Fixture Strain and Spring Force Deflection Limits on High Density Assemblies
Fixture spring force and deflection limits enforce maximum micro-strain thresholds to prevent latent BGA pad cratering and ceramic capacitor fracture during testing.
FEA Strain Simulation
Structural Stress
Computational modeling processes for solder joints predict the mechanical stress distribution during thermal cycling or mechanical shock. Running a fea strain simulation allows engineers to identify where brittle intermetallic layers might fracture under load. This method breaks the physical geometry of the assembly into thousands of small elements to calculate the forces acting on each part.
Simulation Process
Software tools apply mathematical models of thermal expansion and material stiffness to the virtual assembly to see how it deforms. A fea strain simulation accounts for the different expansion rates of the silicon chip, the organic substrate and the solder balls. These calculations show the areas of highest strain where fatigue is most likely to cause a crack.
Assembly Risk
Predicting the failure points before a board is built reduces the number of prototype cycles and helps in choosing better materials. The results of a fea strain simulation guide the placement of large components and the design of board supports to minimize bending. Manufacturers use the data to set limits on how much force a board can handle during the assembly of heat sinks or connectors.
Accurate modeling prevents field failures by ensuring the physical design stays within the safe operating limits of the materials.