Top-Side Cooling for RF Air Cavity Packages
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Solution Overview
Problem
Conventional air cavity packages with bottom-side cooling are unsuitable for application boards that cannot provide a suitable heat path, leading to inefficiencies in heat dissipation for RF devices, and top-side cooling approaches using BGA packages result in increased inductance and unsuitability for higher frequency RF modules.
Innovation Solution
An air cavity composite package with top-side cooling, featuring a substrate, RF component, and a lid structure with a heat transfer structure extending from the top surface through openings in the lid to provide a thermal interface for external heat sinks, using materials that minimize dielectric loading and optimize heat dissipation without increasing RF trace length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If bottom-side cooling is used in conventional air cavity packages, then heat dissipation is achieved through the application board, but the package becomes unsuitable for application boards that cannot provide a suitable heat path
Solution Approach 1:
The patent inverts the conventional bottom-side cooling approach by implementing top-side cooling. The heat transfer structure extends upward through the lid to provide a thermal interface on the top surface, allowing heat to be dissipated away from the application board. This inversion resolves the contradiction by enabling effective heat dissipation even when the application board cannot provide a suitable heat path.
2Temperature
If top-side cooling is implemented using BGA packages, then heat dissipation is achieved away from the application board, but inductance increases making it unsuitable for higher frequency RF modules
Solution Approach 1:
The patent segments the package into distinct functional components: a substrate for mounting the RF device, a lid forming an air cavity, and a heat transfer structure. The RF device remains mounted on the substrate with short RF traces, while the heat transfer structure is positioned away from the RF signal path. This segmentation allows top-side cooling to be implemented without increasing RF inductance, resolving the contradiction between heat dissipation and RF performance.
3Length of moving object
If RF devices are mounted on substrate with bottom-side heat path, then electrical connections are short, but heat dissipation relies on application board which may not be suitable
Solution Approach 1:
The patent creates a universal package structure that can function with any application board regardless of its heat dissipation capability. The heat transfer structure provides an independent thermal path that does not depend on the application board's thermal properties. This multi-functionality allows the same package to be used in applications where the board provides heat sinking and applications where it does not, resolving the contradiction between short electrical traces and heat dissipation independence.
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 solution enables efficient heat removal close to the RF devices, maintaining high operating bandwidth and suitability for RF devices, even in environments without bottom-side cooling, by creating a top-side thermal interface that enhances heat dissipation without increasing inductance, resistance, or capacitance, thus supporting higher frequency operations.
Implementation Method 1
a heat transfer structure comprising an extending from the top surface of the substrate through the at least one opening in the lid to the top outer surface of the air cavity composite package to provide a top-side thermal interface
Implementation Method 2
Air cavity packages are used to minimize dielectric loading effects that limit the bandwidth of high-frequency semiconductor devices
Data Source
AI summary
Top-side cooling of Radio Frequency (RF) products in air cavity packages is provided. According to one aspect, an air cavity package comprises a substrate, a RF component mounted to the substrate, and a lid structure comprising a first material and being mounted to the substrate that covers the RF component such that a cavity is formed within the lid structure and about the RF component. At least one opening is provided in a top portion of the lid. The air cavity package also comprises a heat transfer structure comprising a second material and comprising a heat path extending from the top surface of the substrate through the opening(s) in the lid to the top outer surface of the air cavity package to provide a top-side thermal interface. In one embodiment, the lid is comprised of a molded material that absorbs RF signals and the heat transfer structure is metal.