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Holes

1. Our CAM systems ALWAYS considers tool lists for drill files as finished hole sizes (ENDSIZE): anular ring values as indicated in the service table is measured considering this rule, so AR=(PAD SIZE-HOLE SIZE)/2.

2. Drill’s tool increments 0.05mm one each other ( till 6.5mm size): so we convert the drill sizes given in the drill files or tool lists into millimeters and round to the nearest 0.05mm.
Example:
- Drill size of 35mil is converted to 0.889mm and then rounded to 0.9mm.
- Drill size of 26mil is converted to 0.660mm and then rounded to 0.65mm.

3. Separate drill files for plated (PTH) and non-plated (NPTH) holes are kindly suggested. 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. When no PTH/NPTH info are given we use the following rules:

For pcb with 0 and 1 copper layer: holes are always considered as NPTH.
For pcb with 2 or more copper layers: holes are always considered PTH except in the following cases:
- Non-connected holes without copper pads.
- Non-connected holes where the copper pad size is equal to or smaller than the drill tool size (attention that this is no the END SIZE of the hole diameter); the copper pad will be removed in the pcb artwork film preparation.
- Connected holes with a copper pad only on 1 outer side, no connection on any other layer (outer or inner) and no copper pad on the other outer side.

In these last 4 cases the hole are always considered NPTH.

4. Important: Cu-plated hole with nominal diameter smaller than or equal to 0.5mm (18mil) are considered by default as VIA holes so:
- the nominal hole size could be reduce to respect a different final hole size to production drill size conversion (endsize compared to the drill toolsize)
- the standard diameter size tolerance will be different from other Cu-plated holes.

5. It is to be considered that to produce Cu-plated holes with nominal end size diameter as for drill requirement we are obliged to drill the holes at a larger size prior to go trough the plating line. The used rules are:
- VIA HOLES –> drilled hole diameter = end size hole diameter + 0.10mm (4mil)
- PTH -> drilled hole diameter = end size hole diameter + 0.15mm (6mil)
- NPTH -> drilled hole diameter = end size hole diameter

Using this rules the tolerances for hole diameter size are:

NPTH -> +0.05mm/-0.1mm (+2mil/-4mil)
PTH with diameter end size > 0.50mm (20mil) -> +0.10mm/-0.05mm (+4mil/-2mil)
PTH with diameter end size <= 0.5mm (20mil) -> +0.10mm/-0.40mm (+4mil/-16mil)

When no tolerances are specified in specification, the hole will produce according to these tolerance values.

Only PcbOnDemand service allows different tolerances but these should be clearly indicated in the mechanical layer and/or drill tool list. Considering the higher cost of this service, our suggestion is that different tolerances have not to be used without a compelling reason.

6. Drilled holes that overlap the board contour can be:
- NPTH holes without copper pads: these NPTH holes will be realized as a part of the board outline ( by routing process).
- PTH holes with copper pads: these will be taken as “plated holes on the board edge” or “Contour Cut PTH drills” and should be clearly indicated in the mechanical layer or one other specific file. Remark: these plated holes cut by the board edge are not available in the PcbSaving service.

7. Overlapping drill holes.

It is kindly requested to not overlap drill holes in the files even if connected to the same electrical net. These could cause broken drill tools and/or wrong roughness of the hole wall: material residual and small pieces of material left behind may cause voids in the Cu plated hole barrels. It is to be kept a minimum hole to hole (endsize) distance of 0.250mm (10mil). This is measured edge to edge of the end size holes (as in the gerber files). Also to define slots it is kindly required to not use overlapping drill holes: in the Mechanical Layer section it is explained the correct way to indicate slots and internal cut-outs in the files.

In the case of slot or other multiple holes with particular contours (only for PcbOnDemand service) it is allowed to partially overlap the drill hole: the rule indicate that the center to center distance of the holes must be not lower than the half-sum of the radius increased of 0.15mm ( 6mls).

8. Annular Rings of oblong pads.

Generally the rules for annular rings on oblong pads are not different from round pads, and minimum values are the same; but we allow some exceptions to the rules ( only for PTH):
- on the smallest side of the oblong pad the anular ring must be >= 0.150mm (6mil) (i.e. no breakout is allowed if measured to the drilled size tool). Normally the oblong pads are not used for via holes so the rule respects the PTH anular ring calculation.
- on the longest side of the oblong pad (both over or above the hole) the minimum anular ring must be >= 0.300mm (12mil): it is to be considered that the hole need not be in the centre of the pad but any way it is not allowed that the hole position could disconnect the pad from the track if the anular ring is at the minimum values.

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