Copper Deposition Technology in PCB Production
Perhaps we would be surprised that the base material of PCB only has copper foil on two sides and insulation layer in the middle, so they do not need to be connected between two or more layers of PCB lines? How can the two sides of the line be connected to make the current flow smoothly?
Next, please see the circuit board manufacturer for your analysis of this magic process - copper (PTH).
Copper deposition is the abbreviation of Eletcroless Plating Copper, also known as Plated Through Hole, abbreviated as PTH, which is a self-catalyzed oxidation-reduction reaction. PTH process is needed after drilling two or more layers of plates.
Function of PTH: A thin layer of chemical copper is deposited on the non-conductive pore wall substrates drilled by chemical method to serve as the back electroplated copper substrates.
PTH process decomposition: alkaline deoiling - secondary or tertiary countercurrent rinsing - coarsening (microerosion) - Secondary countercurrent rinsing - preprepreg - activation - Secondary countercurrent rinsing - gelling - Secondary countercurrent rinsing - precipitated copper - Secondary countercurrent rinsing - acid immersion
Detailed process description of PTH:
1. Alkaline degreasing: removing oil contamination, fingerprints, oxides and dust in the hole; adjusting the hole wall from negative charge to positive charge, facilitating the adsorption of colloidal palladium in the later process; cleaning after degreasing should be carried out strictly in accordance with the requirements of the guidelines, and testing with copper backlight test.
2. Micro-etching: removing the oxide from the surface, coarsening the surface, ensuring a good bond between the subsequent deposited copper layer and the base copper; the new copper mask has a strong activity, which can adsorb colloidal palladium well;
3. Pre-immersion: Mainly to protect the palladium tank from the contamination of the pretreatment bath, prolong the service life of the palladium tank. The main components are consistent with the components of the palladium tank except palladium chloride, which can effectively wet the pore wall and facilitate the subsequent activation liquid to enter the pore in time and activate sufficiently and effectively.
4. Activation: After adjusting the polarity of alkaline deoiling by pretreatment, the positive pore wall can effectively adsorb enough colloidal palladium particles with negative charges to ensure the evenness, continuity and compactness of subsequent copper precipitation; therefore, deoiling and activation are very important to the quality of subsequent copper precipitation. Control points: the prescribed time; standard stannous ion and chloride ion concentration; specific gravity, acidity and temperature are also important, which should be strictly controlled in accordance with the operating instructions.
5. Degumming: removing tin ions from colloidal palladium particles and exposing the palladium nuclei in colloidal particles to directly and effectively catalyze the chemical precipitation of copper. Experience shows that fluoroboric acid is a better choice as a degumming agent.
6. Copper precipitation: The self-catalytic reaction of chemical copper precipitation is induced by the activation of palladium nucleus. The new chemical copper and hydrogen, the by-product of the reaction, can be used as catalysts to catalyze the reaction, so that the copper precipitation reaction continues. After this process, a layer of chemical copper can be deposited on the plate or hole wall. During the process, the tank liquid should be stirred with normal air to produce more soluble bivalent copper.
The quality of copper sinking process is directly related to the quality of the production line board. It is the main source of the process which is not open through holes and short circuit. It is not convenient for visual inspection. The later process can only be screened by destructive experiments, and can not effectively analyze and monitor a single PCB board. Therefore, once problems arise, batches are inevitable. Quantitative problems, even testing can not be eliminated, the final product caused great quality risks, can only be scrapped in batches, so strictly in accordance with the parameters of the operation instructions.
