Solders and soldering: materials, design, production, and analysis ... - Google Books Result

Nice Link LynLynch.

I was going to suggest removing half the solder and adding tin plus new solder to replenish, but your link gives better advice.

Looking at this through the lens of "Lean" (or waste elimination) or "muda" I would ask why we have so much solder that the copper can accumulate, ie, why is there so long a dwell time of the solder in process?

milo

Thanks!

If the OP had Googled,"Soldering and Increased Copper Content", he would have found it.

We change solder in our fountain as the contaminants increase which is visibly evident on the PCBs. We will first start seeing them under a scope and reject them for rework. When they can be seen with the naked eye, we replace the solder.

Hello Hari,

Copper contamination at the levels that you describe will provide significant concern in relation to joint reliability as described in the link provided in post 1.

If you are "wavesoldering" then it would seem that there is excessive opportunity for copper to become dissolved into your parent solder. The linked document suggests use of solder resist to mask areas that are not to be soldered. HAL finish on the intended solder locations will also help to reduce the amount of copper dissolved into your tank as will revision of your conveyor speed to reduce the time that any component leads are exposed into the tank.

I presume that you are doing "dross removal" at least each 8 hours of machine operation. That's just good practice.

Reduce the opportunity for copper to get into the tank.

I saw one place where the lead trimmings (That's through hole component wires, not metalic Pb) were being returned to the tank. The copper wires inside what people thought was only solder caused a similar level of contamination to what you described.

Are your fixtures made of copper, or copper coated?

(And the obvious dumb question. Have you checked the purity of the solder bar before use? Once per year in our test samples returned for analysis we return a sample of melted bar.)