Lead-free and Tin-lead Assembly and Reliability of Fine-pitch Wafer-Level CSPs

Category: No-Lead Soldering
Post Date: January 3, 2005
Author(s): Peter Borgesen, and Michael Meilunas of Universal Instruments Corporation, Binghamton, New York; Muffadal Mukadam, and Hari Srihari of Binghamton University, Binghamton, New York

Description
The option of treating fine pitch wafer level CSP (WLCSP) devices as flip chips and assembling them using a flux dipping process appears to be an increasingly attractive alternative to traditional paste printing assembly. However, printing solder paste offers the advantages of increasing standoff and improving thermal cycle performance. This paper discusses solder paste printing and flux dipping assembly processes for 0.4 and 0.5mm pitch lead-free WLCSPs and the corresponding assembly results and thermal cyclic reliability obtained. Variables evaluated include reflow ambient, paste type, and stencil design. Reliability is also compared to results for the same components assembled under identical conditions using SnPb solder.

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