Ramon is correct. Copper makes a good heat spreader and is more efficient at
getting the heat out to the extremities.... On the other hand, It's harder
to machine, and is more expensive than aluminum. Aluminum is popular because
it costs less and is easier to machine extrude or mold into shape, and it's
still a good conductor of heat.
Specific heat is measured by the amount of energy it takes to change one
gram of material 1 degree Celsius. The 'specific heat' numbers for some
thermal conductors respectively are:
Aluminum: 0.900
Copper: 0.385
Silver: 0.232
Gold: 0.128
Now it takes less energy to heat gold than it does to heat silver, copper,
and then Aluminum which is in fact more than twice the energy to heat than
copper is. You can see why copper makes a good heat spreader though. It was
the preferred choice by the makers of pots and pans... Anyone still use
copper bottom pans to cook with?
I think the aluminum is good though and much of the performance of a heat
sink is directly attributable to the surface area and good mechanical
interface between the heat source and the heat sink.
The idea that you can 'hard anodize' the aluminum to make a dielectric layer
has been around for sometime, and since we use surface mount parts on a lot
of our boards it might lend itself to a design that has a lot of heat to
deal get rid of, like for example these high powered LED's we see used in
the street lamps or in cars. I bet they get pretty hot when in use...
I was just wondering if RF amplifiers could take advantage of the concept
and how the impedance of the circuit could be calculated to make a 50 ohm
conductor on the surface of the aluminum oxide layer... We have to deal with
hot components all the time in the RF world... so I keep an eye out for new
ways to do things. It might be worth experimenting with.
I may order a sample of the material to see how it performs.
Bill Brooks - KG6VVP
PCB Design Engineer , C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
e-mail:[log in to unmask]
http://www.dtwc.com
http://pcbwizards.com
-----Original Message-----
From: Dehoyos, Ramon [mailto:[log in to unmask]]
Sent: Thursday, January 13, 2005 11:43 AM
To: [log in to unmask]
Subject: Re: [TN] Aluminum substrates... any issues?
The relative conductivity of Copper is about twice that of aluminum.
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Denis Lefebvre
Sent: Thursday, January 13, 2005 2:25 PM
To: [log in to unmask]
Subject: Re: [TN] Aluminum substrates... any issues?
I've heard of "copper core" boards before, but not aluminum. I suppose it
would preferable with respect to the fact that aluminum is a better
conductor than copper.
-----Original Message-----
From: Brooks,Bill [mailto:[log in to unmask]]
Sent: Thursday, January 13, 2005 11:08 AM
To: [log in to unmask]
Subject: [TN] Aluminum substrates... any issues?
I ran across this supplier of aluminum boards and was interested if any of
you have dealt with this type of thing before? I have seen metal core boards
made with alumina and bonded with the fiberglass/epoxy for heat sinking
needs but this looks like a different process. Possibly less expensive...
???
http://www.irctt.com/pdf_files/thickfilm_aluminum.pdf
Any comments on it are appreciated.
Best regards,
Bill Brooks - KG6VVP
PCB Design Engineer , C.I.D.+, C.I.I.
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
e-mail:[log in to unmask]
http://www.dtwc.com
http://pcbwizards.com
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