In the early stages of product development, it is common to constantly be re-programming PCB's for both firmware development and building prototypes. To quickly flash boards, a simple development fixture can be designed to program boards and run early tests.
This is part 2 in a series that covers FixturFab Development Fixtures. In part 1, we designed a 3D printable development fixture with the Automated Design Service. Part 2 covers fabricating and assembling the fixture.
Development Fixture series
- Designing a 3D Printed Development Fixture
- Assembling a 3D Printed Development Fixture
- Test Instrumentation for Development Fixtures
- Designing a Laser-Cut Development Fixture
- Assembling a Laser-Cut Development Fixture
This guide goes over the parts we picked for the BOM, downloading the CAD files, printing the Fixture Base and Probe Plate, and assembling a mechanical Development Fixture.
This development fixture was designed to be 3D printed by ensuring that all test points were at least 75 mils apart (75 mil pitch). While possible to accurately 3D print smaller resolutions, we wanted to keep this reliable on an entry-level printer.
In the near future, FixturFab will release the files for laser-cuttable Development Fixtures that can handle down to a 50 mil pitch.
To follow along with this tutorial you will need the Development Fixture project designed in part 1 of this series. You will also need access to a 3D printer. We used an Ender 3 and PLA filament.
The BOM for a Development Fixture
- When selecting a test probe (also known as a pogo-pin) we use this guide from Ingun. We picked a pogo-pin with a conical tip because it can hit both SMD and Through-Hole test points.
- It is good to have extras, they can bend when inserting into the probe plate.
- These are available from many suppliers and may have large lead times.
- These should match the pogo-pin you selected.
- Also available from many suppliers and many have long lead times.
- As an alternative, you can solder or wire-wrap directly to the bottom of the test probes, but we prefer jumper wires. They allow connecting to your test instrumentation faster.
4 3mm diameter dowel pins for the Guide Pins
- The diameter should match the PCB’s guide-pin holes and the length should be longer than the test probes.
- Optional, but these make it very easy to use to quickly replace probe plates.
- The FixturFab probe plate has countersinks that are designed for socket head types, but the head-type doesn't matter too much.
And of course, you will need a SparkFun RedBoard Artemis.
Optional, but helpful
- Soldering station
- Drill or Rotary Tool with a set of micro drill bits
3D Print the Base and Probe Plate
Download the CAD files
After designing the Design File Package that was covered in part 1 of this series, download the Fixture Case and STL files.
Parse the Probe Plate and Fixture Base STL Files
We used Prusa Slicer to import the STL files, slice them, and export the G-code for printing both the Base and Probe Plate.
Slicing the Probe Plate STL file.
Exporting the G-code from the sliced Base STL file.
Print the Probe Plate and Fixture Base
Unfortunately, 3D printing will take several hours per part. We’ve 3D printed a stock of bases since they are generic parts. Then we only need to 3D print a probe plate whenever we design a new development fixture.
Assemble the Development Fixture
Use a soldering iron to install heat-set inserts. If you do not have the inserts, pre-drill a pilot hole into the base for the screws from the probe plate.
- Screw the toggle clamp on to the probe plate
- Insert the test probe receptacles, then insert the test probes
- Use a hammer to insert the guide pins from the top.
3D printed parts may struggle with precise holes. It is helpful to have a drill or rotary tool available to ream any tight holes. If a hole is too loose, you can use glue to hold it in place.
Take the finished probe plate and use the screws to attach it to the base. Test that the Artemis board fits and while in place add the plunger to the toggle clamp so it pushed down the center of the device under test (DUT).
You now have a completed mechanical Development Fixture, quickly designed with FixturFab. The next part in this series will cover attaching the jumper wires to some entry-level test instrumentation, powering the board, flashing it with custom firmware, and running basic tests.