Affect of Anneal Temperature on All-Copper Flip-Chip Connections Formed via Electroless Copper Deposition

A fabrication technique for bonding discrete copper surfaces using electroless deposition has been developed in order to form all-copper flip-chip interconnects. The electroless copper fillet which bonds the two copper surfaces would replace solder as the electrical and mechanical connection mechanism at the first-level of packaging. An organic-additive free electroless bath was used to bond adjacent copper surfaces. The effect of anneal temperature on the electroless bond was analyzed. The electroless bond strength was shown to increase as a function of anneal temperature through the elimination of entrapped hydrogen and recrystallization of the copper. The seam between the intimately mated copper surfaces was removed at temperatures as low as 100 degrees C.