Hi Ken,
You would be surprised to see what can and can't be done.... but I think
the question really is... Is it cost effective? manufacturable? reliable?
Are there alternatives? can it be avoided?
I have a design that does exactly what you are suggesting... And, we will
most likely go into production with it. But it is not desirable, not cost
effective, not easily manufacturable... and it might be a reliability
problem if it isn't handled correctly. Problem is... we had no choice! The
functionality of having the particular type of cap is non-negotiable, There
is no room for the cap anywhere else on the board, in fact , it's so large
that I had to cut a hole in the board to let the barrel of the axial body
pass through the plane of the board.... There is no surface mount
equivalent, no potential cross to another part type or package...
Down sides are , it's a hand placed part, you can't auto place it. which
means hand soldering, and special handling. Care must be used when
installing the assembly into it's housing due to close clearances on the
part body and the housing... it's a polypropylene cap, and can't handle high
temps so no wave solder... etc...
To mount it, I placed some long, wide, rectangular pads in such a way as to
get a good mechanical mount from soldering the leads to the pads and no
delamination of the pads... if the pads were too small the part could be
ripped from the board without much trouble...
It works electrically better than expected and makes it possible to have a
product! We have to do it... (and that's the only reason we are doing it).
Believe me, the manufacturing guys don't want to have to del with it, but
they will because we have to do it.
If your cap is radial or axial you will need to stress relieve the leads by
putting a relief bend in them to take up the TCE changes and vibration. A
dab of RTV can do wonders to hold a component to the board or an adjacent
component to keep the stress off the solder joints on the board...
So, to answer your question... yes you CAN surface mount a PTH axial
component to a PWB.... it just takes a bit of creativity and planning. It
may not be the most cost effective but it can be the difference between
having a product and not having one. just be sure to work through the
process with your manufacturing people and ask them to exhaust all other
options before settling for this one.
Bill Brooks
Senior PCB Designer - [log in to unmask]
Zoneworx, Inc.
40925 County Center Drive, STE 200
Temecula, CA 92591
http://www.zoneworx.com
Tel: (909) 296-1226 x 1037
Co-Director / Education Officer / Webmaster
for the San Diego Chapter of the IPC Designers Council
http://www.ipc.org/SanDiego/index.html
http://home.fda.net/bbrooks/pca/
-----Original Message-----
From: Ken Patel [mailto:[log in to unmask]]
Sent: Tuesday, September 12, 2000 6:21 PM
To: [log in to unmask]
Subject: [TN] Axial Cap's lead resting on the board...
Guys,
Do you see any problem in having axial PTH capacitor's leads lying on the
board surface? I have a board with cut out in it
and has two holes across the cut out. Bec' of the height restriction on the
board, we want this axial cap's leads rest on the board leaving body hanging
in the air across the thickness.
I hope you are getting the picture here. Please let me know if you see any
problem or I should be aware off.
re,
ken patel
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