Available Finishes

Organic Solderability Proctectants (OSPs)

OSPs are a viable candidate because they are almost in the same price range as SnPb (about 25 cents/sq. ft. in the current market) and contain no lead. These finishes are also easily processable, relatively free of ionic contaminants, and are smoother than HASL. They also exhibit good solderability (based on flux/solder atmosphere selection) and are reworkable.

These finishes are known for their short storage life, which can be up to 12 months if stored properly (i.e., dry nitrogen, desiccants), but manufacturers with quick turnover of PCBs may not see this as an issue. There are also concerns with handling of these finishes, durability with higher soldering temperatures, and flux chemistries used.

Lead Free Hot Air Solder Level (HASL)

Even though lead free HASL is available for PCBs, some manufacturers may choose to move away from this process if required to produce lead free product.

If chosen, alternative HASL finishes will most likely work well with most alternative alloys and will wet faster than plated finishes or coatings. Concerns with this finish include warpage due to higher processing temperatures and PCB absorbed process chemistries, although they can sometimes be removed with cleaning.

Immersion Finishes

Immersion finishes have been considered as one replacement for HASL because of its surface flatness and ease of process.

Concerns must be addressed regarding the thinness of the coating, because higher soldering temperatures could result in out-diffusion of base metals and oxidation, leading to reduced solderability.

Electroless NiAu

These finishes are attractive because of their resistance to damage during handling/processing and improved shelf life over other finishes. These finishes are also free of ionic contaminants, compatible with most flux chemistries, and smoother than HASL.