Indium Corporation Blogs

Whenever two materials with different coefficient of thermal expansion values are bonded together, they will expand and contract as the temperature changes.

Assuming these two materials are bonded rigidly, there are two things that can happen as the temperature changes: 1) the bond will break apart or 2) the assembly will bend to accommodate the stresses. Either of these outcomes can be disastrous for a sputtering target. The important thing to realize is that this is a function of temperature change. Limit the temperature change and you will reduce the effects of CTE (Coefficient of Thermal Expansion) mismatch.

The answer to this is found in the conclusion of Eliminating Bond Stresses of Sputtering Targets at Operating Temperatures:

“Reactive multilayer foils can be used to form a low stress bond at room temperatures. This is especially important for sputtering target assembly. The same bonding process can also be performed at elevated temperatures for a zero stress point at or near operational temperatures. With a firmly bonded bi-metallic assembly, curvature over a large temperature range cannot be ignored, but the effects of this can be mitigated through selectively setting a zero stress point at a strategic temperature.”

In an earlier post I mentioned one of the presentations we gave at the 2013 SVC TechCon. The other presentation that our team delivered at the show (presented by Jacques Mateau) regarded another very interesting topic. The paper, High Temperature, Pb-Free, Metallic Sputtering Target Bonding Using Reactive Multilayer Foil, deals with creating high temperature NanoBonds®:

“Metallic bonds provide excellent thermal and electrical conductivity, but are limited by the relatively low melting point of the solder material used, 157°C for indium or 217°C for tin-based alloys. This limits the power input, which in turn limits sputtering rates and final film properties. There is a desire for a higher temperature (>300°C) metallic bonding process that can produce flat, stress-free target assemblies, enabling targets to run at higher temperatures for longer periods of time. We will demonstrate a metallic bonding process using reactive multilayer foils and a high temperature alloy with melting temperatures as high 380°C. We will compare this with traditional Sn-based solders typically used, specifically comparing shear strengths, void analysis, and cross sectional analysis.”

The image shown here is a bond formed with a 98Zn/2Al alloy and 60μm thick NanoFoil^®. You can follow the link above to read to paper, and email me if you have any questions or are interested in this process for bonding your sputtering targets.

~Jim

For anyone who couldn’t make it to the 2013 SVC, just email me at jhisert@indium.com and I can make sure you receive a copy of “Eliminating the Bond Stress of Sputtering Targets at Operating Temperatures”. This paper discusses alternative processes for bonding targets - alternative processes that demonstrate the unique capabilities of NanoFoil^® and open your mind to currently undiscovered methods.

Interested? Let me know!

Let’s start with a bit of fiction to get us on the same page…

Mike is working with NanoFoil^®, getting ready to bond a small, round, planar sputtering target. He has prepared his backing plate and target material and is ready to assemble the stack after cutting a piece of NanoFoil^® to fit. He carries the foil from storage to the cutting area on the metal backing sheet on which it was supplied. After marking the foil, he uses a glass cutter to trim off the excess, and brushes the scraps off the table into a metal bucket with the other scrap he cut for the last job. Suddenly he notices a red-orange glow and feels the warmth of the reacting NanoFoil^® near his leg. Mike didn’t get burned this time, but he realized he should not let scrap NanoFoil^® build up. The last piece of foil he threw into the pile had activated by landing on a corner and caused a chain reaction in the metal bucket.

It is natural to have a tendency to treat the scrap as, somehow, less reactive. But, NanoFoil^® scrap pieces are every bit as reactive as the useful pieces from which they are cut. If you are cutting your own NanoFoil^®, make sure you use equal care with both your main pieces and your scrap.

Here are a few tips on how to handle NanoFoil^® scrap:

1. Designate a metal container for NanoFoil^® scrap only
2. Do not allow the scrap to accumulate in the container
3. Be careful not to drop foil into the container

Always follow the NanoFoil^® safety guidelines (like wearing leather gloves while handling) and stay safe!

Feel free to contact our technical support department for best practice suggestions as well.

I’m not the only one presenting new NanoFoil^® data at this year’s SVC (Society of Vacuum Coaters) Conference. Another member of our team will be in attendance to teach you about some of the breakthrough work he’s been doing to help you create better performing target bonds. As his abstract reads:

“There is a desire for a high temperature (>300°C) metallic bonding process that can produce flat, stress-free target assemblies, enabling targets to run at higher temperatures for longer periods of time. We will demonstrate a new NanoBond^® process using a high temperature thermally sprayed Zn/Al alloy with melting temperatures as high 380°C. We will compare this with Sn-based solders typically used in the NanoBond^®process, specifically looking at shear strengths, void analysis, and cross sectional analysis.”

Come meet the Indium Team in booth #313 at the 2013 SVC Technical Conference and Exhibit!

I invite you to come to the Emerging Technology session of the SVC (Society of Vacuum Coaters) Conference on Wednesday April 24^th – where I’ll be discussing interesting new ways to use NanoFoil^® to create sputtering target bonds with better operational performance.

Here’s a little background, if you missed some of our past presentations at the SVC in recent years: NanoFoil^® has been proven to eliminate CTE (Coefficient of Thermal Expansion) stresses imparted during the bonding of sputtering targets. Per the abstract:

“Reactive multilayer foil bonding has been used to eliminate stresses in sputtering target assembly caused by coefficient of thermal expansion mismatches between the target and the backing plate materials. Since a significant portion of the materials (except the innermost few microns) remain at room temperature throughout the reactive multilayer foil bonding process, the materials are bonded with an ambient temperature “zero stress point.” This low stress bond reduces the effects of thermal expansion, leading to less deflection of the sputtering target assembly. In most high temperature large area bonding applications, targets that deflect after bonding are mechanically stressed until they are truly planar again. This compounds the stress resulting from the bonding and flattening operation. In this paper we will explore the possibility of setting the “zero stress point” at other temperatures to further minimize stress and deflection during operation.”

If the presentation doesn’t answer all your questions regarding target bonding, no worries – the Indium Team will be there to chat with at booth #313. You will NOT be disappointed. See you there!

~Jim

There are many sputtering target materials that are tricky to solder to. For those alloys we ‘bring out the big guns’ – in this case, our ultrasonic soldering tool. Since these materials (listed below) require a more easily-bonded coating before NanoBonding, we need to add a layer of activated solder followed by a thicker coating of a traditional solder.

• Aluminum-titanium alloys
• Chromium
• Iron-cobalt
• Manganese
• Manganese-iridium
• Molybdenum
• Nickel-chrome
• Nickel-titanium
• Niobium
• Stainless steel
• Tantalum
• Titanium
• Titanium-niobium
• Tungsten
• Tungsten-titanium

There are some interesting tricks to this process that we can share with you, so feel free to contact us. We can have you bonding these materials in no time! If you are bonding them to copper or aluminum backing plates, check out these links as well:

Applying solder to copper

Applying solder to aluminum

* This post is part of the NanoFoil^® Do-It-Yourself Tips and Tricks series

In order to NanoBond^® parts that are made out of copper, nickel, or platinum, we must first apply solder to the bonding surface. This is most commonly done by melting solder directly onto the surface while applying SS-42 flux. The flux will strip the surface oxides from the copper, nickel, or platinum, allowing proper intermetallic formation.

Copper is a common sputtering target backing plate material, so this method is used quite often. Aluminum is perhaps an even more popular backing plate material, but it is a bit more difficult to get solder to wet onto it’s surface with flux. No worries though, just read this post regarding how to apply solder to aluminum and aluminum alloys!

* This post is part of the NanoFoil^® Do-It-Yourself Tips and Tricks series

Sometimes one piece of NanoFoil^® just isn’t enough…

We often NanoBond^® sputtering targets which are large enough to require multiple sheets of NanoFoil^® to cover the width or length of a bond. You may even need to use two pieces of NanoFoil^® that were sized for a different application, or if someone made a mistake cutting foil. Oops!

Luckily, butting two pieces of NanoFoil^® up to each other is quite easy, and although visible with ultrasonic testing the small gap should not cause much of a difference structurally or performance-wise. To secure the pieces during preparation, you can use high-temperature tape (as long as it is not in the bond interface). The heat from the first piece will active the second if they are in close proximity. This chain reaction is useful for both prototyping with incorrect sized pieces or mass production with pieces that are not large enough.

* This post is part of the NanoFoil^® Do-It-Yourself Tips and Tricks series

We commonly receive questions like: “Can NanoFoil^® be used to bond silicon?” or, “What surface flatness do I need to NanoBond^® this target?”. Well this application note, NanoBond^® of Ceramic and Metal Sputtering Targets not only gives you a listing of many combinations that have been used in the past – but also how to achieve these bonds.

~Jim

In an earlier post I mentioned that cross-sectioning a NanoBond^® was one of my favorite tests. My other favorite test is shear testing.

It’s great to see what is going on in the bondline of a solder interface – but having a numerical value to compare the bond strength is important when you are attempting to maximize bond strength.

For small components, shear testing may be manageable "as is" (such as the component in the image shown here, courtesy XYZTEC). For larger bonded surfaces like sputtering targets, it might be a good idea to cut up your backing plates and target material so you can use less material and create more bond variations. Instead of one large target, I’d much rather have 20 samples to bond with various foil thicknesses, solder coatings, and bonding pressures.

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

Assuming that your application follows the DFNB (design for NanoBond^®) guidelines, you are ready to prepare your parts/components for assembly. Whether you are bonding LEDs, sputtering targets, heatsinks, or any other components – there are a few common points to consider before activating the foil and creating a bond:

• Surface Preparation
• NanoFoil^® Thickness
• NanoFoil^® X and Y Dimensions
• Aligning the Assembly
• Pressure During the NanoBond^® Process

Setup for the NanoBond^® process can be as simple as clamping two plated parts together - with NanoFoil^® in between, or an elaborate setup including a multi-point ignition system and a high capacity press. Generally, the smaller applications (electronic component scale) are fairly simple to set up. For anyone who has seen a NanoFoil^® demo at a tradeshow or visit, you will remember that the NanoBond^® was created using only finger pressure and a 9 volt battery – that’s simpler than hand soldering! (and faster too…)

Ready for activation?

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

Ultrasonic Testing (UT), performed by acoustic microscopy, is a great way to determine the quality of a solder bond without destroying the assembly.

As a very basic description, SAM (scanning acoustic microscopy) uses sound waves to travel through the assembly, much like some animals use sonar to locate objects. Sound waves generated by a transducer travel through the assembly and bounce back when they encounter different materials. Air reflects back much differently than metal, so, by using sound waves, we can locate pockets of air (voids).

In a NanoBond^® you can expect to see 2 things:

1) darker spots where the NanoFoil^® is located in the bond and

2) very little voiding, which will appear as white areas. Here is an example of voiding:

Most of the time we see little or no voiding. We typically achieve <2% when we bond sputtering targets with NanoFoil^® in-house. Here is an example:

If you have experience with traditional large area soldering methods, you will notice that <2% voiding is a sign of a very good bond.

For sputtering targets this is necessary to reduce pump-down times and eliminate ‘virtual leaks’. Contact us if you are interested in learning more.

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

As a primarily METALS materials supplier, we are used to most of our products appearing rather, well, boring. We see many shades of gray!

From solder paste to CIG targets, from solder wire to tabbing ribbon - they're mostly gray!

The indium sulfide (In₂S₃) that we produce for use as a buffer layer in thin film solar cells is quite unlike many of our other products. Visually, it is a bright orange powder or pellet. (The text in the picture is made from indium sulfide powder.) Chemically, it is like many of our other products in our metals and compounds division.

Indium Sulfide is supplied in various forms such as powder, thermal evaporation pellets, or sputtering targets. Since the powder form is very important as a starting material for other forms, we focus on achieving very high purity. We also focus on one other secret detail that helps our customers build better solar cells. (I can’t give everything away, right?)

If you’d like to know more about indium sulfide, feel free to send me an email @ jhisert@indium.com.

As far as elements are concerned, gallium is second only to indium in my heart.

I wanted a very special image of gallium material to use on our website. Rounding up the gallium was no problem, however, the crucible I wanted to use (supplied by Sage Industrial Sales)  was in a shipping crate on the way to InterSolar 2012 three weeks ago. When I arrived at the booth to set things up, the crucible was there waiting for me (along with all the sputtering targets and other display materials) . I patiently planned to come back to the office, find the crucible, and get a good picture of gallium.

Throughout the week at InterSolar I had the chance to talk with many show attendees about gallium. We discussed everything from gallium supply to its use in CIGS thin-film photovoltaics. One gentleman actually wanted to buy some gallium for his son to experiment with.

We had a great show, and, when the week was through, I headed home. Now everything was finally in line for this gallium picture I had been thinking about. I returned to my desk and took a good look at the gallium I was about to photograph, only to notice that it was a sample I had shipped all over the world and had handled many times. This gallium did not look like fresh gallium, but, because of this aging, I like it even more. Gallium is soft and it re-melts very easily. The effects of this gave the sample a ‘worn-in’ look that I really like.

Feel free to contact me if you’d like to learn more about gallium.

This picture (shared by Angstrom Sciences) shows a planar target plate that has developed an advanced case of nodule formation. Nodules occur when material is re-deposited back onto the sputtering target. This is normal for most sputtering targets – although nodules increase the occurrence of arcing by building up charge on the target surface.

Equipment suppliers can suppress nodule formation (and arcing) by offering:

• high yield magnetrons
• full-face erosion magnetrons
• rotary magnetrons

The transfer efficiency of planar targets is based on magnetron design. High yield and full-face erosion magnetrons sweep the sputtering tool’s magnets over more of the sputtering target's surface – so the racetrack is more uniform. The next step is to move to rotary magnetrons for a decrease in arcing and huge increase in target utilization!

Feel free to contact me to discuss this in detail.

Jim Hisert

Because I secretly love cheesy blog titles and because I wish I had a better high school senior portrait:

At our last thin film tradeshow (as of this post), we displayed a molybdenum sputtering target designed for 450mm semiconductor wafer deposition.

What’s so special about this sputtering target? As if materials ready for the next evolution of semiconductor processing aren’t interesting enough – the ~22” diameter piece of Mo was bonded to the aluminum backing plate at room temperature! This method used to join targets and other materials without external heating (and the deformation it creates) is called the NanoBond™ Process.

BTW: That nervous high school look in my eyes is really me thinking: “I hope I don’t drop this on my foot!”

~Jim

I have been asked to explain why someone would want to use rotary sputtering targets instead of planar sputtering targets.

Certainly there is some expense involved with larger targets and new equipment (assuming you are currently using a planar system), but in a high volume process (such as roll-to-roll thin film deposition) the advantages lead to a lower cost of ownership:

• Compared to planar targets, rotary targets generally have more surface area per given length.

• Rotary targets have much more surface area, so the magnetron power can be spread out over a larger area in a given amount of time. This helps keep the target running cooler, decreases nodule formation, and reduces the occurrence of arcing.

1. Since rotary sputtering decreases nodule formation, targets can have longer continuous runtimes.
2. There is generally more material available to sputter on a rotary target, which increases runtimes.
3. Rotary target utilization is usually ~80%, as opposed to ~30% for planar targets – which decreases scrap and increases runtimes.

• Rotary targets are well suited for continuous sputtering processes. Continuous processing increases throughput since there is less time wasted preparing the sputtering chamber.

• Rotary targets are more cost effective for high volume processes. They provide a good platform for long runtime processes, with less chance of defects and downtime.

• Planar targets are still best suited for prototype work or elemental experimentation, especially when large amounts of material are not needed at once.

If you are interested in discussing sputtering targets, contact our team at: Solar@Indium.com

~Jim

It is common to hear people that are skeptical about CIGS technology ask questions like:

• "Aren't indium and indium tin oxide (ITO) thin film deposition processes wasteful and inefficient?"
• “Aren’t we going to run out of indium soon? Doesn't the world use more than we produce!”

What are the truths?

Here they are:

WASTEFUL: A well-run process is NOT wasteful. Why? Recycling!

At first glance, a process like indium planar target sputtering seems ridiculous – generally only 30% of the indium actually makes it onto the substrate it is destined for (and that’s in a well-tuned process). As it turns out, the material that doesn’t land on the substrate is too valuable to just scrap. This translates into recycling, a lot of recycling…

According to presentations given at Minor Metals 2012: “indium production will total 1,500-1,700 tonnes in 2012, with virgin supply accounting for around a third of total output”.  It’s incredible that recycling accounts for such a large percentage of the indium used in the world today.

INDIUM AVAILABILITY AND SUPPLY: Another important conclusion made at the conference was (as reported in Metal Bulletin):

“proven indium reserves from existing mines at 50,000 tonnes, a volume that will be sufficient to satisfy demand for the next 75 years”.

While it’s not news at Indium Corporation, it is definitely assuring news for those looking to get involved with CIGS technology.

~Jim

I recently had a discussion with Frank Zimone (VP of Business Development at Angstrom Sciences) about sputtering target utilization. He stressed the point: although "material by weight sputtered off the target" is how most folks define the ‘target utilization’, when judging the efficiency of a process, it is only the material that makes it to the product that counts. Frank said:

“What is happening now, is that we are seeing that many companies, after the rush to set up a process to create a good product and “get to market”, are now working on dialing in the process to save money by lowering production costs. This can be achieved by putting more of the target material onto thin-film cells, and wasting less by depositing less of the material elsewhere in the production tool.

“We have recently completed a study with a major photovoltaics company which evaluated enhanced magnetics from multiple competitors.  In a back-to-back comparison with identical process conditions (power density, line speed, etc.) both targets were utilized ~85%  as measured by weight loss.” (Remember folks – this is application specific.) “The main difference between the seemingly similar depositions was that one set of magnetics yielded 20% more material on the substrate.”

I asked the obvious question at this point: “How was that possible?”

Frank replied:

“One set on magnetics was able to get the 2 erosion racetracks more closely aligned, and more perpendicular to the target surface. This translated into higher dynamic deposition rate and less wasted material on the chamber shields.”

It’s a simple concept if you understand the physics of sputtering, and Frank agreed that most customers know this from an academic point but do not have the time/resources to properly test. He said, “More established customers are now looking into these particular issues.”

To learn more about moving magnetics, contact Frank Zimone at FZimone@angstromsciences.com or stop by and see him at InterSolar this week!

I'll be there, as well. Look for me in the Indium Corporation exhibit #5325.

~Jim