汽车电子焊盘分流器焊接质量的改善研究

Research on the Improvement of the Soldering Quality of Automotive Shunt

在汽车电子SMT组装过程中,分流器作为一类自身较重且有大面积焊盘的金属器件,其焊接质量的改善是一个非常重要的问题。焊接过程中,锡膏中助焊剂的残留,以及器件或PCB表面氧化等状况容易导致焊点处形成空洞,尤其是大空洞。这些焊点空洞会使得连接点的强度和电性能特性变差,从而影响整个分流器模组信号采集的精确度和稳定性。在分析焊点空洞形成机理的基础上,分别用空气回流焊和真空气相回流焊(凝热回流焊系统)这两种焊接方法对8420规格的铜排分流器焊接质量进行了改善研究。实验结果显示,通过PCB、钢网设计和回流曲线的优化,在空气回流焊下这类器件的焊点空洞率可以减小至22.6%左右,能够满足IPC要求;而在真空气相回流焊下,通过工艺改善,焊点空洞率可减小至约3.6%。进一步对比发现,器件氧化是导致这类大焊盘铜端子焊点空洞较多的最主要原因。

Shunt is a kind of metal device with large weight and large area pad,and the improvement of its welding quality is a very important problem in the process of automobile electronic SMT assembly.During the soldering process,the flux residue in the solder paste and the oxidation of the device or PCB surface tend to cause voids at the solder joints,especially large voids.These solder joint voids will make the strength and electrical performance of the joint worse,thus affecting the accuracy and stability of the whole shunt module signal acquisition.Based on the analysis of the information mechanism of solder joint voids,the welding quality of 8420 copper row shunt is improved by air reflow welding and vacuum phase reflow welding(condersate reflow welding system)respectively.The experimental results show that through the optimization of PCB,stencil design and reflux curve,the solder joint voids of such devices can be reduced to about 22.6%under air reflow welding,which can meet the IPC requirements.And under vacuum phase reflow welding,the void ratio of the solder joint can be reduced to about 3.6%by the process improvement.Through further comparison,it is found that the oxidation of the device is the main reason for the more voids in the copper terminal of this kind of large welding plate.