PCB News - Explanation of copper sinking process in circuit board production

Perhaps we will be surprised that the substrate of the circuit board only has copper foil on two sides, and there is an insulating layer in the middle, so there is no need for them to conduct between the two sides or multiple layers of the circuit board? How can the lines on both sides be connected together so that the current flows smoothly?

Next, please see the circuit board manufacturer for you to analyze this magical process-copper sinking (PTH).

Eletcroless Plating Copper is the abbreviation of Eletcroless Plating Copper, also called plated through hole, abbreviated as PTH, which is a self-catalyzed redox reaction. After the two-layer or multi-layer board is drilled, the PTH process must be carried out.

The role of PTH: On the non-conductive hole wall substrate that has been drilled, a thin layer of chemical copper is deposited chemically to serve as the substrate for subsequent copper electroplating.

PTH process decomposition: alkaline degreasing-two or three-stage countercurrent rinsing-roughening (micro-etching)-secondary countercurrent rinsing-pre-soaking-activation-secondary countercurrent rinsing-degumming-secondary countercurrent rinsing-copper deposition-two Grade countercurrent rinsing - pickling

PTH detailed process explanation:

1. Alkaline degreasing: remove oil stains, fingerprints, oxides, and dust on the surface of the board; adjust the pore wall from negative charge to positive charge to facilitate the adsorption of colloidal palladium in the subsequent process; cleaning after degreasing must strictly follow the guidelines Proceed with the test with the immersion copper backlight test.

2. Micro-etching: remove oxides on the board surface, roughen the board surface, to ensure that the subsequent copper immersion layer has a good bonding force with the bottom copper of the substrate; the new copper surface has strong activity and can absorb colloids well palladium;

3. Pre-soaking: mainly to protect the palladium tank from the contamination of the pretreatment tank solution and prolong the service life of the palladium tank. The main components are the same as the palladium tank except for palladium chloride, which can effectively wet the pore wall and facilitate the subsequent activation of the solution. Enter the hole in time for sufficient and effective activation;

4. Activation: After adjusting the polarity of alkaline degreasing by pretreatment, the positively charged pore walls can effectively adsorb enough negatively charged colloidal palladium particles to ensure the average, continuity and compactness of subsequent copper precipitation; Therefore, degreasing and activation are crucial to the quality of subsequent copper deposits. Control points: the prescribed time; standard stannous ion and chloride ion concentration; specific gravity, acidity and temperature are also very important, and must be strictly controlled in accordance with the operating instructions.

5. Debonding: remove the stannous ions from the colloidal palladium particles to expose the palladium nucleus in the colloidal particles to directly and effectively catalyze the chemical copper precipitation reaction. Experience has shown that it is better to use fluoroboric acid as a debonding agent s Choice.

6. Copper precipitation: The electroless copper 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 reaction catalysts to catalyze the reaction, so that the copper precipitation reaction continues. After processing through this step, a layer of chemical copper can be deposited on the board surface or the hole wall. During the process, the bath 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 process of impermissible vias and poor open and short circuits. It is not convenient for visual inspection. The subsequent processes can only be screened probabilistically through destructive experiments. Effective analysis and monitoring of a single PCB board, so once a problem occurs, it must be a batch problem, even if the test cannot be completed, the final product causes a great quality hazard and can only be scrapped in batches, so strictly follow the operating instructions. .