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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Solder Paste...

Steve Restinetti (aka Bix)


Solder Paste... | 17 October, 1999

Our SMT department uses Alpha Metals WS629 solder paste exclusively. Does anyone else use this paste and what do they think of it? I haven't evaluated other pastes yet and think that I'm sure there is something better out there. Feedback would be appreciated.

Thanks, Steve

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Re: Solder Paste... | 18 October, 1999


What do you mean by better? More/less activity? fewer retouches? longer shelf life at ambient temperature? less hygroscopicity? longer open time on the stencil? easier to wash? easier to treat waste water? easier for washing machine maintenance? better printing? less slump? more tackiness? longer time for component placement? perfect?

If you want them all, or just the last one, come down to earth, man :-) The choice of a paste, especially a water-soluble one, is very much a compromise and the best one is the one YOU can use best with the equipment, process times and so on YOU use.

That having been said, many use WS629, which is a reasonable compromise for them. Many also use Kester, Heraeus, Multicore and other makes, each after extensive trials and these are all reasonable compromises for them.

The only way for you to determine what is best for you is to conduct extensive trials and you can use your current paste as a base line. However, by 'extensive' I don't mean just using each of the others as a drop-in for the Alpha material, but to spend sufficient time to optimise the process parameters for each one (and they will all be very different from one another). Having done this, you can shortlist them down to two or three and run each of them for a full month under production conditions, doing a rigourous fault analysis, yield and costing studies before selecting one as standard and a second one as backup in case the factory of #1 burns down or there is another unforeseen supply stoppage.

You will possibly receive a number of replies to this thread saying "I use X paste and am very happy with it, it is the best". This does not mean it is the best: it may be the best for the way that the sender works, but it may be the worst for you. After all, does he use the same equipment as you, under the same conditions, with the same PCBs from the same maker, with identical finishes, pad sizes and spacings and the same components? (If he does, why have a second factory?!).


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Tim O'Neill


Re: Solder Paste... | 19 October, 1999

Hi Steve,

Brian's right. The best paste is the paste that works best for your application requirements. From equipment to environment to customer demands to the operators noses;all these variables will determine the best product for you. Brian's suggestion of REALLY running a product and optimizing for the manufactures recommendations, is the only true way of finding a good fit. Good Luck! Tim

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