Wafer Head Function
The Wafer Head provides support for wafers (or workpiece parts) that are lapped or
polished by the high-speed lapper machine. Wafers are quickly attached to the head
with vacuum and then brought into controlled abrading contact with the platen's
abrasive disc. The head provides rigid support for the wafers as they are abraded. Its
speed is adjustable from 0 to 3,000 rpm and it rotates in the same direction and speed
as the abrasive platen.
Wafer Head Mounted on Lapper
The wafer head is attached to a rigid high-speed precision machine-tool spindle. This
rotary spindle is attached to a vertical carriage which is moved upward to load wafers
and then moved downward to provide wafer contact with the platen abrasive. A
horizontal carriage allows the wafer head to be used with either 12” or 18” diameter
abrasive island discs.
A “floating” wafer attachment plate provides self-aligning flat-surfaced contact of the wafers with the disc precision-flat abrasive surface. The wafer head has an offset spherical bearing (with a center-of-rotation located at the abrasive surface) that allows for the wafer to conform to the surface of the abrasive disc while preventing abrading friction lateral forces from tilting the wafer. Tilted wafers cause non-flat abraded wafer surfaces. The wafer head has a rigid, low friction sliding housing that assures an adjustable internal abrading pressure exists uniformly across the full wafer surface during abrading.
Rigid Mode Operation
The floating wafer head can also be quickly converted to a “rigid-abrade” mode where non-flat wafers can be flattened and where both of the wafer’s opposed surfaces are made parallel to each other. This is done by locking the floating portion of the wafer head to the rigid outer housing. This prevents the wafer from self-leveling while still allowing it to make use of the slide housing to control abrading pressure.
Groups of Wafers
Groups of smaller wafers are first attached with removable wax to a backing disc and are then vacuum attached to the head. This is the same wax that is commonly used to mount semiconductor wafers.
Wafers and Workpiece Types
There are many different kinds of workpieces that can be attached to the wafer head including Sapphire wafers used for LEDs or SOS semiconductors and display screens for computers or phone screens are attached to the wafer head for abrasive lapping or polishing. Also, industrial parts such as rotary seals having a wide range of hard ceramic or metal materials can be attached to the wafer head for high speed abrading.
Wafers Remain Attached
These workpieces remain attached to the head as they are sequentially subjected to a series of abrasive discs having progressively smaller sized abrasive particles. Not changing the wafer mounting when the abrasive particle sizes are changed provides a great process advantage. Large abrasive particles flatten the wafers, medium particles initiate the polishing, and very small particles provide a smooth surface. All of this is accomplished without having to handle or re-seat the workpiece. For semiconductor wafer polishing, each of the sequentially smaller particles remove material uniformly across the whole abraded surface of the wafer. The thickness of the removed material is proportional to the selected abrasive particle size.