What is Chemical Hole Clearing

By Bester PCBA

Last Updated: 2023-10-16

What is Chemical Hole Clearing

Chemical hole clearing is a process to clean blind holes or buried via holes on a circuit board after laser processing. Blind holes are created during the manufacturing of high-density interconnected PCBs and serve as interconnections between layers. After the blind holes are formed, laser processing is employed to shape them, resulting in a pit-like structure.

Chemical hole clearing involves the use of chemical liquid to effectively clean the blind holes post laser processing. However, due to the small aperture of the blind holes, it can be challenging for the chemical liquid to fully penetrate and reach the bottom of the hole walls. This can lead to the formation of glue slag that cannot be rinsed off effectively. The presence of glue slag on the hole walls can negatively impact the conductivity of the subsequent metal plating process, resulting in poor conduction and the production of substandard products.

To address this issue, a proposed method for chemical hole clearing involves the use of plasma cleaning with oxygen fluorine, carbon dioxide, and fluorine. This plasma reacts with the glue slag, generating volatile materials that can be easily removed. Additionally, a micro-corrosion liquid is employed to further clean the blind holes. Laser ablation is utilized to shape the blind holes with a vertical section that is inverted trapezoidal in shape.

Chemical hole clearing ensures thorough cleaning of the blind holes, eliminating any glue slag and facilitating the formation of a uniform coating during the subsequent electroplating process. This enhances the conductivity of the metal plating within the blind holes and prevents the production of substandard PCBs.

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