Research on the Causes of Blackening of Super-roughened Copper Surface
The super-roughening liquid is a copper surface treatment process designed for the copper surface. The solder mask uses the ultra-roughening process, which have good adhesion between the soldering oil and the copper surface, prevent the soldering ink from falling off.
Therefore, the ultra-roughening process in the PCB industry has been widely used.
In the process of super-roughening, there are a large number of blackening of the copper surface. The picture is as follows:
3 Analysis of the reason of blackening of super-roughened copper surface
3.1 SEM comparison analysis of super-roughened blackening position and normal copper surface position; see the following figure:
3.2 SEM analysis: It can be seen from the above picture that the copper crystal lattice is irregularly irregular in the blackout position. The normal copper lattice is in the form of a honeycomb, and the copper lattice distribution is better. The preliminary analysis of the abnormal black copper surface shows that the copper lattice is poorly distributed or the copper lattice is too coarse, resulting in blackening of the over-roughened copper surface.
4 Test verification
4.1 Compare the simulated test with 20ASF, 27ASF and 38ASF respectively; the results of super-roughening are as follows:
4.2 Comparison test with different current densities, the results show that the current density of copper plating on the VCP pattern plating line is too large, resulting in blackening of the super roughened copper surface.
5 Improvement method and improvement results
5.1 Improvement method: Adjust the copper lattice. (In order to facilitate the over-roughening of the chemical water, the electroplated copper lattice distribution is better, the copper current density is lowered, and the copper plating time is extended).
5.2 Test board verification:
5.2.1 Because there are only two program line speeds for the VCP diagram wire of our pcb factory, the first line speed is 0.8m/min copper plating time 30 minutes, the second line speed is 0.4m/min copper plating time 60 minute.
5.2.2 Quantity 400PNL. (Test board parameters: copper plating time of 60m for the second wire speed of 0.4m/min, copper current density of 18ASF)
5.2.3 Tracking test the effect after improvement.
Verification of VCP pattern plating by test plate The large current density production method has an effect on the super-roughening process of the solder mask. The current density of the VCP pattern plating copper plating is adjusted from 32ASF*30 minutes to 18ASF*60 minutes, which can solve the super roughening copper surface blackening problem.
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