Morphology transformation on Cu₃Sn grains during the formation of full Cu₃Sn solder joints in electronic packaging

Abstract

Purpose This paper aims to analyze the morphology transformation on the Cu3Sn grains during the formation of full Cu3Sn solder joints in electronic packaging. Design/methodology/approach Because of the infeasibility of analyzing the morphology transformation intuitively, a novel equivalent method is used. The morphology transformation on the Cu3Sn grains, during the formation of full Cu3Sn solder joints, is regarded as equivalent to the morphology transformation on the Cu3Sn grains derived from the Cu/Sn structures with different Sn thickness. Findings During soldering, the Cu3Sn grains first grew in the fine equiaxial shape in a ripening process until the critical size. Under the critical size, the Cu3Sn grains were changed from the equiaxial shape to the columnar shape. Moreover, the columnar Cu3Sn grains could be divided into different clusters with different growth directions. With the proceeding of soldering, the columnar Cu3Sn grains continued to grow in a feather of the width growing at a greater extent than the length. With the growth of the columnar Cu3Sn grains, adjacent Cu3Sn grains, within each cluster, merged with each other. Next, the merged columnar Cu3Sn grains, within each cluster, continued to merge with each other. Finally, the columnar Cu3Sn grains, within each cluster, merged into one coarse columnar Cu3Sn grain with the formation of full Cu3Sn solder joints. The detailed mechanism, for the very interesting morphology transformation, has been proposed. Originality/value Few researchers focused on the morphology transformation of interfacial phases during the formation of full intermetallic compounds joints. To bridge the research gap, the morphology transformation on the Cu3Sn grains during the formation of full Cu3Sn solder joints has been studied for the first time.

Shear strength and fracture mechanism for full Cu-Sn IMCs solder joints with different Cu3Sn proportion and joints with conventional interfacial structure in electronic packaging

“…This was corresponding to the observation from the cross-sectional fracture morphology [Figure 11(e)]. It was said that the Cu 3 Sn grains presented coarse columnar shape when the full Cu 3 Sn joints were formed (Yao et al , 2018). From Figure 12(h), it could be also confirmed that the broken Cu 3 Sn grains were the coarse columnar grains which had experienced the transgranular fracture.…”

“…According to the EDS result [Figure 12(i)], it was confirmed that the columnar grains was Cu 3 Sn. In literature works (Li et al , 2011; Yao et al , 2018), researchers also found the Cu 3 Sn grains presented the columnar shape. It was apparent that there existed no trace of fracture happening in the interior of Cu 3 Sn grains.…”

“…As a consequence, the interconnected height of solder joints, within these electronic products, has been decreased from several hundreds of micrometers to less than dozens of micrometers. Under the interconnected height less than dozens of micrometers, full Cu-Sn IMCs (Cu 6 Sn 5 , Cu 3 Sn) joints, which has no residual solder in the interfacial region, are formed with the extension of soldering time as well as the application of suitable pressure (Chiu et al , 2014; Flötgen et al , 2014; Hang et al , 2013; Luu et al , 2013; Liang et al , 2017; Li et al , 2011; Mo et al , 2015; Yao et al , 2017a, 2017b, 2018; Zhang et al , 2013). For the full Cu-Sn IMCs joints, they have the interfacial structure of Cu/Cu-Sn IMCs/Cu.…”

“…There is a need to conduct relevant studies regarding the full Cu-Sn IMCs joints. The studies related to the full Cu-Sn IMCs joints mainly focus on soldering process for the formation of such joints (Chiu et al , 2014; Flötgen et al , 2014; Luu et al , 2013; Yao et al , 2017a), growth kinetics of Cu-Sn IMCs layers (Liang et al , 2017; Li et al , 2011; Mo et al , 2015) and interfacial phase evolution (Hang et al , 2013; Yao et al , 2017b, 2018; Zhang et al , 2013) during the formation of full Cu-Sn IMCs joints.…”

Effects of Co Nanoparticles Embedded in Carbon Skeleton Nanosheet Addition to Sn-0.7Cu Solder on the Interfacial Reaction

“…38 With the increase of the reflow time, the diffusion channel for the diffusion of Cu atoms is hindered, changing the Cu 6 Sn 5 close to the Cu substrate into Cu 3 Sn. 39 The scalloped IMCs are prone to stress concentrations that fracture the solder joint. Moreover, the free diffusion between Cu and Sn atoms can cause the overgrowth of the IMC thickness, i.e., unfavorable outcomes for their application in electronic packaging.…”