SO14 package at 154C/W? Really?

[Joerg]

So here I am, needing more than the usual 32V opamp. Chose ye olde
MC33174 because it can take 44V but was surprised when I read that the
usual SO14 package is only rated at 154C/W. Since I am burning 500mW
that would become too toasty, ouch. Or I'll have to idle two amps each
in there and double the number of chips.

So, is 500mW in a SO14 really too much? What do thee say?

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Joerg]

BobW wrote:

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:kSdwk.20648$mh5.3306@nlpi067.nbdc.sbc.com...
So here I am, needing more than the usual 32V opamp. Chose ye olde MC33174
because it can take 44V but was surprised when I read that the usual SO14
package is only rated at 154C/W. Since I am burning 500mW that would
become too toasty, ouch. Or I'll have to idle two amps each in there and
double the number of chips.

So, is 500mW in a SO14 really too much? What do thee say?

--
Regards, Joerg


If Tj max is 150C, and if Theta(ja) is really 154C/W and you're dissipating
500mW, then your allowable maximum ambient temperature is:

150 - 0.500*154 = 73C

It'll be effing hot, but it should work.

Yeah, and I don't like things getting effing hot

Also, some of the thermal power will go through the leadframe and into your
pcb, so the die temperature won't really be as high as the Theta(ja)
calculation suggests, because (iirc) Theta(ja) doesn't include this path.

Are you sure about that? It would not be too useful to publish data for
a situation that is impossible in practice. I mean, an opamp needs to be
soldered down before it can do anything.

--
Regards, Joerg

http://www.analogconsultants.com/

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[Eric Smith]

Joerg <notthisjoergsch@removethispacbell.net> writes:

Are you sure about that? It would not be too useful to publish data
for a situation that is impossible in practice. I mean, an opamp needs
to be soldered down before it can do anything.

It *is* useful, and nothing about it is impossible in practice. It's
difficult to characterize the heat conduction through the lead frame,
and not including it in Theta(ja) makes the formula more conservative.
If you do the design based on Theta(ja), you'll have a slight bit of
additional margin.

 

[Joerg]

Eric Smith wrote:

Joerg <notthisjoergsch@removethispacbell.net> writes:
Are you sure about that? It would not be too useful to publish data
for a situation that is impossible in practice. I mean, an opamp needs
to be soldered down before it can do anything.

It *is* useful, and nothing about it is impossible in practice. It's
difficult to characterize the heat conduction through the lead frame,
and not including it in Theta(ja) makes the formula more conservative.
If you do the design based on Theta(ja), you'll have a slight bit of
additional margin.

Anyhow, I'll go with single amps in SO8 then. More conservative, I don't
want anything to get hot.

--
Regards, Joerg

http://www.analogconsultants.com/

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Use another domain or send PM.

 

[legg]

On Fri, 05 Sep 2008 11:29:19 -0700, Eric Smith <eric@brouhaha.com>
wrote:

Joerg <notthisjoergsch@removethispacbell.net> writes:
Are you sure about that? It would not be too useful to publish data
for a situation that is impossible in practice. I mean, an opamp needs
to be soldered down before it can do anything.

It *is* useful, and nothing about it is impossible in practice. It's
difficult to characterize the heat conduction through the lead frame,
and not including it in Theta(ja) makes the formula more conservative.
If you do the design based on Theta(ja), you'll have a slight bit of
additional margin.

Actually, one of the few situations where it is possible, in practice,
to characterize the thermal impedance of an IC (in a specific
package), is when you are the manufacturer of that IC. All they need
is a standard panel template for the mounting arrangement in question.
That is where the published data should originate.

Normally, to ensure a reasonable MTBF, you'd want a pre-established
margin between predicted operating extremes and specified junction
limits.

Everyone has their own opinion when it comes to characterization and
employment of thermal data - so it's worth while tracking down any
available info on the specific part in question, should the issue
become obviously relevant. Larger packages, or packages with many pins
(~ more than six) become increasingly predictable, for a fixed
construction.

It is my understanding that the thermal impedance test methods
outlined by jedec (JESD051) include mounting hardware for
surface-captive components, whether surface-mount or through-hole. TI
app notes below reflect this.

Check out:

Nat Semi AN336
Nat Semi AN1028 SOT223
TI SZZA017A - board trace effects
TI SCAA022A - board trace effects
TI SLMA002 - enhanced packaging
FSC AN1029 SO8
FSC AN1025 SOT23

There are on-line tools at some mfr's web sites. eg:

http://www-s.ti.com/cgi-bin/sc/thermal_derating_curve.cgi

RL

 

[Eeyore]

Joerg wrote:

So here I am, needing more than the usual 32V opamp. Chose ye olde
MC33174 because it can take 44V but was surprised when I read that the
usual SO14 package is only rated at 154C/W. Since I am burning 500mW
that would become too toasty, ouch. Or I'll have to idle two amps each
in there and double the number of chips.

So, is 500mW in a SO14 really too much? What do thee say?

NE5532 ? That's rated at +/- 22V IIRC. I think I've seen them in SMT in
recent years.

Large input bias current IIRC though.

Graham

 

[Joerg]

legg wrote:

On Fri, 05 Sep 2008 11:29:19 -0700, Eric Smith <eric@brouhaha.com
wrote:

Joerg <notthisjoergsch@removethispacbell.net> writes:
Are you sure about that? It would not be too useful to publish data
for a situation that is impossible in practice. I mean, an opamp needs
to be soldered down before it can do anything.
It *is* useful, and nothing about it is impossible in practice. It's
difficult to characterize the heat conduction through the lead frame,
and not including it in Theta(ja) makes the formula more conservative.
If you do the design based on Theta(ja), you'll have a slight bit of
additional margin.

Actually, one of the few situations where it is possible, in practice,
to characterize the thermal impedance of an IC (in a specific
package), is when you are the manufacturer of that IC. All they need
is a standard panel template for the mounting arrangement in question.
That is where the published data should originate.

Normally, to ensure a reasonable MTBF, you'd want a pre-established
margin between predicted operating extremes and specified junction
limits.

Everyone has their own opinion when it comes to characterization and
employment of thermal data - so it's worth while tracking down any
available info on the specific part in question, should the issue
become obviously relevant. Larger packages, or packages with many pins
(~ more than six) become increasingly predictable, for a fixed
construction.

It is my understanding that the thermal impedance test methods
outlined by jedec (JESD051) include mounting hardware for
surface-captive components, whether surface-mount or through-hole. TI
app notes below reflect this.

Check out:

Nat Semi AN336
Nat Semi AN1028 SOT223
TI SZZA017A - board trace effects
TI SCAA022A - board trace effects
TI SLMA002 - enhanced packaging
FSC AN1029 SO8
FSC AN1025 SOT23

There are on-line tools at some mfr's web sites. eg:

http://www-s.ti.com/cgi-bin/sc/thermal_derating_curve.cgi

Thanks! Pretty cool tool. Kinda sez to me not to use SO14 ;-)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Joerg]

Eeyore wrote:

Joerg wrote:

So here I am, needing more than the usual 32V opamp. Chose ye olde
MC33174 because it can take 44V but was surprised when I read that the
usual SO14 package is only rated at 154C/W. Since I am burning 500mW
that would become too toasty, ouch. Or I'll have to idle two amps each
in there and double the number of chips.

So, is 500mW in a SO14 really too much? What do thee say?

NE5532 ? That's rated at +/- 22V IIRC. I think I've seen them in SMT in
recent years.

Large input bias current IIRC though.

Max supply current is 16mA. At 40V VCC it'll almost unsolder itself

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[John Larkin]

On Fri, 05 Sep 2008 10:18:59 -0700, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

So here I am, needing more than the usual 32V opamp. Chose ye olde
MC33174 because it can take 44V but was surprised when I read that the
usual SO14 package is only rated at 154C/W. Since I am burning 500mW
that would become too toasty, ouch. Or I'll have to idle two amps each
in there and double the number of chips.

So, is 500mW in a SO14 really too much? What do thee say?

Epoxy a heat sink on top. I have a board right here on my desk that
has a heatsink on an FPGA, and two more on some dual dacs.

ftp://66.117.156.8/DSC01786.JPG


Or put a power pad below on the pcb layout, some thermal vias to a
plane, and use a dab of epoxy between the part and the board.

John

 

[Joerg]

John Larkin wrote:

On Fri, 05 Sep 2008 10:18:59 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

So here I am, needing more than the usual 32V opamp. Chose ye olde
MC33174 because it can take 44V but was surprised when I read that the
usual SO14 package is only rated at 154C/W. Since I am burning 500mW
that would become too toasty, ouch. Or I'll have to idle two amps each
in there and double the number of chips.

So, is 500mW in a SO14 really too much? What do thee say?

Epoxy a heat sink on top. I have a board right here on my desk that
has a heatsink on an FPGA, and two more on some dual dacs.

ftp://66.117.156.8/DSC01786.JPG

A heatsink glued onto a BGA? Wow, that takes guts.

Or put a power pad below on the pcb layout, some thermal vias to a
plane, and use a dab of epoxy between the part and the board.

Nah, I'll go to singles but right now I am trying to knock down the
power via some inductive kicker tricks. It's a HV switch bank where
these opamps have to hold programmable biases. If I can shave off
another 500uA/channel I might just be back to a quad package. Unless
there is a really compelling reason like I am sure there is in many of
your cases I try to keep everything cool, to the point where you can
operate without heatsinks yet touch everything with screaming. Well, ok,
one should not touch this high voltage stuff ...

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[John Larkin]

On Fri, 05 Sep 2008 12:55:09 -0700, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

John Larkin wrote:
On Fri, 05 Sep 2008 10:18:59 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

So here I am, needing more than the usual 32V opamp. Chose ye olde
MC33174 because it can take 44V but was surprised when I read that the
usual SO14 package is only rated at 154C/W. Since I am burning 500mW
that would become too toasty, ouch. Or I'll have to idle two amps each
in there and double the number of chips.

So, is 500mW in a SO14 really too much? What do thee say?

Epoxy a heat sink on top. I have a board right here on my desk that
has a heatsink on an FPGA, and two more on some dual dacs.

ftp://66.117.156.8/DSC01786.JPG


A heatsink glued onto a BGA? Wow, that takes guts.

Guts? Why? It's soldered to the board in 456 places, which should be
pretty stiff.

Or put a power pad below on the pcb layout, some thermal vias to a
plane, and use a dab of epoxy between the part and the board.


Nah, I'll go to singles but right now I am trying to knock down the
power via some inductive kicker tricks. It's a HV switch bank where
these opamps have to hold programmable biases. If I can shave off
another 500uA/channel I might just be back to a quad package. Unless
there is a really compelling reason like I am sure there is in many of
your cases I try to keep everything cool, to the point where you can
operate without heatsinks yet touch everything with screaming. Well, ok,
one should not touch this high voltage stuff ...

I've got used to touching everything to see how hot it is, or to
finagle suspected RF oscillations. And get occasionally
blistered/shocked for the trouble.

John

 

[Joerg]

John Larkin wrote:

On Fri, 05 Sep 2008 12:55:09 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

John Larkin wrote:
On Fri, 05 Sep 2008 10:18:59 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

So here I am, needing more than the usual 32V opamp. Chose ye olde
MC33174 because it can take 44V but was surprised when I read that the
usual SO14 package is only rated at 154C/W. Since I am burning 500mW
that would become too toasty, ouch. Or I'll have to idle two amps each
in there and double the number of chips.

So, is 500mW in a SO14 really too much? What do thee say?
Epoxy a heat sink on top. I have a board right here on my desk that
has a heatsink on an FPGA, and two more on some dual dacs.

ftp://66.117.156.8/DSC01786.JPG

A heatsink glued onto a BGA? Wow, that takes guts.

Guts? Why? It's soldered to the board in 456 places, which should be
pretty stiff.

Yeah but if that number is reduced to 455 places some grief could set in

Or put a power pad below on the pcb layout, some thermal vias to a
plane, and use a dab of epoxy between the part and the board.

Nah, I'll go to singles but right now I am trying to knock down the
power via some inductive kicker tricks. It's a HV switch bank where
these opamps have to hold programmable biases. If I can shave off
another 500uA/channel I might just be back to a quad package. Unless
there is a really compelling reason like I am sure there is in many of
your cases I try to keep everything cool, to the point where you can
operate without heatsinks yet touch everything with screaming. Well, ok,
one should not touch this high voltage stuff ...

I've got used to touching everything to see how hot it is, or to
finagle suspected RF oscillations. And get occasionally
blistered/shocked for the trouble.

So do I. But if I get a blister I want to know why and what can be done
about the circuit to chill it.

Reminds me of a sad case. A very experienced power engineer guided a
tour for some bigshots. He was a neat freak. The whole place looked
spiffy, not a speck of dust. Then, a fly landed on a distribution rail.
Instinctively he wanted to flick it away. That was the last millisecond
of his life :-(

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Eeyore]

Joerg wrote:

Eeyore wrote:
Joerg wrote:

So here I am, needing more than the usual 32V opamp. Chose ye olde
MC33174 because it can take 44V but was surprised when I read that the
usual SO14 package is only rated at 154C/W. Since I am burning 500mW
that would become too toasty, ouch. Or I'll have to idle two amps each
in there and double the number of chips.

So, is 500mW in a SO14 really too much? What do thee say?

NE5532 ? That's rated at +/- 22V IIRC. I think I've seen them in SMT in
recent years.

Large input bias current IIRC though.

Max supply current is 16mA. At 40V VCC it'll almost unsolder itself

I've NEVER known one take 16mA. I use 8mA as a guideline when estimating PSU
requirements (TI typical 352mW). Typical from Fairchild is 6mA i.e. 264 mW.

Graham

 

[Joerg]

Eeyore wrote:

Joerg wrote:

Eeyore wrote:
Joerg wrote:

So here I am, needing more than the usual 32V opamp. Chose ye olde
MC33174 because it can take 44V but was surprised when I read that the
usual SO14 package is only rated at 154C/W. Since I am burning 500mW
that would become too toasty, ouch. Or I'll have to idle two amps each
in there and double the number of chips.

So, is 500mW in a SO14 really too much? What do thee say?
NE5532 ? That's rated at +/- 22V IIRC. I think I've seen them in SMT in
recent years.

Large input bias current IIRC though.
Max supply current is 16mA. At 40V VCC it'll almost unsolder itself

I've NEVER known one take 16mA. I use 8mA as a guideline when estimating PSU
requirements (TI typical 352mW). Typical from Fairchild is 6mA i.e. 264 mW.

Yes, sure, but this is a medical design. There you must always do a
hazard analysis (FMEA and all that) and assume datasheet limits. If no
limits are given you cannot use the part.

When you do medical for a few decades this stuff rattles on
automatically in the back of your head. You can't turn it off anymore ;-)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[Spehro Pefhany]

On Fri, 05 Sep 2008 12:48:03 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 05 Sep 2008 10:18:59 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

So here I am, needing more than the usual 32V opamp. Chose ye olde
MC33174 because it can take 44V but was surprised when I read that the
usual SO14 package is only rated at 154C/W. Since I am burning 500mW
that would become too toasty, ouch. Or I'll have to idle two amps each
in there and double the number of chips.

So, is 500mW in a SO14 really too much? What do thee say?

Epoxy a heat sink on top. I have a board right here on my desk that
has a heatsink on an FPGA, and two more on some dual dacs.

Are those commercial heatsinks? They don't look as nice as the rest of
the board. I wonder why they didn't machine square or rectangular
posts rather than round.

Is that LPI 'silk screen' ?

ftp://66.117.156.8/DSC01786.JPG

Nice.

Is 'MS' your layout guy/gal?

Or put a power pad below on the pcb layout, some thermal vias to a
plane, and use a dab of epoxy between the part and the board.

John
Best regards,

Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[John Larkin]

On Fri, 05 Sep 2008 17:26:36 -0400, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

On Fri, 05 Sep 2008 12:48:03 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 05 Sep 2008 10:18:59 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

So here I am, needing more than the usual 32V opamp. Chose ye olde
MC33174 because it can take 44V but was surprised when I read that the
usual SO14 package is only rated at 154C/W. Since I am burning 500mW
that would become too toasty, ouch. Or I'll have to idle two amps each
in there and double the number of chips.

So, is 500mW in a SO14 really too much? What do thee say?

Epoxy a heat sink on top. I have a board right here on my desk that
has a heatsink on an FPGA, and two more on some dual dacs.

Are those commercial heatsinks? They don't look as nice as the rest of
the board. I wonder why they didn't machine square or rectangular
posts rather than round.

Die cast, I think. They are from Cool Innovations, who are up near
you. What I'd really like is anodized colors.

Is that LPI 'silk screen' ?

ftp://66.117.156.8/DSC01786.JPG

Nice.

Dunno, but the ref desigs are 60 mils high, and are pretty readable.
That doesn't always happen.

Is 'MS' your layout guy/gal?

Mike. He does our pcb stuff and Autocad/Solidworks stuff. He's good,
so I won't give his last name.

Incidentally, this is rev A of the board, and it works: no kluges.

Lower-left is where the Xport ethernet brick goes. We press-released
it and got a lot of hits, so you may see it in a mag or something.

Hey, google T346

This is amazing. Google has changed the whole game.

John

 

[Eric Smith]

legg <legg@nospam.magma.ca> writes:

Actually, one of the few situations where it is possible, in practice,
to characterize the thermal impedance of an IC (in a specific
package), is when you are the manufacturer of that IC. All they need
is a standard panel template for the mounting arrangement in question.
That is where the published data should originate.

Sure, but they don't know what you will have the lead frame soldered to,
how well it will be soldered, etc.

 

[Eric Smith]

Joerg wrote:

A heatsink glued onto a BGA? Wow, that takes guts.

Not particularly. Once the BGA is soldered down, there's nothing special
about attaching a heatsink to the top of it.

 

[Eric Smith]

Joerg wrote:

A heatsink glued onto a BGA? Wow, that takes guts.

John Larkin wrote:

Guts? Why? It's soldered to the board in 456 places, which should be
pretty stiff.

Joerg wrote:

Yeah but if that number is reduced to 455 places some grief could set in

You'd have to be doing something extremely wrong in order for epoxying
a small heat sink to a properly soldered BGA to result in any of the
bonds failing. Are you applying the heat sink with a hammer or crowbar
or something?

 

[Joerg]

Eric Smith wrote:

Joerg wrote:
A heatsink glued onto a BGA? Wow, that takes guts.

John Larkin wrote:
Guts? Why? It's soldered to the board in 456 places, which should be
pretty stiff.

Joerg wrote:
Yeah but if that number is reduced to 455 places some grief could set in

You'd have to be doing something extremely wrong in order for epoxying
a small heat sink to a properly soldered BGA to result in any of the
bonds failing. Are you applying the heat sink with a hammer or crowbar
or something?

No, but I have seen too many BGA failures. Not in my designs because
(with one exception) I never used BGA.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.