Cohesive Sheet Initiator Thermal Stability for Semiconductor Adhesion
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Solution Overview
Problem
The method of forming a semi-cured adhesive layer on a semiconductor wafer and bonding it to a cohesive sheet leads to adhesion failure due to photopolymerization initiator migration, resulting in yield reduction in the semiconductor manufacturing process.
Innovation Solution
A cohesive sheet with a base film and a cohesive layer containing a (meth)acrylate ester copolymer, ultraviolet polymerizable compound, multifunctional isocyanate curing agent, and photopolymerization initiator is used, where the photopolymerization initiator has a weight loss rate of 10% or higher at 250°C, and specific compounds like ethanone or 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide are employed, along with an epoxy resin and/or (meth)acrylate ester in the semi-cured adhesive layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a photopolymerization initiator is used in the cohesive layer to enable UV curing and chip pickup, then the pickup efficiency is improved, but the initiator migrates into the semi-cured adhesive layer causing adhesion failure
Solution Approach 1:
The patent changes the key parameter of the photopolymerization initiator by selecting compounds with high decomposition temperatures (250°C or higher). This parameter change prevents migration into the semi-cured adhesive layer while maintaining UV curing functionality for chip pickup.
Solution Approach 2:
The cohesive layer uses a composite formulation combining specific (meth)acrylate ester copolymers with ultraviolet-polymerizable compounds and carefully selected photopolymerization initiators. This composite material approach achieves both UV curability for pickup and thermal stability to prevent adhesion failure.
2Ease of operation
If the cohesive sheet is separated from the wafer after dicing to pick up chips, then chip pickup is enabled, but the adhesive layer may be contaminated by photopolymerization initiator migration
Solution Approach 1:
By changing the decomposition temperature parameter of the photopolymerization initiator to 250°C or higher, the patent prevents contamination of the adhesive layer during the chip pickup process while maintaining the ability to separate chips from the cohesive sheet.
3Ease of manufacture
If heating is applied at around 260°C during molding to seal the chips, then the sealing is achieved, but separation occurs between the lead frame and the semi-cured adhesive layer due to initiator migration
Solution Approach 1:
The patent addresses the adhesion failure during molding by changing the thermal stability parameter of the photopolymerization initiator. Initiators with decomposition temperatures of 250°C or higher remain stable during the 260°C molding process, preventing separation between the lead frame and adhesive layer.
Solution Approach 2:
The cohesive layer employs a composite material system with thermally stable photopolymerization initiators and appropriate polymers, enabling both UV curing for chip pickup and thermal resistance during high-temperature molding processes.
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 composition improves contamination resistance and adhesiveness, reducing adhesion failure and chip flying during dicing, and facilitates easy separation of the cohesive sheet from the semi-cured adhesive layer.
Implementation Method 1
the temperature of the photopolymerization initiator, at which the weight loss rate thereof, which is calculated by the following equation: weight loss rate={(mass before heating−mass after heating)/(mass before heating)}×100(%) (wherein, the mass before heating is the mass of the photopolymerization initiator at 25° C.; the mass after heating is the mass of the photopolymerization initiator at each temperature when it is heated from 23° C. to 500° C. at a heating rate of 10° C./minute) becomes 10%, is 250° C. or higher
Implementation Method 2
a pick-up step of picking up the cut chips from the cohesive sheet after reduction of the adhesive power between the cohesive sheet and the electronic component composites by irradiation with UV ray from the cohesive sheet side
Data Source
AI summary
A method for manufacturing electronic parts, which is characteristic in that it permits reduction of contamination to the semi-cured adhesive layer formed on semiconductor wafer and the cohesive sheet used therein is superior in adhesiveness for example to the lead frame, the method comprising a semi-cured adhesive layer-forming step of forming a semi-cured adhesive layer by coating a pasty adhesive entirely over the rear face of a wafer and curing the pasty adhesive partially by radiation-ray irradiation or heating into the sheet shape, a fixing step of fixing the semi-cured adhesive layer formed on a wafer and a ring frame by bonding them to the cohesive layer of a cohesive sheet, a dicing step of dicing the wafer together with the semi-cured adhesive layer with a dicing blade into semiconductor chips, and a pick-up step of picking up the chips carrying the semi-cured adhesive layer from the cohesive layer of the cohesive sheet after radiation-ray irradiation, wherein the photopolymerization initiator in the cohesive layer of the cohesive sheet has a particular property.