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PCB Nickle Electroplating gold production process sometimes occurs gold surface discoloration problem, gold is a stable metal element, the theory of gold oxidation is not spontaneous, the analysis that there are three cases will lead to gold surface discoloration. This article will be discolored from the important part of the production process to explore the analysis.
PCB surface Nickle Electroplating gold mainly in the copper surface with Nickle Electroplating, gold plating combination, so that the coating has a characteristic function: (1) nickel as a copper and gold surface between the barrier layer to prevent the migration of copper ions, while etching copper (2) nickel gold coating has excellent wear resistance, also has a lower contact resistance; (3) nickel gold layer surface also has good solderability The
By understanding the physical and chemical properties of gold, the analysis of gold surface discoloration is caused by three cases: (1) nickel layer porosity is too large, copper ion migration caused; (2) nickel surface passivation; (3) The attached foreign matter produced ion contamination. Our experiments will be from the Nickle Electroplating, gold-plated, plate trough, etching control, water quality requirements and other five areas to be analyzed to improve the quality of the problem.
2. Nickle Electroplating gold process
Automatic nickel-plated gold line process is not the upper / lower plate action, manual operation linked to easy to break the plastic, broken plastic hanging with easy possession of medicine, do not replace the special hanging with easy to pollute the gold-plated cylinder.
3 gold surface color processing and experimental part
3.1 Nickle Electroplating (nickel sulfamate system)
3.1.1 Potion use parameters
3.1.2 Current density of nickel plating
Nickel current density of the General Assembly directly lead to the cathode to be plated surface precipitation of nickel showed irregular state, nickel lattice porosity is too large, the appearance of nickel-plated rough. Porosity is too large nickel under the copper will be very easy to encounter acid, water, air oxidation after the outward diffusion, copper ions through the nickel pores to reach the gold layer will directly lead to gold surface color or gold surface color, nickel as copper And the barrier between the gold surface failure.
In order to select the appropriate current density, we have done the current density, plating time, nickel thickness, nickel surface porosity associated experiments, the data show that the best current density of 2.5A / dm2 ~ 2.7A / dm2, the current density Of the porosity of less than 0.5 / cm2, and the plating efficiency is higher. If the use of 2.0A / dm2 ~ 2.2A / dm2 current density plating a long time may affect the production efficiency.
Through the nickel plating when the current density control, get a uniform and fine coating, in the copper surface and gold surface can play a good "barrier" role, can effectively prevent the copper ion diffusion migration.
3.1.3 electrolytic treatment of nickel cylinder current density
Nickel cylinder due to the board will bring impurities, the level of water / auxiliary materials also contain a small amount of impurities, the accumulation of the need to use electrolysis method to remove impurities, electrolysis recommended current density (0.2 ~ 0.3) A / dm2 Is appropriate If the electrolysis current exceeds 0.5A / dm2 will lead to nickel too fast, then the effect of electrolysis to remove impurities will be worse, but also a waste of nickel. (0.2 ~ 0.3) A / dm2 current density for electrolysis (2 ~ 3) H, 0.5A / dm2 electrolysis (0.5 ~ 1) H can be taken later, the electrolysis effect is very it is good.
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