Ask the Experts
June 19, 2020 - Updated
October 16, 2011 - Originally Posted

Wave Solder Pot Contaminated with Lead

Our wave solder pot contains lead free solder. Analysis indicates it contains 0.12% lead. The maximum allowed is 0.10% lead.

Is there anything we can do to promptly bring the lead concentration into compliance?

E. C.

Expert Panel Responses

If you add fresh Pb free alloy of the correct amount to reduce the % of Pb to below the 0.1% this should be enough. How ever this would involve probably taking out some of the alloy already in the pot and adding fresh material.

In theory this could become a large volume, for instance if you wanted to reduce the Pb contamination to below 0.1% to give yourself a fair degree of confidence to say 0.06% you might want to remove 50% of the contents of the pot and add fresh alloy.

I suppose the big question would be where did the contamination come from in the first place. If you know and can be sure it will never happen then it is a one of cost and you can live with it.

If you are not sure then this could be a process you may have to repeat a number of times and this could become a costly procedure. Sources of contamination now tend to be counterfeit components or a genuine mistake in a factory where you are running both process.

If you are running both process try to put a line down your stores and keep PB materials on one side and Pb free on the other (can just be tapes on shelves or on the floor) anything to try to stop it from happening again.

Richard Boyle
Global Product Champion
Henkel Electronics
Richard Boyle is a Global Product Champion at Henkel Electronics. He has over 25 years experience in the electronics assembly industry and is responsible for the global technical service of all of Henkel's solder materials.

The only way to lower the amount of lead contamination is to dump at least a portion of the pot and replace it with fresh, uncontaminated lead-free solder. Since you are only slightly over the 0.10% limit, you should be able to get by with replacing about 1/3 to 1/2 of the pot with fresh solder.

The exact amount that should be replaced is dependent on the purity level (or lead contaminant level) of the fresh solder that will be used for replacement. If your fresh bar solder source has, for example, a lead amount of 0.04%, a 1/2 pot dump would only lower your contamination level from 0.12% to 0.08%.

Check with the Certificate of Analysis from your bar solder supplier and then work through the math to see just how much of the existing contaminated solder pot will need to be scrapped.

This will help you avoid the cost of a complete pot replacement.

Brian Smith
General Manager - Electronic Assembly Americas
DEK International
Mr. Smith has been supporting customers in the electronics assembly industry since 1994. His expertise is focused on solder paste printing and reducing soldering defects. He holds a BS in Chemical Engineering and an MBA in Marketing. He has authored several papers in trade magazines and at industry conferences. He is an SMTA Certified Process Engineer.

Yes. You can dilute your pot to get to the right level. For instance if your pot size is 1,000 Lbs. with a reading of .12% and you add back new material at a value of .02% then for you to get to .1% you will need to decant off based on the following formula:

Decant amount
(New Lead Content %/100)(X) + (.12/100)(Pot volume - X) = .10% of Lead content

.02X/100 + .12(1,000)/100 - .12X/100 = 1,000(.1)/100
-10X/100 + 1.2 = 1 or -.10X/100 = -.2 or .10X = 20 or X = 200 Lbs.

So in this case you would need to decant off 200 Lbs and add back fresh solder. The equation is simple of course if there is no lead in the material you are purchasing but typically most mfg's will have a small amount of lead.

Mike Scimeca
FCT Assembly
Mike Scimeca created FCT Assembly after the purchase of Fine Line Stencil, Inc., and consists of two major operations: stencil manufacturing and the manufacturing of electronic assembly products such as solder paste, flux and solder bar.

My first question: How did the lead get into the solder pot?

I'm not sure there is an easy way to correct this condition. Changing the physical solder pot is the first choice, I don't mean changing the solder, I mean physically changing the solder pot and charging it with new virgin grade lead free solder.

My second choice would be to find out how much solder is in the pot, by weight. Then figuring out how much of the existing pot has to be drained out so when it is replenished with new material it has knocked down the percentage of lead to within the limits of the regulations. Your solder manufacturer should be able to supply you with this calculation.

The third method is to drain the pot completely, flush it out with a high temperature oil, to clean out all the solder which would be attached to the inside of the pot and recharge with new lead-free material.

Cross contamination of the materials is an expensive adventure and needs to be monitored very closely to prevent it from happening.

Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

I do not know of any simple lead scavengers that you could put in the pot to lock up the lead in-situ which leaves the only options of dilution which is relatively inefficient (depending on the level of lead in your dilutant alloy you may need to replace half the pot) or replacement.

The key to the future is to determine where the lead is coming from and stop it at he source other wise any measure will be only temporary.

Neil Poole
Senior Applications Chemist
Henkel Electronics
Dr. Poole is a Senior Applications Chemist in Henkel Technologies, electronics assembly materials application engineering group. He is responsible for all of Henkel's assembly products including soldering products, underfills, PCB protection materials, and thermally conductive adhesives.

The most efficient method to bring the solder pot back into tolerance would be to decant about 50% of the pot and replace it with lead free solder. This should work for a period of time until the lead level grows again.

Kevin Beattie
Quality Manager
Sunstone Circuits
Kevin is part of the Sunstone Management team. In his role as Quality Assurance Manager, Beattieā€™s 25+ year background in Printed Circuit Board manufacturing is a tremendous asset to the Sunstone team. In addition, he brings valuable experience from his previous roles in the following areas: process engineering, new process introductions, support of nearly every manufacturing process, and extensive knowledge of Continuous Improvement, ISO, IPC, and various other industry requirements.

Unfortunately the only thing you can do is bail out an amount of solder to bring you back under 0.1 and then refill with new.

Greg York
Technical Sales Manager
BLT Circuit Services Ltd
Greg York has over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.

Easy, just remove about 1/3rd of your solder and replace it with pure lead free solder.

Daniel (Baer) Feinberg
President and Founder
Fein-Line Associates
Mr. Feinberg is a 52 year industry veteran and President and founder of Fein-Line Assoc, a consulting group serving the Global Interconnect and EMS industries.

The easiest would be to add new pure solder to the bath. This will reduce the percentage of lead contamination.

Edward Zamborsky
Regional Sales Manager
OK International Inc.
Ed Zamborsky is a Regional Sales & Technical Support Manager for Thermaltronics, located in New York. His position requires frequent customer visits throughout North America and the Caribbean and his position encompasses not only sales but the role of trainer and master applications engineer for all of Thermaltronics products. His expertise includes such specialties as hand soldering, convection and conduction reflow techniques, array rework, fluid dispensing equipment, and fume extraction. Ed has authored many articles and has presented many papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead-Free Hand Soldering, High Thermal Demand Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.

You have all of the answers you need as to howto dilute the pot with fresh lead-free solder (and isn't it amazing how many engineers don't have any math skills?), but before you jump in and do that, run a solder analysis on your lead-free bar supply already in stock. It could very well be that your bar solder (as purchased) does not meet the specification limit for lead, or is so close to the limit that any lead leached from the component leads during the soldering process is enough to bring you over the limit. Consider the following possible sources:
  1. Your own in-house component tinning process. Many companies have gone lead-free, but forgot their own in-house tinning process was still using 63-37 solder.
  2. 63/37 solder being used to pre-solder certain components to hold them down, or being used in electronic subassemblies that are soldered to the assembly later.
  3. Component finishes that do not meet the component print, or may not even be specified on the component print.
  4. Component terminations that contain lead as part of the basis metal (not the finish). Some component vendors are savvy to the fact that the basis metal may contain lead, and attempt to plate a nickel barrier over the basis metal. This is usually not very effective, but will pass XRf.
  5. PWB finishes that contain lead (contaminated plating process from the fabricator).
If you do not have XRf, I would encourage you to purchase or lease a smaller handheld unit. You can use it to test the percentage of lead (as well as other alloys) in both the component terminations as received, as well as the PWB finishes. It can save you a lot of headaches down the road in terms of non-compliant product.

Do not assume your SMT component terminations are not the source, as many of the topside SMT components may be soldered to vias or are connected by short traces to through-holes, and during wave solder the topside SMT joints will go into at least a partial reflow also. Of course, the bottom side SMT component terminations must be considered whether or not they are masked by the wave solder fixture for the same reasons.

Richard D. Stadem
Advanced Engineer/Scientist
General Dynamics
Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics.

First, I completely agree that you need to address the root causes of the Pb contamination to avoid a recurrence. As far as getting your pot back in spec, if you need to do this immediately then replacing at least a part of the pot volume is the way to go. If you have capacity and can take the machine offline for a period of time, there may be another path.

It's not widely known, but Pb will stratify at the bottom of a pot that is held near the melting point and left undisturbed. What you would do is to turn down the temperature to the minimum set-point that does not produce solidification, then let the machine sit for 48 hours or more. Now, without stirring the pot at all, carefully decant perhaps 2.5% to 5% of the pot volume from the lowest point. Typically, this can be done through the drain provided by the manufacturer.

It should be done as slowly as possible. Now re-fill the decanted volume, and re-analyze the pot. The decanted volume will be much higher in Pb content, and can be sent for reclaim.

Fritz Byle
Process Engineer
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.

Reader Comment
I agree that find the root causes of the Pb contamination is the first action. I do not know what your lead-free alloy solution is, but maybe you should check also if concentration of copper andiron are above of 0.30% and 0.020%, respectively. In past I was working as consultant and I was presented to a contamination case.

In the first approach the customer told me that the issue was only about 0.50% of lead concentration.When I got access to the machine and the chemical analysis reports and I could see that copper and iron limits were also above the limits. For the iron contamination a quick examination show some machine parts were eroded...

Some parts were changed, others not, remained in the state. They don't tell me but the machine was retrofitted (a bad one) from SnPb to lead-free. For the copper, I could see that machine was dedicated to run OSP mother boards (thousands and thousands boards per week) and they never had controlled copper concentration in the bath. Also they didn't want fully replace solder in the pot. So, I did the calculations and I recommended they should remove 80% of soldering in the pot (about 560kg) putting melted solder into minor molds with capacity of 20kg each.

After solder cooling, each mold produced a contaminated solder bar with 20kg each. So, I asked to complete the machine solder pot with new solder (SN100 alloy), since I could not use SAC305 due to copper be above the limits.When the machine was completed with melted solder (about 700kg) they sent samples to external chemical analysis in the solder supplier lab. After the analytical results, all the concentrations were within the limits again (as expected) and the machine was released to restart production.

No major changes in the yields or line quality indicators were observed in during the week I was there. The contaminated solder bar were used following the rule: for each 100kg of new SAC305 solder bar disposed into the pot a 20kg contaminated solder bar could be used to feed the solder pot. As well, the chemical analysis frequency changed from once per month to once per week (the solder bar supplier did this without cost!).

Also we created a SPC for the chemical elements inside the machine to make easier take decision to abandon use of contaminated solder bar in the pot (if necessary). For my happiness they used all the contaminated solder (split in 20kg minor bars) without cause a new contamination of solder pot. In terms of root cause, I gave them some directions, but I did not take part of the investigation team.
Glayson Figueiredo, Philips Medical Systems, Brazil

Reader Comment
And the best answer goes to Richard Stadem from General Dynamics. He mentioned the Pb will stratify at the bottom of a still pot held at a minimal temperature, the material with the lead concentrate will be more liquid and heavier, so use the bottom port to decant with still solder.

This would best be done after a minimal soak temp over a 12 hour period to obtain the concentration of lead at the lowest possible layer of stratification in the pot.
Bruce Webster, Iridium Communications, USA

Decant about 40-50% of the pot and replace it with the same lead free solder bars. The solder decanted out from the pot can be saved and gradually add it back to the pot with the fresh solder in 1:1 ratio.

David Bao
Director New Product Development
Metallic Resources, Inc
David Bao has more than fifteen years of experience in developing new solder paste, wave soldering fluxes and other SMT consumables. He currently serves as the Director of New Product Development at Metallic Resources Inc. He received a Ph.D. in Chemistry at Oklahoma State University.
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