Low temperature solder - Page 1
Forum section: electronics / beginners

author: daqq
author_rank: Super Contributor
timestamp: December 19, 2014, 03:06:50 pm
content: 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

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 19, 2014, 03:21:14 pm
content: 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?

author: daqq
author_rank: Super Contributor
timestamp: December 19, 2014, 03:33:34 pm
content: 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:QuoteSince the EU went batcrapcrazy and effectively banned Pb based solders.Also, I meant normal as in off the shelf, no specific marking, standard, etc.

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 19, 2014, 03:42:05 pm
content: 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.

author: SeanB
author_rank: Super Contributor
timestamp: December 19, 2014, 05:43:27 pm
content: 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.pdfhttp://www.indium.com/

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 19, 2014, 06:19:19 pm
content: 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.

author: daqq
author_rank: Super Contributor
timestamp: December 19, 2014, 07:22:54 pm
content: QuoteYup, 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.QuoteIt doesn't really seem that clear to me having never dealt with such a problem

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 19, 2014, 08:06:39 pm
content: As SeanB said, it appears that Indium (and Bismuth) is your friend....Here are the "low temperature" solders listed at WikipediaIn97Ag3Wettability and low-temperature malleability of indium, strength improved by addition of silver. Particularly good for cryogenic applications. Used for packaging of photonic devices.In90Ag10Nearly as wettable and low-temperature malleable as indium. Large plastic range. Can solder silver, fired glass and ceramics.Bi100Used as a non-superconducting solder in low-temperature physics. Does not wet metals well, forms a mechanically weak joint.Bi58Sn42Bi58. Reasonable shear strength and fatigue properties. Combination with lead-tin solder may dramatically lower melting point and lead to joint failure. Low-temperature eutectic solder with high strength. Particularly strong, very brittle. 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. Sensitive to shear rate. Good for electronics. Used in thermoelectric applications. Good thermal fatigue performance. 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.In52Sn48In52. Suitable for the cases where low-temperature soldering is needed. Can be used for glass sealing. 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.Bi49Pb18Sn12In21Cerrolow 136. Slightly expands on cooling, later shows slight shrinkage in couple hours afterwards. Used as a solder in low-temperature physics.Bi50Pb26.7Sn13.3Cd10Cerrobend. Used in low-temperature physics as a solder.Bi44.7Pb22.6In19.1Cd5.3Sn8.3Cerrolow 117. Used as a solder in low-temperature physics.Cd70Sn30Cd70, thermal-free solder. Produces low thermal EMF joints in copper, does not form parasitic thermocouples. Used in low-temperature physics.In100In99. 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. 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.Ref:http://en.wikipedia.org/wiki/Solder

author: Richard Crowley
author_rank: Super Contributor
timestamp: December 19, 2014, 08:08:55 pm
content: 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.

author: Zero999
author_rank: Super Contributor
timestamp: December 19, 2014, 11:23:30 pm
content: Quote from: Richard Crowley on December 19, 2014, 06:19:19 pmLol, the legislation is only for consumer products. It doesn't apply to specialist applications such as military, aerospace and rough service.