Unlocking Efficiency with IC Decapsulation in Printed Circuit Boards
Admin, January 25,2024
Flying Probe Test in Printed Circuit Boards
Printed Circuit Board Repair
Flying probe is a technique to test a printed circuit board and these probes fly or move to test various points on the board that’s why the name is so. The flying probe test involves software to send instructions to the probes to move around. In other words, it is a fixture-less test and ideal for small productions.
Manufacturers have to test the quality of the PCB before bringing it to the market. There are many ways to test circuit boards of which the flying probe is quite common. Let’s discuss it in detail in the below section.
Flying Prob Testing Process
The flying probe test involves a machine equipped with multiple probes that can move freely across the PCB. These probes are controlled by software that directs them to contact specific points on the board.
The machine measures electrical properties at each contact point, such as resistance, capacitance, and continuity, to determine if the circuit is perfect in terms of function.
Engineers prepare a machine with several probes to move on the PCB. The software controls the probes, instructing them to connect with certain parts to be inspected. The tool checks each point’s current and other properties, including capacitance, single integrity, resistance, etc. The test helps us to see if the board is functioning well or not
Creating a Flying Probe Test Program
You have to prepare the FTP application that depends on the BOM of the circuit board and an ECAD data or file. You can’t create it with just Gerber as the ECAD should be in specific formats, including IPC-2581 or ODB++format, as well as Altium, Allegro, or PADs format in the case of native ECAD.
After creating the test program, engineers install it on the tester. After that, they place the PCB on a belt to help it move in areas that need testing. Now, you can run the test program to contact the components and vias determined by the test program. The tester will provide the test signals and current to the parts to be tested, making the measurements. The tester processes the measurements to test the function of specific components within the required parameters.
Hence, the flying probe test detects the faults in the PCB. The testing hardware or a machine consists of power supplies (AC and DC), different sensors, signal generators, multimeters, frequency counters, or a multiplexing unit. All these elements help give signals to activate the nodes, as well as measure various parts’ nodes. Moreover, you also have to measure the interconnections in terms of a circuit board’s assembly.
The activation of signals helps an FPT to separate the PCB components from the remaining PCB interconnections. Such a virtual separation helps probes to accurately measure the values of the parts, keeping them intact on the circuit board. In other words, the test does not affect the connection of the components on the board.
The flying probe test also helps test shorts, as well as opens. There is also a camera in an FPT to automatically check the component polarity. The camera helps closely view the unit under test (UUT) to check for any missing elements or flaws.
You can also test integrated devices in terms of diode impedance though the FPT performs other tasks. The latest tests can also measure the IC pads through capacitive probing like in wireless devices such as BGAs and QFNs
What Are The Benefits Of Flying Probes
There are many advantages of flying probe testing compared to other PCB testing methods. Let’s discuss them in detail.
1-Minimum Testing Time
The test time is lower than other methods because flying probes are fast tools in terms of movement. Even, the test involves less time in the case of retesting.
2-Fast Feedback
Since FPT is speedy, the testers provide fast results. Eventually, engineers get fast feedback to proceed with a speedy development. In other words, you almost get instant results.
3-Many Testing Options
You can get many testing currents through a flying probe test, including AC and DC power supplies and signal generators.
4-Low Cost Test
The FPT does not cost much in terms of setup and function. You can use it for smaller jobs, besides, the probes are adaptable according to the circuit boards. All these qualities make flying probes cheaper than other tests in terms of operations.
Flaws of Flying Probe Technique
Nothing is perfect, hence flying probe has its disadvantages, such as:
- Flying probes can physically damage the board as they get in contact with components while moving across. It often skims the surface of the circuit board, creating dents, and misleading the technician as he might consider it a manufacturing fault.
- It can skip poor connections created by pads. Such parts look functional but it is not so as poor soldering gets more attention from the tester.
- Though the setup time is fast in the case of a flying probe, the testing time is more than ICT or AOI, automated optical inspection. The probes have to run to every test point which increases the process time in the case of bigger boards having multiple test points.
However, the above issues can’t reduce the importance of the flying probe test as the best option.
Comparison Between In-Circuit Testing (ICT) and Flying Probe Testing
Both ICT and flying probe testing methods test the individual parts using pins. ICT has been in the PCB industry for years, and engineers know its nature. You have to look at both positive and negative aspects of flying probes, depending on your project. Let’s see the difference between ICT and FPT in detail.
Compatibility With The Circuit Board
Flying probe pins are compatible with the PCB components as they can easily move around due to their smaller size. They can fit in any test pad. Whereas, the ICT pins are bigger and don’t fit all types of PCBs. You have to customize the pins in the case of ICT to make it compatible with the project.
Testing Cost
As already discussed, the flying probe is cheaper than other testing techniques, including ICT. Since FPT depends on software, it goes well with all types of PCB layouts and sizes. You only need the correct CAD data to perform the flying probe test. Whereas, ICT is costly due to customization. ICT suits large productions, however, flying probes are still economical.
Flexible Setup
Flying probe is a flexible option as it goes well with different layouts. But, ICT needs a compatible setup in every case. You have to reconfigure the pins every time a new PCB comes to you for testing. Hence, ICT is not an ideal option for testing different boards. But, it is good for inspecting different units of a single circuit board.
In the case of flying probes, you can program the pins faster according to the board. So, altering the pins becomes fast in a short time for each circuit board.
Access Points
The flying probes can easily access the components without needing special access. Hence, there is no need to create a circuit board according to the inspecting parameters. On the other hand, you have to make compatible testing points for each circuit board to help pins reach the components and test them.
Though in-circuit testing is a standard testing method for circuit boards, the flying probe is getting popular due to evolving technology. You should choose the flying probe test if you are searching for a cost-effective and fast testing option.
Frequently Asked Questions
What is a Flying Probe Test?
Flying probe is a method to test a printed circuit board. The probes fly or move to test various points on the board, hence the name flying probe.
What is ICT in Printed Circuit Boards?
In-circuit testing or ICT is a method to test a printed circuit board. Engineers also call it the bed-of-nails test, as it involves nails or pins.
What is AOI in Printed Circuit Boards?
AOI is an Automated Optical Inspection method for printed circuit boards. A camera visually tests a circuit board during manufacturing.
How Engineers Program Flying Probes For PCB Testing?
Engineers prepare the FTP application that depends on the BOM of the board and ECAD data. The file format includes an IPC-2581 or an ODB++ format, as well as Altium, Allegro, or PADs format, depending on the software.
Final Thoughts
A flying probe test in a PCB is an effective testing technique. It is cheap, flexible, and faster in terms of setup. Though the testing time is higher than other PCB testing methods, FPT is ideal for low-volume projects.
The probes detect the faults in the PCB. The testing hardware or a machine consists of power supplies (AC and DC), different sensors, signal generators, multimeters, frequency counters, or a multiplexing unit.
It also helps to test the shorts, as well as opens. There is also a camera in an FPT to automatically check the component polarity. The camera helps closely view the unit under test (UUT) to check for any missing elements or flaws.
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