The ANCER for Corrosion/Erosion Protection on Copper Micro Channel Coolers
Billy: Welcome and thank you for joining us for today’s webcast, The ANCER for Corrosion Erosion Protection on Copper Microchannel Coolers, sponsored by Advanced Cooling Technologies and Tech Briefs Media Group. I’m Billy Hurley, Associate Editor with Tech Briefs Media Group and I’ll be your moderator today. Our webcast will last approximately 30 minutes and there will be a question-and-answer period at the end of the presentation. If you have a question, you can submit it at any time during the presentation by entering it in the box at the bottom of your screen. Our presenters will answer as many questions as possible at the conclusion of the presentation, and those questions not addressed during the live event will be answered after the webcast. Also twice during our presentation today, we will present you with poll questions and we invite you to answer those at that time.
In order to view the presentation properly, please disable any pop up blockers you may have on your browser. At this time, I’d like to introduce our speakers. Pete Ritt is Vice President Technical Services for Advance Cooling Technologies. Mr. Ritt joined ACT in 2010 to head ACT’s technical services business. During this time, the group had successfully provided thermal consulting, design, and prototyping solutions to commercial customers in the lighting, renewable energy, industrial equipment, medical and other industries. Throughout his career, Mr. Ritt has successfully managed numerous new technology products in a variety of industries.
Also, in the line for our Q & A is Dr. Tapan Desai. Dr. Tapan Desai is the R&D manager of the Defense and Aerospace Products Group at ACT, and he leads a group of 25 to develop and commercialize innovative thermal management technologies. Dr. Desai has successfully led several R&D projects for NASA, the Navy, Air Force, Army, DOE and NSF from the concept stage to commercial products. He uses state-of-the-art computational modeling techniques and experiments, to design and develop a variety of thermal solutions for commercial and military applications operating in extreme conditions. So, at this time, I’d like to hand the webcast over to our first speaker, Pete Ritt. Pete.
Pete: Thanks, Billy. Today, we’d like to present an exciting new coating. We call it ANCER, that has shown excellent results in minimizing corrosion and erosion issues in copper microchannel coolers, MCCs. Used in laser diode thermal management, these corrosion and erosion problems have plagued the laser cooling industry for some time. The most effective solutions usually have some significant cost and complexity associated with them. ANCER is different. It is a thin, conformal coating that our testing has shown to provide superior resistance to corrosion and erosion.
Many people experienced in the microchannel cooler world have told us they have heard these types of claims before. So today, we’d like to explain the ANCER coating, discuss some of the benefits, and summarize our testing that has led us, and hopefully will you, as well, to conclude that a solution for corrosion/erosion effects on copper microchannel coolers is now available. We’ll then explore what other corrosion/erosion protection we may be able to provide benefit for, and then we’ll conclude by answering some questions.
Laser diodes are used in many different industries, including defense, medical devices and analytical instruments. They are generally grouped together or stacked to increase overall optical output. The laser stacked require a uniform temperature to operate, but generate a lot of waste heat. If left unchecked, the higher temperatures can result in unwanted increased wave length shift, and overall deteriorated optical performance of the laser diode. A common cooling solution for these laser stacks is to use a pump liquid system, where the working fluid removes the waste heat and dissipates it through a chiller or other heat exchanger. Deionized water is frequently selected as the working fluid. To insure long-term reliability of the cooling channels, the water quality needs to be closely maintained for several parameters including temperature, flow rate, pH and resistivity.
Water that has resistivity and has pH values that are too high or too low can cause the formation of particulates that block MCC passages, thereby reducing the thermal performance of the coolers. The cooling element that is in contact with the laser diode is a complex, multi level copper microchannel cooler. A sample copper microchannel cooler can be seen on the lower right. High flow rates of DI water, which are necessary to provide the temperature stability for reliable laser performance, can also induce corrosion and erosion defects, causing unpredictable and catastrophic failure.
Until now, there’s been no accepted solution for these corrosion/erosion defects but we believe that is changing with ANCER. Let’s examine the problem a little closer. As we just mentioned, the laser diodes are cooled by a single phase coolant, typically DI water. The laser diodes are stacked as can be seen in the figure on the left, with the diodes mounted on the microchannel cooler. The high velocity flow rate of the DI water is erosive and corrosive to the base copper material. Small defects, imperfections in the copper layer can become dislodged as a result of the fast flow rate. The particulates can build up over time, causing restrictions or clogging along some of the microchannel flow lines.
Simultaneously, flow rates with linear velocities of greater than two meters per second can strip the native oxide layer off the copper surface. Seen in the schematic on the right is the corrosion equation. The presence of bare, native copper with water and oxygen causes electrons to separate from the copper. The free electrons combine with water and oxygen to form a hydroxyl group, which then combines with copper plus two to form copper hydroxide, which is subsequently converted to the native copper oxide.
Let’s take a look at how devastating these erosive/corrosive effects can be. The pictures are from a paper given by [Caramic at Botonics West?] a few years back. The paper is referenced at the bottom of the slide. As we have mentioned, high velocity DI water degrades the heat transfer surfaces by either making them thicker or thinner than the intended design. Today’s copper microchannel coolers are highly engineered devices, having five and six layers, each with unique features. These smaller features are more susceptible to degradations. The picture on the left is a cross section of a virgin copper microchannel cooler. The picture on the right is that same cross section after being exposed to 15,000 hours of a .5 mega ohm centimeter DI water system at a .5 liter per minute flow rate. The degradation seen on the right is quite obvious.
Currently, the solution for minimizing corrosion and erosion defects in copper microchannel coolers are to 1) have a tightly controlled DI system, 2) deposit a gold plating on the MCC, and/or 3) execute a rigorous maintenance plan and replace the coolers before they are likely to cause problems. All of these solutions have drawbacks. The tightly controlled water systems are costly to implement and maintain, and as we have seen, can actually contribute to corrosion/erosion effects. Gold plating can provide good protection, but the liquid coating process is incapable of providing a pinhole-free truly conformal coating for the complex high aspect ratio internal features of these microchannel coolers. The presence of pin holes can result in some of the erosion/corrosion effects that we are trying to eliminate.
Routine maintenance replacement of the microchannel coolers is expensive, not only in terms of cost, but also in loss of productivity from extra down time. So it is a problem, currently without a good solution. ANCER stands for Applied Nanoscale Corrosion Erosion Resistant Coating. It is a new coating solution that is entering the commercial sector after multi-year development by Advanced Cooling Technologies. The project is being funded by DARPA, a well-respected defense advance research projects agency, which has been responsible for many new technology innovations. Science Research Laboratories, SRL, was a key collaborator.
ANCER uses a chemical vapor deposition process to apply a thin nanoscale conformal coating across the surface substrate. The readily controlled vapor deposition enables the ANCER coating to be uniformly applied on difficult to reach, high aspect ratio, internal features of microchannel coolers. Further, the deposition process is readily scalable to handle more or larger part sizes. Our testing of the ANCER coating has shown it to be very effective in preventing corrosion and erosion effects. We’ll share our results with you today. And testing has commenced on materials other than copper to determine if that same benefit can be realized there, as well.
The previous slide introduced the ANCER coating. Here is a summary of its benefits. The chemically inert coating has shown to exhibit a significant reduction in corrosion rates, compared to gold-plating. We’ve seen how high velocity coolant flow can produce negative erosive effects. ANCER is a barrier coating that prevents that. The self-limiting deposition process can cover small defects on the surface substrate, producing a pinhole-free coating. The vapor deposition process ensures uniform coating, even on complex geometries, which are inaccessible to other liquid coating and plating techniques.
The coating is durable. Repeated thermal cycling testing have demonstrated superior bonding between the ANCER coating and the underlying copper substrate, without impact on corrosion resistance. The superior coating strength and durability allows a wider range of coolant specifications of flow velocity, electrical resistivity, and pH, allowing more relaxed operational requirements without affecting MCC performance. So there’s the major advantages of ANCER. Let’s now look at some testing results to explain why we are so excited about this new solution. But first, we’ll turn it back to Billy for a quick polling question.
Billy: Thanks, Pete. At this time, we’d like to present you with our first polling question. It should appear on your screen now. The question is, who does your company use to resolve critical thermal management issues? Your choices are a) in-house resources, b) external experts, c) a combination of both in-house and external resources or d) not sure. And you can make your choice now by selecting the appropriate button on your screen. Again, who does your company use to resolve critical thermal management issues? And while you’re answering that question, I will hand the presentation back over to Pete Riff. Pete.
Pete: Thanks, Billy. First, let’s take a look at the test setup. We used EIS, electro-chemical impedance spectroscopy measurements, for most of our data. You can see at position number one, where the samples being evaluated were placed. Included in the test loop are individually controlled pumps for each of the samples, a deionizing filter and an in-line resistivity meter, as well as a dissolved oxygen sensor.
Let’s now look at some results. First, let’s look at whether ANCER can provide any benefit for long-term corrosion rate as we claim. Here we plot a one thousand hour test of bare copper, a gold plated copper sample, and an ANCER-coated sample. You can see on the upper right the test conditions for the DI water. Cooler linear velocity is 3.8 meter per second. Resistivity is .3 mega ohm centimeter, and coolant pH is 6.0, relatively harsh conditions designed to promote corrosion. EIS measurements of corrosion rate is in millimeter per year, and are plotted for the three samples on the left. Bare copper, seen at the top of the graph, is a homogenous material with a very uniform corrosion rate. The gold-plated sample, seen below the copper, has an order of magnitude slower corrosion rate compared to the copper. But even over the 1,000 hours, there’s a clear trend of increasing corrosion rate.
The ANCER-coated sample, seen at the bottom of the graph, has a corrosion rate more than an order of magnitude slower than the gold-plated sample, and more than two times compared to the bare copper. Further, the corrosion rate does not change, because the changing corrosion rate is minimal also indicates that there are no significant erosive effects either. From this, we conclude that the ANCER coating provides significant reduction, improvement in corrosion and erosion rates.
Next, we will test if the coating has an impact on the thermal performance of the microchannel coolers. Here we test if the ANCER coating affects heat transfer performance of head-to-head, H2H, copper microchannel coolers from SRL. H2H is a single cooler with two coolers integrated head-to-head. One head is connected to a high temperature coolant flow, which serves as a heat source and the other head to a low temperature coolant flow, which serves as the heat removal mechanism. Measurement of the delta-t across the coolers enables the thermal resistant to be determined. The overall resistant network is seen next to the experimental setup.
The samples were tested before and after the ANCER coating was applied. As you can see on the plot on the right, the lines before and after coating are on top of each other. From this, we conclude that the ANCER coating does not impede or degrade the thermal performance of the microchannel coolers. So we have shown that the ANCER coating does provide significantly slower corrosion rate, but does not effect the thermal performance of the copper microchannel cooler. Let’s next look at whether the coating affects flow performance.
Again, we show results for an uncoated and then ANCER-coated sample at zero hours of life. Here we are measuring hydraulic performance, the pressure loss across the microchannel coolers as a function of increased flow rate. This is a test to determine if the ANCER coating affects the flow of the highly engineered microchannel cooler internal features. Hydraulic performance can change by either restricting or expanding flow channel dimensions. Again, we see that the before and after coating results are identical, and we conclude that the coating has not affected the design flow path of the MCC. We’ll next look at some accelerated life tests. But before that, we’ll turn it back to Billy for the final polling question.
Billy: Thanks, Pete. At this time, we’d like to present you with our second and final polling question. It should appear on your screen now. The question is, “Are you facing thermal management issues in the next a) zero to six months, b) six to 24 months, or c) you have no immediate issues. And again, you can make your choice now by selecting the appropriate button on your screen. The question, “Are you facing thermal management issues in the next zero to six months, six to 24 months, or are you having no immediate issues.” So as you answer that question, I’ll hand it back to Pete Riff. Pete.
Pete: Thanks, Billy. Next, we test whether the ANCER coating can provide stability in hydraulic performance over a 200-hour test. Again, test conditions are listed on the left. Note that the pH of six was selected because the corrosion rate of copper is 10 times greater at pH of six, than pH of eight for DI water systems. Results for both the coated and uncoated samples are plotted on the right. ANCER are the solid lines, and the bare copper are the dotted ones. Both ANCER samples, again, are on top of each other. However, a five percent deviation from the starting point can be seen in both uncoated samples. The deviation above the solid ANCER-coated samples suggest a flow restriction caused by a blockage. The dotted line below it suggests some kind of expansion of the flow channel, due to some erosion and corrosion effects. The two ANCER-coated samples are virtually identical, indicating stable performance.
Next, we’ll reevaluate the thermal performance of the coated and uncoated coolers after the 200-hour test we described a few slides back. Again, the ANCER-coated samples showed a less than a 1% change in thermal resistance after 200 hours. The uncoated sample showed a five percent increase in thermal resistance, a measurable change, particularly when MCC failure is generally defined as when the microchannel cooler shows a 20% increase in thermal resistance. Finally, ANCER-coated MCCs were dye-bonded to a set of laser diodes and arranged in a stack, stimulating real-world applications. The laser diode and ANCER-coated MCC stack can be seen on the left. The test conditions are listed on the right. Coolant is DI water, the coolant resistivity is between .25 and .5 mega ohm centimeter, dissolved oxygen content is between six and eight parts per million, pH is six, the coolant inlet temperature is 20 degrees C, drive current is between 120 and 140 amps, total optical power is 420 watts, and the number of laser diodes and microchannel coolers are three and four, respectively. Let’s look at some results after a thousand hours.
Here we see results in hydraulic performance after one thousand hours. The ANCER coating showed a 10% increase in hydraulic performance over this period, while the uncoated sample exhibited a substantial 35% increase in differential pressure. This is clear indication that the ANCER coating is providing protection from erosion and corrosion. The output wavelength and optical performance of the laser stack with the ANCER-coated MCCs were monitored during this time, as well. One can see in the graphs in the center that both the wavelength and the optical power were essentially constant. The ANCER-coated stack exhibited less than .5 nanometer change in wavelength, which equates to less than 1.5 degree kelvin change in junction temperature. To help calibrate a three degree kelvin change in temperature, equals one nanometer wavelength shift. Note also that the electroluminescence from the laser diodes is unchanged after a thousand hours.
At this point, I’d like to go to my screen to share a video with you. This is a quick video showing the ANCER coating in action. The video shows a copper coupon that has ANCER coated all over the plate except where the ACT logo is, which is masked off prior to the coating process. The coupon is placed on a heater and is raised up from 25 to 400 degrees C. It’s a 15 second video so please don’t blink too much. We’ll play it a couple of times so you can see the dramatic color changes. There are three temperature increments from 25 to 150 degrees C, 150 to 200 degrees C, and 250 to 400 degrees C. You can clearly see the bare copper changing color from thermal oxidation.
The ANCER-coated portion of the coupon remains constant throughout this test, a clear indication that the ANCER coating provides a tight bond to the copper, which prevents the thermal oxidation observed on the bare copper, even up to 400 degrees C. The color change seen in the ACT letters and nowhere else is pretty clear evidence that the ANCER is providing protection from thermal oxidation. This video is also available on our website and YouTube channel. Okay, we’ll end this screen share and go back to the presentation package.
So what’s next for ANCER? We are currently working with industry partners to validate and confirm the exciting lab results we have shared with you today. Assuming that continues to go well, we will expand our commercialization activities and offerings. Additionally, we are starting to explore if ANCER can be applied to other materials beyond copper, notably aluminum, which can also suffer from corrosive effects. Here, you can see some of our initial results. As with copper, we are seeing a substantial reduction improvement in corrosion rate versus the bare aluminum. We certainly hope that trend continues, so that we can return next time and share some exciting results on aluminum.
So let’s do a quick review of what we presented today. The Applied Nanoscale Corrosion Erosion Resistant Coating, ANCER, developed by Advanced Cooling Technologies can provide superior corrosion/erosion protection for copper microchannel coolers. Electro-chemical impedance spectroscopy, EIS, showed the ANCER coating reduces the corrosion rate of copper to values less than both copper and gold-plated copper. Thermal performance testing demonstrated that the ANCER coating does not impede MCC performance. One thousand hour testing demonstrated that ANCER-coated MCCs maintained hydraulic performance and exhibit no degradation in optical performance, indicating stable junction temperatures. Thermal oxidation testing indicate the ANCER coating can survive temperatures up to 400 degrees C.
Based on these results, we’re confident in saying that the ANCER coating offers improved corrosion resistance with a chemically inert layer, improved erosion resistance with a hard coating that protects the copper from negative effects of high velocity DI water systems. A completely conformal pinhole-free coating that can be uniformly applied, even on difficult to reach internal features, a good, strong bond to the copper surface, a superior coating that can provide this high-level performance even with relaxed DI water requirements. It truly is the ANCER for corrosion/erosion resistance microchannel coolers, and perhaps many other things, as well. We thank you for your attention, and now I’ll turn it back to Billy to answer some questions.
Billy: Thanks, Pete. At this time, we’d like to begin our Q&A so I’d like to welcome Dr. Tapan Desai to the line. Now, if you out there have a question, you can submit it by entering it in the box at the bottom of your screen. Dr. Desai, we already have some questions here in the queue. Our first question is, what is the typical thickness required to protect the substrate from corrosion?
Dr. Desai: For the application discussed here, ACT found that a 10 nanometer [00:26:02 inaudible] coating was enough to provide the protection in this highly corrosive/erosive environment without contributing to the thermal resistance. ACT has capabilities to perform optimizing of the coating thickness to meet our customer needs, but the coating is more or less concentrated on the nanometer scale.
Billy: How does ACT ensure the channels in the MCCs are coated?
Dr. Desai: This is a good question. It is important to ensure that the internal channels within the microchannel coolers are coated. ACT, in previous projects, has opened this complex micro coolers and performed [MCM?], microscopy to ensure that the coatings were uniformly coated across the channels.
Billy: We have time for about one more question here. Well, what systems…excuse me, let me just pull this up again. What systems other than copper DI water has ACT tested for the ANCER coating?
Dr. Desai: Another type of program that we mentioned here is the performed detailed study on the copper DI water system in axillary corrosion and erosion environments. Briefly, we did mention about the aluminum work that’s ongoing. We also performed testing on other systems, such as preventing leaks in raised joints to corrosion and also protection against acids due to oxidation on the [00:27:37 inaudible] water solutions. That’s some of the ongoing work right now at ACT.
Billy: All right, we’ll end it there. That’ll conclude today’s webcast. Again, if we did not get a chance to answer your question today, our sponsors will do their best to address them after today’s presentation. So our thanks to Pete Ritt, Dr. Tapan Desai and everyone out there for joining us. Just a reminder, this webcast will be available on-demand at www.techbriefs.com for the next 12 months. Have a great day!