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Reliability of WLP Structures Fabricated with ALX Dielectric Polymer
Keywords: WLCSP, Reliability, Spin-on Polymers
For wafer level packaging (WLP) applications, BCB and polyimide are the predominant spin-on dielectric materials used for re-passivation, redistribution, and stress buffering. Each of these materials has their respective strengths and weaknesses in process and in reliability. We have previously presented data on Asahi Glass Corp.'s ALX polymer material (1), which is formulated to have good mechanical and electrical properties with an application process similar to BCB and polyimide and a significantly lower cure temperature. In this work we present the results of a collaborative study of the reliability of WLCSP bump-on-polymer structures fabricated with BCB, PI, and ALX polymers. The test structures have been fabricated with copper RDL structures sandwiched between two polymer layers (PI, BCB, or AL-X) and are bumped using Pb-free solder. The test structure design was designed and previously evaluated by Amkor in previous work by Anderson, et al (2). After fabrication the devices are assembled to boards and then subjected to thermal cycling and drop testing. Comparisons of characteristic lifetimes and failure modes are made for the three polymer materials. (1) Huffman, et al, “Application and Evaluation of AL-X Polymer Dielectric for Flip Chip and Wafer Level Package Bumping”, 2009 IMAPS Device Packaging Workshop, Scottsdale, AZ, March 10-12, 2009. (2) Anderson, et al,
Alan Huffman, Research Engineer
RTI International
Research Triangle Park, NC
USA


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