I remember: Or I think I do. Wake up prints or wake up strokes, some
suppliers' pastes do still need this. If yours does then you might need to
keep it awake up after periods of line inactivity during the day as well.
Assuming your paste is correct grade/OK try checking:
- the paste is fully to temperature before using it. Sometimes people don't
wait long enough for the paste to warm from the fridge or their printer
environment is too low. Some solder pastes rheology can be sensitive to
ambient temperature.
- Squeegee angle and material, a nice shiny [vertical] blade will encourage
the paste to slide off.
- If the squeegee has side fittings to control paste these will give an
anchor area for the paste.
- Do not over load the stencil so the paste bead rolls high on to the
squeegee assembly giving a large area of paste to grip the squeegee.
- Make sure the squeegee has a nice high and vertical step up at the end of
the print stroke and give it a delay before travelling back so the paste has
time and space to slide off.
Regards
Mike Fenner
Applications Engineer, European Operations
Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
E: [log in to unmask]
W: www.indium.com
Leadfree: www.Pb-Free.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Steve Gregory
Sent: Wednesday, March 19, 2003 1:18 AM
To: [log in to unmask]
Subject: Re: [TN] Squeegee blades for printers
Hi Rama,
I have a question to ask, do you see the paste sticking to the blades all
the time, or does it seem to happen at the beginning of a run?
The reason that I ask, is because I experienced this problem in the past
with a paste I was using from AMT. The paste needed to be "shear-thinned",
or worked, for it to perform it's best.
For example, we would see the same thing you see on the first print of a
run, or after lunch-break when the line sat idle for a while. The first
print, if the paste wasn't "worked", wouldn't show the roll of the bead of
paste in front of the squeegee that you normally want to see. When we asked
about this problem with AMT, they did say that the reaology does change when
the paste is more-or-less in constant motion, from what it is when sitting
still for a while.
If I remember correctly, some printers have a function in their programs
where you can set them to "work" the paste before the print stroke...for the
life of me, I can't remember exactly what they call that function...I must
be going senile...hehehe
Could it be that the same thing is happening with your new Kester paste?
-Steve Gregory-
For more than 4 years, we were using Alpha metals, no clean 63/37 paste.
Recently we tried the Kester paste on our DEK printers. The printing
performance is far better than the Alpha Paste. So, we switched to Kester
FL250D no clean paste (63/37, 90%, Mesh -325+500 , VISC 1400-1800 ).
But, we are having serious unexpected problem on MPM printers. The paste
does not drop from the blades after the print stroke causing big voids on
the boards. We are scrapping quite a few boards due the misprints.
Is there any solution for this problem ? Some one suggested 'TEFLON' coated
squeegee blades.
Sincerely,
Rama Vemulapalli
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