Common problems and troubleshooting for PCB copper plating

- Aug 18, 2018-

At present, domestic electroplating is more and more advanced. Bright copper plating takes copper sulfate and sulfuric acid as the basic components and introduces appropriate additives or other brighteners to improve and improve the process characteristics of the plating solution and directly obtain the mirror surface bright copper layer [1].It is widely used in decorative multi-layer electroplating intermediate layer and printed circuit board copper plating layer, eliminating mechanical polishing.However, the plating sometimes does not shine during production.There are many factors causing this situation.

For example, the mass fraction of industrial sulfuric acid is greater than or equal to 92.5%, which contains a lot of iron and organic impurities. If not treated, the plating will make the coating not bright.Even with reagent grade sulfuric acid, this can happen if not treated, as there are more or less impurities in copper sulfate.Before adding sulfuric acid, the dissolved copper sulfate solution (with a pH value of 4) can be combined with H2O21~2mL/L with a mass fraction of 30% and activated carbon 0.5-1.0g /L.Removal of iron impurities by the easy precipitation of trivalent iron hydroxide;Adding activated carbon adsorption can eliminate the influence of organic impurities at the same time.This begins to electroplate, can plating bright copper layer.

The metal impurities and organic impurities produced by long-term use of the plating solution will accumulate more and more, obviously, the plating solution is not pure.If the quality concentration of iron impurities is above 10g/L, the current efficiency and coating brightness will decrease obviously if the treatment is not done regularly according to the process requirements.For example: in a factory, the current of the plating bath is not large, the coating is thin but not bright, and the edge Angle of the plating part is easy to be burnt, once it was unable to produce normally.Sample analysis was conducted under the suggestion of the author, but due to the high concentration of iron in the solution, the analysis of copper sulfate and sulfuric acid endpoint was interfered and the data could not be displayed, so the analysis of iron ions was as high as 40g/L.According to the observation, the plating solution was light in color. 40g/L copper sulfate and 15g/L sulfuric acid were added when the mass concentration of each component in the plating solution was confirmed to be low, so as to reduce the influence of iron impurities.Then according to the normal treatment, so that the plating bath back to normal, plating out the full bright copper layer.

2. Polish consumption

The consumption of brightener in acidic bright copper plating solution is related to many factors, such as type of workpiece, shape, surface state, and quality concentration of inorganic, organic impurity and copper sulfate in the plating solution.Especially the lack of Cl-, it is difficult to obtain the bright coating with good levelness even if the brightener is in the normal range.When the mass concentration of Cl- is too high, the consumption of brightener will be accelerated.

A part of brightener is consumed with the strip out of the workpiece and the inclusion of the coating.A portion will break down into organic impurities;Some of them remain in the bath and change the composition of the brightener itself.These conditions may affect the gloss of the coating, resulting in coating defects.In addition to the use instructions of the brightener used in production, we should try to grasp the consumption of brightener accurately, pay attention to the accumulation of experience and careful observation, and supplement brightener in time with less work to keep the brightener constant in the plating solution.

Excellent bright leveling, less brittle coating;Allows high current density, high cathode current efficiency, fast plating;Without complexing agent, the content of ammonia nitrogen is very small, and the wastewater treatment is simple.The process has become the main process of cyanide-free copper plating and is widely used.Especially in plastic electroplating, indispensable.No other copper plating process is expected to replace it for quite some time.