Posted: Tue Mar 22, 2005 3:04 pm
does the 8 mil annular ring rule apply to mounting holes as well?
Basically I want 70mil holes, and ultiboard is telling me that with an 8 mil annular ring, they'll have 86 mil diameter pads around them. Is this all aboveboard?
Posted: Tue Mar 22, 2005 3:30 pm
Holes are allowed to have a zero annular ring. Hole size can be whatever you need, just make the ring size 0.
Please note - the hole will still be plated but there will be nothing around the hole to connect it to a trace or pour.
Posted: Sat Mar 26, 2005 8:20 pm
Hi, I'm new to this forum and to SFE.
I work in a PCB Factory in Australia.
For anyone who's interested, there are three ways to make unplated holes, that I know of.
This refers to dry film plating resist tenting, NOT solder mask tenting as in 'tented vias'. A hole is tented if the top and bottom copperpads are deleted (or have zero or very small size). If there's no copper on (or very near) a hole then the hole will be covered with dry film and therefore not be plated.
The advantages of this method are that that the unplated holes will be accurately positioned relative to other holes, and post drilling will not be necessary.
The disadvantages are that there MUST be no copper touching (or very near) the hole on either side (sometimes holes in copper areas need to be unplated). Also, the dry film is likely to break if the hole is about 4mm or larger, resulting in partial plating of the hole.
I'll gladly explain the plating process in more detail if anyone is interested.
After drilling, holes to be unplated can be plugged with little rubber cones, this preventing electroless copper plating. I've never seen this done, and it's obviously highly labour intensive and with a high possibility of holes being missed or the plug falling out.
3: Post drilling
Unplated holes are shifted from the primary drill file into the rout (final milling) file. This is what we usually do. The unplated holes may not be accurately positioned in relation to plated holes, however, they WILL be accurately positioned in relation to the routed edges of the PCB, and this might be preferred for mounting holes. Post drilled holes may have a slight burr around them.