A Study of SnAgNiCo vs Sn3.8AgO. 7Cu C5 Lead Free Solder Alloy on Mechanical Strength of BGA Solder Joint

摘要

Eu RoHS Directive for environmental and health concerns have resulted in significant activities to find substitutes for lead-contained solders for microelectronics. The potential candidates such as Sn-Ag1 and Sn-Ag-Cu1 eutectic solders with melting temperatures of 221?°C and 217?°C, respectively are the most prominent solders because of their excellent mechanical properties as compared with that of eutectic Sn-Pb solder2. Other candidates as drop-in replacements for eutectic Sn-Pb solder, such as Sn-In-Zn alloys, may have melting point close to 185?°C, though not eutectic, and an acceptable solidification range but have received only limited attention1. Among the many possible lead-free solder alloy candidates, three commonly used alloys to meet automotive thermal cycling requirement are Sn3.0Ag0.5Cu, Sn3.8Ag0.7Cu and Sn4.0Ag0.5Cu. However, industry has found these commonly applied solder alloys to have certain level of ball drop problem which affects production yield, product quality as well as customers satisfaction. This paper reports a study which was conducted on BGA lead-free C5 solder joint system to compare SnAgNiCo solder alloy versus the conventional Sn3.8Ag0.7Cu solder alloy, with the objective to strengthen the solder joint so as to eliminate ball drop encountered on the conventional Sn3.8Ag0.7Cu solder alloy. This study showed that SnAgNiCo C5 solder system performed better than Sn3.8Ag0.7Cu in terms of joint strength and intermetallic brittle mode failure rate. Experimental works were carried out to observe the melting properties, microstructure and elemental analysis that were obtained by Differential Scanning Calorimetry (DSC), SEM and EDX respectively.