Non-Volatile Memory Charge Retention Mechanics under High-Temperature Environments
High ambient heat accelerates non-volatile memory charge leakage through thermionic emission and trap tunneling, degrading stored radio calibration data over time.
Lattice Thermal Stress
Meaning
Internal mechanical force arising from temperature gradients or mismatching coefficients of thermal expansion between bonded crystalline layers. This lattice thermal stress occurs during high temperature processing or through the heat generated by electrical resistance in a functioning circuit. Variations in the atomic spacing at the interface lead to elastic deformation of the crystal structure.
Excessive force results in the formation of cracks or the delamination of thin films.
Structural Deformation
Mismatch between the expansion rates of different materials induces physical strain during soldering. This lattice thermal stress can cause the silicon die to bow or warp within the package.
Dislocation Density
Crystalline defects multiply when the internal pressure exceeds the elastic limit of the semiconductor. The presence of lattice thermal stress encourages the movement of existing dislocations through the material. New defects act as paths for current leakage and reduce the overall efficiency of the device.
Controlling the cooling rate during manufacture helps limit the growth of these structural flaws.
Reliability Limit
Mechanical failure of the interface occurs when the accumulated strain exceeds the fracture toughness of the material. As the device operates, the fluctuating lattice thermal stress creates microcracks at the grain boundaries. These cracks propagate over time and eventually sever the electrical connections.
Heat sinks and thermal interface materials are selected to mitigate the magnitude of these stresses. Repeated thermal cycles eventually lead to the failure of the device package.