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How to Predict and Prevent Automotive Power Module Failure

Posted by Greg Caswell on Nov 4, 2016 9:30:00 AM

Auto-Power-Module-Failure.jpgJust because an automotive power module has a projected 20-year life expectancy doesn’t guarantee long-term reliability. In fact, these modules are routinely exposed to vibration, shock, humidity, salt spray and other factors that can quickly degrade power and ultimately cause failure. 

Harsh automotive environments combined with the relative delicacy of power modules constructed from direct bond copper (DBC) substrate bonded to a heatsink causes a host of potential failure risks.

Power module reliability, then, lies in creating a robust design that anticipates and addresses common failure mechanisms before they become time-consuming and potentially costly issues.

Failure Challenges

Automotive power modules are not unique. Like those used in other industries, they are susceptible to common failure mechanisms:

  • Thermo-mechanical fatigue-induced failures due to excessive temperature swings or coefficient of thermal expansion (CTE) mismatch with the various materials used in building the modules
  • Bond wire fatigue generated by shear stresses between the bond pad and wire, repeated wire flexure, lift off from fast temperature cycling and heel cracking
  • Die attach fatigue caused by solder fatigue and voids
  • Device burnout

The die-substrate structure of power modules also introduces some threats to structural integrity:

  • Adhered (die or substrate) failure when a silicon die fractures in its mid-portion or at the interface corner
  • Cohesive failure of the bonding/die-attach material
  • Adhesive failure of the bonding material at the adhered/adhesive interface 

Applying these generalities to automotive power modules in particular, failure can take a number of forms including ceramic substrate and heatsink instability; solder joint fatigue; wire bond liftoff; substrate fracture; and, conductor delamination.

Reliability Solutions

How do you ensure reliability with this number of potentially detrimental variables? The foundation of a reliable product is a robust design. The foundation of a robust design is modeling and simulation using automated design analysis.

Automated design analysis introduces a software component to the design phase that mitigates defect risk, provides margin and satisfies customer expectations through on-screen holistic design analysis and comprehensive reporting that informs next steps in improving reliability before failure has expensive impact.

Sherlock Automated Design Analysis™ software uses a three-phase approach to predict and prevent automotive power module failure:

  • Data input automatically parses standard EDA files, uses embedded libraries and builds box-level models
  • Analysis is holistic and includes fundamental options: thermal cycling, mechanical shock, natural frequency, harmonic and random vibration, bending, IC wearout, thermal derating, failure rate, conductive anodic filament and high fidelity PCB modeling
  • Reporting and recommendations provides data in multiple layouts: tabular, histogram, life curve and overlay

Using automated design analysis software in the design phase aligns reliability goals with the projected two-decade lifetime of automotive power modules. Find out more in Introduction to Physics of Failure Reliability Methods. Click the button to download your free copy.

Introduction to Physics of Failure Reliability Methods

Topics: Sherlock