solder paste stencil life
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Normally paste manufacturer specifies stencil life of a paste is 10 hours. the question is, if i run a continuous manufacturing for 40 hours, we will be adding 250 g of paste for every two hours. The addition of 250 g will be mixed with the paste which is already available on the stencil. After first 10 hours of manufacturing, do we need to remove all the paste in the stencil and scrap it?, currently the practice is we keep on adding till the end of production. since this goes by addition mechanism, there may be molecules of paste which has applied 12 hours before. any thoughts in this?
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Only thing I will be wary about is the stagnant paste at ends of squeeegee blades.
Recomemnded precaution is to scoop off paste at ends & discard it everytime fresh paste is added to stencil.
If you are using enlcosed paste container -proflow, paste puck or equivalent. Most paste is unexposed except for leakage on two sides (at ends of blades) which will become dry after certain time. Since this paste is outside work area, it is not going to affect print quality after extended hours.
I am assuming that you are currently using Squeegee blades. There will be stagnant paste at two ends of squeegee blades. As long that paste is not brought back into work area, I do not see issue of dry paste getting into work area. Recharging every 2 hrs and 5 times in 10 hrs is likely to keep the paste refreshed.
Ashok Dhawan