Thermal Management

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

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

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

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

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

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

Have fun testing!

Amanda

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

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

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

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

The complaints grew more dramatic with every passing day.

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

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

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

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

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

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

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

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

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

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

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

At the time of writing, the price of silver (Ag) was approaching the USD$50/tr.oz. (Troy ounce) level, and threatening to go higher. With 1 Troy ounce being 31.1grams, this makes the cost of pure silver ingot close to USD$1.60/gram.

Image from goldsilveroz.com

Materials costs are therefore a major consideration for anyone using silver in any form. Naturally, we are now seeing a few Power Semiconductor packaging houses evaluating the possibility of moving away from silver-filled epoxies for die-attach. The alternatives they are considering include the adoption of solder paste (or solder in some other form: wire / ribbon / preforms) versus a silver-filled epoxy.

Here are some thoughts on the Power Semiconductor assembly pros and cons, based on using solder paste as an alternative to silver-filled epoxies.

Good news (+)

+   Reduced materials costs
+   Improved pot-life / shelf-life *
+   Improved high temperature thermal-cycling
+   Strong, metallurgical joint formed between leadframe (substrate) / joining material / die
+   Improved thermal conductivity
+   Faster throughput (more units per hour, UPH)**
+   Easy clean-up ***
+   Does not wick onto NiPd surface to cause poor wire bondability

 * Although it is true that solder pastes are stored under refrigerated conditions, they do not require the -40C storage that is typical of silver-filled epoxies. 

 ** The dispense of solder paste is very rapid and can be done using multi-dot dispense heads. It undergoes rapid temperature reflow, versus the slow cure needed for metal-filled epoxies, which can be up to typically 1-3 hours, depending on the volume of silver epoxy.

 *** Because the solder paste flux does not cure like a polymeric material,  tubing and other conduits for the solder paste are easily cleaned out using common solvents, or can be simply purged with flux.


  ==================

Bad news (-)

-   Capital costs #
-   Adoption time / new process learning ##
-   Needs a solderable die surface
-   Voiding increase ####

 # The main cost-drivers here are:

- Reflow: Specialty reflow equipment is required for high temperature solders, such as
Heller or BTU reflow ovens

- Cleaning: If wirebonding is required after the reflow process, standard cleaning equipment and cleaning chemistry (aqueous or solvent-based) will be needed to remove flux residues

- Gas: Forming gas (H2/N2) or simple nitrogen may be needed to assist reflow.

Note that increasingly, for clip-bonding (non-wirebonding) applications using the new ultralow residue solder paste Indium9.32, even cleaning may not be needed, as the residue has been found to be compatible with compatible with a number of molding compounds in the industry.

 ## By partnering with a company like Indium Corporation with many years of experience in die-attach soldering, the ramp-up time can be significantly reduced.

 ### A solderable surface is usually a sequence of Ti / Ni / (Ag or Au) plated layers. The thickness of the silver (Ag) or gold (Au) precious metal layer is usually limited to 100nm (0.1microns). Compare this to a standard silver-epoxy bond line thickness (BLT) of 0.5-2mils (12-50microns).

 #### Acceptable voiding of less than 5% of the total die area is fairly easily achieved with good quality substrates and die-finishes.

  ==================

In closing, I am indebted to my friend and colleague Sehar Samiappan (Indium Corporation Area Technical Manager - South East Asia) for his insights.

Contact me to discuss this further.

Cheers!   Andy

Jon major recently joined the Indium Corporation as a Product Manager for Solar back-end assembly products. I greeted him with this impromptu interview.

Jim: First of all Jon, welcome. It’s great to have you as a new addition to the team!

Jon: Thank you Jim – it’s an exciting time to be at Indium Corporation and a fantastic time to be a part of the growing solar industry. I am extremely enthusiastic about my new position and am looking forward to making a positive contribution to the solar industry.

Jim: I noticed it didn’t take you long to get up to speed. Your time in Silicon Valley must have helped.

Jon: Coming from the electronics industry with a focus on product development, new product introduction, manufacturing, and external partner management, I am excited that my past experiences can contribute both to the industry and to Indium Corporation. After joining Indium only a few weeks ago, not only am I getting used to Upstate NY weather, but I have been immersing myself in solar with the goal of gaining a comprehensive understanding of:

•       Both rigid and thin-film technologies

•       Technology trends

•       Global and regional markets (EU, China, US, North America)

•       Solar supply chain (Silicon, wafers, cells, module, equipment, inverters, integrators)

•       Equipment manufacturers, contract manufacturers, and how we can collaborate with them to move the industry forward

•       Our products and pricing

•       Our current and future customers

•       Our short and long term opportunities

•       Our competition

•       Our roadmap

•       Our strengths, weaknesses, and threats

•       Our manufacturing capabilities and our QA process

•       Our sales channels, value proposition, key differentiators

•       All Indium processes

Jim: I know you've got solar products on your mind. Let our readers know a little bit more about your role here at Indium?

Jon: As a Solar Backend Product Manager I will focus (officially) on the business development and growth of Indium’s Solar Back End product offerings.  Now that sounds great but what does it actually mean? I could cut and paste my official job description but I prefer to explain it in my own words. As I think about the first part of that statement, “business development and growth…”, I see my role as:

–      Know the market, the customers, the product, and the competition

–      Develop relationships with the Indium team, reps, partners, equipment manufacturers, and, of course, customers

–      Write valuable data sheets, publications, and sales literature

–      Listen to our customers' needs and provide solutions

–      Manage schedules and orders with minimal surprises

–      Build cross-functional collaboration (sales, distribution, marketing, engineering, R&D, QA, production, management)

–      Never let down partners or customers

–      Support all functions of the organization, both internal and external

–      Deliver above & beyond commitments

–      Make great bets – on technology, customers, and opportunities

–      Understand the product life-cycle

–      Ship high quality, consistent product

The second part of that statement “..of Indium’s Solar Back End product offerings” is fairly straightforward. Of course this means I will focus on Indium’s current back end products (tabbing ribbon, bus ribbon, metallization paste (or as I prefer to call it – “grid ink”), flux and flux cored wire). With a product development background, this also means I have an opportunity to work with customers, partners, and R&D to develop and bring new products to market that will advance the module assembly industry – very exciting for me personally.

Ultimately, I think of my role as both building awareness of Indium’s products and superior technical support available to our customers as well as helping to shape our growing industry.

Jim: Okay Jon, you’ve had a while to settle in and get familiar with our Solar Team’s past and present – what are you planning for the future of module assembly?

Jon: Regarding the future of module assembly it’s a bit early to know for sure but I am excited about our low-temperature bismuth-containing alloys. These low temperature, lead-free, bismuth-containing alloys reduce the soldering process temperatures, thus reducing thermal stresses. I’m also working with the Indium production team to further reduce our tabbing and bus ribbon yield strength. A lower yield strength will reduce mechanical stress on cells during the assembly process. This is crucial to minimizing the possibility of microcracks and cell breakage during the solar module assembly process.

In closing, having lived in California for the last 10 years, I am not 100% familiar with our Upstate New York climate, and especially not all the snow shoveling. I see in my future a solar powered driveway heater!

Jon can be reached at jmajor@indium.com

This is my second post on the implications of using aluminum silicon carbide (AlSiC) metal matrix composite materials as the heat spreader, heat sink, or TEC medium for thermal dissipation. Previously, I described how the CTE of an AlSiC substrate could be altered for matching mating surfaces based on the amount of SiC filler used.

These mating surfaces are assumed to be bonded via a solder bond. That begs the question, “Can AlSiC be soldered directly? Is the aluminum metal filler free and in great enough density to provide for metallic surface bonding?”

In order to be sure of this answer, I went to another AlSiC materials expert, Tom Sleasman, business manager at Rogers Corporation. Rogers Corporation offers a new, special AlSiC variety with an aluminum skin (AlSic-D3), which I thought would have the best solderability of any of these materials, if that was even possible.

 Unfortunately, Tom’s response was, “We do not recommend soldering directly to the AlSiC for the same reasons as to aluminum. Our process yields a part with an Aluminum rich skin on the outside of the part and in all cases [where the AlSiC is soldered] I am aware of utilizing a nickel plating or copper coating process to provide a solderable surface.”

I cannot speak directly to soldering these new aluminum skin AlSiC materials, however soldering to aluminum is a difficult process, which cannot be accomplished without the appropriate flux. That flux is typically acid-based and offered only as a stand-alone product, not as a solder paste or preform flux coating. 

Based on Tom’s remarks, I conclude that the best way to solder AlSiC is to have it pre-coated with an oxide-resistant metal, such as nickel or copper. Regular AlSiC substrates cannot be soldered without this surface treatment.   

Once again, here are some things I learned at this year's IWLPC show 2010 in Santa Clara. Picture below taken at Philadelphia airport, where I drafted this blog posting.

 
I think there could be ten things this time, but who’s counting? 

 

-          TSV stands for “through-silicon via”. AND “through-substrate via”. AND (as one attendee joked) “through-stuff via”. It’s also 2-3 years away from commercial implementation on anything other than camera modules: which I thought I heard last year. Hmmmm… Speaking of which…
 

-          Camera modules are still the only commercial TSV applications at the moment, although I heard arguments that camera modules were not true TSV as either they “weren’t leveraging the real potential of TSV”: simply metal-lined apertures contacting the CCD pixels on the backside of the camera die. So more like “into-silicon vias” (ISV’s) than strictly through them.
 

-          One of the major advantages of 3D stacking is heterogeneous system integration: you can put silicon, SOI, GaAs, MEMS etc all in one stack or some SiP-on-chip array and repartition the chip functionality in three dimensions exactly as you need it. You can also mix joining technologies together: coined metal bumps and ACF with diffusion bonding etc. Dr Peter Ramm of the newly renamed Fraunhofer EMFT gave a fascinating talk on the eCUBE and (new) eBRAINS projects. Peter also confessed that the eBRAINS acronym was a bit of a stretch, and I’m sure the desire for improved technology came before the acronym.
 

-          Thermal management issues for 3D (TSV-based) memory will be less of an issue than previously thought, since the driver for memory integration is reduced power consumption. That’s either 40% or 50% reduction, depending on who you talk to. Fewer RC losses = lower power wastage; less heat. Boom: you’re done. Dr Bradley McCredie of IBM pointed out in his keynote speech that by moving to TSV for DRAM, you may get a significant power saving, but this doesn’t scale: once you’ve stacked the die, that’s it. One time offer, and then as the vias get thinner – the problem starts again.
 

-          No surprise, but known good die (KGD) will be critical for chip-stacking, echoing Peter Ramm’s comments about testing for KGD. Unfortunately there are two issues here: 1/ (from Peter Ramm) that test pads will need to be integrated into the design, consuming real-estate that you thought you just won back 2/ That via-middle or via-last technology TSV will put added stresses on die that WERE KGD, up to the point that you put holes in them.
 

-          The new paradigm for consumer devices is clearly “mobility, customizability and cooooolness (MCC)”. Sorry to seem preachy here, but I heard one marketing expert, and even one engineer trot out the old adage of “smaller / cheaper / faster” (SCF), which I hoped had died out around the end of the last century. The lesson from Apple’s iPAD (at time of writing reportedly selling 1-2million units a month)  seems clear: consumers will pay for MCC no matter what. So how’s that SCF mantra working out for ya? The iPAD is much bigger than a cellphone; it’s priced at top dollar and is (arguably) not as functional as a laptop. SCF is rapidly becoming the Holy Roman Empire of marketing jibber-jabber. Ok: I think I’ve made my point: tell me what you think.
 

-          As I said during the final WLP session I never thought I’d hear the words “Intel, wirebond and leadframe” used in the same sentence. Well, that was simply showing the depths of my ignorance. Dr Saeed Shojaie from Intel’s NAND Solutions Group in Fulsom, CA and his team have been working with PTI, using mixed diameter gold wire bonds (thus eliminating wire sweep) to allow stacking of 8 die or more on a leadframe:  then mounting that stack-up inside something that looks awfully like a gull-wing LSOP (large scale outline package). OK: it IS a gull-wing LSOP. But it’s Intel, so it’s not your grandfather’s LSOP. They have done some interesting work on double-bends (“downset”) of the leads to eliminate distortion of the very delicate leadframe and still maintain the desired lead length.. Ok, you cry “Why not a TSV? They’re so cool!! “ Well, when you understand that this is Intel’s answer to solid state drives (SSD) based on reduced cost; shorter time to market; leveraging existing JEDEC package designs and test infrastucture; known reliability issues…. you realize that it is actually extremely cool, very pragmatic and a perfect example of perfecting a known form, rather than waiting for the next new thing to be half-ready. I’ve got to confess: I saw something similar stacked, one on top of the other (using PoP paste), by an Asian customer and thought it was a joke. It’s not. Saeed told us his team was going to be using 8 stacked 4GB die initially, moving to 8GB by next year. PoP stack two of these and that makes 128GB (0.128TB) of solid state drive. Nice! How about the access speed, though?
 

-          Implementation of 0.3mm WLP (wafer level packaging) is two years away… and always will be. Here’s the background: Jan Vardaman of TechSearch International took a novel approach to her chairmanship of a panel of industry luminaries discussing the future of WLP. She gave a homework preassignment to her four experts (from Broadcom, Qualcomm, Casio and National Semiconductor). There were a lot of common themes in their responses, and the general agreement was that it looks like 0.3mm WLP is easily feasible and has been for years, but it’s the substrate guys who can not reduce the routing costs to make 0.3mm feasible for portable applications. There may be 0.32 or 0.35mm as interim measures for mobile consumer applications, however, but that could be the limit based on costs.
 

-          Rosalia Beica of Applied Materials gave the closing speech, talking about the work done by the EMC-3D group. Basically, the EMC-3D group has the technology and Applied has the tools to copper-fill diffusion-barrier-layer-coated 20:1 aspect ratio silicon apertures (20microns deep, for the record), eliminating issues with voiding and overburden. Now the question is: will copper be the conductive via-fill material of choice? Thermal cycling does seem to put a lot of stress inside the vias from the modeling work I’ve seen. Let’s see how this pads out.
 

-         No news that wafer-thinning will be critical for wafer-stacking, but we heard from Bill Crouch of Süss Microtec that current minimum die thicknesses are 10microns for logic, 40microns for DRAM and 25microns for flash. The critical yield issue for thinned wafers remains debonding at the wafer edges without cracking, with the key being the physical properties of the temporary waferbonding adhesive.
 

-          Finally: too many pennants and “you look like a Russian General” as one wag told me. He’s right. Actually I’m not sure “pennant” is the correct name for those sticky “badges of honor” that the SMTA puts on the bottom of your lanyard name badge, but yes, I did look a bit of a pillock [see picture below].

Quick reminder: Device-in-skull is one year closer - the technology is already appearing.

Cheers! See you all next year.   Andy

剛剛看見一個關於如何使用AuSn預成型焊片 （金錫，主要是Au80Sn20的共晶材料）來做laser bar bonding的短文和錄像，頗受啓發。在此與大家共享。短文和錄像轉載在Finetech:  http://www.finetech.de/micro-assembly/applications/laser-bar-bonding.html

Laser Bar Bonding
In comparison to single lasers, laser bars consist of several single edge-emitting lasers comprised in a silicon bar. Bundling the light results in significantly increased output power as needed in a wide range of applications.

Laser bars are high power products, applied wherever small and efficient light-emitting units are needed. They mainly serve as pumping sources for optical resonators of high power lasers. Another field of use can be found in medical appliances.

What are the challenges?

• Sensitive components with brittle materials and optically active areas
• Delicate edges and facettes
• Perfect coplanarity required to ensure proper thermal management
• Highest placement accuracy needed to ensure defined overhang
• Stacked mounting (lasers to submount) requires different solder materials with their appropriate profiles
• Void free bonding
• Solder materials are prone to oxidation, process integration required
• High magnification of large components
• Indium bonding under process gas atmosphere

First image & English content source: FineTech; AuSn image from Indium Corporation.

Indium Corporation has won the Innova Award for Best Technology for its Heat-Spring^® metallic thermal interface material (TIM).

Heat-Spring is a clean, high-performance thermal solution for the increasing demands of high brightness LEDs. It is a compressible metal foil with proven performance in such demanding environments as electronics, aerospace, and power devices.

The compressible TIM provides low thermal resistance as a result of its high thermal conductivity (86W/m-K) and its ability to conform intimately to interface surfaces.

Unlike other thermal interface materials, such as thermal grease that bakes out, dries out, or pumps out during use, the thermal resistance of the Heat-Spring continues to improve with time and power cycling.

According to Jordan Ross, Market Manager for Thermal Materials, “Indium Corporation is honored to be recognized with the Innova Award for our patented Heat-Spring product. With its patented compressible interface design, Heat-Spring provides optimized surface contact, superior thermal conductivity, and enhanced heat flow.”

Sponsored by LED Journal, the Innova Awards feature leading companies within the LED market which have shown, through their products and services, the most innovative and advanced technology breakthroughs in LEDs. The award is designed to recognize companies each year for industry leadership, product development excellence, best new technology, and outstanding LED applications, which will eventually lead to the widespread adoption of LED technology in the marketplace.

Patty, Rob, and The Professor finished their tasks in Shenzen and were flying to Shanghai for their last set of challenges in electronics assembly.  Then they would head back to the US, Rob and Patty being only a week away from their wedding day.

As usual Rob, conked out as soon as the plane lifted off. Surprisingly, The Professor also drifted off to sleep. Patty was too excited to sleep. Rob’s mother had given her and Rob their wedding presents early … an iPad  for each. They decided to bring only one laptop and one iPad. Patty was a little nervous about using the iPad for presentations but it worked quite well. She was still surprised that the iPad did not have a USB port. The Professor also gave each of them an early wedding present, a Pickett slide rule for Rob and a K&E slide rule for her. She must be the only person in the world right now that was watching a movie on an iPad and solving a math problem with a slide rule!

True to form, The Professor was passionate about how learning to use a slide rule helped improve a person's innate math ability. He showed Patty and Rob how to use them and gave them several assignments. Rob was better with his slide rule than Patty due to the amount of “one on one” time he had with The Professor. She had to admit that using the “slip stick” gave one more of a feel for calculations and it was consistent with one of The Professor’s adages: “Always know approximately what the answer to a calculation should be…..it will help you to avoid errors."

In addition to the iPad and slide rule, Patty was excited to be going to Shanghai at the time of the World Expo 2010. Our trio had scheduled some time at the expo into their busy schedule.

Their plan was for Rob and The Professor to work on some productivity issues and for Patty to take on some of the process materials related problems. The three of them again met with the site GM for ACME’s newly acquired plant in Shanghai, a Mr. Wong. Wong was relieved to find that they all spoke Mandarin, as his English was a little rough. When The Professor addressed him in excellent Shanghainese, everyone was speechless. Patty was determined to ask him about this later. No American spoke Mandarin, Cantonese, and Shanghainese!

They again agreed to stick to Mandarin. Patty headed out to the line, accompanied by a young Chinese engineer, Zhou Chang, who seemed to be taking more interest in her than expected. She tried to make her engagement ring visible, but she wasn’t sure the he knew of the significance of it. When she got to the line that was experiencing yield problems, the Engineering Manager, Fei Ding, met her. He showed her some of the fails and she quickly identified the head-in-pillow (HIP) defect as the likely culprit. After investigating some more fails, looking at stencil printing, some of the BGA components, and component placement, she asked Zhou Chang what spec was used to thermal profile the line.

“I don’t understand what you mean,” Zhou said in Mandarin.

“How do you determine what the reflow profile should be?”  Patty responded.

With more discussion, Patty determined that they had one profile for all products! Fortunately most of the products were of similar, small thermal mass.

“What solder paste do you use for this line?", Patty asked.

The embarrassed silence suggested that Zhou did not know! They grabbed a tube and Patty was relieved to see that it was one of her favor solder pastes. Since profiling was so rarely performed, Patty and Zhou had to go to another part of the complex almost a mile away to find a reflow profiling unit. After taking the profile, the likely solution appeared. The 11 zone oven was very long and the reflow profile had a long thermal  “soak” before the temperature went above liquidus. This long soak probably exhausted the flux, so that when the PWB went above liquidus, there was little flux left, resulting in oxidation and poor reflow.

All during their time together she had mentioned that her fiancé Rob was here, with her on the trip. This information seemed to do the trick.

“Zhou, why don’t you look up the solder paste spec on the web and then set up the right type reflow profile,” Patty suggested.

It was clear that Zhou was troubled. It became obvious to Patty that Zhou did not know how to profile a reflow oven. Patty set about working with Zhou to accomplish this mission. Within an hour they had re-profiled the oven and, over the next two hours, 300 PCBs were manufactured with the yield improved to 95%.

Patty asked Fei if she could give a brief presentation on the head-in-pillow defect to his team and he cheerfully agreed. Fortunately for Patty, her friend Mario Scalzo had given her his presentation that he gave at APEX 2010 on HIP (head-in-pillow). Patty always enjoyed visiting Mario in Utica, NY, as he always knew the best restaurants in town.

Her major points were:

HIP is caused by the failure of the BGA sphere to reflow with the solder paste. There are 3 major reasons for HIP:

1.       Supplier Issues

a.       Solder BGA sphere oxidation

b.      Silver segregation to the BGA sphere surface

2.       Process Issues

a.       Stencil Printing

                                                               i.      Registration accuracy

                                                             ii.      Insufficient solder paste

b.      Component Placement

                                                               i.      Off pad

                                                             ii.      Out of plane

                                                            iii.      Non optimum pressure

c.       Reflow

                                                               i.      Inappropriate reflow profile

                                                             ii.      Flux exhaustion

                                                            iii.      PWB warpage

3.       Material Issues

a.       Poor solder paste transfer efficiency

b.      Insufficient solder flux oxidation barrier

c.      Solder paste slump

d.      PWB or BGA warpage

Patty went on to say that she had investigated all of these issues with Zhou, and that the reflow profile was not optimum as the very long soak time had exhausted the flux. The other possible issues in the list did not seem to be a concern.

At the end of the day Patty, Rob, and The Professor met at the GM’s office to leave together for dinner and the Expo. Patty had to ask, “Professor, how can you possible know Mandarin, Cantonese, and Shanghainese?”

“Actually I speak Min reasonably well too,” he replied.

“How can this be?", Rob inquired.

“Mother and father were missionaries with Wycliffe Bible Translators,” The Professor answered.

“I grew about around many languages during my youth. Mother and father speak more than I do,” he finished.

Patty went on to tell about the interest that Zhou Chang seemed to have in her, and how she had to discourage him.

“The burdens of being a beautiful young woman,” Rob teased.

Patty elbowed him, but they all left the taxi laughing as they headed for a restaurant near the Expo.

Best Wishes,

Dr. Ron 

The Shanghai, slide rule, and HIP images are from: 

http://pool14.files.wordpress.com/2008/12/shanghai_skyline_g.jpg

http://www.hpmuseum.org/powerlog.jpg

http://ppsimanufacturing.files.wordpress.com/2010/03/bga100.gif

Thermal News recently interviewed Amanda Hartnett regarding thermal management with metal TIM (thermal interface materials). You can read the full article here:

http://www.thermalnews.com/eprints/Indium_0310.html

I really like this interview, so I’m not going to give away the best parts – I want you to read it yourself. I do, however, want to provide a couple teasers to pique your interest. I’m leaving out the especially cool parts…

“Pure indium, used as a solder TIM, delivers a thermal resistance to…”

“Also, it is important to consider the reworkability of an interface material. TIMs such as … are very simple to rework. Others, such as conductive epoxies, can be quite difficult.”

“When I measure the performance of thermal interface materials, I characterize them based on ... This value is typically more valuable than bulk thermal conductivity. For a compressible TIM, the … assumes the actual contact which will be made between the interface material and it’s mating surfaces. This provides a measurement of thermal performance which is as close to real-world per Watt or per cm2 as I can provide without being application-specific.”

Are you still reading this blog? Go read the article!

~Jim

If you look for indium on the periodic chart, you will see that it located right by tin (Sn) and lead (Pb) but it is a world away in terms of its properties.

Indium and indium alloys have some unique characteristics that make them ideal for a variety of usages including: soldering to non-metals, low temperature alloys, RoHS compliance, thermal management, battery manufacturing, cryogenic or hermetic sealing and many, many more.

Does your application require you to bond to glass, quartz or ceramic?  Then you know that traditional solders will not work.  But if you choose Indalloy #4 (pure indium) or Indalloy #1E (52In 48Sn) you will get excellent wetting.  If you choose an alloy that includes silver (like Indalloy #290 which is 97In 3Ag or Indalloy #3 which is 90In 10Ag) you will get slightly less wetting but a much stronger solder joint.

Surface preparation along with the proper tools and the proper process are key to acheiving the proper bond.  You can get all the details with our PDS, Bonding Non-Metallic Materials Using Indium and High Indium Alloys.
 

下周在硅谷地区，Indium公司会参加Semi-Therm---“热管理”的盛会！

在微型化(miniaturization)的今天，我们的各种电子产品都越来越小，但是性能更多更齐全，消耗功率更大，那么单位面积上所要求的散热，也应该越来越多。 这是为什么这几年热管理(Thermal Management), 热管理材料(Thermal Interface Materials---TIM) 会成为我们讨论的热门话题。  举个简单的例子吧， LED灯，面临的最大挑战之一就是如何解决热管理问题。

传统的热管理材料， 有导热硅胶(Grease), graphite, 相变导热材料(phase-change materials)等。这些化学材料都很便宜，也能起到一定的导热性能。 但是因为物理性质的限制，金属的导热性能的普遍都比这些化学物质的导热性能强很多。 比如说化学材料，一般能做到几瓦每摄氏度的热传导(thermal transfer efficiency), 已经很不错了。但是金属材料，如纯铟片(pure Indium foil)，在一定的表面处理后，是86W/⁰C.  

好了，先写到这里。 下周再和你分享更多展会等热管理材料的信息！ 

PS:  除了在下周在Semi-Therm展会和客户等一系列活动，3月份我会踏上一段新的征程，转去西雅图工作，负责美国西北部一系列的销售/技术活动。期待与你分享更多新技术，工艺信息，行业动态，客户疑难等！ Cheers!  

Patty, Pete, and John prepare to do battle with "The Big O."

Patty and Pete were able to squeeze in 9 holes of golf, though it was really stressful for Patty. Pete was a good golfer, but not in Patty’s league; he typically shot in the low 80s for 18 holes compared to Patty’s 68-72 range.   Today, going into the 9^th hole, Patty was even par and Pete was one under. He was teasing her relentlessly.   The ninth hole was 532 yards long. Patty used all of her recent training and focused as she drove the ball. Her swing speed hit 114 mph and with a 4 mile an hour tailwind, her drive was 291 yards, 30 yards beyond Pete. Her second shot, with a five wood was 12 feet from the pin. Her putt was dead center for an eagle, Pete’s 8 foot birdie putt lipped out of the hole. Whew! She beat Pete by one stroke! Pete was still thrilled that he gave Patty such a close call.

As they left the golf course, Pete said, “John is really working miracles at the factory, given the constraints he is working under. He has developed a disciplined approach to changeovers and uptime, and has eliminated most waste. But the factory really needs to be cleaner and more organized. With all that is on his plate, and no cleaning staff, he will have trouble implementing a 5S. It will be hard to win new customers with the place looking like it does.”

The next morning, as they prepared for the meeting with Oscar Patterson, Patty noticed that John’s color was ashen.

“John, are you alright?” Patty asked.

 “You’ve never been in a meeting with Mr. Patterson. He can be a bit…uh…. difficult,” John stumbled out.

“From what I hear he is a ruthless, brutal dictator,” Pete added.

John did not disagree.

Patty thought it might be best to call back to her site GM to clarify her mission.

The GM told her, “This guy is a blowhard, it would be great if you could review with him your findings and get his buy-in. But, don’t take any grief from him. He forgets that he sold us his company. Now he has a boss, and it is me. I told him you were going to perform an audit and I want him to work with you.”

So Patty, John, and Pete went to Oscar Patterson’s office to review their findings. Patty was immediately intimidated by him. He was a huge man with a ponderous stomach. But the posters in his office were the worst. One read “I’m the Boss, you aren’t.” Another read, “My way or the highway.” Then she saw, “The Golden Rule of Management: Whoever has the gold makes the rules.” The last one she took time to read was especially troubling: “It’s a question of mind over matter: I don’t mind and you don’t matter.”

Patterson spoke first, “Let’s get this over with, I don’t have time to waste on this nonsense. I’m the boss and I’m responsible for profits, so give me your crap and get out of here.”

The Professor always advised Patty that after an audit it is best to present the strengths first and then the problems. However, never call the problems “problems,” call them “opportunities for improvement.”  “I learned this from my colleague Joe Belmonte,” The Professor told her. She had since met Joe at a few trade shows and was impressed by his wealth of experience and in-depth knowledge of assembly processes.

She started by discussing the very good 25% uptime, and the fact that the operators were quite good at changeovers.  Pete had pointed out that the operators told him that John was responsible for both of these successes. The operators liked and respected John, but realized he had a tough job working for Patterson.

As imagined, Patterson warmed up to this compliments. 

“I told ACME management that buying my company was a good deal. We cut costs and I am able to make a profit even though I have losers like John working for me,” Patterson bragged.

Patty was furious at this comment. Pete looked like he was going to jump across the table and take a swipe at the “Big O.” John just sat there looking defeated.

“This isn’t as bad as I thought it would be,” boomed Patterson. “Continue.”

Patty then reviewed the 7 mudas. She had been surprised that the company did quite well in this part of the audit also, undoubtedly attributed to John:

1. Overproduction

2. Unnecessary transportation

3. Inventory

4. Motion

5. Defects

6. Over-Processing

7. Waiting

Hence, Patty’s comments were positive on this topic.

“You'se guys aren’t so bad,” boomed Patterson. “I told you I was good at generating profits, even stuck with a dufus like John here,” he finished.

At that comment, Pete’s faced turned the most crimson Patty had ever seen.

Patty then went on to “Opportunities for Improvement.” She thought she would start with 5S.

“We performed a “5S” audit of your facility. This manufacturing philosophy consists of:

1.       Sorting

2.       Set in Order

3.       Shining

4.       Standardizing

5.       Sustaining the Improvements,” she started.

“As ACME strives to get more customers for our contract manufacturing services, 5S is an important consideration, as many of our current and future customers practice Lean and especially 5S at their facilities,” Patty added.

As she went on she reviewed the lack of order and cleanliness in the facility. She had photos of dried solder paste on the stencil printers, the flux and dust “stalactites”, and several other examples of 5S violations. Patterson’s face soon matched Pete’s in its level of sanguinity. But he said nothing.

Patty then volunteered that she and Pete would work with John and his team to implement a 5S if desired.

Patty could see Patterson was ready to blow, but she felt she must go on. The only topic left was turning off the nitrogen in the wave soldering machine.  As Patty played the wave soldering video, surprisingly, Patterson seemed interested. 

She continued, “We think an opportunity for improvement would be to re-instate the use of nitrogen in the wave soldering process. First pass yields have dropped from 94% to 87%, thus increasing re-work. Or, perhaps, implementing a more robust wave solder flux. I contacted a wave flux vendor and I have some recommendations.”

At this Patterson became even redder in the face, in a rage he grabbed Patty’s laptop and threw it on the floor, instinctively Pete dove for the laptop, spun around and inserted his chest between it and the floor.  Patty had never seen such agility in a 45 year old man.

“You bozos are worse than John the clown here!" he shouted, as he gesticulated toward John. 

Patterson then kicked the trio out of his office. Pete was ready for a fight, but John and Patty, both visibly shaken, held him back.

Patty immediately called Sam, her GM, and told him in detail their findings and what happened at the meeting. She gave a good impression of what John had accomplished in spite of Oscar Patterson.

“Wow! Patty, I’m so sorry. I didn’t expect it would be this bad. I’ll change my schedule and fly there today. This situation will not stand. Why don’t you and Pete take a break and meet me for dinner at Dinardos at 7PM? Bring John with you.”

Patty was glad that she backed up her files last night on SugarSynch, even though it looked like her laptop was fine. 

Colonial Williamsburg was only a 45 minute drive away, and it was just 10AM. Taking Sam’s advice to “take a break,” she and Pete drove away and toured this beautiful living museum. They also had lunch at the Trellis.

Surprisingly, with the Williamsburg respite and all of the walking Pete and Patty did, they were more relaxed and hungry than they thought they would be. 

On the way back to Dinardo’s Patty asked Pete, “How did you save my laptop, I’ve never seen such an agile, athletic move?”

“Twenty-nine years of beach volleyball,” Pete answered.  “I was good enough that I tried out for the Olympics  in ’92. Humbling experience,” he added.

About 10 minutes before they arrived at the restuarant, Patty's mother called with updates on the wedding plans.....only 10 weeks and counting!

John had arrived early at the restaurant and Patty and Pete met him. He looked very nervous. 

“John, how’s it going?” asked Pete.

“It’s hard to be optimistic,” John answered.

On that note Sam walked into the restaurant.

“This must be John Davis, the new GM, having replaced Oscar Patterson,” Sam stated with great cheer.

These words didn’t seem to register with John.

“Congratulations John, well deserved,” Patty and Pete chimed in.

In the few days they were there, Patty and Pete had grown quite close to John.

As the information sank in, tears welled up in John’s eyes.

“Do you think I’m up to the job?” he asked.

“John, you are already doing the job,” Patty answered.

Epilogue:

Sam had felt it best to have the police accompany him to see Oscar Patterson with the news that he was fired. Patterson became so agitated that the police had to threaten to arrest him before he calmed down and was escorted out of the facility.

With John at the helm, the “shop” was not recognizable in 3 weeks, as he implemented a 5S program that he designed with Patty and Pete.

He performed some DOEs to find a wave solder flux that could perform well, without nitrogen, for most of his applications. However, he still used nitrogen for a few boards that had a large thermal mass. All of these, and the many other, decisions he made were data driven.

Have you performed a Lean audit of your facility? Do you regularly practice 5S and look to eliminate the 7 mudas? Are your decisions “data driven” as John’s are?

Cheers,

Dr. Ron

Tommy: NanoFoil...it's kind of like aluminum foil in thickness and look, but a little stiffer and when you put energy into it, like a spark, it heats to 1500 degrees Celsius (which is hotter than lava in a volcano) for less than a millisecond!

My engineering and non-engineering friends display puzzled looks, you know the ones you get when you start explaining that your favorite sport is water polo and it has nothing to do with horses...ok the look you have right now

Engineering Friend: Umm so what can I blow up with it?

Non-Engineering Friend: So wait, if it's that fast and that hot, I bet you could make really fast grilled cheese. Have you called Healthy Choice yet?

Good Grief!

Al + Ni -> AlNi  (You didn't know there'd be chemistry involved did you?)

At some point we have all had experiences which convinced us that metals have a high thermal conductivity. It may have been the hot spoon you left in your coffee after stirring in a little cream and sugar, or the hot door handle you grabbed on a simmering hot summer day when climbing into that now-vintage car of yours. In fact, the high thermal conductivity of metal can even account for the ability to get your tongue stuck to a metal pole in the cold of winter (or the metal screen door while waiting for the school bus as was my childhood experience). We generally understand the phenomena of metals to have a high thermal conductivity to be true, however what is the basic science behind the high thermal conductivity of metal?

In the July/August issue of Advancing Microelectronics, Dave Saums, Bob Jarrett, Andy Mackie, and Jordan Ross published an article titled, “Thermal Management Materials Choices for Power Semiconductors,” which begins to explain this.   


 

The article describes metal generically as positive ions within a “communal sea of their valence electrons”, together providing a net neutral charge.  The image above depicts this arrangement.   A metal is unique because unlike non-metallics which are viewed as highly organized lattices, valence electrons of metal atoms are not strongly held by the nucleus and are highly mobile. These mobile electrons transfer electric charge as well as heat across the metallic structure.  This freedom of the valence electrons accounts for the high thermal conductivity in metals.  At ambient temperatures, metals are attributed with high conductance, however an additional rise in thermal conductivity is found as environmental temperatures rise.  This activity can be explained using the principles explained in the Wiedemann-Franz Law.  

In electronics packaging, there are many materials to choose from which will provide various thermal dissipation outcomes. Metallic materials are generally preferred for high power devices due to their high thermal conductivity, lending them for adoption in heat sinks, heat spreaders, baseplates, and even thermal interface materials as Indium is most familiar with.  

7:40am

Just got in, fired up the laptop, and made some hot chocolate. This is the best time to get a jump on the day. I clear out my spam that rolled in overnight and prioritize the emails in my inbox. The first tasks that I cleared were:

-         Connected a new potential solar materials rep with the right people at Indium Corporation

-         Recommended the optimal reflow profile for Indium9.88HF PoP solder paste

-         Activated an online Vapor Deposition course

-         Helped specify tabbing ribbon and solder wire for a college student working on a lunar rover project

-         Planned underfill testing for today.

10:00am

After rounding up materials, components, and equipment, Brandon Judd and I assembled some BGAs on a customer's test board. Later today we’ll underfill, and rework some of the components to demonstrate the yield of a reworkable underfill. Each board had 18 components of 2 types. One of them is a very large, coarse pitch BGA. The other one (you guessed it) is exactly the opposite, a small, fine pitch BGA.

Noon

Took a drive and ate lunch.

1:00pm

When I returned to my desk, I noticed a few emails that needed attention. One was regarding the PoP solder paste reflow profile I mentioned earlier. It looks like that will work for the particular application. Another email regarded a barcode design that I am working on for a customer.

1:30pm

Took a call regarding solder sphere attachment. WS3622 was recommended to ease flux cleaning in place of an older tacky flux.

2:00pm

Answered an interesting call regarding thermal management for a cavity CPV assembly. The coolest part – he found my contact information on this blog.   

2:45pm

Worked on editing an interview for Global Solar Technology magazine. I had a chance to discuss many of our solar products in detail, while explaining the advantages of each.

3:00pm

The schedule for the day shifted, so we will reconvene the underfill testing early next week.  This gives me some time to begin the Interfacial Engineering course mentioned earlier. Looks pretty interesting so far.  Spent some time going through the course material and learning some new things.

4:30pm

Posted this blog entry. After looking at the things I’ve mentioned here, I noticed I could tweet all the little parts of my day. If you’re interested, check: http://twitter.com/SolderNinja