Stacked Semiconductor Packaging With Ultra-Thin Semi-Cured Adhesive
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Solution Overview
Problem
The increasing demand for high-capacity, thin, and miniaturized semiconductor devices poses a challenge as conventional adhesive films used in stacked semiconductor packages increase the package thickness due to their predetermined thickness, limiting the miniaturization potential.
Innovation Solution
A method involving a wafer with semiconductor chips, where a liquid adhesive material is directly coated on the wafer surface to form an ultra-thin uncured adhesive layer, which is semi-cured and then fully cured using energy, allowing for thinner adhesive layers between stacked chips, reducing package thickness and enabling efficient chip separation and stacking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional adhesive films with predetermined thickness are used between semiconductor chips, then the adhesive layer provides sufficient bonding strength, but the package thickness increases as the number of stacked chips increases
Solution Approach 1:
The adhesive material undergoes parameter changes through a two-stage curing process: first semi-curing to enable chip stacking, then full curing to achieve maximum bonding strength. This allows the adhesive to transition from a soft, handleable state to a rigid, high-strength state, resolving the contradiction between ease of assembly and bonding strength.
Solution Approach 2:
The adhesive layer is semi-cured before chip stacking to provide preliminary bonding capability, allowing chips to be positioned and stacked. After stacking, the adhesive is fully cured to achieve final bonding strength. This preliminary action enables the thin adhesive layer to provide sufficient strength while maintaining thin profile.
2Length of moving object
If the adhesive layer thickness is reduced to minimize package thickness, then miniaturization is improved, but the adhesive bonding reliability may deteriorate
Solution Approach 1:
The adhesive material's physical and chemical parameters are changed through controlled curing processes. The semi-curing stage creates a tacky, flexible adhesive suitable for thin layers and alignment, while full curing transforms it into a high-strength, reliable bond. This parameter transformation maintains reliability even at reduced thickness.
Solution Approach 2:
The adhesive composition combines multiple components including silane-modified epoxy resin, hardener, and silane coupling agent. This composite formulation provides both the flow characteristics needed for thin layer application and the cross-linking density required for high bonding reliability, resolving the thickness-reliability trade-off.
3Length of moving object
If liquid adhesive material is directly coated on wafer surface to form ultra-thin adhesive layer, then package thickness is reduced, but the process complexity increases compared to conventional adhesive film application
Solution Approach 1:
The adhesive application process extracts the thickness constraint by using liquid coating instead of pre-formed films. The liquid adhesive can be applied as an ultra-thin layer that is then cured in-place, eliminating the need to handle and apply thicker pre-manufactured adhesive films, thus reducing overall package thickness despite added process steps.
Solution Approach 2:
The mechanical process of applying and trimming adhesive films is replaced with a chemical/coating process where liquid adhesive is deposited and then cured through photochemical or thermal reactions. This substitution enables precise thickness control at the molecular level rather than relying on mechanical film thickness, achieving ultra-thin profiles.
4Ease of manufacture
If semi-curing process is applied before chip stacking, then chip separation and stacking becomes easier, but additional process steps are required
Solution Approach 1:
The adhesive is semi-cured as a preliminary action before chip stacking, creating a tacky surface that facilitates chip placement and alignment. This preliminary curing state provides optimal handling properties, allowing chips to be easily positioned and bonded without requiring excessive pressure or complex alignment mechanisms, thus improving ease of manufacture.
Solution Approach 2:
The curing process is divided into periodic stages: first semi-curing to enable stacking operations, then full curing after stacking to complete the bonding. This periodic application of curing energy (UV light or heat) at different stages optimizes both the stacking ease and final bond strength, justifying the additional process 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 approach significantly reduces the package thickness by minimizing the adhesive layer thickness, enhancing miniaturization capabilities and maintaining adhesiveness similar to conventional films, while ensuring a solid bond between chips.
Implementation Method 1
The ground second surface of the wafer is coated with a liquid adhesive material to form an uncured adhesive layer
Implementation Method 2
The uncured adhesive layer is semi-cured by applying any one of ultraviolet light and heat to the wafer
Implementation Method 3
The uncured adhesive layer is semi-cured by applying any one of ultraviolet light and heat to the wafer
Implementation Method 4
The wafer is cut so as to separate the plurality of semiconductor chips from one another
Implementation Method 5
The plurality of semiconductor chips are stacked using the semi-cured adhesive layer
Implementation Method 6
The semi-cured adhesive layer disposed between the plurality of stacked semiconductor chips is fully cured
Data Source
AI summary
A method of manufacturing a semiconductor package includes preparing a wafer having a first surface on which a plurality of semiconductor chips are disposed and a second surface, opposite to the first surface. The second surface of the wafer is ground. The ground second surface of the wafer is coated with a liquid adhesive material to form an uncured adhesive layer having a thickness of 5 μm or less. The uncured adhesive layer on the wafer is semi-cured. The wafer is cut so as to separate the plurality of semiconductor chips from one another. The plurality of semiconductor chips are stacked using the semi-cured adhesive layer. The semi-cured adhesive layer disposed between the plurality of stacked semiconductor chips is fully cured.