overplating is unnecessary and adds risk of cap lifting and
delaminating. This risk is greatest is thermal via farms with a high
density of vias all expanding and acting on the cap in concert.
If your supplier can't fill a .5mm via effectively with
non-conductive paste in this era -- you need to find a different
supplier. That is settled technology.
At 11:37 AM 11/6/2009, Glidden, Kevin wrote:
>Inge,
>
>I would fill the vias completely, and have them planarized and
>capped. This prevents the solder thieving and eliminates air
>pockets in the fill, or the risks of a tented via on one side. I am
>not sure of the limitation on plugging in such a small via - what is
>the aspect ratio? Smaller vias might be candidates for
>electroplating plugging.
>
>
>-----Original Message-----
>From: Inge [mailto:[log in to unmask]]
>Sent: Friday, November 06, 2009 1:18 PM
>To: [log in to unmask]
>Subject: Re: [TN] Via fill for heat transfer
>
>Hey there,
>
>I've a q about via fill for LGA, small ones, package 5x5 millimeters and 8
>I/Os, teflon one layer on thick brass back. Heat transfer vias 0.5 mm. How
>do you fill them before mounting the LGAs? Halfways, even or overfilled? If
>the solder volume is too meagre, there will not be a good SJ against the LGA
>heat sink (under side), if you have too much solder, you may get
>overbridging. There are five vias for the contact with the heat sink, four
>vias in a square and one in the middle. We solder same size of packages with
>J-leads on the same board, and they become perfect, but the LGAs get varying
>result.
>
>/Inge
>
>PS. I regret the deplorable incident in Austin. Bad, very bad in many
>aspects, both socially and politically. The human nature is really
>unpredictable.
>
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