Ask the Experts
April 23, 2019
Selective Solder System Purchased At Auction
My company purchased a used selective solder machine at an auction. At the time we were not sure what kind of solder was previously used in this system. We had the solder analyzed and it was leaded solder instead of our required lead-free solder. What options do we have since leaded solder cannot be used in any of our processes?
Expert Panel Responses
The solder pots for these systems are manufactured to the alloy they are going to use. The reason being is the lead-free runs at a higher temperature and the pots have a special coating to protect them from the added heat and alloy composition.
The best and possibly only option for you is to replace the pot with a lead-free compatible pot as well as all associated tooling and nozzles that are exposed to the solder. Best of luck.
Manufacturing Applications Specialist
Mr. Bush has 20 years experience in electronics contract manufacturing. Major areas of expertise include through hole, SMT, wave and selective soldering.
Really the best solution is to replace the pot. A pot designed for SnPb solder may not be appropriate for Pb-free solder in any case; the materials may be susceptible to erosion by the solder.
You want to be sure that all the materials that contact the solder are compatible with Pb-free solder. By replacing anything that contacts the solder, you are also ensuring that Pb contamination risk is minimized. Also, be sure to clean the wire feed path and make sure the solder wire is replaced with the proper alloy.
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.
Drain or ladle as much of the tin lead solder as you can from the machine. Fill it with chunks or bars of pure tin solder, and run the machine for a short period. Drain or ladle out the pure tin, and keep it separate from the tin lead (small metal pails are good place to store the molten metal while it cools. Add the required lead free alloy.
The solder supplier should be willing to purchase the tin lead and pure tin scrap, and run an analysis of the lead free alloy to confirm your lead level is below 1,000 ppm, and in compliance with ROHS.
Global Director of Customer Technical Support
Alpha Assembly Solutions
As the Global Director of Customer Technical Service (CTS) for Alpha, Mitch sets direction and provides coordination for the Alpha CTS group in a global capacity. A major focus of this position is to provide strategic support to OEM, CEM and Automotive customers and target accounts. Mitch joined Alpha in 1998 and has progressed through positions of increasing responsibilities in Marketing, Product Management and R&D. He is a graduate of Purdue University with a degree in Chemistry and holds an MBA from Temple University.
The standard practice would be to flush pure Sn through the system until the Pb drops below an acceptable limit. Several flushes with fresh Sn each time may be required to do this.
Technical Support Engineer
Kay Parker is a Technical Support Engineer based at Indium Corporation's headquarters in Clinton, N.Y. In this role she provides guidance and recommendations to customers related to process steps, equipment, techniques, and materials. She is also responsible for servicing the company's existing accounts and retaining new business.
The best way is to replace the solder pot altogether, along with all the nozzles/tips that will have been "contaminated" with Lead and any other parts on the machine that could possibly cross contaminate. It may be possible or some companies may offer a way to "re-tin" those items with Lead-Free solder, but I'd never take that risk.
Esterline Interface Technologies
Mr. Hughes has been in the electronics manufacturing field for 20 years. Operating the processes and as a manufacturing engineer for the last 14 years. He is also a CIT as well as an SMTA Certified Process Engineer.
This is a relatively easy fix as selective pots are usually 100 pounds or less. Simply fill the pot with the lead-free alloy you'll be using, dump the pot and refill. Any residual lead will be dissolved into the first fill and the second fill will be compliant. The dumped material can be sold back to you solder vendor with your usual dross.
If your solder pot is large, some solder suppliers offer a 'tin purge' program where lead-free alloy can be 'rented' and returned to perform the purge, but for smaller pots the economics of moving material around doesn't make sense. I would also recommend performing a solder analysis on the pot as evidence that you are within specification. One last note - there is lead present in lead-free solders - so don't expect 0.00% lead after performing these steps, 0.08 - 0.05% are typical.
Technical Marketing Manager
Tim O'Neill is the Technical Marketing Manager for AIM Products. AIM is a global supplier of materials for the PCB assembly industry including solders, fluxes and thermal management materials. Tim has a B.A. from Assumption College and post-graduate studies in education. He has 20 years of experience in the electronics soldering industry, beginning his career in 1994 with EFD and was key in business development of their fine pitch solder paste dispensing technology. Tim joined AIM in 1997 and has since assisted many clients with assembly challenges, specializing in Pb-Free process development and material selection.
You have two basic choices:
- Purchase a replacement solder pot and parts from the OEM.
- You could drain the solder from the existing pot and have the pot anodized. When lead-free first happened, there was a number of companies that were advertising this service.
Supply Chain Engineer
Mr. Dickerson is an engineer with 20 years of manufacturing experience. He has worked supporting SMT, THT, cable assembly, and box build processes. He is a Certified SMT Process Engineer.
You have a few options, but first you might want to check if the machine is compatible to run lead free with supplier. Sometimes the older style pots can be slowly dissolved by lead free but should be ok.
To clean the pot it is normally recommended to drain completely then remove and brush clean all pumps impellors and formers. This should then be followed by a tin wash to remove any Pb, then repeat above. However the pots in selective machines can be cramped and difficult to clean in all the corners. In this case you could use old Pb free alloy from other wave solder pots to wash the pot out as this could be a cheaper option. Then test these alloy washes to see if Pb level is low enough before filling with fresh alloy.
Global Product Champion
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 best option is to drain the leaded solder, clean out the machine and then perform a tin wash. Many solder suppliers can supply pure tin bar. Fill the pot with pure tin and then run it for 4-8 hours recirculating the molten tin through the soldering nozzle. Drain the tin and clean out the machine. Then it can be filled with lead free solder and should be ready to use.
Tony has worked in the electronics industry since 1994. He worked as a process engineer at a circuit board manufacturer for 5 years. Since 1999, Tony has worked for FCT Companies as a laboratory manager, facility manager, and most recently a field application engineer. He has extensive experience doing research and development, quality control, and technical service with products used to manufacture and assemble printed circuit boards. He holds B.S. and M.B.S. degrees in Chemistry.
There are two options. One is to purge the system by removing all solder old from the pot(s). The other is to buy new solder pots.
Senior Manufacturing Engineer
Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.
Obviously you have to throw away your leaded solder since you cannot use it for lead free. But also make sure the solder pot is compatible with lead free solder to avoid corrosion of solder pot. Leaded solder pots are not suitable for lead free use.
Ray Prasad Consultancy Group
Ray Prasad is the founder of Ray Prasad Consultancy Group which provides teaching, consulting and technical expert services in tin-lead and lead free technologies using SMT, BGA, BTC, fine pitch and through hole components. Mr. Prasad is a long time member of IPC, and is currently the chairman of BGA committee IPC-7095 "Design and Assembly Process Implementation for BGA" and Co-Chairman of recently created IPC-7093 "Design and Assembly Process Implementation for Bottom Terminations" surface mount Components (BTCs) such as QFN, DFN and MLF.
Very good question and you have two choices.
Hope this helps - been there and done both methods.
- Buy a second pot for your machine and make it the Lead free pot for your selective solder machine. This choice is if you perform both leaded and lead free soldering which your question implies you only do lead free soldering. I know of two companies that perform lead free selective soldering and they bought new pots to make sure they started with virgin pots because they wanted no chance of having issues with their products shipping into the EU and they did not want to clean out the pot as described in item
- This is probably the most economical approach which is still not cheap, which is to remove the leaded solder from the pot and then reload with lead free solder bars and remelt and then remove the lead free solder which will also remove the lead solder remnants that were not removed when you initially removed the leaded solder from the pot. We had to do that reload and remelt and remove twice with lead free solder to insure that we got the lead to an untraceable level in our lead free solder alloy sample analysis. Again it is not cheap but it does remove the lead and it prevents you from buying a new pot. Depending on pot size this is not an inexpensive proposition but if you only run lead free and never a leaded solder then it is the best method, if you ever need to run leaded solder then buying the new pot is your best course and safest bet from a liability standpoint.
VP Engineering Services
STI Electronics Inc.
Mark T. McMeen is STI Electronics Inc.ʼs Vice President of Engineering Services. He oversees the daily operations of the Engineering Services division of STI. He has over 18 years experience in the manufacturing and engineering of PCBs.
Replace the pot - all the manufacturers have different solder pots for lead free and leaded solder as the lead free runs at higher temperatures than leaded so the solder pot structure is different To avoid any cross contamination a good machine clean-up, anew solder pot and a full set of tools and nozzles is highly recommended.
Engineering and Operations Management
Georgian Simion is an independent consultant with 20+ years in electronics manufacturing engineering and operations.
Contact me at firstname.lastname@example.org.
Depending on the manufacturer of the selective system you have bought you may be able to reuse the solder bath. Some manufacturers produce solder baths that are both lead and lead-free compatible.
Simon Smith, Pillarhouse International Ltd.
If you want to change solder types the previous methods of cleaning and refreshing the solder are the way to go.