Optimizing PCBA Quality: Flying Probe Testing in the AI and HPC Era

Flying probe testing can be divided into two main types:

(1) BBT Flying Probe Testing

Flying probe testing for bare PCBs, referred to as BBT (Bare Boards Test), involves conducting continuity measurements using flying probes on PCBs that have not yet had components mounted. This process aims to identify defects such as opens and shorts between each circuit, thereby enhancing product reliability inspection.

(2) ICT Flying Probe Testing

ICT Flying Probe Testing, abbreviated as ICT (In Circuit Test: PCB with components), refers to test PCBs with components already mounted, which is a key application of flying probe testing. It enables precise measurement of various electrical values between component pins and solder joints, accurately distinguishing between good products, open or cold solder joints, and component abnormalities. The scope of ICT testing includes various components, primarily including resistors, capacitors, diodes, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), jumpers, relays, and voltage regulators. This testing method allows for determining whether individual components on the PCB have failure occurring during the assembly process, providing important test data to ensure manufacturing quality and proper functioning of components.

Below, we will outline how iST ICT flying probe testing service provides engineers with fast testing and feedback during the reliability testing phase, thereby shortening product time-to-market and enhancing competitiveness.

(1) The Three Key Advantages of iST’s ICT Flying Probe Testing

1. No Need for Custom ICT Fixtures:
   iST’s ICT flying probe testing program software is highly flexible and can quickly adapt to various requirements. There is no need to develop custom ICT fixtures to complete PCBA testing. Even when the PCBA needs to be modified or when certain passive components need to be added or removed, there is no need to modify the fixtures, thus saving a lot of time and reducing additional cost expenses.
2. High Test Coverage:
   iST’s reliability laboratory achieves relatively high ICT flying probe test coverage through appropriate test program and fixture designs, ensuring comprehensive testing. Particularly in the face of challenges posed by hardware interference during PCBA functional testing and connectivity testing, well-designed test programs and fixtures are key to increasing coverage.
3. PCB Deformation Compensation Mechanism:
   Considering the possibility of minor deformation (warpage) during PCB manufacturing that may affect flying probe testing, iST’s ICT flying probe testing utilizes laser scanning technology. This technology compensates for probe penetration depth by scanning PCBs in sections when there is bending, ensuring the accuracy and reliability of flying probe testing.

(2) Four Key Timing for Using Flying Probe Testing

1. Verification of Component Functionality in the Manufacturing Process:
   Flying probe testing can be utilized after surface-mount technology (SMT) assembly of passive and active components. Through tests such as power-on testing, connectivity testing, and component testing, it ensures whether the components are functioning properly, thereby avoiding the use of damaged or faulty components in tests. It also helps identify and filter out problems with components on the assembled PCB (PCBA), increasing manufacturing yield and further ensuring overall quality in the reliability testing.
2. Troubleshooting:
   In case of defects during test, flying probe testing can assist in troubleshooting the assembled boards. When component quality concerns arise, or when running different batches of test units with the same boards. The flying probe test record before the tests (T0) can be used to compare and analyze any data discrepancies. Additionally, ICT flying probe testing is also applicable for inspecting and repairing faulty boards during rework processes.
3. Aging Status Check of Burn-In Boards (BIB):
   After undergoing high-temperature test for a period of time, both the boards and components may inevitably experience aging issues. Flying probe testing can be used to compare the test data before the tests to identify aging components.
4. Test Phase:
   In the qualification of automotive electronic products. The Board Level Reliability (BLR) tests aim to evaluate the reliability and durability of semiconductor components after surface-mount technology (SMT) assembly. During this phase, ICT flying probe testing can also be utilized to compare measurement values before and after tests. For tests involving high repeatability such as high temperature, high humidity, and high vibration tests, ICT flying probe testing can quickly conduct measurements. Consequently, it is less affected by external environmental factors and changes, optimizing the reliability and quality of the manufacturing process.

Next, we will share how iST’s reliability laboratory utilizes ICT flying probe testing to identify defects on components mounted on PCBs. Below, we will illustrate this through four major case studies.

(1) Pin-to-Pin Short Circuit Issue

When abnormalities such as circuit short are discovered in a product, it is necessary to confirm whether it is due to defects in the PCB itself or caused by components. In this case (Figure 3), it is a Pin-to-Pin short circuit issue, which is difficult to identify with the visual inspection. However, by using flying probe testing to test the circuits on the PCB, it is easy to pinpoint which circuit has a short circuit. In comparison, manual inspection would require a significant amount of time and cost. Utilizing a flying probe machine can quickly and accurately detect the problem.

Another case (Figure 4) involves defects of short circuit found on the pins of a socket (chip test socket). After using flying probe testing to rule out the abnormalities on the PCBA, it was ultimately discovered that the issue lied with the socket.

(2) Passive Component Damage Results in Abnormal Resistance Values

Damage to passive components on the PCBA can result in abnormal resistance. Using conventional methods to customize ICT testing fixtures can take days to weeks. However, by employing ICT flying probe testing, probes can accurately contact with test points on the components under test, enabling rapid measurement of passive components (resistors, capacitors). This approach swiftly identifies whether component values are abnormal.

(3) Mis-assembly of Jumpers Results in Abnormal Continuity

In advanced manufacturing processes, electronic components on PCBA are typically intricate and densely packed. Even the absence of just one jumper can result in defect. In such cases, using flying probe testing for open and short circuit tests provides a precise method to test the connectivity between various connection points, allowing for the rapid and effective identification of the issue. Once the problematic open or short circuit points are identified, resolving the problem merely requires replacing the jumper, eliminating the need for extensive inspection of the entire PCBA. This saves time and labor costs.

(4) Soldering Issue Results in Abnormal Voltage Values

During iST’s reliability laboratory’s ICT flying probe testing for voltage regulator measurements. The flying probe machine has the capability to detect abnormalities in conductivity. This allows for the precise identification of soldering issue on the IC pins.