Journal of SMT Article

CSP SELF-CENTERING ASSESSMENT USING OFFSET NORMALIZATION METHODOLOGY

Authors: Dr. Paul P.E. Wang and Dr. Katsuji Takasu
Company: Solectron Corporation
Date Published: 7/1/1999   Volume: 12-3

Abstract: The self-centering effect of the CSP and ?BGA packages during reflow soldering was investigated. A design of experiment (DOE) with four control variables was employed to simulate the self-centering phenomenon of various types of packages. Correlation among self-centering, solder volume, thermal field, weight of the package, and percent of offset was established. A placement accuracy test methodology was developed to offset the placement and normalize the data processing (OPNDP) before and after the reflow process. This methodology provided a means to measure the placement offset and displacement due to self-centering. An evaluation of the flux and paste used was conducted. This involved examination of the wetting angle, residue level, SIR, and electronic migration test results.

A mathematical model identifying the key process parameters for this experiment was formulated. Two additional DOEs with identified process variables were conducted. A series of experiments was performed on a high precision placement rework machine to emulate the reflow activities during CSP removal and replacement. Finally, the optimized process parameters were used as control variables for self-centering assessment on CSP and PBGA packages. The mathematical formulation and OPNDP were evaluated by multiple regression analysis to show the performance of these approaches. The self-centering effect exhibited in various array packages was studied.



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