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October 2007

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TechNet E-Mail Forum <[log in to unmask]>, Wee Mei <[log in to unmask]>
Date:
Wed, 31 Oct 2007 07:51:40 +0800
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Hello,

The acceptance criteria would very much depend on respective company. Usually, I would not accept any lead that overhang its solder pad by more than 25% of its width.

Just my contribution.

Regards,
Wee Mei

----- Original Message ----- 
From: "Steve Kelly" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, October 31, 2007 5:54 AM
Subject: Re: [TN] Samtec SMT Connector Woe's...(again)


> Hi Steve,
> We build with these connectors daily. 1) Richard's remarks are correct - the
> post hole is better to be loose than tight because the positional tolerance
> stack of this connector is OK at best- we have learned from experience to
> make the hole bigger or spec the connector without this feature 2) we do
> from time to time get in connectors with the leads at an angle - we reject
> them 3) the question you need to ask is whether the solder joint can handle
> mating and unmating - it takes a lot of force to unmate these connectors and
> how often will it be done. Good luck. Steve Kelly
> 
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
> Sent: October-30-07 5:03 PM
> To: [log in to unmask]
> Subject: Re: [TN] Samtec SMT Connector Woe's...(again)
> 
> 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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