⚡🌡️ PTC – Power Temperature Cycling Test
The Power Temperature Cycling (PTC) test is a reliability test designed to evaluate the mechanical and thermal robustness of semiconductor devices, particularly power devices, when subjected to repeated cycles of internal heating (due to power dissipation) and external cooling.
Unlike traditional Thermal Cycling (TC), where the device is exposed to ambient temperature changes in a thermal chamber, PTC induces heating internally by applying electrical current or voltage to create self-heating, followed by a controlled cooldown phase.
This test simulates real-world power-on/power-off events, where temperature fluctuations occur due to the operation of the device under load, especially in high-current or high-voltage conditions typical of automotive, industrial, or power conversion environments.
How is the LTOL test performed?
The PTC test follows a structured and well-defined procedure involving several critical phases:
1. Device Selection and Preparation
A statistically significant number of devices are selected from different wafer lots and package types.
Devices may be mounted on test PCBs or thermal fixtures to simulate system-level behavior and facilitate temperature control.
2. Setup and Monitoring Infrastructure
Devices are connected to a power supply, temperature control system, and data acquisition unit.
Cooling mechanisms (air flow, Peltier modules, or liquid cooling) are used to manage the cooldown phase of the cycle.
Temperature sensors (e.g., thermocouples) or electrical resistance tracking are used to monitor junction temperature (Tj).
3. Thermal and Power Cycling
Each PTC cycle consists of:
a) Heating Phase (Active Power Dissipation)
A current or voltage is applied to the device to generate internal heat through Joule effect (I²R losses).
Junction temperature is raised to a target value, commonly in the range of 125°C to 175°C, depending on device rating.
Heating is maintained for a defined dwell time (e.g., 3–10 minutes) to reach thermal equilibrium.
b) Cooling Phase
The power is turned off or significantly reduced.
Active or passive cooling brings the device back down to ambient or sub-ambient temperatures (typically 25°C to 40°C).
This phase lasts long enough to allow full thermal contraction of materials.
4. Cycle Repetition
The heating/cooling process is repeated for a predetermined number of cycles—usually 500 to 2000 cycles, or more in critical applications.
The cycle frequency, ramp rates, and temperature ranges are tailored based on application type (automotive, industrial, etc.).
5. Intermediate Electrical Testing
Devices are periodically tested electrically (e.g., every 100 cycles) to monitor:
On-resistance (Rds(on))
Gate threshold voltage
Leakage currents
Forward voltage drop
Short-circuit behavior
6. Post-Test Physical Analysis
Devices that fail or show degradation undergo:
X-ray analysis for internal delamination.
Decapsulation and optical/SEM inspection of wire bonds and die attach.
Bond pull tests to measure mechanical integrity.
Thermal impedance measurements to assess heat dissipation paths.
What types of failures does it detect?
The PTC test helps identify mechanical, thermal, and fatigue-related failures including:
Wire bond lift-off or cracking due to repetitive expansion and contraction.
Die attach delamination, which leads to poor thermal transfer and higher junction temperatures.
Package delamination or cracking of mold compound, especially under high thermal gradients.
Solder fatigue and micro-cracks in interconnects.
Increased thermal resistance (RthJA or RthJC) over time.
Electrical parameter drift caused by stress-induced material changes.
Internal short circuits or leakage paths due to insulation breakdown or corrosion through micro-cracks.
These failure modes are often latent—they may not show up in initial functional tests, but manifest during field operation, causing intermittent or catastrophic device failures.
Related standards
While PTC is not universally defined by a single document, it is often conducted in compliance with established industry reliability standards:
JEDEC JESD22-A105 – Power and Temperature Cycling
AEC-Q101 / AEC-Q100 – Automotive Qualification Guidelines (includes power cycling and thermal stress tests)
MIL-STD-750 – Methods for testing discrete semiconductor devices (some PTC-like procedures)
IEC 60749-34 – Semiconductor devices — Mechanical and climatic test methods
JEITA EIAJ ED-4701/100 – Japanese equivalent for semiconductor reliability
Manufacturers may also develop internal specifications based on customer requirements or specific application environments.
Final thoughts
The Power Temperature Cycling (PTC) test is a cornerstone of power device qualification, providing:
Realistic stress conditions to validate durability.
Early detection of latent or progressive packaging failures.
Reliability assurance in automotive and industrial applications.
Feedback for design and process improvement.
“In power electronics, every cycle counts — and every failure teaches.”
The PTC test ensures that devices can handle heat, survive stress, and last in the field.
What is it used for?
The main purpose of the PTC test is to:
Detect failure mechanisms caused by thermal fatigue, mechanical stress, and material fatigue inside the semiconductor package.
Assess the durability of bonding materials, die attach, wire bonds, solder joints, and mold compounds under cyclic thermal stress.
Evaluate long-term reliability under realistic operating conditions—especially for power devices like MOSFETs, IGBTs, rectifiers, and GaN/SiC switches.
Predict the long-term behavior of the device when subjected to operational heating and cooling cycles across thousands of on/off events.
Qualify manufacturing processes and materials, ensuring they are capable of withstanding thermal expansion/contraction without degradation.
Why is it necessary?
The PTC test is critical for ensuring product reliability, especially for mission-critical or harsh-environment applications:
Automotive and industrial power electronics undergo thousands of power cycles per year during regular operation.
Power-on and power-off events result in substantial internal heating and cooling, leading to mechanical stress accumulation.
Without proper testing, early field failures may occur, which are expensive to repair and damaging to brand reputation.
It unveils manufacturing defects such as poor die attach or improper wire bonding.
It allows manufacturers to optimize materials and assembly processes for better thermal reliability.
It is a standard requirement in automotive qualification flows (AEC-Q100/Q101) and industrial-grade reliability certification.
Who uses it?
The Power Temperature Cycling test is widely used across various industries and engineering domains:
Semiconductor manufacturers of power devices (MOSFETs, IGBTs, diodes, GaN/SiC switches).
Automotive electronics suppliers validating ECUs, inverters, and traction modules.
Industrial equipment providers (motor drivers, power inverters, converters).
Aerospace and defense industries where reliability is non-negotiable.
Reliability labs and OSATs (Outsourced Semiconductor Assembly and Test).
Packaging companies working on novel thermal materials and bonding technologies.
Practical example
Case Study: Automotive MOSFET (60V, used in a motor driver ECU)
Objective: Validate the long-term thermal reliability of a MOSFET used in a load switch that cycles on/off frequently in a hybrid vehicle.
Device: 60V N-channel MOSFET, TO-263 package
Test Configuration:
Heating: Apply 18 A current for 6 minutes → raises Tj to ~145 °C
Cooling: Forced air cool down to 25 °C in 4 minutes
Total Cycles: 1500 cycles
Intervals: Electrical check every 100 cycles
Monitored Parameters: Rds(on), gate charge, leakage current
Results:
2 devices showed a 35% increase in Rds(on)
1 device failed at cycle 1120 with open wire bond (confirmed via SEM)
Average increase in thermal resistance of 12%
Corrective Actions:
Improved wire bond alloy (switch to Pd-coated Cu)
Modified die attach epoxy with better thermal expansion compatibility
Adjusted ramp rate to reduce thermal shock during cooling