Causes of defects in PCB surface mounting welding and prevention measures

- Oct 20, 2018-

It is difficult to predict the bad situation of surface mounting welding. This paper will give some corresponding measures for the bad welding.

Poor wetting

Poor wetting refers to the solder and PCB substrate welding areas in the welding process. After infiltration, no metal reaction is generated, resulting in leakage or less welding fault.Most of the causes are the contamination of the solder area surface, or the contamination of resistance solder, or the formation of metal compound layer on the surface of the solder joint, such as sulfide on the surface of silver, oxide on the surface of tin, etc., which will result in poor wetting.In addition, when the residual aluminum, zinc, cadmium, etc. in the solder exceed 0.005%, the activity degree is reduced by the hygroscopic action of the solder, and bad wetting can also occur.In wave soldering, if gas exists on the surface of PCB substrate, this fault is easy to occur.Therefore, in addition to performing proper welding techniques, antifouling measures should be taken on the surface of PCB substrate and component surface, suitable solders should be selected, and reasonable welding temperature and time should be set.

Second, the bridging

The reason for the occurrence of bridge connection is mostly caused by excessive solder or serious collapse of the side after solder printing, or the size of PCB substrate welding zone is out of tolerance and SMD mounting excursion, etc. In the stage of microrefinement of SOP and QFP circuits, bridge connection will cause electrical short circuit and affect the use of products.