How to deal with rough surface of electroplated copper
Time:2022-11-15
There are many factors that can cause the formation of copper particles on the surface of the board, including the entire process of copper deposition, pattern transfer, and electroplating of copper itself.
The copper particles on the surface caused by the copper deposition process may be caused by any one of the copper deposition processing steps. Alkaline degreasing, when the water quality has high hardness and there is a lot of drilling dust (especially for double-sided panels without removing adhesive residue), can not only cause surface roughness but also result in roughness inside the hole due to poor filtration; However, it usually only causes roughness inside the hole, and slight point like dirt and erosion on the surface can also be removed; There are several main situations of micro corrosion: the quality of the micro corrosion agent used is too poor, such as hydrogen peroxide or sulfuric acid, or the impurities in ammonium (sodium) persulfate are too high. It is generally recommended that it should be at least CP grade. In addition, industrial grade can also cause other quality failures; The slow precipitation of copper sulfate crystals is caused by high copper content or low temperature in the micro etching groove; The tank liquid is turbid and contaminated. The activation solution is mostly caused by pollution or improper maintenance, such as leakage of the filter pump, low specific gravity of the tank solution, and high copper content (the activation cylinder has been used for too long, more than 3 years), which will produce granular suspended solids or impurity colloids in the tank solution, adsorbed on the plate surface or hole wall, accompanied by roughness in the hole. Gelling or acceleration: If the tank solution is used for too long, it may become cloudy because most of the solutions are prepared with fluoroboric acid, which can attack the glass fibers in FR-4, causing an increase in silicates and calcium salts in the tank solution. In addition, an increase in copper content and tin solubility in the tank solution can lead to the formation of copper particles on the surface of the plate. The main reasons for the copper plating tank itself are the high activity of the tank solution, dust generated by air agitation, and a large number of suspended small particles in the tank solution. This can be effectively solved by adjusting process parameters, adding or replacing air filter cartridges, and filtering the entire tank. After copper deposition, temporarily store the copper plate in a dilute acid tank, and keep the tank solution clean. If the tank solution becomes turbid, it should be replaced in a timely manner.
The storage time of the copper plate should not be too long, otherwise the surface of the plate is prone to oxidation, even in acidic solutions, and the oxide film is more difficult to remove after oxidation, which will also produce copper particles on the surface. The copper particles deposited on the surface of the electroplated copper plate during the copper deposition process mentioned above are generally evenly distributed and have strong regularity, except for those caused by surface oxidation. The pollution generated here, whether conductive or not, will cause the production of copper particles on the electroplated copper plate surface. When processing, some small test boards can be used to process and compare them step by step. For on-site faulty boards, a soft brush can be used to gently brush them to solve the problem; Graphic transfer process: residual adhesive during development (even ultra-thin residual film can be plated and coated during electroplating), or inadequate cleaning after development, or prolonged placement of the board after graphic transfer, resulting in varying degrees of oxidation of the board surface, especially in poor cleaning conditions or when there is heavy air pollution in the storage workshop. The solution is to strengthen water washing, enhance planning and scheduling, and increase the intensity of acid oil removal.
The pre-treatment of the acid copper electroplating tank itself generally does not cause copper particles on the surface of the plate, as non-conductive particles can cause plate leakage or pits at most. The reasons for copper particles on the surface of the plate caused by copper cylinders can be roughly summarized into several aspects: maintenance of tank liquid parameters, production operations, material and process maintenance. The maintenance of tank parameters includes high sulfuric acid content, low copper content, low or high tank temperature, especially in factories without temperature controlled cooling systems, which can cause a decrease in the current density range of the tank. According to normal production processes, copper powder may be generated in the tank and mixed into it.
In terms of production operations, excessive current, poor clamping plates, empty clamping points, and the dissolution of boards in the tank against the anode can also cause excessive current in some board components, resulting in copper powder falling into the tank solution and gradually leading to copper particle faults; In terms of materials, the main issues are the phosphorus copper corner phosphorus content and the uniformity of phosphorus distribution; In terms of production maintenance, it mainly involves major processing. When adding copper corners, they fall into the tank, mainly during major processing, such as anode cleaning and anode bag cleaning. Many factories cannot handle them well and there are some hidden dangers. The copper ball treatment should clean the surface thoroughly and use hydrogen peroxide to slightly etch the fresh copper surface. The anode bag should be soaked in sulfuric acid hydrogen peroxide and alkaline solution successively to clean thoroughly, especially the anode bag should use a 5-10 micron gap PP filter bag.
