How Much Do You Know About Flying Probe Test

This Gold Phoenix PCB Knowledge Center article explains the flying probe test, including its definition, working principle, advantages, and disadvantages for PCB fabrication and assembly.

What Is Flying Probe Test?

Flying probe testing can be regarded as an evolution of bed-of-nails fixture testing. A flying probe tester uses movable probes instead of a fixed bed-of-nails fixture. Probe assemblies move along the X-Y axes to access test points on the unit under test (UUT).

During testing, the UUT is transported into the tester, and probes contact test pads and vias to identify defects. The probes can be connected through a multiplexing system to test equipment such as signal generators, power supplies, digital multimeters, and frequency counters. When a component is tested, other components on the same UUT can be isolated from the measurement to reduce interference.

Flying probe testers can test shorts, opens, and component values. A camera can also help identify missing components and inspect component polarity. Probe positioning accuracy and repeatability in the source material are specified in the range of 5 μm to 15 μm.

How Does Flying Probe Tester Work?

Flying probe testers can be programmed more easily and quickly than traditional ICT systems for many applications.

To implement flying probe test programming, testing personnel first convert CAD (computer-aided design) data supplied for the PCB into applicable test files. The generated files are then processed by the test program to create the formats required for the UUT test.

After programming is completed, the required test item is selected, such as a shorts test. Reference-point data corresponding to the UUT is obtained from the CAD data. Once the UUT is fixed on the test platform, the test program can inspect fabrication or assembly issues.

Debugging should be completed before official testing. The source material notes that flying probe test debugging can be completed in a shorter time than conventional ICT test debugging.

Advantages of Flying Probe Test

Based on its definition and working principle, flying probe testing has several advantages:

• Short test development cycle.

• Relatively low test cost.

• High conversion flexibility.

• Rapid feedback for PCB design engineers during prototyping.

Compared with conventional ICT, flying probe testing can require less overall test preparation time. For PCB assembly prototyping, testing can begin relatively soon after CAD data is received and the assembly is completed. Programming and setup are also comparatively accessible.

Disadvantages of Flying Probe Test

Flying probe testing also has limitations.

Because flying probes make direct physical contact with vias and test pads, small marks or pits may be created on the board surface. Some OEMs may regard these marks as fabrication defects.

When a component does not have a dedicated test pad, probes may contact its leads. Loose leads or poorly soldered leads may therefore be missed in some situations.

Despite these disadvantages, flying probe testing remains an important test method for PCB fabrication and assembly.