Working for manufacturer engineering couple years. Sharing the manufacturing experience, skill, DFx, design, and information. Be care of this blog is personal share and content may not be 100% correctly.
Do you know what ICT (In-Circuit Test) is? Please note that we are not talking about Information and Communication Technology (ICT) here. And what about MDA (Manufacturing Defects Analyzer)? If these tests are commonly implemented in PCB assembly manufacturing, what are their pros and cons? How do they differ from ATE (Automated Test Equipment)?
ICT is primarily used for the electrical testing of Printed Circuit Board Assemblies (PCBA). Think of it as an advanced “multimeter” or an LCR meter. It allows us to test the electrical characteristics and check for open/short circuits of all components on the circuit board without removing them.
The operation principle of ICT involves using a Bed of Nails, which connects to pre-arranged test points on the PCB. This enables testing of individual components or nodes. Just like using a multimeter to measure resistance by placing probes on both ends of a resistor, ICT requires test points to be placed on the contact pins of all components for measurement. Sometimes, a series or a section of the circuit can be treated as one component, and its equivalent resistance, capacitance, and voltage can be measured to reduce the number of test points. This is known as Node testing.
(Note: In electrical engineering, a node refers to the point where two or more branches of a circuit intersect. Different nodes have different voltages. Understanding Ohm’s Law (V=IR), we can treat the circuit within two nodes as a single electronic component, measuring impedance, current, and voltage to detect open or short circuits.)
In the PCB assembly process, the main defects often concentrate on issues such as open circuits, short circuits, component shift or skew, missed or wrong components, constituting over 90% of defects. Apart from some defects, the rest can be identified 100% through ICT testing. However, component “shift” and “skew” may not always be detected through electrical testing solution because as long as the component pins are soldered in place and connected, and electrical testing shows no abnormalities, the component shift cannot be detected. Whether such a defect is considered a nonconformity needs further clarification. Additionally, defects caused by cold solder or non-wetting joints leading to intermittent issues might not be 100% detected by ICT too, presenting a significant challenge. Since ICT relies on electrical testing to detect circuitry, if the solder joint is in contact during testing, the defect may not be identified.
The Capabilities of ICT:
ICT can perform a range of tests and measurements, including:
Checking for opens circuit, shorts circuit, wrong or missing components, component polarity, offset/shift, skew, and lifted solder pins.
Measuring electronic component such as resistors, capacitors, inductors, transistors, diodes, voltage regulators, triodes, optocouplers, transformers, relays, field-effect transistor tests (FET), ICs, connectors, and more. In fact, any electronic component that requires soldering of terminals could be measurable.
Utilizing TestJet technology to measure connector PINs without the need for test points.
Conducting DC/AC voltage and frequency measurements.
Using Boundary-scan/JTAG to test active component functionality, even running low-level test programs.
Advantages of ICT Board Testing:
Fast and Efficient Testing: ICT offers quick and time-efficient testing. PCBA testing doesn’t require powering up, reducing startup wait times and minimizing the risk of circuit board damage due to shorts. Testing a PCBA with 300 components can be completed in as little as 3 to 5 seconds, excluding loading/unloading time.
Excellent Repeatability: Testing is controlled by computer programs, ICT ensures precise measurements, significantly reducing the risk of errors and omissions, minimizing production line disruptions. (Note: Contact issues at test points may lead to misjudgments.)
Low Dependency on On-site Expertise: With almost full computer control, ICT significantly reduces human-operated time and errors. General operators, with minimal training, can easily operate equipment and change test fixtures. (Test programs require maintenance by professional technicians or engineers.)
Significantly Reduced Product Repair Costs: General operators can handle product repairs, effectively reducing labor costs. ICT can inform about problematic components or nodes through computer programs, speeding up the troubleshooting process.
Increased Product Throughput: Rapid testing provides real-time feedback to SMT operations, reducing defect rates, minimizing material inventory, lowering defective product accumulation, reducing costs, and enhancing competitiveness.
Enhanced Product Quality: With sufficient test points, ICT can measure all circuits and components on the circuit board, even those in bypass circuits. This improves product quality, reduces customer complaints, and potentially boosts overall performance.
Drawbacks of ICT Circuit Testing:
Cost Considerations: The equipment and fixtures for ICT are generally expensive, especially using pneumatic steel fixtures, which can cost up to fifteen thousand US Dollars. This makes them more suitable for products produced in large quantities.
Impact on PCB Design: ICT testing requires additional test points on the circuit board for probe connections, reducing the utilization of circuit board wiring.
Challenges with Test Points: Test points may encounter contact issues due to different surface finishes. For instance, boards with OSP finished may require printed solder paste on test points to remove OSP film for conductivity. However, the remained flux after soldered can create a protective film, leading to poor contact.
Maintenance Requirements: Regular maintenance of the bed of nails and periodic replacement of probes are necessary to ensure their proper functioning.
Leading Global ICT Automatic Test Equipment Manufacturers:
Major manufacturers include Agilent Technologies (now “Keysight” after HP separation), Teradyne, GenRad (acquired by IET Labs), TRI (Taiwan), JET, Check Sum, AEROFLEX, WINCHY (China), Hioki (Japan), IFR (acquired by AEROFLEX), Takaya (Japan), Tescon (Japan), ADSYS (Systex, Taiwan), SRC (China), Okano (Japan), Concord (Zhenhua, Hong Kong), Seica, Scorpion (ACCULOGIC), Shindenshi, SPEA, Testronics, and more. Different brands share similar testing principles, with those familiar to me listed first.
Distinguishing ICT, MDA, and ATE:
1. MDA (Manufacturing Defects Analyzer):
Considered a lower-tier ICT, examples include TRI-518 series, JET-300, ADSYS-K518 series. These machines can measure basic L/C/R/D components, test PIN components using TestJet but lack features to provide power to the PCB for self-testing. MDA cannot run the low level diagram.
2. ICT (In-Circuit Test):
Typically refers to more advanced testing machines like Agilent 3070, Genrad, TR8100. In addition to basic MDA functions, these machines can download programs to the PCB, perform self-tests, and provide voltage and frequency measurements.
3. ATE (Automatic Test Equipment):
A streamlined testing approach that connects directly to the SMT. ATE’s primary purpose is to test the functionality of the actual board and its components. The board must be powered for the components to function, and signal transmission must consider the characteristics and specifications of components to avoid damage.
This article serves as an introduction, with more discussions on the pros and cons of ICT to follow.
(Because there has been an ongoing debate within the company about whether to discontinue ICT, this article essentially consolidates information about ICT. The content includes references to explanations found online, along with my own insights and understanding. There might be some inaccuracies, so please feel free to provide feedback!)
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