Selective Soldering
Bill Anderson
Product Manager
Tyco Electronics
20 North Wacker Dr., Suite 3305
Chicago, IL 60606
phone:312-782-4345
fax:312-782-4241
mobile:847-274-9111

Is No-Lead Compatible with Solder Systems and Can a Leaded Solder Pot Be Converted to a Lead-Free Solder Pot?

You can hear anything you want to hear, especially when it comes to solder systems and no-lead. You can find horrific images of failed impellers after just a few short hours of operation, and cases made that only cast iron solder pots will hold up to a lead-free alloy. Further investigation can reveal reports supporting coatings such as Titanium Nitride as the only viable method, and others supporting Ceramics, or Porcelain or Titanium construction, and so on. The truth is, I have not found a coating that will hold up to thermal stresses in soldering systems, and related maintenance can damage these very thin coatings. Certainly, Titanium will hold up; however, the cost of the material and the level of difficulty in welding it raises concerns in my mind.

The solder pot, impeller, duct etc. cannot fail due to the no-lead solder alloy unless the parts wet with solder. The parts cannot wet with solder unless the protective oxide layer on the surface of the parts is removed by a strong flux or physically abraded away, as can happen in cleaning or possibly from cavitation. Even if the oxide layer were violated, a repair is simply performed by grinding down to the base metal and re-oxidizing the surface. With this said, it has been reported to the author that there are more than 450 wave solder machines running no-lead solder alloys, and that the vast majority of these are reporting no problems in doing so. This makes sense because tin is a metal that has been worked with for thousands of years with no reported problems in manufacturing.

If most systems really are compatible with the no-lead alloy, converting a leaded solder pot to a lead-free solder pot can be a simple process that can be performed in lieu of spending thousands of dollars on new, specially constructed soldering equipment. The risk vs. the reward is low. The conversion process is as follows:

• Procure 100 percent tin sufficient to fill the volume of the solder bath. The price of tin is just over $4/lb. The tin will be used to scavenge the tin-lead, and then sold as reclaim (current price $2.65/lb).

• Initial clean of solder system — Remove solder duct assembly and thoroughly clean to remove all solder remnants as possible; clean impeller; clean impeller shaft; empty solder reservoir and clean of all solder remnants; and reassemble components.

• Final clean — Repopulate solder system with 100 percent tin; heat solder to temperature (260°C); pump solder approximately 0.5 hours to put any remaining tin/lead into solution in the tin; remove the solder pump assembly; and remove the tin and take to scrap dealer.

• Populate the solder pot with lead-free solder alloy — Replace the solder pump assembly; heat solder to normal operating temperature; pump solder for approximately 0.5 hours, and then pull solder sample for testing to confirm lead contamination levels.