Thermal Aging: How to Test PCBA Against Heat and Humidity

April 24, 2024 | 8:11 am

Introduction to Thermal Aging

Thermal aging is a critical process in the manufacturing and testing of printed circuit board assemblies (PCBAs). It involves exposing the PCBA to elevated temperatures and humidity levels for an extended period to simulate the effects of long-term use and environmental conditions. This process helps identify potential failures, weaknesses, and reliability issues in the PCBA before it is deployed in the field.

Why is Thermal Aging Important?

Thermal aging is important for several reasons:

Identifying Weaknesses: Thermal aging can reveal weaknesses in the PCBA design, components, or manufacturing process that may not be apparent under normal operating conditions.
Improving Reliability: By exposing the PCBA to extreme conditions, thermal aging helps improve its reliability and longevity, reducing the risk of failures in the field.
Compliance with Standards: Many industries have specific standards and regulations that require PCBAs to undergo thermal aging testing to ensure they meet the necessary performance and reliability requirements.

Factors Affecting Thermal Aging

Several factors can affect the thermal aging process and the performance of the PCBA:

Temperature: The temperature at which the PCBA is exposed during thermal aging can have a significant impact on its performance. Higher temperatures can accelerate the aging process and reveal weaknesses more quickly.
Humidity: Humidity levels can also affect the PCBA during thermal aging. High humidity can lead to moisture absorption, which can cause corrosion, delamination, and other issues.
Duration: The duration of the thermal aging process can also impact the results. Longer exposure times can reveal more weaknesses and potential failures.
Component Quality: The quality and reliability of the components used in the PCBA can also affect its performance during thermal aging. Lower-quality components may fail more quickly or have a higher rate of defects.

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Thermal Aging Test Methods

There are several methods for conducting thermal aging tests on PCBAs, each with its own advantages and disadvantages.

Accelerated Thermal Aging

Accelerated thermal aging involves exposing the PCBA to elevated temperatures for a shorter period to simulate the effects of long-term use. This method is faster and more cost-effective than real-time aging but may not fully replicate the actual use conditions.

Advantages of Accelerated Thermal Aging

Faster testing times
Lower costs compared to real-time aging
Can reveal weaknesses and potential failures more quickly

Disadvantages of Accelerated Thermal Aging

May not fully replicate actual use conditions
Can lead to over-stressing of components and false failures

Real-Time Thermal Aging

Real-time thermal aging involves exposing the PCBA to actual use conditions over an extended period. This method provides a more accurate representation of the PCBA’s performance but is more time-consuming and costly.

Advantages of Real-Time Thermal Aging

Provides a more accurate representation of actual use conditions
Can reveal weaknesses and failures that may not be apparent in accelerated aging

Disadvantages of Real-Time Thermal Aging

Longer testing times
Higher costs compared to accelerated aging

Thermal Shock Testing

Thermal shock testing involves rapidly cycling the PCBA between extreme temperatures to simulate sudden changes in environmental conditions. This method can reveal weaknesses in the PCBA’s design and manufacturing process.

Advantages of Thermal Shock Testing

Can reveal weaknesses in the PCBA’s design and manufacturing process
Can simulate sudden changes in environmental conditions

Disadvantages of Thermal Shock Testing

May not fully replicate actual use conditions
Can lead to over-stressing of components and false failures

Thermal Aging Test Equipment

To conduct thermal aging tests on PCBAs, specialized equipment is required. Some of the key pieces of equipment include:

Environmental Chambers

Environmental chambers are used to expose the PCBA to specific temperature and humidity levels during thermal aging. These chambers can be programmed to maintain precise conditions over extended periods.

Chamber Type	Temperature Range	Humidity Range
Benchtop	-40°C to 180°C	10% to 98% RH
Floor-Standing	-70°C to 180°C	10% to 98% RH
Walk-In	-70°C to 180°C	10% to 98% RH

Data Loggers

Data loggers are used to monitor and record the temperature and humidity levels inside the environmental chamber during thermal aging. These devices can provide detailed data on the conditions the PCBA was exposed to during testing.

Data Logger Type	Channels	Accuracy
Temperature	1-16	±0.5°C
Humidity	1-8	±2% RH
Temperature/Humidity	1-8	±0.5°C, ±2% RH

Functional Test Equipment

Functional test equipment is used to verify the performance of the PCBA before and after thermal aging. This equipment can include:
– In-circuit testers
– Flying Probe testers
– Boundary scan testers
– Functional test fixtures

Thermal Aging Test Process

The thermal aging test process typically involves the following steps:

Planning: Determine the test conditions, duration, and sample size based on the specific requirements and standards for the PCBA.
Pre-Conditioning: Expose the PCBA to the specified temperature and humidity levels for a short period to stabilize the components and remove any moisture.
Thermal Aging: Place the PCBA in the environmental chamber and expose it to the specified temperature and humidity levels for the duration of the test.
Monitoring: Use data loggers to monitor and record the temperature and humidity levels inside the chamber throughout the test.
Functional Testing: Conduct functional tests on the PCBA before and after thermal aging to verify its performance and identify any failures or weaknesses.
Analysis: Analyze the data from the functional tests and data loggers to determine the effects of thermal aging on the PCBA and identify any potential issues.

Interpreting Thermal Aging Test Results

Interpreting the results of thermal aging tests requires a thorough understanding of the PCBA’s design, components, and performance requirements. Some key factors to consider when analyzing the results include:

Changes in electrical parameters (resistance, capacitance, etc.)
Physical damage or deformation of components
Corrosion or discoloration of surfaces
Delamination or separation of layers
Functional failures or anomalies

By comparing the results of the functional tests before and after thermal aging, engineers can identify any changes in performance or potential weaknesses in the PCBA design or manufacturing process.

Best Practices for Thermal Aging Testing

To ensure accurate and reliable results from thermal aging tests, there are several best practices to follow:

Follow Industry Standards: Adhere to the relevant industry standards and guidelines for thermal aging testing, such as IPC-9701, IEC 60068-2-2, and MIL-STD-810.
Use Appropriate Equipment: Use high-quality, calibrated environmental chambers and data loggers to ensure accurate and consistent test conditions.
Conduct Thorough Pre-Conditioning: Ensure that the PCBA is properly pre-conditioned before thermal aging to remove any moisture and stabilize the components.
Monitor Conditions Closely: Use data loggers to continuously monitor and record the temperature and humidity levels inside the chamber throughout the test.
Analyze Results Carefully: Thoroughly analyze the data from the functional tests and data loggers to identify any changes in performance or potential weaknesses in the PCBA.
Document and Report Results: Clearly document and report the results of the thermal aging tests, including any failures, anomalies, or potential issues identified.

Frequently Asked Questions (FAQ)

What is the purpose of thermal aging testing for PCBAs?
Thermal aging testing is conducted to evaluate the long-term reliability and performance of PCBAs under elevated temperature and humidity conditions. It helps identify potential weaknesses, failures, and reliability issues in the PCBA design, components, or manufacturing process.
What are the main factors that affect the thermal aging process?
The main factors that affect the thermal aging process include temperature, humidity, duration of exposure, and the quality of the components used in the PCBA. Higher temperatures, humidity levels, and longer exposure times can accelerate the aging process and reveal weaknesses more quickly.
What are the different methods for conducting thermal aging tests on PCBAs?
The three main methods for conducting thermal aging tests on PCBAs are accelerated thermal aging, real-time thermal aging, and thermal shock testing. Accelerated thermal aging involves exposing the PCBA to elevated temperatures for a shorter period, while real-time thermal aging involves exposing the PCBA to actual use conditions over an extended period. Thermal shock testing involves rapidly cycling the PCBA between extreme temperatures.
What equipment is needed for thermal aging testing?
The key pieces of equipment needed for thermal aging testing include environmental chambers, data loggers, and functional test equipment. Environmental chambers are used to expose the PCBA to specific temperature and humidity levels, data loggers are used to monitor and record the conditions inside the chamber, and functional test equipment is used to verify the performance of the PCBA before and after thermal aging.
What are some best practices for conducting thermal aging tests on PCBAs?
Some best practices for conducting thermal aging tests on PCBAs include following industry standards, using appropriate equipment, conducting thorough pre-conditioning, monitoring conditions closely, analyzing results carefully, and documenting and reporting results clearly. By adhering to these best practices, engineers can ensure accurate and reliable results from their thermal aging tests.

Conclusion

Thermal aging is a critical process in the manufacturing and testing of PCBAs, helping to identify potential weaknesses, failures, and reliability issues before the product is deployed in the field. By understanding the factors that affect thermal aging, the different test methods available, and the best practices for conducting these tests, engineers can ensure that their PCBAs meet the necessary performance and reliability requirements for their intended applications. Through careful planning, execution, and analysis of thermal aging tests, manufacturers can improve the quality and longevity of their products, ultimately leading to greater customer satisfaction and success in the marketplace.

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