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Thermal resistance of small SMDs versus Copper Pours

  • Thread starter Klaus Kragelund
  • Start date
K

Klaus Kragelund

Jan 1, 1970
0
Hi

I am looking into how much I can dissipate in a 0805 or 1206 resistor.

A discussion on SED about the topic a while back:

https://groups.google.com/d/topic/sci.electronics.design/3GPk1GPreks/discussion

In the discussion:

Qoute

There is a
National datasheet somewhere that has a bunch of examples of
various-shaped copper pours and their thetas. Maybe someone here
remembers which it is.

Unqoute

So what I am trying to find is that Natinal datasheet or app note. Google was not my frind after extensive search :-(

Anyone got that app note in their archive?

Cheers

Klaus
 
L

Lasse Langwadt Christensen

Jan 1, 1970
0
Den onsdag den 4. december 2013 12.02.50 UTC+1 skrev Klaus Kragelund:
Hi



I am looking into how much I can dissipate in a 0805 or 1206 resistor.



A discussion on SED about the topic a while back:



https://groups.google.com/d/topic/sci.electronics.design/3GPk1GPreks/discussion



In the discussion:



Qoute



There is a

National datasheet somewhere that has a bunch of examples of

various-shaped copper pours and their thetas. Maybe someone here

remembers which it is.



Unqoute



So what I am trying to find is that Natinal datasheet or app note. Google was not my frind after extensive search :-(



Anyone got that app note in their archive?



Cheers



Klaus

maybe this is the one?

http://www.ti.com/lit/ds/symlink/lm1117-n.pdf

-Lasse
 
K

Klaus Kragelund

Jan 1, 1970
0
Den onsdag den 4. december 2013 12.02.50 UTC+1 skrev Klaus Kragelund:




maybe this is the one?



http://www.ti.com/lit/ds/symlink/lm1117-n.pdf

Yes, it certainly has very good information on the subject, thanks :)

It's kind of strange that apparently no information (including thermography plots) of dumping power into 0805 and 1206 resistors exists.

Cheers

Klaus
 
J

Joerg

Jan 1, 1970
0
Klaus said:
Hi

I am looking into how much I can dissipate in a 0805 or 1206 resistor.

A discussion on SED about the topic a while back:

https://groups.google.com/d/topic/sci.electronics.design/3GPk1GPreks/discussion

In the discussion:

Qoute

There is a
National datasheet somewhere that has a bunch of examples of
various-shaped copper pours and their thetas. Maybe someone here
remembers which it is.

Unqoute

So what I am trying to find is that Natinal datasheet or app note. Google was not my frind after extensive search :-(

Anyone got that app note in their archive?

This is pretty good even though the resolution of figure 7 is poor:

http://catalog.osram-os.com/media/_en/Graphics/00017064_0.pdf

If you have to push performance within a given real estate consider
side-contact resistors for increased heat transfer:

http://www.welwyn-tt.com/pdf/application_notes/LRCvsMSR_AN_A.pdf
 
K

Klaus Kragelund

Jan 1, 1970
0
We've done a bunch of work on this, keeping resistors cool with copper pours.

You can push an 0603 to at least half a watt if you keep the end caps cool. The

central hot-spot temperature of 1206 through 0603 resistors are about the same

at equal dissipation if they are on big pours.



0805 on small single-side pours:



https://dl.dropboxusercontent.com/u/53724080/Thermal/140K_per_Watt.jpg





1206 RTD:



https://dl.dropboxusercontent.com/u/53724080/Thermal/RTD_in_air.JPG



https://dl.dropboxusercontent.com/u/53724080/Thermal/RTD_on_board.JPG



https://dl.dropboxusercontent.com/u/53724080/Thermal/RTD_lotsa_copper.JPG



(note the delta-v cursor values on the first and last. I flubbed the middle

one.)

That's a nice trick, using the RTD for both the power dissipation and measurement, will reveal the correct thermal resistance delay

Cheers

Klaus
 
L

legg

Jan 1, 1970
0
Hi

I am looking into how much I can dissipate in a 0805 or 1206 resistor.

A discussion on SED about the topic a while back:

https://groups.google.com/d/topic/sci.electronics.design/3GPk1GPreks/discussion

In the discussion:

Qoute

There is a
National datasheet somewhere that has a bunch of examples of
various-shaped copper pours and their thetas. Maybe someone here
remembers which it is.

Unqoute

So what I am trying to find is that Natinal datasheet or app note. Google was not my frind after extensive search :-(

Anyone got that app note in their archive?

Cheers

Klaus

You may be looking for Nat Semi AN1025 for SOT23.
AN1028 covers patterns for SOT-223
There was one for SOIC parts, but I seem to have mislocated it in
electronic format.

Strangely enough, there are app notes with the same numbers from
Fairchild.

RL
 
L

legg

Jan 1, 1970
0
Hi

I am looking into how much I can dissipate in a 0805 or 1206 resistor.

A discussion on SED about the topic a while back:

https://groups.google.com/d/topic/sci.electronics.design/3GPk1GPreks/discussion

In the discussion:

Qoute

There is a
National datasheet somewhere that has a bunch of examples of
various-shaped copper pours and their thetas. Maybe someone here
remembers which it is.

Unqoute

So what I am trying to find is that Natinal datasheet or app note. Google was not my frind after extensive search :-(

Anyone got that app note in their archive?

Cheers

Klaus

Also - check out IR AN994.

RL
 
L

legg

Jan 1, 1970
0
Hi

I am looking into how much I can dissipate in a 0805 or 1206 resistor.

A discussion on SED about the topic a while back:

https://groups.google.com/d/topic/sci.electronics.design/3GPk1GPreks/discussion

In the discussion:

Qoute

There is a
National datasheet somewhere that has a bunch of examples of
various-shaped copper pours and their thetas. Maybe someone here
remembers which it is.

Unqoute

So what I am trying to find is that Natinal datasheet or app note. Google was not my frind after extensive search :-(

Anyone got that app note in their archive?

Cheers

Klaus


AN1029 is SO8

RL
 
L

legg

Jan 1, 1970
0
Hi

I am looking into how much I can dissipate in a 0805 or 1206 resistor.

A discussion on SED about the topic a while back:

https://groups.google.com/d/topic/sci.electronics.design/3GPk1GPreks/discussion

In the discussion:

Qoute

There is a
National datasheet somewhere that has a bunch of examples of
various-shaped copper pours and their thetas. Maybe someone here
remembers which it is.

Unqoute

So what I am trying to find is that Natinal datasheet or app note. Google was not my frind after extensive search :-(

Anyone got that app note in their archive?

Cheers

Klaus

For a good time, google "Package and Thermal Information" to see some
thermal images for different package patterns from Infineon.....

RL
 
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