[sdiy] Reflow revisited and a bit OT, sorry

[Eric Brombaugh]

On Sep 3, 2010, at 7:35 AM, Ingo Debus wrote:

> While we're at it, is it advisable to place vias directly under BGA "pins"? This makes layout a lot easier. Or should that better be avoided?

Vias placed directly under BGA pads tend to wick the solder away, leading to unreliable connections. There are several solutions to this:

1) offset the vias slightly - this causes routing congestion on the component layer though
2) fill vias with some sort of pucky to prevent wicking - this is an extra (and often expensive) manufacturing step.
3) use blind vias - not all fabs support this.

Usually you'll see folks use option 1)

Eric