|Ask the Experts
February 21, 2024 - Updated
February 8, 2023 - Originally Posted
Solder Paste Stencil Inactivity
How long can we leave solder paste on a stencil without any activity, wiping, etc.?
|Expert Panel Responses
This is highly dependent on both the paste in use and the environmental conditions in the factory (specifically the conditions in the printer itself). Additionally, your results may be affected by how difficult your printing challenges are (are you trying to print very small apertures, for instance?). For easier printing jobs, you may find that much longer idle times are workable, however for very challenging jobs with narrow process windows, much shorter idle times may still be problematic.
You should consult with the paste manufacturer to see what their recommendation is given the specifics of your paste, process and environment.
Solder paste can be left undisturbed on the stencil for 1-4 hours and remain printable. The actual length of time depends upon the solder paste and environmental conditions. It is best practice to knead or mix the solder paste before printing, after pauses of that length. It is best to contact your solder paste supplier for specific recommendations.
The time solder paste can be left on a stencil without printing or wetting it depends on many different factors like solder paste formulation (flux system e.g. water-soluble, resin, epoxy, halogen/halide content…), solder powder size, temperature and humidity conditions. Manufacturers typically indicate abandon time frame within the product datasheet (typically 1 to 4 hours).
Product Manager Soldering
The safe duration of leaving solder paste on a stencil without wiping or cleaning can vary depending on the type of paste, the storage temperature, and the level of exposure to air and moisture.
Typically, it is safe to leave solder paste on a stencil for a few hours without wiping or cleaning. However, as the duration increases, the risk of clogging also increases. In general, it is recommended to wipe or clean the stencil after each use to minimize the risk of clogging and ensure optimal paste transfer performance.
In some cases, the manufacturer of the solder paste may provide recommendations on the safe duration for leaving the paste on the stencil without wiping or cleaning. In such cases, it is advisable to follow the manufacturer's recommendations to ensure optimal performance and minimize the risk of clogging.
The amount of time solder paste can remain on a stencil without activity is going to depend on the formulation of the solder paste. It would be best to check with the solder paste manufacturer. If you are using an automated screen printer, some of these machines have a knead feature allowing you to get the paste back into a workable viscosity before printing.
Manufacturing Applications Specialist
I never let the solder stay idle for more than 4 hours. Some paste solders can remain on the stencil longer than others. For example, no-clean solder can stay on the stencil longer than water-soluble because of the flux properties. Always follow manufacturer’s recommendation.
Senior Manufacturing Engineer
4 hours is a timeframe heavily brought up in this topic. But it will not be the rule as different parameters can influence the paste quality - the flux composition, temperature and humidity conditions, the quantity of paste on the stencil. If you know that the process will be idle for a while, the right thing to do is to not leave the paste on.
Engineering and Operations Management
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