Contact Resistance of Flip-Chip Joints in Wearable Electronic Textiles

Abstract

Flip-chip bonding to a Cu lead frame transferred to a fabric was achieved by use of a non-conducting adhesive. Average contact resistance of the flip-chip joints was evaluated on variation of the Cu and Sn thickness of Cu/Sn bumps of size 150 9 220 mu m(2). The total thickness of the Cu/Sn bumps was fixed at 15 mu m. The average contact resistance of the flip-chip joints on the fabric was 5.4-10.8 m Omega, depending on the Sn thickness of the Cu/Sn bumps; this was lower than for flip-chip joints on a rigid Si substrate (15.6-26.5 m Omega). The average contact resistance of flip-chip joints on the fabric decreased from 10.8 m Omega to 5.5 m Omega when the chip-bump configuration was changed from 15-lm-thick Sn to 7-mu m-thick Cu/8-mu m-thick Sn. The contact resistance of flip-chip joints bonded with the 7-mu m-thick Cu/8-mu m-thick Sn bumps remained below 10 m Omega for up to 750 h in the 85 degrees C/85% relative humidity test and even decreased to below 4 m Omega in the storage test at 125 degrees C for up to 1000 h.