LED heat sink: The Basic Thermal Theory You need to Know
What LED Heat Sink is
LED heat sink is a heat exchanger that conducts thermal from LED COB（chip on board）power source, then converts them into the air.
As known as common sense, high temperature is a dangerous factor to all the things, so is it for an LED lamp. In theory, the LED lamp may only transform about 30% electricity power into light, the rest of electricity power becomes thermal heat. As a result, heat will elevate the temperature of the LED ambient.
The high temperature will not only shorten the LED life cycle but create a safety issue in case the LED lamp to burn out. So it is important to conduct thermal heat from LED COB and convect it into the air to keep the LED lamp working in the desired temperature environment.
How LED Heat Sink work
In the LED lighting industry, the COB of LED lamp mounts on the heat-conducting surface of the heat sink. Consequently, the conducted heat will flow to the heatsink pin fin to convert to the surrounding air.
LED heat sink design scheme
Thermal resistance exists on each object in LED lamp, it is defined as temperature rise per each unit of power, namely Celsius per watt (°C/W). The smaller the unit is, the higher the heat convection ability is.
The thermal resistance of LED COB shells is very high, it makes the ambient temperature around LED elevate very quickly. Heat sink plays the role to conduct heat from COB and dissipate them into the air.
Heat sink classification
The heat sink is divided into two basic catalogs: finned heat sink and die-cast heat sink. The finned heatsink yields the best heat transfer, so it is the first choice to meet design intent or application requirements. On other hand, the finned heatsink may be further classified as pin fin heat sink and straight fin heat sink according to fin arrangement.
Design Consideration
Many factors affect heat sink work performance.
First of all, the designer needs to consider material thermal conductivity. Aluminum or copper is the typical material selection because of its excellent heat conductivity and convection.
Secondly, the designer needs to balance all factors together, such as heat sink weight and economic cost. The design intent is to maximize the heat convection area, but that is not always only one factor to be considered. To maximize heat dissipation capability, the pin-fin ratio is a key design element. Pin-fin ratio is an index number of fin height divided by fin distance. The much bigger the ratio is, the much bigger the convection area of the heat sink will have.
Lastly heat contact surface needs to be considered. A rough and uneven surface may increase overall thermal resistance because of trapped air in the contact gap. Hence, thermal conductive paste or tape may be applied on the contact surface to squeeze out the air.
Heat Sink Workmanship
Heat sink design also reflects the workmanship of heatsink according to its design intent. The below matrix table shows the characteristic of different type of heat sink:
| Heatsink type | Material type | Workmanship | Surface treatment | Heat conductivity |
| Pin fin heat sink | AL1070 or other pure aluminum, high heat conductivity and dissipation(226~237w/m.k) | Cold forging | Anodizing and pigment excellent | no air or void inside, no thermal resistance |
| The straight fin heat sink | Aluminum alloys, such as AL6063, moderate heat conductivity, and dissipation(155w/m.k) | Hot extrusion | Anodizing and pigment good | air bubble or void existed, thermal resistant |
| Die-cast heat sink | Die casting aluminum alloy, poor heat conductivity, and (96w/m.k.) | Permanent mold die casting | Not suitable for anodizing | air bubble or void existed, thermal resistant |
We can figure out from the above table that the cold-forged heat sink is the best choice with considering thermal conductivity. However, the design needs to consider a stack of factors. It is the pursuit target to maximize heat sink thermal conductivity efficiency in an economical way to meet LED lighting application requirements.
Learn more about how heatsink is cold-forged from the article: Metal forging process that forge part strength and toughness.
Summary
In conclusion, LED heat sink has very broad application in lighting industry sector, actual application is varied and requirement is different. As such, heatsink design or manufacturing process will be varied to meet the specific needs.
Visit Sipaitech Mfg site to learn more from specific project and relevant technical artical.
To Learn more, visit Lighting Industry Association to get much more inside of heat sink industry.