Copper plating process in circuit board production
Perhaps we will wonder, the substrate of the circuit board has copper foil only on two sides, and the middle is an insulating layer, so do they not need to be connected between the two sides or multiple layers of the circuit board? How can the lines on both sides be connected together to allow the current to pass smoothly?
Please see the following analysis of this magical process – copper plating (PTH) by Jiepei circuit board manufacturer.
Copper plating is the abbreviation of electroless plating copper, also called plated through hole (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 by chemical methods to serve as the base for the subsequent electroplating of copper.
PTH process breakdown: alkaline degreasing → second or third level countercurrent rinsing → roughening (micro-etching) → second level countercurrent rinsing → pre-impregnation → activation → second level countercurrent rinsing → degumming → second level countercurrent rinsing → copper deposition → second level countercurrent rinsing → acid immersion
PTH detailed process explanation:
- Alkaline degreasing: remove oil stains, fingerprints, oxides, and dust in the holes on the board surface; adjust the hole wall from negative charge to positive charge to facilitate the adsorption of colloidal palladium in the subsequent process; cleaning after degreasing must be carried out strictly according to the guidance requirements, and the copper deposition backlight test should be used for detection.
- Microetching: remove the oxide on the board surface, roughen the board surface, and ensure good bonding between the subsequent copper deposition layer and the base copper; the newly formed copper surface has strong activity and can absorb colloidal palladium very well;
- Pre-immersion: mainly to protect the palladium tank from the pollution of the pre-treatment tank liquid and extend the service life of the palladium tank. The main components are consistent with the palladium tank except palladium chloride, which can effectively wet the hole wall, so that the subsequent activation liquid can enter the hole in time for sufficient and effective activation;
- Activation: after the polarity adjustment of the pre-treatment alkaline degreasing, the positively charged hole wall can effectively absorb enough negatively charged colloidal palladium particles to ensure the uniformity, continuity and density of the subsequent copper deposition; therefore, degreasing and activation are crucial to the quality of the subsequent copper deposition. Control points: specified time; standard stannous ion and chloride ion concentration; specific gravity, acidity and temperature are also very important, and they must be strictly controlled according to the operating instructions.
- Degumming: Remove the stannous ions wrapped around the colloidal palladium particles to expose the palladium nuclei in the colloidal particles to directly and effectively catalyze and start the chemical copper deposition reaction. Experience shows that using fluoroboric acid as a degumming agent is a better choice.
- Copper deposition: The activation of the palladium nucleus induces the chemical copper deposition autocatalytic reaction. The newly generated chemical copper and the reaction byproduct hydrogen can be used as reaction catalysts to catalyze the reaction, so that the copper deposition reaction continues. After this step, a layer of chemical copper can be deposited on the board surface or the hole wall. During the process, the tank liquid should maintain normal air stirring 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 for the failure of vias and short circuits. It is not convenient for visual inspection. The post-process can only be screened probabilistically through destructive experiments. It is impossible to effectively analyze and monitor a single PCB board. Therefore, once a problem occurs, it must be a batch problem. Even if the test is done, it cannot be completely eliminated. The final product will cause great quality risks and can only be scrapped in batches. Therefore, it is necessary to strictly follow the parameters of the operation instructions.
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