Use of a Sn-Ni-(Cu)-(P) solder alloy for flip chip bonding and a corresponding solder ball

摘要

In the past, solder used for flip chip bonding inside a semiconductor package was a Sn-Pb solder such as a Pb-5Sn composition. Lead-free solders which have been studied are hard and easily form intermetallic compounds with Sn, so they were not suitable for a flip chip connection structure inside a semiconductor package, which requires stress relaxation properties. This problem is solved by a flip chip connection structure inside a semiconductor package using a lead-free solder which is characterized by consisting essentially of 0.01 - 0.5 mass percent of Ni and a remainder of Sn. 0.3 - 0.9 mass percent of Cu and 0.001 - 0.01 mass percent of P may be added to this solder composition. The solder may be applied in the form of solder balls (2) having a diameter of at most 0.3 mm. The semiconductor package comprises a silicon chip (1) on a substrate (3). The silicon chip (1) has electrodes treated by Ni plating. The substrate (3) has Cu plated lands or Cu foil lands, treated by Ni plating or not covered by plating.