Investigating Printed Circuit Board shrinkage during reflow soldering

摘要

The paper presents an emerging problem in the field of electronics manufacturing, where the miniature SMD components and the large size of the panelized Printed Circuit Boards (PCBs) cause soldering failures indirectly during reflow soldering. During our investigation, the issue of PCB shrinkage was inspected, which causes linear offset problems along the lateral dimensions of the board during the stencil printing of the second PCB side. The offset in the print causes bridging failures and tombstones on specific fine-pitch SMD components (such as 0402 resistor ladders and 0603 chip-size resistors). To investigate the behavior of the PCB material, Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) measurements were applied on the materials. With the DSC method it is possible to approximate the glass transition temperature parameter of the PCB material itself. A new PCB edge length measurement method was also developed to achieve deeper understanding on the shrinkage effect. The method is evaluated with lab-class measurement devices. With the edge length measurements, it is possible to approximate an overall shrinkage value for the given PCB, enabling efficient compensation and failure reduction.