Thin Heat Sink Structure Using E-Bar Support for BGA Packages
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Solution Overview
Problem
The extension of heat sinks in ball grid array (BGA) packages beyond three times the thickness of the horizontal portion can lead to structural issues such as breakage and warpage, limiting their effectiveness in dissipating heat and providing structural support for tall semiconductor packages.
Innovation Solution
The use of e-bar substrates to elevate the heat sink, reducing the need for vertical extension and maintaining structural integrity by providing a vertical offset, thus minimizing the overall height and enhancing robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the heat sink is extended vertically down to the HDI substrate to provide structural support, then the structural support capability is improved, but the heat sink becomes subject to breakage, warpage, and premature failure due to excessive height
Solution Approach 1:
The heat sink structure is divided into two separate components: a heat sink portion for thermal dissipation and an e-bar substrate portion for structural support. This segmentation allows each component to be optimized independently - the heat sink can be kept short and robust while the e-bar provides the necessary vertical support, eliminating the breakage and warpage issues associated with tall extended heat sinks.
Solution Approach 2:
The e-bar substrate acts as an intermediary element between the heat sink and the HDI substrate. Instead of the heat sink directly extending to the HDI substrate, the e-bar substrate serves as a mediator that provides structural support, allowing the heat sink to maintain a shorter, more reliable height while still achieving the necessary structural support function.
2Reliability
If the heat sink height is limited to 3 times the thickness of the horizontal portion, then the structural integrity is improved, but the ability to provide structural support for tall semiconductor packages is reduced
Solution Approach 1:
By segmenting the support function from the heat dissipation function, the heat sink can maintain its height within the safe 3-times-thickness limit for structural integrity, while the separate e-bar substrate component provides the additional vertical support needed for tall semiconductor packages.
Solution Approach 2:
The e-bar substrate serves multiple functions: it provides structural support for tall semiconductor packages, elevates the heat sink to the appropriate height, and enables the heat sink to maintain optimal dimensions for both thermal performance and structural integrity. This multi-functionality resolves the contradiction between heat sink height limitations and support requirements.
3Strength
If the heat sink is made taller to support tall semiconductor packages, then the structural support capability is improved, but the heat sink becomes more prone to breakage and warpage
Solution Approach 1:
The segmentation of the heat sink and e-bar substrate allows the heat sink to maintain stable, breakage-free dimensions while the e-bar provides the vertical support structure, preventing warpage and dimensional instability in the heat sink portion.
Solution Approach 2:
The e-bar substrate mediates the structural support function, allowing the heat sink to remain a stable, compact component elevated to the appropriate height without undergoing the dimensional instability, breakage, and warpage that would result from making the heat sink itself taller.
Data Source
AI summary
A semiconductor device has a substrate and a semiconductor package disposed over the substrate. An embedded bar (e-bar) substrate is disposed on the substrate around the semiconductor package. A heat sink is formed over the semiconductor package and supported by the e-bar substrate to elevate the heat sink from the substrate and reduce a thickness of the heat sink. A thermal interface material is deposited between the semiconductor package and heat sink. Alternatively, a shield layer can be formed over the semiconductor package and supported by the e-bar substrate. The e-bar substrate has a base layer and a first metal layer formed over a first surface of the base layer. A bump is formed over the first metal layer. A second metal layer can be over a second surface of the base layer opposite the first surface of the base layer. Two or more e-bar substrates can be stacked.