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November 19, 2007

Pros and cons of HASL, OSP and Immersion Gold

What are the pros and cons of HASL, OSP and Immersion gold surface finishes?

T. M.

Experts Comments

A very interesting question and the answers could go on forever.

HASL ( Hot Air Solder Leveling) replaced Electroplated Tin/Lead and became SMOBC (Solder Mask over Bare Copper) with HASL. Good for through hole components, helped with weak knees or the wetting at the knees of the plated through holes. Problems not very flat and problems developed with the introduction of surface mount in the early 80s.

OSP, Organic Solder Protective coating, eliminated one thermal cycle from the board processing process, was flat so it accepted surface mount components relatively easy. Vaporize pretty easily so if the product was double sided, soldering on the second side could be problematic. This was reduced quite a bit with the use of water soluble fluxes in the solder paste.

Immersion Gold, or ENIG, Electroless Nickel, Immersion Gold. Again a flat surface and good for all surface mount components especially BGA components. The soldering was ok, but the board shops had to watch the chemistry involved in the plating process. If the plating process went bad, the opportunity to have black pad existed and when this happen the solder joints could not be made. This has been resolved in the industry but once in a while it happens, so everyone needs to be on the look out for this condition.

Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.
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