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From [log in to unmask] Fri Nov 1 16: |
50:19 1996 |
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A few years back (Long, long ago.....) No, just kidding!
I've built initial prototypes out of DFSM as high as .004" thick
(DryFilm that is). The goal was to have solder paste thickness'
to yield a higher volume of reflowed solder. Two problems came
up.
1: DFSM is not gaining a lot of popularity lately.
Due to many issues. The majority of the parts I see
are moving towards LPI. DFSM conforms with the shape
of the outerlayer circuitry. This can greatly
contribute to gasketing issues during solder
paste application. LPI provides higher
productivity therefore it is more economical.
Some (past) DryFilms are no longer available.
2: LPI provides better image resolution. Finer features
are capable. This is associated with the thickness.
Most assemblers are controlling that solder paste
thickness by stencil thickness. LPI provides a more
planar surface for paste application. (Its' applied
fully wet as opposed to a (dry) film.)
My thoughts anyways......
I'm sure others will join in to.
Groovy
______________________________ Reply Separator _________________________________
Subject: ASSY: Solder Paste Volume
Author: [log in to unmask] at SMTPLINK-HADCO
Date: 10/30/96 10:31 AM
Address,
Is anyone applying solderpaste to PCBAs with an aperture to stencil
ratio of 1.33? I have some .012 pitch QFPs with random opens. The
problem is either related to the device handling (bent leads that are
not visual or automatically inspected prior to assy) in the wafer
prior to pick and place or the soldepaste volume on the land. Past
rules have been to have a ratio of 1.6 or greater, does this still
apply? Has anyone used Dryfilm S/M versus LPI to increase solderpaste
volume on the lands?
Please advise.
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