Strain-Based Flexure Assessment for the Printed Circuit Board Assembly Environment

Mechanical damage to due to over-flexure is an increasing concern in the printed circuit board assembly environment. This damage can result in part rejection during manufacturing, or may combine with other failure mechanisms to result in field returns. Therefore, flexure control during circuit board assembly is a vital part of overall product quality. A metric has been developed for component-specific strain-based flexure limits using a spherical bend mode and a novel strain metric, along with a detailed method for strain gage measurement in the assembly environment. This paper presents a review of the trends that have contributed to the increased risk of damage, as well as the development of the diagonal strain metric and the use of the spherical bend mode. These methods have been successfully employed to identify excessive flexure and reduce risks to function and reliability. Two case studies that demonstrate the application and effectiveness of the procedures are presented.