Like this poster, I am trying to use PCBexpress to make a PCB for a 1mm pitch BGA. Their steep annular ring requirement (smallest via is 8mil hole + 2x8.5mil ring) is making things impossible for me. I'd like to understand better why we need annular rings or why I can't make do with a much smaller one.
Specifically, I read two things. The first, repeated in a few places on the web, is that without a ring the connection between the trace and the in-hole plating is physically weak and liable to crack. The second, that I saw in the above-linked thread, is that a too-small or non-existant ring will cause the copper inside the plated hole to get eaten out and the via will stop being a via (I guess the etching fluid gets inside).
The first scenario doesn't sound too scary. If I just use a thick trace (eg a 10mil trace to my 8-12mil hole) then there'll still be plenty of area to bond if the hole is misaligned to begin with. I'm not concerned about even a 10% failure rate, for example. The second scenario sounds a lot scarier. Also I would like to not use an annular at all on the bottom of vias that aren't connected, but according to scenario #2 that would mean certain death.
Specifically, I read two things. The first, repeated in a few places on the web, is that without a ring the connection between the trace and the in-hole plating is physically weak and liable to crack. The second, that I saw in the above-linked thread, is that a too-small or non-existant ring will cause the copper inside the plated hole to get eaten out and the via will stop being a via (I guess the etching fluid gets inside).
The first scenario doesn't sound too scary. If I just use a thick trace (eg a 10mil trace to my 8-12mil hole) then there'll still be plenty of area to bond if the hole is misaligned to begin with. I'm not concerned about even a 10% failure rate, for example. The second scenario sounds a lot scarier. Also I would like to not use an annular at all on the bottom of vias that aren't connected, but according to scenario #2 that would mean certain death.