LED Thermal Management

ACT has solutions for LED Cooling Applications

Compared to CFL’s and other lighting technologies, Light Emitting Diode (LED) lighting is leading the way to a “greener” lighting solution. LED lighting advantages include:

  • Lower power consumption
  • Longer lifetime
  • More compact
  • No use of Mercury

Effective thermal management is key to realizing the advantages of LED lighting. The operating temperature of the LED largely impacts the lighting color and the overall lifetime. As the LED industry shifts to Higher Brightness LED’s (HBLED) and higher density LED arrays, more effective thermal management solutions are required to maintain the LED junction level operating temperature. Although standardization is common at the junction and printed circuit board level, the variety of lighting applications leads to highly customized thermal solutions at the heat sink level.

During LED operation, 70-80% of applied electrical power is converted to waste heat.  How this heat is removed from the LED has a major impact on device life: Every increase of 10ºC above the maximum operating limit can decrease the operating life of LEDs by up to 50%.  In addition, the LED light wavelength can shift with increasing temperature, which is an important concern for spectrum sensitive products.

heat pipe printed circuit board, led heat pipes, metal core printed circuit boards

Figure 1. Heat pipe embedded Metal Core Printed Circuit Board (MCPCB). ACT’s new heat pipe embedded MCPCBs efficiently spread heat from LED devices, providing a reduction of 45% in thermal resistance compared to pure aluminum MCPCBs.

In most general lighting applications, the heat must be dissipated through natural convection heat sinks (where radiation may play a significant role) to meet acoustic noise restrictions.  However, the thermal management requirements of emerging high intensity LED lighting products often exceed the practical limits of these passive cooling strategies.  Integrating heat pipes, HiK™ plates, or vapor chambers with the heat sink can reduce the LED temperatures, and allow current heat sinks to handle higher heat fluxes.

Heat pipes, HiK™ plates, and vapor chambers can provide the following benefits for LED thermal management:

  1. Transfer heat to a remote heat sink with minimum temperature drop (Heat Pipes)
  2. Isothermalize a heat sink, reducing LED temperature and heat sink mass (Heat Pipes, HiK™ Plates)
  3. Transform the high heat flux directly under the LED to a lower heat flux, that can be removed more easily (Vapor Chambers, HiK™ Plates)

ACT has put together a series of case studies to demonstrate the benefits in using two-phase heat transfer devices to reduce LED temperatures:

The Remote Sink

In tightly compact luminaire designs, heat pipes can be used to transfer to away from the LED to a remote sink location. Read more…

LED Heat pipe heat sink, heat pipe heat sink cooling

Figure 2. IR image and photograph of remote cooling with a heat pipe embedded radial heat sink. The temperature distribution clearly demonstrates that the heat pipe can transport heat almost isothermally, and then deliver it uniformly to the heat sink.


Extrusion Isothermalization

To improve reliability and efficiency from your LEDs, aluminum heat sinks can be optimized with embedded ACT heat pipes to reduce the max temperature at the LED source.  Read more…

LED thermal management with heat pipes

Figure 3. Comparison of identical heat sinks with (B) and without (A) embedded heat pipes, dissipating 100 W. The heat pipes reduce the LED temperature by 10°C, helping to increase life and reliability.


HiK™ Plates to Improve Size, Weight, and Power (SWaP)

Heat Sink SWaP,  performance and thermal conductivity can be improved by the addition of High Conductivity (HiK™) heat sinks.  Read more…

LED Heat pipe heat spreader, heat pipe extrusion, heat pipe heat sink

Figure 4. Thermal images of the two natural-convection heat sinks show that the HiK™ heat sink has similar performance to an all-aluminum heat sink, with a reduction in mass of over 34%. 


PCB Level Spreading

Embedding  heat pipes into the structure of the Metal Core Printed Circuit boards helps dissipate heat at the LED source, providing a local and highly effective thermal management solution. Read more…

LED Circuit board with advanced thermal management, embedded heat pipes for led cooling

Figure 5. IR images and photographs of heat pipe embedded circuit board during LED operation. The heat spreading resistance is reduced by 45% over the standard aluminum MCPCB.


C.T.E. Matched Vapor Chambers

ACT’s unique CTE Matched Vapor Chambers allow direct bonding of the heat sink to the LED eliminating a thermal interface and delivering uniform high heat flux dissipation.  Read more…

LED vapor chamber, Aluminum nitride vapor chamber, ceramic vapor chamber, direct solder with heat pipes

Figure 6. C.T.E. matched vapor chamber allows direct bonding of LEDs, eliminating a thermal interface. The vapor chamber acts as a thermal transformer, spreading the heat so that it can be removed by air cooling.

To summarize, LED design engineers are facing more demanding thermal management requirements as power levels increase and package sizes decrease.  Solutions using conventional metal extrusion heat sinks are becoming thermally ineffective and too large and bulky for emerging products.  The case studies above show that passive two phase heat transfer and heat spreading technologies such as Heat Pipes, Hi-K plates and vapor chambers can provide excellent thermal management solutions for the higher power, more densely packed LED devices.  Please contact us to speak with an ACT representative about your specific LED thermal management application.

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