Precision wafer thinning with the NANO POL vitrified back grinding wheel
Backside grinding is an important process step in semiconductor manufacturing. In this step, the back side of a wafer is machined in a controlled manner to achieve the thickness required for the subsequent production and packaging processes.
As wafer thickness decreases, the demands on the grinding process increase. In addition to material removal, surface quality, mechanical stress on the wafer, and the stability of the wafer edge must also be considered.
The EHWA NANO POL vitrified back grinding wheel combines a segmented diamond grinding layer with a ceramic bond and a specifically adjustable pore structure. This allows the tool to be matched to different wafer builds and process requirements.
Why the tool structure is decisive
A back grinding wheel for wafer machining differs significantly from a conventional grinding wheel.
The tool consists of a precisely manufactured, ring-shaped body. On the face side, individual diamond grinding segments are evenly distributed around the circumference. Defined gaps exist between the segments.
This design supports several important process functions:
- supplying coolant to the grinding zone
- removing the material that has been ground off
- cleaning the contact zone
- controlled engagement of the grinding segments
- even load distribution around the tool circumference
The segment geometry must match the wafer material, the machine, and the desired machining stage.
Ceramic bond with controlled porosity
In a vitrified back grinding wheel, the diamond grains are held by a ceramic bond.
A key advantage of this tool structure lies in the targeted adjustment of porosity. Pore fraction, pore shape, and pore size can be matched to the respective grinding process.
The pores create space for coolant and removed material. At the same time, they support an open and controllable tool topography.
For a stable process, an even distribution of the diamond grains on the grinding segments is also important. This allows the tool to work as evenly as possible around its entire circumference.
Less grinding stress and controlled wafer edges
The NANO POL vitrified back grinding wheel is designed to reduce grinding stress and edge chipping.
At the same time, the matched combination of diamond grain, bond, pore structure, and segment geometry supports a uniform wafer surface and high mechanical strength of the singulated dies.
The tool concept therefore does not aim solely at the required final thickness. The condition in which the wafer reaches the next process step is equally decisive.
Machining very thin silicon wafers
For suitable silicon wafers, NANO POL technology can be used for very low final thicknesses. The technical documentation states a possible wafer thickness of down to 17 µm.
This value should not be understood as a universally applicable process limit. The final thickness actually achievable depends, among other things, on the following factors:
- wafer material and wafer diameter
- starting thickness
- layer and component build-up
- workholding system
- grinding machine and spindle
- process parameters
- coolant supply
- requirements of the subsequent production steps
The tool design must therefore always be matched to the specific application.
Requirements for TSV and compound wafers
Modern back-end and advanced packaging processes frequently work with complex wafer builds.
In TSV, fan-out, and compound wafers, different materials can be combined within a single workpiece. These include, for example:
- silicon chips
- epoxy mold compound
- copper vias
- polyimide layers
- solder and bonding elements
In these cases, the grinding tool does not machine a homogeneous material. The individual constituents can differ significantly in hardness, elasticity, and removal behavior.
The NANO POL vitrified back grinding wheel is also designed for compound materials, TSV applications, fan-out wafers, and corresponding sensor or fingerprint substrates. For different material combinations, multi-stage tool concepts with adapted coarse and fine grinding specifications can be used.
The grinding tool as part of the overall system
The performance of a back grinding wheel is not determined by grain size alone.
For a stable wafer grinding process, several technical factors must fit together:
- diamond grain size and grain distribution
- ceramic bond
- pore structure
- grinding segment geometry
- wafer material and material build-up
- spindle speed and feed rate
- coolant supply
- machine rigidity
- desired final thickness and surface quality
The right specification therefore results from the machining task as a whole.
EHWA develops diamond grinding tools for different wafer and back-end applications. The focus is on technical alignment with the material, the machine, and the specific requirements of the production process.
Technical consulting for your wafer application
Are you planning a back grinding process for silicon, TSV, fan-out, or compound wafers? For an initial technical assessment, information on wafer material, diameter, starting thickness, target thickness, machine, and current process is particularly helpful.
Contact: genc@ehwadia.de