are illustrations of portions of a passage-solder coating Normally was passed through-bore portion for the case in which a no-current solder coating was carried out, and for the case in which no;

Fig. 8 is a flowchart showing the flow of a conventional method for manufacturing a circuit board;

, The portions compare a through hole of a circuit board 9A and 9B are schematic sectional views when a thermal load is applied, in the case that the copper coating thickness of the through hole is small and in the case of a through hole in a normal situation.

Fig. 10 is a flowchart showing the flow of the process for producing a circuit board according to a third embodiment of this invention;

FIG. 11A-11G cuts a sub strats schematically show states with respect to the corresponding steps of FIG. 10;

Compare Figures 12A-12D representations, the portions of a through hole for the case that the electroless solder coating is performed up to a layer thickness of 10 microns or more, and that the electroless solder coating is performed up to 5 microns or more.

Fig. 13 is a flowchart showing a flow of a process for producing a circuit board according to a sixth embodiment of this invention;

Fig. 14 is a flowchart showing the flow of a process for producing a circuit board according to a seventh embodiment of this invention;

Fig. 15 is a graph showing the relationship between the solder thickness and the swing speed of the coating solution in an electroless solder coating; and

FIG. 16A and 16B characteristics which represents the relationship between the pattern size of a copper layer, which is coated with an electroless solder coating, and the electroless Lötbeschichtungsdicke with a comparison of the substrate conditions.

example 1

Fig. 1 is a flowchart showing the flow of a method of manufacturing a printed circuit board according to a first embodiment of this invention, and Figs. 2A, 2B, 2C and 2D are schematic sectional diagrams showing the states of a substrate in the corresponding steps demonstrate.

A masking step is carried out, in which a part which does not require an electroless solder coating, such as a through-hole 3 , is covered with a mask 5 , as is shown, for example, in FIG. 2B with respect to a printed circuit board 4 which has wiring patterns 1 , contacts for parts 2 and the through hole 3 (see FIG. 2A). There is no particular limitation to the masking process, but for example a photosensitive dry film cover (DFR) is laminated on. The dry layer covers the substrate, except for a part which is to be provided with the electroless solder coating ( 1 ) by exposure and development by photolithography.

An acid-resistant photosensitive dry layer cover is preferred. In addition to the photosensitive dry layer cover, a photosensitive cover ink, a thermosetting cover or the like can also preferably be used. In this example, a photosensitive cover is used, the masking is carried out by photo lithography. However, the masking can be done by another application treatment such as screen printing. If the application treatment is carried out using an ink, care must be taken since the ink may remain inside the through hole 3 if the cover is to be subsequently removed. In this example, "Laminar HG" (manufactured by Dynachem Co.) is used as a photosensitive dry film cover, and after exposure, development is carried out in a 1% sodium carbonate solution.

Next, as shown in Fig. 2C, the electroless solder coating is performed. Appropriate treatments such as cleaning (acid-containing cleaning solution, 40 ° C, 5 minutes), soft etching (sulfuric acid / hydrogen peroxide etching liquid, 40 ° C, 30 seconds) and pickling (5% sulfuric acid, 25 ° C, 1 minute), and then the part is immersed in an electroless solder coating solution. A coating solution whose main components are tin (0.1 mol), lead (0.01 mol), organic sulfonic acid (0.2 mol) and thiocarbamide (2 mol) is used as an electroless solder coating solution. The coating is carried out at 70 ° C for 15 minutes. Fig. 3 shows a relationship between the solder thickness and the coating time in the case that the current-free solder coating solution is used with the above composition and a solder alloy is deposited on the copper pattern 1 of the circuit board 4 . As shown in Fig. 3, the solder thickness increases with the coating time. Under the conditions of this example, a solder layer 6 with a thickness of approximately 12 µm is created.

Finally, a 5% sodium hydroxide solution is used as the separation solution and the dry film cover (mask 5 ) is separated as shown in Fig. 2D. In this example, the electroless solder coating is carried out on the circuit board that is covered with the solder cover. However, it is possible to partially perform the electroless solder coating on a circuit board that is not coated with a solder cover by a similar process. In this case, the solder cover or the dry film cover of this example can be applied after the mask 5 has been removed. Furthermore, a pre-flow treatment can be carried out on all or part of the surface to protect pattern parts that are not provided with the electroless solder coating layer 6 and to protect the through hole 3 .

Example 2

Fig. 4 is a flowchart illustrating a procedure of a method for manufacturing a circuit board according to Example 2 of this invention. FIGS. 5A, 5B, 5C, 5D and 5E are schematic sectional diagrams showing states of a gene which ge printed circuit board in the respective steps zei.

A masking is made on portions of the circuit board 4 before, which is provided with the wiring patterns 1 , the contacts for parts 2 , the through hole 3 and the like and is shown in FIG. 5A. It is performed on parts that require an electroless solder coating, such as wiring pattern 1 , contacts for parts 2, and the like, as shown in FIG. 5B. For masking, for example, a photosensitive dry film cover (DFR) is laminated onto the circuit board. The parts that require the electroless solder coating are covered with the dry film by photolithography (with exposure and development).

As in example 1, the selection of the covering material is not particularly critical. However, an acid resistant photo sensitive dry film cover preferred. Apart from that Photosensitive dry film cover can be a photosensi tive masking ink, a thermosetting cover and the like Chen can be used. In this example, the maskie tion carried out by photolithography, the photo sensitive cover is used. The masking can ever but through an application treatment such as screen printing leads. In this example "Laminar HG" (herge produced by Dynachem Co.) as a photosensitive dry film cover used, and development is in 1% Sodium carbonate solution performed after exposure.  

Next, the electroless plating step with a metal that is not attacked by the electroless solder coating solution is performed on parts that do not require an electroless solder coating, such as through hole 3 (see Fig. 5C). The choice of metal in this example is not particularly critical. However, there is a desire for a metal that is not attacked by the electroless solder coating solution subsequently applied. Gold, palladium, indium, rhodium, nickel, tin, lead and alloys of these elements are preferred. In this example, a palladium-coated layer 6 is formed with a thickness of approximately 0.1 μm. Corresponding treatments such as cleaning (acidic cleaning solution, 40 ° C, 5 minutes), soft etching (250 g / l ammonium persulfate solution, 25 ° C, 3 minutes), pickling (5% sulfonic acid, 25 ° C, 1 minute) and palladium activation (palladium chloride solution, 25 ° C, 1 minute) is carried out. The part is then immersed in an electroless palladium coating solution. An electroless palladium / phosphor coating solution APP (manufactured by Ishihara Chemicals Co Ltd) is used as the electroless palladium coating solution. The coating is carried out at 50 ° C for 6 minutes.

Next, the dry film cover (mask 5 ) as shown in Fig. 5D is separated using a 5% sodium hydroxide solution as the separation solution. Finally, the electroless solder coating is carried out. As in Example 1, the corresponding treatments such as cleaning (acidic cleaning solution, 40 ° C., 5 minutes), soft etching (sulfonic acid / hydrogen peroxide etchant, 40 ° C., 30 seconds) and pickling (5% sulfonic acid, 25 ° C.) are used as coating pretreatments , 1 minute). The substrate is subsequently immersed in an electroless solder coating solution. A coating solution is used as the electroless solder coating solution, the main components of which are tin (0.1 mol), lead (0.01 mol), organic sulfonic acid (0.2 mol) and thiocarbamide (2 mol). When the coating is carried out at 70 ° C. for 15 minutes, an electroless solder coating layer 7 can only be deposited on the parts that require coating. Furthermore, when the solder is deposited on the palladium coating 6 covering the through hole 3 , there are no problems, and there is good solder wettability. Almost no decrease in the copper coating thickness is determined at the through hole 3 .

Fig. 6 shows a relationship between the copper thickness decrease in a dimension of the wiring pattern 1 and the copper layer thickness of the through hole 3 and the plating time when the electroless solder plating solution is performed on the circuit board 4 as in the above examples, with no treatment is performed on the through hole 3 and parts of the wiring pattern 1 , which do not require a soldering coating. As can be seen from FIG. 6, the copper thickness decrease increases with the coating time. The decrease tendency of the copper wall thickness essentially corresponds to the increase tendency of the solder thickness according to FIG. 3, the amount of the decrease and the thickness of the increase corresponding approximately 1: 1. It is clear that these amounts correspond to the shift amounts of the solder alloy and the copper.

FIG. 7A shows a section through a through hole in which no electroless solder coating was carried out, and FIG. 7B shows a section in which no treatment other than the electroless solder coating was carried out on the through hole. As can be seen from the comparison of these two cuts, when performing an electroless solder plating as shown in Fig. 7B, the copper thickness in the through hole is remarkably reduced compared to the case of a non-electroless solder plating as shown in Fig. 7A. The result of a thermal fatigue resistance test (230 ° C / 10 second solder reflow test and -65 ° C ← → 125 ° C heat cycle test at 100 cycles) is shown in Fig. 7B for the sample shown in Fig. 7C. As shown in Fig. 7C, parallel cracks occur on the inner walls of the through hole. These experiments make it clear that the reliability deteriorates considerably if no treatment other than the electroless solder coating is carried out on the through hole. It is obvious how important the method of manufacturing a circuit board of this invention is in practice.

In the above embodiment, the electroless solder coating is carried out with the electroless palladium coating layer 6 having a thickness of about 0.1 μm as a mask. When the mask is thin, there are a number of pinholes on the mask. When the electroless solder coating is performed on the electroless palladium coating layer 6 , a small amount of the solder alloy is deposited through these holes. This amount is very small. Therefore, there is a sufficient effect to protect the through holes even when the mask thickness is very small. Furthermore, in the above embodiment, no reflow treatment (melt treatment) is carried out after the electroless solder coating. However, the holes are completely filled when performing the melt treatment (melt treatment).

As described above, according to this invention, the Through hole and parts of the wiring pattern that kei need a solder coating, covered with the mask. The stream los-solder coating is on the parts of the wiring patterns that are not covered by the mask. Parts of the wiring pattern that require a solder coating are covered with the mask. The electroless coating with a metal that is not covered by the coating solution of the electroless solder coating is corroded to the Through holes and on the parts of the wiring pattern performed that do not require a solder coating. The mask will detached, and the electroless solder coating is applied to the free parts. It is possible to use the electricity los solder coating to perform without the copper layer thickness of the through hole is reduced, whereby a method of manufacturing a printed circuit board, with  which increases reliability becomes.

Next can be the soldering alloy that is attached to holes in the metal has put down the mask through a reflow treatment (Melting treatment) are melted (melted), which will fill the holes. This will make the soldering net availability due to a subsequent environmental change worsened.

Example 3

The third embodiment of this invention is referenced described on the drawings as follows.

Fig. 10 is a flowchart describing a routine proceedings of a procedural for producing a circuit board according to a third embodiment of this invention. Figs. 11A to 11G are sections and schematically illustrate states of a sub strats at the respective steps according to Fig. 10.

First, a masking (S1) is carried out, in the case of a printed circuit board 10 which is provided with the fine contacts 11 , contacts for fastening parts 13 , a through-hole 12 and the like, as shown in FIG. 11A, fine contacts 11 , which needs a thick solder alloy layer, can be covered with first mask 14 , as shown in FIG. 11B. The masking is performed by laminating a photosensitive dry film cover (DFR) using the photolithography method with exposure and development. Further, "Laminar HG" (manufactured by Dynachem Co.) is used as the photosensitive dry film cover, and the development is carried out in 1% sodium carbonate solution after exposure.

Next, a first electroless solder coating (S2) is performed as shown in Fig. 11C. Appropriate treatments such as cleaning (acidic cleaning solution, 40 ° C, 5 minutes) and soft etching (sodium persulfate etchant, 25 ° C, 90 seconds) are carried out as pretreatments for the electroless solder coating. The circuit board is then immersed in an electroless solder coating solution. A coating solution is used as the electroless solder coating solution, the main components of which are tin (0.1 mol), lead (0.01 mol), organic sulfonic acid (0.2 mol) and thiocarbamide (2 mol). The coating is carried out at 70 ° C for 5 minutes. Fig. 3 shows a relationship between the solder thickness and the coating time in the event that a solder alloy is deposited on a wiring pattern of the circuit board 10 , using the electroless solder coating solution having the above composition. Fig. 3 shows that the solder thickness increases with the coating time. In this step, it is necessary to minimize the removal of a copper layer because the solder coating is carried out on the through hole 12 . Preferably, the thickness of the solder coating is set to not less than 0.1 µm and less than 10 µm. The value should preferably be not less than 3 μm and not more than 7 μm in order to create good solder wettability. Under the conditions of this example, an alloy layer 15 with a thickness of approximately 5 µm is created.

Next, as shown in Fig. 11D, a step (S3) for removing the first mask is performed. 3% sodium hydroxide solution is used as the separation solution, as a result of which the first mask 14 is separated. After following, fusing (S4) is performed by applying a flux over the entire surface of the circuit board 10 , and the solder alloy layer 15 is melted. Further, although there is no particular limitation on the flow material and the melting conditions, Postflux (RM-26) (manufactured by Tamura Corp.) is used. The melting is carried out in an air melting furnace, the part being heated by preheating at 160 to 180 ° C (120 seconds) and by heating at 230 ° C (30 seconds). After melting, the flux is removed by isopropyl alcohol. In this example, the melting is carried out after the first mask 14 has been separated. However, the first mask 14 can be removed after melting. In this example, the melting is carried out to enhance the adhesive effect of the solder alloy layer 15 . However, this step can also be omitted.

Next, as shown in FIG. 11E, a second masking (S5) is performed, the through hole 12 and the contacts for fastening parts 13 , in which the electroless solder coating has been carried out through the above steps, with a second mask 16 are covered. As with the first masking, the process of this masking laminates the photosensitive dry film cover (DFR) and the masking is performed by photolithography such as exposure and development. Further, "Laminar HG" (manufactured by Dynachem Co.) is used as the photosensitive dry film cover, and the development is carried out in 1% sodium carbonate solution after exposure.

Next, as shown in Fig. 11F, a second electroless solder coating (S6) is performed. As with the first electroless solder coating, corresponding treatments such as cleaning (acidic cleaning solution, 40 ° C., 5 minutes) and soft etching (sodium persulfate etchant, 25 ° C., 120 seconds) are carried out as pretreatments for the electroless solder coating. The part is then immersed in an electroless solder coating solution. A coating solution is used as the electroless soldering coating solution, the main components of which are tin (0.1 mol), lead (0.01 mol), organic sulfonic acid (0.2 mol) and thiocarbamide (2 mol). The coating is carried out at 70 ° C for 20 minutes. Under the conditions of this example, a solder alloy layer 17 with a thickness of approximately 14 µm is created.

Next, as shown in Fig. 11G, a step (S7) for removing the second cover mask is performed. 3% sodium hydroxide solution is used as the separation solution, and the second mask 16 is separated. Finally, melting (S8) is performed by spreading flux on the entire surface of the circuit board 10 , and the solder alloy layer 15 is melted. Further, although there are no particular restrictions on the flow material and melting conditions, Postflux (RM-26) (manufactured by Tamura Corp.) is used. The melting is carried out in an air melting furnace, the part being heated by preheating at 160 ° C. to 180 ° C. (120 seconds) and by heating it at 230 ° C. (30 seconds). After melting, the flux is removed by isopropyl alcohol. In this example, the melting is performed to enhance the adhesive effect of the solder alloy layer 15 . However, this step can also be omitted.

In example 3, the electroless solder coating with a thickness of less than 10 μm is first carried out on the through-hole 12 and contacts for fastening parts 13 and the like. Subsequently, the electroless solder coating is carried out with a thickness of 10 µm or more on the fine contacts 11 and the like. A similar circuit board can be made by reversing these steps. Since the surface of the masked through hole 11 is made of copper, if the masking is not complete, in the case of performing the electroless solder coating of the fine contacts 11, the surface of the copper is first corroded by penetration of the coating solution during a long coating time, which can obstruct a solder coating in a later step. In the example described, the surface of the copper layer is not corroded by penetration of the coating solution, since the masked through-hole 12 is covered with the solder alloy layer 15 .

Furthermore, when the dry film is separated, in the event that the masked copper surface and pattern are electrically connected to a coated solder surface, there is the case that tin can be detached selectively from the solder surface due to an electrochemical potential difference. In this case, the soldering composition differs in part from that in the other part. For the through hole 12 and the contacts for mounting parts 13 , the solder coating is carried out for the purpose of maintaining the solder wettability during the actual assembly process. This can change their soldering composition. However, since the layer provided by the solder coating, which is carried out on the fine contact 11 , is used as the soldering material in the actual assembly process, the change in the soldering composition is problematic. As presented above, this invention has advantages over a method in which these steps are carried out in reverse, since the electroless solder coating first on the through-hole 12 , the contacts for fastening parts 13 and the like, and subsequently the electroless - Solder coating is carried out on the fine contacts.

Fig. 6 shows a decrease in a dimension of the copper pattern and the thickness of a through hole in the event that the above coating solution is used for a printed circuit board in which no treatment is carried out on the copper patterns and the through hole. Fig. 6 shows that the decrease in the dimension of the copper pattern and the thickness of the copper through hole increase with the plating time. From the decrease tendency of the copper thickness in Fig. 6 corresponds essentially to the increase tendency of the coating thickness in Fig. 3. The decrease in thickness and the increase in thickness correspond approximately to 1: 1, which obviously also corresponds to the shift amounts of the solder alloy and the copper. The through hole copper thickness decrease in this example is approximately 6 µm, including that caused by the etch pretreatment step.

FIG. 12A shows a cross section through a through-hole in the event that the coating is carried out to a thickness of 10 μm or more when using the above-mentioned coating solution. FIG. 12B shows a section through a through hole in which the solder coating is performed with a thickness of 5 microns. FIGS. 12C and 12D show sections of the through holes, after a thermal fatigue corrosion test (230 ° C / 10 second solder flow and -65 ° ← → 125 ° C heat cycle test of 100 cycles) to the performed in the Fig. Examples shown 12A and 12B has been.

A comparison of the two sections of FIGS. 12A and 12B shows that the copper layer thickness of the through hole 12 of the printed circuit board 10 , in which the electroless solder coating was carried out up to a thickness of 10 μm or more on the through hole 12 , has decreased considerably, see comparison Chen with the copper layer thickness of the through hole 12 , in which the electroless solder coating was carried out with a thickness of 5 microns. Further, as shown in Figs. 12C and 12D, parallel cracks are formed on the inner wall of the through hole 12 when the electroless solder coating is performed up to 10 µm or more in thickness and a thermal fatigue resistance test is performed. However, there is no parallel crack at the through hole, which is hen with a solder coating with a thickness of 5 microns hen. This experiment makes it clear that the reliability deteriorates considerably if the electroless solder coating is carried out up to 10 microns or more on the through hole 12 . It is also clear that the method according to the invention for producing a printed circuit board has practical importance.

Example 4

Furthermore, the electroless solder coating is carried out on the circuit board 10 on which the solder cover is spread in the above embodiment 3 . However, it is possible to partially perform the electroless solder coating on a printed circuit board 10 which is not covered with the solder cover by similar treatment steps. In this case, the solder cover should be applied after all steps are complete.

Example 5

Further, in the above embodiment 3, masking is performed by photolithography using a photosensitive cover. However, the invention has a similar effect when the masking is carried out by a screen printing application treatment.

As stated above, the method according to this invention is suitable for the production of a printed circuit board, the Ver wire patterns are formed on the substrate, the fine Contacting the wiring pattern with a first Ab cover mask, the first electroless solder coating on the free through hole and the contacts for Mounting parts of the wiring pattern is carried out first cover mask is separated, the through hole and the contacts for assembly parts with the second Cover mask to be covered, the second de-energized solder coating is carried out, the second solder alloy layer is deposited on the fine contacts, the thickness of which is greater than that of the first solder alloy layer on the through hole and the contact is deposited for fastening parts, whereby finally the second cover layer is separated. In order to it is even when a thicker layer of solder on the fei Contact made by the electroless solder coating det, easy to create a minimum copper thickness that is necessary for the through hole, since the decrease in Copper coating thickness of the through hole is small, so that a circuit board with sufficient thermal Fatigue resistance can be created. As further effect of this invention it is possible to use a ladder to create plate that has excellent reliability when  actual assembly operation compared to that against a copper through hole substrate because of a layer on the through hole, the contacts for fastening supply of parts or the like. Is formed for upright maintaining a solder wetting ability is sufficient.

Example 6

In the following, an explanation will be given of Embodiment 6 of this invention with reference to the drawings.

Fig. 13 is a flow chart of a method for manufacturing a circuit board according to a sixth imple mentation of this invention, showing the flow.

On a circuit board that is formed with a pattern and with a Solder cover is coated, first a copper is de-energized coating carried out on parts that have an electroless solder need coating, like the copper foot contact pattern, the through hole and the like. The Stromlos-Kupferbe Layering layer, which is necessary for this, serves as elec Trone supply source for the deposition of a currentless solder coating layer. So none is particularly distinguished nete physical property for the electroless copper layered layer needed.

Furthermore, it is not necessary that the layer be complete is. Accordingly, an electroless copper coating is sufficient granular or powdery precipitate. A mess copper layer containing sufficient is also sufficient.

An alkaline electroless copper coating with formaldehyde as a deoxidizer is generally according to the bath temperature in a low temperature (15-25 ° C) thin coat type of processing, medium temperature (35-55 ° C) high coating rates kind and a high temperature (60-70 ° C) with special physi classified cal cal properties (for additives). No special requirements are for the electroless copper  Layering solution needed in these embodiments is used. Any type of electroless copper plating solution can be used. However, to get the coating in completing a short time becomes a high coating rate type preferred with medium temperature. With regard to the Coating rate is possible at a rate of approximately 5 µm per hour for medium temperature high coating rate type and 2-3 µm per hour with the high temperature type special physical properties. A Example of the composition of the electroless copper coating solution for a medium high temperature coating rate type is specified as follows.

CuSO ₄ : 0.06 mol,
HCHO: 0.20 mole,
NaOH: 0.22 mol,
EDTA: 0.12 mol,
Stabilizer: very small amount,
pH: 12 to 12.5,
Temperature: 60 ° C.

Regarding the activation step before the electroless copper appropriate treatments for cleaning (acidic cleaning solution, 40 ° C, 5 minutes), soft etching (Sulfonic acid / hydrogen peroxide etchant, 40 ° C, 30 seconds) and pickling (5% sulfonic acid, 25 ° C, 1 minute). Subsequently, the circuit board is placed in an electroless copper cup layered solution immersed. In this example the Electroless copper plating at 60 ° C for 3 hours leads, the above. Electroless copper plating bath ver is applied. As a result, under the aforementioned conditions a copper layer with a thickness of 14 µm was created fen.

Next, the electroless solder coating is carried out. Pickling (5% sulfonic acid, 25 ° C, 1 minute) is carried out as activation before the electroless solder coating. After the part is immersed in an electroless solder coating solution. The electroless solder coating solution, the main components of which are tin (0.1 mol), lead (0.01 mol), organic sulfonic acid (0.2 mol) and thiocarbamide (2 mol), is used. The coating is carried out at 70 ° C for 15 minutes. Fig. 3 shows a relationship between the coating thickness and the coating time in the case where a solder alloy is deposited on a copper pattern of a circuit board. Referring to FIG. 3, the loading takes coating thickness increases with the coating time. As a result, a solder layer approximately 12 µm thick is created under the above conditions. As in the conventional technology, a copper layer with a thickness of 0.85 µm is dissolved in the coating solution to deposit a solder alloy layer with a thickness of 1 µm. This means that a copper thickness of 10.2 µm must be dissolved in the coating bath in order to create a solder alloy layer with a thickness of 12 µm as described above. In this example, however, a copper plating layer with a thickness of 10 µm is created as described above. The copper coating can thus compensate for the decrease in copper layer thicknesses due to the electroless solder coating. The reduction in the copper layer thicknesses on the copper foot contacting patterns and the through hole is thus prevented.

Example 7

In the above example 6, the electroless copper coating and the electroless solder coating are carried out on a substrate which is coated with a solder cover. However, the electroless solder coating on a substrate that is not coated with a solder cover can be performed in a similar manner. In this case, as shown in a flowchart shown in FIG. 14, surface conditioning is performed after the electroless copper plating, with the solder cover applied, and then the electroless solder plating is performed.

Example 8

In the examples above, the alkaline currentless Copper plating solution with formaldehyde used as the oxide. However, as an electroless copper plating solution, a acidic electroless copper plating solution with hypophos phorous acid can be used as a deoxidizer. At the alka The solution is the type of soldering cover that is used in the PCB can be used limited. However, can with the acidic solution, a normal solder cover ver be applied, which is advantageous. An example of the Set the acidic electroless copper coating solution is given below.

CuCl ₂ : 0.06 mol,
HEEDTA: 0.074 mol,
NaH ₂ PO ₂ .H ₂ O: 0.34 mol,
pH: 5 to 7,
Temperature: 60 ° C.

Example 9

Although no description of the condition of the circuit board in the above Embodiments in the electroless solder coating the coating is carried out, while the circuit board is at rest or continuously and is swung here. Preferably, the ongoing Swivel movement with a swivel frequency of approximately 1 to 10 times a minute and with a swiveling speed of 0.5 m / minute or less. The will continue Swivel direction in a direction that is parallel to the surface the printed circuit board is preferred.

Fig. 15 is a characteristic curve showing the relationship between the solder thickness of an electroless solder coating and a stirring intensity of the coating solution. The stirring intensity shown here indicates the swiveling speed of the circuit board, which serves as the material for the coating.

Referring to FIG. 15, the solder thickness of the electroless Lötbe coating is considerably influenced by the swing speed be. Up to a certain condition, the solder thickness increases proportionally to the stirring intensity of up to 2 m / minute in this case. From a stirring intensity of 2 m / minute or more, the coating thickness remains constant, regardless of the stirring intensity, since the stirring effect that leads to the supply of ions is saturated. The coating is normally carried out under stirring intensity conditions, in which a constant coating thickness is created regardless of the stirring intensity.

Figs. 16A and 16B are characteristic curves showing a relationship Zvi rule of the pattern size of copper is to be provided with a power los-solder coating, and the solder thickness of an electroless solder coating. The solder thickness of the electroless solder coating is considerably influenced by the pattern size. The smaller the pattern size, the larger the solder thickness. This tendency changes more or less with the intensity of stirring. By comparing a case in which the coating is carried out while the substrate is at rest (shown in Fig. 16B) and a case in which the substrate is coated at a swing speed of 2 m / minute, the effect the stirring intensity is "saturated" (as shown in Fig. 16A Darge), shows a considerable influence of the pattern size in the case in which the circuit board is idle coated, compared to the pivot case. When the circuit board is coated while it is at rest, the coating thickness for a pattern size of 0.5 mm or less is approximately two to three times the coating thickness of the pattern size of 1 mm or more, the coating under the same conditions is carried out. As mentioned above, the diffusion of the ions is of substantial influence, since the coating thickness in the electroless solder coating is considerably influenced by the stirring of the coating solution and the pattern size. That is, the smaller the pattern size, the easier the diffusion of the ions takes place, and a larger coating thickness can be easily created.

Now if the coating with the electroless solder coating is carried out while the circuit board is at rest finds the surface pattern of the circuit board with a thick deposit, whereas the through hole with a thin deposit is provided. If the electroless solder coating is carried out at 70 ° C for 30 minutes While the circuit board is at rest, a solder is made average thickness of approximately 13 µm for surface patterns with created a size of 110 microns and about 5 microns for the Central part of the through hole. This occurs as above mentions for the reason that the diffusion of the ions is small is because the surface area of the through hole in Ver equal to that of the surface patterns of the circuit board is great. Another reason is that it is difficult is another part of the coating solution or fresh Bring coating solution into the through hole, if part of the coating solution within the through aisle bore is used up because the coating is carried out will while the circuit board that is the material for the Coating represents, is at rest.

So it is best to do the coating while rend the substrate stops when the surface pattern of the Printed circuit board with a thick deposit and the passage bore should be provided with a thin deposit. However, there may be a scatter in the coating thickness depending on the distribution of the surface pattern the PCB is caused. To solve this problem the coating is continuously swirling the lei terplatte carried out. The coating can be spread without scatter carried out in the coating thickness of the surface samples be by the circuit board with a swing frequency of about 1 to 10 times per 1 minute and a swing speed speed of 0.5 m / minute or less in one direction is pivoted parallel to the surface of the circuit board  and alternated between the idle state and the swivel state rare.

According to Example 9 above, the coating is carried out in the electroless solder coating while the circuit board is at rest or is continuously pivoted back and forth. So that the surface pattern of the circuit board 1 can be provided with a thick deposit and the Durchgangssboh tion with a thin deposit. Although in the electroless solder coating, the copper layer decreases by an amount that corresponds approximately to the coating thickness, the reliability of the printed circuit board does not deteriorate, since the copper layer decrease in the through-hole can be minimized even if the electroless solder coating is applied to a large extent Surface patterns is performed. Further, the present invention brings an economical effect, and the thickness of the copper layer can be minimized even if a copper layer having a thickness that compensates for the decrease quantity due to the electroless solder coating and the like has been previously deposited.

As mentioned above, the present invention comprises according to one Aspect at least the step of forming the wiring mu ster and the solder cover, the step of performing the Electroless copper coating on the copper foot contact pattern and the through holes of the wiring pattern and the step of depositing the solder alloy, the main comm components are tin and lead, on the wiring patterns with Electroless solder coating.

According to another aspect of the present invention the invention at least the steps that the Wirungsmu ster are formed, the electroless copper plating on the Copper foot contact pattern and through hole of the Wiring pattern is performed, the solder cover on the wiring patterns and the solder alloy, the main components of which are tin and lead  tation patterns deposited by electroless solder coating becomes.

According to another aspect of the present invention the electroless solder coating on the above two Possibilities performed while the PCB is in Is calm or is constantly swung back and forth.

In another aspect of the present invention Electroless copper is used for the two top options coat the copper layer with a thickness equal to or greater than a thickness that is a copper layer thickness corresponds, which is reduced by the electroless solder coating is.

According to another aspect of the present invention the electroless copper plating at the top two poss so that the copper layer thickness of the Wiring pattern after the electroless solder coating about 25 µm remains. Thus, the present invention encompasses a method of manufacturing a printed circuit board which in the Is capable of a decrease in reliability due to the thicknesses Prevent decrease in the copper layer when performing the electroless solder coating on the wiring pattern is caused.

Claims (12)

1. A method for producing a printed circuit board, the wiring pattern part ( 1 ) is provided with a soldering alloy layer ( 7 ) by an electroless solder coating process, characterized by the steps:
Wiring patterns ( 1 ) are formed on a substrate ( 4 ) for the printed circuit board;
a first part ( 1 , 2 ) which requires a solder alloy coating is covered with an insulation mask ( 5 );
electroless plating is performed on a second part ( 3 ) that is not attacked by an electroless solder coating solution that is not covered with the insulation mask ( 5 ), thereby forming a metal mask ( 6 ) on the second part becomes;
the isolation mask ( 5 ) is separated;
the substrate ( 4 ) for the printed circuit board is immersed in a solution for electroless solder coating, as a result of which the solder alloy is deposited on the first part ( 1 , 2 ), which is not covered with the metal mask ( 6 ). 2. A method for producing a printed circuit board according to claim 1, characterized in that the insulation masks ( 5 ) are photosensitive dry film covering means or photosensitive dry ink covering means and that the masking of the insulation masks ( 5 ) is carried out by photolithography. 3. Process for producing a printed circuit board according to a of claims 1 or 2, characterized in that by the electroless plating deposited metal or gold Gold alloy or palladium or a palladium alloy is. 4. A method for producing a printed circuit board according to one of claims 1 to 3, characterized by the further step that a solder alloy deposited on fine holes of the metal mask ( 6 ) is melted by a melting process after the electroless solder coating step, whereby the holes in the metal mask ( 5 ) be filled with the solder alloy. 5. Printed circuit board, the wiring pattern part ( 1 ) with a solder alloy layer is covered by a currentless solder coating method, characterized in that a first thickness of a first solder alloy layer which is deposited on through holes ( 3 , 12 ) is smaller than a second thickness a second solder alloy layer, which is deposited on fine contacts ( 1 , 11 ). 6. Printed circuit board according to claim 5, characterized in that the first thickness of the first solder alloy layer, which is deposited at the through holes ( 3 , 12 ), is not less than 0.1 µm and less than 10 µm and that the second thickness of the second Solder alloy layer, which is deposited on the fine contacts ( 1 , 11 ), is not less than 10 microns. 7. A method for producing a printed circuit board according to claim 5, the wiring pattern part ( 11 ) with a solder alloy layer ( 17 ) is provided by an electroless solder coating process, characterized in that:
Wiring patterns ( 11 ) are formed on a substrate ( 10 ) for the circuit board;
the contacts ( 11 ) are covered with first cover masks ( 14 );
a first electroless solder coating is carried out on accessible through holes ( 12 ), whereby a first solder alloy layer ( 15 ) is formed;
the first masking ( 14 ) are separated;
the through holes ( 12 ) are covered with second masking ( 16 );
a second electroless solder coating is performed on the fine contacts ( 11 ), whereby a second solder alloy layer ( 17 ) is formed on the fine contacts, a first thickness of the first solder alloy layer ( 15 ) being deposited on the through holes ( 12 ) is smaller than the second thickness of the second solder alloy layer ( 17 ) which is deposited on the fine contacts ( 11 ); and that
the second masking ( 16 ) are separated. 8. A method for producing a printed circuit board, the wiring pattern part ( 1 , 11 ) with a solder alloy layer ( 7 , 17 ) is provided by an electroless solder coating process, characterized in that:
Wiring patterns ( 1 , 11 ) and solder covers are formed on a sub strate ( 1 , 10 ) for a printed circuit board;
an electroless copper coating on copper foot contacting patterns and through holes ( 3 , 12 ) on the wiring pattern are performed; and that
a solder alloy is deposited on the copper base contact patterns and the through holes ( 3 , 12 ) by an electroless solder coating. 9. A method for producing a printed circuit board according to claim 8, characterized in that after the wiring pattern ( 1 , 11 ) on the substrate ( 1 , 10 ) for the printed circuit board and the electroless copper coating is carried out on the wiring patterns, which Solder covers are formed and the solder alloy is deposited on the wiring patterns ( 1 , 11 ) that are not covered with the solder cover. 10. Process for producing a printed circuit board according to a of claims 8 or 9, characterized in that he most thickness of a copper layer by the electroless copper coating is created, is no less than one second thickness of the copper layer caused by the electroless solder stratification is reduced. 11. Process for producing a printed circuit board according to a of claims 8 to 10, characterized in that the Electroless copper plating is carried out such that the Thickness of the copper layer of the wiring pattern of 25 µm is maintained. 12. A method for producing a printed circuit board, the wiring pattern part ( 1 , 11 ) is provided with a solder alloy layer by an electroless solder coating method, characterized in that the electroless solder coating is carried out while a substrate ( 1 , 10 ) for the circuit board in the idle state is or is continuously or intermittently moved back and forth in a coating solution.