What are the advantages and concerns with different ROHS complaint finishes?
Below are some of the advantages and concerns with the more popular ROHS compliant finishes. Pb Free Hot Air Solder Level (HASL) Coatings Advantages: Pure metal alloy should work with most Pb-Free alloy choices. Pad wetting is faster and more uniform than other finishes. Another major advantage to Pb-free HASL finish is the use of high temperatures in the process act as an initial “Thermal Shock” test reveling issues such as delamination and out-gassing before the more costly assembly process. Concerns: Non uniform deposits, delamination or warpage due to higher processing temperatures. Possibility of chemicals entrainment in PCB. Immersion Metal Finishes – (e.g. Tin, Silver) Advantages: Simple process, uniform height Concerns: Coating thinness and durability, Non uniformity. Possible formation of non-solderable alloys, and oxidation. Electroless NiAu Advantages: Simple process, uniform finish, good shelf life, compatible with many alloys. Concerns: Possibility of “Black Pad” failure.
