Low temperature solder

[daqq]

Hi guys,

Can I use normal solders ( Pb-free ) for temperatures around -50 deg. C? I've heard of tin pest, but I'm having problems with finding the specific values for which solder alloys are meant.

Thank you,

David

[Richard Crowley]

It is not clear that temperature has anything to do with the "tin whisker" problem.
Since when has lead-free solder been described as "normal"?

What is the context here?  Are you talking about a one-off hobby or custom project?
Or are you designing some mass-produced consumer product?

[daqq]

Thank you for your reply. I was worried more about things like tin pest and solder brittleness rather than whiskers.

The context, well, a small series product that should be able to withstand (though not necessarily work during) low temperature storage and transportation.
Edit:

Since when has lead-free solder been described as "normal"?

Since the EU went batcrapcrazy and effectively banned Pb based solders.

Also, I meant normal as in off the shelf, no specific marking, standard, etc.

[Richard Crowley]

Does the ban strictly apply to YOUR situation?  Are you mass-producing consumer products for general sale?
If you are worried about harsh environmental conditions, you could consider using a conformal coating over the PC boards after assembly.

[SeanB]

He is worried that tin will change crystal structure at around -38C, and go from a lustrous smooth metal to a brittle crumbly paste. The only way is to use a tin free solder, either all lead, or lead alloys or one using Indium.

http://www.aws.org/bsmc/wj1009-43.pdf

http://www.indium.com/

[Richard Crowley]

So, in effect, the EU has banned the manufacture of any low-temperature electronic apparatus?
Will all the European countries be moving out of Antarctica?

It seems rather clear that making something that will survive -50°C requires something more than generic, off-the-shelf solder.

[daqq]

He is worried that tin will change crystal structure at around -38C, and go from a lustrous smooth metal to a brittle crumbly paste. The only way is to use a tin free solder, either all lead, or lead alloys or one using Indium.

Yup, that's what I was asking.

I'm having trouble finding a definite answer to whether I can use specific alloys at specific low temperatures.

It seems rather clear that making something that will survive -50°C requires something more than generic, off-the-shelf solder.

It doesn't really seem that clear to me having never dealt with such a problem 

[Richard Crowley]

As SeanB said, it appears that Indium (and Bismuth) is your friend....
Here are the "low temperature" solders listed at Wikipedia

In97Ag3	Wettability and low-temperature malleability of indium, strength improved by addition of silver. Particularly good for cryogenic applications. Used for packaging of photonic devices.
In90Ag10	Nearly as wettable and low-temperature malleable as indium. Large plastic range. Can solder silver, fired glass and ceramics.
Bi100	Used as a non-superconducting solder in low-temperature physics. Does not wet metals well, forms a mechanically weak joint.[35]
Bi58Sn42	Bi58. Reasonable shear strength and fatigue properties. Combination with lead-tin solder may dramatically lower melting point and lead to joint failure.[28] Low-temperature eutectic solder with high strength.[17] Particularly strong, very brittle.[15] Used extensively in through-hole technology assemblies in IBM mainframe computers where low soldering temperature was required. Can be used as a coating of copper particles to facilitate their bonding under pressure/heat and creating a conductive metallurgical joint.[59] Sensitive to shear rate. Good for electronics. Used in thermoelectric applications. Good thermal fatigue performance.[66] Established history of use. Expands slightly on casting, then undergoes very low further shrinkage or expansion, unlike many other low-temperature alloys which continue changing dimensions for some hours after solidification.[35]
In52Sn48	In52. Suitable for the cases where low-temperature soldering is needed. Can be used for glass sealing.[59] Sharp melting point. Good wettability of glass, quartz, and many ceramics. Good low-temperature malleability, can compensate for different thermal expansion coefficients of joined materials.
Bi49Pb18Sn12In21	Cerrolow 136. Slightly expands on cooling, later shows slight shrinkage in couple hours afterwards. Used as a solder in low-temperature physics.[35]
Bi50Pb26.7Sn13.3Cd10	Cerrobend. Used in low-temperature physics as a solder.[35]
Bi44.7Pb22.6In19.1Cd5.3Sn8.3	Cerrolow 117. Used as a solder in low-temperature physics.[35]
Cd70Sn30	Cd70, thermal-free solder. Produces low thermal EMF joints in copper, does not form parasitic thermocouples. Used in low-temperature physics.[35]
In100	In99. Used for die attachment of some chips. More suitable for soldering gold, dissolution rate of gold is 17 times slower than in tin-based solders and up to 20% of gold can be tolerated without significant embrittlement. Good performance at cryogenic temperatures.[90] Wets many surfaces incl. quartz, glass, and many ceramics. Deforms indefinitely under load. Does not become brittle even at low temperatures. Used as a solder in low-temperature physics, will bond to aluminium. Can be used for soldering to thin metal films or glass with an ultrasonic soldering iron.[35]

Ref: http://en.wikipedia.org/wiki/Solder

[Richard Crowley]

Remember also that other components (besides solder joints) need to be specified for at least that extreme "storage temperature" even if not operating at that temperature.
I would be particularly careful about capacitors, and especially electrolytics, etc.

[Zero999]

So, in effect, the EU has banned the manufacture of any low-temperature electronic apparatus?
Will all the European countries be moving out of Antarctica?

Lol, the legislation is only for consumer products. It doesn't apply to specialist applications such as military, aerospace and rough service.