Mechanism and Prevention of Spontaneous Tin Whisker Growth
Spontaneous Sn whisker growth on Cu leadframe finished withPb-free solder is a serious reliability problem in electrical andelectronic devices. Recently, Fortune magazine had an article to describethe urgency of the problem. The spontaneous growth is an irreversibleprocess, in which there are two atomic fluxes driven by two kinds ofdriving force. There are a flux of Cu atoms and a flux of Sn atoms. TheCu atoms diffuse from the leadframe into the solder finish driven bychemical potential gradient to form intermetallic compound of Cu6Sn5 inthe grain boundaries of the solder, and the growth of the compound atroom temperature generates a compressive stress in the solder. To relievethe stress, a flux of Snatoms driven by the stress gradient diffuses awayto grow a spontaneous Sn whisker which is stress-free. The typicalindustry solution is to inserta diffusion barrier of Ni between the Cuand solder to prevent the diffusion of Cu into the solder. It isinsufficient, because we have to uncouplethe irreversible processes andstop both the fluxes of Cu and Sn. A solution is presentedhere.
- Research Organization:
- Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
- Sponsoring Organization:
- USDOE Director. Office of Science. Office of Basic EnergySciences; Semiconductor Research Corporation Project No. NJ-863, NationalSemiconductor Corporation
- DOE Contract Number:
- AC02-05CH11231
- OSTI ID:
- 889259
- Report Number(s):
- LBNL--59497; BnR: KC0204016
- Journal Information:
- Materials Transactions, Journal Name: Materials Transactions Journal Issue: 11 Vol. 46
- Country of Publication:
- United States
- Language:
- English
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