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 JB: “Will the assembly circuit boards using 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 LF 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, 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, it's just: 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 have already be running some leaded parts through that pot.

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

Jim
Absolutely.

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

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
Absolutely.