How to avoid surprises when you drill holes in PCB ?
2018-11-23 17:54Writer: qyadminReading:
1.Tool lists for drill files are ALWAYS read ( and interpreted) by our CAM systems as finished hole sizes ( so final diameter of the whole after plating and surface finish )
2. PCB drill tools are manufactured in increments of 0.05 mm. We convert the drill size given in the drill files or tool lists into milimeters and rount ot hte nearest 0.05 mm.
Example : Drill size of 31 mil – converted to 0.7874 mm is then rounded to 0.80 mm
Example : Drill size of 32 mil – converted to 0.8128 mm is then rounded to 0.80 mm
Example : Drill size of 33 mil – converted to 0.8382 mm is then rounded to 0.85 mm
3. If possible, provide separate drill files for plated (PTH) and non-plated (NPTH) holes. If this is not possible, always specify different tools for PTH and NPTH holes and mark clearly which tools are PTH and which tools are NPTH.
For 0-layer and 1-layer boards: ALL holes are considered as NPTH by default.
4. When no PTH/NPTH info is given we use the following rules to determine PTH/NPTH:
For 2-layer and multilayer boards: ALL holes are considered PTH except the following cases which are considered NPTH:
Non-connected holes without copper pads.
Non-connected holes where the copper pad size is equal to or smaller than the drill TOOLSIZE (the copper pad will be removed in single image preparation)
Connected holes with a copper pad on 1 side (outer), no connection on any other layer (outer or inner) and no copper pad on the other side (outer).
5. Finished hole sizes (ENDSIZES) smaller than or equal to 0.45mm (18mil) are by default considered as VIA holes You can adjust this limit by selecting another value for” Holes <= may be reduced” in Board technology
IMPORTANT: This default via-rule affects the standard tolerance on via hole ENDSIZE diameter – point 7 below
6. To allow for the plating in the hole we drill holes prior to plating at a larger size (drill over-sizing)
The conversion rules from finished hole ENDSIZE to production TOOLSIZE are:
TOOLSIZE = ENDSIZE
+ 0.10mm (4mil) for Plated Through Holes (PTH)
+ 0.00mm for Non Plated Through Holes (NPTH), so toolsize = endsize
7. Standard tolerances on drill ENDSIZE diameter.
NPTH holes +/- 0.05mm (+/- 2mil)
ENDSIZE on component holes +/- 0.10mm (+/- 4mil)
ENDSIZE on via holes : +0.10/-0.30mm (+4/-12mil)