Perhaps some people who have just contacted the circuit board factory will be strange, the substrate of the circuit board only has copper foil on both sides, and the insulation layer in the middle, so they do not need to be conductive between the two sides of the circuit board or multiple layers of the line? How can the two sides of the line be connected together so that the current passes smoothly?
[Sensitive word] Please see the circuit board manufacturer for you to analyze this magical process - sunk copper (PTH).
Copper Plating is short for Eletcroless Plating Copper, also known as Plated Through hole (PTH), is a self-catalyzed REDOX reaction. The PTH process is performed after two or multiple layers of boards are drilled.
The role of PTH: On the non-conductive hole wall substrate that has been drilled, a thin layer of chemical copper is deposited by chemical method to serve as the base for the subsequent plating of copper.
PTH process decomposition: alkaline degreasing → secondary or tertiary counter-current rinsing → roughing (microetching) → secondary counter-current rinsing → pre-leaching → activation → secondary counter-current rinsing → decagging → secondary counter-current rinsing → copper deposition → secondary counter-current rinsing → acid leaching
PTH detailed process explanation:
1. Alkaline oil removal: remove the oil, fingerprints, oxides, dust in the hole; The pore wall is adjusted from negative charge to positive charge to facilitate the adsorption of colloidal palladium in the later process. Cleaning after oil removal shall be carried out in strict accordance with the requirements of the guidelines, and the copper backlight test shall be used for detection.
2. Micro-corrosion: remove the oxide of the plate surface, coarser the plate surface, and ensure that the subsequent copper deposition layer and the substrate bottom copper have a good bonding force; The newly formed copper surface has strong activity and can adsorb colloidal palladium well.
3. Prepreg: It mainly protects the palladium tank from the pollution of the pretreatment tank solution and prolongates the service life of the palladium tank. The main components are the same as the palladium tank except palladium chloride, which can effectively wet the pore wall and facilitate the subsequent activation liquid to enter the hole in time for sufficient and effective activation;
4. Activation: After adjusting the polarity of pre-treated alkaline degreasing, the positively charged pore wall can effectively adsorb enough negatively charged colloidal palladium particles to ensure the average, continuity and density of subsequent copper deposition; Therefore, oil removal and activation are very important to the quality of subsequent copper deposition. Control points: set time; Standard stannous ion and chloride ion concentration; Specific gravity, acidity and temperature are also very important and should be strictly controlled according to the working instructions.
5. Degumming: Remove the stannous ion coated outside the colloidal palladium particles, so that the palladium core in the colloidal particles is exposed, in order to directly and effectively catalyze the start of chemical copper deposition reaction, experience shows that the use of fluoroboric acid as a degumming agent is a better choice.
6. Copper sedimentation: through the activation of palladium nucleus, the chemical copper self-catalytic reaction is induced, and the new chemical copper and the reaction by-product hydrogen can be used as the reaction catalyst to catalyze the reaction, so that the copper sedimentation reaction is continued. After processing through this step, a layer of chemical copper can be deposited on the surface of the plate or the hole wall. In the process, the tank should maintain normal air stirring to convert more soluble bivalent copper.
The quality of the copper sinking process is directly related to the quality of the production of the circuit board, which is only crucial for the circuit board manufacturers, is the main source of the process of through the hole is blocked, and the short circuit is not convenient for visual inspection, and the post-process can only be probabilistic screening through destructive experiments, and can not effectively analyze and monitor a single PCB board. Therefore, once there is a problem, it must be a batch problem, even if the test can not be completed to eliminate, the final product causes great quality hazards, and can only be scrapped in batch, so it is necessary to strictly operate in accordance with the parameters of the work instructions.
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