The covercoat represents a specialized solution for flexible circuits, fundamentally different from conventional solder mask technologies. Comprising precision-engineered polyimide film with controlled-adhesion coating, this protective layer bonds permanently under lamination conditions to shield circuitry while permitting controlled pad exposure.
Dimensional control begins with the covercoat panel being manufactured slightly undersized relative to the FPC panel. This critical sizing relationship prevents sealing defects and ensures bubble-free encapsulation of the delicate circuit patterns beneath.
Registration accuracy depends on perfectly aligned tooling holes between covercoat and circuit panels. The choice between drilled and punched access holes represents a key production decision - drilling handles smaller batches (5-10 panel stacks), while punching optimizes high-volume economics.
Material-driven adjustments dominate the drilling process, where polyimide's thermal response and absent copper layers mandate customized parameters. These adaptations prevent heat-related defects while maintaining hole wall integrity in the finished product.
At production scale, material science considerations extend to dimensional compensation - up to 0.2% adjustment accommodates the natural movement of flexible substrates during large-panel processing, ensuring final product accuracy. |
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