SMTA International Conference Proceedings


Authors: Sung Chul Joo and Daniel F. Baldwin, Ph.D., Weon Woo Nam, Ph.D.
Company: Georgia Institute of Technology and Samsung Techwin Co., Ltd.
Date Published: 10/11/2007   Conference: SMTA International

Abstract: To evaluate the stencil printing performance of a 01005 component whose size is 200x400um, the stencil printing process has been executed using a lead-free solder (Sn3.0Ag0.5Cu) based on a statistical approach. Statistical approaches such as design of experiment (DOE) are widely known because the statistical package program is commercially available and is ease to use. However, problems arise during the analysis of the results. In most cases, the analysis of the experiment results is performed without validating the statistical model used such as the regression model or the analysis of variance (ANOVA) model in terms of normal distribution, constancy of error variance, or independency of error terms. The model validation is very important because if the model is not appropriate, the results will be incorrect and some remedial techniques such as transformation of the response should be taken before continuing to use the model.

The goal of this paper is to apply the statistical approach from model validation to inferences to the 01005 component stencil printing evaluation and to examine the effect of process parameters on the solder paste release efficiency and the process capability. First, through a gage repeatability and reproducibility (GR&R) study, the inspection system is found to be acceptable for measuring solder deposit volume for 01005 components.

Electroformed stencil tends to be better than laser cut stencil in terms of solder paste release efficiency by between 14% and 30% of the aperture volume with confidence level of 95%. An aperture size designed as 110% of the pad size can have the mean solder deposit volume as between 89% and 144% with 95% confidence level. There are no differences between 90% and 100% and between 100% and 110% of aperture design in the solder paste release efficiency with at least 95% family confidence level. Based on the fractional factorial design experiment, the low print speed of 10 mm/s and the high release speed of 25 mm/s should be selected within the process levels studied in order to produce the maximum solder release efficiency of between 110% and 129% with 95% confidence level. Finally, the process capabilities (Cp) are shown to be equal for all the process factor levels considered based on the experiment performed.

Key words: stencil printing, 01005, electroformed stencil, lead-free solder, DOE, solder paste

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