Now let's see the circuit board manufacturer explain the magic process - copper deposition (PTH).

　　CopperplateIt is the abbreviation of Electroless Plating Copper, also known as Plated Through hole, abbreviated as PTH, which is a self catalyzed redox reaction. The process of PTH shall be carried out after the drilling of two or more layers of boards is completed.

　　Role of PTH:A thin layer of chemical copper is chemically deposited on the drilled non-conductive hole wall substrate to serve as the substrate for subsequent copper electroplating.

　　PTH process breakdown:Alkaline degreasing → secondary or tertiary countercurrent rinsing → roughening (micro etching) → secondary countercurrent rinsing → pre leaching → activation → secondary countercurrent rinsing → degumming → secondary countercurrent rinsing → copper precipitation → secondary countercurrent rinsing → acid leaching

Remove oil stains, fingerprints, oxides and dust in the hole on the board surface; The hole wall is adjusted from negative charge to positive charge, which is convenient for the adsorption of colloidal palladium in the subsequent process; Cleaning after degreasing shall be carried out in strict accordance with the requirements of the guidelines and shall be tested by copper sinking backlight test.

The oxide on the board surface is removed and the board surface is roughened to ensure a good adhesion between the subsequent copper deposition layer and the base copper; The newly formed copper surface has strong activity and can well adsorb colloidal palladium;

It is mainly to protect the palladium tank from the pollution of pre-treatment tank liquid and prolong the service life of the palladium tank. The main components are the same as those of the palladium tank except for palladium chloride, which can effectively wet the hole wall and facilitate the subsequent activation liquid to enter the hole in time for sufficient and effective activation;

After adjusting the polarity of alkaline oil removal by pretreatment, the positively charged pore wall can effectively adsorb enough negatively charged colloidal palladium particles to ensure the average, continuity and compactness of subsequent copper deposition; Therefore, oil removal and activation are crucial to the quality of subsequent copper deposition. Key control points: specified time; Standard stannous ion and chloride ion concentration; The specific gravity, acidity and temperature are also very important, which should be strictly controlled according to the operation instructions.

Remove the stannous ions wrapped outside the colloidal palladium particles, expose the palladium core in the colloidal particles, and directly and effectively catalyze the chemical copper precipitation reaction. Experience shows that it is a better choice to use fluoroboric acid as the gelling agent.

The autocatalytic reaction of chemical copper deposition is induced by the activation of palladium core. Both 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 deposition reaction continues. After being treated by this step, a layer of chemical copper can be deposited on the plate surface or hole wall. During the process, the tank liquid shall be stirred with normal air to convert more soluble 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 blocked vias and poor open and short circuits, and it is not convenient for visual inspection. The subsequent process can only be probability screened through destructive experiments, and can not effectively analyze and monitor individual PCB boards. Therefore, once problems occur, they must be batch problems. Even if the test can not be completed, the final product will cause great potential quality problems, It can only be scrapped in batches, so it is necessary to strictly follow the parameters in the operation instructions.