A Novel Technique for Renewing Old PCBs

Estimates vary, but it is safe to say that more than a hundred million PCBs are manufactured each year. And a significant percentage of those have manufacturing defects or design errors that make them unsuitable for use. In addition to those, there are mountains of e-waste containing billions of PCBs. Until now, those PCBs weren’t worth anything more than the copper that could be scavenged from them — and even that isn’t easy. Now there may be a better alternative thanks to researchers from the University of Maryland's Small Artifacts Lab: a novel technique for “renewing” PCBs to restore functionality or to introduce new functionality.

The team's paper focuses on typical copper-clad FR-4 PCBs, but the idea should apply to alternative styles of PCB. And it should work for most of the PCB fabrication techniques in use today.

To understand how this works, imagine a scenario involving a common PCB design mistake: a trace routed to the wrong pin of a component. Such a mistake usually results in PCBs that go straight in the recycling bin (or trash), unless someone takes the time to put in a bodge wire by hand. But with this new technique, those PCBs can be fixed through an automated process of “erasing” the original trace and “printing” the new trace. At scale, it could save significant time, money, and resources when renewing large lots of PCBs with identical defects.

The “erasing” part is pretty straightforward and can be done using a laser, mill/router, or hand tools —either breaking the trace in a convenient spot or removing the entire trace. The “printing” part is a little more complex, but doesn’t require any exotic processes. Conductive epoxy paste, pushed into milled channels, forms the new trace and that is possible to automate through conventional means with off-the-shelf machines, and it can also be done by hand. Placing the PCB on a hot plate cures that epoxy and testing showed that trace widths over 6 mil were almost as strong as the original copper and with similar electrical performance.

This has obvious applications for restoring the original desired functionality of PCBs with defects or mistakes, but it also has the potential to entirely repurpose PCBs. Many PCBs, even for very different kinds of devices, are quite similar. By making use of this method, it would be possible to take an existing PCB and alter the circuit for a new function. The team demonstrated that by using the same PCB for three devices: a camera roller, a Wi-Fi radio, and an ESPboy handheld video game console.

And this isn’t just abstract research, because you can do all of this yourself. The team published software (a plugin for KiCAD) to GitHub that you can use to compare PCBs and generate stencils for performing these renewals.