Gosh ; thanks for putting my heart at peace Inge ;
for a moment a felt inferior .
Points:
1
the flakes are growing on you (from 50 max to 80 now!)
2
Agree, Able lab is great
3
This French Jos knows any better ?
Love to be enlightened (made in FRANCE specifics please), thanks
4
"Chris's mail" ; seems hands on :
a
apart from hands warming ; one wizard here chucked in 200gr syringe for a
"few" (in his estimate)seconds into a canteen's microwave, with so
frightening results he gained instant fame he never lives down .
If you think cow's make a mess you've seen notin' !
b
repacking from bottom up is bubblelessable , agree, not desirable.
c
would not agree Solder paste is harder to dispense than epoxy ;
see it the other way around . Details are mile long .
d
the top note :
auger (say Camanotsuchalot) is not as suitable for low pressure driven
viscosities as linear pump = piston displacement (say Asymtek or whatever
German or French).
I'm glad you brought the hidden sages from caves Inge :
this horses for courses is so much true .
On paste Camelot's auger is not beaten yet (waiting for Jos's specs) :
Gemini 1 rolls here 3 shits for 2 years now without missing a beat on FULL
board dispense (if only the xyflex development be faster and better i'd
never look at printers).
On low viscosity I would not contemplate anything other than linear pump
(does have few other problems, like top corners sediments)
5
the fact that 50-80 flakes won't go through 200 is indeed obvious .
I'd still prefer camelot's 8x yardstick , balls or flakes(worst) .
6
the in-between conus from auger chamber to needle chamber should not make
difference with correct (8+)ratio.
with (<4) ratio obviously the jam is inevitable , flakes won't make it
easier .
7
I would not believe the solvent method would wash out the truth :
it would/could dissolve even the flakes stack easily :
You can "glue" 2 sheets of paper with water to behave as one ;
to "dissolve" the stack with water again to "disprove" previous fact .
Needles insides > polishing to THAT degree STILL bugs you ?
8
Bright thought on the auger Inge,
yes, to make measured depositions (pressure just brings it to auger ; than
auger slices the "lots").
Not much chance of dispensing water with it (you do indeed need linear pump
for that) .
Quite right with extremely small dots on low viscosities you have it uphill
.
Quite wrong with air "pulse for a No. of reasons :
a
There is no pulse on 642 ; just constant pressure (quite a challenge when
pushing 200gr syringe of lead with 25 psi and coming to end > where you
obviously need much less pressure; luckily the "viscosity" of paste is
nothing flowing on 2psi)
ab
even the pulse systems (pushing silicon on other job) the air memory and
compressibility plays havoc with repeatability and time delays (drips);
totally another can of worms you don't want to know if you can help it .
9
Agree with camelot's "alertness" (to express it gently),the brain drain
after speedline merger did not help ;
apart from that I'd say there are still few wise man who DO know auger is
not the right application ;
but it's unlikely they'll tell you that , is it ?
On other hand if in your shoes i'd :
redesign ,
increase viscosity ,
(??????) ,
if you mail the task ; 'm pretty sure there's easier solution to it .
Perhaps not that obvious (trees&forest classic)
see yo' Inge paul
-----Original Message-----
From: [log in to unmask]
[mailto:[log in to unmask]]
Sent: Wednesday, 18 August 1999 18:08
To: [log in to unmask]
Subject: [TN] Clogging dispenser, cont'd
Good Day to all,
and also Paul: don't be sullen, I said 'Honeywell' not 'Honey'. So I
didn't button up someone, indeed they call themselves Honeywell, small,
little known company. End of joking.
I thank you Paul for your most superiour aid. Drs Dot will be taken
seriously. I also got following advice from another senior in the game:
- use a V-grove plate for size distribution test of silver flakes. He
said that flakes as large as 50-80um is not acceptable if the syringe is
only 200um on inside. Even as far as 6sigma, no large flakes are
allowed, they are a risk.
- today's syringe (Camelot) is a medecin needle, cut and pressed into a
machined steel part, that is mounted on the pump. The interface between
the cut needle and this steel part creates a mechanical step that can be
a silver particle trap, says same senior. He said that simple syringes
for hand dispensing are better, because they are polished on inside.
Anyone who knows?
- another guru advice was to wash out the silver paste particles in a
solvent, and take photos on the dry flakes. The dry geometric
configuration is important: too flat flakes will clogg easier between
the auger and the pumphouse wall, especially sensitive are silver flakes
because they are so soft. Such a work will get the paste maker to the
door in two minutes, he said.
- I also have a thought about the auger: what's the meaning with that
part? To make wanted portions (dots) of paste or to just keep the paste
in good condition? For making extremly small dots, diameter 300um, it
seems to me that the screw rotation is not in proportion to the
dispensed amount of paste. Isn't it in fact the air pulse that decides
the dot?
- Camelot are not very alert to assist and explain, says the machine
responsible at our plant, but Ablestik are rapid and helpful, blessed
they are.
We are now gathering these facts of process importance:
- flake size
- flake geometry
- viscosity
- friction caused temperature rise on tip
- friction caused wear of pumpwalls and screw
- paste humidity (humidity accelerated local curing)
- paste temperature
- screw material
- depth of threads
- pumphouse material
- pressure
- space between screw and house
- screw and house polishing conditions
- screw rotation speed
- tip contact with board (building up local heat)
- syringe inside surface
- syringe-to-interface mechanical steps (flake traps)
- paste sedimentation
- paste mixing conditions
- using of day-and-night paste syringe rollers?
- fluid separation due to locally clogged-together flakes
- dwell time (wetting)contact with the chip mounting pad
- shape of paste drop hanging on tip when lifted up.
- comppressed air content of oil and humidity.
- adiabatic compression of flakes
- search for best paste for this application (dot dia = 300um!)
Ablestik is said to be one of the best in the game. I myself am
curious about the japanese pastes.
- try the needle-dip-into-paste method instead of using a dispenser.
There are possibly a few more, but in the end I think all will be
reduced to, say 5, parameters of most importance.
Thanks all netters, especial attention to Paul Aussimeyer (did that
help?)He-he./
Ingemar Hernefjord
Ericsson Microwave Systems
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