Building a low-cost Test Fixture Guillaume Vier Agenda - - PowerPoint PPT Presentation

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Building a low-cost Test Fixture Guillaume Vier Agenda - - PowerPoint PPT Presentation

Sep 02, 2023 740 likes •954 views

Building a low-cost Test Fixture Guillaume Vier Agenda Background Motivations Architecture Bed of nails Test Controller Flasher Conclusions 2 Background Ubidata founded in 2003 in Brussels

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Building a low-cost Test Fixture

Guillaume Vier

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Agenda

  • Background
  • Motivations
  • Architecture
  • Bed of nails
  • Test Controller
  • Flasher
  • Conclusions

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Background

  • Ubidata founded in 2003 in Brussels
  • Telematics and mobile logistics solutions
  • We design and build our own battery-powered

tracking device

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Motivations

  • Functional testing at the end of the assembly line
  • Run self-test on each PCB
  • Program production firmware
  • Small form factor:
  • PCB: 67 mm x 36 mm
  • Test points: ø 0.6 mm, spacing 1.27 mm

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Motivations

Standard test fixture (€€€)

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Can we build something cheaper with off-the-shelf components?

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Architecture

  • Bed of nails: custom PCB + soldered test probes
  • Test controller: Raspberry Pi Zero
  • Flasher: OpenOCD

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Bed of nails

Custom PCB to:

  • align the Device Under Test over the probes
  • connect test points to larger header

PCB designed with KiCad

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Bed of nails

Step 1: schematics

  • wire test probes to a larger connector

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Bed of nails

Step 2: create custom footprint for probe Constraints:

  • manufacturer’s capability:
  • pad to pad spacing
  • annular ring size
  • Test points spacing
  • Probe diameter

Pad size: 1.1 mm x 2 mm, ø 0.75 mm

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Bed of nails

Step 3: PCB layout

  • DUT’s edges drawn on silkscreen layer
  • Test points’ coordinates extracted from DUT’s gerber

files

  • Set origin point for the grid on new layout
  • Place footprints with:
  • Position Relative To… -> Use Grid Origin

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Bed of nails

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Bed of nails

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Bed of nails

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Test Controller

  • Raspberry Pi Zero running TinyCore
  • Minimal Linux system
  • Runs from RAM
  • Test scripts written in Python
  • Communicate with DUT via UART

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Test Controller

Pimoroni Automation pHAT:

  • 1 relay -> Supply power to DUT
  • 3 ADCs -> Measure voltage rails

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Flasher

  • Connect to microcontroller via SWD
  • OpenOCD compiled with GPIO bitbang support

./configure --enable-sysfsgpio --enable-bcm2835gpio

  • Running on the Pi Zero
  • Define pins for SWD in script

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Conclusions

Standard Low-cost Bed of nails 3000 € - 6000 € 2 PCBs: 24 € 13 probes: 18 € Others: 20 € Test controller 100 € RPi Zero + pHAT: 25 € Flasher 2 x 300 € 0 € Total 3700 € - 6700 € 87 €

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Cost comparison

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Conclusions

  • Cheap
  • Robust
  • Easy to build/replicate

Limitations: not suited if special probes required (e.g. RF probes)

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Assembly

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References

  • Test probes P50 series:

https://be.farnell.com/fr-BE/multicomp/p50-e-120-g/levier-large-point/dp/1568259

  • Automation pHAT from Pimoroni:

https://shop.pimoroni.com/products/automation-phat

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