Eletcroless Plating Copper process for circuit board production
Copper is the abbreviation of Eletcroless Plating Copper, also known as Plated Through Hole, abbreviated as PTH, which is an autocatalytic redox reaction. The PTH process is performed after the two or more layers have been drilled.
The role of PTH: A thin layer of chemical copper is chemically deposited on the drilled, non-conductive, porous wall substrate as the substrate for the subsequent electroplated copper.
PTH process decomposition: alkaline degreasing→2 or 3 countercurrent rinsing→roughening (microetching)→secondary countercurrent rinsing→pre-dip→activation→secondary countercurrent rinsing→debonding→secondary countercurrent rinsing→sinking→two Stage countercurrent rinsing → pickling
PTH detailed process explanation:
1. Alkaline degreasing: remove oil on the surface of the board, fingerprints, oxides, and dust in the holes; make the wall of the hole be adjusted to a positive charge by a negative charge, which facilitates the adsorption of colloidal palladium in the later process; the cleaning after degreasing must be strictly in accordance with the guidelines. Carry out and test with a copper backlit test.
2. Micro-etching: remove the oxide on the surface of the board, roughen the surface of the board, and ensure a good bonding force between the subsequent copper layer and the copper at the bottom of the substrate; the new copper surface has strong activity and can adsorb the colloid well. palladium;
3. Pre-dip: It mainly protects the palladium tank from the contamination of the pretreatment tank and prolongs the service life of the palladium tank. The main component is the same as the palladium tank except palladium chloride, which can effectively wet the pore wall and facilitate the subsequent activation liquid. Promptly enter the well for efficient activation;
4. Activation: After pre-treatment of alkaline degreasing polarity adjustment, the positively charged pore walls can effectively adsorb enough negatively charged colloidal palladium particles to ensure the average, continuity and compactness of subsequent copper sinking; Therefore, degreasing and activation are critical to the quality of subsequent copper sinks. Control points: the specified time; standard stannous ion and chloride ion concentration; specific gravity, acidity and temperature are also important, and must be strictly controlled according to the operating instructions.
5. Degumming: removing the stannous ion from the colloidal palladium particles and exposing the palladium nucleus in the colloidal particles to directly catalyze the initiation of the chemical copper precipitation reaction. Experience has shown that it is better to use fluoroboric acid as the debonding agent. s Choice.
6. Submerged copper: The autocatalytic reaction of electroless copper is induced by the activation of palladium nucleus. Both the new chemical copper and the reaction by-product hydrogen can be used as a reaction catalyst to catalyze the reaction, so that the copper precipitation reaction continues. After this step, a layer of chemical copper can be deposited on the surface of the board or the wall of the hole. The bath should be kept under normal air agitation to convert more soluble divalent copper.
The quality of the copper-plating process is directly related to the quality of the production circuit board. It is the main source process for the through hole and the short circuit. It is not convenient for visual inspection. The post-process can only be used for probabilistic screening through destructive experiments. Effective analysis and monitoring of a single PCB board, so if there is a problem, it must be a batch problem, even if the test can not be completed, the final product causes great quality hazards, only batch scrap, so strictly follow the parameters of the work instructions .