Arduino Forum

Using Arduino => General Electronics => Topic started by: JimboZA on Mar 08, 2013, 06:43 pm

Title: How to measure chip (or other component) temperature?
Post by: JimboZA on Mar 08, 2013, 06:43 pm
This thread (http://arduino.cc/forum/index.php/topic,153070.0/topicseen.html) about an overheating 293 made me wonder how to measure the temp of a chip.

My Christmas Fluke 17B (http://www.fluke.com/fluke/m2en/Digital-Multimeters/Fluke-17B.htm?PID=75002) has a temperature scale (measures up to 400C) and came with a Type-K thermocouple. To measure the temperature of a chip, would it be enough to hold the thermocouple probe against the surface or does it need a better contact, perhaps with some gel or paste or other gloop to get a better contact?
Title: Re: How to measure chip (or other component) temperature?
Post by: bobthebanana on Mar 08, 2013, 06:57 pm
I guess regular old thermal grease would work. Thermal exopy if you want a permenent contact. But either way, thet will be package temp, not die temp. Maybe with a bit of math and the thermal conductivity figures in the datasheet it would be possiblr to get an accurate measurement
Title: Re: How to measure chip (or other component) temperature?
Post by: jonisonvespaa on Mar 08, 2013, 07:08 pm
hi bob
whats die temp, is that the core of the ic?
cheers
Title: Re: How to measure chip (or other component) temperature?
Post by: CrossRoads on Mar 08, 2013, 07:09 pm
We have a Ryobi Non-Contact Infrared Thermometer
http://www.homedepot.com/buy/electrical/electrical-test-meters/ryobi-non-contact-infrared-thermometer-ir001.html
Put its red laser dot on the middle of a chip, or a resistor, or transistor, get a digital reading back.

No more burned finger tips!
Title: Re: How to measure chip (or other component) temperature?
Post by: 3dprinter on Mar 08, 2013, 07:12 pm

whats die temp, is that the core of the ic?
Yes
Title: Re: How to measure chip (or other component) temperature?
Post by: afremont on Mar 08, 2013, 07:36 pm
Thermal imaging is probably the best way I can think of, but it really costs allot of money for an imager.  Guess that's probably why I don't have one.  Next is my your finger. ;)  I have a non-contact thingy, but mine includes too much surrounding area for parts like resistors.  Even held really close, I don't really trust it on small parts.  Gotta watch out for shiney parts too.  IR sensors seem to have trouble with really glossy surfaces like chrome or gloss black harley paint on the oil tank.
Title: Re: How to measure chip (or other component) temperature?
Post by: Docedison on Mar 08, 2013, 07:43 pm
Jim, A little dab of "Elephant Snot" as it is sometimes "fondly" called in Southern California is your best bet. Inexpensive heatsink compound. The thread linked was someone complaining that he didn't do his homework right... or didn't have the tools to do it right... It's all calculable but like writing code requires some training... first. When, without planning or at least writing down the basic requirements first... and starts "throwing parts" at an idea... one frequently ends up complaining about abused parts...
It's Too Hot To Touch, What Do I Do.. ? How many times have you read that here in this group alone?
If you are desiring of making some kind of thermal monitor... either write up your thoughts on preferred method here or PM me... either way I'd be happy to help.
The comment about the math being able to calculate the die temp was correct but I also know that the cooler a device is in operation the longer it will live, so anything uncomfortable to the fingers should be investigated... Probably the best thing is the aforementioned non-contact IR thermometers they can be had (Good quality ones) for less than $25.. on Ebay I didn't read all of it carefully, Edit RKJ

Bob
Title: Re: How to measure chip (or other component) temperature?
Post by: JimboZA on Mar 08, 2013, 07:44 pm
Quote
Thermal imaging is probably the best way I can think of, but it really costs money for an imager.  Next is my finger


.... and in between is my trusty Fluke.
Title: Re: How to measure chip (or other component) temperature?
Post by: JimboZA on Mar 08, 2013, 07:46 pm
Quote
If you are desiring of making some kind of thermal monitor...I'd be happy to help


Thanks Bob, but no it's really just curiosity, wondering how useful my Fluke's thermocouple would be in monitoring temp of a component.

Title: Re: How to measure chip (or other component) temperature?
Post by: oric_dan on Mar 08, 2013, 07:56 pm
Heat kills. There are some guys who think whatever it says, up to thermal shutdown
[eg, 175 degC] is ok, but I don't like my electronics running too hot, or failing prematurely.
So I use the Little Pinkie Test = if it's too hot to hold my little finger on the chip, then it's
too hot. And some redesign should be done. I also have a non-contact IR-Thermometer like Bob.

As Erdin indicated on that other thread, the L293s are bipolar technology, and not MOSFETs,
so there tends to be a collector-emitter drop of upwards to a couple of volts in those parts
[because the output stages have darlington pullup and pulldown ckts], and that times the load
current gives the power dissipation, Pd = Vdrop * Iload. Newer MOSFET h-bridges are much
better.

http://idmax.free.fr/Aide/Stepper/l293.pdf

Also, you might look at the TI 754410 as a drop-in replacement for the L293D. 754410 can go
to 1-Amp load vs 600 mA for the 293.

BTW, one way to tell if an L293 is too hot is, the chip will literally blow up and catch fire. This
actually happened to me once. Not just magic smoke, but the plastic end blew off, and flames
actually came out. So much for thermal shutdown. A mini Boeing 787.
Title: Re: How to measure chip (or other component) temperature?
Post by: Docedison on Mar 08, 2013, 07:57 pm
With the tip about the grease, quite well... Mine does or did until the probe was "Lost".. I own a Fluke 179.

Bob
Title: Re: How to measure chip (or other component) temperature?
Post by: afremont on Mar 08, 2013, 08:02 pm
Seen a 7805 open up once, guess the shutdown had an issue.  I also learned it's also a good idea to pay attention to voltage and polarity with tantalum caps.  Anybody got any really good incendiary stories?
Title: Re: How to measure chip (or other component) temperature?
Post by: Docedison on Mar 08, 2013, 08:03 pm
Isn't the L298 a better IC..?
Title: Re: How to measure chip (or other component) temperature?
Post by: retrolefty on Mar 08, 2013, 08:07 pm
Just because I haven't seen it mentioned here but many of the AVR chips, including the 328P, have an internal die temperature sensor impeded into the chip die. By selecting the proper analog mux selector bits one can read this temperature value. It's an un-calibrated temperature so not too useful and any reading taken is more a reflection of how much current you are sourcing or sinking via the output pins rather then the chip itself is generating, but some have found it amusing in the past to display the value. No one to date as best I can recall has done anything really useful with that sensor.

Lefty
Title: Re: How to measure chip (or other component) temperature?
Post by: Docedison on Mar 08, 2013, 08:10 pm
Yeah it involves some 25 100000uF 3V electrolytics and a 100 foot or 33 meter extension cord... and the police too. I was 14 and found these parts in a surplus electronics store scrap-bin. Most made a hell of a noise... almost had a dud but my mother called me to lunch.. It explodes disconnected from 110Vac 15 minutes later...
Thats when the neighbor called the cops... Seems he tried to kick it off his sidewalk, dern  near blew his shoe laces off... <BG>

Bob
Title: Re: How to measure chip (or other component) temperature?
Post by: oric_dan on Mar 08, 2013, 08:12 pm

Seen a 7805 open up once, guess the shutdown had an issue.  I also learned it's also a good idea to pay attention to voltage and polarity with tantalum caps.  Anybody got any really good incendiary stories?


What, you don't like my flaming 293? Another time, I had a TO-220 MOSFET literally melt off its
heat-tab. Little silvery beads came out from between the chip die and the heat tab.

L298 will go to 1.5-2 Amps, plus it's a Multiwatt15 package, so you can screw a big heatsink to it,
but they're still the same bipolar technology as L293. The 293/754410s are DIP16, but you can epoxy
a smallish heatsink on top if you like.
Title: Re: How to measure chip (or other component) temperature?
Post by: afremont on Mar 08, 2013, 08:22 pm
LOL, yeah caps can be dangerous in more ways than one.  Of course I liked your flaming h-bridge story Dan, that's what set me off.  I apologize for not specifically acknowledging it though.  

I learned to use fuses with my first car stereo self install.  I had a power lead coming out of an unfused connector on the fuse box and I didn't have any fuses inline.  It was a sloppy job, but it worked for quite a while until one day I got tangled in some wire and it shorted.  Lit up several feet of wire just like a toaster element.  The wire didn't burn in to, but it was the weirdest thing to see all the insulation just drop off the wire as it lit up.   :smiley-eek:  Fortunately I was able to yank it apart before things started catching fire.  I do things different now.  I was really lucky in that the wire feeding the fuse box was heavy enough to not melt down.
Title: Re: How to measure chip (or other component) temperature?
Post by: oric_dan on Mar 08, 2013, 08:26 pm
Car electronics is a good place to pay attention to safety measures. Don't want to catch
fire out on the freeway. 50-cent fuse, $25,000 car.
Title: Re: How to measure chip (or other component) temperature?
Post by: afremont on Mar 08, 2013, 08:48 pm
Ham radio mobile HF with 30A from the battery to the interior for minimum noise.  Fuses on the hot and ground at both ends. 

I've seen a couple of cars burn up in my day and it's almost unnatural how they can be consumed like that.  Everything including the metal is flammable.  In the case of magnesium, especially the metal.
Title: Re: How to measure chip (or other component) temperature?
Post by: SirNickity on Mar 08, 2013, 09:57 pm
I learned if you put a 7915 where a 7815 is supposed to go, a TO-220 will split apart between the tab and case.  I always test power supplies on a Variac, so I learned it only takes a few volts to do this, too.  :-)
Title: Re: How to measure chip (or other component) temperature?
Post by: Docedison on Mar 09, 2013, 01:11 am
No, I think a 7905 is different enough (data sheets attached) the input lead (1) is ground the tab/center pin/ground (2) is - supply and the third pin is the - output lead...
The device won't work properly but sorry nothing really reversed... I know I've used
Now IF you REALLY want to EXPLODE a TO-220 transistor, connect the emitter of a TIP42 to a real stiff (> 10A) power supply and then just ground the base... even works with the little TO-92 types... In my career as an engineer I've probably popped... a hundred or more..
I used that "trick" to get rid of my boss... he had a bad habit of looking over my shoulder.. I could never tell if it was something he was looking for to criticize or something to learn... But a "Slip" with a screwdriver or a meter probe always worked... even one time when After I had done for the transistor.. he handed me the negative meter probe and walked away.

Bob
Title: Re: How to measure chip (or other component) temperature?
Post by: SirNickity on Mar 09, 2013, 07:40 am
Come to think of it, it wasn't that I used the wrong part, it's just that I swapped the ground and input pins on the PCB.  First PSU design and I didn't realize they were in a different order between the 78 and 79 parts.  Positive rail worked fine.  Negative rail exploded.  Oops!

That's a great story, BTW.  Ever worry that the boss thought of you as "the clumsy guy that's always blowing up parts?"  ;-)
Title: Re: How to measure chip (or other component) temperature?
Post by: JimboZA on Mar 09, 2013, 10:04 am
Just for laughs I tried the following experiment....

I put a 7805 on a 12V supply and loaded it with a 10  Ohm resistor. Voltages measured at 12 and 5, and current measured as expected (497 Fluke mA to be exact). (Yes the resistor is hefty enough: 10W) So this set up is losing 7V @ 500mA for a power dissipation of 3.5W.

Without a heatsink, that 7805's temp shot to 110C in mere seconds. I turned it off then, since the datasheet said 120C tops.

I rummaged around and the smallest heatsink I could find is about the size of 2-3 Arduino Unos. Mounted the 7805 on there (no conductive goo though) and it settled just under 40C.

I now realise the importance of heatsinks, so that was a useful 1/2 hour of Saturday morning buggering around which beats shopping with Mrs Jimbo.
Title: Re: How to measure chip (or other component) temperature?
Post by: oric_dan on Mar 09, 2013, 08:29 pm
Quote
So this set up is losing 7V @ 500mA for a power dissipation of 3.5W.

Without a heatsink, that 7805's temp shot to 110C in mere seconds. I turned it off then, since the datasheet said 120C tops.

That's pretty close to what the d/s indicates to expect. If you find the lines that say
----------
package thermal data (see Note 1)
PACKAGE BOARD ?JC ?JA
POWER-FLEX (KTE) High K, JESD 51-5 3°C/W 23°C/W
TO-220 (KC/KCS) High K, JESD 51-5 3°C/W 19°C/W
NOTE 1: Maximum power dissipation is a function of TJ(max), ?JA, and TA. The maximum allowable power dissipation at any allowable ambient temperature is PD = (TJ(max) - TA)/?JA. Operating at the absolute maximum TJ of 150°C can affect reliability.
----------

and you plug in, you get 3.5W * (3°C/W + 19°C/W) = 77 °C rise --> 99 °C (including ambient).

There are various heatsinks with different capabilities, but I like a nice compact one (25.9°C/W),

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?freeText=158051&langId=-1&storeId=10001&productId=158051

I'm not quite sure how to calculate overall heatsinking of chip+heatsink, but I guess the two will
work in parallel, so (22 || 25.9) = 12 °C/W --> 42 °C rise at 3.5W. Something like that.

There are also heatsinks made specifically for your DIP16 L293,

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?freeText=2077335&langId=-1&storeId=10001&productId=2077335