The Process of Flying Probe Testing in PCB Assembly
In the realm of printed circuit board (PCB) assembly testing, a method known as flying probe testing (FPT) is gaining popularity due to its flexibility and cost-effectiveness. This innovative approach, which uses test probes that move from test point to test point, eliminating the need for a custom fixture, offers several advantages over traditional in-circuit testing (ICT).
FPT is created offline on a PC using a Test Program Generating Application. The application requires the PCB assembly's Bill of Materials (BOM) and the ECAD file in an intelligent CAD format like ODB++, IPC-2581, or native ECAD design file format.
One of the key benefits of FPT is its cost-effectiveness. Unlike ICT, which requires customized fixtures and specific test points, FPT does not need these elements. This absence of fixture costs and the ability to test boards without requiring specific test points contribute to its cost-effectiveness.
Moreover, FPT offers design flexibility. Flying probe testers can access electrical networks by probing component pads and vias, allowing for more flexible design options compared to ICT, which requires dedicated test pads. This flexibility makes FPT particularly suitable for prototypes, small batches, and designs with frequent changes.
FPT also provides rapid adaptation to design changes or new product introductions. Since it does not require specific test points or custom fixtures, FPT can rapidly adapt to design changes, making it an ideal choice for rapidly evolving industries.
However, FPT is generally slower than ICT, making it less ideal for high-volume production scenarios. Despite this, FPT offers improved test coverage over traditional ICT testing due to fewer accessibility issues and the ability to access smaller pads.
FPT can detect defects such as shorts, opens, and component values, and is also equipped with a camera to help in inspecting component polarity automatically. For SMD components, a solder pad longer than the component pin should be applied to enable the testing probe to contact the test point not on the pin but on the soldering pad itself.
FPT is highly cost-effective for prototypes and low to mid-volume production. However, for larger boards with dimensions greater than 400 mm, local fiducials concerning fine-pitch components should be placed, which must be visible after the component has been mounted. Fiducial recognition requires including 3 fiducials for each board, positioned in a triangle shape on either side of the board, with different arrangements to eliminate side errors.
At Sierra Circuits, they use Seica Spa Pilot V8 for flying probe testing. The maximum component height depends on the tester, with calculations for horizontal Pilot L4 testers being the maximum board height + components on the head side: 40 mm, including the board width, and for vertical Pilot V8 testers being the maximum board height + components on either side: 40 mm, including the board width.
In conclusion, FPT offers a cost-effective and flexible solution for PCB assembly testing, particularly for prototypes, small batches, and designs with frequent changes. Its ability to adapt rapidly to design changes and its improved test coverage make it an attractive alternative to traditional ICT testing.
The Test Program Generating Application, which is essential for FPT, receives the PCB assembly's Bill of Materials (BOM) and ECAD file. This cost-effective method, combined with its design flexibility, makes FPT a suitable choice for industries like manufacturing, where prototypes, small batches, and designs with frequent changes are common. Furthermore, FPT's rapid adaptation to design changes or new product introductions renders it ideal for rapidly evolving technology industries, such as finance and the gadget industry.
