Die/Wafer Mounting and Dicing
Die/Wafer Storage, Handling, and Shipping Contents
Semi-Automatic Wafer Mounter
In preparation for dicing, wafers are mounted to film frames or rings with mounting tape. There are several varieties of tape that can be utilized such as PVC backed or U.V. release tape. Each has its own merits and should be evaluated individually to determine suitability for a particular application. Some things to consider are:
Characteristics of adhesive: chemical properties, tack level, migration potential.
Wafer mounted on Film Frame
using PVC backed mounting tape.
Sensitivity of die to U.V. exposure
(if U.V. release tape is to be used).
Most mounters employ no surface contact in processing wafers making them safe for bumped die and other delicate features.
Dicing
Once mounted, the wafer is ready for dicing. Dicing is performed on specialized equipment utilizing water-cooled diamond tipped blades. There are many variables to be controlled during this process. Among them are:
Blade Selection:
- Grit size designates the diameter (typically in microns) of the diamonds embedded in the blade.
- Concentration indicates the population density of diamond grit on the blade (i.e. a higher concentration results in lower cutting resistance).
- Bond type refers to the characteristics of the material to which the diamond grit is adhered. A low bonding strength will more readily release the diamond grit as it wears and expose new grit.
Exposure height: the distance from the tip of the blade to the hub. This should exceed wafer thickness by approximately 10 mils.
Kerf (cut) width: depends upon scribe street width and desired die size.
Grit size/Concentration/Bond type: depends upon characteristics of wafer to be diced.
Blade Coolant:
Characteristics of water: generally deionized water is used. Consideration should be given to the cleanliness of water supply (chlorine or other contaminants?) and resistivity (should generally be in the 1 M/ohm range).
Position/Flow rate of coolant nozzles: must be optimized for maximizing blade life as well as washing slurry from the wafer surface.
Use of Surfactant: some manufacturers utilize surfactant to minimize chipping and extend blade life.
Equipment Settings:
Feed Rate: determines the rate at which the wafer is advanced to the blade.
Spindle RPM: determines the rate at which the spindle rotates the blade.
Cut Depth: generally set to cut through the wafer and into the mounting tape. If too shallow then backside chipping is often the result.