Wafer Cassette Supporting Ribs Prevent Central Deformation
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Solution Overview
Problem
Conventional wafer cassettes deform the central portion of wafers due to gravity, risking damage when picking them up, and existing solutions like tongue-shaped plates can harm double-side die-arranged wafers.
Innovation Solution
A wafer cassette design featuring first and second supporting ribs that contact specific edge areas of the wafer, with angular ranges between 80° and 110°, and contact area widths between 3% and 8% of the wafer radius, preventing central deformation and protecting double-side die-arranged wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the contacting area of supporting ribs is decreased to prevent damage to dies and increase available process area, then the risk of damaging dies is reduced, but the wafer becomes more prone to central deformation due to gravity when thickness is reduced
Solution Approach 1:
The supporting ribs are segmented into multiple contact points along the wafer periphery rather than a single continuous contact area. This segmentation allows distributed support that prevents central deformation while maintaining small individual contact areas that avoid die damage.
Solution Approach 2:
The supporting ribs are designed with different local characteristics: the contact area width is optimized to be small (to avoid die damage) while the angular coverage (80°-110°) is optimized to provide sufficient support leverage. This local quality differentiation resolves the contradiction between minimal contact and adequate support.
2Stability of the object's composition
If a tongue-shaped plate is added to support the central portion of the wafer, then wafer flatness is improved, but the dies on the bottom of double-side die-arranged wafers may be damaged
Solution Approach 1:
The invention extracts the central supporting surface from the design, removing the tongue-shaped plate that contacts the wafer center. Instead, support is provided only through peripheral contact points, eliminating the risk of damaging bottom-side dies while maintaining wafer flatness through lever-arm support mechanics.
3Area of stationary object
If the wafer thickness is reduced to increase available process area, then the available process area is increased, but the central portion of the wafer deforms downwardly due to gravity
Solution Approach 1:
The supporting ribs are positioned and angled to create counterbalancing support forces that oppose the gravitational pull on the wafer center. The 80°-110° angular range and specific contact area width are designed to maximize this counterbalancing effect, preventing downward deformation without requiring increased wafer thickness.
Data Source
AI summary
A wafer cassette for receiving a wafer is provided. The wafer cassette includes a cassette housing, a first supporting rib and a second supporting rib. The first supporting rib is disposed in the cassette housing, wherein the first supporting rib includes a front supporting portion, a middle supporting portion and a rear supporting portion, the front supporting portion is connected to one end of the middle supporting portion, the rear supporting portion is connected to the other end of the middle supporting portion, and the front supporting portion has a front curved edge. The second supporting rib is disposed in the cassette housing. An edge portion of the wafer is supported by the first supporting rib and the second supporting rib, and the front supporting portion, the middle supporting portion and the rear supporting portion contact the wafer simultaneously.