Ingemar,
Just a thought that may be applicable. We have seen SMT epoxy dispensing
systems were the needle tips would get hot from repeated contact with the
board and from the constant flow of epoxy through them. The problems we
would see were excessive slumping of the epoxy due to a change in viscosity.
Perhaps yours are getting warm enough to partially cure the material?
Scott Severson
Benchmark Electronics Inc - Winona Division
-----Original Message-----
From: [log in to unmask]
[mailto:[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
##############################################################
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
##############################################################
##############################################################
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
##############################################################
|
