Alloy plating solution for surface treatment of modular printed circuit board

[0001] The present invention is a plating solution for a gold-silver alloy applied to a surface treatment for mounting a component of a modular printed circuit board (hereinafter referred to as "modular PCB"). Regarding the composition, more specifically, after applying electroless nickel plating on the pads and terminals of the modularized PCB, it is immersed in a gold-silver alloy plating solution to 90 to 99% gold and 1 to 10%. The present invention relates to a plating solution composition for a gold-silver alloy that forms an alloy plating layer composed of silver.

[0002] Generally, a modularized PCB is formed so as to be electrically connected to an external device by a circuit pattern, a pad portion for mounting an electronic component, and a detachable method on a substrate. The circuit pattern, the pad portion, and the terminal portion are typically made of a copper material. In connection with this, FIG. 1 shows a plan view of a strip of PCB. However, the copper layer exposed to the outside oxidizes with the passage of time and lowers the reliability when mounting the semiconductor and the modularized PCB. As a surface treatment to prevent this, the pad portion 2 and the terminal are used. Soft electroless gold plating is applied on the part 3, and a hard electrolytic gold plating process is further indispensable only on the terminal part 3. On the other hand, the electroless gold plating process is widely known in the art. For example, in Korean Patent Publication No. 2000-53621 (Patent Document 1), one or more water-soluble materials are formed after forming an electroless nickel layer on a copper site to be gold-plated using a photosolder resist (PSR). A method for producing a printed circuit board by contacting a gold dipping plating solution containing a gold compound, one or more organic conductive salts, one or more reducing agents, and water is disclosed. Further, in Japanese Patent Application Laid-Open No. 7-7243 (Patent Document 2), a non-crystalline first electroless nickel film is formed on a copper site to be gold-plated, and then a crystalline second electroless nickel film is formed. Disclosed is an electroless gold plating method in which an electroless gold plating film is formed on the surface of the second electroless nickel film by electroless gold plating whose main reaction is a substitution reaction after the electrolytic nickel film is formed. In addition, improved techniques for forming a nickel-gold plated layer on a copper layer are disclosed in US Pat. Nos. 5,173,130 (Patent Document 3) and 5,235,139 (Patent Document 4).

[0003] In the module PCB, the reason why the hard electrolytic gold plating step is further performed only on the terminal portion is as follows.

[0004] When only the soft gold-plated layer is formed after the electroless nickel-plated layer is formed, the weldability to the pad portion and the terminal portion of the modularized PCB is good, but the wear resistance of the terminal portion is poor. It is sufficient and easily scratches, and has a problem that the exposed nickel layer is corroded. On the contrary, when only the hard gold-plated layer is formed after the electroless nickel-plated layer is formed, the wear resistance of the pad portion and the terminal portion of the modularized PCB is good, but the weldability is deteriorated. The spreadability of the solder paste is poor, and dewetting defects occur during mounting.

[0005] In the manufacture of the modularized PCB, the above-mentioned soft electroless gold plating layer is formed on the pad portion on which the component is mounted to provide weldability, and the terminal portion that is frequently attached and detached is plated with soft electroless gold plating. It is common to further form a hard electrolytic gold-plated layer on the layer to provide abrasion resistance.

[0006] In this regard, FIG. 2 shows a specific example of a schematic gold plating process for a modular PCB according to a conventional technique.

[0007] First, a patterned circuit (not shown), a pad portion 2 and a terminal portion 3 are formed on a substrate 1 by a method widely known in the art, and then a portion to be gold-plated (pad). The photosolder resist layer 4 is formed on the remaining portion excluding the portion and the terminal portion). Then, the electroless nickel plating solution is treated on the pad portion and the terminal portion at about 85 ° C for about 20 minutes to form a nickel plating layer 5 having a thickness of about 3 to 6 μm and a phosphorus content of about 5 to 8%. ..

[0008] After that, a dipping gold plating solution containing citric acid as a main component is brought into contact with the nickel plating layer to form a soft electroless gold plating layer 6 having a thickness of about 0.1 μm inside and outside.

[0009] When the stage of forming the soft gold-plated layer 6 on the pad portion and the terminal portion is completed, the pad portion is masked with a dry film (or photoresist) so that the register against the plating solution can be obtained in the subsequent hard gold plating step. To play a role. After that, a hard electrolytic gold-plated layer 7 having a thickness of about 1 μm inside and outside is formed only on the terminal portion, and the dry film on the pad portion is peeled off.

However, the conventional modular PCB manufacturing process described above involves a number of steps, such as separate exposure and development, and dry film peeling steps, to perform additional hard gold plating steps. This is a situation that has an adverse effect on economic efficiency and productivity because it must be done.

[Patent Document 1] Korean Patent Publication No. 2000-53621 [Patent Document 2] Japanese Patent Application Laid-Open No. 7-7243 [Patent Document 3] US Patent No. 5173130 [Patent Document 4] US Patent No. 5235139 [0012] [Problems to be Solved by the Invention] After repeated studies to overcome the problems of the conventional technique, the present inventor uses a new gold-silver alloy plating solution. , It was discovered that the pad and terminal parts on the modularized PCB can be given the required physical properties at the same time.

[0013] Therefore, an object of the present invention is to provide an electroless gold-silver alloy plating solution that satisfies all the plating characteristics required for each of the pad portion and the terminal portion of the modularized PCB by a single plating process. is there.

[0014] Another object of the present invention is to replace the double plating process of soft electrolytic gold plating and hard electrolytic gold plating performed in the conventional modularized PCB manufacturing with a single plating process, and the process is simple. It is an object of the present invention to provide a non-electrolyzed gold-silver alloy plating solution which can contribute to the conversion, improvement of productivity and cost reduction.

[0015] Still another object of the present invention is to provide a method for plating a modularized PCB using the electroless alloy plating solution.

[Means for Solving the Problems] In order to achieve the above object, the electroless aqueous plating solution for surface treatment of a modularized printed circuit board provided by one aspect of the present invention is based on the weight of the plating solution. At least one sulfonic acid group (-SO₃1 to 30% by weight of organic acid having H), 0.1 to 20% by weight of complexing agent, 0.1 to 15% by weight of thio compound having at least one -S-, 0.05 to 5% by weight of water-soluble gold compound, water-soluble silver It is characterized by containing 0.001 to 1% by weight of the compound and 0.1 to 10% by weight of the metal ion sequestering agent.

[0017] The method of plating a modularized printed circuit board provided by another aspect of the present invention includes a) a pad portion for mounting a component and a terminal portion for electrically connecting to an external device, and is constant. The stage of providing a modularized printed circuit board on which a circuit pattern is formed, b) the stage of forming a photosolder resist layer on a portion of the printed circuit board excluding the pad portion and the terminal portion, and c) the pad portion and the terminal portion. It includes a step of forming an electroless nickel plating layer on the top and a step of d) contacting the electroless aqueous plating solution with the printed circuit board to form a gold-silver alloy plating layer on the nickel plating layer. It is a feature.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the accompanying drawings.

[0019] As described above, according to the present invention, an electroless water-free gold-silver alloy plating solution capable of replacing the conventional double plating process consisting of soft electroless gold plating and hard electrolytic gold plating with a single plating process. It is about. The alloy-plated layer thus obtained as the gold and silver eutectoid layer can provide sufficient weldability required for the pad portion for mounting parts, and also has excellent wear resistance. The advantage of double plating can be obtained at the same time by giving to the part.

The electroless water-free gold-silver plating solution according to the present invention contains an organic acid, a complexing agent, a thio compound, a water-soluble gold compound, a water-soluble silver compound, and a metal ion sequestering agent. The plating principle of the plating solution will be briefly described as follows.

[0021] Prior to plating, a step of forming an electroless nickel plating layer is performed on the pad portion and the terminal portion of the modularized PCB. The principle is that the organic acid in the plating solution dissolves the nickel (Ni) layer, and the water-soluble gold and silver compounds complexed by the complexing agent are precipitated on the nickel layer by a potential difference.

[0022] In the present invention, the organic acid is at least one sulfonic acid group (-SO).₃It has H), and typical examples are methane sulfonic acid, methane disulfonic acid, sulfo salicylic acid, phenol sulfonic acid, and amide sulfone. There are acids (amido sulfonic acid), dodecyl benzene sulfonic acid, etc., and one or more of them are selected. Such an organic acid is contained in an amount of about 1 to 30% by weight, preferably about 3 to 10% by weight, based on the weight of the plating solution. For example, if it is less than 1% by weight, the nickel layer cannot be sufficiently dissolved, so that it is difficult to form a gold-silver alloy plating layer. There is a possibility that the problem that the alloy plating layer is not dense may occur.

[0023] As the complexing agent, one or a cyanide of an alkali metal such as sodium cyanide or potassium cyanide, a cyanide of an alkaline earth metal, potassium ferricyanide, potassium ferrocyanide, or the like. The above can be selected, and it is used in an amount of about 0.1 to 20% by weight, preferably about 0.1 to 15% by weight, based on the weight of the plating solution. For example, if it is less than 0.1% by weight, the complexing force with respect to gold and silver compounds becomes too weak, so it is difficult to keep the gold-silver alloy ratio of the plating layer constant, but if it exceeds 20% by weight, it is in the plating solution. It is possible to increase the concentration of the gold and silver compounds because the stability can be increased, but the loss of the gold and silver compounds that are attached to and removed from a certain substance is large, which is not preferable. In addition, among the plating solutions of the present invention, the molar ratio of the metal in the gold compound and the silver compound to the cyanide of the complexing agent is most ideally in the range of about 1: 1 to 1: 5.

[0024] On the other hand, the thio compound is a component to which the gold and silver compounds are added so as to be stable in the aqueous plating solution, and has at least one -S-. Examples of the components include thiourea, alkylthiourea, mercapto compounds, thioglycolic acid, sodium thiocyanide, ammonium thiocyanide, and the like, with one or more selected from these. use. The thio compound is used in the range of about 0.1 to 15% by weight, preferably about 0.5 to 5% by weight, based on the weight of the plating solution. If it is less than 0.1% by weight, it is difficult to give the stability of the aqueous plating solution, and if it exceeds 15% by weight, it is precipitated by its own solubility.

[0025] The metal ion sequestering agent plays a role of a chelate that suppresses the action of dissolved Ni and Cu, and a derivative of polycarboxylic acid, a derivative of aminoacetic acid, a derivative of nitrilotriacetic acid, or the like can be used. , Specifically, ethylene diamine tetra acetic acid, diethylene triamine penta-acetic acid, N-hydroxyethylethylene diamine triacetic acid, 1,3-diamino- 2-propanol-N, N, N, N'-pentacetic acid (1,3-diamino-2-propanol-N, N, N, N'-tetra acetic acid), bishydroxyphenyl-ethylene , Diamine diacetic acid, N, N-di (hydroxyethyl) glycine (N, N-di (hydroxyethyl) One or more are selected from glycine) and so on. The content of the sequestrant is about 0.1 to 10% by weight, preferably about 0.5 to 5% by weight, based on the weight of the plating solution.

[0026] Typical examples of the water-soluble gold compound include potassium gold cyanide and potassium gold chloride, and one or more of them can be selected and used, but the compound is not always limited to this. Absent. The content of the water-soluble gold compound is about 0.05 to 5% by weight, preferably about 0.1 to 1% by weight, based on the weight of the plating solution.

[0027] The water-soluble silver compound is selected from, but is not necessarily limited to, silver nitrate, silver cyanide, silver potassium cyanide, silver acetate, silver carbonate, and the like. The content of the water-soluble silver compound is about 0.001 to 1% by weight, preferably about 0.02 to 0.2% by weight, based on the weight of the plating solution. In particular, in order to obtain the physical properties required by the present invention, the content ratio of gold and silver in the gold-silver plating layer is important, so the content of the water-soluble silver compound is about 3 to 8 weights of the content of the water-soluble gold compound. It is preferably adjusted to the% range.

[0028] In the present invention, the pH of the plating solution is about 3 to 7, preferably about 4 to 5, and the temperature required in the plating process is about 60 to 90 ° C, preferably about 70 to 80 ° C. is there.

[0029] The alloy plating layer formed on the electroless nickel plating layer on the modularized printed circuit board using the electroless water-based gold-silver plating solution produced in this manner contains about 90 to 99% gold and about. It consists of 1-10% silver. If the gold content does not reach the above range, the weldability is insufficient, and if the gold content exceeds the above range, there is a problem that the reproducibility is not good due to the solder spreadability at the time of mounting.

[0030] In general, the thickness thereof is about 0.01 to 0.25 μm. However, those skilled in the art will be able to fully understand that it is possible to form a plating layer having a thickness that does not reach or exceeds the above range due to changes in various process conditions. In the present invention, the plating step for forming the gold-silver alloy plating layer required in the manufacture of modularized PCB is typically carried out for about 5 to 15 minutes.

[0031] In order to form the optimum gold-silver alloy plating layer, a pretreatment process can be selectively performed during the plating process. That is, first, the terminal portion and the pad portion of the copper material are physically polished to remove foreign substances on the surface, and then chemically remove organic substances. Further, after the surface of the copper layer is etched, it is preferable to treat it with palladium (Pd) which selectively acts as a catalyst prior to the formation of the nickel plating layer.

FIG. 3 shows a schematic step of a method of plating a modularized PCB using the plating solution.

[0033] First, a constant circuit pattern (not shown), a pad portion 12 for mounting components, and a terminal portion 13 for electrically connecting to an external device are formed on the substrate 11, but in general, this is used. Such a process is performed by photolithography, which is widely known in the art.

[0034] After that, a photosolder resist (PSR) is applied to the printed circuit board 11, and the solder resist layer 14 acts as a resist for plating in a plating process described later. A dry film is applied to the solder resist layer 14, and only the solder resist layer portion on the pad portion 12 and the terminal portion 13 is peeled off through exposure and development steps.

[0035] After the completion of the step, the pad portion 12 and the terminal portion 13 are exposed to the outside, and an electroless nickel plating layer 15 is preferably formed on the pad portion 12 and the terminal portion 13. The specific steps for forming the electroless nickel-plated layer on such a conductive layer are the same as described above.

[0036] Then, in order to prevent damage to the nickel plating layer 15 on the pad portion and the terminal portion, the surface of the nickel plating layer is immersed in the electroless aqueous plating solution according to the present invention for a sufficient time. Allows the desired gold-silver alloy plating layer 16 to be formed.

The present invention can be more clearly understood by the following examples. These examples are merely examples of the present invention and do not limit the scope of the invention.

[0038] In the following embodiment, a modular PCB (board size) in which a photosolder resist layer (trade name ST-2 ink of Dowa Tamura Kaken Co., Ltd.) is formed on a portion excluding a pad portion and a terminal portion of a copper material. : 340 × 510 mm, substrate thickness: 0.80 ± 0.08 mm, copper layer thickness: 30 ~ 50 μm) degreased with acid (sulfuric acid concentration: 160 ~ 200 g / L) at 50 ° C for 3 minutes, and palladium (Yu) After catalytic treatment using the trade name cata 1845) of Ichi Material Technology Co., Ltd., it was washed with water and plated with an electroless nickel plating solution (trade name EN-1845 of Yuichi Material Technology Co., Ltd.) at 85 ° C for 20 minutes. At this time, the thickness of the electroless nickel layer on the pad portion and the terminal portion was 4.7 μm.

[0039] As described above, the modularized PCB on which the nickel layer was formed was washed with water, activated with a 3% hydrochloric acid solution at 25 ° C. for 1 minute, and further washed with water. Then, a gold-silver alloy plating step was performed on the nickel layer as follows. (Example 1) After producing an aqueous alloy plating solution having the composition shown in Table 1 below, the modularized PCB treated with electroless nickel plating was activated with a 3% hydrochloric acid solution at 25 ° C. for 1 minute. Then, while changing the temperature of the plating solution to 60 ° C, 70 ° C and 80 ° C, respectively, the PCB was immersed in the plating solution for 10 minutes for plating. At this time, the plating solution is not agitated and has a pH of 4.5.

[0040] [Table 1]<img file="JP3662010B2_D0001.tif" />[0041] After the plating step, the film was washed with water, dried at 80 ° C. for 15 minutes, and then weldability and abrasion resistance were measured under the following conditions and methods.

【0042】<u style="single">Weldability</u>1) Solder paste size: The pad part was printed with 0.04 mm (average particle size).

2) Reflow conditions: 160 ° C ~ 190 ° C ~ 245 ° C ~ 90 ° C (speed: 1.0 m / min) 3) Evaluation method Sn and Pb ratio is 63: to confirm weldability. When heat is applied to the pad portion after placing 37 solder paste materials on the pad portion, the melting point of the solder paste is 183 ° C, so that the solder paste in the pad portion is melted by the heat and spreads on the pad portion. Weldability can be evaluated based on the degree of spread of the solder paste, but the wider the paste, the better the weldability.

4) Evaluation Criteria Weldability (after reflow): If it is 3 times or more (that is, 0.12 mm or more) of the initial solder paste particle size, it is judged that there is no abnormality in weldability.

【0045】<u style="single">Abrasion resistance</u>Clip test: When the clip was repeatedly attached to and detached from the terminal part of the module PCB 100 times, it was observed with an electron microscope whether or not a nickel layer formed under the alloy plating layer appeared.

[0046] Table 2 below shows the test results for the weldability of the pad portion and the wear resistance of the terminal portion.

[0047] [Table 2]<img file="JP3662010B2_D0002.tif" />(Example 2) After producing an aqueous alloy plating solution having the composition shown in Table 3 below, the modularized PCB treated with electroless nickel plating was activated in a 3% hydrochloric acid solution at 25 ° C. for 1 minute. Processed. Then, the plating process was carried out with a plating solution at 80 ° C. while changing the plating time to 5 minutes, 10 minutes and 15 minutes, respectively. At this time, the plating solution is not agitated and has a pH of 4.5.

[0049] [Table 3]<img file="JP3662010B2_D0003.tif" />[0050] Then, after post-treatment by the same method as in Example 1, weldability and abrasion resistance were measured. The results are shown in Table 4 below.

[0051] [Table 4]<img file="JP3662010B2_D0004.tif" />(Example 3) After producing an aqueous alloy plating solution having the composition shown in Table 5 below, the modularized PCB treated with electroless nickel plating was activated in a 3% hydrochloric acid solution at 25 ° C. for 1 minute. Processed. Then, the temperature of the plating solution was adjusted to 80 ° C., and the plating treatment was performed for 10 minutes. At this time, the plating step was performed while changing the stirring conditions to 0.1 m / s, 0.2 m / s, and 0.3 m / s, respectively.

[0053] [Table 5]<img file="JP3662010B2_D0005.tif" />[0054] Then, after post-treatment by the same method as in Example 1, weldability and wear resistance were measured. The results are shown in Table 6 below.

[0055] [Table 6]<img file="JP3662010B2_D0006.tif" />(Example 4) The pad portion and terminal portion on the modularized PCB used in Example 1 were used at 85 ° C. using an electroless nickel plating solution (trade name EN-1845 of Yuichi Materials Technology Co., Ltd.). Was plated for 20 minutes. At this time, the thickness of the electroless nickel layer on the pad portion and the terminal portion was 4.7 μm. Then, using the plating solution produced in Example 3, alloy plating was performed on the nickel plating layer at 80 ° C. for 10 minutes. The reliability of the modularized PCB plated in this way was evaluated by the reliability evaluation criteria for PCB surface treatment of Samsung Electric Co., Ltd., the applicant of the present invention.

【0057】<u style="single">Measurement of plating thickness</u>The thickness of the nickel plating layer using a plating thickness measuring instrument (CMI's trade name CMI900) to check whether the gold-silver alloy plated product has the thickness required by the supplier. , Measure the thickness of the gold-silver alloy plating layer.

【0058】<u style="single">Perforated test</u>Immerse a modular PCB plated in nitric acid and visually check to see if the gold-silver alloy plated structure corrodes and creates pores.

【0059】<u style="single">Heat resistance test</u>After passing 3 times under the temperature conditions shown in Table 7 below using reflow, the presence or absence of surface hue change due to the heat of gold-silver alloy plating, and the presence or absence of surface hue change due to the heat of gold-silver alloy plating, and the nickel plating layer and gold-silver alloy plating layer using adhesive tape. Check the separation.

【0060】<u style="single">Weldability test</u>After immersing the molten solder in the pad portion by treating under the two conditions shown in Table 7 below, it is confirmed whether or not the solder spreads over 95% or more of the pad portion area.

【0061】<u style="single">Adhesion test</u>After passing through the pad part three times under the temperature conditions shown in Table 7 below using reflow, when the aluminum wire is welded to the pad part with a solder and then pulled with a constant force, the nickel plating layer and the gold-silver alloy plating layer Check if the solder and the gold-silver alloy plating layer are separated.

[0062] [Table 7]<img file="JP3662010B2_D0007.tif" />[0063] : It means that the test result satisfies the standard.

[0064] From the test results, it can be seen that the alloy-plated layer according to the embodiment of the present invention satisfies all the physical characteristics required in relation to the above-mentioned items.

[Effects of the Invention] The present invention satisfies all the plating characteristics required for each of the pad portion and the terminal portion of the modularized PCB, and at the same time, soft electroless electrolysis performed in the conventional production of the modularized PCB. Since the double plating process of gold plating and hard electrolytic gold plating can be replaced with a single plating process, there is an advantage that the process can be simplified, productivity can be improved, and cost can be reduced. In particular, the plating solution of the present invention is applicable to all modular PCBs used for semiconductor mounting.

All simple modifications or modifications of the present invention belong to the domain of the present invention, and the specific scope of protection of the present invention will be clarified by the scope of claims.

BRIEF DESCRIPTION OF THE DRAWINGS [FIG. 1] FIG. 1 is a plan photograph schematically showing the structure of a strip-shaped modularized PCB.

FIG. 2 is a cross-sectional view schematically showing a plating process of a conventional modularized PCB.

FIG. 3 is a cross-sectional view schematically showing a plating process of a modularized PCB according to a specific example of the present invention.

[Code description] 1, 11 Substrate 2, 12 Pad 3, 13 Terminal 4, 14 Solder resist layer 5, 15 Nickel plating layer 6 Soft gold plating layer 7 Hard gold plating layer 16 Gold-silver alloy plating layer