Lead manufacturing to lead free transisition

Hi, Bill,

Lead-free solder and paste manufacturers will be a great resource for you during the transition; they've tested their products extensively, and their application groups have been able to help me through the biggest changes.

There are a few things you'll need to consider as you're transitioning. The biggest consideration is that lead-free solder/paste requires higher reflow temperatures than tin-lead solder.

1. Reflow Oven. Sounds like you've already looked at this. Do you have to jump into a new oven right away?? Probably not...but, it'll depend on the boards you're processing, and the capabilities of your current ovens. If you have older 5-zone or less ovens, with blowers not capable of running to 350 degrees, you could encounter issues. This doesn't mean you can't run low heat-load boards (we did it with a 15 year old 4-zone heller); just means that some higher heat-load boards will not solder well.

The additional zones give you, of course, more control over the process window. The TAL window is tighter with lead-free pastes than it was with tin-lead pastes.

2. Wave solder. This is completely dependent on the types of assemblies that you're running. To date, I haven't invested in a pb-free wave, because I haven't run enough volume to warrant it. I'm running with a pb-free solder pot. Existing wave machines can be upgraded to lead-free capabilities. The pot is coated with a special substance that prevents the pb-free solder from corroding it; and the lines have to be cleaned out. If you're completely converting to lead-free, this might be a more economical method than buying a new lead-free machine.

3. Board finish. We've experienced the best results from ENIG finishes. I haven't had a lot of luck with white-tin finishes to date. However, your mileage may vary.

4. Solderer skills. This is one that can be tough to overcome, depending on the attitudes of your personnel. Lead-free solder joints look different than tin-lead joints. Compared to the old standards, they resemble cold-solder joints. I've had a heck of a time convincing people that IPC accepts lead-free solder joints that look like this. If you can provide lead-free solder training for your people, it'd be beneficial. I've also had a heck of a time getting people to turn their irons down. Lead-free does flow at a higher temperature than tin-lead solder, but my people are turning their irons up to 800 degrees in some instances, and that's not necessary.

5. Soldering equipment. Because of the higher temperatures, and the lack of lead, the lead-free solder tends to corrode soldering iron tips much faster than tin-lead solder ever did. This caught me by surprise; the additional expense of replacement tips, and the time-frames involved in replacing the tips.

cheers, ..rob

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you may need to change ovens since you were running lead in there. you probbly have some lead dust still blowing around in there

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Hmmm.... I had Intel survey my process on a mixed alloy line for 2 days. They periodically removed boards from all stations on the line (including post reflow). Boards were "crushed" and spearated into constituent plastic, ceramic and metals. All samples passed with lead below 1K PPM.

I had no idea they were fudging their test results to sell more mother boards in europe? Thanks Larry for opening my eyes!

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