Detailed explanation of Plated Through Hole (PTH) process technology in PCB production process

PTH, short for Plated Through Hole, also known as plated through hole, refers to the deposition of a thin layer of chemical copper on a non-conductive hole wall substrate that has been drilled, using chemical methods as the substrate for subsequent copper plating. So, what are the processes of PTH technology for PCB circuit boards?

Chemical copper is widely used in the production and processing of printed circuit boards with through holes. Its main purpose is to deposit a layer of copper on non-conductive substrates through a series of chemical treatment methods, and then thicken it to a specific design thickness through subsequent electroplating methods. Generally, it is 1mil (25.4um) or thicker, and sometimes even directly deposited to the entire copper thickness of the circuit through chemical methods. The chemical copper process involves a series of necessary steps to ultimately complete the deposition of chemical copper, each of which is crucial to the entire process flow.

The purpose of this chapter is not to elaborate on the manufacturing process of circuit boards, but to specifically emphasize some key points related to chemical copper deposition in the production and manufacturing of circuit boards. For readers who want to learn about the production and processing of circuit boards, it is recommended to refer to other articles, including the reference list listed after this chapter.

1、 PTH process decomposition:

Alkaline degreasing → secondary or tertiary countercurrent rinsing → roughening (micro etching) → secondary countercurrent rinsing → pre soaking → activation → secondary countercurrent rinsing → de gelatinization → secondary countercurrent rinsing → copper deposition → secondary countercurrent rinsing → acid leaching.

2、 PTH detailed process explanation:

1. Alkaline degreasing: removes surface oil stains, fingerprints, oxides, and dust inside holes; Adjust the pore wall from negative charge to positive charge to facilitate the adsorption of colloidal palladium in the subsequent process; After degreasing, it is necessary to strictly follow the instructions for cleaning and use a copper backlight test for testing.

2. Micro etching: Remove the oxide on the surface of the board, roughen the surface, and ensure good adhesion between the subsequent copper deposition layer and the base copper of the substrate.

3. Pre immersion: mainly to protect the palladium tank from contamination by the pre-treatment tank solution, extend the service life of the palladium tank, and facilitate the timely entry of the subsequent activation solution into the hole for sufficient and effective activation.

4. Activation: After pre-treatment with alkaline oil removal and polarity adjustment, the positively charged pore walls can effectively adsorb enough negatively charged colloidal palladium particles to ensure the uniformity, continuity, and density of subsequent copper deposition.

5. Gelling: Remove the stannous ions wrapped around the colloidal palladium particles, exposing the palladium nuclei in the colloidal particles to directly and effectively catalyze the chemical copper deposition reaction.

6. Copper deposition: Chemical copper deposition self catalytic reaction is induced by the activation of palladium core. Newly generated chemical copper and reaction byproduct hydrogen can serve as reaction catalysts to catalyze the reaction, allowing the copper deposition reaction to continue continuously. During the process, the tank solution should maintain normal air agitation 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 of through-hole blockage and short circuit defects. Therefore, once a problem occurs, it will inevitably be a batch problem, which will ultimately cause great quality hazards to the product and can only be scrapped in batches. Therefore, it is necessary to strictly follow the parameters in the operation manual.

The above is an introduction to the copper deposition process of PCB circuit boards, hoping to be helpful to you.