Indium Corporation Blogs

The attachment of concentrated photovoltaic (CPV) cells is the perfect application for NanoFoil^®. Due to the isolated heating during bonding, less stresses are imparted due to coefficient of thermal expansion. Unlike conductive adhesives or epoxies, NanoBonds® are full metal interfaces which offer higher conductivity values. These 2 points together reveal how NanoBonding incorporates the main advantages of other bonding technologies. This sounds great, doesn’t it? Well, here’s the catch:

Most people have experience gluing parts together, and many handy engineers have learned how to solder wires, pipes, or other common items in the past. In contrast, very few people have ever dealt with a bonding process like NanoBonding. The principal of NanoBonding is simple, but it does require a small amount of research. Luckily, you’re in the right place. From here you can browse the many posts regarding the NanoFoil^® material and the NanoBond^® process. After learning the basics, simply click on one of the contact buttons on this page or follow this link for tech service. Our technical support team can help you become confident with the technology quickly.

When dealing with bonding, we often mention CTE (Coefficient of Thermal Expansion). This is a very important topic when designing a soldered interface, whether you are choosing materials that will expand and contract at the same rate or bonding alloys or processes that will handle the stress of deformation caused by these changes. This topic has been explored by hundreds of people, but I like this video because the presenter is both thorough and fun:

A NanoBond^® acts like a traditional solder bond in many ways. After reaction, the bulk properties of NanoFoil^® are similar to that of many solders. To me, the property that is most attractive (since it is similar to that of a solder) is the thermal conductivity of reacted NanoFoil^®.

Just like tradition solder bonds, NanoBonds far surpass the thermal conductivity of conductive epoxy (by around 6x-10x), making it an exceptional material for thermal interface applications.

 

If you’d like to try NanoFoil^® for a thermal application, kits are available here.

NanoFoil^® has many uses, and, sometimes, it has more than one function in an application. For instance, if tin coated NanoFoil^® is used in an interface, it functions as a heat source AND as a source of solder. Indium-coated NanoFoil^® has even more functions in a thermal interface application: it is a heat source, a source of solder, and a heat transfer medium. With a thermal conductivity of 25-30W/mK for the Ni/Al intermetallic and ~86W/mK for the indium coating, this is a highly conductive package – allowing proper heat transfer and minimal temperature excursion for the component.

To learn more about NanoFoil^® or other thermal interface materials, send our tech guys an email!

~Jim

March 13th is the 78th anniversary of the founding of Indium Corporation.  Dr. William S. Murray, J. Robert Dyer JR, and Daniel Gray combined to create a company that was, in 1934, on the cutting edge of technology at the time - and that still is today.

Although some of the initial attempts to utilize indium were decidedly low-tech (plating of silverware and use in gold dental alloys), the first real breakthrough came when Mr. Dyer developed the process to indium-plate aircraft engine bearings to make them last longer.  Today our indium metal is in thermal interface materials, batteries, medical devices, aerospace devices, solar panels, flat panel displays. Of course, the full range of Indium Corporation products (including materials that contain no indium at all) can be found in a myriad of electronic devices.  We hold a wide variety of patents and have conducted endless tests and experiments including some aboard the space shuttle.

In between we have been featured in the Wall Street Journal, Business Week and many other technology journals and received awards for our technical expertise and our customer service.

Our original founders were very "hands on" in their approach to developing their company and we still follow that approach today.  Our sales and technical staff, locally located around the world, are as comfortable in a lab or on a production floor as they are presenting a technical paper.

Contact us at AskUs@indium.com to utilize our expertise and let us help you with your challenge.

Shown here is an original bottle of indium solder preforms with a hand written label.  Today we have a variety of packaging options with printed labels and bar codes to fit your product and application.

Carol Gowans cgowans@indium.com

 

Folks,

Patty is getting ready for her meeting on "Copy Exactly" with Mike Madigan.......

It was after 6:30 PM and Patty was just arriving home.  Since Patty was working late, Rob had agreed to make his signature dish, crispy macaroni and cheese.  Patty and Pete had just finished their project to develop a copy exactly strategy for ACME.  They would present it tomorrow to CEO Mike Madigan.  The local GM, Sam Watkins, would be there too.  Technically Mike was her boss in her Senior VP position, but since she had an office at the ACME facility in Exeter, NH, she reported to Sam - “dotted line.”  Patty had been working late for weeks on this project and was glad that the greatest portion of the work was over.

As she opened the door to her house, her twin 2 year old boys ran up to her in their excitement to see their mom and nearly knocked her over.  She tussled with them for a few minutes and then went to give Rob a hug.  He had the dinner on the table and they all quickly sat down.  Rob and Patty had a "no technology" rule at meals…..no mobile phones, iPads etc.  Meal time was family time.  After discussing the events of the day, Rob’s face lit up.

“I found out today that there is something we look at more than anything else,” Rob stated.

“OK, OK, let me guess,” Patty replied.

After a number of tries, she hadn’t gotten it.

Alright, I give up, Patty said with playful exasperation.

“Indium, or really Indium Tin Oxide (ITO), it is a transparent conductor of electricity.  We look through it when we look at our computer, tablet or mobile phone screens.  Think about it, for most of us we probably look through ITO for 8 to 10 hours a day.  It’s like we have a love affair with the stuff,” Rob explained.

Patty almost choked on some of the mac and cheese on the last comment.

“Why have you become such an expert on this stuff?” Patty asked.

“Well, you remember that ACME may go into component assembly? Sam asked me to look into indium thermal interface material (TIM)  for some of the component packages that need to dissipate a lot of heat,” Rob answered.

Patty knew a little bit about TIMs, but not about ITO.

“But why did you learn about ITO?” she asked.

“Sam is worried that Indium supplies may not be enough to satisfy TIM requirements, so he asked me to look into it,” Rob answered.

“What is the conclusion? Patty asked.

“Well, Indium is about as common in the earth’s crust as silver, but a little more difficult to extract.  This probably gives it the reputation of being rare.  Fortunately for me a recent analysis was performed that showed that the indium supply will be more than adequate for the next 75 years ,” Rob said.

Rob went on, “Indium is a very interesting material, it is one of the few materials that wets glass, so it enables metal sealing to glass.  It was only discovered in 1863 and it wasn’t until the 1930s that the first practical use for indium was discovered: aircraft bearing lubrication.  In a sense, it could be argued that it is one of the materials of the future, as we are just now learning about its potential.”

While he was talking, Rob reached into his backpack and took something out.

“Look at this, or rather listen,” Rob said.

With that, he took a thin bar of metal and bent it. A crackling sound came from the metal.  Patty was fascinated.

“What was that?" she asked.

“When a thin bar of indium is bent, it gives off a sound.  It is called “Indium Cry.”  The salesman for the TIMs we are using let me borrow it for a presentation I am giving to Sam Watkins next week,” Rob answered.

Dinner was soon finished and Patty had to get the boys to bed after playing with them for awhile.  Today was Spanish day and all of their discussions were in that language.  Another day was Mandarin Chinese day.  The boys already understood the three languages spoken at home.

A few hours later, Patty lay in bed - energized by the thought of her meeting tomorrow.

When she woke up the next day, she exercised at home, ate breakfast, and took the boys to day care.  See arrived at the office 30 minutes before the big meeting.  After checking emails, she went to the conference room where the meeting would be held, to set up her computer.  At precisely 8AM, Mike Madigan and Sam Watkins arrived.

“OK Coleman, let’s get this show on the road,” Madigan commanded.

“Since our last meeting we have analyzed assembly equipment and materials to determine which ones would be best for a copy exactly strategy,” Patty began.

She then showed her third slide and spoke to it.

“The winner for component placement equipment is Optoplace, as are their stencil printer and reflow ovens.  Exactotest makes the winning testers and ElectoMaterials the best solder paste and solder preforms,” Patty went on.

“Can you explain your methodology?” Sam asked.

“We looked at what The Professor calls ‘Profit Potential,’ simply the equipment and material that gives the most profit, assuming you are running a well tuned organization.  Fortunately, since ACME has 80 assembly lines we were able to get real process performance data on all of the major machines available, ” Patty answered.

“You answer seems a little evasive, why didn’t you use ‘Cost of Ownership?’” Madigan challenged.

“Some machines cost less to own, but they are down more for assists and when they need repair, we have to wait longer for the repair man.  From what The Professor taught us, uptime is very important. Anything that hurts uptime, like a late repairman or a machine that needs more assist time, will hurt profits.  The same is true for materials like solder paste.  If they cost less, but result in line downtime for response to pause issues or some other fault, they hurt profitability.” Patty responded.

Just then Sam’s administrative assistant, Clare Perkins opened the door.

“As you requested Mr. Madigan, your guest is joining the meeting,” Clare said.

“Well Torant, looks like Coleman said you lost,” Madigan said to the new arrival.

Upon seeing Rex Torant, Patty became a little unsettled and Pete turned his famous crimson red.  Patty and Pete called him “Rex the Torrent” as he spoke so rapidly when trying to sell them something.  Both found this manufacturer’s “rep” annoying.

“Everyone, I invited Rex to the meeting.  We met at the airport last night and started chatting.  He assured me that his Pinnacle equipment line and Ultima solder paste would be the winners today since they have the lowest cost of ownership,” Madigan explained.

Torant saw the slide announce Optoplace, Exactotest and ElectoMaterials as the winners.

“My products are just as reliable and cost 30% a year less to own,” Torant fumed at Patty.

Patty had not anticipated Torant’s attendance at the meeting but had prepared for this type of question.

“Mr. Torant is correct, however Pinnacle’s component placement machines have more downtime for machine assists and, when the equipment does malfunction, it is down for repairs on average for 28 hrs, whereas Optoplace is only down for 14 hrs.  All in all, Optoplace machines are up 6 hrs more a week in a two shift operation,” Patty calmly responded.

Will Patty’s arguments win the day?  Can a 30% more expensive machine really have more “Profit Potential?”  And what about the solder paste and materials?  Stay tuned.

Cheers,

Dr. Ron

 

image

As reported in Metals Bulletin, Malcolm Harrower of Indium Corporation recently addressed the topic of indium availability and supply as he told the delegates at the Minor Metals 2012 conference in Brussels that:

• there is no shortage in the supply of indium metal
• nearly 1,500 tonnes of indium was produced in 2010
• there are 50,000 tonnes of proven indium reserves in existing mines, a volume that will be sufficient to satisfy demand for the next 75 years,

Just 80 years ago, the potential for indium was just being discovered.  An article that I found in the archives of Science News from 1932 indicated that 10 lbs. of indium was due to be produced that year and it would give scientists a chance to do some great research on the possible uses of indium.  Twelve years later in 1944 another article was written on one of those uses which was to lubricate ball bearings to make them last longer (an application still in use today).  That article stated that the output had reached 500,000 troy ounces (34,250 lbs). 

Now 80 years after indium was first commercially produced, the yearly output has reached nearly 1,500 tonnes (3,300,000 lbs) per year, with about two-thirds of that being reclaimed and recycled material.  The versatility of indium has certainly driven that growth into all kinds of applications including:

1) Touch screens

2) Battery chemistry

3) Electronic thermal interface materials

4) Solders

5) Cryogenic and hermetic sealing

6) Solar panels

And as technology evolves, we expect to see more uses as time goes on.  Learn more by visiting our web site at www.indium.com. Or email/call me to discuss your needs.

Carol

cgowans@indium.com

+1-315-853-4900

Here is a question that was posted and answered on our website back in 2006, I think it is still quite relevant:

Question: “Why does your Application Note for cleaning of indium ribbon for thermal interface recommend a mild (5-10%) HCl acid solution, yet [the] MSDS for Indalloy #4 (100%) says to avoid contact with acid? My past indirect experience with indium usage indicated some cleaning procedure of the oxides was necessary to achieve good thermal contact resistance.”

Answer: “Thanks for contacting the Indium Corporation with your request. If the indium ribbon is stored and handled (stored unopened in an argon or nitrogen pack – placed in a dry box) properly and it solders well in your process, this procedure should not be necessary. When following this procedure, the HCl solution should be applied to the indium metal to clean it thoroughly, and then dried with nitrogen.”

If you want to know more about metal thermal interface materials (TIMs) (handling, preparation, or process parameters), send an email to our global technical team at: askus@indium.com. They are ready to answer your question!

~Jim

Indium Corporation is hosting a booth (#809) and will be highlighting a series of products and solutions related to all aspects of LED and lighting manufacturing and assembly at Strategies in Light, Santa Clara, CA, February 7-9, 2012





The show is a who's who in the global lighting industry. Along with the exhibition, there is a full line up of workshops and tutorials encompassing the latest in LED and lighting technology.





Indium Corporation is proud to be a part of the Strategies in Light trade show.  Please stop by and see us. Technically orientated staff will be available to discuss your application, as well as: 



Indium Compounds

Gallium Compounds

Thermal Interface Materials

Gold Alloy Assembly Materials

Unique Bonding Materials and Techniques

最近又有些客户在询问我们公司的铟indium，用作散热材料(TIM--thermal interface material)。其中一个客户是做工业用的激光器。这个客户希望在他的瓷片间隔的两端用一种高效能的散热材料。

纯铟是一种散热效能极高的金属材料，热传导率能到达86W/cm.⁰C. 而且铟是一种软金属，能够“型变”。如果接触面两端有一定的压力，能够很好的把铟夹在中间，那么散热效能更好。

Indium 公司还有一种以铟或是铟锡为材料做成的TIM,叫做HeatSpring^R. HeatSpring^R 的特别之处是我们做了一定的表面加工处理，使其能够和两个接触面更好的全接触，达到全面散热的功效，而不是因为有些地方有接触，有些地方没有接触，导致局部过热。如果切开看HeatSpring^R 的横截面，你会发现它的横截面不是平的，而是有点像高低起伏的锯齿形状。

下面这两张图能够更好的说明HeatSpring^R 随着时间的增加，在热循环(thermal cycle)测试中热传导效能保持得很好。两外一张说明HeatSpring^R在一定的压力下，热传导性能大大好于别的一些thermal grease, thermal pad等硅胶材料。

目前，HeatSpring^R 被广泛地应用在IGBT,RF/PA（Power Amplifier功率放大器），TIM1,TIM2, 高功率高亮度LED，各种激光器的散热等方面。

Cheers!

Pic: Indium Corporaiton   

A new patent has been published for a liquid metal gallium plus carbon nanotube thermal interface that may capture considerably more of the thermal conductivity benefit claimed by researchers of carbon nanotubes (CNTs) than has been possible outside of a laboratory setting previously.  

Admittedly, I am embarrassed not to have come up with this thermal management concept myself! I was so close, and yet so far away. Previously, documented back to 2008, I described how conductive metals are in their liquid state. Those atoms get moving and shaking, and the heat passes right through! 

I also balked at those touting their CNTs…. The technology wasn’t there! Carbon Nanotubes cannot be affordably grown on substrates to make a commercially-affordable thermal interface material, and if you grow them, cut them down, and try to re-apply them, they are no longer oriented to directly connect substrate layers, and the resultant interfacial resistance between tubes adds up fast. 

Well, this patent reveals that Foxconn put 2 and 2 together to make what I’m gambling to be an outright GREAT Thermal Interface Material!!! This patent calls for carbon nanotubes suspended in liquid metal. That liquid metal fills in all the tube-to-tube gaps, and as fast as the heat comes in, it moves on out!

So, for those of you with carbon nanotubes, Indium has the liquid metal, numerous types in fact, to suspend them and make a great thermal interface material.

I love learning new technology, just wish that I had the clarity to have pursued something so obvious myself!

Have fun testing!

Amanda

A fisherman and tech guy at heart.
Ross Berntson
VP Sales Marketing and Tech Support

Here is a story of a PC, a thermal management problem, an advanced metal thermal interface material, a family that was about to mutiny, and a glazed donut. Spoiler alert: This story has a very happy ending.

Background: Our kitchen computer is an HP Slim Line with an AMD Athlon 32 bit processor.  The entire family uses it – and it is now fully cluttered with downloads, games, school programs – you name it.  The tray is filled with programs from who knows where.  In other words, it is the typical family computer – cluttered, SLOW, and NOISY.

Scene 1: My family began complaining about the computer’s resultant speed.  Being a tecchie, I immediately activated the CPU monitor, learning that it often was not running at full speed. The family also complained that simply booting the computer up was taking forever.

The complaints grew more dramatic with every passing day.

Scene 2: My personal complaint was that the fan was excessively noisy.  During dinner and breakfast, with no one working on the computer, the fan would cycle on and off at FULL SPEED. WRRRRRRR (fan noise)  – pause – WRRRRRR – pause –  WRRRRRR.  Aaargh!

Scene 3 (things get intriguing): Initially, I thought the fan was bad.  However, my tech support mind got going and I hypothesized that what we had on our hands was a thermal management challenge. I decided to replace the Thermal Interface Material (TIM) with Indium’s high-end metal Heat-Spring® Thermal Pad.   Mindy Macisco, Product Support Specialist for TIMs, had some of our advanced Heat-Springs® on her desk and gave me one to try.

Scene 4 (taking action):
REMOVING THE POLYMER BASED TIM
With no difficulty, I pulled off the case, unscrewed the heat sink, and observed the grease-type TIM on the backside of the lidded package.  The heat sink was an integrated heat-pipe and fan assembly with spring loaded 4-point screw fasteners.  I grabbed my putty knife from my shop and set to work on removing the grease, thinking it would be a sticky mess.  Nope.  It had dried into a flaky crust (image - left). It scraped off cleanly, with almost NO greasiness.  I was reminded of glaze falling off an old dried-up donut (image - right).   I used a little WD-40 to do the final cleaning.

INSTALLING THE HEAT-SPRING®
Installing the Heat-Spring® thermal pad was easy. I simply placed the TIM in the center of the CPU lid and began reassembling with a random tightening of the screws (tightening each a little bit before seating them completely).  As my friend Guido says, ‘Easy peasy’.

Scene 5 (resolution):
RESULTS
For the family, the computer is instantly faster!  For me, no more WRRRRRRRRRR.  The Heat-Spring® metal thermal interface material solved BOTH problems!!!

Fade to black as I head out the door with my fly rod!

Solder wire is generally used for manual soldering operations, including rework.  But, it can also be used in automated applications such as die-attach soldering.  Solder wire can be flux-cored, or solid with a separate flux used.

Each application can have different requirements for the wire.  For example, wire used in die-attach applications needs tight dimensional tolerances to insure an exact, repeatable amount of solder is deposited each time.  Reduced oxides are also critical to eliminate any "splattering" of the molten solder during the deposition process.

Wire can also be used for non-soldering applications. For example, indium (and indium alloys) wire are often used as a sealing material (particularly in cryogenic sealing applications) - more here) and as a thermal interface / management material.

Decades ago, 0.030" (0.76mm) diameter was the standard size, but today we are able to produce diameters as small as 0.001" (0.025mm) in tin silver (Sn Ag), tin silver copper (SAC) and gold tin (Au Sn) alloys.  Considering that a human hair is about 4X that size, that is a very small diameter!  Pure indium wire is limited to 0.010" (0.254mm), but alloys containing indium can be produced smaller than that.

The wide variety of diameters available in Au Sn make this alloy ideal for the complex applications in medical, aerospace, and other high reliability applications.  However, the Sn Ag and the Sn Ag Cu are used across a variety of standard applications that require lead-free materials.  Sn Ag is particularly good in soldering to Nitinol.

At first look, wire seems like a pretty simple product.  But specifying the right alloy, diameter, tolerances, and packaging can make all the difference.  It can help you achieve a repeatable process that gives you high yields, strong solder joints, and enhanced profitability.  For further information - contact me.

Carol Gowans

Power amplifiers and transistors come in many shapes and sizes. The performance requirements vary as well. Attaching them can be a critical aspect of your design.

Both Pb and Pb-free alloys can be manufactured as a solder preform with a flux coating.(Learn more)  Selecting the right alloy and flux coating can be crucial to meeting your void criteria.  

A high-tech SOLDERING solution might include NanoFoil®, which effects a solder joint while minimizing heat exposure to your components.

There are also thermal interface materials such as the HEAT-SPRING® which utilize the unique properties of indium to create a superior thermal connection, similar to a solder joint.

There are many different attachment methods available, contact me with your design parameters and we can find your solution.  

Sampling, receiving, and testing indium Heat-Spring® compressible thermal interface materials are easier than ever! Not only are standard samples (solder research bundle kits) available for testing on the indium E-Commerce thermal interface material website, but now a Heat-Spring® video has been released depicting exactly what you can expect – what they look like, how they are packaged, how they are handled, and how you can get them. 

 

So watch, learn, and all-the-while enjoy the jiggy music that this new video has to offer!

Then, if you still have questions, before or after you receive your samples, give me a shout!

Note: These compressible thermal interface material samples are offered in limited varieties meant to suit the majority, however custom-engineered thermal interface materials are also available for your outside-the-box needs. 

最近有一个客户，在咨询我们公司的散热材料，用以更好地解决他们产品中IR Detector （红外探测器）的散热问题。

根据百度的介绍“红外探测器(Infrared Detector)是将入射的红外辐射信号转变成电信号输出的器件。红外辐射是波长介于可见光与微波之间的电磁波，人眼察觉不到。要察觉这种辐射的存在并测量其强弱，必须把它转变成可以察觉和测量的其他物理量。一般说来，红外辐射照射物体所引起的任何效应，只要效果可以测量而且足够灵敏，均可用来度量红外辐射的强弱。现代红外探测器所利用的主要是红外热效应和光电效应。这些效应的输出大都是电量，或者可用适当的方法转变成电量。”  

就是因为有大量的电量，就会产生热，就会有散热问题(Thermal Issue)。 目前，客户的IR Detector下面用的是TEC半导体致冷器, IR detector和TEC之间用的是环氧树脂 epoxy. 但是因为epoxy的导热效能一般只有2w/mk, 容易老化(bake out)，各个接触面也很有可能不均匀(pump out), 而且使用起来比较麻烦messy, 所以现在有更多的朋友们在寻求更好的解决办法。

Indium公司提供的TIM（thermal interface materials）都是基于金属材料。 很多金属材料本身就比化学材料有更好的导热性thermal conductivity。 Indium公司专利的可压缩性TIM---HeatSpring （compressible TIM），导热效能高86w/mk, 不会老化，接触面均匀，使用方便。“There are lots of HEAT in the world this year; It is the ‘HOTTEST’year for TIM!”。在这许多电子产品微型化，多性能，高功率，对散热的要求越来越高的“大热年”里，我们十分乐意和你一起分享更多关于Indium公司TIM材料方面的信息，为你度身订造出更好的解决方案！欢迎随时联系我们 askus@indium.com !

Cheers!

 

Pic: Google Image

昨天先生终于带回来了刚刚上市的Kinect! 我们也一起感受了这个新技术产品带来的游戏娱乐。

以前的Wii或是别的电脑/电视游戏，游玩者都拿着或是触摸一些固定的设备---感应器，遥控器，键盘，或是鼠标等。Kinect的发明，能遥控感应人体各个部位动作发出的信号，不需要人体在“附加”其他硬件；这让游玩者更能全身心地享受游戏的乐趣。

出于好奇（我不想那么快就拆了家里新的Kinect）, 我上网查了一下Kinect的组成，特别是电路板的构造。乍看之，其实也不是特别复杂的板子或是特别密或是小的难组装的元器件。Kinect是用小风扇和heat sink来处理散热问题的，其实也可以考虑我们Indium公司提供的一系列散热材料(TIM---Thermal Interface Materials) J

在玩Kinect的过程中(这里指英文版本的)，如果你想换代表自己的小人图像，可以选择“Change Avatar”(中文就是改变人物图像的意思)。大家都知道Avatar阿凡达是一部著名的电影。这让我想起了电影中各种的高科技，特别是人可以在“空中”随时调出一台电脑的界面，并且电脑界面根据人手指的“非触摸”动作，能够执行指令！ 哈哈，不知道那一天有多远。

还是那句我很喜欢的老话“科技以人为本”！

Cheers!

Pic:
1. http://www.simplemobilereview.com/new-xbox-360-4gb-ships-aug-3-and-kinect-and-connect-bundle-for-holiday-season/
2. http://www.gamesradar.com/xbox360/kinect-sports/news/naked-kinect-pics-are-sexy-geek-porn/a-2010080611184826095/g-2010061320105946075
3. Youtube video

PS: 先生最近在研究的项目之一，就是把Kinect这种人体动作“非触摸指控”的技术，应用到电脑中来。热切期待中！

I have previously discussed various reasons why thermal considerations in a device cannot be an afterthought. There are various methods for handling the thermal needs of a device before it becomes a problem. One of my well-known colleagues, Ross Wilcoxon, Principal Mechanical Engineer at Rockwell Collins, knows a great deal about these. His article, “a spreadsheet based matrix solution for a thermal resistance network: part 1” was highlighted in Electronics Cooling Fall 2010, and in it he discusses a method using Excel to do thermal resistance modeling. 

 

My inquisitive nature couldn’t let the article stand on its own. I had to tack on a few more questions. Ross was accommodating enough to help me out.  

 

[Amanda Hartnett] Why is it important to characterize the thermal resistance of each material used in a device?  
 

[Ross Wilcoxon] It may not be - sometimes the best lesson learned from a resistance network analysis (or any modeling effort for that matter) is determining which things are really important to the final results (component temperatures, reliabilty, etc.) and which things aren't.  For example, if the aluminum chassis in a system plays a critical part in the overall thermal resistance and has a large temperature gradient, then it is pretty important to know what alloy it is so that you can better estimate its thermal conductivity.  On the other hand, if the chassis is pretty much uniform in temperature, then knowing exactly what its thermal conductivity is probably doesn't matter so much.
 

[Amanda Hartnett] What information is needed from the material vendors in order to complete a resistance network analysis?
 

[Ross Wilcoxon] Obviously, thermal conductivity is a good start and if you are doing a transient analysis (I plan to talk about that in part 3 of the series that I would like to do for Electronics Cooling), information on specific heat and density are pretty important.  For interface materials, the overall interface resistance is needed more than the thermal conductivity.  In many cases, it would be really nice to have data not only for nominal values but also some indication of uncertainty.  The resistances in a thermal network can be calculated using best or worst case numbers as easily as they can with nominal material properties.  It is pretty easy to switch between these values within the spreadsheet and it is a good way to get a feel for how important knowing the precise value really is by looking at how varying between best and worst values impact the overall temperatures.  Also, I have done a few spreadsheet based Monte Carlo simulations for getting my hands around the cumulative effects of uncertainty in things like thermal gap fillers and a thermal test stand.  For that type of analysis, you have to have some understanding of the uncertainty as well as the nominal values.
 

[Amanda Hartnett] Could a model like this be used to characterize the effect of degradation in a single layer?
 

[Ross Wilcoxon] I guess I'm not sure exactly what you mean on this.  If the effect of the single layer (I suppose you mean a thermal interface material) is accounted for in the thermal resistance calculation, sure - you can just apply a factor in the equation to account for something like voiding to say that the effective thermal conductivity of the interface material decreases by X% to assess how much that impacts the overall effect.  I suppose it just comes down to how complicated you get in converting material and geometry parameters into thermal resistance.
 

[Amanda Hartnett] In a typical cooling solution, have you found that one boundary was more critical than another?
 

[Ross Wilcoxon] In a lot of cases, the thermal battle is lost in the first mm of the thermal path (the interface between a component and whatever it is attached to - I bet you like that answer, huh?!) but in a lot of our systems the choke point is in the last mm (moving the heat from the system to the surroundings).  One of the big benefits of network resistance analysis is the fact that you can very easily adjust the resistances, including these boundary conditions, by just changing a couple cells in the spreadsheet. This can give a good feel for which parameters are the most critical and what needs to be better understood.  For example, in the next article for Electronics Cooling (assuming that I get it written), I plan to talk a bit about an analysis that I did for some of our equipment going into a missile pod along with equipment from a number of other suppliers.  At the time of the analysis, we didn't know certain details about things like the surface finish to which we were attaching our module, the specific alloys in the missile pod, etc.  Having a quick-look analysis tool helped us determine which unknowns were really critical for the thermal analysis and we could concentrate in chasing down that information.
 

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Ross – Thank you for your time and for sharing your knowledge and experience!  

I’ve received numerous questions about using gallium liquid metal alloys, so thought I’d present some of my answers for all.  The customer questions are in black, and my responses in red.     

1. Indium’s product data sheet, "Indalloy Metals Liquid at Room Temperature" mentions that "any liquid metal will wet another clean metal surface". Can you please elaborate on the conditions that make such wetting possible? 

As far as wetting, gallium alloys (Indalloy 46L, Indalloy 51E, Indalloy 60, etc.), coat nearly any organic, ceramic, or metal surface. It is difficult to come up with materials used in packaging and processing these alloys that come clean of the alloy after use.   The physics of this affinity is unknown, however the low melting point and surface tension are the source/consequence.

 

Many metals will form some alloy with the gallium, but the solubility in gallium is limited. The gallium wets the surface and forms a solid gallium-alloy layer, which then acts as a diffusion barrier. In the case of aluminum, gallium forms an amalgam which ends up consuming a large volume of aluminum before a stable solid layer.

2. Do you assume an oxygen atmosphere (gallium oxide does wet most surfaces)? Or, to the opposite, do you refer to the wettability of plasma-clean metal surfaces?

 

3. Can you let me know if Indium Corporation sells droplet dispensing equipment for liquid solders/metals?

 

Liquid metals are typically offered in a syringe and various needle gauges can be screwed to the tip to adjust the dispensed droplet size. For dispensing thin layers of liquid metal, such as for a thermal interface, we recommend PVA selective coating equipment.

 

4.  We are interfacing our thermoelectrics with both steel and aluminum and the hottest point will be around 600°C. Can liquid metals be used for this?

InGa alloys are selected typically because they remain liquid at all times, negating any contact resistance between substrates.  The typical application for these has temperatures up to approximately 100°C or slightly higher.  At these temperatures we have noted some aluminum corrosion by the gallium, which will only become worsened by your elevated temperature. 

There are other alloys which do not contain gallium and have only a slightly higher temperature, such as the Bi/In alloys. At 70°C, the eutectic composition of this alloy will also be liquid in phase, however is much less reactive with your bonding metals, and therefore may be better suited.  

最近在一些客戶拜訪中，許多客戶對我們Indium公司各種形態的銦金屬都頗感興趣。以前，我也只是知道銦在導熱界面材料中(TIM: Thermal Interface Materials)中所起到的重要作用；但是和各種不同application的客戶們交流，也讓我自己更進一步的學習和了解到了銦的其他廣泛用途：

²       indium 低的蒸汽壓常數能使它應用在高真空的環境中

²       indium 自己就能夠冷焊（cold weld）在一起，bonding兩個要組裝的部件

²       indium 加入合金中，能很有效地減低焊接合金的熔點溫度

²       少量的indium也能大大增強焊接材料的抗疲勞表現（thermal fatigue）

²       indium 可以與玻璃，石英等一些陶瓷材料bond在一起

²       indium 有很高的熱膨脹系數(high CTE: Coefficient of Thermal Expansion), 是兩個有很大CTE差別的連接面，都能很好的bond在一起。

Indium公司提供3N (99.9%), 4N(99.99%), 5N(99.999%)或是更高純度的銦金屬。 歡迎聯係  metchem@indium.com.

Pic: Indium Corporation.