This is more promising if you have deep enough pocket (well, if you want to operate at that temp and bias, you must have deep pocket, like oil well).
"
High temperature alloy may be perfect solder for well electronics
Wed, 04/17/2013 - 9:01am
Meg Marquardt, Materials 360 Online
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Sandia National Laboratories researcher Tom Crenshaw, co-author on the paper, sets up a specimen in a test frame that will pull a solder joint apart to determine its tensile strength. Credit: Sandia National Laboratories
Technology used in downhole applications—such as geothermal or oil-well monitoring—must endure punishing conditions, from very high temperatures to tremendous pressures. In developing such technology, researchers have run into various materials snags, not the least of which is finding a solder material that can perform under these harsh environments. But researchers at Sandia National Laboratories in New Mexico have repurposed a solder alloy once intended for defense applications to meet these challenges.
Originally developed for neutron tube components, a gold-silver-germanium alloy has all the right properties for downhole applications, says Paul Vianco, an electronics manufacturing and reliability researcher at Sandia Labs, who specializes in soldering technologies. The components for high temperatures electronics, such as microprocessors and capacitors, are ready for testing, he says. Unfortunately, electronic packaging, including soldering technology, has lagged behind, because of the unique service conditions.
“Having a higher strength material, starting with the solder, was a driving force to begin looking at alternative materials,” says Vianco.
When he began to investigate high temperature solder options, the gold-silver-germanium alloy looked like a perfect fit. When he and fellow researchers were first investigating the material 15 years ago, they created a full profile of the alloy’s properties, including its ability to hold up to vibrations based on initial strength performance.
The alloy was also able to clear the biggest solder hurdle: melting temperature. Most solders melt around 350 C, which is problematic for downhole applications that can easily reach much higher temperatures. The other option is to use a brazing material, a technique that is not ideal for most electronics. Most brazing materials melt around 700 C, temperatures that would damage even electronics designed for downhole use.
Though there are solders available that are usable around 450 C, they are almost universally lead-based, says Vianco. Though functional, lead-based products work counter to the current environmental movement to use materials that are as nontoxic as possible.
“A lot of the high temperature, lead-based solders were usable, so people were making high temperature electronics with them, but such lead-containing solders were obviously not the best choice,” says Vianco. It became a hunt, then, for other, less toxic materials that would enable electronics to be used in high temperature applications.
The gold-silver-germanium alloy fits the bill perfectly, says Vianco. It has a melting range of 420–440°C and is lead-free. And since it was nearly fully characterized during the previous study over a decade ago, the alloy is ready for prototyping, says Vianco. The research, which was presented at Surface Mount Technology Association International where it won best of proceedings category, has generated some buzz in the industry. All that’s missing now is a substrate to solder the circuits onto, says Vianco. Once that piece of the puzzle is in place, a new wave of high temperature electronics can be developed for the downhole oil, gas, and geothermal industries.
Source: University of Cambridge "
Product that are built around function alone have not been designed at all, but merely engineered. -prof. Ashby
Original Message
From: Joyce Koo
Sent: Wednesday, December 18, 2013 6:24 AM
To: [log in to unmask]
Reply To: TechNet E-Mail Forum
Subject: Re: [TN] High Temperature Solder Migration/Creep
With testing temp 200 to 250 and bias ý48 volt,you possiblly close to melting temp and got some Pb vapor Re deposit. The whole test and selection of alloy sounds iffy to me. Is it someone's science project try to accelerate tests to "ultra highly" state? Or you really have requirement operated in that temp range? (you do not need to answer my questions. Really!).
Product that are built around function alone have not been designed at all, but merely engineered. -prof. Ashby
Original Message
From: Mike Fenner
Sent: Wednesday, December 18, 2013 5:45 AM
To: [log in to unmask]
Reply To: [log in to unmask]
Subject: Re: [TN] High Temperature Solder Migration/Creep
I've never heard of migration associated with 10/88/2 or similar alloys, but
that's not to say it's never happened. That alloy starts to melt around 270C
giving soldering temps of 300 plus. At that sort of temperature everything
organic is pretty friable and likely to come unstuck/delaminated/thermally
degraded into ???. Including conventional rosin/resin fluxes which will
probably be caramelising. Certainly, if you're doing it, post solder
cleaning is difficult and likely to be compromised. Therefore I think the
cause is more likely to originate in those areas rather than directly from
the solder. An area to go on to your investigate list anyway. It would be
useful to know what the assembly process and material types are.
Regards
Mike
BS&P
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Tuesday, December 17, 2013 10:15 PM
To: [log in to unmask]
Subject: [TN] High Temperature Solder Migration/Creep
We have an FA project that appears to be migration of 10Sn/88Pb/2Ag solder
across a 0.024 inch antipad to ground plane on the surface of the polyimide
board.
It is not dendritic in appearance. Looks more like Ag creep corrosion.
Failure occurred under dry heat testing at our lab.
Bias is 48 volts
The test temperatures are 200-250C over 12 weeks
Ran at atmosphere, no added moisture
The failure coincides with the loss of solder mask adhesion, under which the
metal can be seen...sort of, as mask is just about charcoal now.
There is also some evidence of flux residue, which would likely be very
corrosive, but don't we need moisture?
Literature searches get swamped by Ag migration/creep. Anyone got an idea?
Keywords? Tests for differential diagnosis.
Chris
Chris Mahanna
Robisan Lab
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