1. HASL means hot air solder leveling. After solder mask is applied and
cured, panels are fluxed and then the panel are dipped into molten solder
(usually 63% tin/37% lead eutectic solder at about 500 deg F) for 3-6
seconds. Then the panels are passed through blowing hot air (usually around
30-60 psi or more and around 600+ deg F) to blow the solder flat and out of
the holes. This process puts a tremendous amount of thermal stress on the
panels, will usually warp the panels and you have a lot of lead, which is on
the environmental hit list these days. On the other hand, you end up with a
pretty much flat surface of solder on your surface mount pads and plated
through holes and soldering components to this is usually pretty easy (solder
solders to solder pretty good!).

2.OSP is a very thin organic coating applied to the surface of copper surface
mount pads and plated through holes and inhibits oxidation of the copper.
OSP's have shorter shelf lives that HASL, is very susceptible to handling
because the coating is so thin (put a fingerprint on an area and it is
toast!), and does not take multiple thermal excursion well (solder past
fusion followed by wave soldering can cause problems). On the other hand, OSP
puts much less stress on the panels, panels don't warp and it is
environmentally friendly.

So which one do you use? Many people have been successful with both systems
and many board shops (probably most) have the capability for processing both
systems. It really depends on you and what your needs are.

Hope this helps.

Larry Fisher

Allen Woods & Associates