Yeah, it blows, but basically we toss it when it quits printing. We've never seen any visible quality issues we could attribute to recycling paste like this so we keep doing it. When we start doing BGA and X-raying stuff we'll take a closer look at what effects we might be missing. I hate it but you do what you can with limited resources.
At my last job paste handling was tightly controlled...here, we use up what we're able to.
We don't buy jars, just the 600ml cartridges. At the end of the day we transfer what's left on the stencil to a jar (IF that paste came out of a tube) and cram the plug down on it to slow down the inevitable. If the paste on the stencil had been dispensed from a jar, we toss it. The cartridge goes into the fridge and gets used up first when we run again, then we dip into the jar to see how it prints. If it won't, we toss it.
Anything from 25 mil pitch or tighter gets fresh paste from a new tube.
Fortunately we don't have to worry about going past expiration dates because we only buy a box at a time and use it up well within the specs.
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