Leaded Parts Through a Lead-free Wave

Phil
We're coming to you today from the 44th floor of our glorious Boston office here with a very cloud obscured view of Logan Airport. Today's question is from J.B.

We will be assembling circuit boards using a RoHS compliant assembly line, however the customer does not have a RoHS lead-free requirement. Are there any concerns if we use a few leaded components in this process? Are we likely to contaminate our wave solder bath?

Jim and Phil
The answer is YES. Don't take the chance!

Jim
This is a classic example of not wanting to introduce anymore variability or chances into your process. Could you put tin lead plated parts through your lead-free wave soldering? Lead is going to get into that pot. Your limit is 0.1%. Yeah, could you get away with a few parts? Sure.

Is it a good idea? No, it's not because sooner or later the contamination build up in that pot will come back to harm you; and if you contaminate that pot; if you get too much lead in it; you will have to completely drain the pot and flush it.

It's just a very complex and a costly procedure to get that pot back again. But thinking in a more philosophical vein; don't enter variability into your process. It's not a good idea. You got a lead-free process; you want to keep it lead-free.

Do not allow any contamination anywhere on the line - parts, stencil printer, anyplace that contamination can occur. You're taking a risk, and you don't want to introduce additional risks into your process if you don't have to.

Phil
Now chances are you're probably not auditing your incoming components. It would be great if you were, but chances are you're probably not (if you're like most people) and there's a possibility you could already be running some leaded parts through that bath.

So we recommend to get a feel for what's going on, that you send a sample from your bath out for analysis to your solder company or analysis lab to monitor to the various levels of contaminates in your solder bath.

You should do this more frequently at the front end until you get a good feel for what's going on.

Jim
Right, but keeping tin lead and lead-free separate has been a continuing logistical problem. Don't take any chances. And with process concerns such as contaminating a pot, taking risk is just not worth it.

Phil
Thank you for listening to board talk and remember...

Jim
Don't solder like my brother.

Phil
And don't solder like my brother.

Jim
And keep those kids away from the flux pot.

You should be checking a sample of all component lots intended to be used on lead-free assembly using XrF to ensure incoming parts meet RoHS requirements. Some parts will have other finishes that can contain small amounts of lead as a byproduct. Your monthly solder sample analysis performed on each pot as per J-STD-001 requirements will ensure you remain in compliance.

Also, have you checked that all those non-RoHS components are actually suitable for the higher soldering temperatures typically associated with lead-free solder? When we made our connectors RoHS compliant, in many cases we changed the plastic to better resist these higher temperatures.