6.4 Testing and reliability considerations for MEMS/NEMS devices

Testing and reliability are crucial for MEMS/NEMS devices. Engineers use various methods to ensure these tiny machines can handle real-world conditions. From accelerated life tests to failure analysis, each technique helps identify and fix potential issues before products hit the market.

Environmental testing puts devices through their paces. Shock, vibration, and humidity tests mimic harsh conditions these miniature marvels might face. By pushing MEMS/NEMS to their limits, we can build tougher, more reliable tech that stands up to whatever life throws at it.

Reliability Testing

Accelerated Life Testing and Environmental Stress Screening

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• Accelerated life testing exposes devices to elevated stress levels (temperature, voltage, humidity) to identify potential failure modes and estimate the device's lifetime under normal operating conditions
• Involves testing devices at higher than normal stress levels to accelerate the occurrence of failures that would typically occur over a longer period of time under normal operating conditions
• Environmental stress screening is a type of accelerated testing that subjects devices to a series of stresses (thermal cycling, vibration, shock) to identify latent defects and weak components early in the product life cycle
• Helps to improve product reliability by identifying and eliminating potential failure modes before the product is released to the market (burn-in testing)

Mean Time Between Failures (MTBF) and Burn-In Testing

• Mean time between failures (MTBF) is a reliability metric that represents the average time between failures of a device or system during normal operation
• Calculated by dividing the total operating time by the number of failures observed during that time period
• Burn-in testing involves operating devices at elevated temperatures and voltages for a specified period to identify and eliminate early-life failures (infant mortality)
• Helps to improve the reliability of the remaining population by weeding out devices with manufacturing defects or weak components
• Temperature cycling is a type of burn-in testing that subjects devices to alternating high and low temperature extremes to identify potential failures caused by thermal stress (solder joint cracking, delamination)

Failure Analysis

Failure Modes and Effects Analysis (FMEA)

• Failure modes and effects analysis (FMEA) is a systematic approach to identifying potential failure modes, their causes, and their effects on system performance
• Involves analyzing the design, manufacturing process, and operational use of a device to identify potential failure mechanisms and prioritize them based on their severity, occurrence, and detectability
• Helps to identify areas for improvement in the design, manufacturing, or testing process to mitigate potential failures and improve overall reliability
• Electrical characterization involves measuring the electrical properties of a device (resistance, capacitance, leakage current) to identify potential failure modes or performance degradation

Testing Methods for Failure Analysis

• Functional testing involves testing the device under its intended operating conditions to verify that it meets its performance specifications and identify any functional failures
• Non-destructive testing methods (X-ray imaging, acoustic microscopy, infrared thermography) allow for the inspection of devices without causing damage or altering their functionality
• Used to identify internal defects, delamination, voids, or other structural anomalies that may lead to failure
• Destructive testing methods (cross-sectioning, decapsulation, scanning electron microscopy) involve disassembling or destroying the device to analyze its internal structure and identify the root cause of failure

Environmental Testing

Shock, Vibration, and Humidity Testing

• Shock and vibration testing evaluates the device's ability to withstand mechanical stresses encountered during handling, transportation, and operation
• Devices are subjected to controlled levels of shock (drop tests) and vibration (sinusoidal, random) to identify potential failures caused by mechanical stress (wire bond breakage, package cracking)
• Humidity testing exposes devices to controlled levels of humidity and temperature to evaluate their resistance to moisture-induced failures (corrosion, electrical shorts)
• Helps to identify potential failure modes related to moisture ingress, such as package delamination or degradation of materials
• Temperature and humidity bias testing (THB) involves applying electrical bias to the device while it is exposed to elevated temperature and humidity levels to accelerate the occurrence of moisture-induced failures