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I am working on making footprints in Eagle for a through-hole connector I want to use. I am running into some issues as I try to determine the appropriate diameter and drill size I need for the through hole pads. I am using this schematic as I design the footprint: enter image description here

My through holes will be copper plated, so I am working from the diagram on the left. This portion of the datasheet for the connector clearly states that the finished hole diameter is 1.02 mm, but at the bottom of the drawing there is a figure given for a drilled hole diameter of 1.15 mm. Which of these two numbers should I use for my drill diameter in Eagle. Also, what should the hole diameter be in Eagle. In other words, how much copper should surround the hole?

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I have always specified the desired finished hole size, and let the board shop determine the required drill size and plating to get that size.

The board shop knows the sizes of drill bits they have, and how much their standard plating process will reduce the hole size, so are in the best position to determine the drill size.

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  • \$\begingroup\$ To clarify, you are suggesting I choose a drill size of 1.02mm for this particular application. Do you have any recommendations for pad diameter, or is that more of a judgement call. I am struggling to see where the overall pad diameter suggestion is on the included diagram. \$\endgroup\$ – Saunders Aug 6 at 18:10
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    \$\begingroup\$ Yes, specify a 1.02mm hole in the CAD footprint. the pad diameter is not shown in that drawing - it is up to you to decide how large an annular ring you want around the hole. \$\endgroup\$ – Peter Bennett Aug 6 at 18:32
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When through-holes and vias are plated, this reduces the diameter of the finished hole. Board houses generally want you to give them the finished hole size. So, you would enter 1.02 mm into Eagle.

The standard via plating thickness is 0.025 mm. So, if your design calls out a finished hole size of 1.02 mm, the board house will use a 1.07 mm drill.

The diagram in your question suggests a 1.15 mm drill. This gives a bit of room for tolerance variations, and is a standard drill size. But you don't need to mention this value; it will be determined by the board house.

Similarly, in imperial units, plating is generally 1 mil. A finished hole size or 12 mil will require a 14-mil drill.

To summarize: your documentation should give the finished hole size, and the board house will determine the actual drill to use.

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