In order to investigate the use of Sn-8Zn-3Bi solder as a potential substitute for Sn-Pb solder, which has a lower melting point than Sn-Ag family solders for CSP assembly, we studied mechanical properties of CSP joints plated with varying thicknesses of Au and Ni on Cu pad. Joint strength and other mechanical properties were evaluated in relation to reflow peak temperature. The combination of 0.05 mm Au plating thickness and reflow peak temperature of 498 K resulted in the best joint reliability in the as reflowed condition and also after aging treatment. The joint was founded to have thin Ni 3 Sn 4 type interfacial reaction layer that included Cu and Zn between the solder and the Ni plating. This interfacial structure was shown to improve the joint strength.
The lead-free soldering technology has been devoloped all over the world while IEEE ReHS prohibits the use of lead contained solder in 2006. Sn-Ag-Cu solder of which melting point is 219C has the highest solder joints reliability of leadfree solder materials. This melting point is much higher than that of the conventional solder of 183 C. So reflow process for low heat-resistant components on Print Circuit Board needs lower melting point solder. Sn-Zn-Bi solder with low melting point of 197 C has a high barrier to apply to electric products due to lower reliability at high tempereture, in high humidity and after reheating a joint comparing to conventional solder. Adding both bismuth and indium into Sn-Ag solder alloy is effective especially for decrease of melting point of Sn-Ag solder and Sn-Ag-Bi-In solder which had a melting point of 206 C was devoloped. In this paper, we mentioned design of the solder alloy and soldering properties of Sn-Ag-Bi-In to the point of apearance and microsructure of solder joints concerning about the influences of temperature, humidity and heat story of joint surface after 1000 cycles at À40 C/125 C and after 1000 hours of 85 C/85%RH. But the solder joint strength of Sn-Ag-Bi-In in comparable to that of Sn-Pb eutectic solder in each test. And no significant deterioration of Sn-Ag-Bi-In solder had the same reliability as conventional solder and could be useful to expand the practical use of lead-free solder for a lot kinds of products.
Fracture mechanics concepts for describing creep crack growth in terms of ductility exhaustion in a process zone at the crack tip are reviewed and extended to include damage accumulation in the ligament ahead of a crack. Applications are considered which show that net section damage has most influence for short cracks and plane stress conditions where significant damage can develop in the uncracked ligament. It is shown that, under plane strain loading, insufficient ligament damage occurs during the crack growth phase for it t Q have an appreciable effect on failure times. A method is also presented for accounting for the influence of an incubation period prior to the onset of cracking and for making residual life estimates.
In the present paper, a deformation induced in a new bonding technology of chip-scale package (CSP) using resin encapsulation sheets is examined numerically and experimentally. Deflections after cooling from a bonding temperature are measured experimentally for various kinds of substrate and the thickness of an integrated circuit using a laser beam. In particular, a simple theory on the basis of a multilayered plate theory considering a viscoelastic property in the substrate is presented, and the thermo-viscoelastic analysis for the deflection of CSP is performed. Furthermore, the thermo-elastoplastic finite element method analysis is performed under the same temperature history. We could show that the simple formula for multilayered plates based on the thermo-viscoelatic theory can estimate fairly well the deflection of CSP in experiment.
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