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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Control the solder paste

Wister

#7928

Control the solder paste | 10 January, 2000

Hi,how to control the solder paste,condition as belows? place at room temp.or put it into refrig.again if the unopened paste has been warmed up 8 hours but it would not been used at once in case of schedule changing.Assuming that this solder paste will be used after 16 hours. Rgs, Wister

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#7929

Re: Control the solder paste | 10 January, 2000

Don�t put it back when you can foresee the future need as mentioned. You would have to go through the warmup again.

What�s this storage in a fridge good for anyway ?

Wolfgang

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#7930

Re: Control the solder paste | 10 January, 2000

First, I agree with Wolfgang, in response to Wister.

Second, Wolfgang: Sometimes, our blanket purchase order for paste schedules delivery of the paste in advance of production requirements. (What!!!???? In-bound material schedules don't match out-bound ship plans????) We refrigerate this excess, redundant paste inventory at 40�F to double the shelf life, compared to room temperature storage.

Ta

Dave F

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#7931

Re: Control the solder paste | 11 January, 2000

Hi Dave, that was kind of a more rhetorical question. Normally paste is used before shelflife expires and delivery time is short enough to get in no trouble. The normal situation is that you try to get your equipment running means constant use of paste with predictable amount needed over certain period of time. That calls for special agreement with your supplier about the total amount used in one year and delivery at call and short notice.

What I didn�t expirience yet is how cool storage actually prolonges the shelflife. All I can think of is that it slows down the separation of solid and fluid contents. I thought it was something out of the old times and shelflife isn�t that critical today.

Although my hair starts looking whitish my heart is still full of colour

Wolfgang

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#7932

Re: Control the solder paste | 11 January, 2000

Wolfgang: Boy it's tough to convey context in this medium, isn't it?

Clipped from our paste storage work instruction, environmental effects on paste are:

1a Avoid excessive heat (over 80� F). It causes flux separation, reducing print quality. 1b Avoid freezing. It causes precipitation of paste activators, reducing wetting ability. 1c All pastes absorb moisture. Minimize this, because moisture in paste causes slump, solder balling, flux/solder splatter, and other defects.

Fundimentally you're correct ... use the paste before shelf life becomes an issue. While we do that, we feel that taking modest precautions to preserve the life of paste is win/win.

White hair eh? Mine's gone down the drain.

Dave F

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