Rigid Interposer Encapsulant Layer for Thinning Dishing
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Solution Overview
Problem
The process of carrier wafer attachment and removal in semiconductor integrated circuits is problematic, particularly due to mechanical thinning processes that cause dishing of the interposer substrate, and existing encapsulants are not sufficiently rigid to prevent this issue without compromising thermal stress protection.
Innovation Solution
A multi-layer encapsulant structure is introduced, comprising a more rigid lower layer with a lower coefficient of thermal expansion (CTE) to match the interposer and die, and a compliant upper layer to provide mechanical protection, which can be used without the need for a carrier wafer, thereby reducing dishing during interposer thinning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single compliant encapsulant layer is used to protect the interposer, then thermal stress protection is improved, but mechanical strength and resistance to dishing during thinning deteriorate
Solution Approach 1:
The encapsulant is divided into two distinct layers: a rigid lower layer (first encapsulant layer) and a compliant upper layer (second encapsulant layer). This segmentation allows each layer to perform its specialized function - the rigid lower layer provides mechanical strength and prevents dishing, while the compliant upper layer provides thermal stress protection.
Solution Approach 2:
The encapsulant structure uses composite materials with different mechanical properties - a rigid material for the lower layer and a compliant material for the upper layer. This composite structure combines the advantages of both material types to simultaneously achieve mechanical strength and thermal stress protection.
2Length of moving object
If the interposer substrate is thinned to reduce assembly size, then miniaturization is improved, but mechanical fragility and warpage increase
Solution Approach 1:
The rigid first encapsulant layer is formed on the interposer substrate before the thinning process. This preliminary action provides mechanical support during subsequent thinning operations, preventing warpage and fragility even as the substrate becomes thinner.
Solution Approach 2:
The rigid first encapsulant layer is applied specifically to regions of the interposer substrate that require mechanical support during thinning, such as areas between contact pads or in regions prone to warpage, while allowing other areas to be thinned as needed.
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 solution effectively reduces dishing and stiffens the interposer, enhancing mechanical strength and handling while maintaining protection against thermal stresses, without increasing the interposer thickness or compromising thermal expansion matching.
Implementation Method 1
the first layer has a lower coefficient of thermal expansion (CTE) than the second layer, wherein the lower coefficient of thermal expansion (CTE) of the first layer matches a coefficient of thermal expansion of the interposer and the die
Implementation Method 2
the second layer has a lower room-temperature elastic modulus than the first layer
Data Source
AI summary
Die (110) and/or undiced wafers and/or multichip modules (MCMs) are attached on top of an interposer (120) or some other structure (e.g. another integrated circuit) and are covered by an encapsulant (160). Then the interposer is thinned from below. Before encapsulation, a layer (410) more rigid than the encapsulant is formed on the interposer around the die to reduce or eliminate interposer dishing between the die when the interposer is thinned by a mechanical process (e.g. CMP). Other features are also provided.