Roughness evolution of Cu6Sn5 intermetallic during soldering

Abstract

The roughness evolution of the Cu6Sn5 intermetallic compound during the soldering reaction of 40/60% (by wt %) PbSn solder on Cu and its effects on wettability were studied due to their importance in the reworking of microelectronic components. The roughness parameters investigated were Rrms and the ratio, Rrms/λa, where Rrms is the root mean square roughness and λa is the average distance between asperities. It was found that Rrms increased with soldering time for the range of soldering times studied. The evolution of Rrms was found to follow a parabolic relation with soldering time—which is similar to that observed for the intermetallic thickness. However, the ratio Rrms/λa was found to increase very gradually for the range of soldering times investigated. From the ratio Rrms/λa obtained, the average inclination of the intermetallic morphology was calculated. The average inclination of the Cu6Sn5 intermetallic morphology was found to be greater than the apparent contact angle observed during the wetting of the 40/60% PbSn solder on Cu substrates. This inconsistency was attributed to the difference in the roughness of the Cu6Sn5 intermetallic in the inner regions and at the reaction band at the edge of the solder cap.

Growth mechanism of Ni3Sn4 in a Sn/Ni liquid/solid interfacial reaction

“…Copper has been the most widely used solderable metal substrate in the under bump metallization (UBM) for flip-chip and in the bond pad for ball grid array (BGA) applications [1][2][3][4][5]. Because Cu dissolves into molten Sn-rich solders very quickly during the soldering process and the Sn-Cu IMC layers grow at a very high rate to become thick during thermal aging, this excessive growth of Sn-Cu IMC layers may have a deleterious effect on the reliability of solder joints when electronic devices are used in service at high temperatures [5][6][7][8]. Often, Ni and Ni-based alloys, which are also solderable metals, are considered to be excellent alternatives for Cu substrates.…”

The growth and roughness evolution of intermetallic compounds of Sn–Ag–Cu/Cu interface during soldering reaction

“…In addition, understanding the roughness and evolution of the IMC during soldering process is important because the roughness of a surface has an effect on its wettability by liquid solder [5,6]. The roughness of IMC surface is quite important especially during the rework of component to form good joints [7].…”

The Effects of Surface Finish Roughness on Intermetallic Layer Growth, Intermetallic Interface Roughness, and Solder Joint Reliability

“…Such growth exponents correspond to a volume diffusion model [2]. To compare; in this study 94% of our η+ε growth curves produced average correlation constants of R 2 = 0.91 with an average exponential growth factor of 0.37.…”

“…Several previous studies [2,3,4] have focused on the issue of interfacial roughness evolution during the soldering process and the resultant effect on the joint reliability [5,6]. The study herein addresses the solid-state growth of the dual Sn-Cu IMC layers formed in solder joints and the accompanying roughness evolution.…”