I. Impacts of Poor Surface Flatness of IGBT Chips
Concentration of Mechanical Stress
Uneven surface topography of IGBT chips causes irregular stress distribution under external forces, leading to mechanical stress concentration.
Long-term stress concentration may induce cracks and internal damage to the chip, thereby impairing its electrical performance and reliability.
Deteriorated Heat Dissipation
IGBTs generate substantial heat during operation, which must be dissipated promptly via the cooling system. Poor chip flatness reduces the contact area and tightness between the chip and heat dissipation components.
This results in degraded heat dissipation and elevated internal temperature. High temperatures accelerate chip aging and shorten service life.
Bond Wire Detachment
IGBT chips are generally connected to external circuits via bond wires. Uneven chip surfaces weaken the bonding integrity between bond wires and the chip.
II. Short-Circuit Failure Mechanism of IGBTs
Internal Short Circuit
Cracks, damage or impurities inside an IGBT may trigger internal short circuits. Such faults generate excessive transient current, resulting in overheating and permanent device damage.
External Short Circuit
Short-circuit faults in external circuits can also damage IGBTs. For instance, a short circuit at the load side subjects the IGBT to extreme current and voltage surges, eventually leading to short-circuit failure.
III. Correlation Between Poor Flatness and Short-Circuit Failure
Indirect Impact
Poor surface flatness does not directly cause IGBT short-circuit failure. Nevertheless, it raises the failure risk indirectly by impairing heat dissipation and compromising the reliability of bond wire connections.
Combined Effect
In practical operation, IGBT failures are generally caused by multiple interacting factors. Coupled with temperature cycling, power cycling, material aging and other issues, poor chip flatness will accelerate the degradation and failure of IGBTs.
IV. Countermeasures
Improve Chip Flatness
During the manufacturing of IGBT chips, strictly control production processes and parameters to ensure the chip surface flatness meets specifications.
Optimize Thermal Design
Improve the thermal design of IGBT modules to enhance heat dissipation efficiency and lower the operating temperature of chips.
Regular Inspection and Maintenance
Perform periodic inspection and maintenance on IGBT modules to identify and resolve potential faults in a timely manner.
In conclusion, poor surface flatness of IGBT chips is correlated with the short-circuit failure mechanism of IGBTs. Therefore, great importance shall be attached to chip surface flatness throughout the manufacturing, application and maintenance stages, and effective measures shall be adopted to address relevant issues.
Field Measurement Case of Lamination Flatness for IGBT Packaging
(The color temperature map reflects 3D height information; the table records the measured deformation values.)
V. Introduction to Laser Frequency Comb 3D Optical Profilometry System
Based on the principle of laser frequency comb, this 3D optical profilometry system adopts high-frequency laser pulse time-of-flight ranging. It is immune to the occlusion issues common in traditional optical measurement, and well suited for various large and complex structural parts. It overcomes measurement difficulties for deep holes, grooves and similar features. With a laser repetition rate of 500 kHz, it delivers technological innovations for automated inspection.
Technical feature 1: Coaxial epi-illumination, flight ranging and scanning method, eliminating the traditional optical "obstruction" issue.
Actual case: Valve body oil circuit board with criss-crossing grooves
Technical feature 2: With an accuracy of ±2um, it can achieve scanning and imaging up to a maximum height/depth of 130mm
Technical feature 3: It can be equipped with multiple lens combinations to achieve scanning with a wide field of view spanning tens of meters.
