Common problems and solutions in PCB copper plating process

Acid Copper Plating Frequently Asked Questions

Copper sulfate electroplating occupies an extremely important position in PCB circuit board electroplating. The quality of acid copper electroplating directly affects the quality and related mechanical properties of the electroplated copper layer, and has a certain impact on subsequent processing. Therefore, how to control the quality of acid copper electroplating Quality is an important part of PCB electroplating, and it is also one of the most difficult processes for many large factories to control.

The common problems of acid copper plating mainly include the following:

1. Rough plating;

2. Plating pits;

3. Electroplating (PCB board surface) copper particles;

4. The surface of the circuit board is whitish or uneven in color.

In view of the above problems, some conclusions are made, and some brief analysis, solutions and preventive measures are carried out.

Generally, the corner of the board is rough, which is mostly caused by the high plating current. You can lower the current and use a card meter to check whether the current display is abnormal; Tomorrow, the temperature in winter was low, and the content of brightening agent was insufficient: sometimes some reworked fading boards were not treated cleanly, and a similar situation would occur.

There are many factors that cause copper particles on the surface of PCB circuit boards. From copper sinking, the entire process of pattern transfer, and electroplating copper itself are all possible. The author has encountered copper particles on the surface of circuit boards caused by sinking copper in a large state-owned factory.

The copper particles on the board surface caused by the copper sinking process may be caused by any copper sinking process step. Alkaline degreasing will not only cause the surface of the board to be rough, but also cause the inside of the hole to be rough; but generally it will only The micro-corrosion of slight point-like dirt on the board surface can also be removed due to roughness in the hole; there are several situations for micro-corrosion: the quality of the micro-etching agent hydrogen peroxide or sulfuric acid used 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; too high copper content in the micro-etching bath or low temperature will cause slow precipitation of copper sulfate crystals; the bath is turbid and polluted.

Most of the activation solution is caused by pollution or improper maintenance, such as air leakage from the filter pump, low specific gravity of the bath solution, and high copper content (the activation tank has been used for too long, more than 3 years), which will produce particulate suspended matter in the bath solution Or impurity colloid, adsorbed on the surface of the plate or the wall of the hole, this time will be accompanied by roughness in the hole. Degumming or acceleration: The bath solution is turbid after being used for too long, because most of the degumming solution is prepared with fluoboric acid, so that it will attack the glass fiber in FR-4, resulting in the increase of silicate and calcium salt in the bath solution. In addition, the increase of copper content and dissolved tin in the bath solution will cause the generation of copper particles on the board surface.

The sinking copper tank itself is mainly caused by the excessive activity of the tank liquid, dust in the air agitation, and many small particles of solid suspension in the tank liquid. It can be adjusted by adjusting process parameters, adding or replacing air filter elements, and filtering the whole tank. Effective solution. After sinking copper, temporarily store the dilute acid tank of the sinking copper plate. The bath should be kept clean, and should be replaced in time when the bath is turbid. The storage time of the sinking copper plate should not be too long, otherwise the surface of the plate is easy to oxidize, even in an acidic solution, and the oxide film is more difficult to dispose of after oxidation, so that copper particles will also appear on the surface of the plate. In addition to the oxidation of the board surface, the copper particles on the PCB surface caused by the copper sinking process mentioned above are generally distributed evenly on the PCB board surface with strong regularity, and the pollution generated here is irrespective of whether it is conductive or not. It will cause the generation of copper particles on the surface of the electroplated copper board. During the treatment, some small test boards can be used for step-by-step comparison and judgment. For the on-site faulty board, it can be solved by lightly brushing with a soft brush; graphic transfer process: developing excess glue (very thin It can also be plated and covered during residual film electroplating), or the cleaning is not clean after developing, or the board is placed for too long after the graphics are transferred, resulting in different degrees of oxidation on the board surface, especially when the board surface is not cleaned well. Or when the air pollution in the storage workshop is heavy. The solution is to strengthen water washing, strengthen planning and schedule, and strengthen the intensity of acid degreasing.

The acid copper plating tank itself, at this time, generally does not cause copper particles on the PCB surface, because the non-conductive particles at most cause missing plating or pits on the board surface. The reasons for the copper particles on the board surface caused by the copper cylinder can be roughly summarized into several aspects: maintenance of bath parameters, production operation, materials and process maintenance. The maintenance of bath parameters includes high sulfuric acid content, low copper content, low or high bath temperature, especially in factories without temperature control cooling system, which will cause the current density range of the bath to drop. According to the normal production process Operation, may produce copper powder in the bath, mixed into the bath.

In terms of production operation, the current is too large, the splint is bad, the pinch point is empty, the plate is dropped in the tank and is dissolved by the anode, etc., which will also cause the current of some plates to be too large, produce copper powder, fall into the bath, and gradually produce copper particle failure ;In terms of materials, it is mainly the problem of phosphorous copper horn phosphorus content and phosphorus distribution uniformity; in terms of production and maintenance, it is mainly a large-scale treatment. They are not handled well, and there are some hidden dangers. For the major treatment of copper balls, the surface should be cleaned, and the fresh copper surface should be slightly etched with hydrogen peroxide. The anode bag should be soaked in sulfuric acid hydrogen peroxide and lye successively, and cleaned. In particular, the anode bag should use PP filter bags with a gap of 5-10 microns. .

There are also many processes caused by this defect, from copper sinking, pattern transfer, to pre-plating treatment, copper plating and tin plating. The sinking copper is mainly caused by poor cleaning of the sinking copper hanging basket for a long time. During micro-etching, the pollution solution containing palladium and copper will drip from the hanging basket on the board surface, forming pollution. pits. The graphics transfer process is mainly caused by poor equipment maintenance and developing and cleaning. There are many reasons: brushing machine brushing copper water-absorbing sticks to pollute glue stains, drying the internal organs of the air knife fan in the drying section, oil and dust, etc., filming on the board surface or dust removal before printing Improper, the developing machine is not clean, the washing after developing is poor, and the silicon-containing defoamer contaminates the board surface, etc. pre-plating treatment, since neither the acid