Hidden defects in solder joints such as interfacial Cu-Sn intermetallic compounds (IMC) layer and porosity have been investigated in order to obtain reliable solder joints in microelectronic packaging and assembly. The interfacial IMC layer, containing only the η-phase Cu_6Sn_5 in as-solidified solder joint, is found to increase linearly with reflow time and increase with increasing reflow temperature up to 250°C. The thermal fatigue life of 1206 LCCC solder joint is shown to decrease rapidly as the interfacial IMC layer grows to about 1.4 μm thick. Further thickening in interfacial IMC layer will only degrade the joint's thermal fatigue life moderately. This is probably due to the roughening of the solder/IMC interface with increasing thickness. Finally, the viscosity of solder paste is shown to have a negative effect on the area fraction of porosity in surface mount solder joint.
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