In a message dated 3/22/99 11:35:58 AM Pacific Standard Time,
[log in to unmask] writes:
<< Anyways, this guide recommends that solder paste viscosity be between 1000
KCPS
+/- 10%. Does anyone know what this is? How would you go about testing to
verify this?
What test methods and equipment would you use to do this?>>
Hi Rob!
It's a measurement of viscosity in what's called centipoise. 1-Million
centipoise +/- 10% is a decent number...but I would say the plus or minus 10%
is pretty restrictive. I've printed with paste quite a bit outside those
ranges. The higher the number the thicker the paste by the way...
There's quite a number of instruments out there that you can use to check your
paste viscosity Malcom Instruments, and a company called Brooksfeild makes
them, but to tell ya' thruth, the last time I've measured any paste viscosity
is well over 2-3 years ago (at least)...for a few reasons.
1. Every paste I've bought from any vendor specifies a viscosity range of the
paste that they'll be shipping to me. If they can't give me paste that falls
into the range they say they're gonna ship me, and I have to check it when I
get it, then guess what? I'm gonna look for another vendor. Nowdays though, I
can safely say that practically EVERY vendor understands at least that much
about their paste and rarely, if ever, will you get paste that's out to lunch
viscosity-wise.
2. Kinda' the same thing as the last part above, when I WAS checking paste
viscosity before, it was just a exercise and a waste of paper, because I never
found anything outside of the ranges...I was always checking good paste.
3. If you ever SHOULD get paste that's a viscosity nightmare, you'll know it
as soon as you put it on the stencil...you won't need an instrument to tell
you that. The print quality will tell you that right away. Most paste vendors
won't have a problem (should you ever get a bad lot of paste), with exchanging
it for a new lot. Once in a rare blue moon, you could get a bad lot...not much
of a chance, but you could.
I guess measuring it when you get it could be something one could do if you're
REALLY, REALLY paranoid, but personally, I think it's a waste of time. Since
the rheology of solder paste is thixotropic (even I can use big words every
once in a while...hehehe), the viscosity that you measure at incoming
inspection, may not be anywhere close to what it's working viscosity is.
Thixotropic by the way, basically means that that'll measure one viscosity
while it's sitting still, but another after it moves and gets sheared a bit.
-Steve Gregory-
################################################################
TechNet E-Mail Forum 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's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################
|
