PORTLAND, Ore.—Solder pads could soon be made obsolete by a new nanotape material created by the Semiconductor Research Corporation (SRC) and Stanford University.
By sandwiching thermally conductive carbon nanotubes between thin metal foils, nanotape transfers heat away from chips better than solder but with a lightweight flexible material that is cheaper and and more compliant, according to researchers.
"Today, solder is made very thick to provide mechanical compliance, but our nanotape can replace those solder pads with a thin lightweight material that improves thermal energy management," said professor Ken Goodson, lead researcher for SRC at Stanford University. "Our tape consists of a vertically aligned carbon nanotube forest at its central core, with carefully chosen alloys on both the top and bottom that wet the carbon nanotubes and also will contact to the heat sink and the chip."
To the unaided eye, the nanotape will look like a conventional solder pad, because both the top and bottom are metallic. But inside it will harbor the superior thermal conduction of the carbon nanotubes.
Mettalic adhesion layers on each side of the central core wet the carbon nanotube forest.
"The nanotape will look like a conventional solder pad, and will work with in same equipment, but it has the mechanical characteristics of an aerogel and the thermal conductivity of a metal," said Goodson.
Initially the material, which has a thermal conductivity comparable to copper, will be fabricated as a direct replacement for solder pads, according to SRC. However, its foam-like flexible compliance which allows it to shrink and expand in concert with semiconductors in a manner impossible for solder, could form the basis for entirely new semiconductor packaging techniques.
Early adopters of nanotape will likely be graphic-accelerator and gaming semiconductors, which today must grapple with hot spots on their chips that limit their performance. Using nanotape, however, will better cool hot spots by remaining compliant to the semiconductors as they expand and contract during heating.
"Nanotape will cool hot spots better, removing a current roadblock to increasing chip performance," said Goodson.
Side-view SEM of an aligned carbon nanotube film fabricated on a MEMS resonator for measuring thermal and mechanical properties.
Besides semiconductors, Stanford is also working with the National Science Foundation (NSF) on a project with the Department of Energy Partnership on Thermoelectric Devices for Vehicle Applications. Here, the nanotape will facilitate the recovery of electrical power from hot exhaust gases using thermoelectric energy converters. According to Goodson, nanotape can more reliably transfer heat to thermoelectric generators, enabling greatly improved fuel economy.
The researchers predict that early adopters will be start using the nanotape by the end of next year, with mainstream benefits to end users commencing circa 2014. The SRC-funded nanotape material will be made available to all SRC members, which include Advanced Micro Devices, Applied Materials, Axcelis Technologies, Cadence Design Systems, Freescale Semiconductor, Hewlett-Packard, IBM, Intel, LSI Corporation, Mentor Graphics, Novellus Systems, Rohm and Haas Electronic Materials, Texas Instruments and Tokyo Electron.
All new technologies will have their teething problems. If this does have the potential to overcome tin whiskers and allow long term, reliable, electronics, then that is worth pursuing.
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Nanotape will actually decrease the incidence of whiskers, according to the researchers, who claim that while nanotape technology still uses metallic alloys at the thermal interface, as part of the multilayer sandwich, the mechanical and thermo-mechanical mechanisms that induces whisker formation are both mitigated by novel properties of the nanotape.
I agree with many of the above observations and so while the technology may prove helpful in increasing board density, I will certainly not like my boards to fail 3yrs down the line because of wiskers. the material science for the board manufacturing needs to be customized for such new approachs as trying to hybridize traditional SMD tech with nanopads may and will have longivity related issues.
This sounds like an exciting advance in technology. I'll be very interested to hear the results of extreme environmental and life cycle testing to better understand the failure modes and the technology life expectancy. Also, how easily can items be "desoldered" if necessary?
Is this technology will result some chnages only to the IC packaging or also impact any PCB manufacturing process. What would be the cost impact of this technolgy on the final PCB assembly? Does this material stand higher temparatures than the normal Tin-Lead solder pads?
Well, apparently it is a flexible material, that should relieve some of the strain thought to be a cause of whiskers: "Using nanotape, however, will better cool hot spots by remaining compliant to the semiconductors as they expand and contract during heating." And since carbon is not a metal, I don't see how it can whisker.
But this is true, the technology has to be tested against this effect, since we can imagine the nanotubes will stress the alloy, and nothing is said about the alloy itself.
It is nice to raise this point.
Sounds interesting, but what will carbon nanotubes do for tin whisker formation? Tin whisker problems were reintroduced with the RoHS regulations banning lead in solder. From my limited work, carbon only accelerates whisker growth in tin alloys similar to bright tin deposits. Trust that someone will still raise millions to fund a "nano" solder venture w/o mentioning this fly in the ointment.
Tin whiskers, even without nano-carbon, will be killing a lot of equipment within 5 years of unit manufacture regardless of IC chip reliability. The recollection of operational 20 year old electrical appliances (TVs, computers, radios etc) will be a passing memory. DVD players are not lasting two years now.
Manufacturers may smile at the new built-in product obsolescence, but landfills will groan with the new flood of premature eWaste. We can do better.
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