Hussain Shaukatullah

Design and optimization of pin fin heat sinks for low velocity applications

In a number of electronic cooling applications, the air flow velocity and direction are not very well defined or controlled. In these applications, pin fin heat sinks are widely used because they are not sensitive to air flow direction. A study was undertaken to optimize the design of pin fin heat sinks for use in low velocity applications where there is plenty of open space around for the air to bypass the heat sink, if it encounters high pressure drop across it. The goal of this study was to maximize the thermal performance and keep the design such that it is easily manufacturable to keep the cost low. A special test fixture using a heat flux meter was designed to test the heat sinks for thermal performance. Several aluminum pin fin heat sinks having a 25/spl times/25 mm base size, heights from 5 to 25 mm, pin arrays of 4/spl times/4 to 8/spl times/8, and pin fin cross sections from 1.5/spl times/1.5 mm to 2.5/spl times/2.5 mm were fabricated and tested for thermal performance. Some of the commercial aluminum heat sinks with various surface finishes (such as black anodized, gold chromated, clear anodized and untreated) were also evaluated to determine the effect of surface treatment on thermal performance. The heat sink tester and the test data for the heat sinks used in this optimization study are reviewed in this paper. The results show that it is possible to design an optimum pin fin heat sink for any flow situation. However, it is not realistic to have several heat sink designs to cover various applications. In low velocity (about 1 m/s or less) open flow situations, the best compromise for pin fin heat sink with about 25/spl times/25 mm base size and heights up to 15 mm is the 6/spl times/6 pin fin configuration with fin cross-sections of 1.5/spl times/1.5 mm.

Effect of thermocouple wire size and attachment method on measurement of thermal characteristics of electronic packages

During thermal characterization and testing of electronic equipment, the temperature of electronic components has to be measured. Thermocouples are commonly used for this purpose. The presence of a thermocouple on the surface of the component causes a local distortion of the temperature field and introduces errors in the measured temperature. This paper reviews the effect of thermocouple size and attachment method on the measurement of surface temperature to determine the thermal characteristics of plastic quad flat pack (PQFP) and tape ball grid array (TBGA) packages. Various size ANSI type T thermocouples were used. The methods of attachment included thermally conductive epoxy, nonthermally conductive epoxy, aluminum tape, and polyimide tape. Thermocouple wire size and attachment method can have a significant effect on the measurement of surface temperature and thermal characterization parameters. Small size and low thermal conductivity thermocouple wires are better to minimize errors due to heat losses through the wires. Using tapes and non-thermally conductive epoxy to attach thermocouples results in larger errors.

bibliography of liquid cooled heat sinks for thermal enhancement of electronic packages

A bibliography of 847 publications dealing with air cooled heat sinks for thermal enhancement of electronic packages is presented. The bibliography also includes papers dealing with design and performance analysis of heat sinks, extended surfaces and adhesives for bonding heat sinks. The papers are classified in several categories.A bibliography of 225 publications dealing with liquid cooled heat sinks for thermal enhancement of electronic packages is presented. The bibliography also includes papers dealing with design and performance analysis of heat sinks and extended surfaces cooled with liquids. The papers are arranged in several categories.

Thermal enhancement of flip-chip packages with radial-finger-contact spring

Power dissipation, size and circuit density of integrated circuit chips are increasing and flip-chips are getting popular. Flip-chips may be joined to the substrates using small solder balls (commonly known as controlled collapse chip connections or C4s) on the circuit side of the chips, and are capable of providing a very large number of input and output connections. This paper describes a radial-finger-contact (RFC) spring for thermal enhancement of packages with C4 type flip-chips. This spring, in the shape of a disk, is made from a thin sheet of high conductivity copper alloy. A number of radial slots are cut in an alternating pattern to make it flexible. It is plated with nickel to prevent corrosion and formed into a dome shape such that when placed inside a flip-chip package it makes contact with the chip and the cap, thus providing a direct heat transfer path from the back side of the chip to the cap. To establish the feasibility and thermal reliability of this concept, a number of flip-chip packages were built with and without the RFC spring and tested for thermal performance. In one set of packages with the RFC springs, a silicone gel was used at the chip interface to further improve the thermal performance. The packages were exposed to a number of accelerated stresses and the package thermal performance (internal or the chip-to-case thermal resistance) was periodically measured. The results show that significant improvement in thermal performance is possible with the use of the RFC spring and this remains stable after exposure to accelerated stresses. This method of thermal enhancement is easily extendable to multi-chip packages with flip-chips.