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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Solder Paste Wetting issue


Solder Paste Wetting issue | 24 May, 2004

Hi everyone,

I'm new to this Forum and still a young'n the electronics manufacturing industry so be gently on me :p

I'm currently trialing different solder pastes with our small 5 stage oven and I am having wetting issues with a particular paste. Could it be just a dodgy paste or is the problem most likely to be a process issue?

I've checked the reflow profile of the oven and it is within the recommended process window listed on the paste's datasheet. Can someone please explain to me what the possible causes are for poor wetting? I.e insufficent ramp-up/reflow time/temperature?

Any help would me much appreciated!

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Solder Paste Wetting issue | 24 May, 2004

Here's an interesting fact, some pastes just don't wet as well as others!.. there I've said it and now people will complain but that's life. Some pastes are formulated to run in air, some in N2, soem are specifically designed to be more aggressive for things like OSP and some lest so to let them meet things like bellcore and the like. 1st thing to do is look at the rating of your paste, not all RMA's / RA etc are the same to check the activity rating to make sure your comparing apples with apples. Then look at the profiles for yoru pastes, again they are all slightly different. The thing that set's the paste window (forget everything else for the moment) is the flux carrier, this will be designed to activate & burn off at set temperatures and will only last for a certain amount of time at given temperatures. If you expend the flux then the wettign is automatically worse as you start oxidising the joints. Also make sure yoru getting non wetting & not dewetting.

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