Thermal Shock vs. Thermal Cycling Test:

Understanding the Different Types of Reliability and Accelerated Life Testing

Temperature Testing Equipment

Thermal shock tests and thermal cycling tests are crucial for pinpointing failure mechanisms triggered by extreme, repeated, and rapid temperature changes.

Collecting life cycle data for electronic systems, components, or products to analyze time-to-failure is a laborious task. Fortunately, this process can be made more efficient through accelerated life tests. These tests expedite failure by subjecting the electronic systems, components, or devices to conditions that induce quicker failures than they would experience under normal operating conditions. This approach is essential for ensuring the reliability of the tested devices.

Among the various accelerated life tests, thermal shock tests and thermal cycling tests are specifically designed to uncover temperature-induced failure mechanisms. While both tests serve similar purposes, they differ significantly in aspects like temperature profiles, transfer times, dwell (soak) times, and their respective applications. Let’s explore the differences and similarities between thermal shock tests and thermal cycling tests in detail.

 

What are the real differences between Thermal Shock and Temperature Cycle Testing?

Both types of tests subject products to cycles of alternating hot and cold temperatures, inducing stresses from thermal expansion and contraction. Often, components expand and contract at different rates, resulting in cumulative fatigue damage with each cycle, potentially leading to fatigue failure.

Thermal shock tests involve rapid temperature changes typically exceeding 15°C per minute. In contrast, temperature cycle testing features transition rates below 15°C per minute, typically ranging from 1 to 10°C per minute based on our experience.

 

Thermal Shock Tests

Thermal shock testing and temperature cycle testing both subject a device under test (DUT) to alternating high and low air temperatures to speed up failures that may occur due to repeated temperature changes in normal use.

In thermal shock testing, the transition between extreme temperatures happens very quickly, at a rate greater than 15°C per minute. In contrast, temperature cycle testing involves slower transitions between high and low temperatures.

Failures caused by thermal shock can differ from those resulting from temperature cycling. Thermal shock failures often involve overstress, with solder joints failing due to tensile overstress and tensile fatigue. On the other hand, temperature cycle failures in solder joints are usually due to shear creep fatigue and stress relaxation.

Thermal shock testing is generally conducted using equipment with a single specialized test chamber. In a thermal shock test chamber, the DUT or samples remain in the chamber while the air temperature is rapidly cooled and heated. This typically results in a slower rate of change in the product’s temperature response, as the entire chamber must be cooled down and heated up.

MPI Thermal’s test chambers and enclosures are driven by the TA-5000 or TA-3000 MPI ThermalAir Stream systems. Temperature test systems allow engineers greater control of the ramp rate, soak, and cycle providing the fastest temperature transition rates possible for device under test (DUT). 

PCB Temperature Test Chamber

MPI Thermal Hood (Test Enclosure) w/ PCB 

Thermal Cycling Tests

 

The thermal cycling test, also known as the temperature cycle test, subjects a specimen to stress at extreme temperatures. These tests are conducted to identify failure mechanisms that result from a mismatch in the coefficient of thermal expansion (CTE) of materials. Thermal cycling tests assess the ability of a device under test (or a part of it) to withstand very high and very low temperatures, as well as repeated exposure to these extreme temperature cycles.

The thermal cycling test is generally conducted in a single chamber, where the transition from hot to cold temperature (or vice versa) depends on the chamber’s ability to shift between extreme temperatures and the thermal mass of the specimen and the limitation of the test chamber’s transition time. The specimen is held at a stabilized extreme temperature, and the next transition occurs only after this stabilization period, referred to as soak time. The soak time and the number of thermal cycling test cycles are varied to exacerbate the various failure modes in the component or device under test.

Thermal cycling tests are typically performed to detect the following failure mechanisms:

  • Ball grid array (BGA) interconnect defects
  • Delaminations in printed circuit boards (PCBs)
  • Solder joint cracking
  • Hermetic seal failures
  • Lead or terminal damages

These tests are essential for ensuring the reliability and durability of electronic components under conditions of fluctuating temperatures.

Benchtop Environmental Test Chambers

MPI Thermal Test Chamber w/ PCB

Thermal cycling is a pivotal process extensively applied to assembled Printed Circuit Boards (PCBs). This meticulous method involves subjecting the assembled board to various temperature changes over an extended period, ensuring its durability and reliability in real-world scenarios. Unlike thermal shock testing, which entails rapid temperature shifts, thermal cycling offers a more measured and practical approach for evaluating PCB performance. This article delves into the intricacies of thermal cycling, its benefits, and why it stands superior to thermal shock testing for assembled PCBs.

Thermal cycling involves exposing the PCB to a series of temperature fluctuations, typically ranging from low to high extremes, in a controlled manner. This process is executed over numerous cycles, allowing the board to experience gradual temperature changes. The primary objective is to simulate the thermal stresses that a PCB might encounter throughout its operational life.

 

The Process of Thermal Cycling

 

  • Preparation: The assembled PCB is first inspected for any visible defects or issues that might affect the testing process.
  • Initial Testing: The board is powered and tested to ensure it is functioning correctly before thermal cycling begins.
  • Temperature Cycling: The PCB is subjected to a series of temperature changes, usually involving heating and cooling phases. Each phase is maintained for a specified duration to ensure uniform temperature distribution.
  • Intermediate Testing: Throughout the thermal cycling process, the PCB is periodically powered and tested to monitor its performance and detect any emerging issues.
  • Final Inspection and Testing: After completing the thermal cycling, the board undergoes a thorough inspection and final testing to evaluate its performance and identify any potential failures.

 

The Superiority of Thermal Cycling

Thermal cycling emerges as a more practical and reliable method for testing assembled PCBs. By simulating realistic operational conditions and identifying latent defects, thermal cycling ensures the durability and performance of PCBs over their lifespan. In contrast, the rapid transitions and extreme temperatures of thermal shock testing can induce unrealistic stress and potential failures, making it a less effective testing method for assembled PCBs. As such, thermal cycling remains the preferred choice for evaluating the reliability and robustness of assembled PCBs in real-world scenarios.

 

Benchtop Environmental Test Chambers

Real Time vs. Temperature Review Screen

The Future of PCB Testing

Advancements in PCB testing technologies are continually emerging, driven by the need for more reliable and durable electronic devices. Innovations such as automated testing systems, advanced thermal chambers, and real-time monitoring tools are revolutionizing the way PCBs are tested and evaluated.

Automated Temperature Test Systems

Automated testing systems enhance the efficiency and accuracy of PCB testing by reducing human error and increasing the throughput of tested boards. MPI Thermal’s TA-5000 and TA-3000 series systems can perform a wide range of temperature tests, including thermal cycling and thermal shock, in a fully automated manner.

Advanced Thermal Chambers

MPI Thermal’s thermal test chambers offer precise control over temperature conditions (combined with the TA-5000 or TA-3000 series systems), allowing for more accurate and repeatable thermal cycling tests. These chambers can simulate a wide range of environmental temperature conditions, providing valuable insights into the PCB’s performance under different scenarios.

Real-Time Monitoring Tools

Real-time monitoring tools enable continuous observation of the during thermal cycling and other tests. These tools can control ramp, right, and soak time parameters, providing valuable insights into mechanical stresses, allowing engineers to collect detailed data for analysis and improvement. MPI Thermal TA-SERIES of ThermalAir stream systems incorporate these features into all our temperature forcing systems for localized thermal inducing. These features and functions are all user settable for real time monitoring. MPI Thermal air stream systems can be set for Ramp Rates, Dwell/Soak Times, All Temperature Parameters, and test article (The DUT/UUT) and their user settings such as temperature test set points can be monitored by the user real time dynamically at power or non-powered up test devices. This all can also be done with MPI Thermal remote commands over several MPI Thermal systems interfaces such as IEEE-488, RS-232, USB, LAN using basic ASCII string commands set.

Reliabilty Testing: Meeting Your Specific Testing Application Needs

MPI Thermal’s Test Chamber and Compact Hood temperature test systems offer greater adaptability, able to accommodate a variety of sizes and shapes for devices, components, and PCBs for Thermal Shock Test or Thermal Cycling Test to ensure your products and devices reliabilty.

In addition, MPI Thermal’s Temperature Testing Solutions and Test Chambers can be used for other test applications and are designed for an array of temperature test applications right at your test station localized. The MPI Thermal systems are mobile where many large fixed stationary type chambers cannot provide In-situ test simulating the test environment when required for the test. The driving temperature technology is in the TA-5000 and TA-3000 series test systems. Not only does MPI Thermal’s solutions provide rapid temperature cycling allowing you to control ramp rate, soak, and cycle, but also brings the power of large walk-in chambers to small test articles device test scenarios from -80°C to +225°C

MPI Thermal Temperature Testing Systems

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