Evaluating the accuracy of a non-destructive thermocouple Attach Method for Area-Array Package Profiling

Using aluminum tape to attach a TC directly onto the top of the BGA provides a goodapproximation of the temperature readings under a BGA. Furthermore, this offset can becalculated with a reasonable level of confidence by using a formula developed in this researchand displayed in this article. For a relatively small BGA and thin PCB, that offset is less than 2 C.Thicker boards and larger BGAs produce larger offsets, which can be approximated by thereferenced formula and associated graph. Many electronics assemblers do not have the luxury of sacrificing production PCBs and BGAs for the purpose of measuring their profiles. Yet they need to make sure that these assemblies are processed in spec. Area‐array packages have solder balls hidden under the package, making it particularly difficult to achieve the correct thermal profile. Improper melting of solder balls will lead to poor solder joint formation and will damage the BGAs or the entire assembly. These components also tend to be expensive and, hence, represent a particular challenge for assemblers. The goal of this study was to identify a non‐destructive method for TC attachment that provides a small offset to the “actual temperature under a BGA.”