How the Thermal Cycle Works

Among the most common tests that can be performed in a climatic chamber are thermal cycles.

In the following article we will illustrate the generalities of thermal cycles and thermal cycle chambers, with some examples taken from international regulations governing testing of products and materials.

What are Thermal Cycles?

A thermal cycle is defined as any recursive thermal test in which the temperature is regularly altered, reaching a high temperature peak and a low temperature peak. 

A single thermal cycle is considered complete when the temperature returns to its starting values, but in most tests the procedure must be repeated a minimum number of times to achieve the desired results. As we will see, this minimum number is determined by the applicable regulations for the particular product category.

Thermal cycling differs from thermal shock tests due to the time it takes to transfer from the hot to the cold environment. The so-called "settling time" of the specimen in a thermal cycle is at least ten minutes, and the edge of the new temperature zone must be reached within 15 minutes.

Instead, in the so-called thermal shock test, only a few seconds are needed to transfer the sample from one environment to another to obtain the "shock" factor. The shock is in fact caused by the so-called "heating and cooling rate,"or the speed of heating and cooling that differentiates it from standard thermal tests.

The Thermal Cycle Chambers

Although the timing of the transfers and the precision of the temperature values ​​are fundamental, in its generality the thermal cycle is among the simplest tests and can be performed in any climatic chamber that allows for the alteration of the temperature values ​​and the control of the humidity values.

All standard climate chambers are therefore also thermal cycling chambers.

Most thermal cyclers can be programmed to run the cycle autonomously.

International Procedures for Thermal Cycles

There is no single international procedure for thermal cycles.

Thermal cycling in a climatic chamber is such a common environmental test that it is required for many types of products and materials. Among the most widely used sectors is the electronics industry , where the MIL-STD-883E standard is a prime example. Corrosion tests on metals also include thermal cycling, as per ISO 13573:2012 .

These procedures are very specific and prescribe:

• temperature of the cold end of the cycle
• temperature of the hot end of the cycle
• maximum transfer time duration
• minimum settling time duration
• minimum number of thermal cycles required

For more precise information, it is necessary to find the technical documentation relating to the sector and the materials we need to test.

FDM Thermal Cycling Chambers.

FDM climatic chambers are the ideal tools for carrying out a large part of the thermal cycles for materials testing.

If the values ​​required by the test reach extreme temperatures, it is advisable to use an environmental chamber.

Both the climatic chambers and the FDM environmental chambers implement the best technologies and can program the thermal cycles autonomously thanks to the innovative revoFACE.

For further information, please do not hesitate to contact us.

Thermal Cycle vs. Thermal Shock vs. Automotive Cycles

The terms "thermal cycle," "thermal shock," and "automotive thermal cycles" are not synonymous. Let's look at the main differences:

The thermal cycle covered in this guide is the generic category: programmed transitions between high and low temperatures with a controlled ramp, on a single chamber. The variants (shock, automotive, ICH) specialize parameters and standards for specific purposes.

Frequently Asked Questions about Thermal Cycling

How many thermal cycles are needed for a standard test?

It depends on the standard. IEC 60068-2-14 Nb typically calls for 2-100 cycles for consumer and general electronics applications. Automotive AEC-Q100 calls for 1,000 cycles. MIL-STD-810 Method 501/502 : 3-10 cycles at high severity. For aerospace qualifications according to RTCA DO-160: 20-100 cycles. This number should always be calibrated to the product's mission profile.

What is the difference between “linear” and “shock” ramp?

The linear ramp involves a controlled transition at a constant rate (e.g., 5°C/min) between the two test temperatures, with an intermediate dwell period. The shock (or rapid change) profile involves transitions in a few minutes or less than 30 seconds (pure shock). The choice depends on the standard: IEC 60068-2-14 Nb uses linear ramps, Na uses shocks. The ramp dramatically influences the induced mechanical stress.

Is controlled humidity required during the thermal cycle?

Not always. The "dry" thermal cycle only affects temperature—the typical use case of a thermostatic chamber —and is sufficient for mechanical expansion tests. The thermo-hygrometric (with controlled humidity) is required for corrosion, moisture penetration, and electronic package delamination tests. Standards such as IEC 60068-2-30 (damp heat cycling) and MIL-STD-810 Method 507 add humidity control to the thermal profile.

Can I simulate real (non-sinusoidal) usage profiles?

Yes, with chambers equipped with an advanced programmer (such as the revoFACE FDM), you can load custom profiles from CSV, replicate real-world telemetry data collected on vehicles or systems, and reproduce nonlinear multi-step cycles. This mission profile testing is increasingly in demand in the automotive, aerospace, and energy storage industries (where tests are performed in battery test chambers) to reduce overdesign and better correlate lab results with real-world product life.

Reference Standards

• IEC 60068-2-14:2009 — Environmental testing – Test N: Change of temperature. Covers Na (rapid), Nb (linear), Nc (rapid, two liquid baths).
• JEDEC JESD22-A104F — Temperature Cycling, JEDEC standard for IC qualification with 6 conditions (A-T3) between -65°C and +150°C.
• MIL-STD-810H Method 501/502 — High/Low Temperature for Military Equipment, with 8 procedures for storage, operational, and cycling.
• ISO 16750-4:2023 — Road vehicles – Climatic loads, automotive reference for thermal cycle on ECUs and electronic modules.
• AEC-Q100 Grade 0/1/2/3 — Temperature cycling test required for automotive IC qualification, with 1000 Grade 1 cycles.
• RTCA DO-160G Section 5 — Temperature Variation for avionics, profile with ramps defined by operating altitude.
• EN 50155:2017 — Railway applications – Electronic equipment, with thermal cycle classes T1-T3.

Authoritative Sources

• IEC – International Electrotechnical Commission. International electrotechnical standards body, responsible for the IEC 60068 series of environmental testing standards.
• JEDEC Solid State Technology Association. American organization that publishes the JESD22 reference standards for semiconductors.
• Automotive Electronics Council (AEC)issues AEC-Q100 for automotive IC qualification and calls for thermal cycling as a mandatory test.
• RTCA. American organization that publishes DO-160 for avionics, the world reference for aerospace environmental qualification.

Other Frequently Asked Questions about Thermal Cycling

How do you calculate the acceleration of a thermal cycle compared to real life?

The most widely used model is the modified Coffin-Manson for thermomechanical fatigue: N_f,test / N_f,field = (ΔT_field / ΔT_test)ⁿ × (f_field / f_test)^m × exp[E_a/k × (1/T_max,field – 1/T_max,test)]. Typical exponents for SnAgCu welds are n ≈ 1.9-2.5 and m ≈ 0.33. For a ΔT_test of 165 °C (AEC-Q100 Grade 1) versus a ΔT_field of 60 °C (under-hood automotive), an acceleration factor of 10-20x is obtained, so 1000 AEC-Q100 cycles correspond to approximately 15 years of vehicle life. The typical activation energy E_a is 0.5–0.7 eV for thermal fatigue mechanisms, while it is 0.9–1.1 eV for metal diffusion (combined electromigration). OEMs generally require a safety factor of 1.5–2x on the calculated cycle count.

What is the difference between a long and short dwell thermal cycle?

Dwell time (time spent at the extreme temperature) determines which failure mechanism predominates. Short dwell times (2-10 min) primarily accelerate reversible related to elastic expansion, useful for BGA and MLCC fatigue testing. Long dwell times (30-60 min) allow for diffusion and creep, relevant for solders, adhesives, and intermetallics. JEDEC JESD22-A104 Condition G prescribes a 10-min dwell (typical for consumer electronics), while for ESCC ECSS aerospace testing, 60-120 min is recommended to simulate long periods in orbit in the shadow. This choice also impacts overall life: 1,000 cycles with a 10-min dwell and 5-min transitions last approximately 500 hours; with a 30-min dwell, this becomes 1,000-1,500 hours. Very long dwells require long-term chamber stability of ±0.5°C, with repeatability verified via IEC 60068-3-5 mapping.

How to combine thermal cycle and humidity in a THB profile?

THB (Temperature Humidity Bias) is a heat-damp test with electrical bias, typically according to JEDEC JESD22-A101 (85 °C/85% RH, 1000 hours) or IEC 60068-2-30 Db (24-h cycles between 25 °C with ≥ 95% RH and 40 or 55 °C with 93% RH). In the JEDEC THB, temperature and humidity remain constant; in the Db, the temperature cycles and condensation forms on the sample during the rise, with humidity ≥ 95%. Condensation + applied voltage accelerates electrochemical corrosion, ion electromigration, and passivation delamination. THB chambers must manage the “dew point” without freezing or overheating the humidity sensors: humidification is achieved by injecting ultrafiltered vapor, with capacitive HMI sensors at strategic points not exposed to direct condensation. Typical tolerance is ± 2 °C/± 3% RHis usedHAST at 130 °C/85% RH in a pressurized autoclave.

What are the differences between ISO 16750-4 Code 01, 02 and 03 profiles?

ISO 16750-4 Code defines three automotive thermal load severities. Code 01 (passenger compartment): -40 °C to +85 °C for components in the passenger compartment, 1000 typical cycles. Code 02 (engine compartment, not directly on the engine): -40 °C to +125 °C, 1000 cycles, for ECUs in the engine compartment not in direct contact. Code 03 (on engine): -40 °C to +150 °C or +155 °C, for sensors and actuators mounted on the engine block, 500-1000 cycles. The profiles include a 30-minute dwell at each extreme, 1-3 °C/min ramps, and stabilization for at least 50% of the chamber time dedicated to the thermal regime. Correspondence with AEC-Q100 is: Code 01 ≈ Grade 3/2, Code 02 ≈ Grade 1, Code 03 ≈ Grade 0. Tests require environmental chambers with a range of -50/+170 °C to have margin on set points and post-test verification of electrical parameters on 100% of the samples.