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Im talking about electronic devices, which may be handheld or similar, so nothing exposed to "artificial" temperature (welding, soldering, cooling with liquid gas). Devices designed to be operated by ("unprotected") humans, indoors or outdoors, such is the temperature range.

My question is: What are the especially temperature sensitive parts? I guess Im interested in the lower end (0°C and below). Are the batteries sensitive? What is also likey to fail when it gets too cold? - Which in turn also mean: which part must be kept warm if one has to attempt to operate such device in too cold a enviroment?

Example: I have recently bought a laser distance meassure, a UNI-T UT391A+. The specified operating temperature range: 0°C to 40°C. Many similar devices (even the UT391A, without +) specify -10°C or lower as their lowest. Why is that? The most obvious difference between UT391A+ and others is that the former has integrated bubble levels. Could that be what bumps the temperature tolerance by 10°?

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    \$\begingroup\$ I think the question should be re-worded. From the elaboration it is clear that OP is curious why this particular and very specific device has so relatively small operating temperature range. The question should read: "What is the (most likely) technical reason behind narrow temperature specifications of a laser rangefinder?" \$\endgroup\$ – Ale..chenski Oct 4 '16 at 0:27
  • \$\begingroup\$ The answer should explain which functional block of rangefinder limits the temp range to 0-40C. Or -10+40C. Bubble levels by itself routinely have -20+70 range, but I am not sure how the vial is interfaced to electronic. I would guess that the weakest spot is the photo receiver block, which likely has a difficulty of handling temperature compensation of dark current. \$\endgroup\$ – Ale..chenski Oct 4 '16 at 0:27
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Usually the semiconductors are the least temperature sensitive devices at low temperatures, a far as functionality goes. They may be rated for 0-70°C (commercial temperature range) but in fact many will operate fairly well down to liquid nitrogen temperatures (77K).

Capacitors (especially electrolytic and many ceramic types) will drop in value, sometimes precipitously or the internal resistance will increase greatly.

Batteries often perform very poorly at only moderately low temperatures- internal resistance increases and capacity shrinks. LCD displays can have problems with speed and temperature compensation.

Aside from the ceramic caps, some of which are just very temperature sensitive, most of these devices have liquid contained within them.

There is not a lot of reason to specify devices over a very wide range (and test them with margin to ensure that) if they are not going to be used in an automotive or military environment, and the testing and spec'ing allows the semi makers to segment the market and charge quite a bit more money for wide range devices. Many commercial semis will typically operate over a much wider range with relaxed specs- for example if you clock the chip at 250MHz rather than 300MHz.

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  • \$\begingroup\$ Many semiconductors start failing as high as -30°C. Several years ago it was widely known in overclocking community as "cold bug" where CPUs would stop working when overcooled. \$\endgroup\$ – Agent_L Oct 4 '16 at 13:14
  • \$\begingroup\$ Semiconductors have to be designed to operate in a specific temperature band. You can sometimes find that 10°C is the lower operating limit. When the device is colder it can require so little energy to cause a gate to open that noise will trigger electron flow across the gap. Your CPUs and other complicated silicon ICs may work poorly or fail at much higher temperatures than freezing. They tend to get designed with the idea that it will be easy to keep them at 20C or higher, so why compromise top end temperature or performance to extend the temperatures to freezing. \$\endgroup\$ – TafT Oct 5 '16 at 10:56
  • \$\begingroup\$ I have some stuff working at 4K \$\endgroup\$ – Spehro Pefhany Oct 5 '16 at 15:18
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The most common reason for electronic limits on freezing is the moisture absorption in molecule sizes large enough when frozen and expand cause microscopic wirebonds to shear. (popcorn effect)

Although there is no problem with storage to -40°C, the rapid self-heating with microscopic amounts of frozen water vapour can cause the most damage.

Over the decades, plastic has improved in black encapsulated epoxy to improve the grade of moisture seals.

But for clear plastic epoxy encapsulation or lens, the seal technology is not there yet.

I do not know which laser is used, but here is an example of such a specification.

You might be able to keep it running and go outside in sub-zero weather without the thermal shock of heating frozen H2O molecules in a well, sealed case, but operating when stored below 0°C can be a problem, but not guaranteed to fail.

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One simple explanation of a conservative temperature spec is just the cost of testing, compared with the value-add to the product. You might test a batch of prototypes at -10°C, and claim 0°C as the minimum supported temperature. Testing at -40°C costs more, in terms of time and test equipment. Due to component spread and tolerances, over a wider temperature range, the range of behaviour that you should expect will increase.

Its not unknown for the same product to be labeled with different specs and sold at different prices (assuming that there are no yield factors to consider). Equally, fairly trivial features can limit the temperature range if they require specific components.

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There are three main temperature ranges for electronic devices:

commercial: 0°C to 70°C industrial: -40°C to 85°C military: -55°C to 125°C

when the temperature range increases, so does the price because the design complexity increases.

Pretty much any physical parameter depends on temperature: metal changes in size, things burn, and transistors do funny things. A circuit that works perfectly at room temperature might start misbehaving if brought too far from it, either increasing or reducing temperature. A common resistor would change in size due to metal expansion/contraption, changing its resistance value. Such an effect can even be used to measure temperature.

Guessing what starts to fail in your device is hard if not impossible without having a look inside, but there is a big catch: it is a measurement instrument. I guess laser measurement sends a light pulse and measures how long does it take for it to bounce back, then converts the time into distance since light speed is known.

How can you measure time? For example you can use a counter. You reset the counter, then when the pulse is sent you start it. When the pulse gets back you read the value, and knowing clock speed you can find out how much time has passed.

And what about the clock? A crystal with some fancy analog thingies generates it. Crystals are pretty stable, but they do change with temperature.

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    \$\begingroup\$ I've heard it quoted as "every sensor is a thermometer". \$\endgroup\$ – MSalters Oct 4 '16 at 12:28
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There are three main drivers for a specified temperature limit:

1. Physical considerations

Material science is non-trivial. Component manufacturers must deal with expansion coefficients. A typical IC will be packages with silicon + aluminum bondwires + some form of plastic housing. All these materials expand at different rates and while an attempt is made to match their expansion as close as possible, at some temperature it will literally rip itself apart.

2. Material considerations

Coupled with expansion is the ability for a compound to still be viable at temperature. Silicon semiconductors stop behaving as expected around 175°C. Polyester (capacitor dielectric) starts to break down over 100°C. Epoxies go through a glassification stage beyond a certain temperature.

3. Stated component characteristics

Component manufacturers want as high a yield as possible from their manufacturing process. Likewise they are "bound" to what is stated on their datasheets. Due to production tolerances and spreads not all parts are constructed equally.

If a particular batch meets the datasheets for the Military temperature range (-55°C to 125°C) they are marked for such usage. If they fail Military they are checked against Automotive (-40°C to +125°C), then Industrial (-40°C to 100°C) and finally Commercial (0°C to 85°C).

If a particular batch cannot meet the datasheet spread they then scrap the parts.

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At the top of the list of suspects for the temperature range limits would be the battery. Many/most battery chemistries do not do well in very cold temperatures (or very hot, either for that matter).

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