Angie,
I sent an earlier reply, but I have a couple of more comments based on the info
in the attached message. If you are wave-soldering other parts to the pcb that
are heat-sinked to the copper areas (consequently, having wave parameters
adjusted accordingly), then the PCI connector areas make be getting too much
heat since they do not have the copper areas around them. Also, check the
gerber data to see how the copper area is distributed layer-to-layer. To
prevent warpage, it is necessary to have copper distribution symmetrical about
the middle of the board stackup (planes opposite planes, signals opposite
signals, etc.). An additional measure would be to make copper distribution as
uniform as possible on each layer by filling with ground plane around features
(on signal layers).
Denis Mori
_______________________________________________________________________
I am currently testing a new e-mail client called Outlook.
If present, please disregard the "winmail.dat" attachment.
_______________________________________________________________________
-----Original Message-----
From: Non-HP-AngieM /HP-Roseville,[log in to unmask]
Sent: Monday, December 14, 1998 9:58 AM
To: Non-HP-TechNet /HP-Roseville,[log in to unmask]
Cc: Non-HP-AngieM /HP-Roseville,[log in to unmask]
Subject: Re: [TN] Warped boards at PCI connector?
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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