Warpage of Flexible-Board Assemblies with BGAs During Reflow and Post-Assembly Usage
Authors: Pradeep Lall, Kartik Goyal, Ben Leever and Jason Marsh Company: Auburn University, US Air Force Research Labs and NextFlex Manufacturing Institute Date Published: 10/14/2018
Abstract: Flexible printed circuit boards lack the structural stiffness of the rigid printed circuit counterparts. Thermo-mechanical deformation in flexible printed circuit assemblies may be very different from that in rigid board assemblies. The double-sided board used for the experiment is of BGA 256-144 combination with dummy components, A-PBGA256-1.0mm-17mm and A-CABGA144-1.0mm-13mm. The three-dimensional measurements of deformation and strain have been visualized on the geometry of the solder joints in the package. Digital volume correlation (DVC) method has been used to find the displacements and strains in interconnects of operational electronics. The x-ray microscopic computed tomography (µCT) system has been used to generate the 16-bit digital volume data. The x-ray detector has ability to image the x-ray attenuation of x-rays through the object. Reliability testing of SAC 305 solder interconnects has been performed on double-sided flexible circuit board using x-ray µCT by heating the package to 100C. 3D-finite element models have been developed to ascertain the degree of error in the model prediction from non-destructive experimental measurements in reflow and thermal cycling.