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LOW-SILVER BGA ASSEMBLY PHASE I - REFLOW CONSIDERATIONS AND JOINT HOMOGENEITY - INITIAL REPORT

机译:低银BGA组装阶段I-回流注意事项和接头均质性-初始报告

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Some Ball Grid Array suppliers are migrating their sphere alloys from SAC305 (3% Ag) or 405 (4% Ag) to alloys with lower silver contents. There are a numerous perceived benefits to this move in terms of cost and performance, but process compatibility and reliability concerns have yet to be addressed.rnProcess compatibility concerns stem from the fact that the low-silver SAC replacement alloys have higher melting temperatures than SAC305, approximately 227C as compared to 221C. Certain families of electronic assemblies, such as consumer portables, are often heat-sensitive and are reflowed in the low end of the established lead-free peak temperature range, typically 230-235C. The small temperature difference between the spheres' melting temperature and the peak reflow temperature raises questions about the reliability of the solder joints that are formed under this tight thermal margin. These are similar to the concerns raised with the backward compatibility of SAC305/405 spheres with tin-lead solder processes. Some of the solutions identified in the lead-free ball/tin-lead paste scenario may apply to the low-silver ball/SAC305 paste combination, but they require review for their applicability with this new set of mixed metals.rnA study has been undertaken to characterize the influence of alloy type and reflow parameters on low-silver SAC spheres assembled with backward compatible pastes and profiles. The DOE combines low-silver sphere materials with tin-lead and lead-free solders at different combinations of peak temperature and times above liquidus. Solder joint formation and reliability are assessed to provide a basis for developing practical reflow processing guidelines.
机译:一些球栅阵列供应商正在将他们的球形合金从SAC305(3%Ag)或405(4%Ag)迁移到银含量更低的合金。就成本和性能而言,此举有许多可观的好处,但仍需解决工艺兼容性和可靠性问题。工艺兼容性问题源于以下事实:低银SAC替代合金的熔融温度高于SAC305,与221C相比约为227C。某些系列的电子组件,例如家用便携式设备,通常对热敏感,并在已建立的无铅峰值温度范围(通常为230-235C)的低端回流。球体的熔化温度和峰值回流温度之间的温差很小,这引发了有关在这种严格的热裕度下形成的焊点可靠性的疑问。这些与SAC305 / 405球与锡铅焊料工艺的向后兼容性所引起的关注相似。无铅球/锡铅膏场景中确定的某些解决方案可能适用于低银球/ SAC305膏剂组合,但需要对其在这套新的混合金属中的适用性进行审查。表征合金类型和回流参数对低银SAC球体的影响,这些球体具有向后兼容的焊膏和型材。 DOE在峰值温度和液相线以上时间的不同组合下,将低银球材料与锡铅和无铅焊料结合在一起。评估了焊点的形成和可靠性,为制定实用的回流焊工艺指南提供了基础。

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