sOLDER PASTE NOT COMING OFF SQUEEGEE

Paste sticking to squeegee:

* Squeegee is heavily magnetized

* Some pastes stick more than ...

* Plastic squeegees stick more than metal

* Old metal squeegees stick more than new

* Paste needs to be worked

* Paste needs to be at room temperature

* Some flux formulations are very sensitive to humidity

* Need enough paste for thumb sized roll. Too little and it won't fall off.

* Can't have too much paste just enough for a thumb sized roll. Too much and it won't fall off.

* Temperature in your screen printer needs to stable. Paste suppliers say that 1°C change can affect paste viscosity by about 10%.

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+paste was not stored properly Paste doesn't have enough flux and is more sticky than usual. Could be a lot code related or a purchase order related. I wold order a new jar and try immediately.

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This problem frequently becomes an issue with lead free solder paste, because it has very different rheology than leaded pastes. While not a 100% of the time, the squegees are very ofen the cause. When the regular blades are used (steel squegees), the aspect of the surface is very rough at the microscopic level, which is why the paste is sticking. I would recommend upgrading to very good quality squegees to be smoother, and the paste doesn't stick, now in ALLPCB, we didn't have this problem

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