Thin Plate Using Espi Ball In Board-level Bga Package Device Failure Detection

Ball Grid Array(BGA) and Plastic Leaded Chip Carrier(PLCC) devices are welded to PCB by solder reflow process.The solder joints are served as interconnections between device and PCB.As the solder joints are usually hidden below the device body,the fast and nondestructive quality inspection of solder joints is relatively difficult.Electronic Speckle Pattern Interferometry(ESPI) is a kind of nondestructive optical testing technology.The sensitivity and precision of ESPI are high and can be in nanometer range.Taking the advantages of ESPI,it is possible to compare the difference of assembly deformation due to damaged solder joints and good counterparts under simple mechanical loadings.Hence the failed joints can be identified and located with further analysis.In this study,a novel testing method combing ESPI and FEM is proposed to inspect welding quality of solder joints in surface-mount devices.Its procedure consists of the following two steps:testing the out-of-plane displacement of samples under mechanical loadings by ESPI technology,thus localizing damaged joints according to ESPI fringe patterns and displacement distribution;and conducting finite element analysis on devices in different joint connection status,thus analyzing the failure mode according to the comparison on surface displacement between ESPJ experiments and FEM models.To verify this method, tests were carried out on pseudo BGA samples each with the corner solder joint good, delaminated and missed,actual board-level surface-mount BGA devices each with the corner solder joints good and delaminated,and actual PLCC devices mounted on PCB when the joints were good,the corner joint delaminated and the inner joint delaminated.Abrupt changes of ESPI fringe patterns and remarkable increment in displacement values at failed solder balls were observed while testing pseudo BGA samples.In good accordance with FEM simulation,displacement fields recorded by ESPI rose proportionally to the damaged degree at the failed solder joint.This demonstrates the above-mentioned method is valid for surface-mounted devices with a small I/O array.In the tests of actual BGA and PLCC devices,ESPI measurements also showed good sensitivity to damages at corner.The fringe patterns and displacement distribution both revealed the position of delaminated joints,and agreed with the FEM results.However,this method failed to recognize inner joint failure.Therefore the above method performs better in identifying corner joint failures.In all,the testing method combing ESPI and FEM proposed in this study can be used to inspect welding quality of solder joints in surface-mount devices quickly and nondestructively, and is especially effective for testing corner joints.