Very small holes can always be drilled, but
it's best to use 0.6 or larger for via's. Smaller sizes force us to
reduce the number of boards in a drilling stack, which increases our
production cost. This is either due to inability of the drills to clear
the debris or excessive wandering as the drill flexes to find the easiest
route though the stack.
Large holes above 5mm are often routed but at
only a small extra cost to the std drilling price. Whereas the dimensional
tolerance of a drilled hole is very good, small variations in size are
usual with routed holes. To avoid problems larger holes are normally
treated as +.1mm -0mm
The main size price break point for routing is
1.6mm below which the price starts to climb. Again it's the problems in
clearing the debris and the shorter life span of the smaller
routers.
Where a larger volume of conventional PCBs are
to be routed yet again the laminate make a big difference. The std FR4
grade is very abrasive and quickly degrades the tool bits if the
circuits can be made on a softer material cost savings will result.
