Modern manufacturing strategies drive continuous improvement in ICT online testing

By: Choon-Hin Chang, Product Marketing Manager, Keysight Technologies

Printed Circuit Board Assembly (PCBA) manufacturers rely on in-circuit test (ICT) systems to detect defects in manufacturing processes and components. Manufacturers tend to use ICT systems to test electronic components because they are easy to program, can easily identify various faults, and have many advantages such as high test throughput, low false alarm rate, and high fault diagnosis accuracy.

In recent years, PCBA technology has continued to advance, testing concepts have continued to evolve, and the business model of the manufacturing industry has also been constantly changing. The resulting series of impacts have caused major changes in the industry landscape of ICT systems. These changes have put forward many new and diverse requirements for ICT manufacturers, prompting them to constantly explore ways to break through. In particular, in specific product areas, the number of test access points has continued to decrease. At the same time, low-voltage differential signal integrated circuits for high-speed signal transmission equipment and ball grid array packaging devices are becoming increasingly popular, and the test challenges that come with it are becoming more and more severe. These complex situations have prompted ICT manufacturers to actively innovate and change with the times to ensure the effectiveness of their test solutions and their applicability to different application scenarios.

This Keysight-signed article explores the latest advances in ICT and how these technology advancements are revolutionizing manufacturing test by expanding in-circuit test coverage, improving reliability and throughput, and ultimately reducing costs.

A comprehensive look at the “ICT system”

In the late 1970s, the introduction of in-circuit test (ICT) systems during production became an important milestone in the development of the electronics manufacturing industry. The industry landscape at that time was completely different from today: printed circuit board assemblies (PCBAs) generally used socket technology, and all components were placed on one side of the circuit board; and the power supply voltage of these circuit boards usually did not exceed 15V. During this period, functional testing during the manufacturing process was a complex and time-consuming task.

In the electronics manufacturing industry, precision and high efficiency are indispensable core elements. With the continuous advancement of technology and the ever-changing consumer needs, the importance of strict and precise testing methods in the manufacturing process has become increasingly prominent. Among the many testing methods, in-circuit testing (ICT) has become a powerful guarantee for ensuring the quality and reliability of printed circuit board assemblies (PCBA) with its unique advantages. The advent of the ICT system has brought about a disruptive change in PCBA manufacturing: the evaluation focus of the entire testing process has shifted from the inspection of the overall function of the circuit board to the detailed evaluation of the functionality of individual components, while also ensuring the rigor and integrity of the entire assembly process.

As shown in Figure 1, the ICT system uses a bed of nails test fixture to evaluate the functionality of the circuit board. The fixture consists of multiple spring test probes, the positions of which precisely correspond to the test points on the printed circuit board assembly (PCBA). During the test, the tester only needs to place the PCBA to be tested on the bed of nails and gently press down, and the test probes will come into close contact with the test points or leads of the components on the PCBA, allowing the tester to inject signals and power at specific locations on the PCBA, while accurately measuring electrical characteristics and response parameters, including resistance, capacitance, inductance, and voltage levels.

With powerful electrical test access capabilities and innovative circuit protection and voltage output technologies, ICT test systems can accurately test each component. The test results obtained help verify the connection status of components and check for manufacturing defects such as open circuits, short circuits, or incorrect component values. The underlying basic principle is that as long as the ICT system can verify and confirm that all components are operating normally and the assembly process is correct, manufacturers can fully trust the functional performance of the circuit board.

Figure 1: Bed of Nails ICT Test Fixture

Coping with the complexity and diversity of testing

With the rapid development of technology, printed circuit boards (PCBs) are evolving towards smaller and more complex directions, which undoubtedly increases the difficulty of ensuring comprehensive electrical performance testing. On the one hand, low-voltage differential signal integrated circuits are widely used in high-speed differential signal transmission; on the other hand, the use of ball grid array (BGA) packaged devices is also increasing, and the input/output speed is also constantly increasing. These changes together constitute new challenges. In order to adapt to this development trend, manufacturers have begun to carefully create complex high-density interconnect circuit boards. These circuit boards not only use concealed and buried through-hole designs, but also reduce track spacing and reduce the copper area of ​​the entire board for electrical test access.

在满足技术需求的同时，ICT系统的制造商还积极调整自身以适应日新月异的测试理念并抓住新的业务驱动因素。然而，ICT供应商在努力满足各制造商多样化需求的过程中也面临着诸多挑战。毕竟，每位制造商对于ICT系统的要求都各具特色，对于系统功能的期望也各不相同。举例来说，利润比较低的制造商往往更注重寻求具有成本效益高的ICT解决方案；而那些生产可靠且复杂产品的制造商，则要求ICT解决方案具备全面的故障诊断覆盖范围以及更多的引脚数量；对于大批量生产的制造商而言，他们期望的是测试吞吐量的显著提升；至于采用外包模式的制造商，他们则更加看重设备的兼容性。

Over time, ICT suppliers have been able to successfully meet a variety of different and even conflicting customer needs by providing multi-layered ICT systems. As shown in Figure 2, this strategy allows manufacturers to obtain precisely the test functions they need and can flexibly adjust and expand them according to actual needs without making any changes to the test equipment itself.

However, if manufacturers only use test equipment such as the Manufacturing Defect Analyzer (MDA+), they may face challenges due to its limited testing capabilities when facing complex PCBAs. Conversely, for simple PCB assemblies, choosing a high-performance ICT online test platform may seem overkill, because in this case not only are the advanced functions useless, but program development also requires highly professional operators to complete.

Figure 2: The ICT platform is highly adaptable and can seamlessly meet various testing requirements during the manufacturing process.

Expanding test coverage

In the 1990s, the birth of TestJet technology was a major breakthrough in improving online test coverage. However, in the face of today's PCBA testing, capacitive probe measurement technologies such as TestJet are gradually becoming outdated, and vectorless test enhanced probe (VTEP) technology has emerged.

Non-vector technology

The use of VTEP has expanded the test coverage of ICT, especially for circuit boards with difficult-to-test packaging types, such as BGA, micro BGA and SMT edge connectors. Today's nanoVTEP technology not only greatly improves test throughput and meets the urgent needs of mass production, but also effectively reduces the cost of test fixtures. More importantly, nanoVTEP provides a reliable and efficient solution for PCBA testing with its excellent fault diagnosis coverage.

Boundary Scan Test

As technology continues to evolve, chipset testing becomes increasingly difficult with complex interconnects, limited access points, and increasing component density. For example, when designing server boards with high clock frequencies and component density, designers need to consider how to maintain signal integrity and minimize distortion. Closely adjacent parallel traces may generate electromagnetic interference, while test pads on high-speed signal transmission paths may cause reflections and signal attenuation.

Due to limited electrical access, the PCBA test coverage that ICT can cover is relatively small. Manufacturers can use boundary scan testing to check the functionality of the PCBA, without accessing all points of the internal circuit to ensure the accuracy and reliability of the test. However, the premise is that manufacturers need to design the PCBA in accordance with the IEEE 1149.1 standard, which requires that each pin must be connected to a boundary test unit. With the information provided by the IEEE 1149.1 standard, manufacturers can easily verify the overall functionality of the PCBA without having to check each component one by one.

Improving test efficiency in high-volume manufacturing environments

In a high-volume manufacturing environment, efficient and reliable production of PCBAs is key to meeting market demand and staying competitive. As the speed of placement equipment soars and production lines begin to measure production cycles in seconds, the presence of online test equipment may become a production bottleneck.

This situation puts manufacturers in a dilemma: either increase test capacity by adding more equipment, or maintain the expected production cycle by shortening test time. However, both approaches have challenges. Adding equipment is not only expensive, but also requires more test fixtures, which may be difficult to achieve due to space constraints in the production site. Reducing test time means more program maintenance work is required, and it also weakens the ability of the ICT system to effectively detect faults.

The ideal solution to the above problems is to continue to improve the execution speed of test equipment until it is no longer a limiting factor on the production line. At present, some ICT systems have been upgraded to support simultaneous testing of multiple components. This upgrade requires adding instruments to the test system so that test execution personnel can test multiple components at the same time (usually on circuit boards produced as part of a panel).