"Double 85" Test: How Constant Temperature and Humidity Chambers Simulate Extreme Conditions to Forge Product Reliability

  In industrial manufacturing, particularly in sectors like electronics, automotive, photovoltaics, and new materials, a specialized term is frequently heard—the "Double 85 Test." This test, which might sound somewhat enigmatic, is an indispensable part of modern product quality and reliability verification. The core equipment tasked with executing this critical procedure is the Constant Temperature and Humidity Chamber. This article provides a detailed look into what the "Double 85" test entails, the standards it conforms to, and how these chambers accomplish this harsh environmental challenge. The test indicators comply with international standards such as IEC61215 and IEC61646, as well as domestic specifications such as GB/T19394.

What is the "Double 85" Test? – Definition and Essence

"Double 85" is a common industry term that precisely describes a specific set of temperature and humidity conditions:

The First "85": Refers to a temperature of +85°C.

The Second "85": Refers to a relative humidity of 85% RH.

Thus, the "Double 85 Test" typically involves placing test samples inside a Constant Temperature and Humidity Chamber and maintaining the environment at a constant +85°C and 85% RH for an extended period to conduct aging, durability, or reliability evaluations.

Deeper Understanding:
The "Double 85" test is not merely the simple combination of two numbers. It simulates the extreme high-temperature and high-humidity environments commonly found in summer in many regions of the world (e.g., tropical and subtropical areas). This environment is highly aggressive and acts as a powerful catalyst for products, especially electronic and electrical components, rapidly exposing potential defects.

Why 85°C and Not 95°C or 60°C?

  The Double 85 test is a standard established by reliability testing engineers to accelerate the product lifecycle testing process. In real-world scenarios, it is rare to encounter conditions of 85°C temperature and 85% humidity. Therefore, the Double 85 test is not intended to replicate actual usage environments but rather to simulate product reliability under extreme conditions.

While higher temperature and humidity levels might more closely resemble certain real-world environments, why not opt for even harsher test conditions? The reason lies in statistical analysis, which shows that failures occurring under such extreme test conditions often do not reflect issues that would arise during actual product use. Instead, they are frequently caused by excessive stress imposed by the test conditions themselves. Through accumulated practical experience, the Double 85 test method has been recognized as more aligned with real-world scenarios. It effectively meets the need for evaluating product reliability under extreme conditions, making it an ideal and reasonable testing approach.

Why Conduct the "Double 85" Test? – Purpose and Significance

  The core purpose of the "Double 85" test is accelerated stress testing. Issues that might take years to manifest under natural environmental conditions can appear within just hundreds or even tens of hours under the stringent "Double 85" conditions. Its main assessment objectives include:

  Evaluating Material Tolerance: Checking whether non-metallic materials like plastics, rubbers, coatings, and adhesives will deform, discolor, age, or decompose under high temperature and humidity.

  Inspecting Component Reliability: Testing whether electronic components such as integrated circuits, PCBs, capacitors, and resistors can operate stably under extreme conditions, preventing internal corrosion, ion migration, open circuits, or short circuits caused by damp heat.

  Verifying Overall Product Stability: Assessing whether the sealing performance, mechanical properties, and electrical performance of the final product (e.g., mobile phones, automotive controllers, solar inverters, batteries) meet standards.

  Accelerated Life Testing: By applying stress far exceeding normal usage conditions, quickly estimating the product's service life and failure rate, providing data support for design improvements and quality control.

  In simple terms, a product that passes the "Double 85" test demonstrates its potential for long-term stable operation in harsh environments, indicating higher reliability and more trustworthy quality.

The Constant Temperature and Humidity Chamber: Key Equipment for "Double 85"

  A Constant Temperature and Humidity Chamber capable of performing the "Double 85" test must possess the following key systems and characteristics to meet the precision requirements of the aforementioned standards:

  Heating System: Uses high-quality heating elements to rapidly and uniformly raise the chamber temperature to 85°C.

  Refrigeration System: Crucial for the cooling phase and for controlling humidity (via dehumidification), even though the test requires high temperature. Typically uses mechanical compression refrigeration.

  Humidification System: The core for achieving 85% RH high humidity. Usually employs a boiler to produce pure steam or a water pan evaporation method to inject steam precisely into the chamber.

  Control System: An advanced microprocessor controller acts as the "brain," allowing precise setting and maintenance of temperature and humidity values, with real-time monitoring to ensure fluctuations stay within tolerance (e.g., Temp ±0.5°C, Humidity ±2% RH).

  Sensors: High-precision PT100 temperature sensors and capacitive humidity sensors provide real-time data feedback to the control system for closed-loop control.

  Chamber Construction: The interior is typically made of corrosion-resistant, easy-to-clean stainless steel. It features excellent insulation and sealing to ensure a stable internal environment without energy loss.

Typical "Double 85" Test Procedure

  A standard "Double 85" test typically follows these steps (using JESD22-A101 as an example):

  Sample Preparation & Initial Testing: Perform visual inspection and electrical performance tests on samples, recording baseline data.

  Parameter Setting: Strictly set the target temperature (+85°C), target humidity (85% RH), duration (e.g., 1000 hours), and connect the bias supply according to the standard on the controller.

  Startup: The equipment begins operation, heating and humidifying according to the preset program. Temperature and humidity are strictly controlled within the set values (e.g., Temp ±0.5°C, Humidity ±2% RH).

  Continuous Operation & Monitoring: The chamber maintains the "Double 85" conditions and bias voltage for the entire set period, while the equipment status is monitored.

  Recovery: After testing, samples are stabilized for a specified period (e.g., 24 hours) under standard room temperature/humidity recovery conditions.

  Final Inspection & Evaluation: Conduct comprehensive final inspections on the samples. Compare results with pre-test data and determine pass/fail based on the failure criteria defined in the standard (e.g., whether parameter drift exceeds limits, functional failure).

85°C Temperature and 85% Relative Humidity. This stringent test environment accelerates material aging and reveals potential defects, thereby playing a critical role in quality control across multiple industries. The following sections detail typical products and materials that require the Double 85 test and analyze the necessity of such testing.

Electronic and Electrical Products

  Electronic components, circuit boards, and end-devices are primary subjects of the Double 85 test. Components such as integrated circuits (IC), resistors, capacitors, and inductors are prone to issues like metal migration and decreased insulation performance under high humidity and temperature. For example, if a smartphone motherboard exhibits solder joint oxidation or circuit shorting after a 500-hour Double 85 test, improvements in packaging processes are needed. The Potential Induced Degradation (PID) test for photovoltaic modules (solar panel) also relies on Double 85 conditions, as humidity accelerates ion migration between the glass and EVA film, leading to reduced power generation efficiency. Additionally, LED driver power supplies and Automotive Electronic Control Units (ECU) require this test to verify their reliability in tropical climates or high-temperature environments like engine compartments.

Polymer Materials and Coatings

  The weather resistance evaluation of non-metallic materials such as plastics, rubbers, and adhesives is inseparable from the Double 85 test.      Examples include:

-Engineering Plastics:PA66 (Nylon) tends to absorb moisture and depolymerize in damp-heat environments, leading to reduced mechanical strength. Components like automotive intake manifolds require testing for hydrolysis resistance.

-Sealing Materials:When silicone rubber gaskets are used for sealing the edges of photovoltaic modules, the Double 85 test can simulate 25 years of outdoor aging. If cracking occurs, formula adjustments are necessary.

-Coatings and Platings:The test is used on automotive electrocoat paint and UV coatings on appliance housings to check for blistering or peeling. For instance, cracking observed in a brand's air conditioner panel coating after 240 hours of testing was traced back to an insufficient curing process.

New Energy and Energy Storage Equipment

  Materials used in lithium batteries, such as anodes, cathodes, separators, and electrolytes, are highly sensitive to humidity. The Double 85 test can accelerate electrolyte decomposition, helping detect gas production that might cause battery swelling. In one case, an 18650 battery cell experienced an internal short circuit due to separator shrinkage during testing, prompting the manufacturer to switch to a ceramic-coated separator. The coating on bipolar plates for hydrogen fuel cells also requires this test to verify corrosion resistance, as humidity exacerbates electrochemical corrosion of metal plates.

Critical Components in the Automotive Industry

  Beyond the automotive electronics mentioned earlier, the following components also require testing:

-Wiring Harnesses and Connectors: PVC insulation may become brittle in damp-heat conditions, and oxidation of terminal platings can lead to poor contact. The Volkswagen Group, for example, requires wiring harnesses to withstand 1,000 hours under Double 85 conditions without failure.

- Interior Materials:During damp-heat aging tests for seat polyurethane foam, if formaldehyde emissions exceed standards, low-volatility additives must be used.

-Rubber Products:If windshield wiper blades show hardening or cracking after testing, adjustments to the vulcanization system are needed.

Military and Aerospace Products

  Airborne equipment and satellite components must withstand extreme environments. For instance, Double 85 testing on an avionics module for a fighter jet exposed cracking issues in the epoxy resin potting compound, leading to a switch to polyurethane material. Silicon solar cells for spacecraft solar panels are screened using this test to select models resistant to PID.

Medical and Packaging Materials

-Medical Plastics:If the transparency of PP material used in syringes decreases after testing, it might affect the stability assessment of medications.

-Pharmaceutical Packaging:Aluminum-plastic blisters are prone to delamination in damp-heat environments, requiring verification of adhesive performance.

- Sterilization Packaging: Materials like Tyvek need to maintain their microbial barrier function after being subjected to the test.

Test Standards and Industry Regulations

Different fields adhere to specific standards:

-Electronics Industry:IEC 60068-2-66 (HALT Testing), JESD22-A101 (Steady-State Temperature Humidity Bias Life Test)

-Photovoltaics Industry: IEC 61215 (Damp Heat Cycle Test), UL 1703

-Automotive Industry: ISO 16750-4, Volkswagen PV1210

-Military Standards:GJB 150.9A-2009 (Damp Heat Test for Military Equipment)

Conclusion

The "Double 85" test, with its seemingly simple pair of numbers, embodies a pursuit of product quality, backed by a rigorous system of international and national standards. The Constant Temperature and Humidity Chamber, as the tool enabling this goal, simulates extreme environments. It acts like a strict "quality examiner," following a defined "syllabus" (the various standards) to expose product weaknesses proactively. It is this philosophy of "basing actions on standards and preparing for rainy days" that ensures products reaching end consumers can withstand the tests of time and environment, being safer, more reliable, and more durable.