There are several reasons why today’s power supplies can experience reliability issues, including solder joint fatigue as a top contributor. Space constraints and large components in a power supply can prove problematic for solder joints, along with thermal expansion issues that can occur during thermal cycling. To help effectively predict and mitigate potential solder joint fatigue in a device's power supply, an understanding of common problems that can arise, along with a proactive design and analysis strategy, can help conserve engineering resources and speed time to market.
Problematic Power Supply Characteristics
Power supplies have several characteristics that can make them susceptible to solder joint fatigue, including:
- Large components which can aggravate thermal mismatch between materials
- Thicker boards, necessitated by the size and number of components, which can induce more strain on the solder joint
- Very thick copper layers (some designs have up to 6 oz. in certain layers) which can result in a high copper-glass ratio, increasing the coefficient of thermal expansion for the printed circuit board
- Extensive solid plane areas and embedded heat sinks, used to help remove heat from the board, which can add excess weight and strain
These characteristics can cause excessive stress and strain on solder joints, often leading to deformation and fatigue under thermal cycling. This is exhibited in Figure 1, which shows the differing expansion and contraction rates of the component material and signal trace material in a power supply. The rate of expansion and contraction of the solder joint itself, which often differs from the materials to which it is connected, can also play a large role in fatigue under thermal cycling. The level or extent of these strains can determine the lifetime of the solder joint.
Figure 1: Expansion and contraction of a solder joint connecting materials in a power supply
By using Physics of Failure algorithms, along with the modeling and simulation capabilities of design analysis software like Sherlock, engineers can more efficiently predict the expected lifetime of solder joints under thermal cycling. The information gathered through analysis also provides a comprehensive device overview that can help evaluate potential weaknesses and provide solutions for a more reliable design. This information gives engineers the power to make more informed product design decisions before prototyping, in turn helping to reduce device lifetime warranty claims and speeding up time to market.
To learn more about how about how solder joint failures can be detected through early accelerated stress tests, watch our free System Level Effects on Solder Joint Reliability webinar now by clicking below.