LED thermal problems

I just got a (free) DVD from OPTEK that goes into great detail on issues with high power LEDs and heat management, including a discussion of the quantum level causes and effects.

www.optekinc.com

Electronic packaging engineers deal with this problem all the time. If the LED is in chip form, a conventional method is to bond the back of the chip to a material that has the same expansion coefficient as the chip, and very high thermal conductivity. This allows the heat to be conducted to an ultimate heat sink. The problem is that such materials are expensive. An example of a material that is sometimes used for this is a tungsen/copper powder metallurgy material. Alternate methods include the use of fluids and/or vapor to transfer the heat to another location. If you are dealing with packaged LEDs, you must consider the thermal resistance of the manufacturer's packaging. You can obviously do a better job if you package the chips yourself, but you must be prepared to perform semiconductor assembly processes.

Major problem I think this person is talking is degrading of the LED with time. LED problem is same which I use to see and that is hot spot. This is caused by pinhole size voids and imperfection in the cured adhesive under chip to bond to substrate. LED does not produce as much heat as microprocessor chip or RAM, SRAM or DRAM chips.

Having metallic substrate is good enough to pull the heat down but if we have hot spot or we have unlevel chip adhecive between chip and substrate material then there will be temperature gradient across the chip surface will creat thermal gradient issue and that will creat biased voltage flow in wrong direction causing low glow and eventually death of the chip.

Dr. T. Settu in India is expert on this topic and he can help you more if you are interested. I can provide you contact details of this person. He has presentated paper at Anna University in Chenni, India.

Here's another one I got in the mail today:

http://www.lumex.com/marketingdownloads/CoolSolutions.html