I need to reduce costs on solder paste wasted

What is causing you to throw it away ?

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All I can tell you about what people do with solder paste at the end of the day or for the weekend is.

What the manufacturer recommends. What people say in public? What companies actually do as far as reusing it?

I am not passing judgment on 1 or 3 it depends on a lot of things and the type of products you are running. If you are making Blinking LED novelty buttons reusing paste, maybe no big deal. Making aircraft electronics, maybe a big deal. Most companies I have seen are all over the place on their reuse policy’s if they even have one.

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Could this be an opportunity to explore the use of cartridge-type paste dispensers? Or maybe a reason to keep working over the weekend.

* Re-Storing & Re-Using “Used” Solder Paste. Though not a recommended practice, used solder paste from the stencil may be stored in a container for re-use. This used paste should be applied back onto the stencil along with an equal amount of fresh paste in order to revitalize the older material. The ratio of fresh-housed solder paste will vary in order to achieve a good printing consistency. It is recommended that small amounts of used paste be added to the stencil throughout the shift or entire day to minimize any degradation it may cause, and to ensure that all used paste is consumed prior to cleaning the stencil off for the last time at the close of shift or day. It should be noted, however, that many companies choose to discard used paste in order to avoid potential problems; remember, discarding old paste is much less expensive that unnecessary rework or a field failure. Do not store used and unused paste in the same container. This can add moisture and/or other contaminants to the new paste resulting in degraded performance. [AIM Tech-Sheet] * Paste removed from the stencil for future use should be placed into a separate jar reserved for used paste. [Indium Procedures for Handling Solder Paste, Form No. 98039 R3] * This is not normally recommended, because it typically generates more problems than it is worth. If you do decide to reuse solder paste, these pointers may be helpful. First, Qualitek recommends putting any used solder paste in an empty jar, so any fresh paste will not become contaminated. This paste should be tightly sealed and refrigerated. Then, the paste may be reused at a later date, provided that the paste has not separated or thickened significantly compared to its original properties. If you have success in printing the reused paste, the paste is acceptable for use. If significant printing problems occur, discard the paste. You also may want to mix 50% “used” and 50% new to get maximum utility of the paste. This will keep the paste relatively fresh while consuming the used paste. [Qualitek Specifications, Technical Data Sheet Sn/Ag/Cu. 888 Rev.C] *   * Using time-expired solder paste [University of Bolton] The problems in using time-expired solder paste arise from the possibility that: ** Paste rheology may no longer be correct ** Flux activity may have reduced because of oxidation and the loss of solvents ** Flux residues may have become less easy to clean ** Solvent loss may have lowered the tack force and tack time of the paste ** Solder particles may have oxidised

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Seika make a solder paste recycling unit that will melt solder paste and separate the solder from the flux. You end-up with liquid flux in a jar and a block of solid solder, which you could re-use in a solder wave if the type is the same.

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