PCB assembly testing techniques are essential to the manufacturing workflow.

We continuously adjust and improve our testing approaches alongside our failure analysis. Below, we provide detailed descriptions of various PCB testing methods. This guide is intended to give a precise and instructive synthesis of these findings.

 

1.Incoming Quality Control

(1) Purpose : PCB assembly materials consist of PCB substrates and electronic components.

Make sure the materials you’re employing meet all performance, specification, and reliability requirements.

(2)Inspection Content:

Inspecting incoming materials allows you to spot some errors ahead of time.

Prior to assembly, you must inspect the component’s packing and silkscreen. If the component’s pins rust, you must notify the provider and make an order for replacements on time.

Before assembling the components, make sure that their electrical properties fit the norm.

Before assembling the PCB, ensure that the pad flatness and thickness are correct.Check the surface coating and via quality.

 

2.Stencil Inspection

(1) Your purpose: you must make sure that the stencils are clean. Make sure that the SMT stencil tension, and aperture accuracy are within specified parameters.

(2)Inspection Content:

Verify stencil opening dimensions match design-specified process parameters. Tests include the shape, tolerance of placement, and aperture size.

Make sure the stencil is free of impurities and solder paste residue.Check stencil tension with a tensiometer to ensure consistent printing.

incoming quality control and stencil inspection

 

3.Solder Paste Inspection (SPI)

(1) Use: You need to check the quality of solder paste. It can help to avoid many soldering errors. This includes excessive soldering, insufficient soldering, bridging and misalignment.

(2)Inspection Content:

Inspection Content: Check that the paste volume and thickness meet the standards. Place the solder correctly. The solder paste shape should also correspond to the print parameters.

You should correct the misplaced solder paste as soon as feasible.

You should also check for edge clarity and bridging.

 

4.In-line automated optical inspection (In-line AAOI)

(1) Use: Reflow soldering allows you to spot surface mounted faults immediately. This provides rapid feedback on the procedure. AOI inspects PCBs with 2D and 3D cameras. The board isn’t powered, and several components are missing.

(2)Inspection Content:

In-line AOI allows you to spot misplaced or missing components immediately. This is also useful for determining component polarity, skewing, and tombstoning.In-line AOI allows you to spot flaws early. You may quickly rework issues like bridging and pad contamination.

AOI systems use machine vision and cameras to detect faults. Open circuits, pad damage, lead deformation and other defects can be detected quickly. It helps reduce the errors and costs that come with PCBs with defects.

solder paste inspection and in-line automated optical inspection

 

5.SMT First-Article Inspection (FAI).

(1) Purpose ：Before mass-production, you should verify that the production process is correct. You can then verify that the PCB is assembled correctly. This will prevent errors in batches.

(2)Inspection Content:

Verify the BOM to ensure that the component mounted is the proper model. The polarity and component package must also be evaluated.

In addition to the X/Y offset, the rotation angle is factored into the placement accuracy. If the machine’s accuracy is off.

It should be debugged.QFP and BGA parts require coplanar pads and leads. If you don’t, it’s quite easy to spot soldering flaws.

 

6.Reflow Profile Monitoring

(1)Purpose:Verify the temperature curve for the reflow-oven. The temperature curve should meet the requirements for solder pastes and components.  It can be utilized to avoid faults such as cold soldering and pad separation.

(2)Inspection Content:

The temperature curve focuses mostly on the peak temperature and heating rate. Correcting inappropriate cooling rates and holding times should be completed on time.

Thermocouple plates may be used. The thermocouple plates can measure temperature variations between areas.

 

7.In-Process Quality Control

(1) Purpose：It is critical to use real-time sampling when constructing PCBs.

Check essential processes like reflow parameters and mounting circumstances. Early detection and rectification of flaws is critical in the PCBA production process.

(2)Inspection Content:

Using the different shifts, you can then determine the scope of the batch sample.

Verify process parameters such solder paste thickness.

Ensure that the production environment is appropriate. Temperature and humidity levels must be appropriate. ESD shielding should also be present.

smt first article inspection, reflow profile monitoring, and in-process quality control

 

8.In-Circuit Test (ICT)

(1) Use: You can test circuit connectivity with a bed-of-nails or flying probe device. This tool is used to identify open circuits, component values, and shorts. The system is intended to cover all of the components, however it actually covers 85-90%. (There are no human errors. ICT focuses on BGAs and big connectors.

(2)Inspection Content:

Confirm that the resistance values are not normal.

You should also inspect the function pin connections on diodes, transistors, and other components.

You can quickly fix a short or open circuit network.

 

9.Functional Test (FCT).

(1) Use: Confirm that the completed PCB works as expected. This test ensures that the board performs as expected.

(2)Inspection Content:

The inspection process turns on the board and sends signals. The output is also checked to ensure that it matches the expectations. It evaluates the performance of the PCBA under real-world conditions, unlike component-level testing.

 

10.Offline Automated Optic Inspection (Offline AOA)

(1) Use: Test complex structures of high density. This is a supplementary tool for in-line AOI.

(2)Inspection Content:

It follows the same concepts as inline AOI, albeit in a slightly different order. It targets hard-to reach areas such as BGA peripheral pads.

 

11.X-ray Inspection

(1) Use: X-ray is available in 3D and 2D. The 3D version works faster. This approach detects faults in non-visible solder junctions, such as the BGA bottom joint. This method is effective, but it requires trained operators.

(2)Inspection Content:

This inspection allows you to assess the condition of both the solder points and the solder. This inspection is necessary to look for cracks in solder junctions and other problems with soldering.

Tests for solder ball coplanarity, connection integrity and the strength of the connections are also required.

If the component’s bottom is not aligned with the PCB pads, correct the problem immediately.

 

12.Wave Soldering Inspection

(1)Purpose :After wave-soldering, it is critical to evaluate the through-hole junction quality.

(2)Inspection Content:

This is an excellent approach to assess the look of solder joints. Rework immediately if any of the gloss, icicles, or saturation are incorrect.

This is a test for solder penetration. If there is poor solder penetration, rework it quickly.

Replace any heat-damaged components as soon as you locate them.

 

13.Manual Visual Inspection (MVI).

(1)Purpose: This inspection is a complement to automated tests. It is a qualitative assessment of complex or irregular defects.

(2)Inspection Content:

Check for cosmetic faults, such as a warped silkscreen. Please contact the assembly manufacturer as soon as possible to resolve this issue.

Rework the joint if it isn’t wettable or glossy enough. Please clean the boards if there is residue of flux on them.

You should act quickly if the connector/cable does not feel firm when you inspect it.

 

14.Reliability Testing

(1)Purpose:Usually used to test PCBA stability in extreme conditions. This is a critical issue for automotive and military electronics.

(2)Inspection Content:

Reliability testing include mechanical stress and burn-in tests.

These tests represent the harsh conditions that a PCB may encounter throughout its lifetime. Extreme circumstances can include high temperatures, high voltages, and mechanical stress. Humidity, bend strength, and vibration are all external environmental influences.

 

15.Final Quality Control (FQC).

(1) Purpose : Final quality control is a thorough final inspection of the completed PCBA. You can test if the assembled PCB meets customer requirements and specifications.

(2)Inspection Content:

Sample X-rays and AOIs at random based on product category.

You can conduct functional retesting by focusing on features that are unique to your clients.

During this test, you should pay close attention to the package and labels.

 

16.Quality Assurance Shipment Inspection

(1)Purpose: Before shipment, you must confirm the quality of the constructed PCB. Stop defective products from reaching the client.

(2)Inspection Content:

Use standards such as MIL-STD-105E to inspect samples’ packaging, functionality, and appearance. Verify all shipping documentation, including certifications of compliance, test reports, and traceability records. Test the package for shock resistance and compression.

 

17.Possible Problems And Solutions during PCBA Testing

17.1 Incoming Quality Control

Common Issues	Solutions
Resistance/capacitance values IC models exceeding tolerance Inconsistent with BOM	Install barcode scanners to scan intelligently Automatically match BOM data to component labels. Integrate with RoHS compliance database
Oxidized component leads Blurred image of PCB pads contaminated with PCB Silk screening is a form of silk-screening.	Automated optical measuring instruments Check lead coplanarity with pad flatness.
QFP package dimensions are not matched to PCB pads.	Visual positioning systems can be used to identify polar components and reduce the rate of misjudgments.

17.2 Stencil Inspection

Common Issues	Solutions
Insufficient solder paste due to reduced openings.	Use 3D laser scanners for measuring stencil apertures.
The tension will be below the rated value if you use excessively. This can compromise printing precision.	Create stencil lifecycle management system. Replace stencils at a specific value tension using automatic calibrators.
Dry solder paste can clog up the apertures and cause printing to leak.	Ultrasonic cleaning + ionized dry air. Manually sampled apertures using a 10x magnifier.

17.3 Solder Paste Inspection (SPI)

Common Issues	Solutions
Edge thickness can vary due to scraper pressure instability.	Closed-loop pressure control systems can be installed with a pressure sensor and servomotor.
Misalignment of PCBs due to worn out PCB locator pins	Use real-time positioning of PCBs with vision alignment systems.
Solder paste adhesion between fine-pitch pads.	Apply stepped stencils and edge anti-squeeze design for fine-pitch components. SPI 3D measurement corrected.

17. 4 First article inspection (FAI)

Common Issues	Solutions
The capacitor was misapplied to a resistor. BOM updates were not synced.	Use an AI-based visual FAI System. Compare component shapes, silkscreens, and BOMs automatically. Calculate the component recognition rate.
The pick-andplace vision is not correct and this leads to the incorrect orientation of electrolytic capacitors.	Dual-light imaging (red + Blue) is used to detect polar components. Machine learning can be used to detect polarity.
Solder joint openings due to QFP warpage.	Introduce coplanarity laser detectors for lead scanning. Automatic line stops are triggered for results that are out of tolerance.

17.5 Incoming Quality Control

Common Issues	Solutions
Faulty thermocouples can cause a peak temperature of >250°C (lead free limit).	Equip multichannel temperature testers to collect curves every 2 hours and automatically alarm when the limit is exceeded.
Increased temperature variations within the board are caused by an uneven hot air motor speed.	Weekly dynamic balance tests are recommended to calibrate the hot air motors. Test temperature uniformity using temperature test boards.
Leaks in the cooling system can cause it to cool faster than specified, causing cracks.	Use nitrogen reflow for soldering. Control cooling fan speed using PID algorithm.

17.6 Inline AOI Inspection

Common Issues	Solutions
Low contrast can cause invisible bridging at small solder joints.	Multi-angle lighting (0deg/45deg/90deg), paired with 3D AoI, will enhance contrast and height analysis.
False positives due to component color variation.	Create component feature databases that have independent detection thresholds for colors/materials.
BGA shadows can obscure the detection of adjacent capacitor solder joints.	Install tilted cameras (15deg angle) for BGA peripherals. AI image segmentation can be used to identify occluded joint.

17.7 In-Circuit Test (ICT)

Common Issues	Solutions
Resistance/capacitance values IC models exceeding tolerance Inconsistent with BOM	Install barcode scanners to automatically match BOM data and component labels. Integrate with RoHS compliance database
Oxidized component leads Blurred image of PCB pads contaminated with PCB Silk screening is a form of silk-screening.	Automated optical measuring instruments Check lead coplanarity with pad flatness.
QFP package dimensions are not matched to PCB pads.	Visual positioning systems can be used to identify polar components and reduce the rate of misjudgment.

17.8 Functional test (FCT)

Common Issues	Solutions
Signal interruptions can be caused by oxidized connector pins.	Apply moisture-resistant coatings + gold-plated connectors with automatic pin cleaning.
Incorrect firmware and testing programs can lead to a misjudgment.	Set up firmware version management systems to automatically verify compatibility.
Undetected functional failures when input voltages exceed the rated +-10%.	Simulate wide voltage inputs (+-20%) using programmable power supply (high accuracy).

17. 9. X – Ray Inspection

Common Issues	Solutions
BGA solder joint voids >20% area compromises reliability.	Use low-void pastes (voids less than 10%) and optimize reflow profiles.
Low-resolution images can miss the invisible inner-layer delamination.	Upgrade to computed tomography with microfocus X-ray system for delamination identification.
The small solder joints are difficult to evaluate due to blurred details.	Create solder joint defect databases using deep learning to auto-identify internal issues.

17.10 Reliability Testing

Common Issues	Solutions
After 500 cycles at -4085, cracks in the solder joint are visible.	Use underfill to improve fatigue resistance.
Loose connector contacts cause intermittent shorts.	Use pre-vibration force testing and screw torque monitoring systems (>5N).
Pad rust is caused by an inadequate conformal coating.	Use nano-coating to increase salt fog resistance up to 1,000 hours.

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18.PCBA Testing: Top Practices

PCBA testing is a key component to ensuring product quality, reliability, and functionality. The following are key strategies for optimizing testing:

 

18.1 Process control and Quality Assurance

Verify operational durability by following standard test protocols and performing environmental tests.

 

18.2 Testability design

Plan PCBs to have a large number of test points. Leave enough space around the PCBs for access to probes and other equipment.

 

18.3 Ongoing optimization

Analyze data and test strategies regularly. It is able to adapt well to changing technologies and requirements.

 

18.4 Documentation

Document all test results, defects, and procedures. Create clear feedback loops for the design, assembly and testing teams. It promotes continuous improvement and early problem resolution.

 

19.PCBA Testing Challenges

PCBA testing is hampered by:

 

19.1 Time and Cost Constraints

The cost of high-quality tools such as X-ray and ATE systems is expensive. Some tests can also cause production delays.

 

19.2 Integration of Software and Hardware

Integration of multiple hardware and software tools is often required for testing. It is a challenge to ensure seamless compatibility among these systems.

 

19.3 Signal integrity risks

Noise, reflection and crosstalk can cause input signals to weaken or be distorted. Signal integrity is important when assembling PCBs.

 

19.4 Dense Component Layouts

Modern PCBs are made up of miniature components that have a tighter spacing. Visual inspection is impossible, and the test points are difficult to reach.

 

19.5 Accessibility and Coverage

It is hard to integrate comprehensive test points and functionality into PCB design. This also limits the full coverage of tests.

 

20.Summary

PCB Assembly Testing Methods–including Visual, X-ray (in-circuit), Functional and other tests. They are crucial for component performance. They detect defects and confirm compliance with industry and design standards. Testing thoroughly reduces failures and costs of recalls, increasing customer confidence. Testing techniques for complex electronics are becoming more advanced.

Looking for a PCBA professional partner? Orinew Technology Co.,Ltd offers complete PCBA solutions that cover everything from design and production to component procurement.  For additional information, please visit our website or contact us online.