Processing and Reliability of CSPs with Underfill
Processing and Reliability of CSPs withUnderfill
Jing Liu & R. Wayne Johnson
Laboratory for Electronics Assembly &Packaging– Auburn University
162 Broun Hall, ECEDept.
Auburn, AL 36489 USA
Erin Yaeger, Mark Konarski & Larry Crane
Loctite Corporation
1001 Trout Brook Crossing Rocky Hill, CT06067 USA
Abstract
The use of CSPs is rapidly expanding,particularly in portable electronic products. Many CSP designs will meet thethermal cycle or thermal shock requirements for these applications. However, mechanicalshock and bending requirements often necessitate the use of underfills toincrease the mechanical strength of the CSP-to-board connection. This paperexamines the assembly process withcapillary and fluxing underfills. Issues ofsolder paste versus flux only, solder flux residue cleaning and reworkabilityare investigated with the capillary flow underfills. Fluxing underfillseliminate the issues of flux-underfill compatibility, but require placementinto a predispensed underfill. Voiding during placement is discussed.
To evaluate the relative performance of theunderfills, a drop test was performed and the results are presented. All of theunderfills significantly (5-6x) improved the reliability in the drop testcompared to non-underfilled parts. Test vehicles were also subjected toliquid-to-liquid thermal shock testing. The use of underfill improved thethermal shock performance by >5x.
Key Words: Chip scale packages, Underfill, DropTest
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