The growth and morphology of intermetallic compounds between the solder and substrate play an important role in the solderability and reliability of electronic solder joints. Solder on thin films, as in chip joint, acts as an electrical and mechanical/physical interconnection between the chip and the substrate. We have studied the interfacial reactions between eutectic SnPb (63Sn37Pb, wt%) and Cr/Cu/Au thin films. Our results found here have been compared to the solder reaction on bulk Cu. The eutectic solder has 7° of wetting angle on Cr/Cu/Au thin films rather than 11° on Cu substrate. Sideband around the solder cap was found in both the thin film case and the Cu case. Spalling of Cu6Sn5 compound grains occurred in the thin-film case when the Cu film was consumed but not in the case of bulk Cu. We observed a shape change from hemispherical ‘‘scallops’’ to spheroids before spalling took place. The shape change is assisted by ripening a reaction among the scallops. We have calculated a critical size of the scallop, depending on the Cu film thickness, when the shape change or spalling starts.

The glass-passivated, face-down semiconductor chip joining technology employed in IBM's SLT (Solid Logic Technology), has become not only a fundamental element in the hybrid circuitry of System/360 but also the basis for later metallurgical designs.The "flip-chip," copper ball terminal, solder reflow technique is comprehensively reviewed and a discussion is given of its extension, through the use of ductile, all-solder terminals, to monolithic applications. P. A. Totta is at the IBM Components Division laboratory, East Fishkill, New York; R. P. Sopher is at the IBM Components Division laboratory.

In reacting eutectic SnPb solder with Ti/Cu and Cr/Cu/Au thin film metallization on Si wafers, we have observed spalling of Cu6Sn5 spheroids when the solder consumes the Cu. The formation of the spheroids is assisted by the ripening reaction among the compound grains. In addition we have observed an asymmetric spalling phenomenon using a sandwich structure, in which two wafers were soldered face-to-face. The spalling occurs predominantly at the interface at the bottom of the solder joint. It suggests that gravity plays a role.

Electrochemical fabrication of PbSn C4s (controlled collapse chip connection) offers significant cost, reliability, and environmental advantages over the currently employed evaporation technology. A continuous seed layer is required for through-mask electrodeposition of the solder alloy. This layer becomes the ball limiting metallurgy (BLM) for the solder pad after etching. The seed layer metallurgy and the BLM etching are crucial to obtaining mechanically robust C4s. In the present study, the issues related to the selection of seed layer metallurgy, uniformity of plating and etching, and mechanical integrity of C4s have been investigated. The resul~s demonstrate the feasibility of electrochemically fabricating highly reliable PbSn (97/3) C4 structures with a high degree of dimensional uniformity on a variety of wafer sizes ranging up to 200 ram.

On Au/Cu/Cr thin film surface, a drop of molten Sn first spreads out to wet the surface, but it then pulls back to dewet. The latter is due to the spalling of Cu–Sn compounds and exposing the Cr surface to the molten Sn when all of the Cu film has been consumed by the wetting reaction. Dewetting is clearly undesirable for solder joints in electronic packaging; the phenomenon is presented here.