Thermo-compression bonding of electrodes between FPCB and RPCB

In this study, the electrodes on the flexible printed circuit board (FPCB) and rigid PCB (RPCB) were bonded by a thermo-compression bonding. The surface finishes on Cu electrodes of RPCB and FPCB were electroless Ni/immersion Au (ENIG) and electroless Ni/electroless Pd/Immersion Au (ENEPIG), respectively. In order to determine the optimum bonding conditions, a 90° peel test of the FPCB-RPCB joint was conducted. The optimum bonding pressure and time were 2.04 MPa and 5 s at 260°C, respectively. Thin and uniform (Ni, Cu)₃Sn₄ intermetallic compound (IMC) layers formed at both ENEPIG(FPCB)/Sn-3.0Ag-0.5Cu/ENIG(RPCB) interfaces. We successfully accomplished the thermo-compression bonding for a reliable FPCB-RPCB connection by using a Pb-free Sn-3.0Ag-0.5Cu interlayer.