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| Content Provider | IEEE Xplore Digital Library |
|---|---|
| Author | Kumar, P. Cornejo, O. Dutta, I. Subbarayan, G. Gupta, V. |
| Copyright Year | 2008 |
| Description | Author affiliation: Dept. of Mech. & Astronaut. Eng., Naval Postgrad. Sch., Monterey, CA, USA (Cornejo, O.) || Dept. of Mech. & Astronaut. Eng., Washington State Univ., Monterey, CA, USA (Kumar, P.; Dutta, I.) || Semicond. Packaging Div., Texas Instrum., Dallas, TX, USA (Gupta, V.) || Sch. of Mech. Eng., Purdue Univ., Lafayette, IN, USA (Subbarayan, G.) |
| Abstract | Sn-Ag-Cu (SAC) solders are susceptible to appreciable microstructural coarsening during storage or service, resulting in evolution of joint properties, and hence reliability, over time. Although the problem of microstructural coarsening in joints has been studied extensively, the effect of joint scale on aging kinetics has never been investigated. Understanding the scale dependence of aging is particularly relevant in light of the continual decrease in joint sizes and the increased reliability demands placed on solder joints. This paper compares the coarsening behavior of a bulk Sn-Ag-Cu (SAC) solder with that of small joints (650 ¿m diameter) attached to bond-pads with a Ni-based surface finish and shows that the aging behavior displays significant joint-scale dependence. Not only do $Ag_{3}Sn$ precipitates in small joints coarsen faster, the coarsening is more rapid nearer the bond-pads than farther away. Through energy dispersive x-ray (EDX) analysis of the solder-pad interfaces, it is determined that these effects are attributable to the depletion of Cu from the small solder joints due to solution / reaction with the Ni present in the bond-pads. Longer aging times enhance this depletion. Based on an analytical model, it is shown that the coarsening kinetics of the $Ag_{3}Sn$ precipitates depends directly on the solubility limit of Ag in Sn As a result, smaller joints, which would show greater Cu depletion and hence higher Ag solubility, would display faster $Ag_{3}Sn$ coarsening kinetics. Furthermore, there is greater Cu depletion from the solder nearer the solder-pad interfaces, and hence the coarsening kinetics are faster near the interfaces than in the middle of the joint, giving rise to spatially inhomogeneous coarsening.. |
| Starting Page | 903 |
| Ending Page | 909 |
| File Size | 2475105 |
| Page Count | 7 |
| File Format | |
| ISBN | 9781424421176 |
| DOI | 10.1109/EPTC.2008.4763545 |
| Language | English |
| Publisher | Institute of Electrical and Electronics Engineers, Inc. (IEEE) |
| Publisher Date | 2008-12-09 |
| Publisher Place | Singapore |
| Access Restriction | Subscribed |
| Rights Holder | Institute of Electrical and Electronics Engineers, Inc. (IEEE) |
| Subject Keyword | Aging Kinetic theory Soldering Microstructure Packaging Mechanical factors Bonding Lead Temperature Material storage |
| Content Type | Text |
| Resource Type | Article |
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