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Heatsink Orientation to Maximize Thermal Performance

IP.com Disclosure Number: IPCOM000244349D
Publication Date: 2015-Dec-03
Document File: 5 page(s) / 134K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a design methodology to maximize frontal area of an air-cooled heatsink and thus mass flow rate and total cooling capacity.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 36% of the total text.

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Heatsink Orientation to Maximize Thermal Performance

This article discusses a method of increasing the effectiveness of heatsinks by orienting the chips, add-in cards, etc., in such a manner as to maximize the frontal area and thus the volumetric flow rate of air through the heatsink.

    In the electronics industry, almost every single silicon chip is made in square or rectangular package in order to maximize the number of chips per wafer. The rectangular structure is often mirrored into the add-in card or system-level packaging used to contain the chips and, furthermore, the chips and add-in cards are placed in the system in neatly-defined orientations for a variety of reasons including wiring lengths and ease of design. In air cooling, finned heatsinks are fixed to the chips and air blown over said heatsinks in order transfer heat from the chip to the stream of air. As chip powers continue to increase, thermal constraints are becoming a key limiting factor in the number of chips that can be placed in a single compartment.

    A more ideal approach to maximizing the frontal area of the heatsink, and thus the total volumetric airflow through the heatsink, is the subject of this article. Orienting the chips (and thus heatsinks) perpendicular to the long diagonal of the heatsink is mathematically shown to increase the frontal area by up to 41%. By doing this, however, the length of each fin is dependent on the position of the fin; in the corners, the length is less than the normal length fins in the center of the heatsink. A formula is derived for determining the pitch of fins of the non-full length fins in order to maintain a consistent pressure drop across the full width of the frontal area.

    The current state of the art heatsink typically looks like Figure 1 from a top view. The black represents fins, while the blue represents flow paths for the air. The fins pitch is constant across the full width of the heatsink, and the heatsink has a height (h), which is not visible in this top view. In the orientation shown, the frontal area of the heatsink is simply B times h; for a given height and constant airflow rate, the cubic feet passing through the heatsink is directly proportional to the maximum width. Increasing the maximum width increases the total volume of airflow used to dissipate heat from the heatsink.

1


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Figure 1

    
The annotated heatsink oriented to maximize front area is shown in Figure 2. The chip and/or heatsink are placed at an angle such that a diagonal drawn through the rectangle is perpendicular to the airflow. More specifically, the heatsink rotation is defined by Eqn 1 (see Figure 3 below).

Figure 2

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E q n : 1

    This orientation sets the longest possible dimension (C, the hypotenuse calculated by Pythagorean Theorem) perpendicular to the airflow; adding fins along the C allows for the greatest possible volume of air to enter the heatsink. In order to best utilize the airflow entering the heatsink, th...