1. Gold plating
Cost of Gold plating process is the highest of all surface treatment, but it is the most stable surface finishing all of the existing treatment at present and the most suitable for use in lead-free process of the PCB, especially in some high-priced or require high reliability electronic products are recommended to use this surface treatment.
OSP finishing is the lowest cost, easy to operate, but it requires some re-adjustment on equipment and process conditions in assembly plant and it not quite suitable for re-working assembly, therefore popularity still not big.
If use of this surface treatment, after high-temperature heating, The protective film overlying on PAD is bound to be damaged, so solderability is reduced, especially when the PCB after the second solder reflow, the situation is more serious, so if PCB still need to go through the process of process, then the DIP solderability will face some difficulty.
3. Immersion Silver
Although the "silver" itself has a strong mobility, resulting in the case of the occurrence of leakage electric, but at present "immersion silvering" is not a conventional pure metallic silver, but with organic co-plated "organic silver" have therefore been able to meet the demand of the lead-free process, which can also have longer solderability shelf time than OSP board.
4. Immersion Gold
The biggest problem of ENIG finishing is the "black mat" (BlackPad) problem, which mean some pads are not immersion with gold, or the gold has been oxide, so there are many manufacturers do not agree to use ENIG for the lead-free process, but most of the domestic PCB manufacturers in China like SysPCB(www.syspcb.com) are using this process.
5. Immersion Tin
This surface finishing can be easily contaminated, scratched, plus in the process FLUX occur oxidation and color changing, most domestic manufacturers do not want use this process, the cost is relatively high.
HASL has the advantages of low cost, good solderability, good reliability, strong compatibility, although the good welding characteristics, due to the presence of lead in HASL, so it can not be used in lead-free process.