How to do a good job of circuit board production of copper sinking process?

Have you ever thought about this question: the substrate of the circuit board has only two sides of the copper foil, and the middle is the insulating layer, then in the circuit board two or more layers of lines between them do not have to pass on?


How can the two sides of the line be connected together so that the current passes smoothly? Copper sinking is the abbreviation of electroless copper Plating (Eletcroless Plating Copper), also known as the plating through Hole (Plated Through hole), abbreviated as PTH, is a self-catalyzed redox reaction.


Two or more layers of board after the completion of drilling, it is necessary to carry out the process of PTH.


The function of PTH: On the non-conductive pore wall substrate that has been drilled, a thin layer of chemical copper is deposited by chemical method as a substrate for copper plating at the back.

PTH process decomposition: alkaline oil removal → two or three class countercurrent Rinse → coarsening (micro etching) → two class countercurrent rinse → pre-dip → activation → two-stage countercurrent rinse → gel → two class countercurrent rinse → sinking copper → two class countercurrent rinse → acid dipping.


PTH Detailed Process Explanation:


1. Alkaline Oil Removal: Remove the plate surface oil, fingerprint, oxide, hole dust, so that the hole wall from the negative charge adjusted to the positive charge, easy to the post-process colloidal palladium adsorption, after the oil cleaning should be carried out in strict accordance with the guidelines, with the sinking copper backlight test for testing.


2. Micro-etching: Remove the oxide on the plate surface, rough plate surface, to ensure that the subsequent sinking copper layer and substrate copper between the good adhesion; The new copper surface has a strong activity, can be very good adsorption of colloidal palladium;

3. Pre-immersion: mainly to protect palladium trough from the pre-treatment tank fluid pollution, extend the service life of Palladium groove, the main components except palladium chloride and palladium groove composition, can effectively moisten the hole wall, easy to follow the activation fluid into the hole in time for sufficient effective activation; 4. Activation: After treatment of alkaline oil removal polarity adjustment, the positively charged hole wall can effectively adsorb enough colloidal palladium particles with negative charge to ensure the average, continuity and compactness of subsequent copper; therefore, oil removal and activation are very important to the quality of subsequent copper sinking.


Control points: Specified time; standard tin ion and chloride ion concentration; specific gravity, acidity and temperature are also important, according to the work instructions strictly controlled.

5. Gel: Remove the tin ions outside the colloidal palladium particles, so that the palladium nuclei in the colloidal particles exposed, in order to directly and effectively catalyze the initiation of chemical copper sinking reaction, experience has shown that fluorine boric acid as a gel is a better choice. 6. Copper sinking: Through the activation of palladium nucleus induced by the chemical sinking copper self-catalytic reaction, the new chemical copper and reaction by-product hydrogen can be used as a reaction catalyst catalytic reaction, so that the sinking copper reaction continues. After this step is processed, a layer of chemical copper can be deposited on the plate surface or on the wall of the hole.


During the process, the groove fluid should be kept in normal air stirring to convert more soluble divalent copper. The quality of the copper sinking process is directly related to the quality of the production circuit board, is the main source process of the poor open short circuit, and is not convenient for visual inspection, the process can only be through destructive experiments for probabilistic screening, can not be effective analysis and monitoring of a single PCB board, so once the problem is bound to be a batch problem, even if the test can not complete the elimination, the final product caused great quality hidden danger, can only batch scrap, so to strictly follow the parameters of the work instructions operation.