A Numerical Technique to Evaluate Warpage Behavior of Double Sided Rigid-Flex Board Assemblies during Reflow Soldering Process

Abstract

High-performance computing and data center demands for complex form factor solid state drives (SSD) are driving the use of thinner electronic components and double-sided printed circuit board (PCB) in the assembly process. The use of thinner and multiple rigid-flex panel-level PCBs has led to warpage issues in the surface mount technology (SMT) assembly process, which in turn impacts the board assembly quality and yield performance. The selection of rigid-flex PCB/panel design, component density, and reflow thermal profile can affect warpage behavior during reflow soldering leading to SMT assembly defects, such as pad cratering, joint cracking, and open joint. The aim of this work is to provide a comprehensive board level assessment by considering those selection parameters before mounting packages on rigid-flex PCB. Residual strain from reflow process plays a role in the stress generated in the finished product, especially for double-sided SMT assembly. It is therefore important to consider the SMT process sequence in numerical modeling. A strategy of using imported trace on rigid-flex PCB coupled with element birth and death technique to simulate the effect of double sided SMT is outlined. Through the simulation results, it is apparent that the warpage behavior has a strong correlation with the SMT process sequence. Results demonstrate the excellent capability of the proposed modeling tools for identifying the excess warpage of PCB assembly. Implementation of the proposed pallet design will help to address the double-sided rigid-flex board warpage issue, and improve yield performance. The proposed approach greatly reduces evaluation time, shortens product life cycle development, and is more cost effective to address quality issues.