Thermal Shock MIL-STD-202 Method 107

Reviewed by SEMI Gr

MIL-STD-202 Method 107: Thermal Shock

Method 107 is for equipment or parts that move between heated shelters and Arctic conditions. This is the situation described in the standard. Similar temperature changes can happen when equipment is used on and off in cold regions or during transport. The test is for individual components and parts, not complete systems.

MatX Lab performs thermal shock testing on electronic components, connectors, relays, capacitors, transformers, hermetic packages, and assembled boards.

What the MIL-STD-202 Method 107 Determines

The test establishes a part’s resistance to extremely high and low temperatures and to the shock of alternating exposure between them.

The standard is explicit about the mechanism. Permanent changes in operating characteristics and physical damage from thermal shock result mainly from variations in dimensions and other physical properties, rather than from the temperatures themselves.

The standard also allows a practical compromise. Thermal stability during each exposure is preferred, but parts can be tested at the minimum exposure times specified to save time. These shorter exposures may not provide full stability and may only get close. This is an option built into the method, not a shortcut, and the basis for using it should be included in the report.

Test Conditions

Condition letters are selected based on application severity, procurement requirements, and the applicable part-name specification, not convenience.
Transfers between chambers are usually limited to five minutes or less. The method’s tables set the time spent at each temperature, not the operator. Changing those times also changes the test conditions and what the result represents.

The method covers air and liquid arrangements alike, with separate tables for thermal shock conditions in air, exposure times at the temperature extremes in air, and thermal shock conditions in liquid.

Liquid Transfer and Fluid Selection

Liquid-to-liquid transfer creates a much more severe thermal shock than air because liquid moves heat into and out of the part much faster.
Fluid choice is also limited. The method lists recommended thermal fluids and specifically prohibits ethylene glycol as a thermal shock test fluid.

Tap water is acceptable within its temperature range, provided its chemical suitability is established before use, and a water-alcohol mixture may be used to prevent freezing at the low extreme. The water must not be allowed to boil at the upper extreme, which sets a practical ceiling on the range it can achieve.
Fluorocarbon fluids can cover temperature ranges that water cannot, and the method lists several proprietary fluid families by name.

The important point is whether the fluid is compatible with the part. A fluid that gets into a connector, swells a seal, or leaves residue on a contact surface can cause a failure caused by the fluid, not the part.

Failure Modes and Method Names

The standard lists the effects thermal shock produces, and the list is a useful checklist for post-test inspection:

• Cracking and delamination of finishes
• Cracking and crazing of embedding and encapsulating compounds
• Opening of thermal seals and case seams
• Leakage of filling materials

Other issues include solder joint fatigue, ceramic fracture, coating delamination, and mark degradation, which regularly occur on components that undergo hard enough cycling.

Inspect after the final cycle to cover the case, leads, seals, and markings. Any damage constitutes a failure, and so does any deviation from the specified end-point measurements.

Method 107 Against Related Methods

Three methods cover similar ground and are not interchangeable

1. MIL-STD-202 Method 107 is used for electronic and electrical components and parts. The test can be run using either air or liquid.
2. MIL-STD-883 Method 1011 is for thermal shock in microcircuits and uses liquid-to-liquid transfer. Method 1010 covers air-to-air temperature cycling for the same type of devices. The temperature changes are controlled to build up fatigue over repeated cycles rather than cause immediate damage.
3. MIL-STD-810 Method 503 covers temperature shock at the equipment and system level, not the component level.

A specification named one should be met with data from that one. Conditions, transfer times, and sample requirements all differ enough that results do not transfer between them.

Programme Requirements

Baseline electrical and physical characterization before the first cycle, since the failure criterion includes deviation from specified end-point measurements and there is nothing to deviate from otherwise.

Part quantity sufficient for the sampling plan plus spares, since the test is destructive in effect where failures occur, and parts are not returned to stock.
For liquid work, confirm fluid compatibility with the part construction before the program begins. A connector with a wicking path or a part with a porous marking is a candidate for a fluid-induced failure that tells you nothing about thermal shock.