Barbara,
It really depends on the environment you are working, storing, and ultimately the environment your product is going to be used in.
IAg (Immersion Silver) is good from a manufacturing point of view because it is flat. Also solder does not spread as much and therefore you will have fewer shorts. You need to have a clean environment because if there is pollution (especially sulfur) the surface will begin to tarnish (create silver sulfides)and become unsolderable, ugly, and uncleanable. You also have to read up on creep corrosion and pick your fluxes correctly. There are several papers presented at APEX on this. Look for Chen Xu, Joe Smentana, and Richard Coyle from Alcatel-Lucent. They are industry leaders in this topic. The environment to which your products we live it life is also important. If it is in an environment like Asia where pollution is high the exposed silver with tarnish, turn brown and black, and become difficult to test (probe), and repair.
For this reason I always try to cover all exposed metal with solder to protect it like HASL.
From an assembly standpoint HASL is the best for longevity. You cannot beat it for solderability, shelf life, appearance, repairability, etc. The only negative aspects are it is getting harder to find a PWB Fab house with the capability. Pb-free HASL has not really caught on. And the issue that HASL is not the flattest surface to work with. Flatter is always better.
OSP is flat and cheap but you have the same environmental issues as IAg.
Good luck in your choice. I just really cannot stress enough to take the environment that your product will operate into consideration. Also the life of your product is important. I have a 25 year life cycle that I have to deal with. You may have a 5 year life cycle and most of this is not an issue.
FYI, I prefer HASL in most cases.
Russell Nowland
Alcatel-Lucent
Advanced Manufacturing Engineer
Address: 14000 Quail Spring Parkway, Suite 100
Oklahoma City, OK 73134
email: [log in to unmask]
Desk: 405-302-1660
Cell: 405-203-0034
Fax: 405-302-1622
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Barbara Burcham
Sent: Wednesday, June 01, 2011 8:17 PM
To: [log in to unmask]
Subject: [TN] Best Board Finish - beyond gold
Hey Y'all,
I am looking for a reliable bare board finish that beats the cost of gold.
What experience is out there?
What would you recommend?
Thanks,
Barbara Burcham
pcb Trace Design
[log in to unmask]
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