Method for improving in-hole binding force of aluminum-based PCB (printed circuit board)

Abstract

The invention belongs to the technical field of surface treatment, and discloses a method for improving in-hole binding force of an aluminum-based circuit board, which comprises the following steps of: immersing an aluminum-based copper-clad plate with a through hole in oil removal liquid for 3-5 minutes; immersing into an alkali wash solution, and washing clean; then, immersing into an acidic coarsening solution for 1-3 minutes; the acidic coarsening solution comprises 0.1-2 g / L of an aluminum protecting agent solution, 0.1-2 g / L of an accelerant solution and 0.1-3 g / L of a copper protecting agent solution according to 1 L of acid; and after the chemical nickel plating is completed, the copper plating is carried out in an electroplating bath, and finally, tin immersion is carried out in a tin furnace at the temperature of 288-300 DEG C. According to the method, the in-hole roughness of the aluminum-based circuit board is improved through the acidic coarsening liquid, and the binding force between an electroplated copper layer of the aluminum-based circuit board and a tin-immersed electroplated copper layer and the heat tolerance of the electroplated copper layer are enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of surface treatment of aluminum-based printed circuit boards, and in particular to a method for improving the bonding force in holes of aluminum-based PCBs. Background Art

[0002] Printed circuit boards, or PCBs for short, are one of the most basic components of electronic products. With the continuous development of science and technology, the application scope of electronic products is becoming increasingly wide, covering various electronic devices needed in daily life, such as computers, mobile phones, tablets, etc., as well as circuit boards inside cars, automation equipment in industry, communication equipment, military electronic equipment, aerospace electronic systems, etc. Printed circuit boards are almost everywhere and are the core components of various electronic products we use. Traditional circuit boards mainly use polymer materials as substrates and aluminum as the metal base layer, which has good heat dissipation, and its heat dissipation is more than 20 times that of ordinary FR-4 copper clad laminates. This design can effectively solve problems such as heat dissipation and thermal expansion and contraction. However, aluminum-based circuit boards cannot be directly welded and bound, so they usually need to undergo chemical nickel plating and other treatment processes to improve their wear resistance and weldability. In the process of chemical nickel plating, coarsening is an indispensable key step. The degree of coarsening will directly affect subsequent nickel plating, copper plating and tin immersion processes, so it is of great significance. Different concentrations of hydrochloric acid are usually used in industry for corrosion treatment. However, during the tinning process after copper plating on aluminum-based circuit boards, the difference in thermal tolerance between the copper layer and the nickel layer has always been a difficult problem to solve. Recently, a patent with application number 201911407178.7 proposed a new method for etching aluminum-based circuit boards, and its formula uses organic acids and deionized water. This method simplifies the process flow and brings the degreasing and roughening steps together. However, the disadvantage of this method is that the solution contains organic matter, which is not conducive to the treatment of COD organic wastewater. Based on this, the present invention provides a method for improving the bonding strength in the holes of aluminum-based PCBs. Summary of the invention

[0003] In view of the defects of the prior art, the purpose of the present invention is to provide a method for improving the bonding force in the hole of an aluminum-based PCB to solve the problems raised in the above-mentioned background technology.

[0004] The present invention solves the technical problem by adopting the following technical solution: The present invention provides a method for improving the bonding force in a hole of an aluminum-based PCB, comprising the following steps: S1. Immerse the aluminum-based circuit board with through holes in the degreasing liquid for 3~5 minutes, rinse it clean, then immerse it in the acid roughening liquid for 1~3 minutes and rinse it clean; The acidic roughening solution is calculated based on 1L of acid, including 0.1-2 g / L of aluminum protective agent solution, 0.1-2 g / L of accelerator solution and 0.1-2 g / L of copper protective agent solution; S2. Immerse the aluminum-based circuit board obtained in step S1 in a nickel plating solution for chemical nickel plating, place it in an electroplating tank for copper electroplating, and finally immerse it in tin in a tin furnace at 288~300℃.

[0005] Preferably, the aluminum protecting agent is one of copper chloride, copper sulfate and copper nitrate; The accelerator is one or more of nickel sulfate, nickel chloride, nickel acetate and nickel nitrate; The copper protective agent is one or more combinations of triethanolamine, hydroxyethylidene diphosphoric acid, and mercaptobenzothiazole sodium salt.

[0006] Preferably, the acid in the acidic roughening solution is one or more of hydrochloric acid, acetic acid or sulfuric acid, and the mass concentration of the acid is 5-20%.

[0007] Preferably, the nickel plating solution in step S2 is calculated based on 1L of deionized water, including 30~50g / L of nickel sulfate solution, 1~30g / L of sodium hypophosphite solution, 1~10g / L of sodium acetate solution, 1~10mL / L of lactic acid, 2~10g / L of malic acid, and 3~10g / L of trisodium citrate solution.

[0008] Preferably, the copper electroplating solution in the copper electroplating includes 50-100 g / L of copper sulfate pentahydrate solution, 20-40 mg / L of chloride ions, and 150-200 g / L of sulfuric acid solution, calculated based on 1 L of deionized water.

[0009] Preferably, the degreasing liquid is a sodium carbonate solution with a mass fraction of 5%.

[0010] Preferably, the nickel plating temperature in the chemical nickel plating is 35-40° C., and the current density of the electroplating is 20 asf.

[0011] The present invention immerses the aluminum-based copper-clad plate with through holes in a degreasing liquid for 3 to 5 minutes; then immerses it in an alkaline washing liquid, rinses it clean; then immerses it in an acidic roughening liquid for 1 to 3 minutes; the acidic roughening liquid is calculated according to 1L of acid, including 0.1 to 2 g / L of aluminum protection agent solution, 0.1 to 2 g / L of accelerator solution and 0.1 to 3 g / L of copper protection agent solution; after rinsing, immerses it in a nickel plating liquid for chemical nickel plating, puts it into an electroplating tank for copper electroplating after the chemical nickel plating is completed, and finally tins it in a tin furnace at 288 to 300°C. The present invention improves the roughness of the aluminum-based circuit board hole by using an acidic roughening liquid, enhances the bonding force between the electroplated copper layer of the aluminum-based circuit board and the tinned layer, and the thermal tolerance of the electroplated copper layer.

[0012] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses an acidic roughening liquid to enhance the bonding force in the holes of an aluminum-based circuit board, improves the bonding force in the holes of the aluminum-based circuit board, and enables the subsequent aluminum-based circuit board to pass a thermal shock test and meet production requirements; it is beneficial to the process of tinning after copper electroplating on the aluminum-based circuit board, enhances the bonding force between the electroplated copper layer of the aluminum-based circuit board and the tinning layer, and also enhances the thermal tolerance of the electroplated copper layer; the acidic roughening liquid includes an accelerator, an aluminum protective agent, and a copper protective agent. The addition of copper ions prevents aluminum oxidation, and provides active points for the subsequent nickel plating process, thereby enhancing the activity during chemical nickel plating. The aluminum protective agent can replace a thin layer of copper on the aluminum surface, and can protect aluminum from being oxidized in subsequent processes. The accelerator can provide active sites on two metal substrates for the next step of chemical nickel plating. The copper protective agent acts as a corrosion inhibitor, which can significantly reduce the corrosion rate of the metal in the corrosive medium, improve the quality of the roughening morphology, and improve the roughening efficiency and uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a 200-fold magnified longitudinal section of the copper-plated aluminum-based circuit board coating that has not been treated with an acidic roughening solution. Figure 2 This is a photograph of a transverse section of a hole in an aluminum-based circuit board magnified 200 times using an acidic roughening solution in Example 1; Figure 3 This is a morphological photograph of the longitudinal section of the aluminum-based circuit board coating using an acidic roughening solution at a magnification of 200 times in Example 2; Figure 4 This is a morphological photograph of a transverse section of a hole in an aluminum-based circuit board magnified 200 times using an acidic roughening solution in Example 2. DETAILED DESCRIPTION

[0014] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] A method for improving the bonding force in a hole of an aluminum-based PCB according to this embodiment includes the following steps: S1. Immerse the aluminum-based circuit board with through holes in the degreasing liquid for 3~5 minutes, rinse it clean, then immerse it in the acid roughening liquid for 1~3 minutes and rinse it clean; The acidic roughening solution is calculated based on 1L of acid, including 0.1-2 g / L of aluminum protective agent solution, 0.1-2 g / L of accelerator solution and 0.1-2 g / L of copper protective agent solution; S2. Immerse the aluminum-based circuit board obtained in step S1 in a nickel plating solution for chemical nickel plating, place it in an electroplating tank for copper electroplating, and finally immerse it in tin in a tin furnace at 288~300℃.

[0016] The aluminum protecting agent of this embodiment is one of copper chloride, copper sulfate and copper nitrate; The accelerator is one or more of nickel sulfate, nickel chloride, nickel acetate and nickel nitrate; The copper protective agent is one or more combinations of triethanolamine, hydroxyethylidene diphosphoric acid, and mercaptobenzothiazole sodium salt.

[0017] The acid in the acidic roughening solution of this embodiment is one or more of hydrochloric acid, acetic acid or sulfuric acid, and the mass concentration of the acid is 5-20%.

[0018] The nickel plating solution in step S2 of this embodiment is calculated based on 1L of deionized water, including 30~50g / L of nickel sulfate solution, 1~30g / L of sodium hypophosphite solution, 1~10g / L of sodium acetate solution, 1~10mL / L of lactic acid, 2~10g / L of malic acid, and 3~10g / L of trisodium citrate solution.

[0019] The copper electroplating solution in the copper electroplating of this embodiment is calculated based on 1L of deionized water, and includes 50-100 g / L of copper sulfate pentahydrate solution, 20-40 mg / L of chloride ions, and 150-200 g / L of sulfuric acid solution.

[0020] The degreasing liquid in this embodiment is a sodium carbonate solution with a mass fraction of 5%.

[0021] In the chemical nickel plating of this embodiment, the nickel plating temperature is 35-40° C., and the current density of the electroplating is 20asf.

[0022] Example 1 Prepare an acidic roughening solution, calculated based on 1L of hydrochloric acid (mass concentration 5%), including 0.1 g / L nickel chloride solution, 0.1 g / L copper chloride solution, and 1 g / L mercaptobenzotriazole solution.

[0023] Put the aluminum-based circuit boards with through holes into the degreasing liquid for 3 minutes and rinse them clean; Place the aluminum-based circuit board treated in step 2 in the acidic roughening solution for 1 minute and rinse it clean; The aluminum-based circuit board treated in step 3 is placed in a nickel plating solution (calculated according to 1L of deionized water, including 10-50g / L of nickel sulfate solution, 10-40g / L of sodium hypophosphite solution, 20g / L of sodium acetate solution, 1-15mL / L of lactic acid, 1-20g / L of malic acid, and 1-30g / L of trisodium citrate solution) for chemical nickel plating for 15 minutes; then placed in an electroplating tank for copper electroplating for 45 minutes; The aluminum-based circuit board plated with nickel and copper in step 5 is finally placed in a tin furnace at 288°C to immerse in tin, forming an aluminum-based circuit board / nickel / copper / tin layer, with a nickel layer thickness of 0.2~2μm and a copper layer thickness of 10~25μm, thereby improving the roughness of the holes in the aluminum-based circuit board.

[0024] The following reactions occurred during the acidic coarsening process of this system 1. Reaction formula for coarsening aluminum: 2Al+6HCl=2AlCl3+3H2; 2Al + 2H2O + 2NaOH = 2NaAlO2 +3H2 2. Reaction formula for protecting aluminum: 2Al+3CuCl2=2AlCl3+3Cu Observe the test board through a metallographic microscope. Figure 1 This is the metallographic morphology of the aluminum-based circuit board after copper plating without acid roughening liquid treatment. Figure 2 This is a morphological photograph of the longitudinal section of the aluminum-based circuit board coating using an acidic roughening solution in Example 1 at a magnification of 200 times. Figure 1 It can be seen that the bonding between the copper layer and the tin layer is good, and there is no Figure 1 The expansion and separation conditions meet the production requirements.

[0025] Example 2 An acidic roughening solution suitable for improving the roughness of an aluminum-based circuit board, calculated based on 1L of hydrochloric acid (mass concentration 10%), includes 0.5g / L nickel chloride solution, 0.5g / L copper chloride solution, and 0.3g / L hydroxyethylidene diphosphonic acid solution.

[0026] After adopting the copper electroplating process on the aluminum-based circuit board in Example 1, the aluminum-based circuit board coating obtained forms an aluminum-based circuit board / nickel / copper / tin layer, the nickel layer thickness is 0.2~2μm, and the copper layer thickness is 10~25μm. Figure 3 This is a morphological photograph of the longitudinal section of the aluminum-based circuit board coating using an acidic roughening solution at a magnification of 200 times in Example 2. Figure 3 It can be seen that the bonding between the copper layer and the tin layer is good, and there is no Figure 1 The expansion and separation conditions meet the production requirements.

[0027] Example 3 An acidic roughening solution suitable for improving the roughness of an aluminum-based circuit board, calculated based on 1L of hydrochloric acid (mass concentration 5%), includes 1g / L nickel chloride solution, 1g / L copper chloride solution, and 0.2g / L mercaptobenzothiazole sodium salt solution.

[0028] After adopting the copper electroplating process on the aluminum-based circuit board in Example 1, the aluminum-based circuit board coating obtained forms an aluminum-based circuit board / nickel / copper / tin layer, the nickel layer thickness is 0.2~2μm, and the copper layer thickness is 10~25μm. Figure 4 This is a morphological photograph of the longitudinal section of the aluminum-based circuit board coating using an acidic roughening solution at a magnification of 200 times in Example 3. Figure 4 It can be seen that the bonding strength between the coatings of the aluminum-based circuit board is good, and there is no separation of the coatings. Figure 3 It can be seen that the bonding between the copper layer and the tin layer is good, and there is no Figure 1 The expansion and separation conditions meet the production requirements.

[0029] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0030] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for improving the bonding strength in a hole of an aluminum-based PCB, characterized in that: The following steps are involved: S1. Immerse the aluminum-based circuit board with through holes in the degreasing liquid for 3~5 minutes, rinse it clean, then immerse it in the acid roughening liquid for 1~3 minutes and rinse it clean; The acidic roughening solution is calculated based on 1L of acid, including 0.1-2 g / L of aluminum protective agent solution, 0.1-2 g / L of accelerator solution and 0.1-2 g / L of copper protective agent solution; S2. Immerse the aluminum-based circuit board obtained in step S1 in a nickel plating solution for chemical nickel plating, place it in an electroplating tank for copper electroplating, and finally immerse it in tin in a tin furnace at 288~300℃.

2. A method for improving the bonding strength in a hole of an aluminum-based PCB according to claim 1, characterized in that: The aluminum protecting agent is one of copper chloride, copper sulfate and copper nitrate; The accelerator is one or more of nickel sulfate, nickel chloride, nickel acetate and nickel nitrate; The copper protective agent is one or more combinations of triethanolamine, hydroxyethylidene diphosphoric acid, and mercaptobenzothiazole sodium salt.

3. The method for improving the bonding strength in the hole of aluminum-based PCB according to claim 1, characterized in that: The acid in the acidic roughening solution is one or more of hydrochloric acid, acetic acid or sulfuric acid, and the mass concentration of the acid is 5-20%.

4. The method for improving the bonding strength in the hole of aluminum-based PCB according to claim 1, characterized in that: The nickel plating solution in step S2 is calculated based on 1L of deionized water, including 30~50g / L of nickel sulfate solution, 1~30g / L of sodium hypophosphite solution, 1~10g / L of sodium acetate solution, 1~10mL / L of lactic acid, 2~10g / L of malic acid, and 3~10g / L of trisodium citrate solution.

5. The method for improving the bonding strength in the hole of aluminum-based PCB according to claim 1, characterized in that: The copper plating solution in copper electroplating is calculated based on 1L of deionized water, including 50~100g / L of copper sulfate pentahydrate solution, 20~40 mg / L of chloride ions, and 150~200 g / L of sulfuric acid solution.

6. The method for improving the bonding strength in the hole of aluminum-based PCB according to claim 1, characterized in that: The degreasing liquid is a 5% by mass sodium carbonate solution.

7. The method for improving the bonding strength in the hole of aluminum-based PCB according to claim 1, characterized in that: The nickel plating temperature in chemical nickel plating is 35-40°C, and the electroplating current density is 20asf.

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