Workpiece Grinding Method for Thin Wafer Strength
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
When grinding wafers to a thickness of 50 μm or below, the die strength is reduced, leading to damage and handling difficulties, and existing methods face high grinding loads during finish grinding, especially with highly doped or hard materials, causing spindle motor overload and heat generation.
Innovation Solution
A workpiece grinding method involving a first grinding step using a grindstone with a larger particle diameter to form a non-flat bottom surface in a circular recess, followed by a second grinding step with a smaller particle diameter grindstone to achieve a uniform thickness, reducing the grinding load and enhancing the dressing effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a wafer is ground to a thickness of 50 μm or below, then the wafer can be thinned for size reduction and weight reduction, but the die strength is lowered and the wafer becomes liable to be damaged
Solution Approach 1:
The invention applies different grinding treatments to different regions of the wafer. The device region is ground to a thin thickness (50 μm or below) for size reduction, while the peripheral surplus region is left with a larger thickness to maintain mechanical strength. This creates a non-uniform thickness distribution that satisfies both the thinning requirement and the strength requirement locally in different areas.
2Productivity
If a rough grinding wheel with coarse particles is used first, then material removal is efficient, but the finish grinding wheel cannot achieve a high dressing effect and grinding load becomes excessively high
Solution Approach 1:
The invention introduces a preliminary action step before finish grinding: the rough grinding wheel is intentionally used to create a non-flat bottom surface with a specific shape (concentrical and differing in thickness in radial direction). This preliminary shaping action prepares the surface in a controlled manner that enables the subsequent finish grinding wheel to achieve a high dressing effect and maintain low grinding load.
Solution Approach 2:
The grinding process is segmented into two distinct stages with different objectives. The first stage (rough grinding) creates a specific non-flat shape, while the second stage (finish grinding) achieves the final uniform thickness. This segmentation allows each stage to be optimized independently, with the rough grinding stage preparing the surface geometry that enables effective finish grinding.
3Productivity
If the bottom surface is ground flat by the rough grinding wheel, then material is removed efficiently, but the second grinding wheel cannot dress effectively and the spindle motor becomes overloaded
Solution Approach 1:
The rough grinding wheel performs a preliminary shaping action that creates a non-flat bottom surface with a specific radial thickness profile. This preliminary action is deliberately designed to enable the subsequent finish grinding wheel to dress effectively, thereby preventing motor overload during the second grinding step.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method stabilizes the grinding process under low load conditions, preventing wafer damage and maintaining rigidity by achieving a high dressing effect on the second grinding wheel, thus ensuring stable and efficient grinding of the wafer.
Implementation Method 1
a first grinding step of grinding a part of the back surface corresponding to the device region of the workpiece held by the chuck table, by use of a first grinding wheel
Implementation Method 2
a second grinding step of grinding at least a bottom surface of the first circular recess by use of a second grinding wheel including grindstones having a particle diameter smaller than that of the first grinding wheel
Data Source
AI summary
A workpiece grinding method includes a first grinding step of grinding a part of a back surface corresponding to a device region of a workpiece using a first grinding wheel to form a first circular recess and an annular projecting part in the back surface, and a second grinding step of grinding at least a bottom surface of the first circular recess using a second grinding wheel including a grindstone having a particle diameter smaller than that of the first grinding wheel. In the first grinding step, the bottom surface of the first circular recess is ground into a concentrical shape differing in thickness in a radial direction from a center to a circumference of the first circular recess. In the second grinding step, the bottom surface of the first circular recess is ground to have a uniform thickness, thereby forming a second circular recess.