Solder joint embrittlement—it’s not just gold
Figure 4. Etched section of solder joint showing the crystalline platelet-structure of Pd2
Hyun-Kyu, Duksan HI-Metal Co., South Korea.
Sn/Pd3
creep-fatigue to the overall solder damage resulting from the TC3 cycle leads to the significantly earlier failures for the TC3 thermal cycle. At the same shear strains, fatigue lives
for the TC1 are longer than the TC2 ther- mal cycle; this results from the fact that cyclic loading at lower temperatures results in a more incomplete creep process—and, hence, a smaller creep-fatigue damage, than cyclic loading at higher cycling tem- peratures.
References: 1. Engelmaier, W., “Solder Joint Formation & Intermetallic Compounds (IMCs),” Global SMT & Packaging, Vol. 3, No. 4, May 2003, pp. 36-38.
2. Engelmaier, W., “Soldering Pad Surfaces—Gold, Silver & Teir IMCs: Solder
Joint
SMT & Packaging, Vol. September 2003, pp. 29-32.
‘Embrittlement’,” Global 3, No.
6,
3. Lee, H. K., et al., “A Study of Solder Optimization Development for Portable Electronic Device,” Proc. IPC Midwest Conference & Exhibition, Schaumburg, IL, September 23, 2009, pp. S07:02:1-33. Duksan HI-Metal Co., South Korea. E.,
4. Stafstrom, Palladium:
“Why Electroless Study on Impact of
Electroless Palladium on Electroless Nickel Deposits,” Proc. IPC Midwest Conference & Exhibition, Schaumburg, IL, September 23, 2009, pp. S07:01:1-31.
5. Milad, G., “ENEPIG: A Final Finish Tat’s Time Has Come,” CircuiTree, Vol. 23, No. 5, May 2010, pp.16-19.
6. Engelmaier, W., “Te Case Against ENIG,” Global SMT & Packaging, Vol. 5, No. 6, June/July 2005 [EU-edition], pp. 39-40.
7. Lambrinou, K., and W. Engelmaier, “Te Microstructural Aspect of the Ductile- to-Brittle Transition of Tin-Based Lead- Free Solders,” J. ASTM Int., Vol. 7, No. 7, July 2010, available at
www.astm.org, Paper ID JAI103064.
www.globalsmt.net
Figure 6. The fatigue lives for the TC3 -50⇔+100°C thermal cycle are significantly shorter than those of the other two thermal cycles at a given shear strain level. This results from the transitioning from temperatures significantly below the ductile-to-brittle transition region and the combination of the effects of both low-temperature embrittlement and high-temper- ature creep-fatigue. Cracks nucleating during the high-temperature creep-fatigue stage of solder damage more easily propagate in the solder during the low-temperature part of TC3 -50⇔+100°C thermal cycle due to the notch sensitivity of the partially embrittled Sn-rich phase in the solder. [Source: Ref. 11]
8. Lambrinou, K., et al., “A Novel
Mechanism of Embrittlement Affecting the Impact Reliability of Tin-Based Lead-Free Solder Joints,” J. Electronic Materials, 2007, pp.1881-1895.
9. Limaye, P., et al., “Low-Temperature
Embrittlement of Lead-Free Solders in Joint Level Impact Testing,” Proc. 9th Elec. Pack. Tech. Conf., (Singapore, December 2007), pp.140-151.
Continued on page 61 Global SMT & Packaging – February 2011 – 59 Sn IMC. Courtesy of Lee
Figure 5. Impact energy, ∆E, as a function of test temperature for some solders. The shaded areas superimposed on the impact resistance curves of solders SAC 305, SAC 405, and Sn- 5Ag emphasize the fact that the ductile-to-brittle transition in their fracture behavior occurs over a whole temperature range and not at a single DBTT value. [Source: Ref. 10].
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