wire. Such a condition rarely occurs in today’s modern packaging configura- tions. Elongation in aluminum wires can increase as much as 30% under high temperature aging but again, reliability is not threatened.
Gold wires are typically stabilized and annealed at elevated temperatures so that their strength and elongation properties will be affected less by the high temperature environment. Again, as shown above under proper circumstances, the gold-gold interface will remain strong and stable to at least 5008C temperatures.
While the metallurgical interfaces are stable after long periods of annealing (storage) at high temperature, the question remains as to the fatigue resistance of these wires when subjected to temperature cycling over wide temperature ranges (Ts). LargeT environments can occur in space, oil wells, engines and under certain operational conditions (power cycling).Ts, in these environ- ments can range from 2008C to over 5008C in certain applications with lower temperature in the –1408C range and high temperatures exceeding 350–4008C.
Little or no data exists on fatigue of wirebonds under temperature cycling at elevated mean temperatures. Benoit, et al. [7], studied fatigue at room tempera- ture after the wires were anneal at 3008C. His findings indicate that the annealed wires failed more rapidly than their unannealed counterparts. Much more work in this area is needed to ensure wirebond reliability in high temperature, large T environments.
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Lead-Free Soldering
Ning-Cheng Lee
Abstract Due to the global trend of green manufacturing, lead-free becomes the main stream soldering choice of electronic industry. SnAgCu alloys are the prevailing choices, with SnCu(+Y), SnAg(+Y), and BiSn(+Y) families also being adopted, where Y represents minor additive elements. The soldering processing window is narrower than that of Sn63, mainly due to the elevated melting temperature of SnAgCu solder and the limited high temperature toler- ance of components and board. The high surface tension of Sn aggravates the difficulty in wetting, while the high reactivity of Sn puts more constraint in contact time allowed between molten solder and base metal or solder container.
The creep rate of SnAgCu is slower at low stress, but faster at high stress than Sn63. This results in a longer temperature cycling life at low joint strain applications, but a shorter cycling life at high joint strain applications. Higher Cu content stabilizes IMC structure at interface between SnAgCu solder and NiAu. The high rigidity of SnAgCu solders enhances the fragility of joints, although significant improvement has been accomplished via low Ag or high Cu content or doping approaches.
Keywords Solder
Soldering Lead-free Pb-free SnAgCu SACTin-silver-copper
Surface finish Reliability