Enhanced Adhesion Strength of Copper/Epoxy Composite Build-Up Films for Flip-Chip Ball Grid Array Substrates via Interfacial Chemical Modification

The interfacial adhesion strength of fine lines for flip-chip ball grid array (FCBGA) substrates is highly dependent on the surface desmear process during substrate manufacturing. However, the extremely narrow window for optimal desmear processes limits the improvement of the adhesion strength of fine lines. Herein, a polydopamine-modified epoxy build-up film substrate was fabricated to increase chemical bonding action and broaden the process window. The chemical structure, surface roughness, morphology, surface chemical state, and adhesion strength of the modified substrate were characterized. The results showed that the adhesion strength of the substrates increased from 2.2 N/cm to 4.1 N/cm under suboptimal process conditions. Meanwhile, the effect of the polydopamine deposition time on the adhesion strength of the copper-deposited epoxy resin composite films at the interfaces was systematically investigated; furthermore, the mechanisms and reasons for the increased adhesion strength and interfacial adhesion failure for the copper-deposited epoxy resin composite build-up film substrates were revealed. This work will provide guidance in both theory and experiment to enhance the interfacial adhesion force for advanced substrates in the future.