Pan Pacific Symposium Conference Proceedings


A SIMPLE FLEX-CSP AND ITS RELIABILITY

Author: Yii-Tay Chiou
Company: Material Research Laboratories
Date Published: 1/25/2000   Conference: Pan Pacific Symposium


Abstract: With the fast growth in a wide variety of applications, chip scale packaging (CSP) has been drawn a lot of attention in IC packaging industry. From over 40 different packaging structures, the criterions for a smart selection might be cost, yield and reliability. Considering the infrastructure of IC packaging industry in Taiwan, we chose a wire-bonding type CSP with PI substrate as the test vehicle to evaluate its reliability. The geometric aspect of the CSP is 12mm×12mm×1mm of length, width and thickness. A 10mm×10mm of size with 112 I/O daisy-chained test die and 0.75mm ball pitch are used to fit the CSP definition. In the development, C-MOLD and ANSYS are applied to analyze the molding feasibility and package structure stress. A multi-plunger mold originally for 35mm×35mm BGA is used to encapsulate the package. The C-MOLD analysis has been confirmed according to the short-shot patterns at molding, and the structure analysis according to ANSYS is in a good agreement with the warpage data of the package after post molding cure.

In the assessment of reliability, both short term (JEDEC Standard) and long term tests are conducted with the molded CSP samples. Level III of JEDEC (30ºC/60%RH, soaked for 192hrs) was implemented to confirm the IR reflow reliability of the samples. After 3 times of IR reflow( i.e., short term test), there is no additional delamination, crack or popcorning detected during the inspections of X-ray and Scanning Acoustic Topography (SAT). On the other hand, long term tests such as PCT Level C (121ºC/100%RH/15psi for 96hrs), PCT Level D (121ºC/100%RH/15psi for 168hrs) and TCT Level C (-65ºC ~ 140ºC for 1000 cycles), all showed that the interface delamination was growing but not more than 50% of its area. As the same case in the short term test, crack and popcorn were not found during X-ray and SAT inspections after long term tests.



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