Temperature shock test cycle number setting basis

——Thermal shock test chamber in the industry application of standardization analysis

In product reliability testing, the Thermal Shock Test (TST) is a key method for verifying structural integrity, solder joint fatigue life, and material thermal stability. The rapid conversion between high and low temperatures can simulate the thermal stress load of devices in extreme environments, and the thermal shock test chamber is a standardized equipment to realize such tests.

In this paper, we will set the basis for the number of temperature shock cycles, the structure of the thermal shock test chamber classification, the typical selection requirements of various industries in three dimensions, systematic elaboration of the thermal shock test application technology and equipment configuration recommendations.

I.The standardization of temperature shock cycle number setting basis

Cycle number is defined as the product in the high temperature and low temperature between the completion of a complete switching process, for example: high temperature → low temperature → high temperature, that is, a complete cycle.

The scientific nature of the cycle number setting directly affects the adequacy and representativeness of the product verification, so the international standards are clearly defined:

Literature support: IEC 60068 series, JESD22 Reliability Test Standard, MIL-STD 883H document, ISO/TS 16949 Reliability Verification Guidelines, and so on.

In the test, the specimen surface temperature after conversion in the specified time to reach the target temperature (such as MIL standards within 16 minutes to reach ± 10%), the conversion mechanism and response speed of the thermal shock test chamber has become a key performance indicator in the cycle test.

II. The type of structure of the thermal shock test chamber: two-box and three-box

According to the structure of the test equipment, the thermal shock test chamber is mainly divided into ** two-box (Two-Zone) and three-box (Three-Zone)** two kinds of:

1. Two-box thermal shock test chamber

Structural features: high-temperature zone, low-temperature zone of the two independent space, the product by the mechanical arm or tray in the two zones of rapid movement;

Conversion mode: physical movement of the sample; conversion time: within 5 to 10 seconds; Advantages: simple structure, fast conversion; easy maintenance; Limitations: can not pass through the middle of the normal temperature zone is not applicable to the requirements of “through the standard test” (room temperature).

Conversion method: Physical movement of the sample;

Conversion time: within 5-10 seconds;

Advantages: Simple structure, fast conversion, easy maintenance;

Limitations: Cannot be intermediate through the room temperature zone, not applicable to the requirements of the standard test “through the room temperature” (such as some of the IEC / MIL specifications).

Detailed advantages, types of applications, etc. can refer to the two-box thermal shock test chamber in the reliability of applications

2. Three-box thermal shock test chamber

Structure features: Three independent temperature zones: high temperature, normal temperature, low temperature;

Conversion mode: Air conversion through airflow guidance or valve switching;

Applicable standards: Applicable to the requirements of the “through the transition to room temperature” of the norms, such as MIL-STD-810G, JEDEC JESD22;

Advantages: Closer to the ambient temperature process, suitable for testing of high precision structural components and brittle materials;

Limitations: Slightly longer changeover time, high structural costs.

Practical applications can refer to the application of the three-box thermal shock test chamber

III. The cycle number set the five core factors

1. Product applications

Consumer electronics: cell phones, wearable devices, etc., the recommended number of cycles 10 ~ 30 times;

Automotive electronics: ECU, battery management system, etc., usually performs a three-box cold and thermal shock test chamber, recommended 100 ~ 1000 times;

Semiconductor devices: die, packaging module often perform ≥ 500 times the impact cycle;

Military aerospace products: extreme environment, high reliability requirements up to 1000 times

High reliability requirements, the number of cycles up to 1000 times or more.

Citation: JEITA-ED4701 standard suggests that IC devices should be subjected to ≥1000 cycles of thermal shock test (-65°C ↔ 150°C).

2. Material Structure and Failure Mechanism

The main types of failure verified by thermal shock include:

Solder joint fatigue (SnPb / SAC solder)

BGA package cracking

Plastic-metal interface peeling

Flexible Printed Circuit Board (FPC) interlayer separation

If the material has a large difference in thermal expansion coefficient, such as the glass + metal mixed structure, it is more suitable for the use of the three-box thermal shock test chamber to increase the “room temperature buffer” process to prevent the instantaneous thermal shock. Buffer" process to prevent instantaneous cracking.

3. Purpose of testing (screening/lifetime/quality acceptance)

4. Standard/Customer Certification Requirements

Customers such as Apple, Tesla, Bosch, Intel, etc. have clear specifications, e.g.:

Tesla specifies that the BMS module must pass 500 cycles of cold and hot shocks from -40°C to +85°C;

Intel's JEDEC JESD47 specifies that the IC needs to complete 1,000 cycles of shocks in a triple-boxed device;

Apple's MFi standard specifies that The number of cycles needs to be combined with a room temperature buffer section, which needs to be supported by a three-box device.

In this kind of high-end verification, the thermal shock test chamber should not only support programmed control, but also equipped with temperature data logger and thermocouple interface to meet the IEC 60068-2-14 Recovery Time verification.

5. Conversion Control and Thermal Balance Confirmation

The standard requires that the center temperature of the sample reaches the set point in the thermal shock test chamber before the cycle is counted as complete. The following conditions must be reached:

Temperature conversion time: ≤ 10 seconds (GJB 150A);

Setting temperature stability: ± 2 ℃ (GB/T 2423.22);

Thermocouple to confirm the sample temperature response speed (MIL-STD-883);

Soaking time: 10~30 minutes depending on the product heat capacity setting.

IV. The number of recommended thermal shock test cycles in different industries

The number of cycles in the temperature shock test is not “the more the better”, but needs to be based on the product application, test purpose, structure material and customer standards. The two-box thermal shock test chamber is suitable for mass production testing or rapid stress testing, while the three-box thermal shock test chamber is more in line with the actual use of environmental simulation, suitable for high-reliability industries.