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October 2005

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Subject:
From:
Karl Sauter <[log in to unmask]>
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Date:
Wed, 19 Oct 2005 08:47:12 -0700
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Dwight,

How is heat to get from the device to the thermal via if you don't plate
over it?  Agree that CTE of the non-conductive fill must be a very close
match.

Regards,
Karl Sauter, Sun Microsystems


Dwight Mattix wrote:
> We have a lot of experience w/ this type failure.  I'm working on the
> assumption that there's a thermal via farm in that center gnd slug area.
> A couple recommendations ff the cuff...
>    * Stay away from conductive via fill material whenever possible when
> vias are tightly packed in "thermal via farms."   Conductive fill is almost
> never needed -- adds very little actual thermal/conductive benefit. We've
> modeled it and test it.  For my money, conductive fill is almost always a
> waste of time and a real pain in the patootie from reliability standpoint.
> The biggest benefit is that it's easier to plate over and get good copper
> adhesion and that usually only matters on probe sites. Esp
> evil/unpredictable in this application is CB100 (I've had lots of dialogue
> w/ Dupont over the years on this type failure).
>    * Use a non-conductive fill that's more closely matched in CTE (e.g.San
> eh) and don't overplate the fill.
>    * Arguably the most significant factor:  don't plate over the thermal
> vias.  All overplating does is give the fill something to push against and
> force the whole plated area up during thermal excursions. It's like
> screwing a cylinder head on tightly and then pushing all the pistons up
> against it (expanding fill at temp).  Pop goes the weasel!  Overplating
> doesn't add any grounding or thermal benefit. The solder joint in the gnd
> slug will still be fine w/ the dot pattern that emerges.
>    * As a work around/mod: We've eliminated a couple of these problems on
> finished product by just etching or laser ablating a dot of copper off over
> the fill.
>
> there's my $.02.  Free and worth every penny.  ;^)
>
> cheers,
> dw
>
> At 07:29 AM 10/19/2005, Steve Gregory wrote:
>
>> Hi Wee Mei!
>>
>> I've got your pictures posted. Go to:
>>
>> http://www.stevezeva.homestead.com/files/U2_top.JPG
>> http://www.stevezeva.homestead.com/files/U2_bottom.JPG
>> http://www.stevezeva.homestead.com/files/U2_delamination.JPG
>>
>> Are the vias filled? Are you seeing this delamination on very many
>> PCB's? Are you seeing it only on the bottom of the PCB?
>>
>> Kind regards,
>>
>> -Steve Gregory-
>> Senior Process Engineer
>> LaBarge Incorporated
>> Tulsa, Oklahoma
>> (918) 459-2285
>> (918) 459-2350 FAX
>>
>>
>>
>> |---------+---------------------------->
>> |         |           Wee Mei          |
>> |         |           <[log in to unmask]
>> |         |           SG>              |
>> |         |           Sent by: TechNet |
>> |         |           <[log in to unmask]>|
>> |         |                            |
>> |         |                            |
>> |         |           10/19/2005 03:47 |
>> |         |           AM               |
>> |         |           Please respond to|
>> |         |           TechNet E-Mail   |
>> |         |           Forum            |
>> |         |           <[log in to unmask]>|
>> |         |           ; Please respond |
>> |         |           to Wee Mei       |
>> |         |           <[log in to unmask]
>> |         |           SG>              |
>> |         |                            |
>> |---------+---------------------------->
>>
>>  >--------------------------------------------------------------------------------------------------------------|
>>
>>   |
>>                                         |
>>   |       To:       [log in to unmask]@SMTP@Exchange
>>                                         |
>>   |       cc:       (bcc: Stephen R
>> Gregory/LABARGE)
>> |
>>   |       Subject:  [TN] Delamination at Thermal Via
>> area?                                                       |
>>
>>  >--------------------------------------------------------------------------------------------------------------|
>>
>>
>>
>>
>> Hello,
>>
>> Just asked Steve to download 3 pictures on the defects. Kindly take a
>> look
>> at them and would appreciate some feedback on the possible root cause.
>>
>> Steve : Thanks for the downloading.
>>
>> Regards,
>> Wee Mei
>>
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