0.4mm Thin Circuit Board

A 4-layer thin rigid PCB with overall plate thickness of 0.4mm and immersion gold surface finish, supporting minimum drilled hole diameter of 0.150mm, minimum BGA pad of 0.22mm, and minimum IC pad of 0.2mm. The thin FR-4 stack-up squeezes 4-layer routing density into a sub-half-millimeter envelope, fitting inside compact handheld and wearable enclosures where every fraction of a millimeter of thickness is contested. Typical applications include smartwatch main boards, hearable device control boards, smart-ring electronics, ultra-thin IoT sensor nodes, and miniature wireless modules. Immersion gold delivers the flat, oxidation-resistant solder surface required for fine-pitch SMD reflow and probe testing. Manufacturing demands tightly controlled copper imaging, registration, and lamination because the thin core leaves little tolerance for warpage or copper-to-edge variation.