SMTA International Conference Proceedings


Author: Polina Snugovsky et al.
Company: Celestica International Inc.
Date Published: 9/22/2002   Conference: SMTA International

Abstract: In the transition period from Lead-bearing solder to Lead- Free solder, four metallurgical combinations will be in use: Lead-Free solder with Lead-Free components, Lead-bearing solder with Lead-bearing components, Lead-Free solder with Lead-bearing components, and Lead-bearing solder with Lead-Free components. It is necessary to characterize the joints resulting from these metallurgical combinations in order to optimize process parameters and insure reliable joints.

In this study, BGA locations on electroless Ni/ immersion Au (ENIG)-finished boards were reflowed with Sn-3.8Ag- 0.7Cu or Sn-37Pb solder balls using Sn-3.8Ag-0.7Cu or eutectic Sn-Pb solder pastes. Some boards were aged at 150 °C for 310 hr, 480 hr, and 2160 hr. The four metallurgically different types of solder joints, both as-reflowed and after aging, were shear tested and examined using transmissive X-ray, optical microscopy, scanning electron microscopy, and dispersive X-ray spectroscopy.

Some as-reflowed joints were analyzed with Differential Scanning Calorimetry. Solder joint microstructure and composition, intermetallic formation, surface roughness, and voiding were investigated. The influence of structural parameters on shear strength and fracture modes was shown. The differences and similarities between the four different joint metallurgies are discussed.

Key words: lead-Free, microstructure, intermetallic, roughness, voiding, solder joints.

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