Re: gEDA-user: PCB suggestion

["Daniel Nilsson" <daniel@xxxxxxxxxxxxxxx>]

Karel Kulhavy (clock@xxxxxxxxxxxxx) wrote*:
>
>On Fri, Jan 07, 2005 at 05:58:10AM -0500, Bob Paddock wrote:
>> On Friday 07 January 2005 01:57 am, Stephen Meier wrote:
>> > I feal like I have to step in here. With a 900 pin BGA (30 rows by 30
>> > columns) at a 1mm (39 mil) pitch. Four signal layers are just bearly
>> > able to route all the signals out from under the bga. That was using via
>> > in pad and squeezing two 4 mil traces between pads/layer.
>>
>> I know you can not post the design, but could you post the section relevant to
>> the BGA?  I'd like to know how to do these large BGA's myself.
>>
>> Via "via in pad" does that mean each ball falls into a via, or are the balls
>> on non-hole pads?
>
>Is putting vias through SMD pads a bad practice? Can it influence reliability
>of the soldering?

It depends on the size of the via, for large through hole vias (large in my mind are
drill sizes around 12-15 mils) you run the risk of solder wicking down through the
via and you get a bad solder joint. For this reason you sometimes see people use
partial microvias in pads to limit the amount of solder that can wick into the via
barrel.

--
Daniel Nilsson