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Last updated on: March 25, 2024, 9:45 a.m.

Test System Development Process

Test Systems are designed to execute automated functional test plans and are most often implemented in production-level fixtures (development-level fixtures also occasionally fall into this category). Simple Test Fixture designs (mechanical-only fixtures) do not require this level of design effort.

FixturFab has developed a standard, comprehensive process for designing Test Systems that will be explored in this series of articles.

Test System Development Process

Design Phase

Design-phase
Test System Design Phase

In the Design Phase, FixturFab engineers develop the mechanical and electrical components of the Test System that were defined in the Blueprint Phase. Design outputs from both disciplines are then made available to FixturFab customers for review and approval.

FixturFab provides all final design files (STEP models, assembly drawings, schematics, board layout, etc.) in a Design File Package to the customer at the end of the project that can be used for maintenance, support, modifications, or even to manufacture additional replicas.

Mechanical Engineering

FixturFab conducts some of the most important initial engineering work on the various mechanical aspects of the Test System. Fitting exercises are completed in the Blueprint Phase to ensure the correct Test Fixture size has been selected for the project, but detailed work must now be completed to unblock the electrical engineering work that must also be done (PCBA size and mounting hole locations for the TPCBs (Test Point CArrier Board), for example).

An example render of a CAD model of a panelized fixture is shown below. In this fixture, six DUTs (Device Under Test) are tested in a single test run, so the spacing is a big design element. All components of the Test System, including the CPU subsystem and test instrumentation, are contained inside this particular example, requiring precise and thorough mechanical consideration.

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Render of a panelized Test Fixture

The interior of a Test System can be a busy place, with a multitude of power supplies, communication hubs, computers, instrumentation, various other components, and all the wiring that connects the system together. Careful planning is conducted in the mechanical realm to optimize the placement of all these internal parts and wiring pathways.

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Placement modeling for the system base

Each DUT location that can be simultaneously loaded in the Test System (one to many) has an associated mechanical stack-up made of the fixture’s probe plate, DUT guide pins, TPCB, test instrumentation, etc. Each stack-up is designed to be mechanically (and electronically) independent of each other because FixturFab’s Test Runner software framework makes it simple to run each DUT’s Test Plan in parallel, independently, and asynchronously.

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Mechanical stack-up

The back panel of the Test System provides connectivity for power, the monitor, and other peripherals (mouse, keyboard, scanner, etc.). A small fan is common to evacuate heat and normalize interior moisture levels with the surrounding environment in the event of fast temperature changes. Each back panel is customized to the particular Test System requirements.

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Mechanical Assembly Drawing for Back Panel
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Example Back Panel (Connectivity)

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Electrical Engineering

Utilizing the KiCad EDA (Electronic Design Automation) platform, PCBA schematics are prepared by FixturFab for the TPCB and other circuit boards that have been designed into the Test System. Many times, support circuits must be custom-designed to implement the customer’s Test Plan, and these generally fall into the following categories:

  • Power injection circuits (to safely power DUTs)
  • Continuity test circuits (supplies, connectors, etc.)
  • Driver circuits (LEDs, motors, relay control, solenoid control, etc.)
  • Multiplexer & demultiplexer circuits (analog & digital)
  • Voltage level shifters
  • Peripheral interfaces (memory card, etc.)
  • Networking interfaces (Ethernet, WiFi)
  • Simulated loads (battery simulation, charging)
  • GPIO control instrumentation & related circuits
  • Communication translators (USB, UART, SPI, I2C, CAN)
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Support Circuit Schematic

After the schematic review and approval by the customer, the boards undergo layout activities, a bill-of-material is created, and design files are submitted to a Contract Manufacturer for fabrication and assembly. Modern PCBA manufacturing companies can typically turn around the finished boards quickly, and they are back in the FixturFab lab in approximately two weeks or less.

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TPCB PCBA Board Layout

A 3D model of the finished PCBA is rendered and checked by FixturFab engineers to ensure it fits properly into the fixture as designed. All of the attached components are modeled to make sure we can determine if there is any mechanical interference between the PCBA and other Test System internal components.

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3D Model of a TPCB

Procurement

As soon as the various mechanical and electrical design work begins to solidify, procurement activities kick in to order any non-stock components of the Test System to ensure materials are on hand for manufacturing (CNC-machining, laser cutting, 3D printing, cabling, etc.). Common items that get purchased at this time are:

  • CPU subsystem and related components (DRAM, Drives, etc.)
  • Fixture base & blank cartridge plates
  • Rack components
  • Instrumentation
  • Electrical components for PCB assembly
  • Wiring and cabling

Next

In the next part of the Test System Development Process series, we show how FixturFab fabricates custom components and assembles all of the parts during the Manufacturing Phase.

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