Industry Developments: Extrusion Profile Heat Sinks

Industry Developments: Extrusion Profile Heat Sinks

Extruded metal heat sinks are among the lowest cost, widest used heat spreaders in electronics thermal

management. Besides their affordability, extruded heat sinks are lightweight, readily cut to size and shape, and

capable of high levels of cooling.

    Most extruded heat sinks are made from aluminum alloys, mainly from the 6000 alloy series, where aluminum

dominates. Trace amounts of other elements are added, including magnesium and silicon. These alloys are easy to

extrude and machine, are weldable, and can be hardened.

    Common alloys for extruded heat sinks are the 6063 metals. These can be extruded as complex shapes, with very

smooth surfaces. 6061 aluminum is also used for extrusions. Its tensile strength (up to 240 MPa) is superior to

6063 alloys (up to 186 MPa). In addition to heat sinks, these aluminum alloys are popular for architectural

applications such as window and door frames. 

    The surfaces of these metals can be anodized to replace their naturally occurring surface layer of aluminum

oxide. Anodizing provides more heat transfer, corrosion resistance and better adhesion for paint primers. It is an

electrochemical process that increases surface emissivity, corrosion and wear resistance, and electrical

isolation.

    The Extruding Process

    Aluminum alloys are popular for extruding as heat sinks because they provide both malleability and

formability. They can be easily machined and are as little as one-third the density of steel. This results in

extrusions that are both strong and stable, at a reduced cost relative to other materials.

    The aluminum extrusion process starts with designing and creating the die that will shape the

heatsink extrusion. Once this has been done, a

cylindrical billet of aluminum is heated up in a forge to high temperatures, generally between 800-925°F (427-496

°C). Next, a lubricant is added to the aluminum to prevent it from sticking to any of the machinery. It is then

placed on a loader and pressure is applied with a ram to push heated aluminum through the die.

    During this process, nitrogen is added in order to prevent oxidation. The extruded part will pass completely

through the die and out the other side. It has now been elongated in the shape of the die opening. The finished

extrusion is then cooled, and if necessary, a process of straightening and hardening creates the finished product.

    They can be cut to the desired lengths, drilled and machined, and undergo a final aging process before being

ready for market. [4]

    Finished heat sinks typically come with anodized surfaces, which can enhance their thermal performance.

Alternatively, a chromate finish provides some corrosion protection, or can be used as a primer before a final

paint or powder coating is applied. [5]

    Shapes of Extruded Heat Sinks

    Extrusions tooling heat

sink profiles range from simple flat back fin structures to complex geometries for optimized cooling. They

can be used for natural (passive) or forced convection (active) with an added fan or blower. Extruded profiles can

also include special geometries and groove patterns for use with clip or push pin attachment systems.

    6063 aluminum alloy has a thermal conductivity of 201-218 W/(mK). Higher tensile strength 6061 aluminum’s

thermal conductivity ranges from 151-202 W/(mK).

    Besides choosing the aluminum alloy, selecting an optimal extruded heat sink should factor in its overall

dimensions and weight, the specified thermal resistance, and the extrusion shape (flat-back, flat-back with gap,

hollow, double-sided, etc.). [7]

    Extruded heat sinks can be designed with very thin, and thus more, fins than other sink types. They can be

extruded with aspect ratios of around 8:1, which can greatly optimize heat sink performance. A heat sink’s aspect

ratio is basically the comparison of its fin height to the distance between its fins.

    In typical heat sinks the aspect ratio is between 3:1 and 5:1. A high aspect

extruded heat sink has taller fins

with a smaller distance between them for a ratio that can be 8:1 to 16:1 or greater.

    Linear Cellular Alloys (LCAs) are metal honeycombs that are extruded using powder metal-oxide precursors and

chemical reactions to obtain near fully dense metallic cell walls. Either ordered periodic or graded cell

structures can be formed. In this work, the performance of heat sinks fabricated from stochastic cellular metals

is compared to that of LCA heat sinks. Flash diffusivity experiments are performed to determine the in situ

thermal properties of cell wall material. The pressure drop for unidirectional fluid flow in the honeycomb

channels and the total heat transfer rate of LCA heat sinks are experimentally measured. These measurements are

compared to values predicted from a finite difference code and commercial computational fluid dynamics (CFD)

software.

    A three-dimensional finite element model of a multichip module (MCM) has been developed by using ANSYS? finite

element simulation code. The model has been used for thermal characterization of the module. In addition, optimum

dimensions of an external heat sink, which maintains the specified device’s junction temperature within desired

operating temperature limits, are determined as functions of air flow rate and power density of surrounding

semiconductor devices. Parametric studies have been performed to study the effects of heat sink height, width and

length on junction-to-ambient thermal resistance of a high power application specific integrated circuit (ASIC)

device found in the MCM assembly. A set of curves are generated to select either heat sink dimensions or air speed

for a given design requirements. Influence of the power output of surrounding devices on the thermal performance

of the high power ASIC device is also assessed. The predicted results indicate that the ASIC device’s junction

temperature as well as junction-to-ambient resistance increase as the power of the surrounding packages increases.

This effect diminishes if a sufficiently large heat sink is used to cool the package.

    There are different metals with different properties, some metals are used for luxury purposes such as diamond

and gold, others are used for building purposes such as brass, nickel, steel, copper, and many more. Every piece

of equipment, to work efficiently, requires a good building block. And while engineering important components it

is extremely important to look at the qualities of the material that are going to be used and it is also important

to keep a check on the factors that can affect the material, Aluminium in this case.

    Aluminum is considered the best option for engineering heat sinks because it is cost-friendly, lightweight and

most importantly has great thermal conductivity.

    Which Metals Conduct Heat The Best?

    Copper and Aluminium among other metals have the highest thermal conductivity. Before using metal in any sort

of application it is very important to check the thermal conductivity of that metal. The rate of thermal

conductivity helps to decide which metal should be used for a specific purpose. Aluminum is a great conductor of

heat, which makes it useful for constructing heat exchangers. On the other hand, steel is a very poor conductor of

heat which makes it useful for high-temperature environments. This is why Aluminum is preferred to be used in

constructing a heat sink.

    Thermal Conductivity

    Heat transfers in three ways; radiation, convection, and conduction. Thermal Conduction is a process where two

objects of different temperatures come into contact with one another and when they meet fast-moving molecules from

the warmer object transfer the energy to the slow-moving molecules in the cooler object.

    Aluminum heat sinks

    Aluminum is considered beneficial for electrical device managers. It is a great metal to be used in the

construction of critical power cooling systems. Improvement in extrusion profile technology has made it possible

to engineer heat sinks which call for a blend of greater strength and lighter weight.

    Aluminum in comparison with other metals such as copper has lower thermal conductivity but it is far too

difficult to extrude them into the shape of a heat sink. Secondly, Aluminium is a lightweight metal, which is also

another property that other metals do not possess.

    Heat Sinks

    Heat sinks are mainly used inside computers to cool down the CPU(Central Processing Unit), they are also used

in lighting devices, LEDs, and power transistors.

    Heat sinks are designed in a way to have a large surface area to maximize the contact with the fluid medium,

such as air or liquid coolant to absorb heat and direct it away from the device.

    Aluminum alloys are preferred to be used in constructing heat sinks. This is because Aluminium is lighter and

cheaper than copper.

    How does a heat sink work?

    Computers heat up and if the heat is not removed from the device it can actually damage the entire system. To

direct the heat away from the system it is necessary to install a heat exchanger. Heat sink directs the heat away

from the computer, it does this by transferring the heat generated in the system to a fluid medium such as air or

a liquid coolant, whereby it is directed away from the device. 

    What is the purpose of a heat sink?

    The purpose of a CPU heatsink is basically the

maintenance of the computer. Without a heat sink, the system can overheat and therefore can stop working

efficiently. To ensure smooth working of the device it is important to install a heat sink to direct generated

heat away from the system and prevent overheating.

    Why is a heat sink important?

    As stated above, a skived fin heatsink is vital

for extending the life of a lighting device. It absorbs unnecessary heat and directs it away from the device. Heat

sinks increase the efficiency of the device by removing the excess heat which is why it is an extremely important

component. Without a heat sink, computers or other related devices can expire quicker. Heat sinks keep the system

cool and provide a good working environment to the other components which heat up quite quickly.

    Factors Affecting Aluminum Heat Sink Quality

    Quality Requirements For Ingots

    The blend of alloys in an ingot must be strictly monitored and controlled, for purification purposes. To make

sure that the structure and properties are not imbalanced it is important to make sure that the alloys are

homogenized. The surface of the ingot must be smooth and there must not be any sand. The end of the ingot must be

flat.