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Effect of Germanium Addition to Sn3.5Ag Lead Free Solder System for Overall BGA Package Robustness Improvement
Keywords: Germanium, Sn3.5Ag, BGA Packaging
A study was conducted on BGA lead-free C5 solder joint system to assess the effect of Germanium addition to Sn3.5Ag solder alloy through comparison study of Sn3.5Ag vs Sn3.5AgGe. The main objective of this study is to find a way to resolve solder surface oxidation after thermal processes, while determining if theres any adverse effect on the solder joint by Germanium addition. The result of this study showed that addition of Germanium in Sn3.5Ag C5 solder system did not have solder surface oxidation after thermal processes, while Sn3.5Ag alloy alone showed discoloration. Also, addition of Germanium helped to improve solder joint strength of Sn3.5Ag. Experimental works were carried out to observe the melting properties and solder surface microstructure by Differential Scanning Calorimetry (DSC) and SEM. Shear and pull strength was measured by Dage which is representative of the intermetallic (IMC) strength between the C5 solder sphere and Cu/Ni/Au pad finishing. Solder surface oxidation was measured by EDX. Tray and Packaging Drop Tests were done to gauge solder joint performance against impact force. A comprehensive study was done to study the effect of microstructure and interface intermetallics of both solder system at ambient, high temperature storage (HTS) at 150C for 24, 48, 96, 168, 504 and 2000 hours and multiple reflow of 1x, 2x, 3x, 6x towards the joint integrity. In each read point, Sn3.5AgGe has significantly higher ball shear and ball pull strength. EPMA microstructure analysis after cross-sectioning on bulk solder and IMC revealed traces of Germanium that contributed to the significant increase in ball shear and ball pull strength, while did not cause any bulk solder and IMC morphology changes. In conclusion, addition of Germanium in Sn3.5Ag lead-free solder is able to resolve surface oxidation problem after thermal processing, with improvement to solder joint strength for overall lead-free package robustness.
Eu Poh Leng, Process Development Manager
Freescale Semiconductor Malaysia Sdn Bhd
Selangor 47300,
Malaysia


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