Copper sinking process for circuit board production
Maybe we are surprised that the substrate of the circuit board has copper foil on only two sides, and the insulation layer is in the middle. So they don't need to be conductive between the two sides of the circuit board or the multilayer circuit? How can the two sides of the line be connected together so that the current flows smoothly?
Look at the circuit board manufacturers to analyze this magical process—Pink Copper (PTH) for you.
Scour copper is the abbreviation of Eletcroless Plating Copper, also known as Plated Through Hole (PTH), which is abbreviated as PTH. It is a self-catalyzed redox reaction. After two or more layers are drilled, the PTH process is performed.
The role of PTH: chemically deposit a thin layer of chemical copper on the substrate of the non-conductive hole wall that has been drilled to serve as the substrate for copper electroplating.
PTH process decomposition: alkaline degreasing → second or third stage countercurrent rinsing → roughening (micro-etching) → second stage countercurrent rinsing → pre-soaking → activation → second stage countercurrent rinsing → degumming → second stage countercurrent rinsing → copper sinking → Grade countercurrent rinsing → pickling
PTH detailed process explanation:
1. Alkaline degreasing: remove oil stains on the surface of the board, fingerprints, oxides, and dust in the pores; adjust the pore wall from negative to positive charges to facilitate the adsorption of colloidal palladium in subsequent processes; clean after degreasing according to guidelines Carry out, use the copper back light test to test.
2. Micro-etching: remove the oxide on the board surface and roughen the board surface to ensure a good bonding between the subsequent copper deposit layer and the base copper; the new copper surface has a strong activity and can absorb colloids well palladium;
3. Pre-immersion: It mainly protects the palladium tank from contamination of the pretreatment tank liquid and prolongs the service life of the palladium tank. The main ingredients are the same as those of the palladium tank except palladium chloride, which can effectively wet the pore wall and facilitate subsequent activation of the liquid. Enter the pores in time for sufficient effective activation;
4. Activation: After the pretreatment alkaline degreasing polarity is adjusted, the positively charged pore walls can effectively adsorb enough colloidal palladium particles with a negative charge to ensure the uniformity, continuity and compactness of subsequent copper deposits; Therefore, degreasing and activation are very important for the quality of subsequent copper deposits. Control points: prescribed 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: Remove the stannous ions from the colloidal palladium particles and expose the palladium nucleus in the colloidal particles to directly and effectively start the chemical copper precipitation reaction. Experience has shown that it is better to use fluoboric acid as a degumming agent. s Choice.
6. Copper sinking: The chemical copper sinking autocatalytic reaction is induced by the activation of the palladium nucleus. Both the new chemical copper and the reaction by-product hydrogen can be used as the reaction catalyst to catalyze the copper sinking reaction. After processing through this step, a layer of chemical copper can be deposited on the plate surface or the hole wall. During the process, the tank liquid should be kept under normal air agitation to convert more soluble divalent copper.
The quality of the copper sinking process is directly related to the quality of the production circuit board. It is the main source of through holes and short circuits, and is not convenient for visual inspection. The subsequent processes can only be carried out by destructive experiments for probabilistic screening. Effectively analyze and monitor a single PCB board, so once the problem is bound to be a batch problem, even if the test cannot be completed, the final product will cause great quality risks and can only be scrapped in batches, so it is necessary to strictly follow the parameters of the operation instructions .