Design Considerations When Selecting the Base Metal Layer
- Coefficient Of Thermal Expansion And Heat Spreading
- Coefficient Of Thermal Expansion And Solder Joints
- Strength, Rigidity And Weight
- Electrical Connections To Base Layer
- Surface Finish
Coefficient of Thermal Expansion and Solder Joints
Solder joint fatigue can be minimized by selecting the correct base layer to match component expansion. The major concern with thermal expansion is the stress the solder joint experiences in power (or thermal) cycling. Solder joints are not mechanically rigid. Stress induced by heating and cooling may cause the joint to fatigue as it relieves stress. Large devices, extreme temperature differential, badly mismatched materials, or lead-free minimum solder thickness may all place increased cyclic strain on solder joints.
Solder joint fatigue is typically first associated with ceramic based components and with device termination. The section on “Assembly Recommendations” (page 18-19) covers these issues in more detail.
Click here for larger chart (PDF).
Coefficient of Thermal Expansion and Heat Spreading
The adjacent graph depicts the CTE of the base material in relationship to the heat spreading capability of the metal. Although Aluminum and Copper are the most popular base layers used in Thermal Clad, other metals and composites have been used in applications where CTE mismatch is a factor. The adjacent table represents standard and non-standard base layers.