How Improved Extruded Aluminum Heatsinks Are Used

Due to the malleability of an aluminum alloy, extruded aluminum heatsinks can be created in a variety of unique designs. Aluminum conducts and reflects heat well. Those qualities make it useful in applications of heat transfer and reflective heat shields. An aluminum alloy is low in cost and can be tempered in various ways. Through smelting, scraping, and refining the aluminum alloy can be pounded into sheets, fins, and foils.

Aluminum provides less thermal conductivity than other metals like copper. However, it is easier by far to make heat sink extrusions from aluminum that those other metals. Creating custom aluminum heat sink variation profiles is also considerably easier. Aluminum fin profiles can be attached easily to a copper base that conducts more thermal energy to the less expensive and lighter cooling fins made of an aluminum alloy.

Heat sink extrusions serve electronic, medical, military, automotive, electrical, and telecommunication industries. A liquid cooling solution that combines extrusions made of aluminum with friction stir welding makes air-cooled heat sinks higher quality and more thermally efficient that pressed or bonded fins.

Complex fin structures are created by forcing raw aluminum through extrusion dies. The complex fins allow more heat dissipation and increased surface area. Time and cost associated with machining a shape that is equivalent from block aluminum are eliminated.

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Heat Sinks Used in LED Lighting Designs

The correct LED heat sinks must be determined for new LED lighting designs. The approach of integral models and verification test discussed here give an insight into the functional integrity and operational reliability of design in meeting market expectations.

Each LED has its set of parameters. Ambient temperature is one of the parameters. Different lights require different temperatures. Mounted, open air spotlights need 30ᵒ C, recessed ceiling lights 50 to 55ᵒ C, and automotive lighting 45ᵒ C.

The parameters must be defined. The LED Chips on Board module manufacturers provide lifetime expectations under conditions that are ideal. They calculate 90 percent reliability for the maximum junction temperature.

In calculating the required LED heatsinks, it must be understood that each part of a design adds heat due to the material’s thermal resistance. The total design should be below the maximum junction temperature required.

A mathematical calculation is made to define the maximum thermal resistance heat sinks should have or the maximum rise in temperature LED heatsinks create when dissipating power. Thermal resistance is expressed as a Rth value. Some manufacturers give thermal resistance value for heat sinks that are independent of dissipation power and ambient temperature. The Rth value of LED heatsinks is not the same under all conditions.

After applying thermal pads and heat sinks, verify the design. Manufacturers include safety margins in their designs. A maximum of 97.4ᵒ C thermal measurement point should not be subjected to temperatures more than the range of 87 to 92ᵒ C.

All high power LEDs need to dissipate the heat produced to keep it below the maximum operating temperature. Overheating can cause a shortened life, a reduction in light output, an output color change, or complete LED failure.

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All About Heat Sink Extrusions and Extruded Aluminum Heatsinks

Heat sink extrusions provide more natural convection solutions for high-powered systems and components. Complex fin structures are made by forcing raw aluminum through extrusion dies. The process of manufacturing aluminum heatsinks is somewhat like a Play-Doh factory. Pick the desired shape and squeeze Play-Doh through the shape.

The difference is extruded aluminum heatsinks exit the press opening at approximately 1000ᵒ F. In addition to the high temperature, the extrusion press pushes with a force in excess of 1500 tons. The pressure and temperature are controlled to obtain the profile required.

The complex fin profile allows greater heat dissipation by increasing the surface area while eliminating the time and cost associated with the machination of an equivalent shape made from block aluminum. The benefits of heat sink extrusion are:

• Greater efficiency than stamped heatsinks

• Cost less than assemblies that are fully machined

• Availability of many standard sizes and shapes

• Any application is easily customized

• A weight advantage over copper that is significant

• Tool and hardware mounting are eliminated by a clip system

When manufacturing extruded aluminum heatsinks, the press speed needed to maintain a steady extrusion pull-force, the weight, and the profile complexity are taken into consideration. Benefits of the system include:

• Reduced billet to billet dead cycle time

• Improved straightness

• Minimized scrap

• Improved yield throughout the process of manufacturing

The need for customized extruded aluminum heatsinks continues to grow. The growth reduces product cycle time and overall costs. Customized extruded aluminum heatsinks include:

• Shapes that require stretching and bending

• Detailed precision computerized numerical control used to make customized components that meet product application needs

• Aluminum fabrication from simple to complex precision machination

• Finishes such as heat treating, plating, painting, anodizing, or mechanical finishes

• Heat dissipation requirements.

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Characteristics of Bonded Grid Arrays and BGA Heat Sinks

Bonded grid arrays are heat sink assemblies that are highly efficient, cost effective, reliable thermal management solutions for density packed or high-power packaged applications. These characteristics hold true in demanding vibration and shock environments. Bonded grid arrays are used when simple extrusions are impractical. They lower thermal resistance and increase surface area. There are various configurations that can be assembled.

Any industry, employing high-powered electronic circuits can use bonded grid arrays. A partial list of industries includes factory automation, medical equipment, wireless and RF, military, broadcast, telecommunications, and renewable energy. When choosing bonded grid arrays consider the overall dimensions, specified thermal resistance, and the finish. Finishes include gold iridite, clear iridite, gold chromate, or unfinished.

Finding the device that is appropriate for a cooling system to be effective is important to the overall design of a component. BGA heat sinks are available in ceramic and plastic. A major benefit of BGA heat sinks is the increased heat dissipation rate.

The ball grid design is achieved by advance circuitry that allows quick thermal energy conveyance without the levels of resistance, prone to occur with the surface mounting approach of the gull wing. Gull wing leads cannot reach the heatsink pin count capacity of BGA heat sinks.

The most innovative BGA heat sinks aspect is the ability to self-align based on the heat flow from its source. This characteristic has the potential to allow greater thermal energy transfer levels and increase efficiency throughout the heatsink.

There are some drawbacks to consider before making a final decision. Because of the joint solder complexity, standard reworking and inspection methods cannot be achieved. Solder joints cannot be individually adjusted and basic visual inspection is not possible. A proposed solution to this problem is x-ray use to ensure reliable BGA heat sinks.

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Designers Use Copper Heatpipes for Superior Performance

Heatpipes offer highly effective thermal conductivity and energy efficiency. Other positive characteristics are the low cost, light weight, and flexibility that provides many different shape and size options. Heatpipes offer a heat transfer system that is simple and reliable to operate. The system has no moving parts, transports heat over a long distance, and is a quiet, vibration-free operation.

Heatpipes are filled with small quantities of working fluid such as sodium, ammonia, methanol, nitrogen, acetone, or water. The working fluid is vaporized as heat is absorbed. The vapor transports the heat to a condenser region. The heat is released to a cooling medium by condensed vapor. Capillary action is created as the condensed working fluid returns to the evaporator by the heatpipe’s wick structure or gravity. Planar and cylindrical heatpipes have an inner surface that is lined with wicking material capillaries.

Military and commercial designers turn to copper heatpipes for superior power density, regardless of orientation or gravity. Copper heatpipes are designed specifically for applications where gravity or high heat loads present thermal challenges. Long life and reliability are critical. The copper heatpipe operates flawlessly against gravity and is rugged enough to withstand temperatures that range from 55ᵒ below zero to 180ᵒ C, and numerous freeze-thaw cycles.

Copper heatpipes use water as the working fluid. It smoothly moves heat from the source to an area where it can be managed effectively through liquid or air dissipation or radiation to space. These heatpipes are integrated into customized metallic cold plates or heat sinks. The integration improves the efficiency and conductivity. It allows the thermal designer to improve the performance of the overall system. The heatpipes can be integrated into extended surfaces, cold plates, and heat sinks through mechanical interference, solder, or epoxy.

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Uses for LED and Copper Heatsinks

LEDs are a solid-state lighting form. Typical LED lights are made of small semiconductors; optical lenses, integrated to shape the radiation pattern; and LED heatsinks to keep a low operating temperature for the semiconductor and dissipate heat.

The life expectancy and performance of LED lights are directly linked to operating temperatures. The lower the operating temperature is, the longer the operating life and the better it performs. Thermal management is critical in a LED light design aspect. Thermal management increases the lighting quality and durability. LED lights are cooled by LED heatsinks using natural convection.

Honeycomb LED heatsinks have a LED chip located in the center of the heatsinks. Air passes through the hexagon-shaped holes and is carried away from the chip. The cooling performance of the heatsinks is affected by the rib-space ratio, the honeycomb aspect ratio, and the number of cells that surround the heat source.

Each new generation of devices having semiconductors has shrinking packages and a rise in the levels of power dissipation. Because of this trend, copper heatsinks are being used more often in a variety of applications.

A common technology available in copper heatsinks is the pin fin technology. Copper’s superior thermal properties satisfy challenging cooling requirements. When comparing aluminum and copper heatsinks  types of cooling scenarios and the value of copper, copper was recommended.

To understand the impact of copper heatsinks the thermal conductivity of aluminum versus copper must be considered. Applications demanding thermal stability are best served by copper heatsinks. Heatsinks having significant thermal mass are needed when power dissipation has a wide fluctuation, but a constant temperature is needed. In such a situation, copper with its 40 percent higher thermal mass is a better choice than aluminum.

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The Difference between Bonded Grid Arrays and BGA Heat Sinks

Engineers are faced with increased performance demands and miniaturization. Heat dissipation is an issue for both challenges. If heat dissipation were not necessary, all electronic devices would operate faster. Heat dissipation is necessary to keep devices from becoming unreliable, overheating, and failing. To produce reliable devices with long life and acceptable performance, heat dissipation must be introduced. Heat sinks are a method of removing heat.

Heatsinks are devices that dissipate heat from a heat generating component to a medium, usually air that is cooler. Heat sinks placed on hot components improve the transfer of heat by an increase of surface area that has direct air contact. The component’s operating temperature is lowered as heat is dissipated. Heat sinks maintain the temperature of a device below the maximum specified by the manufacturer. 

To choose the appropriate heat sink necessary for thermal performance various parameters are considered and calculations performed. Extruded heatsinks allow two-dimensional profile formations that dissipate large heat loads. BGA heat sinks are simple extrusions. BGA heat sinks typically convert extruded fins into pins. The BGA heat sinks are crosscut to allow more diverse applications.

Bonded grid arrays are built to customer specifications. Very few power electronic applications are the same. A one-size-fits-all theory is not feasible. Bonded grid arrays dissipate as much as three times the amount of heat dissipated by the average extruded heatsink. Two styles of bonded grid arrays are available. They are single and folded fins. Fin density, thickness, and height are used in countless combinations to provide the desired performance.

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