Steve,
The first board we ran we left the pins on the connectors, the second
board I removed the pins and the results were the same. I have also
viewed the gerber and found that the board has a lot of copper in other
areas but not around the connector. I also made a selective wave
fixture, unfortunately they did not isolate each connector and we got
the same results. My next fixture will have a cross bar between each
connector (x8) this should keep the board nice and flat. It sure points
back to the design of the board, I was hoping someone out there that is
familiar with designs could tell me where the customer went wrong and
how they could avoid this in the future.


Angie

> -----Original Message-----
> From: Stephen R. Gregory [SMTP:[log in to unmask]]
> Sent: Monday, December 14, 1998 9:21 AM
> To:   [log in to unmask]
> Subject:      Re: [TN] Warped boards at PCI connector?
>
> In a message dated 12/14/98 7:35:23 AM Pacific Standard Time,
> [log in to unmask]
> writes:
>
> << From:   [log in to unmask] [SMTP:[log in to unmask]]
>  Sent:   Friday, December 11, 1998 6:23 PM
>  To:     [log in to unmask]
>  Subject:        [TN] Warped boards at PCI connector?
>
>  To technet
>  I have this board that is 18 by 14 though hole and SMT. After reflow
> the
>  board looks good not warped. Once assembled and sent to wave the
> board warps,
>  only around the PCI connectors. It warps so bad I don't have any lead
>  protrusion. I have tried to run this board many ways fast slow and
> minimal
> preheat. I
>  still have this problem. Has anyone ran into this problem before? Is
> this
> common
>  around PCI connectors? I recall this happening once before many years
> ago,
>  I resolved it by tacking down the edge and middle of the connectors
> then
>  masking. Is this the only fix? Any other suggestions
>
>  Thanks in advance
>  Angie >>
>
> Hi Angie,
>
>      Sounds like that there's something a lot different about the
> board in
> close around your PCI connectors as far as copper content in the inner
> layers
> compared to the rest of the board, are there heavy power or ground
> planes
> everywhere else except where the connectors are? Hold the board up to
> the
> light and look through it. Another thing that could be adding to
> things is
> possibly a very tight fit of the plastic guide pins that usually are
> on the
> bottom of the connector...at least on the connectors I've worked with
> before
> had them.(I have't had to wave any PCI connectors in a while).
>
>      The reason I say it might be the hole diameter for the pins on
> the
> connector, is that I ran into something like this before at another
> place I
> worked at. We got one lot of boards from one of our customers that had
> the
> hole diameters swapped for the two plastic pins on the connector
> (usually one
> pin was larger than the other so you couldn't put them in backwards),
> how that
> happened I don't know. But what we wound-up doing was having to clip
> the pins
> off on the connector. We had been doing the same thing as what you
> talked
> about...tack-soldering a few pins on the ends and center before wave
> because
> of the warping. But found with the pins gone, the warping problem was
> eliminated, which caused me to realize what had been causing the
> problem. The
> CTE of the connector material was a lot less than the board, and the
> pins were
> constraining the board when it needed to move as it expanded. We asked
> our
> customer to increase the hole diameter a tad, and we didn't have to
> tack the
> connectors down from then on.
>
>
> The pins are there to take the force of insertion and removal of cards
> instead
> of the solder joints bearing the brunt of it, so be aware of that. We
> had to
> clip them so we could use the connectors, otherwise the customer would
> have
> had to scrap the fabs. But you might want to try an experiment on a
> solder
> sample fab of the ones you're running and some connectors by doing the
> same
> thing...clipping the pins and not tack-soldering the connector. Then
> you can
> ask for bigger holes on the fabs too.
>
> Hope this helps in some way...
>
> -Steve Gregory-
>
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