Platform forum

Through-hole footprints

Tom Yunghans , 01-27-2021, 09:19 AM
Hi Robert,

I have taken most of your PCB courses and watched a lot of your blogs, but I don't recall you ever discussing much about how to determine the size of the holes and pads for through-hole components (connectors are what I am concerned about at this time). The datasheets seem to show drill information (hole size and spacing) but not much on pad size. The Altium wizards are not much help either. The IPC wizard only addresses SMT parts and the Footprint Wizard wants you to specify the pad sizes manually. Here are a few questions that come to mind.

When you select the hole size and specify plating are you specifying the hole size before or after plating? Will the manufacturer assume you are specifying after plating, and drill the hole bigger to account for the plating?

What if the component pin is not round? Altium Designer allows you to make rectangular and slot holes. It seems like rectangular and slot holes might be a manufacturing issue.

How about the pad size? I have been looking at some IPC-2221 specifications, which specifies some large "manufacturing allowances" to drive the size of the pad (e.g. 0.5mm for level B). Is that what you use? I am looking at some of the pads in the iMX6 Rex design and even though they have round holes, the pads are not round. For example, you use a 9 pin DSUB which has a 1.09mm hole (for the round pin), but the pads are not symmetrical, they are 1.6mm x 2mm. Why are they not round or rectangular?

Any guidance would be greatly appreciated.
robertferanec , 02-01-2021, 03:28 AM
- Pad size: I just do it by eye (is it big enough for a good soldering?) and I also consider if I need to route at least 1 track between pins (then I consider minimum clearance and minimum tracks to calculate pad width).

- Hole size: It may be different between PCB manufacturers, but this is for example what I found on Euro Circuits website: "Tool lists for drill files are ALWAYS read by our CAM system as the finished hole sizes (ENDSIZE)." https://www.eurocircuits.com/pcb-des...0if%20required.

- Slots: If the pin shape difference between x and y distance is small (if you use a circle hole and you still can solder the pin), I still use a hole (it may be sometimes cheaper). If one of the pins dimensions is much different from the other, I use slot.

qdrives , 02-05-2021, 04:25 PM
PCB library expert pro has the option to create through hole components, although I have never used it for TH.
I do like Robert, by eye (and gut feeling).
There is a trade-off between ease of mounting (and removing) and having stability during the soldering process (i.e. soldered straight).
Pads can be made asymmetrical to help with the soldering process, to increase pad size and clearance without have the space between the pins. Another option is to use solder thieves. This is mostly required for wave soldering <= 2mm pitch components.
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