Study of Solidification Cracks in Sn-Ag-Cu Lead-Free Solder Joints

Abstract

In the present work, solidification cracks in Sn-Ag-Cu solder joints were investigated. Experimental results indicate that solidification cracks existed in significant numbers in the miniature Sn-Ag-Cu solder joints. In order to create solidification cracks in the miniature solder joints during solidification and evaluate the susceptibility of Sn-Ag-Cu alloys to solidification cracking, a copper self-restraint specimen was designed, which can simulate the process of solidification crack formation. The solidification crack susceptibility of the Sn-Ag-Cu solder alloy was evaluated using the total crack length of the solder joint. In addition, the effect of trace amounts of elemental additions on solidification cracking of Sn-Ag-Cu solder joints was studied. It was found that adding trace amounts of Ni or Ce could depress the solidification cracks in Sn-3.0Ag-0.5Cu solder joints. However, P additions aggravated the formation of solidification cracks.

Interface reaction between SnAgCu/SnAgCuCe solders and Cu substrate subjected to thermal cycling and isothermal aging

“…SnAgCu solder has been proposed as the most promising substitute for lead-containing solders because of its relatively low melting temperature, its superior mechanical properties, and its relatively good wettability, thus the SnAgCu solders are extensively used as solder materials in the electronic industry [5][6][7]. The ternary-eutectic composition is now thought to be close to Sn3.5Ag0.9Cu with a melting point of 217 • C. The main benefits of this alloy system are its relatively low melting temperature compared with SnAg binary eutectic alloy and its generally superior mechanical properties, as well as relatively good solderability [8,9]. Thus, SnAgCu alloys have been proposed by the Japanese (Sn3.0 wt.%Ag0.5 wt.%Cu), the EU (Sn3.8 wt.%Ag0.7 wt.%Cu) and the US (Sn3.9 wt.%Ag0.6 wt.%Cu) consortiums as replacements for conventional SnPb eutectic solder [10].…”

Effect of Ag Content on Solidification Cracking Susceptibility of Sn-Ag-Cu Solder Joints

“…The peak soldering temperature was 260°C, and then the specimen was cooled in air to room temperature. In the soldering process, flux solution of 22 wt.% ZnCl 2 plus 2 wt.% NH 4 Cl was applied to the solder.…”

“…However, solidification cracking, which has a great influence on the failure of solder joints, is easily neglected, because the dimensions of solder joints employed in actual components are usually too small. 4 Several studies have been performed to prove that microcracks exist in Sn-Ag-Cu solder joints. Dong et al 4 and Biocca 5 discovered microcracks in miniature Sn-Ag-Cu solder joints on printed circuit boards (PCBs).…”

“…4 Several studies have been performed to prove that microcracks exist in Sn-Ag-Cu solder joints. Dong et al 4 and Biocca 5 discovered microcracks in miniature Sn-Ag-Cu solder joints on printed circuit boards (PCBs). Meanwhile, Blattau and Hillman 6 proposed that microcracks in Sn-Ag-Cu solder joints were initiation sites of subsequent fatigue cracks.…”

“…In addition, the effect of adding small amounts of Ni, P, and Ce on the solidification cracking of SAC305 solder joints was investigated. 4,12 At present, the Sn-3.0Ag-0.5Cu and Sn-3.8Ag-0.7Cu alloys proposed by Japan and the European Union (EU) have become the mainstream solders employed in surface-mount technology. It is well known that Ag is a precious metal, which increases the cost of these solder alloys.…”