2017 Volume 58 Issue 8 Pages 1217-1222
The contact resistance and microstructure of the flip-chip joints processed using anisotropic conductive adhesive (ACA) were characterized on flexible printed-circuit-board (FPCB) and stretchable FPCB/polydimethylsiloxane (FPCB/PDMS) substrates. On the FPCB substrate, the contact resistance was remarkably reduced from 56.9 mΩ to 13.3 mΩ when the bonding pressure increased from 10 MPa to 200 MPa. However, at a bonding pressure of 300 MPa, it substantially increased to 74.8 mΩ with an excessive deviation of ±37.7 mΩ. On the more compliant FPCB/PDMS substrate, the contact resistance decreased from 43.2 mΩ to 31.2 mΩ when the bonding pressure increased from 10 MPa to 50 MPa. Severe distortion of the FPCB/PDMS substrate occurred at bonding pressures above 50 MPa because of the softness of the PDMS. A more compliant substrate has a lower appropriate bonding pressure for the flip-chip process.