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March 26, 2014

Wave Solder Pot Alloy Adjustment Formula

Test reports indicate we have a tin level of 62.04% and a lead value of 37.96% in our 63/37 leaded wave solder pot. The solder pot capacity is 300KG.

How many KG of pure tin should we add to the wave solder pot to restore the alloy to 63/37?

Is there a formula to follow?


Experts Comments

The formula for adding pure tin to restore the alloy to 63/37 is:

W(Sn) = (0.63-0.624)*W(ap)/0.37

W(Sn): Weight of tin need to be added; W(ap): Weight of alloy in the pot.

 For example: If you have 280 kg alloy in the pot now, the pure tin added would be: W(Sn) =(0.63-0.624)*280/0.37 = 4.54 kg
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.
I'll assume that you have room in the pot to make a small addition without first removing some. We will be adding pure tin, so the total amount of lead in the pot will remain the same.

We know that after the addition, we want the percent lead to be 37.0%. So we can calculate directly the total mass of solder required to meet the goal: (37.96%/37.0%)*300kg = 307.7838kg

The difference between the starting mass (300kg) and ending mass (307.7838kg) is the required tin addition, in this case approx. 7.8kg.

It's normal for the percentage of tin to drop over time because tin will be lost at a higher rate in dross than lead. So we will occasionally have to add some pure tin. You can minimize corrections by adding some pure tin periodically.

Track how much pure tin you need to add in total over a long period (say, six months) to maintain the proper tin-lead ratio, then determine how much would need to be added per week. Institute a weekly addition of a little less than this amount, and track again. Optimize as necessary.
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.
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