Effect of polyimide baking on bump resistance in flip-chip solder joints

Hsi-Kuei Cheng, Shien-Ping Feng, Yi-Jen Lai, Kuo-Chio Liu, Ying-Lang Wang, Tzeng-Feng Liu, Chih Ming Chen

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

The effect of polyimide (PI) thermal process on the bump resistance of flip-chip solder joint is investigated for 28 nm technology device with aggressive extreme low-k (ELK) dielectric film scheme and lead-free solder. Kelvin structure is designed in the bump array to measure the resistance of single solder bump. An additional low-temperature pre-baking before standard PI curing increases the bump resistance from 9.3 m Omega to 225 m Omega. The bump resistance increment is well explained by a PI outgassing model established based on the results of Gas Chromatography-Mass Spectrophotometer (GC-MS) analysis. The PI outgassing substances re-deposit on the Al bump pad, increasing the resistance of interface between under-bump metallurgy (UBM) and underneath Al pad. The resistance of interface is twenty-times higher than pure solder bump, which dominates the measured value of bump resistance. Low-temperature plasma etching prior to UBM deposition is proposed to retard the PI outgassing, and it effectively reduces the bump resistance from 225 m Omega to 10.8 m Omega. (C) 2013 Published by Elsevier Ltd.
Original languageEnglish
Pages (from-to)629-632
Number of pages4
JournalMicroelectronics and Reliability
Volume54
Issue number3
DOIs
StatePublished - Mar 2014

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