|Ask the Experts|
November 23, 2020
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
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.
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.
Director of Reclaim Business
Alpha Assembly Solutions
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
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
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
You have two basic choices:
Supply Chain 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
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.
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
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
Very good question and you have two choices.
VP Engineering Services
STI Electronics Inc.
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
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.
I would first contact the company that manufactured the selective soldering system and supply them with the machine serial number. They will be able to let you know if the solder pot is lead free compatible. Check for any corrosion and pitting? If the solder pot is not lead free compatible you will need to purchase a new solder pot.Gus Mavrou, SEHO North America
If the solder pot is lead free compatible then you can remove the leaded solder, and clean the pot with new tin. Have the tin used for cleaning the solder pot analyzed for lead. Then you should be able to load with your choice of lead free solder. Have your new lead free alloy analyzed.
The selective nozzles and solder pot tools supplied with the selective system cannot be used for lead free. You will have to purchase new selective nozzles and tools.
If the selective system has an automatic wire solder feeder you will also need to purchase wire solder for replenishing the lead free solder in the solder pot.
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