无铅PCB组件再流焊焊接工艺的热变形仿真分析

PCB在再流焊接过程中过大的热变形一方面可能造成元器件偏移或虚焊等组装故障,另一方面可能使焊接界面产生较大的工艺应力和微裂缝,严重影响焊点的组装质量和长期可靠性.随着TFBGA的广泛应用和ROHS指令的实施,这一问题已变得更加严峻.针对该问题,采用AN-SYS软件建立了FR-4 PCB高密度组装组件的三维有限元模型,设计了3种不同的PCB边界条件,分别进行了无铅再流焊热变形仿真分析,根据GB4677.5-84计算得出PCB在不同边界条件下的翘曲度.结果显示,在无铅焊接条件下,对PCB边缘沿厚度方向的夹持极大地减小了PCB的热变形,实现了应力最小化和变形最小化的双重目标.

The thermal Distortion Simulation of Lead Free PCB Assembly During Reflow Soldering Process

Too large thermal distortion of PCB during reflow soldering process may cause assembly defects such as components deflection and pseudo soldering,and it may induce heavy process stress and even micro crack on the soldering interface.It reduces the assembling quality and long-term reliability of solder joint seriously.This problem is more serious with wider application of TFBGA and implementation of ROHS directive.ANSYS software was employed and a 3D model of high density FR-4 PCB assembly was developed,three different boundary conditions of PCB were designed and their thermal distortion during reflow soldering processes were simulated respectively.The warp degrees of PCB under the different boundary conditions were calculated according to the Standard GB4677.5-84.The results show that the thermal distortion of PCB are reduced greatly when the two edges of PCB are clamped along the thickness direction during the lead-free soldering process,the double objective that the stress minimizing and the distortion minimizing is carried out.