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Perhaps we will be surprised that the substrate of the circuit board only has copper foil on both sides, and the middle is an insulating layer, so they don’t need to be connected between the two sides or multi-layer circuits of the circuit board?How can the lines on both sides be connected together to make the current flow smoothly?

Let’ stake a look at the circuit board manufacturer’s analysis of this magical process – copper precipitation (PTH).

Copper precipitation：It is the abbreviation of electroless plating copper, also known as plated through hole, abbreviated as PTH. It is a self catalyzed redox reaction.PTH process shall be carried out after drilling of two or more layers of boards.

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

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

PTH Detailed process explanation:

1.Alkaline degreasing:

Remove oil stain, fingerprint, oxide and dust in the hole;The pore wall is adjusted from negative charge to positive charge to facilitate the adsorption of colloidal palladium in the subsequent process;The cleaning after oil removal shall be carried out in strict accordance with the requirements of the guidelines, and the copper precipitation backlight test shall be used for detection.

2.Micro etching:

Remove the oxide on the plate surface and roughen the plate surface to ensure good adhesion between the subsequent copper deposition layer and the bottom copper of the substrate;The new copper surface has strong activity and can adsorb colloidal palladium well;

3.Prepreg:

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

4.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 precipitation;Therefore, oil removal and activation are very important for the quality of subsequent copper precipitation.Control points: specified time;Standard stannous ion and chloride ion concentrations;Specific gravity, acidity and temperature are also very important and should be strictly controlled according to the operation instructions.

5.Degumming:

Remove the stannous ion coated on 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 fluoroboric acid is a better choice as degumming agent.

6.copper plated

The activation of palladium nucleus induces the autocatalytic reaction of chemical copper precipitation. The new chemical copper and reaction by-product hydrogen can be used as reaction catalysts to catalyze the reaction, so that the copper precipitation reaction can continue.After 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 divalent copper.

The quality of the copper deposition process is directly related to the quality of the production circuit board. It is the main source process of blocked vias and poor opening and short circuit, and it is inconvenient for visual inspection. The subsequent process can only be probabilistic screened through destructive experiments, and it is impossible to effectively analyze and monitor a single PCB. Therefore, once a problem occurs, it must be a batch problem, and even the test can not be completed,The final product can only be scrapped in batch because it causes great potential quality hazards, so it should be operated in strict accordance with the parameters of the operation instruction.