Testing component temperature with IPA and thermal shock

Question

Not infrequently a question will be asked on this site about components that are hot to the touch. I generally consider hot to the touch to be about \$140^{\circ}\$ F or \$60^{\circ}\$ C. While I, like many people, prefer my electronics to run cool, this temperature is generally quite far below the maximum safe operating temperature of electronic components. So, when people say their component is hot to the touch, I am tempted to suggest, if they lack a thermal camera or thermal sensor, to place a small drop of isopropyl alcohol (IPA) on the component and note whether it boils. IPA boils at \$180^{\circ}\$ F or about \$82^{\circ}\$ C, which, although still within the safe operating temperature of most components, is at least closer to the maximum than "hot to the touch".

I refrain from suggesting such a test because I am concerned that the thermal shock might damage the component, much as pouring cold water on a hot engine block might cause it to crack.

My question is this. Is it generally safe to put IPA on a hot component as a temperature test, or are there some common components that could be damaged by such a procedure.

Answer 1

Frame challenge - how does knowing whether a component is at 60 or 80 help?

60 C is a good definition of hot to the touch. Dry skin can be pressed on a 60 C surface for a few seconds before you need to remove it (I learnt this test when doing oxalate titrations in chemistry, which need to be 60 C to go).

If you want a test for 80 C, that's dry skin doesn't get damaged, but you can't hold it there for long enough to count a duration.

To answer your question. I've not yet had a component damaged by putting a wetted finger on it. The sizzle of boiling saliva indicating a temperature of over 100 C. This is perhaps a better threshhold temperature for 'too hot', a bit nearer to the 150/175 figures often quoted in data sheets for max junction temperature. Saliva is easier to come by than IPA as well. While I've not yet broken a component, I've not tested all components, and I've not yet seen a thermal shock specification for packages involving IPA or saliva.

I understand many phone cameras will see infrared, which is only a filter and an app away from having a thermal camera.

Answer 2

I can't say I've seen a failure myself, but I also don't think this is a strongly or easily falsifiable question.

I suspect the more likely case is: if the circuit is weak or faulty to begin with, maybe thermal shock or cycling pushes it to failure; but only because it had poor solder joints, cracked components, etc. already.

An interesting counterpoint: IPA has less heat of vaporization than water. Suggesting it, is likely a gentler alternative to water (e.g. the classic licked-finger sizzle test).

I don't have any problems using either liquid, personally.

Liquids even have a distinct advantage over, say, thermal probes: intimate contact is ensured, whereas a (dry) thermistor or thermocouple typically reads, oh, 5 or 10% low [closer to ambient] due to poor contact and boundary layer (air). Obviously, the fast evaporation, or boiling, doesn't tell you anything very accurate either, but it's interesting to note. (When I use probes, I typically put a blob of thermal grease on the tip, so it can be smooshed into the component under test with lower thermal resistance.)

Answer 3

Is it generally safe to put IPA on a hot component as a temperature test, ...

Answer for this part of question

From this translation by "google" ...

What are the side effects of isopropyl alcohol?
Isopropyl alcohol is highly flammable. The use of a heat source or any device likely to cause a flame or spark can cause a significant risk of burns, which is why it is important to ensure that the skin is completely dry and free of residue. 'alcohol.
Also, this compound is irritating and should not be applied in occlusion (dressings, skin folds, clothing, etc.), nor in excess (risk of skin symptoms and toxicity in the event of absorption). It should also not come into contact with the eyes or mucous membranes. The main adverse effects are local reactions such as erythema (redness), inflammation, itching, or even dry skin or even peeling.
These signs are more common when isopropyl alcohol is applied to weakened skin or if its use is repeated. The skin must be dry and without alcohol residue Isopropyl alcohol vapors can cause eye and respiratory irritation, coughing and even difficulty breathing.
In case of significant ingestion or inhalation, isopropyl alcohol can cause poisoning manifested by headache, nausea, vomiting, dizziness, central nervous system depression, hypothermia, rhythm disturbances cardiac and respiratory functions, convulsions, coma or even death. Allergic reactions (erythema, rash, pruritus, blisters, blisters) are possible although very rare.