Printed Circuit Boards – What Surface Finishes Are Best For Various Applications?

Surface finishes for PCBs fluctuate in reliability, shelf life, flatness, price, and assembly procedures. All finishes have their own benefits; however, the process, product, and / or final use determine which surface finish works best for use with a specific application. The designer, end-user or assembler needs to work with the PCB manufacturer to choose the correct finish for the product design.

Hot Air Solder Leveling (HASL)

Hot Air Solder Leveling, a 63/37 tin lead solder, has served as the industry standard since the start of the circuit board.. HASL is the favorite because “Nothing Solders like Solder.” In situations where you have no concern about lead, HASL proves cost effective as well as a reliable finish for the making of PCBs of standard technology. This finish does, however, further stress on high layer circuit boards, resulting in ineffective long-term use. The added stress, short shelf life, and uneven soldering height on thick SMT or BGA pads make HASL a bad choice for wire bonding or chip technology. New technologies, tighter design principles and environmental issues are starting to make HASL obsolete. There are many Lead-free alloys that can replace the 63/37 tin lead solder process to make the board ROHS or Lead Free.

Lead-Free Hot Air Solver Level (LF HASL) is the ROHS compliant version of HASL. It is applied in the same but it is a different composition of the Solder. To comply with Lead-Free, the lead is removed and replaced by Gold, Nickel or other metals depending on your PCB manufacturer – thus the thickness varies anywhere between 1 to 15 mm.

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