The Mask of the Red Yeoman

We're introducing a new DFM feature - solder mask checking! And we're giving current beta participants a first crack at checking it out.

Some characters can really make an impression, even if they only appeared for just a few episodes in a moderately successful TV series. We think that our next DFM function, code-named "Rand", will be much the same way - a minor feature that we think will be of immense utility to our users.

Solder mask DFM looks for two things: copper-to-mask clearance, and "slivers". Here's a quick rundown of how to get your mask output just right. And then we'll post the URL for Rand, for folks that want to get an early taste.

First, you should ensure that your EDA package is set to a mask swell, or mask expansion, of 4 mil (or 0.1025 mm for folks using a rational system of measurement). At the same time, if your package supports it, you should set mask-mask clearance to a minimum of 4 mil, or 0.1025 mm as well. If your package doesn't support that kind of setting, well, read on.

Here's a pretty standard land pattern - it's a QFN-12, .65 mm pin pitch:

Here's an example of insufficient mask clearance - just 2 mil, which is not enough, and will trigger an error in Rand:

OK, no problem. Let's set the mask swell/expansion to 4 mil, and we get the correct copper-to-mask clearance:

Great! Our work is done... except that by putting in the correct copper-to-mask clearance, we've just triggered some new errors - our mask-to-mask clearance must also be 4 mil, and now it's not:

Remember, we're looking at a negative layer when it comes to mask, so the space between the red areas is where the solder mask is applied on the PCB. And really skinny areas ("slivers") have a bad tendency to just peel right up. It can ruin your day. So what to do? Well, for packages that don't do this kind of housekeeping for you, you'll need to manually adjust the mask swell until it looks something like this:

And that's correct, and won't make our DFM cranky. Although we're not enforcing this standard right now, we do correct all designs to this standard behind the scenes. Or our fabs won't make your boards, and then everything is terrible. And trust us - we're going to make it so that folks that do the right thing benefit mightily. Soon. Promise.

So, here's how to mess about with Rand: instead of using our normal url to access the beta, try using this instead - https://beta.pcb.ng/rand - which is just like the current release, but with mask-checking goodness. As always, we want your feedback, and we want folks to break it. And if you break it good, well, let's just say that we'll make it worth your while.