Subject: | |
From: | |
Reply To: | TechNet Mail Forum. |
Date: | Wed, 26 Nov 1997 08:32:19 +0000 |
Content-Type: | multipart/mixed |
Parts/Attachments: |
|
|
AL, The problem that you have is that the wet adhesive is
sticking to the needle better than to the solder mask. It is all
based around surface tension. You either have to decrease the
adhesion to the needle, or increase the adhesion to the pad.
There could be a variety of ways of doing this. Changing to
another solder mask could change the surface tension of the glue
on the mask. Increasing the dot area on the board would increase
the adhesion. Possibly changing the needle standoff height from
the board might help. Changing to a smaller diameter needle would
reduce the surface area of needle in contact with the wet paste.
If your machine allows it changing the retract speed of the needle
could improve things. There are needles available with specially
shaped ends that supposedly help paste release. These are of
course more expensive than flat ended needles. What you need to do
is change the balance of surface tensions between glue, mask and
needle so that the glue always ends up on the board and not the
needle when the needle is retracted.
Jeremy Drake
Design to Distribution Ltd
|
|
|