PTFE Sheet for Vacuum Die Mounting
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Solution Overview
Problem
Vacuum adsorption of dies with bump electrodes leads to air leakage and contamination due to protrusion heights, and existing porous tapes are unsuitable for high-temperature processes as they shrink, melt, or deform, affecting adsorption stability and maintainability.
Innovation Solution
A polytetrafluoroethylene (PTFE) sheet with fibers of 1 μm or less diameter, a Gurley value of 1 to 3 s/100 cc/in², and a shrinkage factor of 10% or less is used between the tool and die, matching the bump electrode height and being softer than the tool, to stabilize vacuum adsorption and prevent adhesive creeping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a sheet is interposed between the tool and die to prevent adhesive creeping, then adhesive contamination is prevented, but vacuum adsorption stability deteriorates due to air leakage from gaps caused by bump electrode protrusions
Solution Approach 1:
The patent employs a porous PTFE sheet with controlled pore structure (Gurley value 10-100) that allows the sheet to be permeable to vacuum pressure while physically blocking adhesive material. The porous structure enables the sheet to conform to the bump electrode surface topology, eliminating gaps that cause air leakage, while the pore size and distribution prevent adhesive penetration yet maintain vacuum adsorption effectiveness.
Solution Approach 2:
The patent uses PTFE (polytetrafluoroethylene) as the sheet material, which combines multiple desirable properties: chemical inertness to adhesive materials, thermal stability for high-temperature processes, low surface energy to prevent adhesive adhesion, and mechanical flexibility to conform to irregular surfaces. This composite approach integrates structural, chemical, and physical properties to simultaneously address both contradictions.
2Object-affected harmful factors
If conventional porous tapes (sponge, paper, synthetic rubber) are used, then adhesive creeping is prevented, but the materials shrink, melt, or deform at high temperatures (250°C or higher)
Solution Approach 1:
The patent fundamentally changes the material parameter from conventional organic porous materials to PTFE, which has a melting point above 327°C and maintains dimensional stability up to 260°C. This parameter change in thermal resistance and chemical stability allows the sheet to withstand high-temperature die bonding processes without degradation, shrinkage, or deformation while maintaining its adhesive-blocking function.
3Reliability
If the sheet thickness is increased to cover bump electrode protrusions, then vacuum adsorption stability improves, but the sheet may deform or shrink under heat
Solution Approach 1:
The patent utilizes PTFE's inherent thermal stability and low coefficient of thermal expansion to maintain sheet dimensional integrity at elevated temperatures. The material's crystalline structure and chemical bonds prevent thermal degradation, shrinkage, or deformation even when the sheet is thick enough to bridge bump electrode protrusions and maintain vacuum adsorption stability throughout the high-temperature bonding process.
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
The PTFE sheet stabilizes vacuum adsorption, prevents adhesive contamination, and maintains tool cleanliness by filtering fume gases, enhancing overall process reliability and maintainability.
Implementation Method 1
the PTFE sheet may serve as a filter which inhibits fume gases generated when the die or the adhesive material is heated entering a suction hole of the tool
Implementation Method 2
a bare chip on which bumps are provided on terminals thereof is vacuum-adsorbed on a surface side opposite to a circuit function surface of the bare chip including terminals and bumps
Data Source
AI summary
A PTFE sheet in which PTFE fibers having a diameter of 1 μm or less are spun, the PTFE sheet having a Gurley value in the range of 1 s/100 cc/in2 to 3 s/100 cc/in2 and a shrinkage factor in a direction orthogonal to a sheet winding direction of no more than 10% when heated to 300° C. The PTFE sheet makes a die adsorbable via a tool, which is for heating the die when the die is mounted on a mounting body, by being sandwiched between the die and the tool, and suppresses the adhesion, to an adsorption surface of the tool or to the die, of an adhesion member for fixing the die to the mounted body. Through this configuration, a PTFE sheet capable of stabilizing vacuum adsorption and improving maintainability and a method for mounting a die are provided.