1. Thickness of the support
The thickness of the circuit board makes the difference between the HASL with lead and the HASL without lead. The leaded support PCB thickness ranges between 25.4µm and 50.8µm; the lead-free variant supports thicknesses between 2.54µm and 25.4µm.
2. Cost of surface treatment
Lead-free HASL has an intermediate cost compared to other PCB finishes such as ENIG and HASL. It is less expensive than the ENIG surface treatment and somewhat more expensive than the traditional HASL process.
3. Properties
The properties or composition also make the two different; HASL lead uses a combination of tin and lead, while lead-free HASL uses more tin and less copper.
4. Typical applications
The surface finish of HASL lead is ideal for use in circuit boards where a greater thickness is required. For example, it can be used for simple/traditional flame retardant (FR4) PCBs, especially those over 0.5 mm thick.
The HASL lead-free surface treatment can be used for circuit boards with a thickness of less than 0.5 mm. An example is rigid printed circuit boards (PCBs).
5. Safety precautions
The opposite is the case with lead-free HASL finishes, which do not use lead as one of the solder alloys. This makes it safer for both the person using it and the environment in which it is used.
6. Melting point
Just as HASL lead-free uses a higher temperature, this also means that a lot of time must pass before its solder melts. In contrast, with the HASL lead finish, the solder melts much more quickly.
7. Presentation
The presentation of the surface treatment also distinguishes between HASL lead-free and HASL leaded. Commonly, HASL surface finishes consisting of lead and tin have a brighter interface due to the brighter and shiny composition of the properties.
In contrast, lead-free HASL finishes tend to appear dull when applied to the surface of PCBs.
