Comparison of Flip-Chip Bonding Characteristics on Rigid, Flexible, and Stretchable Substrates: Part II. Flip-Chip Bonding on Compliant Substrates

Abstract

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 m Omega to 13.3 m Omega 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 m Omega with an excessive deviation of +/- 37.7 m Omega. On the more compliant FPCB/PDMS substrate, the contact resistance decreased from 43.2 m Omega to 31.2 m Omega 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.