When you’re working with PCBs and making single units to knock out in those Chinese fabs, going from layout to manufacturable Gerber files is just a few button presses, no matter what PCB layout tool you prefer. But, once you get into producing sets of PCBs that form a larger system, or are making multiple copies for efficient manufacturing, then you’re not going to get far without delving into the art of PCB panelization. We’ve seen a few options over the years, and here’s yet another one that’s looking quite promising — hm-panelizer by [halfmarble] is a cross platform Python GUI application, which leverages Kivy, so it should run on pretty well on most major platforms without too much hassle. The tool is early in development, so is restricted to handling only straight PCB edges, with horizontal mouse-bites for now, but we’re sure it will quickly grow more general purpose capabilities given time and support.
In an ideal world, open source tools like KiCAD would have a built-in panelizer, but for now we can dream and hm-panelizer might just be good enough for some people. For more choices on panelizing, checkout our guide to making it easy, and just to muddy the waters here’s another way to do it.
Most of us are familiar with the concept of producing PCBs in a panel, and snapping them apart afterwards. V-grooves that go most of the way through a PCB are one way to go about this, but a line of perforations along which to snap a tab is another. But what’s the best size and spacing of holes to use? Sparkfun’s [Nick Poole] spent some $400 on PCBs to get some solid answers by snapping each of them apart, and judging the results.
The nice thing about creating a perforation line (or “mouse bites”) is that drill hits are a very normal thing in PCB production, which makes creating this kind of breakaway tab a very straightforward and flexible method. However, it can be tricky to get results that are just right. Too sturdy, and breaking apart is a hassle. Too weak, and the board may break or twist before its time. On top of that, edges must also break cleanly. We’ve covered panelizing PCBs in this way before, but this is the first time we’ve seen someone seriously look into how to create optimal breakaway tabs.
Placing holes tangent to the board edge (as shown above) isn’t the prettiest, but keeps PCB edges free from protrusions. This is best for boards that are rail-mounted, or have tight enclosures.
Data on designing mouse bites was sparse and a bit inconsistent, so [Nick] decided to figure it out empirically and share the results. The full details are available in Building a Better Mousebite (PDF download) but the essence of the recommendations are: 0.015″ unplated holes, spaced 0.025″ apart (center-to-center), tabs a maximum of 0.118″ wide (so as to be compatible with depanelizing tools), and holes that extend into the corners of the breakaway tab to avoid sharp edges. Holes should be placed slightly differently depending on whether one wishes to optimize the cosmetic appearance versus the physical smoothness of the board edge, but those numbers are the core of the guidelines.
To fine tune, [Nick] suggests increasing the spacing between holes to add strength, or just adding additional tabs. What about thickness of PCB? [Nick] tested boards both 0.8 mm and 1.6 mm thick, and while different amounts of torque were needed to snap the boards apart, things still worked as expected regardless of PCB thickness.
When it comes down to it, the best numbers will ultimately be the ones that your process or fab house can most efficiently handle, but [Nick]’s numbers should not steer anyone wrong, and it’s fantastic to see this kind of work go into refining such a common PCB feature.
