热风整平工艺上锡不良问题的探讨

Study on dewetting of hot air solder leveling

热风整平工艺能得到一个平滑而均匀的焊料涂覆层而被广泛的应用于PCB行业。然而,针对该工艺的品质保证绝非易事。热风整平工艺受助焊剂、温度等因素的影响,在品质上容易出现上锡不良、涂层不均匀等不良问题。本文利用X-Ray、SEM、EDS等分析手段对热风整平工艺中的上锡不良问题进行了分析探讨。结果发现:上锡不良PAD位存在克氏空孔,锡层中含有铜元素,其原因是基板中的Cu原子以扩散方式通过界面Cu6Sn5层进入锡面基体中所致,造成上锡不良,导致可焊性差。

HASL is widely applied in PCB industry for its ability of obtaining an even and smooth layer of plated solder.However,it＇s not so easy to always keep the good quality of such a process.HASL is influenced by factors like the flux quality,temperature etc,so it＇s inclined to cause to defects like dewetting,unevenness of the plated solder layer.The paper hereby studies defects like dewetting in the HASL process through application of the analysis methods like X-Ray,SEM,EDS and so on.Achievements of the study are： PADs with dewetting is found out of Kirkendall Voids inside and Cu element in the solder layer.The reason is that Cu atoms in the substrate spread into the tin layer through the Cu6Sn5 layer which leads to dewetting of the layer that reduces the solderability.