Design For Test (DFT)

In-Circuit Test (ICT) has remained one of the most popular and cost-effective test methods for medium and high volume electronic printed circuit board assembly (PCBA) for many years. This is due to its component level fault diagnosis capability and its speed.

ICT checks each component on a PCB individually, delivering highly reliable results. It detects defects such as faulty, wrong or missing components, solder bridges and short circuits. While investing in this solution requires a larger initial upfront cost when compared to flying probe, the cost per unit is negligible (often less than £1) due to the swift test time (usually less than one minute).

The ICT method comprises a test fixture and program dedicated to the target test platform and unit under test (UUT). In order to optimise the effectiveness of the test, the circuit design and layout of the PCBA itself must be suitable for ICT. Therefore, design for test (DFT) is an integral stage of PCB realisation; without taking this phase into account, you will not be able to get the most from your test strategy.

Investing in an ICT solution can help your business to consistently deliver fully functional PCBs, on time and to specification. The time and money saved can be redirected back into other core aspects of your operation.

 

Basic DFT requirements

Fixture Type

Recommended Test Pad Size

Standard Fixture

0.024”

Standard fixture with funnel top plate

0.022”

 

Probe Spacing

Combination

Spacing

0.100” – 0.100”

0.081” (2.05mm)

0.100” – 0.075”

0.074” (1.88mm)

0.100” – 0.050”

0.066” (1.68mm)

0.075” – 0.075”

0.067” (1.70mm)

0.075” – 0.050”

0.059” (1.50mm)

0.050” – 0.050”

0.050” (1.27mm)

 

Probe to Component Spacing – based on 0.100” probes

Components under 0.125” (3.175mm)

Minimum distance of Test pad centre to component edge 0.039” (1mm)

Components over 0.125” (3.175mm)

Minimum distance of Test pad centre to component edge 0.050” (1.27mm)

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