Jon's Imaginarium – PCB Design Tip: Ensuring Mounting Hole Clearance

[Visitor]

I always hate it when I lay out a printed circuit board and discover I haven't left enough clearance around mounting holes to tighten up a nut or spacer with a nut driver, or to even get a spacer in place. This is a simple method to eliminate that problem.

I designed a mounting hole "component" for 3mm or 4-40 screws that include the clearance for a nut and nut driver in the PCB document layer. These lines, which won't show up on the finished circuit board, show the clearance needed for a nut (where you always want to avoid placing components) and a nut-driver (where it is desirable to avoid placing components. I have two different mounting hole components, one with a pad, and the other with just a hole.

The white lines are in the document layer, so they don't show up on the circuit board.

Here's an actual board layout, showing the results of using these mounting hole components.

I try to keep traces out of the nut driver clearance area, to avoid any possible damage if a nut driver has a sharp edge.

Here are the dimensions I used for 3mm / 4-40 mounting hardware. The are close enough to the same size that the same diameter hole and pattern work for both. A few minutes laying out a footprint like this saves a lot of time during board layout and poor board designs.

 

[schmitt trigger]

Two thumbs up for the tip!
I have also had this exact same problem.
But it never occurred to me to create a nut outline.
What CAD software did you use? Is it EasyEDA?
If so, how did you name the component?

 

[Visitor]

I have recently made the wholesale switch from Eagle 5 (the pre-subscription version) to EasyEDA. I'm loving it and find it truly easy to use. I've never been able to wrap my head around Kicad.

These patterns are called:

MOUNTING_HOLE_&_PAD-3MM/4-40

MOUNTING_HOLE_3MM/4-40

Owner name: jonchandler

Let me know if you can find these patterns.


One other thing I've done is to create board outlines to fit some enclosures. When laying out a board to fit one of these enclosures, delete the suggested outline, choose the outline "footprint" and plop it down. I like to center my boards on (0, 0) because components tend to be laid out somewhat symmetrically (switcheds, LEDs, terminal blocks).

 

[schmitt trigger]

Same here;
Once that one gets the gist of EasyEDA, and sees the inexpensive yet good quality boards they produce, one simply won’t go back to the previous platform.

I don’t have EasyEDA at work, but definitely will check it out in my home computer.

 

[Visitor]

BTW - are you familiar with the utility to parametrically search JLC's component library? Much easier if you're searching for ICs with particular functions. The database is (automatically) downloaded locally, then this program searches to find the parameters you specify.

JLC PCB SMD Assembly Component Catalogue

 

[schmitt trigger]

I found the mounting hole symbols, thanks.

 

[granddad]

Have downloaded the free linux version and i'm going to give EasyEDA a go .. thanks.

 

[Visitor]

Feel free to ask if you need any help getting started. For the most part, it's pretty straightforward.