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What reliability tests are generally included for LCD modules?

What reliability tests are generally included for LCD modules?

LCD module reliability testing generally includes the following items:

  • High-temperature operation
  • High-temperature/high-humidity
  • Low-temperature operation
  • Temperature cycling
  • Vibration
  • Mechanical shock
  • Electrostatic discharge
  • Key or connector life
  • Backlight life
  • Optical performance stability

In simple terms, reliability testing is to verify whether the LCD module can continue to display, maintain stable connection, and retain brightness, contrast, and structural integrity under specified environmental and usage conditions. Here, "reliability" refers to the ability of a product to continue to operate normally within a specified time and under specified conditions; an "LCD module" is a display assembly composed of an LCD panel, backlight, drive circuit, flexible printed circuit, and connector.

金鹏 recommends establishing a test matrix according to the product application scenario, installation method, and target life, and using the IEC 60068 series, ISO 16750 series, or customer technical specifications as the basis.

  • IEC 60068: mainly used for environmental testing, such as high temperature, low temperature, damp heat, vibration, and shock.
  • ISO 16750: mainly used for environmental conditions and test methods for electrical and electronic equipment in road vehicles.
  • Test matrix: a table or scheme that maps test items, test conditions, sample quantities, test sequence, and acceptance criteria.

[Source: IEC 60068 series standards, ISO 16750 series standards, and customer technical specifications; the specific test conditions of the above standards shall be subject to the applicable version and product specification.]

I. Environmental Reliability Test Items

The environmental reliability testing of LCD modules first focuses on temperature and humidity changes. Common items include:

  • High-temperature operation
  • Low-temperature operation
  • Steady-state damp heat
  • Cyclic damp heat
  • Temperature cycling

For example, some products may refer to IEC 60068-2-78 for a steady-state damp heat test at 85 °C and 85% relative humidity for 500 hours; the specific temperature, humidity, and duration still need to be confirmed according to the product grade, and the relevant values are for reference only.

  • "Steady-state damp heat" means placing the sample continuously in a relatively stable high-temperature, high-humidity environment.
  • "Cyclic damp heat" means periodically changing temperature and humidity according to a specified procedure to simulate changes in the actual environment.
  • "Relative humidity" is the ratio of the actual water vapor content in the air to the maximum water vapor content at that temperature.

High-temperature testing mainly observes the following items:

  • Whether the LCD response speed slows down or becomes abnormal;
  • Whether the backlight brightness decays;
  • Whether the drive circuit shows abnormalities;
  • Whether the packaging materials soften, deform, or fail.

Low-temperature testing focuses on checking:

  • Whether the module starts up normally;
  • Whether motion blur appears on the image;
  • Whether the response time increases significantly;
  • Whether the flexible cable flexibility and connection reliability decrease.

Here, "response time" is the time required for a pixel to switch from one display state to another; "motion blur" refers to the phenomenon in which the previous image remains on the following image when the image changes.

According to the test approach in IEC 60068-2-14, temperature cycling can be set from -30 °C to 80 °C with 100 cycles, but the actual conditions should be determined by the product specification and the operating environment; the test data are for reference only.

  • Temperature cycling: the sample is repeatedly changed between high and low temperatures according to a specified procedure to check failures of materials, solder joints, and connection structures caused by thermal expansion and contraction.
  • Number of cycles: the number of times the sample completes a full process from high temperature to low temperature and back to the specified state.

Damp heat environments may cause the following problems:

  • Oxidation of metal terminals;
  • Adhesive failure;
  • Polarizer blistering;
  • Non-uniform display;
  • Degraded insulation performance.

After testing is completed, the following items are usually re-measured:

  • Power-on display;
  • Brightness;
  • Contrast;
  • Chromaticity;
  • Appearance;
  • Insulation performance.

Here, "brightness" is an indicator of how strongly the display image emits light; "contrast" is the difference in brightness between the brightest area and the darkest area; "chromaticity" is used to describe the hue, saturation, or color coordinates of a displayed color; "polarizer" is an optical film in a liquid crystal display used to control the polarization direction of light.

The core requirement of the IEC for environmental testing is "to evaluate the adaptability of equipment in real environments through specified stress conditions." Therefore, a single temperature test cannot replace complete environmental reliability verification.

[Source: IEC 60068-2-14 Environmental testing – Test method for temperature change, and IEC 60068-2-78 Environmental testing – Test method for steady-state damp heat. The conditions of 85 °C, 85% relative humidity, 500 hours, and -30 °C to 80 °C, 100 cycles, are example conditions and do not represent the unified requirements for all products.]

II. Mechanical, Electrical, and Life Test Items

Mechanical reliability testing mainly includes:

  • Sinusoidal vibration;
  • Random vibration;
  • Mechanical shock;
  • Free drop;
  • Connector insertion/withdrawal life.

IEC 60068-2-6 covers sinusoidal vibration testing, and some applications use a sweep frequency range of 10–500 Hz; IEC 60068-2-27 is used for mechanical shock verification. The frequency, acceleration, duration, and number of directions must be determined according to the equipment structure; the relevant parameters are for reference only.

  • "Sinusoidal vibration" is vibrating the sample according to a regular sinusoidal waveform to check structural resonance or looseness at specific frequencies.
  • "Random vibration" is irregular vibration within a certain frequency range to simulate transportation or equipment operation environments.
  • "Mechanical shock" is applying a short-duration, high-intensity acceleration change to the sample to verify its ability to withstand sudden collisions.
  • "Sweep" is when the vibration frequency changes from low to high, or vice versa, at a set rate.

For display modules installed in mobile devices, industrial control cabinets, or vehicle interiors, it should also be checked whether the following occur after vibration:

  • Screw loosening;
  • Cable detachment;
  • Solder joint cracks;
  • Screen flickering;
  • Poor connector contact.

The ISO 16750 series proposes systematic requirements for environmental conditions and test methods for electrical and electronic equipment in road vehicles, and can be used as a reference source for developing mechanical and environmental test plans for vehicle-mounted display modules.

[Source: IEC 60068-2-6 Environmental testing – Sinusoidal vibration, IEC 60068-2-27 Environmental testing – Shock, and ISO 16750 series standards. The specific vibration frequency, acceleration, and shock conditions should be determined according to the product installation location and vehicle grade.]

Electrical reliability testing usually includes:

  • Rated voltage operation;
  • Operating voltage upper and lower limits;
  • Power on/off cycling;
  • Electrostatic discharge;
  • Electrical fast transient bursts.

IEC 61000-4-2 is an important reference standard for electrostatic discharge immunity; after testing, it should be confirmed whether the module shows:

  • Freezing;
  • Restart;
  • Garbled characters;
  • Abnormal image;
  • Permanent damage.

Here, "electrostatic discharge" is the phenomenon of static electricity rapidly transferring from one object to another; "immunity" is the ability of equipment to maintain normal operation when subjected to external electromagnetic interference; "electrical fast transient burst" is a group of fast, repetitive interference pulses generated by relay, motor, or switch operations.

The National Institute of Standards and Technology (NIST) emphasizes in its electrostatic protection-related materials that electrostatic risk comes not only from the equipment itself, but is also related to personnel, materials, and grounding conditions. Therefore, the test should also review:

  • Structural grounding;
  • Assembly process;
  • Operator ESD protection measures;
  • Packaging and production site materials;
  • Ground continuity.

[Source: IEC 61000-4-2 Electromagnetic compatibility – Electrostatic discharge immunity test; NIST electrostatic protection-related materials. The test levels, discharge methods, and performance criteria should be confirmed according to product standards or customer specifications.]

Life testing may include:

  • Continuous backlight illumination;
  • Key or touch operation;
  • Connector insertion/withdrawal;
  • Long-term power-on.

After the display module completes the test, the following items should be compared before and after:

  • Brightness decay;
  • Color difference;
  • Bad pixels;
  • Flicker;
  • Light leakage;
  • Display uniformity.

Here, "brightness decay" is the phenomenon in which display brightness decreases relative to the initial value; "bad pixel" is a pixel that cannot normally display the specified color or brightness; "light leakage" is the phenomenon in which backlight escapes from the frame, screen edges, or positions that should not emit light; "display uniformity" is the degree of consistency in brightness and color across different areas of the image.

If an LED backlight is used, a life model should also be established based on actual current, heat dissipation conditions, and target usage duration; long-term performance cannot be inferred from short-term lighting results alone.

  • Actual current: the real operating current of the LED backlight in the product, rather than an estimate based only on rated values.
  • Heat dissipation conditions: the combined effect of product structure, ambient temperature, and materials on heat conduction, spreading, and removal.
  • Life model: a method for estimating the change in product performance over time based on factors such as temperature, current, and usage time.

III. Optical, Structural, and Evaluation Methods

Optical reliability testing focuses on whether the display effect changes significantly over time and environment. Common measurement items include:

  • Brightness;
  • Contrast;
  • Chromaticity coordinates;
  • Viewing angle;
  • Response time;
  • Uniformity;
  • Display defects.

The International Committee for Display Metrology (ICDM) emphasizes in Display Measurements Standard that display performance evaluation must specify:

  • Measurement conditions;
  • Instrument configuration;
  • Measurement location;
  • Measurement method;
  • Ambient light requirements;
  • Data recording method.

Otherwise, data from different batches are not directly comparable.

  • "Viewing angle" is the angular range from which the screen can still meet brightness, contrast, or color requirements when viewed from different directions.
  • "Chromaticity coordinates" are a way of expressing color position numerically, often used to compare color changes before and after testing.
  • "Optical performance" is the performance related to display effects such as brightness, color, contrast, viewing angle, and uniformity.

Structural reliability inspection includes:

  • Glass;
  • Frame;
  • Backlight assembly;
  • Flexible printed circuit;
  • Connector;
  • Fixing adhesive.

Appearance inspection and functional recheck should be performed before and after testing, with emphasis on recording:

  • Cracks;
  • Warpage;
  • Debonding;
  • Foreign objects;
  • Light leakage;
  • Terminal deformation;
  • Display abnormalities.

For 金鹏 LCD module projects, it is recommended to establish a closed-loop archive of "test conditions—sample number—initial data—process records—final inspection results" to facilitate tracing the source of abnormalities.

  • "Flexible printed circuit" is a bendable circuit board, usually used to connect the display panel with the main control circuit.
  • "Closed-loop archive" is a management method in which complete records are kept from the start of testing, through process recording, to final judgment, and which can trace the sample and cause of abnormalities.
  • "Final inspection" is the final appearance, function, and performance check after the test is completed.

[Source: ICDM Display Measurements Standard and related display measurement specifications. The specific measuring instruments, ambient light, distance, and judgment thresholds should be determined according to the product specification or the test method confirmed by both parties.]

Recommended Tiered Test Strategy

For general-purpose industrial display modules, the following basic tests can be performed first:

  • Temperature/humidity;
  • Power-on life;
  • ESD;
  • Vibration.

Then, add the following according to the customer application:

  • Drop;
  • Salt spray;
  • Dust;
  • Mechanical shock;
  • Connector insertion/withdrawal life.

For outdoor, transportation, or high-frequency operation scenarios, it is recommended to prioritize increasing the coverage of the following tests:

  • Temperature cycling;
  • Damp heat;
  • Mechanical vibration;
  • Connector life;
  • Continuous backlight illumination;
  • Electrostatic discharge.

金鹏 recommends that customers define acceptance criteria at the sample confirmation stage, for example:

  • Brightness change rate;
  • Number of bad pixels;
  • Startup time;
  • Function recovery requirements;
  • Appearance defect limits;
  • Color difference before and after testing;
  • Display uniformity changes.

Test results should be based on the mutually confirmed specification, IEC 60068, IEC 61000-4-2, ISO 16750, or other applicable standards, and should not be judged simply as "normal" or "abnormal." This makes the reliability testing of LCD modules more executable and also facilitates subsequent mass production quality management.

[Source: IEC 60068 series, IEC 61000-4-2, ISO 16750 series, ICDM display measurement standards, and the product specification confirmed by both parties. The test items, conditions, and acceptance criteria for different application scenarios shall be subject to the final applicable documents.]