Plating (Eletcroless) is also referred to as PTH (Plated Through hole), which is an autocatalytic redox reaction. After the completion of the two or multi-layer board drilling process to be PTH.
The role of PTH: a thin layer of electroless copper is deposited on a substrate of an electrically non-conductive hole wall, which is used as a substrate for the subsequent plating of copper.
PTH detailed process explanation:
1 alkaline degreasing:
Remove surface grease, fingerprints, oxides, dust hole; the hole wall is adjusted by the negative charge for positive charge, the adsorption process of Colloid Palladium is; oil cleaning should be in strict accordance with the requirements of the guidelines, for testing the copper backlight test.
2 micro etching:
After removing the oxide on the surface of the plate, the plate surface is roughened, and a good bonding force between the subsequent copper depositing layer and the bottom copper of the substrate is ensured;
3 pre dip:
The main is to protect the tank from palladium pretreatment tank liquid pollution, prolong the service life of the main channel of palladium, palladium chloride and palladium component in addition to tank ingredients can effectively, wetting the hole wall, to facilitate the subsequent activation of liquid timely into the hole enough effective activation;
After pretreatment of alkaline degreasing polarity after adjustment, the positively charged hole wall can effectively absorb enough of negatively charged colloidal palladium particles, to ensure that the average follow-up of copper deposition, continuity and compactness; therefore oil quality is critical for the subsequent activation and depositing copper. Control points: the specified time; standard stannous ion and chloride ion concentration; specific gravity, acidity and temperature is also very important, must be strictly controlled according to work instructions.
5 solution glue:
The removal of colloidal palladium particles outside the stannous ion, the colloidal particles in the palladium nuclei exposed to direct and effective catalytic start of copper deposition reaction, experience shows that with fluoroboric acid as the glue solution is a better choice.
6 heavy copper:
The chemical reaction of copper precipitation was catalyzed by the activation of palladium, and the new chemical copper and the by-product hydrogen could be used as catalyst to catalyze the reaction. A layer of chemical copper can be deposited on the surface of the plate or the hole wall. In the course of the bath to maintain normal air agitation to convert more soluble two copper.
The quality of the copper deposition process is directly related to the PCB production quality, is the main source of hole is not open, short circuit process bad, and not convenient for visual inspection, after the process only through destructive experiments of screening probability, not for a single PCB board for effective analysis monitoring, so once the problem is inevitable the bulk of the problem, even if there is no way to complete the test, the final product quality caused great hidden danger, only batch scrap, so to strictly according to the instructions of the operating parameters.