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Date: | Thu, 17 Sep 2009 08:42:10 -0700 |
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At 08:33 AM 9/17/2009, Stadem, Richard D. wrote:
>I have been following this link, somewhat, but what Dave says below is
>the most important point so far, the avoidance of soldermask defined
>pads and ground planes on the top layer (solder layer).
>Soldermask-defined pads are somewhat problematic during manufacture, but
>more importantly they can significantly reduce the long term reliability
>of the solder joint.
* unless you commit to underfill
>All of the other issues pale in the face of
>fractured SJs due to soldermask compression during cyclic operation.
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Schaefer
>Sent: Thursday, September 17, 2009 8:54 AM
>To: [log in to unmask]
>Subject: Re: [TN] Ground Pour Under BGA
>
>Toby,
>
>For HDI designs (via in pad) I pour ground underneath BGAs and ensure
>that
>any connections to the BGA ball are thermals. This eliminates soldermask
>defined land areas which are problematic during manufacture.
>
>For most non-HDI designs your observation is correct - there's not
>likely a
>lot of pour under the BGA anyways, so not much point in having it there,
>and
>I'll normally block out the area if pouring on the surface. I do
>normally
>employ a stackup where the adjacent layer (t-1, b-1) is a plane in these
>situations. The one reason I would consider keeping the pour under the
>BGA
>is if it is large enough (and required) to provide some thermal benefit.
>
>Hth,
>Dave
>
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