Re: BGA Assembly

[Dimiter Popoff <tgi_earth@yahoo.com>]

Peter,

>I was specifically recommended not to put vias or holes under the ball, by
>someone with past experience of solder being drawn through the hole and away
>from the BGA. I guess this isn't what you wanted to hear - sorry.

I guess you just saved a board from an unsuccessful experiment :-).

Overall, though, this is no problem, because I don't expect the
device to go into automatic production quantities soon, and manually
I seem to manage it quite successfully. Moreover, from what I have
seen so far the solder drawn through the holes is not much (it
never makes a drop beneath the board, just fills the hole), unless
there is a big pad at the opposite side to be wetted; and even then
there is no problem, the connections are quite intact. Actually I
have hard times imagining what should happen to make the solder
be drawn away so there is no more a connection between the BGA
and the board (I guess we all know how do solder drops of this
size behave), but as I said earlier, I'll take easily avoidable
risks at a later stage :-) (trying if the BGA will float on
this without limiting feet, that is).

All this is valid for holes drilled with 0.3mm or less; this makes
about 0.2mm after plating. The holes had anyway to be that tiny
in order to allow 3 traces between each pair of BGA pads; which, in
turn, made routing possible on only two signal layers.

Thanks,
Dimiter