EEVblog #622 - How To See-through Objects With A Thermal Camera

[EEVblog]

Dave shows you a handy tip on how to see through your product using a thermal imaging camera with the cover *on*. Thus being able to maintain the correct airflow, whilst at the same time being able to view the thermal map as if the cover was off!

[Taucher]

Nice vid

I've read the E8 has an upgrade by Flir (grin) available to include manual (fixed) temperature range - that might have been handy to stop the camera's auto-ranging to just follow the temp-profile.
If you want a "Just Dave it" edition then just drop us a note *G*

Btw - used my thermal cam in fixed mode while performing hot air re-soldering of a a BGA - was quite helpful not to burn surrounding stuff - and one doesn't have to use the spot measurement feature to see the real temp

[NiHaoMike]

Any concerns with ESD?

[EEVblog]

Any concerns with ESD?

Meh.
You generally wouldn't wrap the PCB in the stuff.

[Taucher]

Any concerns with ESD?

Meh.
You generally wouldn't wrap the PCB in the stuff.

This reminds me that I was wanting to investigate further details about that nice little ESD measurement device that I've seen some times in your blog ... but never a teardown of it
(seen it in ep #247 - ) - AlphaLab Surface DC Voltmeter KV@1

Found two quite interesting texts regarding such devices:
http://www.qsl.net/k/k0ff/7Manuals/Static%20Electricity/The%20Surface%20DC%20Voltmeter%20and%20its%20included%20accessories%20make%20a%20complete%20%93kit%94,%20used%20to%20measure%20all%20the%20forms%20of%20static%20electrici.htm

https://e-reports-ext.llnl.gov/pdf/374701.pdf

[TVman]

Nice video Dave!

[Odysseus]

That's some out of the box thinking!

I wonder how much heat escapes via infrared radiation through the transparent cling wrap that normally would be absorbed or reflected with an opaque case.  My hunch is that it's quite small compared to convection/conduction. Off to Wikipedia...

EDIT

Here we go: http://en.wikipedia.org/wiki/Stefan-Boltzmann_law , http://www.irf.com/technical-info/appnotes/an-1057.pdf

If my calculations are correct, an object of unity emissivity at 70C will radiate ~30mW per cm^2 of surface area in a room temperature environment.  Pretty insignificant.

[Taucher]

That's some out of the box thinking!

I wonder how much heat escapes via infrared radiation through the transparent cling wrap that normally would be absorbed or reflected with an opaque case.  My hunch is that it's quite small compared to convection/conduction. Off to Wikipedia...

That's not so far off - AFAK some 2/3 of the overall thermal transport is done by photons - but as it's in an equilibrium with the surrounding that effect is usually neglectable for ventillation tests - I'd say if the construction overheats with the cover but does not with the wrapping, then that design is way too close to a critical point anyway.

[EEVblog]

I'd say if the construction overheats with the cover but does not with the wrapping, then that design is way too close to a critical point anyway.

That would be my thinking too.
In any case the effects of forced air flow would dominate, and the cling wrap keeps the air flowing where it's supposed to.

[DJ]

Neat vid.

I would be a little cautious regarding static charge. Back in the 80's I had a static charge meter, which was possibly more critical - fet's tended to be more delicate, and we'd see increased fallout during the drier winter months. I seem to recall peeling off a bit of scotch tape as easily generating 5 or more kv. Cling wrap I would expect could be in that neighborhood.

Most devices are of course more secure once in-circuit, but most esd testing is designed for assembled product.

Tearing a sheet of plastic off, then laying it on metal to drain off any charge would mitigate risk, I'd think.

[SeanB]

Cling film is easy to handle static wise if you are prepared to lose the cling ability. Simply take an old household spray bottle ( the common use once ones you get cleaners in are fine) and rinse it out, then add a tablespoon of liquid fabric softener and fill with water and shake well to mix. Pull the cling film off away from the bench, and place on a flat surface and tape it down, then spray lightly with the softener, wipe dry, turn over and tape down again and repeat for the other side. You lose the ability for it to cling, as that is a function of surface static charge, so you will have to tape it down.

[EEVblog]

Bit of a cheeky title. 
It'll be interesting to see the YT view stats. I'll bet the same crowd that got excited about the camcorder IR seethrough clothing nonsense will turn up.

You gotta be an SEO whore in this business 
Seems the video is already number 3 on youtube for the generic search term "thermal camera" ?

[miguelvp]

Find a large antistatic bag and cut it. IR will go through it like if it was transparent instead of dark silver/grey.
An old large xray totally exposed film should be transparent to IR as well.

[Taucher]

Find a large antistatic bag and cut it. IR will go through it like if it was transparent instead of dark silver/grey.
An old large xray totally exposed film should be transparent to IR as well.

The far-IR transmission of a material depends on its bandgaps - LDPE is quite transparent in thin layers

Much more fun: inspect a chip-wafer (germanium or silicon) - depending on the N/P/bare type you'll be able to see through in IR... or not

[miguelvp]

Find a large antistatic bag and cut it. IR will go through it like if it was transparent instead of dark silver/grey.
An old large xray totally exposed film should be transparent to IR as well.

The far-IR transmission of a material depends on its bandgaps - LDPE is quite transparent in thin layers

Much more fun: inspect a chip-wafer (germanium or silicon) - depending on the N/P/bare type you'll be able to see through in IR... or not

Even red wine or coca cola will be transparent on IR and will look like water.

The problem with the anti-static bags or the film is that it will block visible light, but then again, if you only care about the thermal image then it doesn't matter.

[Legit-Design]

Bit of a cheeky title. 
It'll be interesting to see the YT view stats. I'll bet the same crowd that got excited about the camcorder IR seethrough clothing nonsense will turn up.

I think one camcorder IR seethrough had boobs in it. Maybe that was the reason.
https://www.youtube.com/results?search_query=see+through+clothes

this one with 37,934,405 views

[speedyant]

Try those for microwave oven.




Yes, i have used google translator... 

[SeanB]

Find a large antistatic bag and cut it. IR will go through it like if it was transparent instead of dark silver/grey.
An old large xray totally exposed film should be transparent to IR as well.

the large ones I use at work are quite reflective in IR, as they are designed to both reduce static and reflect heat away to control the inner side temperature. Big enough to use when camping as a sleeping bag outer liner, 10 minutes under one and you are cooking.

[cyr]

Even red wine or coca cola will be transparent on IR and will look like water.

The problem with the anti-static bags or the film is that it will block visible light, but then again, if you only care about the thermal image then it doesn't matter.

I think you must be thinking of other IR wavelengths. Water is basically opaque as far as my thermal camera is concerned, and I'm sure that will apply to any beverage (and of course the glass you are likely to keep it in).

My anti-static bags are also very thermally reflective, not transparent at all.

[tinytim]

as a side thought, i wonder if Dave would put the Flir in front of the Atten 858 so we can see the airflow and adjust the flowrate and temp.
I am interested in knowing if there is any advantage in using just enough temp and low airflow as opposed to high temp, a larger distance and flowrate. I assume that by using just the minimum temp and min airflow required would substitute "perfect" conditions for reflow.
Also i wonder how good the calibrated temp control is, just where is the temp point measured from, the nozzle? from a distance?

Your thoughts?
Tim

[EEVblog]

as a side thought, i wonder if Dave would put the Flir in front of the Atten 858 so we can see the airflow and adjust the flowrate and temp.

I thought about this. The max temp range on the E8 is only 250C, but still should be fine for seeing a board/part come up to temp.

[tinytim]

as a side thought, i wonder if Dave would put the Flir in front of the Atten 858 so we can see the airflow and adjust the flowrate and temp.

I thought about this. The max temp range on the E8 is only 250C, but still should be fine for seeing a board/part come up to temp.

I wonder how effective Kapton tape is since i use it primarily as a masking for adjacent smd devices, would be great to see some airflow maps so we can see what goes on either side of the tape - so many questions on what seems to be a largely ignored / dismissed subject.  Thanks for the vids Dave. Awesome.

[max_torque]

The interesting point is that this video demonstrates the benefits of a "precision" cooling design.  The Filter instrument doesn't really has a precision cooling design.  So, lid on or lid off, the bulk of the cooling is driven by local convection.
 
Yes, the fan removes that heated hot air from inside the box when the lid is on, but the mean velocity over the individual heat sinks (even those close to the fan) is too low to significantly boost the performance (degC/W) of those sinks via forced convection.  (This is because forced convection really only starts to occur when local flow in the heat sinks boundary layer becomes turbulent. i,e, that largely static boundary air is broken down by high velocity air moving and swirling around it).

  So in that case, the heat sink temps don't change too much between having the lid on or off (when the lid if off, the lower density hot air natually rises away, pulling cold air into it's place).
In the case of the filter instrument, the fan really is there to ensure the bulk temperature inside the device stays within a few degrees of ambient, NOT to ensure any particular component of sink is cooled!  (This is important for instruments that may be mounted in racks (where they get upheat from their neighbours) and/or used in higher ambient temperatures etc)

For the 'scope, the individual ICs that are rejecting heat don't have a good sink (high thermal impedance), so they require the fan to be blowing high velocity air.  This is getting closer to a precision cooling design, where you need to have the covers on (or cling film instead) to ensure the air paths impinge on the correct location.  Without that turbulent air flowing over the specific ICs the device overheats.

We of course see proper precision cooling in devices like DC loads, Power supplies or modern PC's laptops etc, where specific and direct airflow is used to ensure sufficient heat is removed directly from the device being cooled, and not just allowed to spread into the general internals of the device.  In those cases, fans directly on heat sinks, or moulded channelling etc (or even heat pipes etc) are used.


It's also worth noting that with IR measurement "emissivity" is everything.  Generally, the camera will be set for a fixed value (usually a "black body" value.  So, for accurate measurements you either need to correct the camera settings for the objects you are pointing it at, or another common option is to just lightly spray the entire pcb with black spray paint!!

[Taucher]

as a side thought, i wonder if Dave would put the Flir in front of the Atten 858 so we can see the airflow and adjust the flowrate and temp.

I thought about this. The max temp range on the E8 is only 250C, but still should be fine for seeing a board/part come up to temp.

the "calibrated" scale goes to 250 ... the camera will actually show temperatures up to 280°C and then just ">280°C"

@Airflow - due to a lack of mass the airflow is never visible - only its effects.
I've attached a couple of images taken with my Flir E4+
... the solder iron tip had 350°C temperature (ERSA iCon iTool)
two images show my hot air station in action - please note that some components around the BGA chip seem to be really hot and others seem to be very cold - both is due to metallic (mirror) reflection and should not be confused with the medium-hot reality

The last image shows a simple PCB under load - one can see how the chip-die is much smaller than the outside package.
Note the temp-scale when comparing images!

[zapta]

Find a large antistatic bag and cut it. IR will go through it like if it was transparent instead of dark silver/grey.
An old large xray totally exposed film should be transparent to IR as well.

Or even better, run the unit with the stock cover, open it and take a quick snapshot with the FLIR.  Then you have all the time in the world to analyze it with the FLIR software. Air flow and heat dissipation will be more realistic.