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Due to various reasons, the quality of PCB nickel plating will be more or less unqualified. If corresponding remedial measures can be taken, unnecessary deplating and rework can be reduced. In addition to polishing and repairing on non-bright, burr plating, repair plating on parts that are not easy to polish or exposed to the substrate after polishing is also a common method.
PCB nickel plating is easy to passivate, especially in air and alkaline solution, so the key to re-plating on the nickel layer is to activate the surface of the nickel layer. Only when the surface of the nickel layer is in a good activated state can the re-plating be successful. grasp.
For repair plating, different methods should be selected according to the nature, shape and requirements of the parts. For example, if acid copper plating is suitable, you can directly plate copper or nickel for repair plating when the substrate of the plated part is not exposed to iron after surface activation, such as If it is not suitable for acid copper plating or the substrate of the plated part is exposed to iron, it should be directly plated with nickel for repair plating after the PCB surface is activated.
The specific method is as follows: Dechrome the chrome-plated PCB parts, and remove the blistered and skinned parts of the PCB plating. According to the specific conditions of the parts, the selection methods are as follows.
(1) Suitable for copper and nickel replating: degreasing (preferably chemical method)-cleaning-water-casting brushing (large parts)-concentrated hydrochloric acid activation-cleaning-dilute sulfuric acid etching-acid copper plating-cleaning-dilute Sulfuric acid etching-nickel plating-cleaning-chrome plating-cleaning (recycling)-drying-sending for inspection.
(2) Suitable for nickel plating: degreasing (preferably chemical method)-cleaning-water polishing (large parts)-concentrated hydrochloric acid activation-cleaning-nickel-plating-cleaning-chrome-plating-cleaning (recycling)-drying- Submit for inspection.
(3) The electro-polishing activation method can also achieve better results. Recipe and process parameters of electro-polishing activation method:
Industrial sulfuric acid (density 1.849/mL), please refer to "preparation" chromic anhydride 509/L ’glycerin 509/L
Solution density l. 58～1.629/mL temperature room temperature
Anode current density l～10A/dm2 time 3～5s
Solution preparation: first inject 2/3 volume of concentrated sulfuric acid (density 1.849/mL) into the lead tank (or ceramic tank, plastic tank), and add 509 glycerin to each liter of concentrated sulfuric acid, and in another lead tank (Or ceramic tank, plastic tank) dissolve chromic acid (Cr0.) in a little water, the amount of chromic acid is 509 per liter of sulfuric acid, and then slowly add the concentrated sulfuric acid solution with glycerin to the chromic acid solution, plus time Be very careful, add several times, as the solution is added, the electrolyte begins to heat up and violently release gas. Each addition of glycerin-containing sulfuric acid mixture must be vigorously stirred, and it must be carried out after the gas evolution was stopped last time. The density of the solution after preparation should be 1.58～1.629/mL. Cool the solution to 30°C, use a lead plate as a cathode and a nickel plate as an anode, and conduct electrolysis. The electrolysis voltage is not less than 10V until the solution contains 109/L of nickel ions. The time is generally about 25min.
In the circuit board, inferior copper, nickel, chromium re-plating process: hanger cleaning, electropolishing activation, cleaning, dipping in dilute hydrochloric acid, cleaning, pre-plating, dipping in dilute sulfuric acid, cleaning, nickel plating, cleaning, hot water Click the rack, dry, send for inspection, clean, chrome-plated, clean, hot water, and the hanger, dry, send for inspection.
