Jason,
once you'll go over 24 gauge (25, 26) ; you'll need 400-500 mesh ;
we use indium nc-smq90 in 200 gms cartridges ; on 644 head ;
2x 200 on back (2x 50 on front) .
eventually (after a year we found the mesh price difference did justify the
yields ; about 1-2 blocked needles a week with nonstop three shifts) we
dropped the 325 all together ;
dispensing 400-500 only across all gauges .
The pressure running up to auger is 25 psi (on 200 cartridge); 10 (on 50
cartridge).
We run second year on it ; it's proven , no problems ; ask indium guys for
200gr ResMed's package and give it a shot (you need to make yourself custom
clamp ; to counter the G's generated)
And > Inge did cry about silver loaded polymer, not solder/flux paste: not
quite the same .
Scott,
never experienced the increased temps even after 8 hour literally non stop ;
on Gemini's validations all went in (paste, silver, glue, thermal transfer
compounds) ;
and the needle never touches the board (the foot does) .
Tim decided to stay incognito ; which is a pity ; not what the net is about
.
So finally , dear nett(?)er Inge :
When you look onto those suspended silver particles under your trusted scope
;
you find that those ain't particularly balls (camelot says for example the
inner needle dia should be minimum of 8x the ball [solder]size)
I particularly do not think you need a rocket; morphology; fluid dyno's;
rheologies and polishing compounds and tolerancing sciences to give you a
hint you're applying wrong needle gauge for the job . The auger's side walls
(twiddling in ceramic shaft I presume) are precision ground ; the inner of
needles is good enough .
By the sound of it you just started this applications ; therefore you have
in front of you a lot of trials and validations, and the simple men from
manufacturer (not paste supplier) would do you good as they did (should) a
lot of it .
Being simple man myself ; I'd (perhaps naively) presume to push down up to
50(!)um silver boulders through 100(!)um inner orifice may cause you a
mighty pain :
this being caused by sheer wishful thinking .
Familiar indeed
Anyhow, wish you luck ; keep in touch if you're still stuck ;
and let me know what you thought (don't hold back ; I can take it) about my
reflection on the thermal transfer = how did your bubbles go ???
Werner said he prefers steaks to snitzels ; and I have to admit I always saw
the breadcrumbs "extension" as poor culinary pretences .
Sorry Norman , done now
Paul Klasek
http://www.resmed.com
-----Original Message-----
From: jason gregory [mailto:[log in to unmask]]
Sent: Saturday, 14 August 1999 0:20
To: [log in to unmask]
Subject: Re: [TN] clogging dispensers
I had the same problem and addressed it on the smtnet.com site. I was using
a paste mesh that is suitable for screening, not dispensing (325/500 mesh).
I figured the only bad thing that would occur would be that the paste
wouldn't flow as easily through my nozzle. After purging the pump to remove
all air bubbles, the flow would stop and I would disassemble the pump and
find a hard, shiny chunk of solder at the end of the pump, before the
nozzle, impeding the flow, that appeared reflowed. My guess, coupled with
knowledgeable persons agreeing, was that the mesh indicates a larger ball
size and the "resistance" of the balls to flow through the nozzle was
causing great friction inside the pump, compounding the balls together and
possibly the constant friction was causing the backing-up solder to, in
essence, "flow". Check your paste mesh. BTW, I am using a Camalot 5000 with
an Archimedes-style pump. Hope some of this helps.
> -----Original Message-----
> From: [log in to unmask]
> [SMTP:[log in to unmask]]
> Sent: Friday, August 13, 1999 8:41 AM
> To: [log in to unmask]
> Subject: [TN] clogging dispensers
>
> Out of 1,700 netters, someone should have an idea about this:
>
> We need expertise advice immediately to solve a mystery with clogging
> high speed automatic dispensers. Three silver epoxy pastes give same
> clogging. Fresh pastes are bought. Same. Dispenser screws, tubes, pumps,
> all details are cleaned thoroughly. Same. New dispenser parts installed.
> Same. Whatever we do. Same. After running some minutes-hours: clogging
> in the needle. Some say that the room humidity must be very exact in
> order to make the dispenser epedize well. Others talk about local curing
> inside the paste. And some think sedimentation can be the plague.
> Experts from the paste manufacturer will be here in one or two days, but
> according to my experience, they seldom have that kind of knowhow,
> machine makers can have, this one not. Most oftenly, the knowhowers are
> people like you, dear nett(l)ers.
>
> I have my own theory, but can't prove it yet. Namely, that this
> "conglomerate" or mix of fluids and silver flaws (1-50um) can be
> PRESSURE DEPENDENT, i.e. at certain constant or momentary pressure,
> there will be a separation in the narrowest part, the needle, fluids
> will drop out and separate, leaving the coarser silver flaws without
> fluency, they will clog. Also, I have seen that the inside of the needle
> (inner dia 100um) is not polished, but has a rather grainy stucture,
> likwise the rotating helix that feeds paste. Both should be polished, I
> suppose. There is a science that use morphology and fluiding dynamics
> that possibly can give a clue, but I'm rather far from that art, maybe
> some of you have education of the sort.
>
> Familiar to someone?
>
> Remo@Alenia, if you read this, please contact me, I have lost your
> adress.
>
> Thanks in advance/
> Ingemar Hernefjord
> Ericsson Microwaves Systems
>
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