Prototype Drilling:
Sizes:
AP Circuits is capable of drilling in any number of drill sizes down to 0.013" finished. However, we can keep our costs down (in terms of setup time) by providing a pre-selected set of drill sizes. Costs we save are then passed on to our customers. For this reason we provide a group of common drill sizes for you to choose from:
| Drill Number Set | Drill Size | Finished Size | Approximate Use |
| #76 | .020" | .017" | via holes |
| #70 | .028" | .025" | via holes, fine lead devices such as trim pots etc. |
| #65 | .035" | .032" | IC's, 1/4 watt resistors, small diodes, ripple caps etc. |
| #62 | .038" | .035" | Square posted pins that measure .025" on the flat. |
| #58 | .042" | .039" | TO-220 packages, IDC type square posted headers, 1/2 watt resistors, 1N9000 series diodes, IC chip carriers etc. |
| #55 | .052" | .049" | larger connectors, transformer leads, etc. |
| #53 | .060" | .057" | similar to .052" above |
| #44 | .086" | .083" | TO-220 mounting holes, screw holes, general mounting |
| 1/8 in. | .125" | .122" | mounting holes |
| #24 | .152" | .149" | mounting holes |
- We do not stock Metric diameters or off wire size diameters. Please click here for a complete drill list.
- Drill sizes are BEFORE PLATING diameters. Expect after plating hole size to be between 0.003" and 0.005" smaller.
- The common use information above is only a guideline. When placing an order, be sure to calculate the required pre-plate hole sizes using the drilling guidelines
If your project requires drill sizes not outlined above there will be an extra charge for each additional size.
Guidelines - Drilling
Terminology
| Finished Hole | diameter after plating |
| Unfinished Hole | diameter before plating |
Plating Reductions
Over sizing of a pin by .010" is a generous measurement and will include the plating factor. Hole sizes in a plated through hole board reduce by .003" to .005" from the drilled size.
Designs requiring hole locations guaranteed non-conductive must use our affordable post-process drilling option.
For non-critical locations you can attempt a process known as "tenting". "Tenting" uses process film to dam both sides of a drilled hole. This may prevent chemistry from entering and plating but there is no way guarantee success. You can improve your chances of a non-plated location if you ensure that both sides of the board meet these minimum requirements:
| Holes .100 inches and over | clear 0.025" from the edge of the hole to any other feature |
| Holes under .100 inches | clear 0.015" from the edge of the hole to any other feature |
Features include ground planes, any pad or trace, board edges, slots, notches, other holes. There is no "tenting" fee as non-plated results are not guaranteed.
Providing us with any of the following:
- tool list that identifies non-plated holes
- non-plated drill file included with the data
- mechanical layer that identifies non-plated locations
- readme.txt file with specific directions
Will automatically result in premium-fee post-process drilling.
Hand Assembly
The .042" is a very versatile size for prototyping. It's finished size (.039") is a bit too sloppy for machine assembly (IC's and resistors), but it's great for hand assembly.
In many cases you could use .028, .035 and .042 for most of the board's IC and related "glue" hardware. The larger diameters will come into play for interconnects, transformers and mounting hardware etc.
Always Measure With Calipers
It is best that you never "guess" when it comes to the size of the required hole. Instead use calipers to measure the devices you intend to use.
Using Calipers:
- squeeze the device into the calipers.
- carefully rotate the device's lead in the caliper so that the largest surface feature is measured (especially important for flat or square pins).
- add approximately .010" for plating.
Note: Some component leads are very delicate. Be careful you don't twist them out of shape. It may be necessary to relax the caliper's grip when rotating the lead.
Example: If a dual-row ribbon cable header uses a .100" space from pin center to pin center and is square posted, then the actual measurement (cross corner) will be in the .032" to .036" range. Adding .005" to .010" would suggest that you may want to drill it at .039" to .046". Ideally, you also want to maintain a minimum .010" annulus on the pad after it's drilled (improves solderability), this would then indicate that you should use a .061" to .066" pad.
Calculations
A device that has a symmetrical square post can use the following calculation:
For example, the following calculation will be required to provide the absolute minimum diameter of a "finished hole" for a .025" square post:
High Density Drilling (HDD):
Boards with an average of more than 24 holes per square inch are subject to a high density drilling premium of $0.01 per hole per square inch to compensate for additional drilling time.
Example: an order of 2 4"x5" boards with 600 holes
| 600 holes / 20 sq. in. (single board area) | = 30 holes per sq. in. |
| 30 holes - 24 free holes | = 6 holes per sq. in. extra. |
| (6 holes x 20 sq. in.) x $0.01 | = $1.20 per board premium. |
| $1.20 x 2 (number of boards required) | = $2.40 total drilling premium. |