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ICT Testing Vs Flying Probe Testing

Deciding on the best testing method for your printed circuit board can be a daunting task. There are plenty of factors to take into consideration, including costs, coverage, and development lead time. However, there are two popular test strategies you’ll often find yourself choosing between: ICT testing vs flying probe testing.

Which of the two is a better automation test solution to fully inspect whether your specific product will perform well in the market? Would it be wise to use a combination of both to achieve the desired test coverage? How complex is your design, and would it be better to consult a contract manufacturer who can offer an array of test options beyond just these two?

All these are questions you should ask yourself. Discuss your options with your manufacturer, too. Each option has its strengths and weaknesses, and your contract manufacturer can help you settle on the best one by analyzing each test’s:

  • Up-front and per-unit costs
  • Scope of coverage
  • Development lead time
  • Customization
  • Ability to adapt to varied designs

Contrasting ICT Testing Vs Flying Probe Testing

In-circuit testing (ICT) and flying probe testing offer similar coverage in their tests, discovering most manufacturing defects that often occur in printed circuit boards (PCBs). These include:

  • Opens
  • Shorts
  • Resistance
  • Capacitance
  • Component orientation

The two, however, differ on their:

  • Test time periods
  • Per-unit costs
  • Custom tooling
  • Non-recurring engineering charges
  • Digital logic testing

In-Circuit Testing

ICT is a powerful tool for PCB testing. It uses bed of nails in-circuit test gear to access the circuit nodes of a board and check the performance of each component. It can also test some functionality of digital circuits, although the complexity involved can make it economically prohibitive.

ICT is most suitable for testing products that are more developed and high-volume. However, the up-front costs and development lead time with ICT are higher and longer, respectively, than those of flying probe testing (FPT). This is because your manufacturer must explicitly create a custom tool for each PCB.

The good thing with ICT is that after the tool is developed, costs per unit tend to be lower than with FPT because it only takes about 1 minute for one test cycle. With FPT, it can take up to 15 minutes per board.

Strengths

  • Quick tests per PCB unit
  • Lower costs per unit than FPT
  • Checks for shorts, opens, resistance, capacitance, and component tolerance
  • Tests components individually
  • Tests for logic functionality
  • Capable of performing on board verification FPGAs
  • Can be set to turn on and test LED components – say by enabling verification of color and brightness
  • Ability to check the integrity of BTC components' soldering using a pressure test

Weaknesses

  • Long development lead time
  • High up-front costs
  • Programming and custom tooling are required
  • Doesn’t test connectors or non-electrical components
  • Doesn’t test components working together

Flying Probe Testing

ITC testing vs flying probe testing 2

(Photo courtesy Doxals)

Unlike an ICT machine, an FPT does not utilize a bed of nails fixture. Instead, it uses a small number of movable and fixed probes to easily make a simultaneous in-circuit test of the top and bottom of your PCB. It’s made up of high-precision needles -- some machines use as few as four needles, while others can use as many as 20 per PCB side. They’re programmed to contact component pins and perform electrical and functional tests to determine if the board is fit for the field.

FPT is most suitable for products that are in the early stages of development and are low-volume orders. It requires no custom tooling, and customization for each PCB is carried out through programming using the CAD data you provide to the manufacturer. With FPT, costs-per-unit are higher compared to ICT because of longer test cycle time periods per board (up to 15 minutes).

Strengths

  • No custom tooling needed
  • Programming requires less time
  • Checks for shorts, opens, resistance, capacitance, and component tolerance
  • Tests components individually
  • Low up-front costs
  • Ability to test LEDs
  • Capable of performing on board verification FPGAs

Weaknesses

  • Higher cycle test period times and cost-per-unit costs
  • Doesn’t test connectors or non-active components
  • Doesn’t test components operating together

Which Suits Your Project?

All in all, the choice between ICT and FPT will depend on several important factors of your project. To recap, these include:

  • Expected volumes
  • Budget
  • PCB design/complexity
  • Lead development times

Remember to consult a well-rounded contract manufacturer for professional guidance. There may be other PCB testing and inspection options that are better suited to your design.

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Author: Matric