Heat Dissapation Problem LME49720/OPA1632 Preamp

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Dear Forum,

I realized a preamp in using a schematic of alexw88 which is pictured on his homepage SCHEMATIC

I did not use a circuit board in lack of beeing able to design one :rolleyes:. So i made it with p2p connection. I hope alexw88 will answer someday my mail so i hope to get a pair aof pcb's ?

Initial Situation:
Soldering Side:
An externally hosted image should be here but it was not working when we last tested it.

Mounting Side:
An externally hosted image should be here but it was not working when we last tested it.


As i have used the DGN OPA 1632 Version with PowerPad wich is soldered on an HTSSOP Adapter board, i measured max. 70°C with my IR-Thermometer. The Sound is superbe, really, alltough during hours of playing music and making measurements with RMMA it's hot like a ... whatever.

Here are some results of the measurements. I post this, beacause i find this preamp really great to be built more. As it beats in measurements the results of my older 6H30 tube preamp and also the results of my Vincent SA93 Preamp (wich in fact is a great preamp).

For example measurements with RMAA 6.06 for reference
Noise Level
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Stereo crosstalk
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Problem

I need a possibility to cool down the OPA1632. Maybee drilling a hole in the Adapterboard and mounting the OPA1632 vice versa, and putting some copperbar on the thermal Pad ?

Any suggestions ? Or anyone in here who can design a circuit board of this preamp ? Maybee others would be interested ...

Best regards and thanks in advance for any suggestions
artQuake
 
peranders said:
1 You can lower the supply voltage

2 You can clue a heatsink (of some sort) on top of the IC.

70 deg C is not a problem if you think so. If it stops at this temperature you don't have to do anything.

Voltage is allready @ 13V

Instant glue with a small massive peace of copper ?

70°C, no problem ? Really ? Also for a long period of time ? I can't find notes @ TI-Product Information
"POWER DISSIPATION AND THERMAL CONSIDERATIONS
The OPA1632 does not have thermal shutdown protection. Take care to assure that the maximum junction temperature is not exceeded. Excessive junction temperature can degrade performance or cause permanent damage. For best performance and reliability, assure that the junction temperature does not exceed +125°C."


That's why i think in my case it's critical too, because the thermal pad (very near to junction temperature) is on the downside of the ic, which on the other hand is very near to the adapter board that acts like an isolator, and as i mentioned, i measured (+/-) only the surface temperature on top of the part.

nevertheless, thanks peranders for your informations ...
 
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artquake said:
That's why i think in my case it's critical too, because the thermal pad (very near to junction temperature) is on the downside of the ic, which on the other hand is very near to the adapter board that acts like an isolator, and as i mentioned, i measured (+/-) only the surface temperature on top of the part.

That thermal pad on the bottom of the device is meant to be soldered to a copper plane that acts as a heat sink. You really should have some kind of thermal mass attached to that thermal pad. It could be something as simple/cheap as a thin strip of aluminum from a soda can that you place under the part with a little thermal paste before soldering it down. That will help much more than any heat sink you put on the top of the plastic package.
 
Any affections/influence into sound by doing this strip of aluminum or let's say copper strip to the pad ?

What do you think, when i would use D instead of DGN Model of the OPA1632 would it solve this thermal issue ? (mind you without heatsink) The problem was i currently could not find any supplier for SO-Type ...
 
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Joined 2005
I don't know how much it would influence the sound or if you would be able to hear any difference at all. Try it and find out.

Using the SO8 package that doesn't have the thermal pad probably has worse thermal performance than the MSOP8 package with the thermal pad properly connected to some kind of heat sink (or soldered to copper on a PCB as it was meant to be).
 
Take a look at the THS4631 datasheet. In which, the thermal performance difference of DGN package, with or without solder, is revealed. THS4631 cosumes similar current to OPA1632.

http://focus.ti.com/lit/ds/symlink/ths4631.pdf

Thermal resistance is 58.4degC/W for DGN with solder,
98degC/W for SOIC, and 158degC/W for DGN without solder.

I did blown one THS4631 after about an hour of operation. Since I have failed to solder the bottom powerpad to ground plate. Supply rail was +/-13V.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=104608&highlight=
 
Thanks to all for the informations up to now.

The problem is that i am using this ADAPTOR, SMD, TSSOP-8, 0.65MM. And there is no PowerPad on it.

On the other way:
BWRX wrote
strip of aluminum from a soda can that you place under the part with a little thermal paste before soldering it down

Banana wrote
Since I have failed to solder the bottom powerpad to ground plate

It's somehow logic that heat transfer is better when the pad has a direct connection to a bigger materialarea or mass with a high heat capacity. How can I solder/realize this ? Is it not problematic that the IC get's to hot while soldering a bigger mass to it ? (because when heating the solder the addad mass will also heat up until the solder melts) I don't want to destroy the OPA thru heating during the soldering process.

Aren't there any MSSOP adapterboards in which a PowerPad is embedded ?

Or shall i file a gouge into the existing adapterboard and insert a copperplate into that gouge ? Like the following
An externally hosted image should be here but it was not working when we last tested it.

I don't think thats enough area ...

As i have really pairs of "sausagefingers" for this sort of surgery job (soldering the OPA1632 on the adapter was already an extreme artifice) i would better prefer a ready done adapterboard.

Any sources available on such adapterboards in here ? Or maybe someone who's able to make some ?

Thank in advance for any suggestions ...

regards
artQuake
 
OK peranders, i'll give the following SMD heat sink a try.
An externally hosted image should be here but it was not working when we last tested it.

Rth=33K/W 6.3x30x7.5mm

Would you really glue them ? I mean the expansion of ic material during heating up/down/up and so on will lift of the heatsink with the time. In the other hand using an adhesive pad to fix heatsink will genarate more thermal resistance. Have you tried instant glue successfull with these temperatures ?

Thank you
 
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Joined 2005
artquake said:
It's somehow logic that heat transfer is better when the pad has a direct connection to a bigger materialarea or mass with a high heat capacity. How can I solder/realize this ? Is it not problematic that the IC get's to hot while soldering a bigger mass to it ?

BWRX said:
It could be something as simple/cheap as a thin strip of aluminum from a soda can that you place under the part with a little thermal paste before soldering it down. That will help much more than any heat sink you put on the top of the plastic package.

The part is meant to be soldered in a reflow oven but it could be done by hand since the part is rather small. It does take some skill and a proper layout though.

Like I said above, try placing a thin strip of some kind of aluminum or copper under the part BEFORE soldering it down. I.E. cut the thin strip of aluminum to size and place it in between the pads, place a little thermal grease on the thermal pad of the part, place the part down onto the board, then carefully solder it into place. You can bend up the extra aluminum sticking out the sides, curl it, cut it, or whatever.

Here's a picture of what I'm talking about: http://www.diyaudio.com/forums/attachment.php?s=&postid=619288&stamp=1113442445
(from this thread: http://www.diyaudio.com/forums/showthread.php?postid=619288#post619288 )

The chip in the picture has a thermal pad on the bottom of its package and it didn't come soldered to the PCB like it was supposed to be.
 
PowerPad Made Easy http://focus.ti.com/lit/an/slma004b/slma004b.pdf

I'm going to assume that the bottom of the adapter has no "wiring on it" -- if it has a ground plane so much the better.

If you can rework the adapter by removing the IC and make a VIA with a 37 mil drill (I'm thinking in inches/pounds/seconds so you have the conversion to mm.) Use a small piece of wire of the same diameter through the VIA to the other side. To this attach a piece of copper tape to spread the heat.

With SOIC, MSSOP etc it really is better to design the PCB yourself -- I learned this making a bunch of class D guitar amplifiers with the Texas Instruments chips. You punch a bunch of vias through to a copper plane and spread the heat out. It's easier to get it right in the first place.

wrt Peranders recommendations of SuperGlue some of these cyanoacrylates won't stand up to a lot of heat and some are used in very stressful industrial applications -- i couldn't find from their website the point at which it will break down. time and heat are not necessarily your friends.
 
a heavy Cu (or maybe Al) foil strip under the package could be glued to the adapter for stability, avoiding shorting the inner edges of the pcb pads, and a small dot of heatsink compound applied to the pwr pad, then the chip could be soldered to the adapter in the normal orientation with a little bending of the leads – a miniature hobby C or spring clamp could be helpful

@~1mm length the pins should easily bend down 0.1-0.2mm to accommodate the foil thickness – much easier than milling the adapter pcb at the desired tolerances on parallelism

the foil strip could be longer than the width of the adapter, and wider than the chip except where it threads under the chip, bend the ends up in a “U” shape

I would use nonconductive ceramic/oxide filled thermal compound – the silver filled stuff could give capacitive and possibly DC electrical shorting if it spreads to the pcb pins

another option is belly-up mounting, then the heat sink can be attached to the pad, I've used heatsink compound and clamping but the PC video memory heatsink people have made thermal conductive epoxies readily available in small quantity
I bent the leads down on a TPA6120 one at a time as I soldered them but that was a standard SO pitch, not the MSOP – the TPA is actually totally symmetric so I didn't have to change the wiring like you'd have to with the 1632 mounted upside down
 
I know I plug this stuff way too much, but J-B KWIK WELD epoxy works wonders for holding heatsinks on. It's a whole lot cheaper than "real" thermal epoxy too.

http://jbweld.net/products/jbkwik.php

And yes, those little OPA1632 get blazing hot :hot:. I cut a fin off of an old CPU heatsink and used some KWIK WELD to hold it on.

2ce4561.jpg

2jbad0k.jpg
 
Hi all,

thanks again for your constructive informations.

Trying to attach the SMD heatsink with superglue failed. The contact area is to small and the surface of the heatsink or even the chip is to flat, that when I press (wich i really should, to achieve a high conductivity) it never will be friction-fitted. So i forget glueing.

BWRX all ok, good solution, but i can't do it in case of aesthetics. Thank you nevertheless.

Jackinnj, that would be also a solution. If I understand you correct, you ment drilling holes from the adapters downside to top (or vice versa ), while placing the holes in the thermal pad area mentioned in the TI-Spec. Sheet of OPA1632. And then sticking wires thru the frilled holes and attaching them to a peace of copperfoil. Right ?
How can achieve good contact pressure with the wire from the bottom side to the PowerPad plane ? Designing a pcb in the beginning for this would be the best. Nice for the one who can do this.

Well if alexw88 would join and make an offer for the gerber files that would be great !

On the other side i found a Thread of Stef1777 wich designed an outputboard for the DEQ2496 from Behringer which i own too. He uses the OPA1632 and considered also thoughts relating to high temperatures. TEXT



So i quote the statement of janneman:
„Originally posted by janneman



Steff,

I think the OPA1632's are fine at 75degrees. If you feed them from +/- 15V, they dissipate about 450mW. They are designed for that. Even if you cannot touch them, 75degr is not hot by ss standards. With 450mW and at 170degree/Watt thermal resistance, the die will be about 76degr above ambient. If the case air temp is 40degr, the chip will be internally, the die, at 40+76 is 116 degr. The max is 150degree, with recommended operating max of 125degree. So, no problem.
You should stop thinking about this with your 'human' feelings of heat

Jan Didden“


Do i have also have some human feelings of heat ? Or is this temperature not critical ? If so that would be really good. Anyway i could not improve sound while using a p2p connection board. It really has to be a well done pcb, which alexw88 has done really well.

best regards
artQuake
 
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Paid Member
artquake said:
[snip]Do i have also have some human feelings of heat ? Or is this temperature not critical ? [snip]best regards
artQuake


What I mean, at 50degr Celcius, you get unbearable pain and blisters on your fingers. The opamp just gets cozy at that temp. So we tend to judge the chip temp with our 'human' fears of heat.

If you worry about the OPA1632 temperature (for instance if you expect the ambient temp in your case to grow above 50degr Celcius), you have two options:

- lower the supply voltage to, say, +/-9V. That gives you 1/3 less dissipation. In my DCX2496 replacement board I run them at +/-9VDC (because also the CS3318 runs on +/-9VDC) for about 5V RMS max undistorted output. Very good sound.

- change to the MSOP PowerPad package and design the pcb as shown in the data sheet for the PowerPad package. That gives you more heat removal capacity.

Jan Didden
 
°

Thanks Jan for reply,

if you expect the ambient temp in your case to grow above 50degr Celcius
I don't, as the enclosure will be vented thru the bottom plate, and so heat will flow in natural convection thru the enclosure out of the top of the enclosure to ambient. So the temperature of the air (not including the radiation of parts) inside of enclosure will get max. to 40 °C (dependig on the position inside the enclosure). Let's estimate Radiation for 70% and convection 30% of entire dissapated power. But the p2p-Board at present is on free air, so when mounting the board into a enclosure these parts will get basically hotter. How hot who knows. To simulate that with FEM is to complex for that dead time it needs, and for, in fact results that are far away from reality. No way but:

Asked in short words some further questions:
Do you think now that a surface temperature on the MSOP OPA1632 of 70...75°C has to be minded critical or not ? Still cozy for the OPA ?

and:
lower the supply voltage to, say, +/-9V
Wouldn't this action increase the THD + Noise ? In my case it's allready noted as average @ -75.5 db(A) / +0.017% and i think this preamp could perform even better @ 15V ...
 
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