Effect of a Backing Material on the Bendability of Flexible Substrates with Passive SMD components

Bendability of printed circuits on flexible substrates has created a significant interest in the wearables and IoT industry. Flexible circuits on plastic substrates with SMD components that can be bent sharply (small radius of curvature) and show little or no change in electrical and mechanical properties are useful for wearable applications. Component adhesion of the flexible circuits can be low if there is a mismatch in Youngs moduli and thickness ratios of the trace, substrate, component, and bonding adhesive. We demonstrate a method that can be used to increase the adhesion of passive SMD components on flexible substrates through the addition of a backing layer. Analysis of the shear strength of bonds were used to characterize the adhesion of the component with and without the backing layer. COMSOL and MATLAB were used to develop an understanding of the difference in adhesion between different material stacks. Bending stress reduction through incorporation of a backing layer can be beneficial for multiple solder pastes and substrate combinations.