SMTA International Conference Proceedings


EFFECT OF STRUCTURAL DESIGN PARAMETERS ON WAFER LEVEL CSP BALL SHEAR STRENGTH: EXPERIMENTAL AND COMPUTATIONAL

Authors: Nikhil Lakhkar and Dereje Agonafer
Company: Department of Mechanical Engineering, University of Texas-Arlington
Date Published: 10/4/2009   Conference: SMTA International


Abstract: Ball shear testing is typically conducted on Wafer level chip scale package (WLCSP) fabrication to estimate the strength of the solder ball attachment. Generally, the solder ball shear strength is dependent on the solder ball size, pad size, solder/pad interface treatment, reflow temperature and time. Solder ball strength is also a function of ram speed and height at which the ball is sheared with respect to the wafer. Recent investigations suggest that ball shear test is being used as an indicator for board level reliability of assemblies. In current market lead time for launching a new product is very short. Unfortunately, it takes several weeks to qualify a new product by board level qualification process. If there is a methodology through which one can predict the board level performance by extrapolating the wafer level test, it will save great amount of resources in testing and millions of dollars worth of testing time.

In this study, we conducted a wafer level ball shear tests and the study was validated computationally. A DOE was created for varying wafer level structural parameters like solder ball size and type, dielectric thickness and type of UBM. Ball shear tests are often easy to perform in the fabrication routine and are very important to check the process reliability.

Key words: Lead-Free Solder; Surface Finish, Solder Joint Reliability, Accelerated thermal cycling, and Finite Element Modeling.



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