Authored By:
Jeffrey Colish, Luis Lopez, and Carlo Viola
Northrop Grumman Corporation
Summary
A study was performed to investigate, evaluate and qualify new reworkable underfill materials to be used primarily with ball grid arrays (BGAs), Leadless SMT devices, QFNs, connectors and passive devices to improve reliability. The supplier of the sole source, currently used underfill, has indicated they may discontinue its manufacture in the near future. The current underfill material is used on numerous circuit card assemblies (CCAs) at several sites and across multiple programs/business areas.
In addition, it is used by several of our contract CCA suppliers. The study objectives include evaluation of material properties for down select, dispensability and rework evaluation for further down select, accelerated life testing for final selection and qualification; and process development to implement into production and at our CCA suppliers. The paper will describe the approach used, material property test results and general findings relative to process characteristics and rework ability.
Conclusions
This effort helped to identify and down select reworkable underfill materials to replace a current underfill that may be discontinued. Although we do not have final results, the preliminary results obtained from the accelerated life testing (ALT) on test articles underfilled with suppliers 3 and 4 materials are promising.
The project methodology to survey available underfill materials from the different adhesive manufacturers, to validate the material properties and to incorporate these new materials into a qualified BGA underfill dispensing process, was fully developed and validated during this effort. The evaluation process included, not only a compatibility assessment of these new materials against the current underfill material, but the design and fabrication of a test board for a performance comparison.
The approach used for process and rework development, to down select these reworkable underfill candidates can be used to evaluate similar materials and processes. The lessons learned are many and they provide a common perspective to approach replacement material evaluations for qualified products that may be subjected to the constraints of diminishing material sources (DMS).
Initially Published in the IPC Proceedings
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