4 Layer Flexible PCB Production Record #FPC-20260418-0008

This production record covers 35 units of a 4-layer flexible board using rolled copper on a 0.23 mm polyimide construction. Boards measured 61.48 × 40.77 mm with ½ oz copper, 4/4 mil trace and spacing, 0.2 mm minimum holes, yellow soldermask, white silkscreen, immersion gold ENIG finish, and selective FR4 stiffeners. The combination of thin cross-section, tight geometry, and impedance requirements distinguished the order from conventional flex work and called for exact control at every lamination and patterning step.

Material preparation emphasized careful polyimide handling to eliminate wrinkles and ensure uniform thickness. Stackup impedance engineering guided trace width compensation during inner layer imaging, etching, and high-pressure lamination. Coverlay lamination, solder mask application, electroless nickel, and immersion gold deposition were sequenced to maintain registration across the fine features while preserving flexibility in non-stiffened zones.

Each board underwent TDR impedance testing, dynamic flex cycling, and full electrical verification. All 35 pieces met the specified electrical and mechanical criteria after 28 days of fabrication, confirming repeatable performance for this impedance-controlled flexible circuit.