Wafer Thermocompression Bonding for Gap-Free Chip Division
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Solution Overview
Problem
The annular protruding portion on wafers hinders chip division and requires removal, but adhesive tapes used for this purpose create gaps that lead to chipping or cracking, reducing the useful wafer area and productivity due to stress application and gap widening over time.
Innovation Solution
A thermocompression bonding method using a sheet with an annular frame to securely attach to the wafer, distributing stress and minimizing gaps, allowing for efficient division of the annular protruding portion without significant reduction in device-forming area and reducing long-term gap widening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If adhesive tape is affixed to the wafer including the circular recessed portion and annular protruding portion, then the wafer can be held for processing, but a gap is generated between the adhesive tape and the wafer at the outer circumferential portion of the circular recessed portion due to the step structure
Solution Approach 1:
A sheet is introduced as an intermediary component between the wafer and the holding mechanism. The sheet conforms to the stepped structure of the wafer (circular recessed portion and annular protruding portion) and is thermocompression-bonded to the wafer surface, eliminating gaps that would occur with direct adhesive tape application. This intermediary sheet enables proper wafer holding while maintaining surface contact integrity.
Solution Approach 2:
The bonding method is changed from simple adhesive application to thermocompression bonding. By applying heat and pressure parameters, the sheet is bonded to the wafer in a controlled manner that allows it to conform to the stepped structure without creating gaps, particularly at the outer circumferential portion of the circular recessed portion.
2Ease of operation
If adhesive tape is affixed to the annular protruding portion first and then elongated to the circular recessed portion, then the wafer can be held, but large stress is applied to the adhesive tape causing the gap to widen over time
Solution Approach 1:
The sheet acts as a stress-distributing intermediary between the holding mechanism and the wafer. Unlike adhesive tape that concentrates stress at the elongation point, the sheet distributes stress evenly across the entire wafer surface through thermocompression bonding, preventing gap widening over time while maintaining stable wafer holding.
Solution Approach 2:
The mechanical stress application method is replaced from elastic elongation of adhesive tape to thermocompression bonding. This substitution eliminates the stress concentration and elastic recovery issues that cause gap widening, providing stable long-term wafer holding without composition changes.
3Reliability
If the dividing groove is formed in a region that does not overlap with the gap, then chipping and cracking are prevented, but the useful area of the wafer is reduced and productivity decreases
Solution Approach 1:
The sheet serves as a mediator that eliminates the gap problem entirely, allowing dividing grooves to be formed in regions that would otherwise be unusable due to gap-related chipping and cracking. By providing uniform support across the wafer surface including the outer circumferential portion of the circular recessed portion, the sheet enables full utilization of the wafer area for device formation.
4Strength
If the annular protruding portion is left on the wafer, then the thinned circular recessed portion is reinforced, but the annular protruding portion hinders division of the wafer into individual chips
Solution Approach 1:
The sheet is bonded to the wafer surface before the division process. This preliminary action provides continuous support during the division operation, allowing the annular protruding portion to be cleanly separated without causing chipping or cracking in the remaining wafer structure, thus maintaining wafer rigidity while enabling easy division.
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 ensures a small gap between the sheet and wafer, maintaining a large useful wafer area and improving chip productivity by distributing stress evenly and preventing adhesive tape-like issues of gap widening.
Implementation Method 1
a thermocompression-bonding step of heating the sheet and thermocompression-bonding the sheet to the one side of the wafer
Data Source
AI summary
A wafer processing method for processing a wafer which has one side in which a circular recessed portion is formed in a region surrounded by an annular protruding portion is performed by a thermocompression bonding apparatus including a first recessed portion, a second recessed portion, and a holding table that is disposed on the second recessed portion. In the method, the wafer the one side of which is oriented upward is held from a lower side by the holding table, a sheet is sandwiched by the first recessed portion and the second recessed portion, the first recessed portion is depressurized while the second recessed portion is depressurized, pressure inside the first recessed portion is increased, the sheet is caused to come into contact with the one side of the wafer, and the sheet is heated, to thermocompression-bond the sheet to the one side of the wafer.