Upgrading a Pick-and-Place Machine with an Automated Solder Paste Dispenser
This is how Stephen Hawes, the creator of the LumenPnP machine, added automatic solder paste dispensing to his manufacturing process
The LumenPnP project
When it comes to assembling PCBs at home, there are two main approaches: either placing each component by-hand with a pair of tweezers or using a CNC machine. In both cases, someone is needed to put down a layer of solder paste onto the SMD pads so that everything will become electrically and mechanically connected when reflowed. But for Stephen Hawes, the founder of Opulo and creator of the open-source LumenPnP pick-and-place machine, he wanted to skip this tedious step and instead delegate the task to his automated system.
Extending a previous concept
Back in September, Hawes was experimenting with a way to place components onto a powered PCB and have each LED illuminate the moment it completed the circuit. For it, he sourced a highly conductive ink that, although not nearly as secure as solder, would achieve the goal. Next, the ink was placed into syringes and tested manually before Hawes ran a pick-and-place job on the machine.
This ink-dispensing implementation inspired him to develop a new toolhead for dispensing solder paste, and it required a few modifications before it could be used, as the paste's increased viscosity requires far more torque than ink. One run of the 3D printer later and Hawes had his new-and-impoved dispensing toolhead ready for testing.
Once he was confident in the concept, he designed an improved version with a higher gear ratio and larger motor.
Usage with a Lumen pick-and-place machine
The LumenPnP, owing to its open-source nature, is controllable from Python scripts via a library called leash. With it, the machine's position, lighting, toolheads, and cameras can all be controlled, which is how Hawes was able to automate his solder paste dispenser. After entering the coordinates of each surface mount pad and instructing the machine to home, it iterates through every pad in the list by traveling to its position, feeding the dispense motor for a small amount of time, and then retracting upwards for the next pad.
Results
The addition of a paste dispenser makes the LumenPnP capable of nearly 100% end-to-end autonomy and helps ensure the correct amount of paste gets deposited on each pad. In the future, Hawes plans on improving his software to automatically generate pad coordinates from PCB design files and reduce his manufacturing time even further. To see the machine in action and how Stephen developed his time-saving toolhead, you can watch his video here on YouTube.
