Thermal Interface Materials (TIM) Blog
The TIM Blog serves as a clearinghouse for information relating to thermal interface materials including products, technologies, news, and events. We encourage comment and feedback on anything thermal interface material related.
Recent Entries
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Posted by Amanda M. Hartnett
Friday, September 5th, 2008
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The process of applying a solder thermal interface material typically
includes applying flux to a solder preform and reflowing it in a sandwich
between two substrates. When a preform
comes flux coated, it’s a no-brainer how to apply the flux to the preform. It’s
already done for you.
There are so many great types of flux available for specific
applications, that you might want to use a specialty flux formulation matched
to the substrates you are soldering to and the reflow temperatures you will be
running. This flux formulation is
commonly a Tacflux and the key to good flux application is not to overdo it. A little bit goes a long way.
This past week I ran a soldering experiment in which I
was soldering a 1” preform of 121 alloy (96.5Sn3.5Ag) to copper and wanted to
use TacFlux 023 because it is specifically formulated for soldering lead free
solders to standard soldering metallizations such as copper. I knew that in the soldering process, the
flux needed to make contact with the entire substrate I was soldering to, but I
didn’t know how far out the flux would wet or how much flux I should apply. I ran a few trials to test out various dispensing
methods and amounts. What I found in the
end was that one dot of flux dispensed onto the center of the substrate was all
that was needed to remove the surface oxides and wet the solder over the entire
1” surface
Posted 12 hours ago by Amanda M. Hartnett |
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Posted by Amanda M. Hartnett
Friday, August 15th, 2008
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This week at SMTAI we will be discussing hot topics with some of the electronic industy's most knowledgable representatives. Please Stop by to see us!
Posted August 15th, 2008 by Amanda M. Hartnett |
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Posted by Amanda M. Hartnett
Thursday, August 14th, 2008
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One of the electronics largest trade shows of the year, SMTAI is nearing on the week of August 18th. At this show in Orlando, Florida, Tim Jensen and I will be presenting a paper titled, “Halogen-Free Solder Pastes and Fluxes: Implementation Challenges.
Who is this presentation intended for?
The intended audience for this paper is anyone who is using or has considered using solder pastes or fluxes in their electronics. This includes the solder fluxes used for TIM1 thermal applications. This presentation will focus on the use of halogens in solder fluxes. There is both environmental as well as a reliability repercussions to including halogens in solder fluxes, and their impact will be discussed at this session.
When is it?
Join us on August 20 at the 1:30 Environmental Compliance session to join in the discussion and hopefully learn a bit about halogen-free solder fluxes.
Posted August 14th, 2008 by Amanda M. Hartnett |
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Posted by Amanda M. Hartnett
Wednesday, August 13th, 2008
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Liquid Metal Thermal Interface Materials
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Dispensing Thermal Grease. Image Courtesy of computershopper.com
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So far this year, we have had so many discussions of the various types of metal thermal interface materials, their thermal conductivity benefits, their thermal test performance and the various applications they fit into, that I thought it was about time to bring the conversation back to the basics.
What types of thermal interface materials are available?
There are no shortage of thermal interface materials out there. Among others, there are various possibilities such as:
1) Thermal Greases
2) Metal Filled Thermal Greases
3) Polymer Phase Change Thermal Interface Materials
4) Thermal Pads
Each of these have their benefits and are suited for niche applications, but most high power/high heat applications are best suited with metal TIMs for their superior reliability and thermal resistance benefits.
Posted August 13th, 2008 by Amanda M. Hartnett |
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Posted by Amanda M. Hartnett
Tuesday, August 12th, 2008
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Celsia Technologies, an established name in the electronics cooling market for their advanced heat spreaders recently unveiled an advertisement in Electronics Cooling Magazine which was unlike others I have seen in the industry, and I was personally impressed by their creativeness which pushes existing industry boundaries for an eye-catching message, as controversial as it may be. This advertisement sends a strong message about the capability of traditional heat pipes vs. Celsia’s new nanospreaders.
According to
George Meyer, CTO of Celsia Technologies, “Most people got it for what it was, a way to get your attention. Some did not like it!”
This ad personally caught my attention and I thought, “Wow! Something New.” But what do you think of it?
Posted August 12th, 2008 by Amanda M. Hartnett |
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Posted by Amanda M. Hartnett
Thursday, August 7th, 2008
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A typical thermal cycling chamber used for accellerated life testing of TIMs.
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To quantify reliability parameters, accelerated life tests are performed on electronic devices, including all thermal materials, including thermal interface materials. Most new materials are implemented before enough testing time has passed to mimic a typical lifetime and determine failure modes of that material.
Standard accelerated life tests were adopted to mimic the reliability issues which would surface during a device’s lifetime, but in a time period which was testable in the device’s design stages.
One of the accelerated factors examined is severe temperature cycling. The standard temperature cycling test for thermal materials is to cycle the temperature up to 125°C for 1000 cycles.
Does this same standard cycling test apply to solder thermal interface materials (TIMs)? Yes, sometimes. Not always though. Some solder TIMS melt at or form composites that melt at temperatures below 125°C. One example is Indium’s alloy 1E (52In 48Sn) which melts at 118°C. For examples like this, temperature cycling is still an option, but the temperature cycles should be altered. Instead of running 1000 temperature cycles at 125°C, more temperature cycles should be run at a lower temperature to mimic the same stress level to the interface.
Posted August 7th, 2008 by Amanda M. Hartnett |
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Posted by Amanda M. Hartnett
Thursday, July 31st, 2008
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Solder TIMs are the bonding and joining material used to connect small, powerful dies to their substrates. Some of these dies are exposed to severe temperature conditions which cycle into opposite extremes during device operation. In April, Dr. Rudiger Bredmann with the University of Applied Sciences published an article about the reliability of these dies.
His article highlighted a point contrary to the theory I am familiar with, which is the negative thermal reliability issues associated with a shrinking die size. Although a shrinking die size does typically lead to a hotter chip which is difficult to cool, from a solder TIM perspective, a larger die is more heavily stressed by slow operating temperature cycles.
For this reason, Bredmann cites a trend that the larger the die size and solder TIM is, the fewer numbers of temperature cycles it takes for failure. It is written that the number of cycles to failure is “inversely proportional to the size (radius) of the solder joint squared.
Posted July 31st, 2008 by Amanda M. Hartnett |
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Posted by Amanda M. Hartnett
Thursday, July 24th, 2008
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The data is in! Indium thermal interface materials (TIMs) have been put through the rigors of reliability testing and been proven to pass the typical as well as atypical tests required by the thermal materials industry.
For obvious reasons, there is a maximum operational temperature each interface should be exposed to so that it does not melt in operation. For pure indium, the melting temperature is 156°C. A standard requirement of many cooling solutions is to withstand a bake test at 100°C, not too far below that maximum temperature. The good news…Indium TIMs passed this without a hitch.
The next obstacle of reliability testing is heat + humidity. For any metal, this is the ultimate test. Metals, especially at elevated temperatures are capable of oxidizing. When humidity is added to the mix, the impact on some materials is detrimental. The concern on a metal thermal interface material (TIM) was that the TIM may form excessive oxides and delaminate from its substrates. Fortunately, under the standard heat + humidity test, that did not happen and the pure indium TIM passed both reliability tests.
Posted July 24th, 2008 by Amanda M. Hartnett |
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Posted by Amanda M. Hartnett
Wednesday, July 16th, 2008
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As previously posted, Indium’s Table of Specialty Alloys and Solders contains hundreds of solder alloys used as thermal interface materials and for each of them, we have listed melting temperatures. The method by which these were calculated is a repeatable one using a piece of equipment called a Differential Scanning Calorimeter.
In this method, a small sample of the solder alloy is input into the system and slowly heated until the solder alloy melts. Throughout the reading, a graph is created, from which the solidus and liquidus temperatures are interpreted.
The graph appears as a steady baseline, and at the melting point of the solder alloy, a peak is generated (See Image). At the point where the peak first deviates from the baseline, the solder alloy has begun to melt. This is the solidus point. At the point where the deviation returns to the baseline, the solder alloy is completely molten. This is the liquidus point. The entire deviation period is defined as a phase change period.
The tolerance of the scan is related to the scan rate. The slower the scan, the more accurate the reading. The tolerance on a typical reading is +/- 3ºC.
If you have a question about the melting temperature of any of our solder alloys or a solder alloy you are purchasing from us, we will be happy to share the differential scanning calorimeter readings with you for your personal interpretation.
Posted July 16th, 2008 by Amanda M. Hartnett |
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Posted by Amanda M. Hartnett
Tuesday, July 15th, 2008
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Heat generation in a power chip. Chip can be cooled by a careful selection of solder TIM and heat sink.
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Devices with pulsing power are often among the most critical to cool due to the temperature-sensitive films they are packaged with. If these films overheat, the resistance running through the package may become altered which complicates the device performance.
There are various common heat sink/solder TIM combinations to choose from depending on the nature of the device. For instance, in the most difficult cases, (those with high frequencies and long thermal cycles) a popular choice is a Copper/Tungsten heat sink used with a TIM closely matched in CTE. One possible choice is gold/germanium preforms, which can be used to create a hermetic package. When the thermal requirements of the pulsing device change however, such as going to a shorter thermal cycle, often the CTE stresses decline and other choices (which are often more economical) in heat sink and solder choice become available.
If you would like help designing your heat sink/TIM design in a pulsed power package, please contact an indium application engineer for material suggestion and design advice.
Posted July 15th, 2008 by Amanda M. Hartnett |
Want to read more? Browse the archive of past entries.
