Common Problems and Solutions of PCB Copper Sulfate Electroplating Process (2)

2. Electroplating Plate Surface Copper Particles

There are many factors that cause the production of copper particles on the PCB board. From the copper sinking to the entire process of pattern transfer, or even copper electroplating. I met in a large state-owned factory, copper particles on the plate surface caused by copper sinking.

Copper particles on the board surface caused by the copper immersion process may be caused by any copper immersion treatment step. Alkaline degreasing will not only cause roughness on the board surface, but also roughness in the holes when the water hardness is high and the drilling dust is too much (especially the double-sided board is not de-smeared). Poor filtration will not only cause roughness on the board surface, but also roughness in the holes. The internal roughness and slight stains on the surface of the board can also be removed. There are mainly several cases of microetching: the quality of the microetching agent hydrogen peroxide or sulfuric acid is too poor or the ammonium persulfate (sodium) contains too many impurities, generally it is recommended that it should be at least CP grade. In addition to industrial grade, it will cause other quality failures. Excessively high copper content or low temperature in the micro-etching tank will cause slow precipitation of copper sulfate crystals, the tank liquid is turbid and polluted.

Most of the activation solution is caused by pollution or improper maintenance, for example, the filter pump leaks, the specific gravity of the bath is low, and the copper content is too high (the activation tank has been used for too long, more than 3 years), which will produce particulate suspended matter in the bath, or impurity colloid, adsorbed on the plate surface or hole wall. At this time it will be accompanied by the generation of roughness in the hole.

Dissolving or accelerating: the bath solution is used for too long time to appear turbid, because most of the dissolving solution is prepared with fluoroboric acid, so that it will attack the glass fiber in FR-4, causing the silicate and calcium salt in the bath to rise. In addition, the increase of the copper content and the amount of dissolved tin in the bath will cause the production of copper particles on the board surface.

The copper sinking tank is mainly caused by the excessive activity of the tank liquid, the dust in the air stirring, and a large amount of suspended solid particles in the tank liquid. You can adjust the process parameters, increase or replace the air filter element, filter the whole tank, etc. to effectively solve these problems. After the copper is deposited, the dilute acid tank for temporarily storing the copper plate should be kept clean. If the tank liquid is turbid, it should be replaced in time. The storage time of the copper immersion board should not be too long, otherwise the board surface will be easily oxidized, even in acid solution, and the oxide film will be more difficult to deal with after oxidation, so that copper particles will also be produced on the board surface.

The copper particles on the surface of the board caused by the copper sinking process mentioned above, except for the surface oxidation, are generally distributed on the board surface more uniformly and with strong regularity.The pollution generated here will cause the production of copper particles on the surface of the electroplated copper plate, regardless of whether it is conductive or not. It can be treated with some small test boards step by step and individually processed for comparison and judgment. For on-site faulty boards, you can use a soft brush to solve the problem. Graphics transfer process: there is excess glue in the development (extremely thin residual film, it can also be plated and coated during electroplating), or it is not cleaned after development, or the plate is placed for too long after the pattern is transferred, which causes the plate surface to be oxidized to varying degrees, especially when the plate surface is poorly cleaned or stored when the air pollution in the workshop is heavy. The solution is to strengthen the water washing, strengthen the plan and arrange the schedule, and strengthen the acid degreasing intensity.

The acid copper electroplating tank, its pre-treatment generally does not cause copper particles on the surface of the board, because non-conductive particles can at most cause leakage or pits on the board. The reasons for the copper particles on the plate surface caused by the copper cylinder can be summarized into several aspects: the maintenance of bath parameters, the production and operation, the materials and the process maintenance. The maintenance of bath parameters includes too high sulfuric acid content, too low copper content, too low or too high bath temperature, especially in factories without temperature-controlled cooling systems, this will cause the current density range of the bath to drop, according to the normal production process operation, copper powder may be produced in the bath and mixed into the bath.

In terms of production operation, excessive current, poor splint, empty pinch points, and the plate dropped in the tank against the anode to dissolve will also cause excessive current in some plates, resulting in copper powder, falling into the tank liquid, and gradually causing copper particle failure. The material aspect is mainly the phosphorus content of the phosphor copper corner and the uniformity of the phosphorus distribution. The production and maintenance aspect is mainly large processing, and the copper corner falls into the tank when adding, mainly for large processing, anode cleaning and anode bag cleaning, many factories are not handled well, and there are some hidden dangers. The copper ball treatment is to clean the surface, and use hydrogen peroxide to etch the fresh copper surface. The anode bag should be soaked in sulfuric acid hydrogen peroxide and lye successively to clean it, especially the anode bag should use a 5-10 micron gap PP filter bag.