Thermodynamic Micro-Strain Relaxation in Die Attach Adhesives during Thermal Soak
Thermal soak accelerates die attach viscoelastic micro-strain relaxation, reducing shear stress while driving physical aging, interface delamination, and Rth growth.
Warpage Evolution
Mechanical Change
Change in the out-of-plane deformation of a semiconductor wafer or substrate occurs during successive processing steps. This progression, described as warpage evolution, is driven by the accumulation of residual stresses from thin-film deposition and thermal cycling. Excessive deformation interferes with lithographic focus and automated handling systems in the fabrication line.
The shape of the wafer can shift from a simple bow to a complex saddle as different layers are added or removed. Understanding this evolution helps in selecting the correct clamping method for subsequent steps.
Stress Accumulation
Coefficients of thermal expansion between the substrate and the deposited layers create internal forces. These forces drive the change.
Metrological Tracking
Optical profilometry and laser scanning systems provide non-contact measurements of the wafer surface at each process node. These tools generate a topographical map that quantifies the warpage evolution over time. Engineers use this data to predict the risk of cracking or delamination in the final package.
Compensation Boundary
Edge-clamping and vacuum chucking can temporarily flatten a warped substrate for certain operations. However, if the warpage evolution exceeds the mechanical limits of the equipment, the wafer cannot be processed. Stress-compensation layers are often deposited on the backside of the wafer to counteract the forces of the active circuitry.