Improving Fuel Cell Reliability: A Case Study of Ballard Power Systems Inc.

Ballard Power Systems Inc. is a Canadian company that operates in the power industry. The company designs, develops, and manufactures zero-emission PEM fuel cell stacks. Ballard Power Systems Inc. is working with leading automobile manufacturers to develop the next generation of engines that are more efficient and cleaner than internal combustion engines. Engines using Ballard fuel cells can help manufacturers reach new environmental performance levels demanded for automotive power. The company's Ballard MK9 series of cell voltage monitoring (CVM) systems are electronic devices used in automotive fuel cell stacks that monitor the voltages produced by cells during operation.

Ballard Power Systems Inc., a Canadian company that designs, develops, and manufactures zero-emission PEM fuel cell stacks, faced a significant challenge with their MK9 series of cell voltage monitoring (CVM) systems. These systems, used in automotive fuel cell stacks, monitor the voltages produced by cells during operation. However, the company was experiencing CVM chip solder joint failures, which could prompt a false failure signal to the vehicle control unit, potentially shutting down the operation of the fuel cell and even the entire fuel cell engine. This issue was directly impacting the reliability of the entire fuel cell stack. The thermal expansion of the PCB and potting material, which protects the CVM from the environment, was causing deflections that resulted in stress on the solder joints. The company needed to gain insight into the structural load on electronic components during thermal cycling, identify probable areas where excessive stress could cause early CVM chip failure, and identify a potting material that would not exert thermal expansion stress on the CVM components.

To address the challenge, Ballard Power Systems Inc. used ANSYS Multiphysics software to conduct a thermal-structural coupled field analysis. This analysis helped to calculate the stress on the solder joints from board deflections. High-stress areas and components were identified on the assembly model. The software was also used to develop a finer mesh for the individual chip/solder joint detail analysis through a process called submodeling. This process was effective in helping to calculate more accurate results in a specific region of interest. After identifying the solder joint stress as the primary cause of CVM solder joint failure, the company selected a new potting material with a suitable coefficient of thermal expansion (CTE). This new material eliminated stress components for the CVM chip and averted failures. The potting material was close to the PCB’s CTE and eliminated the “bulge” of other material tested.

• The solution implemented by Ballard Power Systems Inc. had significant operational results. By using thermal-structural coupled field analysis and submodeling, the company was able to pinpoint the primary cause of CVM solder joint failure and solve a major reliability problem. The selection of a new potting material with a suitable coefficient of thermal expansion (CTE) eliminated stress components for the CVM chip and averted failures. This not only improved the reliability of the CVM systems but also the overall reliability of the fuel cell stacks. The new potting material was close to the PCB’s CTE and eliminated the “bulge” of other material tested, reducing peak stress by more than 3X and eliminating the root cause of solder joint failure. The process verified that CVMs potted with the new material showed no sign of solder joint failure, further enhancing the reliability of the company's products.

• The process identified the primary cause of CVM solder joint failure, solving a major reliability problem.
• The selection of a new potting material with a suitable coefficient of thermal expansion (CTE) eliminated stress components for the CVM chip and averted failures.
• The new potting material reduced peak stress by more than 3X, eliminating the root cause of solder joint failure.