Phil
Welcome to board talk. This is Phil Zarrow and Jim Hall, pick and place of the assembly brothers. Sometimes known as ITM consulting consultants. Today we've got an interesting one from an aerospace guy.

Jim
This question is from EB. We work with an aerospace manufacture on PCB assembly that includes lead free components, but no BGA's. We process using tin lead 60/40 solder. But this does not solve the issue with tin plating on the leads and the risk of tin whiskers. According to information on the nasa.gov whisker website (http://nepp.nasa.gov/whisker/), tin whisker formation is an issue on the exposed component leads outside the solder region.

Is there a process that can be used to re-plate component leads to add lead? Well, this is a very common topic which we discuss regularly in our technical workshops entitled lead free for the excemptee where we have people dealing with backward compatibility.

Phil
Typically your brethren from aerospace military avionics, medical, and all you other guys. I thought you were going to get it easy when you didn't have to comply with lead free but we've found just the opposite.

Jim
The NASA website is absolutely correct. When you solder tin plated leads, even matte tin over nickel, the solder cannot be counted on to wick all the way up the lead so you end up with a small section of lead close to the component body that still has tin coating on it. And it can cause whiskers.

If you look at the INEMI (http://www.inemi.org) recommendations for surface finishes, they say that matte tin over nickel is acceptable, it's all under the caveat not for high-rel applications.

Phil
That’s right, so Jim, what's an engineer to do?

Jim
The standard procedures are affectionately called strip and dip. Basically a chemical or a metallurgical process is used to remove the tin coating and replace it with a tin lead coating. Some use chemistry and acids to strip the tin off and then usually they dip it to replace it. Some use sequential dips in a tin lead pots so each time you dip it you get a purer and purer tin lead coating on the leads. The bottom line is you end up with all of the lead completely coated with tin lead.

Phil
This has become quite a little bit of a cottage industry.

Jim
If you’re doing a significant volume, there's automated equipment you can buy to do this yourself.

Phil
Well, great, that hopefully answers EB's question. This had been Jim Hall and Phil Zarrow, the assembly brothers. Talking to you on board talk and we thank you. Keep those questions coming in. And whatever you do in the meantime ...

Jim
Don’t solder like my brother.

Phil
And don’t solder like my brother.