Dry Preparation
A dry surface-preparation process utilizes ionized gas in a low-pressure chamber to clean and chemically activate board substrates before lamination or plating. Applying vacuum plasma pretreatment removes organic contamination and increases the surface energy of dielectric materials like polyimide. This treatment improves the adhesion of subsequent copper layers or protective coatings without using wet chemicals.
Chamber Mechanism
The process begins by placing the boards in a sealed chamber, evacuating the air, and introducing a process gas such as oxygen or argon. When high-frequency electrical power is applied, it ionizes the gas to create a plasma containing reactive ions and free radicals. In vacuum plasma pretreatment, these active species collide with the board surface to break chemical bonds and create polar functional groups.
This chemical modification increases wettability, which allows subsequent solder masks or plating layers to bond firmly with the substrate. The process runs under a vacuum to ensure the uniform distribution of the plasma around complex board features like small vias.
Adhesion Result
The resulting surface activation is temporary and must be followed quickly by the next manufacturing step to prevent re-contamination. Enhanced adhesion prevents delamination during the high temperatures of lead-free solder reflow and subsequent thermal stress. This preparation step is particularly useful for rigid-flex boards where diverse materials must be laminated together.
Properly treated surfaces exhibit higher peel strengths and lower defect rates in final testing.
