Hi Tana,
"Abandon time" is the same as the more common term "stencil life"
and is sometimes called "lunch time".
When I first got hired into this industry, since I knew nothing, I
figured a trip to the local library would do me good. After reading a half
a dozen books on the topic, I became very frustrated that none of the books
would give me specifics (typical stencil lives, reflow profiles, washer
nozzle pressures, etc.). They all said the process had to be "optimized".
So the answer to you question is "it depends".
It depends on the solder paste manufacture
It depends on the local relative humidity
It depends on the aperture opening sizes
The list continues
At one time we used a paste that had a stencil life of 10 minutes
when using 16mil fine pitch and the RH is 20%. We now use a paste that
performs great after sitting unused on the stencil for 2 hours; even on fine
pitch.
Sorry for the long answer, so to give you a generic short answer;
put the paste back into the jar if it will be unused for an hour or more on
non fine pitch. For fine pitch, the paste should be kneaded before printing
if the paste sits for 20 minutes or more.
For driving really low DPMO values for solder defects, many of us
like to get really anal and require kneading of the paste if it sits for
more than 6 minutes. (I can't wait to get in a rheometric head).
Kneading paste on very large boards must be done by printing a board
and then scraping and washing the paste off it.
> -----Original Message-----
> From: tn [SMTP:[log in to unmask]]
> Sent: Tuesday, January 04, 2000 4:00 AM
> To: [log in to unmask]
> Subject: [TN] Solder Paste "Abandon Time" and "Stencil Life"
>
> Dear TechNetters,
>
> Happy New Year to you all.
>
> I would like to know what "abandon time" is normally used in the
> industry with solder paste stencil printing [1, 2, 4, 8, 10, 14+
> Hours]. Your response will be highly appreciated.
>
> Regards
> Tana
> PS: I have heard of stencil life, are these synonymous?
> Dr. Tennyson Nguty, Electronics Manufacturing Research Group,
> AeroMech Department, Newton Building, Salford University
> Manchester M5 4WT, UK. Tel: 0161-295 5951/4696, Fax: 0161-295 5575/5108
> Email: [log in to unmask]
> >> If you want to make your dreams come true, wake up!
>
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