Plating is a very versatile industry. With the continuous improvement of customer requirements for printed boards, printed board manufacturers are facing various new problems. Customers' requirements for gold-plated plugs, in addition to the thickness of the usual nickel-gold plating layer, the bonding force and consistency of the plating layer, and the hardness of the plating layer, some customers with strict requirements, the porosity of the gold plating and the resistance of the gold plating layer Corrosion is also used as a condition for its acceptance, which puts new requirements and new challenges on the production process and quality control of the manufacturer. 1. Printed circuit board plug Nickel platingGold The quality requirements of printed circuit board plugs with nickel and gold plating are mainly good wear resistance, low porosity, and a certain number of insertions and removals. The thickness of the electroplated nickel layer on the plug part should be 3~5μm, and the thickness of the electroplated nickel layer should be 0.5~1.5μm. In most printed board plug gold plating, hard gold plating is used in acidic micro cyanide plating solution. Paste protective tape on the upper part of the plug→remove the tin-lead alloy of the plug→surface brushing→nickel plating→activation→gold-plating the plug→recycling→remove the tape→washing→drying→inspection. The solution formula and operating conditions for removing the tin-lead alloy are shown in Table 1. It uses chemical methods to remove the tin-lead alloy from the plug part.  The solution must have certain conditions: no corrosion to the substrate of the printed board, low corrosion to the copper, fast removal speed, and no residual plating after removal. Summary of the reaction effect of the solution formulation: Formulation 1: Removal of tin and lead is faster, less corrosive to copper, the temperature rises quickly during the reaction, and the self-decomposition speed is accelerated. Formulation 2: Removal of tin and lead is fast, and it is more corrosive to copper, the temperature rises slowly during the reaction, the pollution is small, and the cost is low. Adding a copper protective agent to the formula can reduce copper corrosion and requires good ventilation. Formulation 3: The removal rate of tin and lead is moderate, the corrosion to copper is small, and the cost is high. 2. The plug is nickel-plated Generally, two processes of semi-bright nickel and bright nickel are used, and the nickel coating should be uniform, fine, low stress, low porosity, and good ductility. In the nickel plating solution for printed board plugs, a reasonable process formula and suitable operating conditions are very important, which is conducive to maintaining the stability of the solution and facilitating subsequent operations. The specific process formula and operating conditions are shown in Table 2.  1 Maintenance of nickel plating solution Perform regular tests on the solution in the plating solution and adjust it in time to maintain the stability of the composition of the plating solution. Pay attention to the change of the pH value and adjust it in time. When the liquid is polluted, treatments such as activated carbon adsorption and electrolysis must be carried out. 2 Common faults and solutions of nickel plating solution (1) Poor adhesion of the plating layer: poor pre-plating treatment or electrical contact, and the influence of impurities. (2) Uneven plating: low current density, insufficient main salt concentration or blooming on the substrate surface. (3) Pinholes in the coating: insufficient anti-pinhole agent or boric acid, and the temperature is too low. (4) The coating has rough crystals and burrs: the pH value or current density is too high, the plating solution is not thoroughly filtered, and the anode bag is damaged. (5) High brittleness of the coating: impurity contamination, caused by excessively high pH or low temperature. 2. Solution (1) Strengthen the pre-plating treatment, and then carefully check the electrical contacts and make adjustments. (2) Increase the current density, analyze the plating solution and add it in an appropriate amount, and pay attention to cleaning the board surface in time. (3) Replenish the ingredients in the plating solution in time, increase the temperature appropriately, and strengthen the filtration. (4) Check in time and make corresponding adjustments for comprehensive treatment. 3, the plug is gold-plated The plug is gold-plated and plated on nickel, and the purity is 99.9%, the hardness is 120~190kgf/mm^2, and the wear resistance is high. It can be plugged and unplugged 500 times at 0.5μm without peeling and without revealing the underlying metal . Good temperature resistance, no discoloration at 350℃ at 0.5~1μm. The porosity is small, and the pores are not allowed to appear concentrated in the same part. In addition, the weldability is good, the plating solution is stable, and the maintenance is convenient. 1 Plug gold plating process chooses gold plating method: alkaline cyanide gold plating, micro cyanic acid gold plating, sulfite non-cyanide gold plating, gold plating on the principle of complex complexation. The advantages and disadvantages of the gold plating scheme are compared with alkaline cyanide gold plating: the plating solution is highly toxic, and the electrolyte is strongly alkaline, which will etch the copper foil substrate, which will reduce the adhesion between the copper foil and the substrate and cannot be used for printed circuits. Plate plating. Slightly cyanic acid gold plating: using a non-cyanide complexing agent, the solution is weakly acidic, it is a good organic complexing agent, and has no corrosive effect on the copper foil and substrate. The coating is bright, the equipment is simple and non-gold anodes are used, the formula is simple, the plating solution is stable, the investment is small, and the management is convenient. Sulphite cyanide-free gold plating: it has the advantages of dispersibility, brightness, leveling, ductility, and good solderability, but the stability of the plating solution is poor. Using sulfite as a cyanide-free complexing agent, solution Unstable and easy to decompose. Principle of complex complexation: Gold plating must be used in conjunction with conductive agents, stabilizers, buffers and complexing agents, etc. The solution preparation is too cumbersome and difficult to achieve. In summary, it is the best electroplating process to choose a weak acid microcyanide gold plating scheme. This method is relatively mature and safe to operate. 2 Plug gold plating solution process recipe and operating conditions Plug gold plating solution process recipe and operating conditions In the preparation of gold plating solution, it is necessary to understand and analyze the composition of the solution. The preparation and adjustment of the electrolyte should also not be ignored. The process formula and Operating conditions are shown in Table 3  |
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