On the increase of intermetallic compound's thickness at the cold side in liquid Sn and SnAg solders under thermal gradient

• Synchrotron radiation imaging technique is applied for thermomigration study.
• The thermotransport of Cu in Sn has been modelled using FEM.
• Higher temperatures enhances the rate of increase of cold end intermetallic compound size.
• The smaller cold end Cu6Sn5 in Sn–3.5Ag than Sn may be attributed to the role of Ag3Sn.

The thermal gradient induced intermetallic compound growth at the cold side of the Cu/Sn/Cu and Cu/Sn–3.5Ag/Cu solders heated at 350° has been in situ studied using synchrotron radiation imaging technique. Finite element model for thermotransport of Cu from hot end to cold end in Cu/Sn/Cu solder is implemented for the description of the associated growth of the compound. Higher temperature and bigger solder volume are observed as favorable parameters for the rate of thickness increase in both Sn and SnAg solders. In case of SnAg system, the formation of Ag3Sn particle, causing retardation effects in the growth of Cu6Sn5 compound, subsequently induces a lowered resulting thickness.