Flexible PCBs employ a distinct solder mask solution known as covercoat, differing significantly from rigid board applications. This specialized layer consists of a polyimide film pre-coated with semi-cured, non-tacky adhesive that gets laminated onto the circuit under controlled heat and pressure. The process fully encapsulates all copper traces while strategically exposing solder pads through precisely created access openings.
Manufacturing specifications require the covercoat production panel to be cut approximately 0.1-0.3% smaller than the corresponding flexible circuit panel. This dimensional difference prevents premature edge sealing that could otherwise trap air bubbles within the finished assembly, compromising product reliability.
Precision alignment is achieved through carefully positioned tooling holes that maintain register between the covercoat and FPC production panels. While most applications utilize drilled access holes, high-volume production runs often transition to punching operations for improved cost efficiency and throughput.
The drilling process for covercoat materials follows similar stacking principles as rigid boards, typically processing 5-10 panels simultaneously. However, parameter adjustments are necessary to account for polyimide's unique thermal properties and the absence of copper's heat dissipation effect during the drilling operation.
For large-format panel processing, additional compensation of up to 0.2% must be incorporated to accommodate inherent dimensional variations in the flexible substrate. This adjustment ensures proper alignment throughout the manufacturing process and final product assembly. |
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