Improvements in Decision Making Criteria for Thermal Warpage

Abstract

Surface mount components are commonly evaluated for out-of-plane warpage levels across reflow temperatures. Decision making for acceptable warpage levels is primarily made based on signed warpage levels of a single component surface, per industry standards. This paper discusses how a single signed warpage value is an oversimplified and incomplete way to describe a surface mount attachment between two mating surfaces that change in shape over temperature. Specific examples are shown where current industry standard gauges for thermal warpage are misleading. Issues include current industry standard equations for calculation of signed warpage. Optimal understanding of effects of warpage on surface mount attachment includes analysis of both mating surfaces under the same thermal and test conditions. Examples are shown of dual surface analysis, where gap between mating surfaces becomes the critical value in place of signed warpage. Evaluating both sides of two attaching surfaces is the optimal way to understand surface mount defects related to thermal warpage. However, many companies dealing with SMT will not have reasonable access to the surfaces to which their products will be attached. The paper goes on to discuss different approaches to more effectively quantify a single surface over temperature. This includes, but is not limited to, adding equations for signal strength values to currently established signed warpage standards.