Wafers normally undergo a cleaning and surface lamination process prior to the actual backgrinding process. Surface lamination involves the application of a protective tape over the surface of the wafer to protect it from mechanical damage and contamination during backgrinding.
The surface-laminated wafers are then loaded into cassettes that will go into the cassette holder of the backgrinding machine. The machine picks up the wafer from its backside (untaped side) with a robotic arm, which positions the wafer for backgrinding. The backgrinding process is automatically accomplished by a grinding wheel, following a precise set of parameters to ensure proper backgrinding.
To remove debris from the wafer while backgrinding, the wafer is usually washed continuously with D/I water while undergoing backgrinding. Once the wafer has been background, the wafer is returned to the cassette, and the cycle is repeated for the next wafer.
Parameters set for backgrinding include spindle speed, spindle coolant water temperature and flow rate, D/I water temperature, initial and final wafer thickness, and feed speeds.
Common Wafer Backgrind-related Failure Mechanisms:
Die Cracking/Chipping - occurrence of fracture or chip-out anywhere in the die. Common Causes in the context of Backgrind: incorrect backgrind parameters resulting in excessive stresses on the wafer.
Die Scratching - inducement of any mechanical damage on the die, as when an operator scratches a die with tweezers due to mishandling. Common Causes: insufficient operator training, disorderly workplace, use of improper tools.
Die Metallization Smearing - depression or deformation of any metal line on the die surface. Common Causes: foreign materials on the backgrind tape, wafer mishandling
Die Corrosion - corrosion of the metallic parts of the die as a result of prolonged exposure to water during backgrinding.