Thermo-compression bonding of electrodes between FPCB and RPCB by using Pb-free solders

In this study, electrodes on a flexible printed circuit board (FPCB) and rigid PCB (RPCB) were bonded by a thermo-compression bonding. The surface finishes on the Cu electrodes of the FPCB and RPCB were organic-solderability-preservative and electroless Ni/immersion Au (ENIG), respectively. Pb-free Sn-3.0 Ag and Sn-3.0 Ag-0.5 Cu solders were used as interlayers. In order to determine the optimum bonding conditions, such as bonding force, time, and temperature, a 90° peel test of the FPCB-RPCB joint was conducted. The relationships between the bonding conditions and peel strength were investigated. We successfully accomplished the thermo-compression bonding of reliable FPCB-RPCB joints by using Sn-Ag and Sn-Ag-Cu interlayers. The thermo-compression bonding method is a stable and well-controlled process and can produce robust and reliable connections.