1997 Volume 15 Issue 4 Pages 591-599
For higher reliability of bonding on TCP (Tape Carrier Package), research has been done on the bonding of leads coated with Sn and Sn-Pb on Au bumps formed on LSIs. Major defects of bonding are (1) insufficient bonding, (2) vanishing of Au bumps, and (3) solidification of solder in lumps. Defects (2) and (3) occur when the coating reacts with Au bumps excessively, that is, if the coating is thick or the bonding temperature is too high. As for defect (3), it has been revealed that lumps form when excessive solder flows along the lead and solidifies because its melting point rises as Sn is taken in from the coating. This is more likely with Sn-Pb coating than with Sn coating, probably because the melting point of solder formed at the time of bonding falls due to Pb, allowing reaction to take place more easily. As a result, bonding conditions for practical uses have been formed Sn and Sn-Pb coatings.