Impact of Test Vehicle on Process Development for Fine Pitch WLP-CSP AssemblyAuthors: Domingo Vazquez, Alfredo Garcia, Ricardo Macias, Surasak Sripanyavich, Joe Smetana, Richard Coyle Humberto Ramirez, Cristina Amador, Mulugeta Abtew, Iulia Muntele, Shane Lewis
Company: Sanmina, Nokia
Date Published: 9/17/2017 Conference: SMTA International
The usage of fine pitch components on mixed technology assemblies – containing both coarse and fine pitch components - has risen in the recent years. One of the main concerns is maintaining a high SMT yield while not extending significantly the cycle time, or upsetting the line balance. Two series of experiments were conducted, one basic assembly experiment using an off the shelf kit containing one type of 0.3 mm pitch CSP component, and one experiment based on a custom test vehicle containing several sizes and ball arrays of 0.3, 0.4 and 0.5 mm pitch WLP components. For the custom test vehicle, additional processes were investigated: cleaning off no-clean assemblies, followed by underfill application and thermal cycling evaluation of solder joints reliability. A couple of reworkable and non-reworkable underfill material options were chosen based on supplier recommendations. Assembly of the components using flux dipping or solder paste printing methods was demonstrated successfully for a reasonably wide lead free process window (reflow profile length between 3 and 5 minutes) with low DPMO and low voiding level. Post assembly inspection included visual, Xray and electrical continuity measurements, followed by initial cross-section characterization of the solder joints, and parallel sectioning for underfill characterization.
WLCSP, fine pitch, underfill, lead free
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