Joe: We have used a similar approach with good success on a lot of our
product requiring supplemental solderpaste.
To answer your questions:
We use a GPD with an auger positive displacement valve.
Z axis is easily controlled thru the program settings and height sense
control to produce a clean deposit separation.
Normally 20-24 gauge needles are used.
We do not dispense on existing paste.
Dots are the most common feature, these can varying quite a bit in deposit
size depending on the application. We also do some arcs and circles for
certain component types.
The most critical aspect is the solderpaste itself. It must be formulated
for dispensing using the correct flux to metal loading relationship. The
dispensable paste is prepackaged in syringes from the manufacturer, 10 or
30cc are the most common size. We use a type III powder, however you may be
able to get by with a type II. The filling of the syringes is also critical
you don't want voids, air pockets, flux separation, etc. Make sure whoever
your are working with as a supplier on this has their act together on
dispensable paste or it will be a processing headache.
Regards
Michael Barmuta
Staff Engineer
Fluke Corp.
Everett WA
425-446-6076
-----Original Message-----
From: Kane, Joseph [mailto:[log in to unmask]]
Sent: Thursday, June 26, 2003 7:25 AM
To: [log in to unmask]
Subject: [TN] Solder Paste Dispensing
We're looking at dispensing solder paste from an automated system
(we have Asymtek and Camalot). Intent is to get some extra bulk into
solder joints on larger chip components to extend the life. Parts are
about size 1005 and up, paste is RMA. The operation is low volume,
high mix.
The idea would be to
1. Screen print paste as we do now (6-mil stencil).
2. Dispense some glue dots to build up a little standoff (higher solder
joint), and add mechanical coupling.
3. Dispense more solder paste only on those pads that need it.
4. Populate and reflow.
After looking at the archive, I get the idea that some of you are
using paste dispensing, at least for intrusive reflow. Can anyone
provide guidance on the following:
1. What kind of positive-displacement dispensing head works best?
Paste probably won't string, so do you need suck-back?
2. Does the paste dot snap off repeatably from the needle? How
critical is z-axis control?
3. What size needle?
4. Can you dispense a dot onto a solder paste brick without making
a mess, or should you dispense onto a clean pad?
5. When dispensing onto (for example) a square 1005 pad, do you
dispense a series of small dots, or one large glob, or line, or fill?
6. Can you use your normal screen-printable paste, or do you need
paste with finer mesh? Is paste available in pre-filled syringes?
Joe Kane
BAE SYSTEMS Controls
Johnson City, NY
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