Steve, I think your problem probably lies in two different print notes,
both of which state the same thing, "2 deg. maximum sway". One of these
is for the pins themselves, the other is for the positioning posts. If
the posts allow a small amount of "whole-connector-body" mispositioning,
and the pins themselves can move 2 degrees, you can end up with a
cumulative worst-case scenario that looks like what I am seeing in the
previous pictures, the result of the stackup tolerance after soldering.
One cannot help but believe that this is due in part to having to place
these manually and push them firmly down to the board.
The question that is in the back of my mind is whether there is enough
mounting hole slop to allow the connectors (as well as the connector
pins) to pull themselves into alignment during solder reflow. If they
are pressed down such that the loose pins are firmly being held down
(out of alignment with the pads) by the tension of the small mounting
holes on each end of the connector, there is no way they can float
freely into alignment somewhere near the centers of the pads during
reflow.
I also note that every other pin is off the pad and off in the same
direction. Is this always the case?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, October 30, 2007 2:52 PM
To: [log in to unmask]
Subject: [TN] Samtec SMT Connector Woe's...(again)
Hi All,
I'm running into a problem with some Samtec connectors again, and maybe
you all can guide me on how I should handle this...
First here's a picture of the connector:
http://stevezeva.homestead.com/files/Samtec_Connector.jpg
Next, here's a picture of the problem:
http://stevezeva.homestead.com/files/Samtec_Solder_Joints.jpg
QA is calling these solder joints as rejectable. These leads aren't
gull-wing leads. I view them as some sort of mutated butt joint leads
(sort of). I don't know what you would call them really, so I'm not
quite sure what inspection criteria you would use. As you can see, the
toe of every other lead doesn't sit 100% over the pad, and it continues
like that through-out the length of the connector. I see that as a
connector manufacturing issue, not something we have any control over.
Here's a picture of the bottomside of the connector so that you can see
what the bottom construction of the connector looks like:
http://stevezeva.homestead.com/files/Samtec_Bottom.jpg
In the top of the picture you see what Samtec calls a locking tab, one
at each end of the connector. It has barbs that dig into the PCB and you
have to force them into the holes. Obviously, we're hand placing them.
What's funny is that they come in tape and reel and the have a pick and
place pad on them! I don't know of any pick and place machine that has
enough force to place these connectors and push the locking tabs into
the holes so that the leads sit flush on the pads. I've also posted
Samtec's drawing of the connector:
http://stevezeva.homestead.com/files/SAMTEC_ROLC.pdf
My gut feel is that the solder joints are acceptable. If the toe of
these leads are tweeked a little, there's still a good percentage of the
lead over top of the pads in which to form a decent solder joint because
of the way the connector and leads are constructed.
What say you all?
Thanks!
Steve Gregory
P.S. I HATE Samtec connectors!!!!!
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