Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Chris Chorley

#16830

Solder Paste | 23 January, 1998

What is the lifetime for a typical solder paste ? How long can boards be stacked waiting before the paste goes off ?

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Scott

#16832

Re: Solder Paste | 24 January, 1998

| What is the lifetime for a typical solder paste ? | How long can boards be stacked waiting before the paste goes off ? Lifetime and tack time depends on: - Manufacturer - Flux/mixture - Environmental conditions Typical lifetime is dependent on storage, check the date code on the container. A viscosity test will verify if it's still "good". Tack time, how long it can set before reflow, is typically around 4-6 hours though I've had some vendors claim as much as 24 hours (???).

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Steve Gregory

#16833

Re: Solder Paste | 28 January, 1998

| | What is the lifetime for a typical solder paste ? | | How long can boards be stacked waiting before the paste goes off ? | Lifetime and tack time depends on: | - Manufacturer | - Flux/mixture | - Environmental conditions | Typical lifetime is dependent on storage, check the | date code on the container. A viscosity test will | verify if it's still "good". | Tack time, how long it can set before reflow, is | typically around 4-6 hours though I've had some | vendors claim as much as 24 hours (???). I agree with the above three variables; Manufacturer, Flux Type, and Environmental conditions. From my experience, you need to get the components placed and the PCB reflowed within an hour or two using a water soluble paste otherwise you'll run into problems (I'm out here in "Silly-con Valley", so I'm not all that hot or dry out here). Now with a no-clean or RMA flux paste, I've hand placed prototype boards starting on one day, covered the boards and put them in the 'fridge at quitin' time, and then finished hand placing them the next day...believe it or not they reflowed fine!!

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Dave McFadyen

#16831

Re: Solder Paste | 20 February, 1998

Looks like (so far) we have a concensus. Follow the paste manufacturers guidelines on storage. Normally, refrigeration is required to achieve max shelf life between 3 and 6 months in original closed container. Water-wash pastes are much more active than noclean and RMA and also more hygroscopic. This decreases open time on the stencil and time between print and reflow because the moisture it sucks up causes steam-powered explosions in the oven accompanied by major solder-ball problems Hand assembly would be the only excuse for wanting to leave printed (populated??)boards around any longer than 1/2 a shift.

| What is the lifetime for a typical solder paste ? | How long can boards be stacked waiting before the paste goes off ?

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