CPU socket warpage measurement during reflow temperature variation using shadow moiré

Abstract

When soldering electronic components onto the Printed Circuit Board (PCB), the coplanarity of the solder joints between electronic components and a PCB is a crucial element determining the soldering quality. For those electronic components using solder balls as soldering joints, such as Ball Grid Array (BGA) and CPU socket, component makers or SMT assemblies only can inspect the coplanrity of the solder ball in room temperature. During reflow process, both of components substrate (housing) and PCB warpage will affect solder joint coplanarity. Shadow moire is widely used to measure the warpage of the PCB and electrical assembly components. During soldering stage, the change of the temperature will cause the deformation of electrical assembly components and PCB. The maximum acceptable degree of deformation is clearly defined. As for the components, it only defines the maximum warpage of BGA and Fine Pitch Land Grid Array (FLGA). There is not related regulation of the CPU socket.