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
##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe: SUBSCRIBE TECHNET <your full name>
To unsubscribe: SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################
|
