Indium Corporation Blogs

Folks,

In the category of interesting requests, Ron, a gold worker, from Guyana, sent me the following note:

Dr. Ron,

My colleagues use a “wet” gold technique to measure gold alloy density.  Is this valid?  Where does the formula come from?

Sincerely,

Ron

Well, to tell the truth, I had never heard of it and was skeptical.  How can you measure density (mass/volume) by only measuring weight?  So, I investigated. The technique claims that one can measure density with only a scale, by measuring the alloy’s weight in air and in water.

I could find no derivation, so I thought about it and derived it on my own.  As far as measurements go, as stated, you only have to measure the weight in air and water.  If you don’t have a scale that can handle being immersed in water, you can use a hanging scale (think weighing a fish).  So, after weighing the alloy in air, you immerse it in water. It will weigh the amount of water it displaces less.  The derivation is below:

As an example, let’s say you have a gold alloy ingot that weighs 1,000 grams (OK, I know grams is mass, but we are all sloppy and use it as weight, too) in air.  You weigh it in water and it weighs 930 grams. From the formula below, the alloys density is:

r = 1000/(1000-930) = 14.29g/cc

Since the density of gold is 19.3g/cc, the alloy is not pure gold.  If you knew the alloying element, say copper, you could use Indium’s Solder Alloy Density Calculator to determine that the alloy was 69.8% gold, 30.2% copper.  If there are multiple alloying elements, since most of the common elements have a density of about 9 g/cc, you can even estimate the fineness of the gold.

Could this technique be used to measure the alloy density of say a handful of solder preforms. Sure, you could put them in a woven bag of non-hygroscopic material and weigh them in air and water.  Admittedly, measuring the density of solder paste, with this technique, would be a challenge.

Next posting, I will show how this technique is used to measure the quantity of gold in gold/quartz ore.

Cheers,

Dr. Ron

There have been a variety of people who were key to the development of indium metal in general, and Indium Corporation in particular, over the years.

People such as:

• Hieronymus Theodor Richter and Ferdinand Reich who discovered indium metal in 1863
• Daniel Gray, William S. Murray and J. Robert Dyer who formed the original Indium Corporation back in March of 1934 and who hold patents on processes and applications involving indium
• Frieda Nojeim who joined the company in 1966 and was elected vice president in 1971

 

And, in 1972, Charles E.T. White joined the Indium Corporation as a vice president (he was elected executive vice president in 1981).  I had the pleasure of knowing Mr. White before he retired.  He was indeed a character, but he also knew a LOT about indium.

In 1986 (a lifetime ago in the electronics industry) Mr. White published an article called: Indium: High Technology Metal in Advanced Materials and Processes magazine.  I ran across a copy of it the other day and, after reading it, was interested in how relevant it still is today, even though technology has marched forward.

Of course the physical characteristics of indium are still as valid today as they were then. 

• Resistance to thermal fatigue
• High thermal conductivity
• Wetting of non-metals (glass, quartz, ceramics)
• Malleability and ductility, even at cryogenic temperatures
• Electrical conductivity for a variety of screens
• Indium does not work harden

 

But one might expect the technology described in an article from nearly 30 years ago to have evolved or gone entirely away, resulting in the elimination of the need for the indium.  The truth is, many of applications that Mr. White mentioned still exist today:

• "Conforming gasket material for cryogenic vessels."
• "Indium is present in every wristwatch and computer screen that uses a liquid-crystal display."  Okay, so no one wears wristwatches anymore, but the screens on our phones (the new time-telling devices) have indium tin oxide coatings.
• "...used in lens blocking and in temperature-overload devices such as safety links, fuses and sprinkler plugs."
• "Many solder alloys containing indium have been developed to take advantage of indium's enhancement of thermal-fatigue resistance, reduced gold scavenging, and resistance to alkaline corrosion."
• "Glass sealing alloys containing indium ...have been developed for electronic device packaging where high temperatures cannot be used."
• "Indium's use in solder alloys is likely to increase as specialty solders become more important in electronic assembly techniques."
• "The whole area of conductive films of indium oxide and indium-tin oxide has good potential for growth.  This includes solar cells: silicon-cell efficiency can be improved with an indium or indium-tin oxide coating."
• "New applications such as solar cells made of indium-copper-diselenide/cadmium-sulphide are under active development."

 

And while these indium applications still exist today, R&D continues to find new opportunities for this very unique metal.  We have several Research Solder Kits that you can use to evaluate the value of indium in your process.  Just go to our e-commerce page or contact our engineers to see how indium can work for you.

Carol Gowans

Since the NanoBond^® process is almost instantaneous, fluxes are not used. (They just don’t have enough time to heat up to their activation temperature and remove oxides.)

So, because this is a fluxless soldering application, surface choice and preparation become very important. We no longer have the chemical power of a flux to break down surface oxides, instead we must make sure our surfaces are ready to be joined.

The first choice to make is: will you have solder on the parts to be bonded, or will you use solder-coated NanoFoil^®?

If you decide to use bare NanoFoil^®, the parts must have a solder finish such as pure indium, SAC 305, or tin. If you choose to use a solder-coated NanoFoil^®, you can bond gold and silver metallized parts.

 

Need help figuring out what to do? Ask us: AskUs@indium.com

*This post is part of the NanoBond^® Process series

The first time I was taught how to solder (as a child), I was told: “All the surfaces need to be mechanically cleaned and chemically cleaned.” The person who told me this was referring to pipes, I was learning about plumbing. (I would have never thought we'd be using nanotechnology to create solder joints!) Although your application is probably far from a plumbing job, the basics of soldering remain the same. The best solder bonds are formed when oxides and contaminants are not present.

These two points are taken care of in traditional electronics soldering by using a flux. Flux can flush away light contaminants like dust, and reduce oxides on certain metal surfaces. But, in the NanoBond^® process, we aren’t using flux.

Luckily, NanoFoil^® can power through the soldering process as long as the proper surface finishes are used, and they are ready to be soldered to. Different surfaces are prepared in different ways. Here is a list of some common surface finishes and what preparation they require:

• Gold – Wipe with isopropyl alcohol if aged
• Silver – Wipe with isopropyl alcohol if aged
• Tin – Remove oxides with 10% HCl if aged
• Solder coating - Remove oxides with 10% HCl if aged
• Aluminum – Add solder coating
• Molybdenum – Add solder coating
• Titanium – Add solder coating
• Naval Brass – Add solder coating

And for any surface you don’t see, feel free to contact askus@indium.com so we can find a solution for you.

 

*This post is part of the NanoBond^® Process series

One of the biggest misconceptions about NanoFoil^® is that it is a form of solder. While it may contain a solder coating if specified (usually tin), it is really a heat source. A NanoBond^® requires solder, whether it comes from a plating on the joining surfaces, additional solder preforms, or on the NanoFoil^® itself.

Surface Coating

There are many ways to deposit solderable coatings onto parts that will be NanoBonded. Sputtering, thermal evaporation, thermal spray, plating, and HASL (hot air solder leveling) are just a few of the options. Coating the parts that will later be bonded tends to make assembly a bit easier.

Solder Preforms

If the parts have a gold or silver surface finish already, a thin solder preform is a very simple way to apply solder in the assembly. Preforms are sold as custom-shaped foil for your application.

NanoFoil^® Coating

Although Sn is the most popular solder coating for NanoFoil^®, it has been custom plated for individual customer applications with indium, traditional solder alloys, and even Au/Sn.

By the way, make sure there is solder on both sides of the NanoFoil^®. I almost overlooked this very point today while I was bonding a set of industrial batteries. There was solder on the battery terminal, and I was about to use bare NanoFoil^® to bond it to a gold plated board. Luckily we had some tin plated NanoFoil^® that I used instead – to ensure there was sufficient solder on the board side of the interface.

 

*This post is part of the NanoBond^® Process series

Individually, indium and gallium each have some pretty interesting characteristics.

Gallium is liquid at 30°C (86°F) and, because it is less toxic than mercury and has a lower vapor pressure at higher temperatures, it is used as a mercury replacement in thermometers and other applications. 

Indium, as I have discussed in previous blogs, has many unique characteristics including high thermal and electrical conductivity, resistance to thermal fatigue and reduced scavenging of gold in soldering.

But, combine the two, add a little tin, and the resulting alloys are liquid at, and below, room temperature (8°C to 25°C) and are very effective in conducting or dissipating heat away from temperature sensitive components. They can also conduct heat and/or electricity between metallic and non-metallic surfaces.

A recent study published by researchers at the McCormick School of Engineering, working with scientists around the world, discusses the use of an indium-gallium based alloy (EGaIn) to make stretchable electronics.  The indium-gallium content overcomes the loss of conductivity that occurs when the material is stretched.  The liquid alloy allows the "electricity to flow consistently even when the material is excessively stretched".

In 2009, researchers at the North Carolina State University used InGa to form antennae that would not break.  Again it is the flexibility and the electrical conductivity of the liquid alloy that make this work.  Michael Dickey and Gianluca Lazzi who headed the research, indicated they "were surprised" that the alloy operated at about 90% efficiency, similar to the efficiency of copper.

So whether on their own or combined, indium and gallium can be the solution to a variety of electronic challenges faced today.  The Possibilities Are Endless!

Carol

Maria Durham, Indium’s new Technical Specialist in Semiconductor and Advanced Assembly Materials, has been doing some research on indium lead (In/Pb) solder alloys. We chatted about her findings this week. 

 [Andy C. Mackie: ACM] Which indium/lead solder alloys are most common, and what are their properties?

[Maria Durham: MD] Firstly, the use of lead-(Pb-)containing solders in some soldering applications is restricted due to local environmental and RoHS compliance, but there are still many applications where they are  allowed. Many military, aerospace, and industrial equipment uses, as well as many applications related to vehicles, are exempt. The table below shows the most common indium/lead (In/Pb) alloys (pink) and their properties, sorted by liquidus temperature; the higher of the two melting points (solidus and liquidus) seen for non-eutectic alloys. In blue are three comparison materials.

 

Indalloy 205 is the most commonly used, probably because it has the closest liquidus temperature to the tin/lead eutectic (183°C), 63Sn/37Pb (Indalloy 106). This means it can be reflowed using a standard Sn/Pb eutectic profile. The next most common alloys that are used are Indalloy7, 204, and 206.  Besides the melting range, indium has comparable thermal and electrical conductivity to standard materials.

 

[ACM] What makes indium-lead (In/Pb) solders so attractive, and why have we seen a recent resurgence in their usage?

 [MD] One main attraction to using indium/lead (In/Pb) solder alloys in soldering to precious metal surfaces is that, unlike tin-containing solders, they do not leach gold. That is, gold does not dissolve in them to any appreciable extent. During discussions at Semicon West in 2011, one of our California customers reported going through 8 simulated reflows with Indalloy 205 in contact with a gold surface with no loss of joint strength and no joint embrittlement. That is pretty impressive. Note that embrittlement is often caused by gold-intermetallic formation. It has been noted that even at 250°C, 50In/50Pb dissolves Au at a rate 13 times slower than it does into 63Sn/37Pb, although this, of course, is a kinetic, not a solubility limit, study.

 

The higher melting Indalloy 164 (92.5Pb/5In/2.5Ag) has the lowest coefficient of thermal expansion (CTE) of all of the In/Pb solders and is able to withstand the higher temperature excursions that can be seen in step-soldering type applications (where a very high melting solder is used to form the first joint, followed by a next lowest melting alloy, and so on). This is seen in applications such as power electronics assembly, where the first step solder is often used for die-attach either as a solder paste, wire, or preform. The high melting point helps the solder withstand the operational temperatures associated with under-the-hood electronics, in applications such as engine control modules, where Indalloy 151 (92.5Pb/5Sn/2.5Ag) or Indalloy 163 (95.5Pb/2Sn/2.5Ag) are most commonly used. In/Pb solder is excellent on very rigid structures such as ceramic-to-metal or ceramic-to-ceramic. The desired solidus / liquidus temperature range can be adjusted by changing the indium:lead ratio, making it very easy to “dial in” the alloy to a specific reflow process.

Another attraction to using In/Pb solders is that they exhibit good fatigue resistance in thermal cycling from -55°C to 125°C.  In testing, the 50In50Pb solder joint fatigue life is about 100 times greater than that for 63Sn/37Pb.

 [ACM] What fluxes are used in these applications, and how are they formulated differently?

 [MD] The fluxes most compatible with the lower melting point (<200°C) indium-containing solders are NC-SMQ-80 (solder paste) or the lower-tack TacFlux® 012 (suitable for use with wire, preforms, and spheres). These are no-clean fluxes, specifically formulated for lower temperature reflow.  Under appropriate low temperature reflow these fluxes leave behind benign residues that do not need to be cleaned off (“no-clean” flux), although they are often cleaned off in most practical applications, usually to ensure reliable wirebonds absent of flux spatter.

 To learn more, please contact us.

 Cheers!  Andy

Solders, as a class, are "interesting" metals.  And the properties of indium-containing solders are exceptionally interesting.  Indium’s (and indium's alloys') physical and mechanical properties are unique when compared to the metallic elements and alloys typically examined.

To put this into context, a metallurgist from a customer company called me because, after looking over our table of solder alloy properties, he claimed our data couldn’t possibly be correct!  After a detailed conversation, I understood the nature of his concern.  His background was not in solder materials, and the shear strength data for indium (890PSI) is exceeded by its tensile strength (273PSI). This "interesting" situation prompted further questioning.  These numbers are, however, accurate.

The graph on right numerically depicts the shear nature of this material.  Over a test area of approximately 0.5 square inches, a soldered interface that was sheared at a rate of 1mm/minute to fracture extended 1.6mm before yielding. This extension is indicative of the putty-like nature of pure indium.  As expected, The load at yield roughly matched the shear strength cited above for the bulk material  because the yield location in this assembly was through the bulk material, rather than along the intermetallic edge.    

More extensive information on the physical constants of indium can be found in this application note.

Finally, click here to link to more information on indium metal properties and its uses.

As a sneak peak:

• Indium has a low vapor pressure when molten, rising quickly as the boiling point approaches (2080°C)
• Indium cold welds to itself
• Molten indium will wet glass and glazed ceramics
• Although the softest metal, indium will impart hardness, when added as an alloying agent to other metals such as gold. In fact, the gold indium alloys are used in dental crowns.

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

 

Back in 2005 a customer left a question on our website and it was answered by one of my solder heroes. Here is the Q&A:

Question: “With regard to Indium Corporation's indium sulfamate plating bath… …can it be deposited onto platinum-gold thick film inks? Namely DuPont solderable inks on 96% alumina?”

Answer: “Thick film inks often contain low melting glass frit particles which enhance bondability to the alumina substrate. Solderable thick film inks are designed so that the glass particles do not reside on the surface, thus allowing the solder to wet. As in solder wetting, having a glass frit-free particle surface will also allow electrodeposition of any metal. Therefore if the ink is solderable it should be plateable.”

I learned from this answer so I thought it would be good to share with you. Call me or email me to discuss your questions.

~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

Indium and indium-containing alloys see wide use in a multitude of soldering applications. Indium has many attractive properties such as remaining ductile at cryogenic temperatures, compatibility with thick gold metallizations, and excellent thermal cycling performance.....to name just a few.

However, indium and indium-containing alloys may not be appropriate for every application. One such possible inappropriate scenario is the use of indium and alloys of indium against copper or copper-containing alloys, such as brass and bronze. This is because, even in the solid state, indium will diffuse into the copper material over time. The rate of diffusion is a function of temperature. The indium and copper react and form intermetallics. This intermetallic layer is much harder and stiffer than the parent indium and copper materials. This intermetallic layer can be subject to fracture. Depending on the application and the exact nature of the materials being used, this may or may not be a problem. It is recommended that one investigate the long term implications of this interaction. Given that the phenomenon is a function of time, it is important to understand that the effects of the interdiffusion, may not be readily evident. It make take several months or years for any effects to manifest. Accelerated life testing is suggested.

It should be noted that there are several applications where indium is used against copper successfully and reliably, everyday, the world over. This post is not meant to generate panic, but rather to empower the end user to make the best decision for their application.



One way to by-pass the whole issue is to plate the copper with a layer of nickel. Literature suggests a minimum thickness of 50 microns of nickel. Nickel is known to act as an effective diffusion barrier, preventing the indium from ever coming in contact with the copper.

For more information on this phenomenon, please read a work titled "Effects of Interdiffusion on the Properties of Indium-Plated Contacts" by R.W. Barnard Ph.D. of Bell Telephone Laboratories, August 1974.

Let me know if I can help you with this issue.

Eric

Folks,

I’m taking a few moments from Wassail Weekend , held annually in my village, Woodstock VT, “The prettiest small town in America”, to write a post about last week’s workshops at ACI.

Indium colleague Ed Briggs and I gave a 3 hour presentation on “Lead-Free Assembly for High Yields and Reliability.” I think Ed’s analysis of “graping” and the “head-in-pillow” defect is the best around. 

There was quite a bit of discussion on the challenges faced by solder paste flux in the new world of lead-free solder paste and miniaturized components (i.e. very small solder paste deposits.) One of the hottest topics was nitrogen and lead-free SMT assembly. There seemed to be uniform agreement that solder paste users should be able to demand that their lead-free solder paste perform well with any PWB pad finish (e.g. OSP Immersion silver, electroless nickel gold, etc.) without the use of nitrogen. Not only does using nitrogen cost money, but it will usually make tombstoning worse. However, in the opinion of most people, nitrogen is a must for wave soldering and, since it minimizes dross development, it likely pays for itself.

After Ed and I finished, Fred Dimock, of BTU, gave one of the best talks I have ever experienced on reflow soldering. He discussed thermal profiling in detail, including the importance of assuring that thermocouples are not oxidized (when oxidized they lose accuracy). He also discussed a reflow oven design that minimizes temperature overshoot during heating, and undershoot when the heater is off. Understanding these topics is critical with the tight temperature control that many lead-free assemblers face.

Fred Verdi of ACI finished the meeting with an excellent presentation on “Pb-free Electronics for Aerospace and Defense.” Fred’s talk discussed the work that went into the “Manhattan Project.” A free download of the entire project report is available.

There appears to be agreement that acceptable lead-free reliability has been established for consumer products with lifetimes of 5 years or so, but not for military/aerospace electronics where lifetimes can be up to 40 years in harsh service conditions. These vast product lifetime and consequences of failure differences are depicted in the Fred's chart (above). Commercial products are in quadrant A and military/aerospace products in quadrant D.

One of the greatest risks faced by quadrant D products is tin whiskers. Fred spent quite a bit of time discussing this interesting phenomenon. One of the challenges of this risk is that there is no way to accelerate it, so you can’t do an equivalent test to accelerated thermal cycling or drop shock. Fred mentioned that there have now been verified tin whisker fails, the Toyota accelerator mechanism being a confirmed one.

In addition to tin whiskers, lead-free reliability for quadrant D products (with a service life of up to 40 years) in thermal cycle and other areas remains a concern.  I mention that tin pest was not on the list of issues for this quadrant.

Fred and the Manhattan Project Team have identified many "gaps" that need to be addressed to determine and mitigate the risk of lead-free assembly for quadrant D products.  They plan to start this approximately $100M program in 2013.

For those that missed this free workshop, ACI host Mike Prestoy is planning another one in 6 months.

Cheers,

Dr. Ron

Here is a question that was received and answered on our website almost a decade ago – but it is still quite relevant:

Question:
“I have an application where I need to solder to 0.5µm thick gold. What alternatives do I have? What alloys are likely to work?”

Answer:
“Being that your gold is relatively thin, you really do not have any limitations as far as [indium-based solder] materials go. You should consider the temperature that the solder will see and try to choose an alloy that melts at least 40°-50°C higher. You should also consider the sort of mechanical strength that you will need.”

Here is a list of solder alloys we offer, including indium based alloys: Indalloy Chart

CONTACT ME if you have any further questions:

Jim Hisert
Applications Engineer
Ph: +1.315.853.4900 x7592
Email: jhisert@indium.com

Folks,

I was at SMTAI 2011 last week and, as usual, JoAnn Stromberg and team did an amazing job.

I think SMTAI's technical program is the best around, offering scores of topics and world class speakers.  I chaired a session (MFX4) Alternate Lead-Free Alloys, with papers by Dr. Ning-Cheng Lee, Srinivas Chada, and Jasbir Bath.

I also co-authored three papers:
 
The technical sessions were extremely well attended, with 30-60 people in each.  An emerging trend is that the tech sessions are  swamped and the show floor not so much.  I think the Internet allows people to get a sense of products online, while the technical talks enable one-on-one discussions with experts in the Q&A after the papers.  It is tough to beat this interaction, even in an Internet world.

The new hot topic, to me, is the interest in "Conflict Minerals."  I participated in a panel discussion on this topic (see image).  It appears that the Dowd-Frank act will require publicly held companies to show "due diligence" in investigating their supply chain to determine if their tin, tantalum, gold, and tungsten come from "conflict" mines.  This requirement will likely ripple up and down the supply chain.  So we all need to become knowledgeable in this topic. Indium Corporation is very involved in this.

As for the venue, Forth Worth was nicer than I expected (not that a business traveler ever gets to see much). There was a nice restaurant area near the conference center. It reminded me of the Gaslamp Quarter in San Diego.  But for me, I longed for Disney World a little. Next year!

Cheers

Dr. Ron

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

Many, many thanks to the hundreds of you who came by the Indium Corporation booth at Semicon West this year. Some of you came to hear about our recent global Semiconductor Assembly Materials Roadmap presentations, and all of you wanted to talk about your specific materials needs. Special thanks to those of you who shared the many successes you are having with our growing portfolio of applications-specific materials.


Based on these discussions, just a few of the topics that you will be hearing about in this blog in the coming months are:

- Lead/indium paste for multiple reflow applications onto gold pads
- Tin antimony solder paste
- Fluxes for 2.5D and 3D flip-chip applications
- Waferbumping fluxes for microbumps
- Jetting epoxy fluxes
- Tombstoning in semiconductor applications

Also: a final big THANK YOU to our friends at Nordson/Asymtek for showcasing the Indium halogen-free PoP paste Indium9.88-HF which was still dispensing after over 3 days of continuous usage at room temperature: proving its hard-earned reputation as the Energizer bunny of Pb-free (lead-free) dispense pastes. Here is a picture from the final day.

We look forward to seeing you all in 2012 (Exhibits: July 10-12th, 2012).


Cheers!  Andy

Folks,

I have occasionally written on calculating solder alloy density, as there is surprisingly more interest than I thought there would be in this topic. Recently, it occurred to me that it might be beneficial to compare the calculated densities to actual densities of a few alloys to see how accurate the correct formula is (for the derivation of the correct formula see below). The formula assumes “perfect mixing” (i.e. no interactions between the alloy elements). The alloys we investigated were tin-bismuth-silver, tin-silver, tin and tin-bismuth.

To measure the density, I obtained a few alloys from Indium Corporation. My student, Evan Zeitchik, determined that a good technique to measure density is to machine the alloy into a rectangular parallelepiped (see photo), weigh it, and calculate its volume from its dimensions.  The results agree with the correct formula to about 1 to 2 %. Some people would ask why there is any difference. The reason is that all alloys form different phases, and some form intermetallics. These phases and intermetallics would typically have different densities than that calculated for the alloy. I will have more detail on this work in a future post. 

Here is a derivation of the correct density formula:

Many people incorrectly assume that if you have an alloy of x % tin and y % silver, that the density of this alloy would be 0.x*Density tin +0.y*Density silver. This intuitive linear formula is incorrect however, as density has two units (mass and volume).  An easy way to understand the derivation of the correct formula (proposed by Indium Corporation engineer Bob Jarrett) is to consider a 96% tin, 4 % silver example.

Lets assume I have 1 g of this alloy, 0.96 g is tin and 0.04 g is silver.

The volume of the tin is 0.96 g/7.31g/cc = 0.131327cc

The volume of the silver is 0.04g/10.5g/cc = 0.00381cc

So 1 g of the alloy has a volume of 0.131327 + 0.00381 cc = 0.135137 cc

Hence it's density is 1g/0.135137cc = 7.39989g/cc

Hence, the general formula is:

1/Da = x/D1 + y/D2 + z/D3

Da = density of final alloy

D1 = density of metal 1, x = mass fraction of metal 1

same for metals 2, 3

The formula continues for more than 3 metals.

I have developed an Excel spreadsheet that calculates density automatically. If anyone wants a copy, send me an email at rlasky@indium.com

Cheers,
Dr. Ron

PS:  Interesting thought: About 165,000 tonnes of gold have been mined throughout history. If all of this gold was gathered into a cube it would only be about 21 meters on a side. At $1550/oz, its value would be $8.5 trillion, quite a bit less than the almost $15 trillion debt of the US government.  Yikes!

Folks,

 A few people asked some questions after my last post on bismuth solders. Here they are:

1.      The low melting point of these solders is encouraging. What are realistic field use conditions?

Bismuth solders tend to be brittle, so drop shock environments such as mobile phones would not be recommended. However, thermal cycle performance from 0 to 100C is good, so stationary office equipment, televisions, desktop computers, etc may be good candidates.

 

2.     I am working with your colleagues on an automotive application and I am curious whether you have any idea how this alloy will perform between -40 and 0°C? We have not been reviewing bismuth-containing alloys due to their lower sheer strength, but may need to look at them in the future.

We can find no information on thermal cycle performance at these low temperatures.

3.     I hear that bismuth is rarer than silver, if we start using bismuth in solders couldn’t that make it very expensive.

An old number from Prismark puts the world solder use at about 50,000 metric tons (MT) per year.  Assume bismuth solders took a 5% market share (I think this would be the highest) that is 2,500 MT of bismuth solder (Bi57Sn42Ag1) or 1,425 MT of bismuth.

 

Although bismuth's occurrence in the earth's crust is 0.009 ppm (silver is 0.075 and gold 0.004 ppm), about 22,000 MT are produced each year.  In comparison, about 2,000 MT of gold, 20,000 MT of silver, 400 MT of indium and 5 MT of rhodium are produced each year.  In comparison to more common metals, total lead production is 8,000,000 MT/year and tin a little less than 700,000 MT.

 

 Realistically, it would seem to me to be unlikely that use of bismuth in solder, at 1,425MT/year out of 22,000 MTs,  would affect the price much, especially if the adaptation rate is more like 1-3%, instead of 5%. 

For those interested in how bismuth is produced, this Wikipedia quote may be of interest:

 

"According to the United States Geological Survey, world 2009 mine production of bismuth was 7,300 tonnes, with the major contributions from China (4,500 tonnes), Mexico (1,200 tonnes) and Peru (960 tonnes).^[11] World 2008 bismuth refinery production was 15,000 tonnes, of which China produced 78%, Mexico 8% and Belgium 5%.^[9]

The difference between world bismuth mine production and refinery production reflects bismuth's status as a byproduct metal. Bismuth travels in crude lead bullion (which can contain up to 10% bismuth) through several stages of refining, until it is removed by the Kroll-Betterton process or the Betts process. The Kroll-Betterton process uses a pyrometallurgical separation from molten lead of calcium-magnesium-bismuth drosses containing associated metals (silver, gold, zinc, some lead, copper, tellurium, and arsenic), which are removed by various fluxes and treatments to give high-purity bismuth metal (over 99% Bi). The Betts process takes cast anodes of lead bullion and electrolyzes them in a lead fluorosilicate-hydrofluorosilicic acid electrolyte to yield a pure lead cathode and an anode slime containing bismuth. Bismuth will behave similarly with another of its major metals, copper. Thus world bismuth production from refineries is a more complete and reliable statistic."

So I don't think bismuth supply and price would be affected by its use in solders.

Cheers,

Dr. Ron

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