Introduction to PCB surface treatment process:HASL and Lead-free HASL
Spray tin, also known as "hot air leveling",which is an important process of PCB production.Spray tin are mainly two types of technology:HASL and Lead-free HASL(LF-HASL), but both of them are comparison commonly used,which are widely used in PCB manufacturers.The quality of Spray tin will be directly affect the customer welding quality subsequent,so spray tin has become the focus of PCB manufacturers quality control, the following to introduce the characteristics of HASL/ LF-HASL and related basic knowledge.
HASL and LF-HASL are the most commonly used process, this process is more practical, its welding performance is good, have a good antioxidant effect and the costs is cheaper than other surface treament,such as ENIG,plating gold,immersion Ag/Sn and so on.
HASL according to a certain proportion of modulation, lead will improve the activity of tin in the welding process, lead-tin wire is relatively easy to use than lead-free tin, but lead is toxic and harmful to humans. Lead eutectic temperature is lower than the lead-free, depending on the composition of lead-free alloys, like SNAGCU eutectic is 217 degrees, the soldering temperature is eutectic temperature plus 30 to 50 degrees, depending on the actual adjustment. Lead eutectic is 183 degrees,which is better than lead-free for the mechanical strength, brightness, etc. But lead-tin is not environmentally friendly, and the world to promote a certain degree of environmental protection, therefore, the birth of a LF-HASL.
LF-HASL is an environmentally friendly process, it is very small harm to the human body, also it is recommended to use at this stage, lead-free tin for lead content of not more than 0.5,So that the welding point will be more solid. Substantial HASL and LF-HASL is a same process, only the purity of lead is not the same. The LF-HASL for the human body and the environment more environmentally,friendly and more safety, also a future development trend, it is recommended to use this process.
We had introduced the HASL and LF-HASL two types of technology features and shortcomings,HASL is more useful, but unsafe, not environmentally friendly, harmful to the human body.It is recommended to LF-HASL, non-toxic harmless, is currently advocated the use of surface treatment process.