A CNC Machine Built Solely to Apply Adhesive to PCBs

When most people hear the term “CNC,” they think of mills and lathes — if they’re familiar with the term at all. But just about any kind of machine performing a repetitive task is suitable for CNC. Many industrial robots are CNC machines when you get down to the fundamentals. However, few makers have a need for CNC outside of those mills and lathes, because they only tend to be worthwhile when a task is repetitive or requires great precision. But Rahix did have a repetitive task: attaching displays to PCBs. So, they built this CNC Adhesive Applicator for the job.

Rahix needed to add round displays to the Flow3r Badges, which you’ve seen if you’ve watched coverage of the 2023 Chaos Communication Camp. Those Flow3r Badges are small music synthesizers with PCBs the shape of a flower. In the middle is a GC9A01-based round 1.28” TFT LCD screen with a resolution of 240×240. But that display doesn’t have mounting holes, which meant that adhesive was necessary to attach it to the PCB. If Rahix were only making a couple, it would have made sense to apply the adhesive by hand. But because they had many to assemble, they built this machine.

The CNC Adhesive Applicator looks a lot like a 3D printer, just with a mount for the PCB in place of the print bed. And instead of a typical Z-axis motor/lead screw arrangement, the adhesive dispenser can move up and down on a pneumatic piston. That may seem like an odd choice, but it makes perfect sense when you know that pneumatic pressure is also what pushes the adhesive out of the syringe-like reservoir and on to the PCB. Rahix used an off-the-shelf air pump controller built for that purpose and it can dispense a predetermined amount of adhesive.

The machine also has a gripper for picking up a display and placing it on to the PCB, saving more labor. The operator puts the display in the pickup location and grabs the completed PCB from its mount.

Rahix’s own custom-designed Poppy Logic Controller (based on a Raspberry Pi Pico) directs the machine with the help of an Arduino paired with a CNC shield. The latter runs GRBL firmware so it can easily receive commands via UART from the Poppy Logic Controller, which runs MicroPython code to interface with Rahix’s web-based HMI software.

In the end, the CNC Adhesive Applicator enabled a great deal of automation that helped Rahix assemble the Flow3r Badges for CCCamp 2023.