28

September

During the printed circuit board (PCB) manufacturing process, we need to ensure the quality of each board. Therefore, every bare or assembled board (PCBA) must undergo rigorous electrical testing before it leaves Apple's PCB manufacturing facility. These tests detect circuit problems such as shorts, opens, and faults in resistors and capacitors to ensure high performance in the final application. Flying probe testing (FPT) is one of these efficient and accurate test methods. In this article, we will explain the flying probe testing, including application scenario, test procedure, application cost and the importance of FPT for PCB manufacturing.

What Is Flying Probe Test in PCB Manufacturing?

Unlike traditional bed-of-nails fixture testing methods, flying probe test utilize movable probe to test electrical connections on PCB without the need for fixed fixtures or tools, which is why it is also known as fixtureless in-circuit testing. The positioning accuracy and repeatability of the probes range from 5μm to 15μm, allowing accurate detection of short circuits, open circuits and component values.

In addition, it is equipped with a specialized camera to check component problems (e.g. missing, wrong polarity). As a result, flying probe testing for PCB offers comprehensive electrical coverage and high-precision probe positioning, making it ideal for prototypes and small-lot board testing.

Key Components of a Flying Probe Tester

To get an in depth understanding of the workflow of flying probe testing, we should first understand what a flying probe tester is. A flying probe tester is made up of four key component. They are the motion system, the probe drive unit, the probe control software and most importantly the flying probe head.

● Motion System

The motion system consist of XYZ axe: the XY-axis load table provides precise positioning of the probe head, while the Z-axis controls the force to ensure proper contact force during probing.

●Probe Drive Unit

This unit is equipped with a signal generator, DC and AC power supplies, various types of sensors, a digital multimeter, a frequency counter, and more. As a result, it can generate test signals to be applied to PCBs, measure the electrical response of circuit boards, and be able to check for short circuits, open circuits, impedance, and other problems.

●Probe Control Software

Probe control software can create test sequences on its own using the PCB CAD information to optimizing the probe route and testing frequency for efficient testing purposes.

●Probe Heads

Probe heads generally have 4 to 16 flying probes. There are four types of flying probes, namely vertical probes, Cobra probes and MicroSprings series. ApplePCB uses the most advanced MicroSprings, which is a compact spring-loaded probe capable of probing at ultra-fine pitches and suitable for pad sizes down to 25μm.

PCB Flying Probe Tester VS PCBA Flying Probe Tester

The fact is that flying probe testers were initially designed to test the electrical capabilities of PCBs, but as flying probe testers continue to evolve, they are gradually being utilized for PCBAs. Next we will introduce in detail what are the differences between PCB flying probe testers and PCBA flying probe testers.

PCB flying probe tester specializes in testing unsoldered components of the PCB electrical connectivity and reliability. It usually uses high-speed moving flying probe to contact the test points on the PCB to conduct electrical testing, mainly relying on program settings and test point arrangement. Therefore, it has high flexibility and can test PCBs of different sizes and shapes.

The test content of PCBA flying probe tester is more complex, which includes the soldering quality of components (e.g. false soldering, short circuit), polarity correctness, and installation correctness. There may also be additional electrical tests (analog signal tests), functional tests, power-up tests, and so on. In addition, due to the presence of components, the trajectory of the flying probe needs to be set more precisely to avoid scratching the components. Therefore, PCBA testers require more software support and hardware configurations, which are more difficult to test and require more elaborate test solutions.

How Does Flying Probe Test Work?

1. Test Program Creation

This process is similar to creating an SMT program. The test program needs to be generated on the PC before flying probe testing. The user needs to prepare the Bill of Materials (BOM) and ECAD file for the board components.

It is important to note that the BOM needs to be provided in Excel format, and the ECAD file needs to be in ODB++, IPC-2581 format, or in the native ECAD design file format. So that the subsequent can be loaded into the FPT tester smoothly.

2. Load Test Program

The generated test program is loaded into the probe control software of the FPT tester. The board or array of boards to be tested is placed on a conveyor belt to be moved to the test area.

3. Test Program

When the test program is running, the probes are controlled by the program to “fly” and contact several defined test points such as pads, vias, etc., and apply electrical signals and power to them for testing.

The preferred test points are solder mask free pads, holes, PTH and SMD component pads. The minimum test point size is 6 mil (depending on the probe type), and the spacing between two test points should be at least 10 mil. hole diameters should range from 8-20 mil, with 10 mil being optimal.

4. Generate Data

These measurement will be processed within the tester to determine if the circuit data is within the preset tolerances. With the data, we are able to clearly identify if there are any defect on the board.

Flying Probe Test vs ICT

In addition to flying probe testing, there is another common test method for circuit boards: in-circuit testing (ICT).The main difference between ICT and flying probe testing is that ICT require a customized test rack for each PCB. In the table below, ApplePCB provide a visual comparison of these two test method from seven perspective.

What Factors Affect the Price of Flying Probe Testing?

1. Initial Investment

The initial investment for flying probe testing usually includes the purchase and installation of the equipment and this cost can be affected by a number of factor:

• Number of probes: the more probes installed on the equipment, the higher the speed and efficiency of the test, but it will also increase the initial cost of the equipment.
• Maximum board size capacity: The larger the PCB size capacity of the flying probe test equipment, the overall price of the equipment will increase accordingly.
• Measurement capability: High precision, wide frequency range measurement capability can better meet the need of complex PCB testing, but will lead to higher equipment costs.
• Software features and customization options: Some advanced flying probe tests will have features such as capacitive coupling, thermal imaging, high-frequency testing, and data integration. More advanced software may support faster test programming and diverse test functions, but will also increase the purchase and maintenance cost.

2. Operating Costs

In addition to the initial investment, flying probe testing come with ongoing operating cost, including:

• Probe Tip Replacement: As the frequency of use increase, the probes wear out and require periodic replacement of the probe tip, especially when operating frequently on HDI PCB.
• Software update and maintenance: Software need to be updated regularly to maintain compatibility and functionality, and may also involve technical support and maintenance costs.
• Operator training: To ensure efficient use of flying probe test equipment, operator need regular training to keep up to date with the latest software features and operating procedure.
• Energy consumption: Although the operation of flying probe test equipment does not consume a lot of energy, energy consumption is still part of the operating costs during long production runs.

3. PCB Complexity

While flying probe testing is indeed flexible and can effectively cover tightly designed area and test them accurately, as PCB complexity increases, so does the cost of testing. This is because more complex boards mean more test points, more delicate probe operations, and longer test times. All of these factors increase the load on the test equipment, which leads to higher costs.

The Importance of Flying Probe Testing in PCB Manufacturing

Flying probe testing play a vital role in PCB manufacturing, especially in detecting electrical capabilities and manufacturing defect in circuit boards. Its key role includes:

1. Diversified Detection Capabilities

Flying probe testing not only detects common problems such as open circuits, shorts, and resistances, but also checks more complex parameters such as capacitance, isolation, component polarity, and inductance of individual parts. This gives it a significant advantage in the overall quality inspection of complex circuit boards. Here are the specifics of what ApplePCB's flying probe test can detect:

2. Flexibility and Adaptability

Flying probe test probes can move flexibly according to the design of the PCB to quickly detect dense or hard-to-reach areas. This flexibility allows flying probe testing to adapt to a variety of different types of PCB, effectively reducing the leakage rate. Below are specific benefit of flying probe testing for several common PCB type:

High Density Interconnect (HDI) PCBs

• Accurately testing fine-pitch components and microvias
• Testing blind and buried vias
• Non-contact testing (for sensitive areas)

Multi-layer PCBs

• Access to inner test points (through vias)
• Possibility to test multilayer PCB interconnection networks

Flexible/rigid-flexible PCBs

• Avoids damage to flexible substrates
• Adaptable to flexible PCB testing with different shapes and curves

Large Size PCBs

• No panel size limitation
• Tests large boards more efficiently

3.Component friendly

In modern electronic products, PCB often include many precision components, such as microchips and opto electronic components. These components are very fragile and traditional testing methods may damage the components during contact. The non-destructive nature of flying probe testing mean that no damage is caused to the board and its components during testing.

Advantages of Flying Probe Test of ApplePCB

After equipment update and technology upgrade, ApplePCB's flying probe tester not only have the basic functions mentioned above, but are also equipped with many advanced testing technology.

1. Multi-Probe Systems

ApplePCB's modern flying probe testers are typically equipped with 8 probes(4 top and 4 bottom), offering the following advantages:

• Simultaneous testing of multiple points: The multi-probe system can access multiple test points at the same time, which greatly reduces testing time and improves inspection efficiency(up to 180 cycles/second).
• More complex measurement and comparison: Multiple probes are also able to handle the comparison and analysis of complex circuit, adapting to higher technical requirement.

2. Non-Contact Testing

In order to ensure the protection of sensitive components, the flying probe test of ApplePCB adopts non-contact testing method, which is especially suitable for testing point that are hard to reach or easily damaged. Advanced non-contact techniques include:

• Capacitive coupling: this technique is particularly suitable for testing component that are difficult to physically contact, ensuring that their electrical capabilities are not compromised.
• Thermal Imaging Detection: Flying probe testers are able to detect thermal anomalies on power supply board through thermal imaging, quickly identifying potential overheating problem.

3. High Frequency Testing

For RF and high-speed PCB, ApplePCB's flying probe test use specialized probes that can accurately detect the capabilities of these complex circuits to ensure the integrity and stability of signal transmission.

4. Advanced Testing Functions

In addition to some conventional testing, ApplePCB's flying probe test also supports some more advanced test functions:

• Phase Difference Measurement Unit (PDM): Measure the phase difference between the reference line and the signal line by sending a highfrequency signal between the two. Avoid the need for more complex isolation tests within the network.
• High Voltage Stress Test (HVS): A method for detecting high resistance isolation defect. By applying highvoltage pulses between signal lines, HVS quickly identifie high-resistance problems that may not be detected by PDM.
• Micro Short Circuit Detection: During isolation testing, the sudden application of high voltage can cause damage to the board, while micro short circuit detection avoid this problem by gradually increasing the voltage. Through this method, ApplePCB is able to detect high resistance shorts located between multiple layers.

5. Automatic Optical Inspection (AOI) Integration

ApplePCB combines flying probe test with AOI function, which reduces the time of a single test process and greatly improves the test efficiency.

6. Industry 4.0 and Smart Factory Integration

ApplePCB's flying probe test system follows the trend of Industry 4.0, and our smart factory in Chongqing has the following advantages:

• Data Integration: Connection with MES (Manufacturing Execution System) and ERP (Enterprise Resource Planning) systems ensures smooth articulation of the entire manufacturing process.
• Remote Monitoring: Supports real-time monitoring and control of the testing process, ensuring instant feedback on test progress and quality.
• Predictive Maintenance: By analyzing test data, it can predict potential equipment problems, prevent equipment failures in time, and reduce production downtime.

Final Thoughts

PCB flying probe test is necessary for prototypes and low volume production, and it can be considered as a solid line of defense to ensure the final quality of PCB. ApplePCB has 15 years of experience in PCB and advanced production equipment, can provide reliable PCB for customers in a wide range of industries. If you're interested in learning more about PCB flying probe testing service feel free to reach out to us at your convenience.