[SI-LIST] Re: backplane connector
- From: Michael_Greim@xxxxxxxx
- To: julian.ferry@xxxxxxxxxx, howiej@xxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Wed, 27 Mar 2002 13:03:02 -0600
Hi Julian,
There are some tricks that you can play with
press fit connectors that you can't really
do with a solder tail connector to help
reduce parasitics. I think that the two
most popular techniques are back side counter
boring of the board to remove the via stub
and using a top side blind via that is just
long enough to get past the contact of the
press fit 'bubble'. The problem with these
techniques is that it adds cost to the board
due to extra processing. I've personally always
questioned the reliability of counterboring.
The mechanical challenges are always the first
thing that comes up regarding SMT backplane connectors.
Thermal expansion, coplanarity, having something
other than the solder contacts to absorb the force
of mating and unmating are all big barriers to
adoption of these connectors. Another issue that
I have heard regarding these connectors is overcoming
the thermal mass of the connector so that the solder
melts but the housing doesn't. I agree that you
can have an easier time with parasitics. You can
also have increase routability with these.
Just my 0.02
Michael
-----Original Message-----
From: Julian Ferry [mailto:julian.ferry@xxxxxxxxxx]
Sent: Wednesday, March 27, 2002 12:43 PM
To: 'howiej@xxxxxxxxxx'; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: backplane connector
In my opinion, this is almost like asking "Which is better, red wine or
white wine?" Both have their advantages and disadvantages in various
applications.
Surface mount can most definitely offer some electrical advantages. If you
keep your vias under control, routing options on inner layers are much more
flexible with surface mount connectors. Surface mount also allows you to
use stopped or drilled via technologies to eliminate stub effects. With
press fit, you need full length vias.
There are some different mechanical challenges associated with surface mount
connectors. Probably the most significant is in trying to maintain
acceptable coplanarity in the terminals across a large connector.
Coplanarity is important in reflow processing. Thermal expansion of the
board vs the connector is another concern. And sometimes additional means
of mechanical support might be required for surface mount versions. The
press fit connectors tend to be much more rugged, as-is.
-----Original Message-----
From: Dr. Howard Johnson [mailto:howiej@xxxxxxxxxx]
Sent: Wednesday, March 27, 2002 12:02 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] backplane connector
I'm doing some research for an EDN column about the use of
surface-mounted backplane
connectors as opposed to press-fit types for high-speed
serial backplanes (in the
GHz+ speed range).
Of course the press-fit conectors have the advantage of not
requiring soldering on
your backplane, which means you can incorporate cheezy
plastic parts into the connector
shells.
The surface-mounted connectors work well with very small
blind
vias which are good for high-speed signals.
Which is best? Where are we going in the future?
Any comments you would care to submit to my attention (
howiej@xxxxxxxxxx ) or post
here on the si-list would be greatly appreciated. Please
include the words:
"backplane connector" in the subject line to make sure I see
the message.
Best regards,
Dr. Howard Johnson, Signal Consulting Inc.,
tel +1 509-997-0505, howiej@xxxxxxxxxx
http:\\sigcon.com -- High-Speed Digital Design articles,
books, tools, and seminars
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