The purpose of temperature and humidity testing is to determine how components, subsystems, and complete systems will perform in harsh environments involving high temperatures and fluctuating relative humidity levels. The test can be a static test with constant temperature and humidity, a cycle involving both, a temperature-humidity bias test (where moisture is used to induce electrical equipment failure), or some combination of all of these.
Temperature/humidity tests study, inter alia, the effects of climate change on electronic components, such as failures due to parameter changes, mechanical failures (due to rapid formation of water or frost), optical failures (fogging), water tightness (encapsulation) failures, material failure degradation (epoxy coating, etc.) and so on. Temperature/humidity testing is a key component of a complete qualification program.
Many electrical components, while inexpensive to purchase, can be expensive to replace. The failure of LCDs on oil exploration equipment or marine instrumentation can cause significant downtime costs. The combined temperature and humidity testing of complete systems and finished products extends beyond electronic components: copiers, computers, automobiles, etc.
You must ensure that your products can withstand all environmental loads and stresses they will face once they enter the production, transport, storage, and use environment.
Temperature and humidity are the two most important environmental factors in determining whether your product will still function optimally while in use. Through temperature and humidity testing, manufacturers can gain insight into how an object responds to the environmental conditions it encounters throughout its lifecycle.
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1. What is temperature and humidity testing?
Temperature and humidity testing is an umbrella term. It is an engineering and manufacturing overview of a series of environmental stress tests, such as high/low-temperature testing, moisture resistance testing, or temperature cycling testing. Programs such as temperature and humidity deviation tests also belong to it.
Regardless of what each test type is called, they determine the performance or behavior of complete systems, subsystems, and individual components of manufactured products under normal and harsh environmental conditions. In most cases, the extreme changes are temperature and humidity. However, other environmental factors such as sand, dust, corrosion, and vibration also fall under the scope of performance testing.
The basic premise of temperature and humidity testing is to subject your product to elevated environmental stress and induce failure. During temperature and humidity testing, a variety of forces are applied, depending on the specific product.
Material under test is placed in a controlled-environment test chamber, and temperature, humidity, and other factors are artificially adjusted. Variations in these high and low parameters can lead to mechanical failure of the product, fogging or condensation, water ingress, and degradation of materials of construction.
There are several good reasons why you make temperature and humidity testing a top priority of their quality control programs. In the right hands, environmental testing will expose a product to the extremes of what it will experience in the real world, whether those conditions are natural or artificial.
Electronic assemblies and components, for example, are prime candidates for temperature and humidity testing. Manufacturers with experience know that it is better for parts to fail in a test chamber than in operational applications, where downtime and repairs can be prohibitive.
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2. What is the purpose of the temperature and humidity test?
Packages and the products they carry can be exposed to many extreme environments in the manufacturing, shipping, and delivery processes. Containers, trucks, and warehouses are themselves microclimates during transport and storage.
When packages leave the East Coast during the winter, they may encounter cold, wet conditions en route to the warm, humid climate of Florida or the scorching deserts of Arizona. As packaging and products pass through these climates, appearance or performance may change, altering their integrity.
You can explain how their product or packaging will react to various environmental conditions by conducting temperature and humidity tests. Armed with this information, you can identify and address potential vulnerabilities in their products and/or packaging systems.
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3. Two basic forms of Temperature and Humidity Test
There are two basic forms of environmental testing here. Temperature and humidity tests fall into two categories, called mock and stimulus. To clear up any confusion over these similar-sounding terms, here is a brief description of two very important parts of temperature and humidity testing:
- Test Simulation
An environmental laboratory that artificially simulates or simulates the conditions a product might reasonably experience in its final operating environment. The normal use environment test is a “test pass” benchmark that periodically evaluates expected stresses such as temperature, humidity, wear, and vibration. If the product complies with the conventional marks, it is certified and sent for production and distribution.
- Test Stimuli
This test procedure or method goes a step further than conventional simulations. Increased environmental pressure can reveal product weaknesses and failure points. In contrast, accelerated stimuli of extreme stresses, such as temperature and humidity, demonstrate a product’s ability to withstand environmental factors beyond its usual use. Test stimuli are also known as accelerated tests.
In environmental fluctuations, temperature is the most common product stress. Temperature changes can cause the product to expand or contract. Rates vary based on the type of material tested. Temperature test parameters are always set according to the materials involved in the test procedure, as plastics react differently than metals.
Humidity is the second largest environmental stressor affecting finished products. Humidity fluctuations can also cause expansion and contraction, but environmental test technicians are more concerned with how humidity affects the inner workings of a product.
Moisture penetration or leakage is an important factor in oxidation and corrosion. Moisture resistance is a major performance consideration for products involving electrical or computer mechanisms.
While most product testing procedures focus primarily on temperature and humidity, many test chambers include additional checks. Vibration testing is often accompanied by basic temperature and humidity testing.
When combined with physical vibrations, expansion, contraction, ingress, and leakage behaviors often lead to complex problems. These three stressors combine to cause the product to lose mechanical strength through cracking, swelling, shifting, and impaired physical properties. They contribute to product fatigue and premature failure.
Finally, the temperature and humidity umbrella can include additional testing for stressors caused by altitude or groundwater compression. Corrosion is an ongoing concern for metal products. Sand, dust, and grit also cause wear on all types of products, whether they are made of metal, plastic, or any form of composite material.
Product testing through controlled and intentionally induced environmental stressors is the only way to artificially determine how a designed and manufactured component or subassembly will perform in its intended role. Different pressure products ensure that they perform as intended during normal use. The key to accurately evaluating products is how to conduct temperature and humidity tests.
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4. How to conduct temperature and humidity tests?
Temperature and humidity tests are conducted in an artificial environment. It involves test chambers that induce, control, monitor and evaluate changes in temperature and humidity. Test chambers typically include vibration shaker tables and equipment to condition exposure to abrasives such as sand and dust.
Test chamber sizes vary. Some chambers are small and designed to test tiny components like circuit boards and controllers. Medium-sized chambers accommodate larger objects or multiple loads of small products for large-scale testing. Sometimes very large candidates such as vehicles and machinery require temperature and humidity testing. Custom test chambers are often built for these applications.
Each chamber has specially designed physical controls for temperature and humidity testing. These limits depend on the range of simulated environmental stressors engineers expect the product to be exposed to. One of the most common temperature and humidity testing controls involves the 85/85 test.
5. 85/85 test
The 85/85 test uses temperature and humidity test thresholds suitable for most environmental assessments. It sets the test chamber conditions to an internal temperature of 85 degrees Celsius and a relative humidity index of 85%. Several engineering evaluation specifications specify that this hot and humid environment can be maintained for up to 1,000 hours.
For a given product, the 85/85 test simulates 20 years of moisture intrusion. This number is an approximate parameter and is usually improved by implementing a bias application or so-called temperature-humidity bias (THB) reliability test.
Bias refers to the inductive induction of a steady voltage to electrically activate a device or test object. The THB test is especially useful for objects exposed to corrosive elements.
A thousand hours seems like a long time for an 85/85. In practical applications, however, the possibility is very real, and many manufactured products are expected to function. In order to shorten the lengthy test cycle, the temperature and humidity testing specialists use two accelerated processes：
- Highly Accelerated Life Testing (HALT)
This testing process implements severe temperature and humidity changes. Highly accelerated life testing also uses multi-axis shock vibration, greatly reducing test time while remaining accurate in artificially inducing real-time stressors.
The HALT test identifies product weaknesses and strengths more quickly than passive chamber testing. This accelerated approach detects flaws in the design and prototyping phases and enables product engineers to quickly develop proactive solutions.
- Highly Accelerated Stress Screening (HASS)
Prior to shipping, defective products and their parts are quickly screened using this temperature and humidity testing procedure. Testers use the HASS stress screening process on designed and validated products that undergo final quality control checks before shipment from the manufacturing center. HASS is a similar test to HALT, but less aggressive.
Thermal cycling is another term often associated with performing temperature and humidity tests. It involves exposing test subjects to controlled cycles of heat/cold and wet/dry for varying periods. The length of exposure and extreme environments depends entirely on the type of product and its intended application.
The final temperature and humidity evaluation that is typically performed is a thermal shock test in a thermal shock test chamber. It involves heating or cooling the product to its maximum extent and then rapidly reversing the temperature. Thermal shock testing is an extreme method. It is generally reserved for products used in the military and aerospace industries where parts and assemblies experience harsh climatic conditions.
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6. Temperature and Humidity Test Certification and Specifications
It is the goal of every professional temperature and humidity testing program to meet and exceed industry standard certifications and specifications. Many government and non-government agencies specify test thresholds and benchmarks for thousands of common products. Unique products also comply with the guidelines and parameters set by regulatory and advisory bodies.
The most commonly used product standards come from the US Department of Defense. They are called MIL-SPEC Defense Specifications, MIL-STD Defense Standards, and MIL-HDBK Defense Handbook. Each standard, code, and manual item is detailed and commonly used for civil manufacturing test controls.
Other agencies provide guidance and control standards for the temperature and humidity testing industry. The two common authorities are the American Society for Testing and Materials (ASTM) and the Society of Automotive Engineers (SAE). For most temperature and humidity tests, the following are the main standardization documents:
- MIL-STD 883
- MIL-STD 810
- Military Standard 750
- Military Standard 202
- ASTM B117
- SAE J1455
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7. Weaknesses found through temperature and humidity testing
In fact, temperature and humidity testing is the primary method used by the manufacturing industry to identify and correct various product defects. During testing, weaknesses are exposed through high and low temperatures, high and low humidity, thermal cycling, and thermal shock. These complex tests expose product vulnerabilities and predict product viability.
All products that have passed the temperature and humidity test have passed the life test and passed the analysis. The result is a recognized certification that protects consumers and propels manufacturers to become industry leaders. The following are some of the weaknesses commonly found through temperature and humidity testing:
- Epoxy Coating
Many products used in harsh environments contain epoxy coatings. Temperature and humidity testing puts epoxy-coated products under extreme stress, exposing any weak points from expansion, contraction, moisture ingress, and surface corrosion or wear.
- Fogging
Typically tested for seals such as windows and windshields. Weaknesses in any product can quickly become apparent when stressed by hot and cold cycles of humidity and dryness. It is a sure sign that a product will fail if moisture fogs between layers.
- Watertightness
Products exposed to moisture are the best candidates for testing. For example, bathtubs, and sinks. If the bathtub manufacturer finds a leak or seepage weakness after testing, it means that the product test fails. These failures can appear quickly in testing, or they can require a long evaluation period.
- Mechanical Failure
Thermal cycling and cold cycling can damage many products, often leading to minor or catastrophic failures. Testing is front-line insurance against a product failing in the field and causing damage or injury.
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8. Products suitable for temperature and humidity testing
Various industries, including medical, automotive, defense, aerospace, energy, and telecommunications, rely on temperature and humidity testing. In these industries, humidity and temperature testing can be used for the following products:
- Medical equipment
- Electrical components
- Engine assembly
- Batteries and Solar Panels
- Adhesives and caulks
- Glass product
- Medical Diagnostic Products
- Medicine container
- Military Ammunition and Weapons
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9. Conclusion
Any component of your products that needs to be shipped is subject to some degree of heat. Whether transported by road, rail, or ship, all components are exposed to some kind of dry or humid heat. It is therefore common to perform temperature and humidity tests on these products.
Linkotest performs the necessary checks and balances across a wide range of industry sectors. Our engineers and technologists take pride in being problem solvers. Our team simplifies complex tasks and delivers fast, accurate results in testing for temperature, humidity, corrosion, and other types of product failures.
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