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Electronic manufacturing industry
PCB thermal expansion coefficient

The PCB thermal expansion coefficient refers to the change in the length, width, and thickness of the PCB material as the temperature varies. Since different PCB materials have different thermal expansion coefficients, it is necessary to consider the impact of these coefficients when designing and manufacturing circuit boards.

A higher thermal expansion coefficient indicates that the PCB will undergo more significant deformation with temperature changes. FR4 material is one of the most widely used materials, and its thermal expansion coefficient in the range of 25-260°C is approximately 12-18 ppm/°C. In contrast, aluminum substrate typically has a thermal expansion coefficient of 23-25 ppm/°C.

The PCB thermal expansion coefficient is usually expressed in ppm/°C (parts per million per degree Celsius). For example, if a material has a thermal expansion coefficient of 20 ppm/°C, the length of the material will increase by 0.002% of its original length for every 1-degree Celsius temperature rise.

The PCB thermal expansion coefficient can significantly impact the dimensional accuracy and stability of materials, especially for electronic devices. Accurately understanding and controlling the thermal expansion coefficient is crucial for ensuring the quality and reliability of products.

Table of Contents

What is PCB Thermal Expansion Coefficient?

What is PCB Thermal Expansion Coefficient

The PCB thermal expansion coefficient of a material is a measure of how its dimensions change with temperature variations. Specifically for PCBs, it involves the change in length, width, and thickness as the temperature fluctuates. This property is essential to comprehend because materials exhibit different thermal expansion coefficients, influencing the performance and reliability of electronic devices.

Significance in Design and Manufacturing

When designing and manufacturing electronic circuits, understanding and accounting for the thermal expansion coefficient is crucial. Failure to consider this factor can lead to issues such as warping, misalignment of components, and overall degradation of the device’s performance. It becomes particularly crucial when dealing with temperature-sensitive applications or devices that experience varying operating conditions.

Importance for Electronics Reliability

The PCB thermal expansion coefficient directly impacts the dimensional accuracy and stability of materials. In the realm of electronic devices, precision is not just a design consideration but a reliability and quality assurance imperative. Accurate measurement and control of the PCB thermal expansion coefficient are vital to ensure that devices perform consistently under diverse operating conditions.

Material Variations

Different PCB materials exhibit varying thermal expansion coefficients. For instance, FR4, one of the most widely used materials, typically has a coefficient in the range of 12-18 ppm/°C. In contrast, aluminum substrates may have coefficients around 23-25 ppm/°C. The choice of material is often dictated by the specific requirements of the electronic application.

Measurement methods

PCB thermal expansion coefficient-Measurement methods

1.Expansion Cantilever Beam Method

The expansion cantilever beam method is an indirect measurement method commonly used for small sample testing of PCB materials. The principle involves calculating the PCB thermal expansion coefficient by measuring the deflection of the material under temperature changes.

The specific experimental steps are as follows:

(1) Prepare thin slice samples of suitable dimensions and fix them on a support beam, forming a cantilever.
(2) Place the cantilever in a constant temperature environment and record the baseline deflection.
(3) Gradually heat or cool the cantilever, recording deflections at different temperatures.
(4) Utilize Hook’s law to calculate the PCB thermal expansion coefficient based on deflection changes at different temperatures.

The advantage of this method is its relatively simple testing process and low requirements for instrumentation. However, due to the small sample size, the measurement accuracy may be limited.

2.Thermal Expansion Coefficient Meter Method

The PCB thermal expansion coefficient meter method is a direct measurement technique used for testing large-sized PCB board materials. This method calculates the PCB thermal expansion coefficient by precisely measuring the linear expansion of the material at different temperatures.

The specific experimental steps are as follows:

(1) Prepare PCB board samples of suitable dimensions.
(2) Fix the samples in the PCB thermal expansion coefficient meter and establish the zero position of the measuring instrument.
(3) Adjust the temperature and record the sample lengths at different temperatures.
(4) Calculate the PCB thermal expansion coefficient based on the recorded length changes.

The advantage of this method is its relatively high testing accuracy, allowing for accurate measurement of the thermal expansion coefficient of large-sized samples. However, the instrumentation is relatively expensive, and the testing process requires operators with a certain level of technical expertise.

In addition to the common measurement methods mentioned above, there are other methods such as the cantilever beam method, thermal difference method, and expansion volume method. Each method has its applicable range and advantages, and the choice depends on specific requirements.

In summary, the PCB thermal expansion coefficient refers to the change in the material’s length per unit length for a unit temperature change. Accurately measuring the thermal expansion coefficient is crucial for ensuring the quality and reliability of electronic devices. Common measurement methods include the expansion cantilever beam method and the thermal expansion coefficient meter method, each with its pros and cons, requiring consideration based on practical circumstances.

Conclusion

In conclusion, the PCB thermal expansion coefficient plays a pivotal role in the design and manufacturing of electronic devices. Designers and manufacturers must carefully choose materials, considering their thermal properties and employing accurate measurement methods. By understanding and controlling the thermal expansion coefficient, the electronics industry can continue to produce reliable, high-performance devices that meet the demands of an ever-evolving technological landscape.

FAQ

The thermal expansion coefficient of a PCB refers to the change in dimensions (length, width, and thickness) of the material in response to temperature variations.

Common measurement methods include the Expansion Cantilever Beam Method and the Thermal Expansion Coefficient Meter Method, each offering different levels of accuracy and applicability.

The thermal expansion coefficient is crucial in PCB design to prevent issues like warping, misalignment, and performance degradation due to temperature fluctuations.

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