Yes - we do accept four layer PCB designs .. at least for now. However, demand for this has been low - it is possible that we will drop this if demand does not increase. Right now we have a four layer panel that has been filling for a couple of months and it is still only 25% full! What this means is that four layer boards have been taking a very long time to turn around .. there is some discussion about this as it becomes a problem for us and you because of the long wait.
The charge is very reasonable: $8.00 / sq. inch. and the mininum charge will be for one inch. The tolerances are better than the two layer boards - 6mil (~0.15 mm) trace and space width and 13mil (~0.33 mm) drill sizes. Compared to other services this is a very good deal - we want to be able to offer it but only if it makes sense to do so.
So here is the deal - I have resisted dropping support for four layer boards at the request of some of the members; but we really need to do more of these to keep it up. You can help with this by either ordering some four layer designs or getting the word out that you can have them done cheaply here. I will say "four layer PCB" a whole bunch here in hopes that google will pickup on it .. but other than that there is not much we can do but just try to get the word out. A panel is only 10" x 15" so we don't need millions to fill one - but we do need more than we have been getting to turn a panel in a reasonable time.
We will try to send the current panel soon - even if it is not completely full (which we did with the last panel). I would like to give everyone a couple of weeks to respond and get on the current four layer panel. If response is good and we don't lose money on this panel again we can keep support for four layer PCBs. If not .. sadness might happen.
Please Note: Four layer orders should be made separately from two layer boards - the turn around time is different and we have to ship them separately.
Thanks from us and all the four layer PCB proponents - now go out and design some cool four layer stuff, ok?