2W from a SOT-223 ?

[Adam. Seychell]

The thermal resistance from junction to "soldering point" of a
PZT2222/PZT2907 SOT-223 is 26 K/W. Say I were to soldering the SOT-223
tab to a copper strip, which in then clamps to a large heatsink.
Assuming Tj rise of 50°C then;

Pd_max = 50/26 = 2 Watts

Anyone else heatsinked a SOT-223 this way ?
I would use a device with a larger package but there isn't anything else
around with similar specs and/or availability. The PZT2222/PZT2907,
replace the old metal canned TO-39 2N2219/2N2905.

 

[Pooh Bear]

"Adam. Seychell" wrote:

The thermal resistance from junction to "soldering point" of a
PZT2222/PZT2907 SOT-223 is 26 K/W. Say I were to soldering the SOT-223
tab to a copper strip, which in then clamps to a large heatsink.
Assuming Tj rise of 50°C then;

Pd_max = 50/26 = 2 Watts

Anyone else heatsinked a SOT-223 this way ?
I would use a device with a larger package but there isn't anything else
around with similar specs and/or availability. The PZT2222/PZT2907,
replace the old metal canned TO-39 2N2219/2N2905.

SOT-223 doesn't ring immediate bells with me.

I can't believe there's no other suitable substitute. How far did you look ?

Have you looked at D-pak for power dissipation ? IR have an app note on
using pcb foil area for heatsinking.

Graham

 

[Graham Holloway]

"Adam. Seychell" <invald@invalid.com> wrote in message
news:42b79bdd$0$16490$afc38c87@news.optusnet.com.au...

The thermal resistance from junction to "soldering point" of a
PZT2222/PZT2907 SOT-223 is 26 K/W. Say I were to soldering the SOT-223
tab to a copper strip, which in then clamps to a large heatsink.
Assuming Tj rise of 50°C then;

Pd_max = 50/26 = 2 Watts

Anyone else heatsinked a SOT-223 this way ?
I would use a device with a larger package but there isn't anything else
around with similar specs and/or availability. The PZT2222/PZT2907,
replace the old metal canned TO-39 2N2219/2N2905.

You are correct in your assumptions. I have used a SOT223 linear regulator
in a similar manner although I use thermal vias to conduct the heat to a
baseplate below the PCB.

Graham Holloway

 

[Winfield Hill]

cbarn24050@aol.com wrote...

Adam Seychell wrote:
The thermal resistance from junction to "soldering point" of a
PZT2222/PZT2907 SOT-223 is 26 K/W. Say I were to soldering the
SOT-223 tab to a copper strip, which in then clamps to a large
heatsink. Assuming Tj rise of 50 C then; Pd_max = 50/26 =
2 Watts. Anyone else heatsinked a SOT-223 this way?

I would use a device with a larger package but there isn't
anything else around with similar specs and/or availability. The
PZT2222/PZT2907 replace the old metal canned TO-39 2N2219/2N2905.

That's 50deg rise above the heatsink temp, not above ambient.

Yes, 50 C rise above the connection point. The thermal resistance
of the [ SOT-223 tab -> copper strip -> clamps to large heatsink ]
path is at issue, especially the 2oz PCB copper-strip portion.

Or does Adam really mean a mean old copper strip? That could work.


--
Thanks,
- Win

 

[SioL]

"Graham Holloway" <eng@wps-electronics.demon.co.uk> wrote in message news:d98b1n$ku2$1$8300dec7@news.demon.co.uk...

You are correct in your assumptions. I have used a SOT223 linear regulator
in a similar manner although I use thermal vias to conduct the heat to a
baseplate below the PCB.

Graham Holloway

How effective is this method in terms of conducting heat to the underside of the PCB?

Nowadays SMD packages are taking over even for power devices and it is often quite
difficult to heatsink them


--
Siol
------------------------------------------------
Rather than a heartless beep
Or a rude error message,
See these simple words: "File not found."

 

[Graham Holloway]

"SioL" <Sio_spam_L@same.net> wrote in message
news:TsUte.12839$F6.2770987@news.siol.net...

"Graham Holloway" <eng@wps-electronics.demon.co.uk> wrote in message
news:d98b1n$ku2$1$8300dec7@news.demon.co.uk...


You are correct in your assumptions. I have used a SOT223 linear
regulator
in a similar manner although I use thermal vias to conduct the heat to a
baseplate below the PCB.

Graham Holloway

How effective is this method in terms of conducting heat to the underside
of the PCB?

Nowadays SMD packages are taking over even for power devices and it is
often quite
difficult to heatsink them


--
Siol
------------------------------------------------
Rather than a heartless beep
Or a rude error message,
See these simple words: "File not found."


Siol

I don't have any specific details for you. However, I would flood the area
beneath the device with copper and then add the vias. Say, 28mil holes on a
staggered rows/columns pitch of 30mil would be a good start. I used a thin
Berquist insulator between the underside of the PCB and a raised section of
a baseplate, but I've seen other people used the gapfiller quite effectively
to get the heat across several mm. I think you might need to experiment.
Also bear in mind the vias will fill with solder (extra conduction) unless
you take specific steps to avoid it.



Graham Holloway
WPS/Accuphon Electronics
(Tel/Fax 0(044)1233 662599)

 

[Terry Given]

Winfield Hill wrote:

cbarn24050@aol.com wrote...

Adam Seychell wrote:

The thermal resistance from junction to "soldering point" of a
PZT2222/PZT2907 SOT-223 is 26 K/W. Say I were to soldering the
SOT-223 tab to a copper strip, which in then clamps to a large
heatsink. Assuming Tj rise of 50 C then; Pd_max = 50/26 =
2 Watts. Anyone else heatsinked a SOT-223 this way?

I would use a device with a larger package but there isn't
anything else around with similar specs and/or availability. The
PZT2222/PZT2907 replace the old metal canned TO-39 2N2219/2N2905.

That's 50deg rise above the heatsink temp, not above ambient.


Yes, 50 C rise above the connection point. The thermal resistance
of the [ SOT-223 tab -> copper strip -> clamps to large heatsink ]
path is at issue, especially the 2oz PCB copper-strip portion.

Or does Adam really mean a mean old copper strip? That could work.

there was a nice paper published in the 1996 High Frequency Power
Conversion conference proceedings about using multilayer PCBs as
heatsinks, along with some detailed measurements. thermal performance is
actually pretty good, and transient behaviour is excellent.

Cheers
Terry

 

[John Larkin]

On Tue, 21 Jun 2005 14:47:24 +1000, "Adam. Seychell"
<invald@invalid.com> wrote:

The thermal resistance from junction to "soldering point" of a
PZT2222/PZT2907 SOT-223 is 26 K/W. Say I were to soldering the SOT-223
tab to a copper strip, which in then clamps to a large heatsink.
Assuming Tj rise of 50°C then;

Pd_max = 50/26 = 2 Watts

Anyone else heatsinked a SOT-223 this way ?
I would use a device with a larger package but there isn't anything else
around with similar specs and/or availability. The PZT2222/PZT2907,
replace the old metal canned TO-39 2N2219/2N2905.

Yup. Two watts sounds feasible. If you can afford a couple of square
inches of copper top and bottom, and if there's some air flow, you
probably don't need the heatsink at all.

Keep in mind that 1 oz copper foil has a significant thermal sheet
resistance, about 70 K/W per square. So you've got to be concerned
with spreading the heat laterally. Put the package in the center of a
copper island and use lots of fat flooded (not thermal) vias to
another island on the flip side. Parallel that with inner layers if
available.

But the 26 K/W theta of the device itself seems high; that's throwing
away 52 degC of junction temp right there. You might consider
something with a bigger die.

See pic in a.b.s.e.

John

 

[SioL]

"Graham Holloway" <eng@wps-electronics.demon.co.uk> wrote in message news:d99745$110$1$8300dec7@news.demon.co.uk...

"SioL" <Sio_spam_L@same.net> wrote in message
news:TsUte.12839$F6.2770987@news.siol.net...
How effective is this method in terms of conducting heat to the underside
of the PCB?

Nowadays SMD packages are taking over even for power devices and it is
often quite
difficult to heatsink them
Siol

I don't have any specific details for you. However, I would flood the area
beneath the device with copper and then add the vias. Say, 28mil holes on a
staggered rows/columns pitch of 30mil would be a good start. I used a thin
Berquist insulator between the underside of the PCB and a raised section of
a baseplate, but I've seen other people used the gapfiller quite effectively
to get the heat across several mm. I think you might need to experiment.
Also bear in mind the vias will fill with solder (extra conduction) unless
you take specific steps to avoid it.

Gapfiller = that white thermal conduction paste?

I have been using aluminum block under the pcb, lots of vias and lots of copper
on both sides. The problem with filling vias with solder is that it creates uneven
surface, which adds extra thermal resistance to the aluminum block underside the pcb.
It would be best to have a copper block under the pcb, a hole in the pcb and
solder the part directly to the block. But it might be unhealthy for the part, its hard to
get that block hot enough to solder and it cools slowly.

--
Siol
------------------------------------------------
Rather than a heartless beep
Or a rude error message,
See these simple words: "File not found."

 

[Graham Holloway]

-"SioL" <Sio_spam_L@same.net> wrote in message
news:nNXte.12841$F6.2771965@news.siol.net...

"Graham Holloway" <eng@wps-electronics.demon.co.uk> wrote in message
news:d99745$110$1$8300dec7@news.demon.co.uk...
"SioL" <Sio_spam_L@same.net> wrote in message
news:TsUte.12839$F6.2770987@news.siol.net...
How effective is this method in terms of conducting heat to the
underside
of the PCB?

Nowadays SMD packages are taking over even for power devices and it is
often quite
difficult to heatsink them
Siol

I don't have any specific details for you. However, I would flood the
area
beneath the device with copper and then add the vias. Say, 28mil holes
on a
staggered rows/columns pitch of 30mil would be a good start. I used a
thin
Berquist insulator between the underside of the PCB and a raised section
of
a baseplate, but I've seen other people used the gapfiller quite
effectively
to get the heat across several mm. I think you might need to experiment.
Also bear in mind the vias will fill with solder (extra conduction)
unless
you take specific steps to avoid it.

Gapfiller = that white thermal conduction paste?

No, the thermally conductive rubber that comes in various thicknesses, up to
about 6mm.

I have been using aluminum block under the pcb, lots of vias and lots of
copper
on both sides. The problem with filling vias with solder is that it
creates uneven
surface, which adds extra thermal resistance to the aluminum block
underside the pcb.
It would be best to have a copper block under the pcb, a hole in the pcb
and
solder the part directly to the block. But it might be unhealthy for the
part, its hard to
get that block hot enough to solder and it cools slowly.

--
Siol
------------------------------------------------
Rather than a heartless beep
Or a rude error message,
See these simple words: "File not found."

 

[John Larkin]

On Tue, 21 Jun 2005 18:18:48 +0100, "Graham Holloway"
<eng@wps-electronics.demon.co.uk> wrote:

No, the thermally conductive rubber that comes in various thicknesses, up to
about 6mm.

It's not very "thermally conductive." The best thing, by far, is
classic messy silicone grease, which will squeeze down below 100
microinches if the surfaces are flat.

John

 

[Pooh Bear]

SioL wrote:

How effective is this method in terms of conducting heat to the underside of the PCB?

Suggest you take a look at this.

http://www.irf.com/technical-info/appnotes/an-994.pdf

I think IR may have another app note too but I didn't find it instantly using the site search.

Graham

 

[SioL]

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message news:42B86C06.674BAAEC@hotmail.com...

SioL wrote:

How effective is this method in terms of conducting heat to the underside of the PCB?

Suggest you take a look at this.

http://www.irf.com/technical-info/appnotes/an-994.pdf

I think IR may have another app note too but I didn't find it instantly using the site search.

Graham

This one's a keeper, very usefull, thanks!


--
Siol
------------------------------------------------
Rather than a heartless beep
Or a rude error message,
See these simple words: "File not found."

 

[SioL]

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message news:0ljgb19v4gimq597ain2i1dp9nen83m9mv@4ax.com...

On Tue, 21 Jun 2005 18:18:48 +0100, "Graham Holloway"
eng@wps-electronics.demon.co.uk> wrote:


No, the thermally conductive rubber that comes in various thicknesses, up to
about 6mm.


It's not very "thermally conductive." The best thing, by far, is
classic messy silicone grease, which will squeeze down below 100
microinches if the surfaces are flat.

John

I think even silicone grease is not very conductive unless it is squeezed out
almost entirely. If two surfaces are not reasonably flat, it doesn't help much.


--
Siol
------------------------------------------------
Rather than a heartless beep
Or a rude error message,
See these simple words: "File not found."

 

[Pooh Bear]

SioL wrote:

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message news:0ljgb19v4gimq597ain2i1dp9nen83m9mv@4ax.com...
On Tue, 21 Jun 2005 18:18:48 +0100, "Graham Holloway"
eng@wps-electronics.demon.co.uk> wrote:


No, the thermally conductive rubber that comes in various thicknesses, up to
about 6mm.


It's not very "thermally conductive." The best thing, by far, is
classic messy silicone grease, which will squeeze down below 100
microinches if the surfaces are flat.

John

I think even silicone grease is not very conductive unless it is squeezed out
almost entirely. If two surfaces are not reasonably flat, it doesn't help much.

You need Motorola's AN1040 or something !

2 secs I'll find it.

Even better - it's on my bookshelf in rev 6 of the power devices manual.

Should be compulsory reading for anyone involved with power semis.

I looked in the book. It is indeed AN1040. Does that make me a power semis nerd ?

Here's the link. Everyone should read this.

https://www.onsemi.com/pub/Collateral/AN1040-D.PDF

Graham

 

[SioL]

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message news:42B895CA.5D85DF42@hotmail.com...

SioL wrote:
I think even silicone grease is not very conductive unless it is squeezed out
almost entirely. If two surfaces are not reasonably flat, it doesn't help much.

You need Motorola's AN1040 or something !

2 secs I'll find it.

Even better - it's on my bookshelf in rev 6 of the power devices manual.

Should be compulsory reading for anyone involved with power semis.

I looked in the book. It is indeed AN1040. Does that make me a power semis nerd ?

Here's the link. Everyone should read this.

https://www.onsemi.com/pub/Collateral/AN1040-D.PDF

Another keeper, definitely.

Thanks.


--
Siol
------------------------------------------------
Rather than a heartless beep
Or a rude error message,
See these simple words: "File not found."

 

[Pooh Bear]

SioL wrote:

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message news:42B895CA.5D85DF42@hotmail.com...

< snip >

Here's the link. Everyone should read this.

https://www.onsemi.com/pub/Collateral/AN1040-D.PDF

Another keeper, definitely.

Thanks.

You're *very* welcome.

There are some snippets of information out there that are absolutely invaluable and likely never ever to be
bettered.

I was lucky to find AN1040 early in my working life ! Before the internet and stuff - when you had still had to
ask for data manuals. How times have changed !

Graham

 

[Terry Given]

Pooh Bear wrote:

SioL wrote:


"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message news:0ljgb19v4gimq597ain2i1dp9nen83m9mv@4ax.com...

On Tue, 21 Jun 2005 18:18:48 +0100, "Graham Holloway"
eng@wps-electronics.demon.co.uk> wrote:


No, the thermally conductive rubber that comes in various thicknesses, up to
about 6mm.

It's not very "thermally conductive." The best thing, by far, is
classic messy silicone grease, which will squeeze down below 100
microinches if the surfaces are flat.

John

I think even silicone grease is not very conductive unless it is squeezed out
almost entirely. If two surfaces are not reasonably flat, it doesn't help much.


You need Motorola's AN1040 or something !

2 secs I'll find it.

Even better - it's on my bookshelf in rev 6 of the power devices manual.

Should be compulsory reading for anyone involved with power semis.

I looked in the book. It is indeed AN1040. Does that make me a power semis nerd ?

Here's the link. Everyone should read this.

https://www.onsemi.com/pub/Collateral/AN1040-D.PDF

Graham

yep, it does. welcome to the club. Become a senior member by casually
referring to Jim Williams AN47.....

Cheers
terry

 

[Terry Given]

Pooh Bear wrote:

SioL wrote:


"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message news:42B895CA.5D85DF42@hotmail.com...


snip

Here's the link. Everyone should read this.

https://www.onsemi.com/pub/Collateral/AN1040-D.PDF

Another keeper, definitely.

Thanks.


You're *very* welcome.

There are some snippets of information out there that are absolutely invaluable and likely never ever to be
bettered.

I was lucky to find AN1040 early in my working life ! Before the internet and stuff - when you had still had to
ask for data manuals. How times have changed !

Graham

Ask? beg, more like. Here in NZ the component distributors used to be
real stingy bastards with databooks. If you were a $100,000,000 company
they'd give you boxes of the things; anyone else had to pay, sometimes
$50 per book. I used this argument to convince the Intel agents to give
me a complete set of databooks in about 1988, rather than make me pay
about $600.

Cheers
Terry

 

[SioL]

"Terry Given" <my_name@ieee.org> wrote in message news:s12ue.9281$U4.1234224@news.xtra.co.nz...

Ask? beg, more like. Here in NZ the component distributors used to be real stingy bastards with databooks. If you were a
$100,000,000 company they'd give you boxes of the things; anyone else had to pay, sometimes $50 per book. I used this argument to
convince the Intel agents to give me a complete set of databooks in about 1988, rather than make me pay about $600.

That was not even that long ago (or am I getting old).

Nowadays google is your friend.
Can't imagine any engineering work without internet anymore. Even though I
am saving many PDFs and have a large collection, searching google is often
faster and more convenient than searching the hard drive.
--
Siol
------------------------------------------------
Rather than a heartless beep
Or a rude error message,
See these simple words: "File not found."