In electronics manufacturing, even small PCBA defects can cause big problems. That’s why In-Circuit Testing (ICT) is so important. It ensures your PCBA boards are reliable and meet top-quality standards. ICT quickly detects issues before deployment, keeping your devices running smoothly.

At Elecrow, we understand that precision and reliability are the backbones of any good PCB assembly. For this, we provide a gamut of testing services, which includes ICT to make sure that your products meet the highest standards in quality and performance.

For our part, we utilize delicate test equipment and very sophisticated software to deliver test results, accurate and reliable ones, that meet the needs of our customers. From prototyping to ramping up to mass production, Elecrow can find faults better than any other company with unmatched levels of precision diagnostics.

With flawless PCBA boards that defy expectations, we set new benchmarks in terms of quality and innovation.

What is In-circuit Testing in PCBA?

In-circuit testing is an extensive process used in electronic circuits to check the integrity and functionality of individual components. It is very important to enhance the reliability and efficiency of the devices. It ensures that the board is assembled correctly before deployment. As electronic devices become more complex to build, confirming each board’s integrity becomes crucial.

It diagnoses prospective defects like short circuits, open circuits, incorrect values, or incorrectly placed components, assuring the board is good for deployment. ICT measures electrical parameters, such as resistance and capacitance with voltage, using probe placement on specific test points. Besides reducing the risks of field failure for manufactured devices, it improves general product quality. Electronic designs are becoming increasingly complex, making ICT a crucial stage in production so companies can meet today's demanding reliability and performance standards.

Key Components of In-circuit Testing in PCBA

The various key components that ensure the integrity of Printed Circuit Board Assemblies (PCBAs) work together during the in-circuit testing (ICT) process. These components allow precise testing, fault detection, and validation of the board operation against the design specifications.

Test Fixture 

A custom-made mechanical fixture establishes electrical contact with the PCB's test points. Designed for near-complete coverage, it achieves around 85-90%. The fixture uses spring-loaded test pins (probes) perfectly aligned with the PCB's designated test points.

ICT Testing PCBA Machine

This core equipment controls the testing process, verifying the quality and integrity of the circuit board assembly. It measures parameters such as resistance, capacitance, voltage, and current. The machine also includes a power supply to energize the PCBA boards during testing.

Test Points

These are dedicated points on the PCB for monitoring or injecting test signals. Typically unmasked, test points enable direct contact with probes without interfering with the board's normal operation.

Control Program

This software contains scripts tailored to the specific PCB design. It guides the machine to perform customized tests and compare results against design specifications.

Analysis Tools

Integrated tools such as multimeters, oscilloscopes, and digital analyzers test ICs and logic gates, facilitating fault detection. These tools identify anomalies like open/short circuits and incorrect component values.

Testing Process

The In-Circuit Test in PCBA has a series of steps to evaluate the integrity of the components and connections. This test process is widely automated. It is designed to detect manufacturing defects like short circuits, open circuits, and faulty components. Let’s check out the step-by-step process of the ICT testing method:

● Analyze the PCB to ensure it includes test points and is compatible with ICT.

● Prepare a custom test fixture and software tailored to the board design.

● Mount the PCB securely onto the test fixture to align it properly with the test probes.

● Configure the in-circuit testing machine and set the test parameters for initialization.

● Electrical signals are applied to the board’s test points and components for digital in-circuit testing.

● Measure parameters such as resistance, capacitance, voltage, and current during analog in-circuit testing.

● Compare the test results to the expected values to identify flagged components or connections.

● Generate a test report detailing the pass/fail status and any detected faults.

● Use the report to debug, replace components, or fix faulty connections.

● Perform retesting if requested, repair the PCB, and repeat the steps above.

Types of Defects Detected

In-circuit testing (ICT) identifies defects in PCBAs to ensure proper functionality and reliability. It detects issues in components, connections, and circuit functionality, helping manufacturers address problems early in the production process. Some of the major defects are listed below: 

1.  Component-Related Defects

a.  Missing parts - Components that were not placed during assembly.

b.  Wrong components - Components with wrong values, ratings, or types.

c.  Reversed polarity - Polarized components installed in the wrong orientation.

d.  Damaged components - Components that are physically damaged or fail to operate.

2.  Connection-Related Defects

a.  Open circuits - Disconnected traces, solder joints, or pads.

b.  Short circuits - Unintended connections between two or more points.

c.  Poor solder joints - Weak or incomplete soldering resulting in unreliable electrical connections.

3.  Functional Defects

a.  Defective IC(integrated circuits). Damaged ICs that fail to output the expected signals.

b.  Faulty networks - problem in RLC(resistor, capacitor, inductor) networks.

c.  Logic errors - Incorrect operation of digital components such as microcontrollers.

Pros and Cons of In-circuit Testing

In-circuit testing (ICT) offers precise and efficient fault detection in PCBAs, making it ideal for high-volume production. However, it requires significant initial investment, design accommodations, and setup time, and it cannot simulate real-world operational conditions.

Pros:

1.  High Fault detection: In-circuit testing machines can detect a wide range of manufacturing defects. This includes open circuits, shorts, and faulty components. 

2.  Accurate diagnosis: It can pinpoint specific defects and their locations on the PCB. 

3.  Speed: The process is highly automated and has great speed, which makes it suitable for high-volume production. 

4.  Repeatability: The machine guarantees consistent test results across multiple units. 

Cons: 

1.  High Initial Cost: ICT machines have higher initial costs than other testing methods like flying probe tests. Also, they are hard to maintain in time intervals.

2.  Design Requirements: The ICT machine requires dedicated test points on the PCB. This can increase board size and cost. Also, the boards must be designed with ICT compatibility in mind which limits the design flexibility.

3.  Time-Consuming setup: For the in-circuit testing of the PCBA, creating the test fixtures and programs for each PCB design requires a great amount of time. So there will be a delay in the production of the PCBs. Retesting the modified PCB will also take too much time to test as the fixture may have to be changed. 

4.  Isolated testing: In-circuit testing primarily focuses on testing individual components that don’t make up for the real-world operation of the entire circuit. It cannot evaluate performance under varying loads. 

In-circuit Test VS Functional Test

In-circuit testing is a method used to test electronic components and connections on a PCB whereas functional testing evaluates the overall functionality of the PCBA. Below, we have differentiated them on many aspects. 

1.  Purpose

● ICT: Verifies the assembly and electrical integrity of individual components.

● Functional Test: Guarantees that the entire PCB operates correctly as a whole. 

2.  Testing Scope

● ICT: Tests individual components in isolation. 

● Functional Test: Tests the components in the entire circuit. 

3.  Methods of testing

● ICT: Uses a mechanical fixture(bed of nails) to contact the test points. 

● Functional Test: Uses power supply to power up the PCB and run test hardware or software simulations.

4.  Defects detected

● ICT: Open circuits, short circuits, missed or incorrect parts, poor solder joints.

● Functional Test: Firmware issues, timing errors, improper communication, power loss under different loads.

5.  Setup and Costs

● ICT: It requires a high initial cost but is cost-effective for testing PCB in large quantities. 

● Functional Test: More flexible than IC. but can be expensive to set up if complex designs are involved.

6.  Time and complexity

● ICT: Faster testing as it involves static checking, which is less complex to execute.

● Functional Test: Slower, as it involves dynamic testing of the entire system and is more complex, requiring custom scripts. 

Conclusion

In-circuit testing in PCBA is an excellent method for validating component assembly and soldering quality. It focuses on the integrity of individual components and their electrical connections. It utilizes a bed-of-nails fixture to make contact with designated test points, offering high fault coverage, precise fault diagnosis, and rapid automated testing. So, ICT is ideal for mass production. Its ability to isolate defects improves debugging and repair. However, there is a very high initial investment in custom test fixtures and programming for ICT. Its dependence on test points requires compatible PCB designs. It is less suitable for high-density or high-frequency boards due to space and signal integrity challenges. ICT focuses solely on structural and assembly-level testing, ensuring the PCB is correctly built. Despite its limitations, ICT remains a key component of quality assurance, excelling at finding assembly errors early, therefore reducing rework costs and improving overall reliability.