Indium Corporation Blogs

Being the Indium Corporation, we know what indium is, where it comes from, and how to use it.  But sometimes we forget that not everyone is as immersed in indium as we are.

So what is indium?  Of course it is an element with an atomic number of 49, an atomic weight of 114.818amu, a relative density of 7.31g/cm³, and a melting point of 157°C.  I have known that for most of the 27 years I have worked at Indium Corporation, but what exactly does that mean?

Well, the atomic number is important because it is the number of protons in the nucleus - and this is what gives each element its physical characteristics.  It also places it in the periodic table (directly to the left of indium on the chart is cadmium which has an atomic number of 48 and to the right is tin, which has an atomic number of 50).  This puts indium in the group of metals known as "Other Metals", along with bismuth, tin, zinc, antimony, gallium, and germanium.  The atomic weight is a measurement of the total number of particles in the nucleus of the atom.  If you want to know more about protons, electrons, and neutrons, go to the Jefferson Lab site.

The specific gravity or relative density of an element, which, in the case of indium, is 7.31g/cm³, depicts its relative density compared to water.  If the relative density of an element is less than one, then it will float in water.  If it is greater than 1 then it will sink.  If you compare indium's relative density to that of lead, which is 11.35, you will see that, if you had a piece of each material cut to the exact same dimensions, the lead would be heavier than the indium.

Between the atomic number and the specific gravity, I use the specific gravity more often.  It is used in a formula to find the weight of a solder part, or of a length of wire or ribbon.

So where does indium come from?  Since indium is an element, it comes from the earth's crust.  It is generally refined as a by-product of zinc ore mining.  There is an ongoing debate about the availability of indium.  But a lot of work is being done to create more efficient extraction methods and reclaim, particularly of ITO targets, to assure an adequate indium supply for existing and emerging technologies for decades to come.

Okay, now for the fun part. Where is indium used?  It would probably be shorter to say where it ISN'T used!  If you are involved in any of the following areas, you have a need for indium:

• Cryogenic sealing
• Hermetic sealing
• Low temperature soldering for temperature sensitive devices
• Step soldering
• Solar panels (CIS & CIGS)
• Coatings for displays and glass (ITO & IGZO)
• Pb-free soldering
• Fuses
• CTE mismatch when bonding dissimilar materials
• Thermal management

 

Indium is certainly one of the more versatile metals because it works and plays well with others.  Read more about indium:

Indium Solder and Sealing

Thermal Management

Heat Spring

Low Temperature Solder

We like new challenges and applications, so if we can help you (or you think you can stump us), email me at cgowans@indium.com.

 

 

 

Reducing the surface oxides of Nitinol is just the first step in getting a good solder joint with this versatile medical assembly material.

Next you have to choose the right solder alloy.  You will probably want to stay away from anything containing lead, cadmium, or antimony, particularly in medical applications.  And you will want something with a high tensile strength.

The best choice is Indalloy #121 (96.5Sn 3.5Ag).  It has a tensile strength of 5,620 PSI and a melting temperature of 221C and is obviously lead-free.  It wets well to the cleaned Nitinol.

If you need a higher melting temperature solder (one that can withstand autoclave temperatures for example) you should consider Indalloy #182 (80Au 20Sn) which melts at 280C, has a tensile strength of 40,000 PSI, and has long been considered a highly reliable solder.  Additionally, this alloy is available in very fine diameter solder wires to minimize waste.

Soldering temperatures should be 25C to 50C above the liquidus temperature of whichever solder you use and proper cleaning should be always be performed afterwards.

Contact us at medical@indium.com for more information about soldering for medical devices or visit our web site at www.indium.com/medical

Carol

 

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,

Many people responded to my recent post, In Search of Tin Whisker Fails in Lead-Free Soldering.  A few pointed out that the recent NASA report on the Toyota Unintended Acceleration Issue  discussed numerous tin whiskers that were found, one implicated in a failure.  The tin whiskers were emanating from tin plating.

We don't know, however, if tin whisker mitigation techniques were used. In a mission critical application, such as this, it would appear unwise to use RoHS-compliant electronics, especially since they are not required for automobiles.  In other words, autos are exempt from RoHS.  Let me be very clear, from a tin whisker perspective, I am uncomfortable with RoHS-compliant tin plating in mission critical applications.  Much more work needs to be done before such tin plating should be used in mission critical applications.

In addition, in response to my post, a number of people pointed out the difficulty of proving a tin whisker fail and the reluctance of any manufacturer to admit that their products had them.

But my quest remains unfulfilled; the question remains:

"... who knows of any verified tin whisker fails when tin whisker mitigation techniques where used? Tin whisker mitigation techniques typically use 2% bismuth or antimony in the tin, assure that the tin has a matte finish and use a nickel strike plating between the copper and the tin to minimize copper diffusion into the tin."

Restated, here is my point.  Since RoHS, quite a few people take a position something like this:

With RoHS-compliant assembly, even the world of non-mission critical electronics is at considerable risk of numerous catastrophic failures, due to tin whiskers, that will cost $100s billions.

I still maintain, that with mitigation techniques, such as recommended by iNEMI, tin whisker control, for non-critical electronics, can be manageable.

As I pack up to leave my office today at Thayer Engineering School at Dartmouth, I am across the aisle from the chaps that provide our computers and IT support.  They buy millions of dollars of electronics a year.  In chatting with them they state two things:

1. They have noted no difference in electronics reliability since RoHS implementation

2. On the very rare occasion that they get an electronics failure, it is almost always a hard drive.

Bottom line: Except for hard drives, modern electronics are very reliable for their use life.

I expect my quest will uncover some tin whisker fails, even with mitigation, but the fails will most likely be isolated and not a significant threat to the industry at large.

Cheers,

Dr. Ron

The image is from Dr. Henning Leidecker of NASA, one of the world's leading tin whisker experts.

Folks,

In a recent post, I shared my perspective on the pluses, minuses and neutral aspects of lead-free solder assembly. In the minus category, I listed tin whiskers. A few people commented that tin whiskers were the biggest concern in lead-free assembly. I have trouble understanding this perspective. I’m not saying these folks are wrong, just that I don’t understand their viewpoint.

First, let me say that I appreciate the concern for tin whiskers in mission critical electronics such as military, aerospace and medical. I am also sympathetic to the fact that, even though these types of electronics are exempt from RoHS, they may have to use RoHS compliant products because non-RoHS compliant products may not be available.

When I discuss the topic of tin whiskers, people will point me to NASA’s tin whisker failures website . However, when one goes to the site, there are only about twenty tin whisker fails referenced, many due to bright tin plate. Bright tin plate should never be used in mission critical electronics as it is virtually assured of producing tin whiskers. In addition, many of the articles referenced do not talk about tin whisker fails. Few if any fails are discussed relevant to RoHS (i.e. almost all fails discussed are prior to July 2006.)

I do not want to minimize the significance of tin whisker fails, some of them cost 100s of millions of dollars (e.g. satellite failures). In addition, there have been a few papers that have discussed the formation of tin whiskers even if mitigation techniques are used. Tin whiskers clearly can cause problems, but do not appear to be common, especially if mitigation techniques are used.

So here is my question, who knows of any verified tin whisker fails when tin whisker mitigation techniques where used? Tin whisker mitigation techniques typically use 2% bismuth or antimony in the tin, assure that the tin has a matte finish and use a nickel strike plating between the copper and the tin to minimize copper diffusion into the tin.

Surely if tin whiskers are a major concern, there should be many fails in the over $3 trillion worth of RoHS compliant electronics manufactured since July 2006.

Cheers,

Dr. Ron

The image is from: http://nepp.nasa.gov/whisker/photos/pom/2001august.htm.  It shows tin whiskers on a passive's contacts.

I recently had the opportunity to discuss several issues in Pb-free die-attach and other solder applications with Jennie Hwang PhD, DSc, and world-renowned consultant in solder and  electronics assembly processes. 

Cheers! Andy

Greenpeace has just updated their "Guide to Greener Electronics."  There are a couple of interesting tibdits that I took from their report:

1. They are really focusing on the phase out of BFR's and PVC from electronics.  They dropped HP and Dell down because they are loosening their timeline of BFR and PVC phase-out.  I find it interesting that they make no note of what the replacements should be.  This is concerning that the replacements could potentially be MORE toxic than what they are replacing.  It took years to fully characterize the situations where BFR's and PVC are of concern (dioxin formation and bioaccumulation).  In addition, all BFR's are not the same.  If companies are phasing out these materials, how can they do a full risk assessment of the replacements in one to two years?
2. They have added Antimony (Sb) to their list of materials that need to be phased out.  This can be challenging for a number of soldering applications.  Component manufacturers have been using Sn/Sb alloys inside their components.  Sn/Sb is the highest melting point Pb-Free alloy that actually solders reasonably well (other than Au/Sn which is 1000x as expensive).  The component guys are using this so that those alloys are not remelting when that component is assembled in a SAC SMT process.  Eliminating Sb will create a number of assembly challenges as well as potentially significant reliability issues.
3. By reading the summary of the report, they praise Apple for phasing out virtually all BFR's and PVC.  However, their ranking is still in the bottom half.  I will write more about this one in a future entry.

I am all for designing electronics for the environment, but I think there needs to be more focus on the consequences of making those design changes.  Are the alternatives actually any better?  What is the impact on product reliability and functionality?

 

 

Annika writes:

Dear Dr. Ron,

I'm a chemist and a PhD student working in the field of atmospheric corrosion of lead and lead-tin alloys in historical organ pipes in Europe.
I read your article on the web about tin pest and Napoleon's Buttons and Lead-free Soldering. In the article you write:

As a general rule of thumb, metals readily soluble in tin suppress or eliminate tin pest formation. Examples of these alloying metals are bismuth, antimony, and lead. As little as 0.5% bismuth or antimony by weight essentially eliminates tin pest, while about 5% lead by weight is needed. Since tin-lead eutectic solder is 37% lead, tin pest has not been an issue in soldering with traditional lead-based solder paste.

Do you think you can give some more information about this "rule of thumb" and that 5% lead will stop the pest?

Annika:

Tin pest in church organ pipes was one of the first known examples of the phenomena. Sadly, little work has been performed on this important topic in recent years. It is an issue of considerable concern for the current move to lead-free solders. I wrote a posting on it some time ago. For those interested, I have a paper with quite an extensive tin pest bibliography, that has the papers with the tables from which I got the "5% lead" information. Send me a note if you would like a copy, rlasky@indium.com.

Cheers,

Dr. Ron