Capability Enhancement in SMT Defect Mitigation and AOI Driven Defect Detection on a Medical Electronics SMT LineAuthors: Stephanie Gomez, Christine Braun
Company: Micro Systems Engineering, Inc.
Date Published: 9/16/2015 Conference: Medical Electronics Symposium
The high reliability requirements of medical electronics mandate constant review of defects in the manufacturing processes associated with the electronic module. In a set of recent studies at MSEI, a two-pronged approach was adopted to mitigate SMT defects - determination of the root causes of the key SMT defects and subsequent implementation of appropriate process improvements to drive down defect rates, and development and implementation of post-reflow AOI capability with enhanced detection of SMT defects. Impacts of factors such as component case size, component spacing, pad size, aperture geometry and size on defects such as tombstone frequency, component misalignment, bridging, and solder balling were determined. Misalignment of component placement with respect to paste deposit was found to be a significant factor impacting tombstone frequency; as a result change in aperture shape from homeplate to oval was implemented. Since this implementation on 0402 components, the defect rate has decreased significantly from 0.20% to 0% for one product. For the second product, the tombstone rate decreased from 0.16% to 0.07%. The integration of AOI to the SMT line was completed in phases: image capture & archive capability, traceability integration, limited defect inspection and, finally, detection of major defect categories. Initial results indicate that the AOI has been able to successfully address some of the inherent limitations of manual visual inspection (subjective, poor repeatability, and risks associated with handling of electronic assemblies). So far, the AOI process has been able to maintain a < 1% false failure rate in production, and is able to consistently catch some of the major defect types.
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