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Sorry guys I'm using analog clock, I'm planning to use digital one, those that could display multiple time zones!

Master

It's unique molecular made it the wolrd's most versatile supermaterial! it has the broadest electronic transmission of any material known to man.

Master

Diamond is one of the most exciting materials available today, scientists are currently researching new applicationswith the potential to transform performance in the industry.

 

Master

Brian, I'll have to buy you a proper clock that will display multiple time zones.

Blogger

OOps. sorry I missed that chat. Missed that it was eastern time! Problems with the analog nature of the earth!!!!

 

Blogger

Later folks. Thanks for the forum Brad.

Master

Thanks. Good day, all.

Newbie

Thank you for providing the forum!

Blogger

Thanks for your participation guys---this was a very useful and informative chat session!

I'm thinking maybe integrated RF ICs for next month

Well folks, looks like the comments are winding down. We'll leave the chat window open a bit longer. I'd like to thanks all of our guests for their comments and for the other folks who were observers. We will do another chat next month - topic TBD.

Blogger

Yes mechanical strength is very high.  Which means in specific heat pipe type geometries you can get away with a very thing diamond heat spreader and still keep mechanical integritiy. 

@Daniel--diamond is also very strong/tough, yes?  So it could withstand a lot of stress cycling due to thermal mismatch?

Blogger

1.5 mm thick CVD diamond with those dimensions can be made.  Depending on the device and the geometry aspects CTE also need to be considered.  Diamond has a small CTE at around 1 ppm/k

@Barry - knew that's what you meant.

Blogger

Make that 2000u wide at the base

Blogger

For larger TECs, I suspect it may be a long while before it pays for itself. Also, we haven't yet discussed the coefficients of thermal expansion amongst all the parts within the TEC itself. If there's too much of a mismatch, the TEC can tear itself apart.

Newbie

@daniel twitchen  Well, for a little die of 500u on a side, I guess a base of 200u wide and perhaps 1500u tall.  That turns out to be a LOT of diamond.

Blogger

@eafpres---sounds like it would work well in a military satellite project in today's world----cost is not a barrier there

@eafpres - suitable for some very specialized high-speed, low-noise apps

 

Blogger

Keep in mind a TEC is a bunch of P-N junctions.  Normally, all tied together in a module.  But you could independently energize groups of them via a circuit etched in the metallization of the diamond layer.  You would attach the P-N dice to the diamond wafer and attach to the IC to cool hot spots and spread through the diamond.  On the other side you would probably metallize and either put a larger TEC to pump more heat out, or a heat sink.  Pretty complex and spendy, but it could be done.

Blogger

I know your costs are coming down in time, so maybe there might be an opportunity in the future for eTECs

Barry, what does thick mean? 100s microns or many mms

It's an amazing technology!  I wish I could use the eTEC coolers.

Blogger

@eGaN FET---understood

@TETECH Yes, a tiny peltier must still somehow spread out its waste heat.  Comes down to needing a mound of thick diamond spreading heat from THIN silicon to big wide base, then conventional heatsink.  Get me a mound 3x wider at its base compared to the die, and this will work well passively.  Anybody know how to fabricate such a diamond platform cheaply?

Blogger

EPC's GaN products compete with power MOSFETs.  There's not a lot of room to add costs at this point.

Blogger

Alex,

Have you ever considered a need for an eTEC device?

@Steve - that's quite sophisticated - a tiny TEC as part of the IC. Very cool (figuratively and literally).

Blogger

@TETECH---so that's where synthetic diamond comes in

@SteveTaranovich--Right, Nextreme and any other Peltier manfucturer though must still be able to dissipate the waste heat to the local ambient. So, thermal spreading would still be an issue.

Newbie

@Scott >>That ugly brown color aging see on white skin products. That explains why some companies pick ugly brown shades for the case material. Not in a DMM (viz Fluke) of course, but in some other very high speed equipment.

Blogger

Thanks for your expertise Bruce

 

Nextreme says that for the most efficient in-package or thru-package hot spot cooling, their eTECs act as a microscale heat pump, providing pinpoint thermal control for high heat fluxes. Nextreme devices are very thin, able to embed directly inside a semiconductor package and even fit inside a TO-56 package.

My apologies, but I'm going to have to sign off - however, Dan will be on line awhile longer if there are any more questions about synthetic diamond use for thermal management

Newbie

@TETECH---I see that Nextreme has embedded thermoelectric cooling (eTEC) technology enables micro-scale thermal management products

@Brad - You're right.  I know a few of them that recently gained that knowledge from HardKnocks U.

Blogger

SteveTaranovich--I take that back. Nextreme Thermal is attempting to market their tiny modules into the IC packaging. 

Newbie

Here is my two cents on value for backside heat removal.  There are numerous small form factor products (read: hand held) where top side package temperature is critical.  I've seen specifications down to 60C maximum for a power product.  This keeps discoloration of the product skin down to a minimum. That ugly brown color aging see on white skin products.

Blogger

@Scot >> I also have to worry about bond wire inductive ringing that will wear out my transistor for low voltage switching power supplies. That's one that a lot of design engineers pro'ly don't even think of. Good point.

Blogger

Barry - agreed - high power density, small devices benefit most from diamond heat spreading

Newbie

@scott.  I agree -it's a long list.  As we go to higher frequencies, the inductances become more and more critical to minimize.  It's easier to do with a flip chip than with wirebonds

Blogger

@SteveTaranovich--As far as I know, there has been no concerted effort to integrate TECs into IC packaging.

Newbie

Diamond seems to have best possibilities as a bonded wafer element, where all devices on a wafer are isolated and heatsunk on a "handle" wafer.  Here the thinness of the diamond is more to scale with the small devices and lateral heat spreading can work.  Teeny RF power transistors with huge power densities can benefit.  However, large transistors would not enjoy the geometric advantage and I think diamond is really debateable for circuit-sized transistors.

Blogger

@Brad, agreed its chemical inertness while attractive for some applications can be an issue when you are trying to stick/bond things to it.  In practise its only a subset of metals that can form a carbide on the diamond surface at relatively low temperatures.  This is also the reason why you get strong adhresion when growing on Si - effectively a few monolayers of SiC form to chemically attach

@eGaN FET - I think the list of tradeoffs for top side vs. bottom side signal paths is pretty long.  If I have to add bond wires in my high current path, then I add more power drop.  So my FET has to become larger to counter the bond wire loss.  I also have to worry about bond wire inductive ringing that will wear out my transistor for low voltage switching power supplies.  The list is long...

 

Blogger

Yes, it's the high power density applications where diamond heat spreaders are most effective for thermal management - enables even higher power or longer life times

Newbie

Using diamond makes sense for high-value applications like radar where the power density directly impacts the system performance.

Blogger

@TETECH, are TECs being considered for integrating into IC packaging or even into ICs? I would guess that power elements might be the first area to look at?

some GaN power device companies are also considering using diamond heat spreaders

Newbie

@daniel - I'll have to go back to my high-school or college chemistry textbook. Wouldn't have thought it would be that easy to bond anything to that almost inert diamond structure.

Blogger

@Jian, I suspect RF clients

Master

right now, we have RF customers, laser diode customers, and ASIC customers using diamond as heat spreaders

Newbie

In power applications it's best if the top surface is "quiet" (close to ground potential) for noise reasons.  It also helps with heat sinking because you don't need electrical isolation between the devices and the heatsink.

Blogger

@BBolliger-- Just curious, what type of the end customers for using your product? 

Newbie

@Scott-- I agree that the copper bonding issue, but many IC companies put efforts on it. We have seen many products using copper bonding. Obviously, flip chip is the trend, but it waste the top surface to transfer signals. The 3-D structure might be the future trend from this point of view.

Newbie

@BBolliger--Right---good points

what bonding temperature is required to form TiC?

Blogger

very thin layers are used (100 to 150 nm) - mostly to keep the thermal resistance low - but keeps costs reasonable too

Newbie

Titanium is a good metal for diamond, as on a relatively low temperature anneal, you form a Titanium carbide interface with the diamond.  This chemical bond is crucial for minimizing thermal barrier resistance and giving longevity to the contact.  Once this is formed most standard metal schemes can be applied

@Steve - miniscule quantities used tho'.

Blogger

@Bolliger--the material sounds expensive Pt, Ti

@Jian Yin - Copper bonding forces lots of compromises because it is harder material.  Not everyone has figured out how to solve these problems yet.  I think everyone would go to flip chip if the assembly issues (flow solder under pkg) were solved.

Blogger

Platinum - that sounds much safer. Thanks.

 

Blogger

Pt is platinum (misspelled before) - Pt is barrier layer

Newbie

@Brad--I'm thinking Pt, not Pl?

Blogger

@BB, so, sputter titanium onto the diamond (and somehow, it sticks) then two more metals. What - does that say Pl - plutonium? That can't be right....

Blogger

Hi Brad.  I've designed several chipscale packages and I hated them.  These were precision amplifiers.  You have to keep the sensitive circuitry away from the solder balls, so there's not much good layout area left.  For analog circuits, you exchange package cost for silicon cost.  For power circuits, the issue is getting heat through restricted silicon paths, increasing effective thetaJ compared to backside heatsinks.  All that said, the trend is away from wires.

Blogger

wafers can be singulated to any size desired using laser cutting

Newbie

diamond thickness can be from 200 microns to 2mm on wafers up to 5" in size

 

Newbie

@Bruce, and what thickness of diamond is feasible vs. x-y dimension of a single piece, say, a square "sheet"?

Blogger

yes, we can etch patterns in the metal layer on metallized diamond - all std. etching/photo resist processes can be used

Newbie

Typically, we have flip chip to avoid bonding. Copper wire bonding is another choice to lower the cost

Newbie

@eafpres, I think yes. They do that in soft lithography

Master

correction - PolarPak has no bondwire. Forgot about that. It uses all solder connection to leadframes to bring out heat from IC

Master

@Bruce--can you use photoresist/etch processing to pattern the metal layer on the metallized diamond?

Blogger

Vishay has the PolarPak device that has a clip on the top for the source connection as well. This is a soldered clip onto the top of the die. But there is still the gate bond wire. Bottom is drain.

Master

@Barry, like Steve asked Jian, what is your experience with Intersil as to chip scale packaging with no bond wires?

Blogger

@RedDerek - Well the price of gold was a non issue in packaging for a long time.  That's obviously no longer true.  So I see everyone racing to flip chip.  Die - ball - board copper.  Get rid of all bond wires.  So as soon as you can take heat out the top side, it seems like backside spreading becomes less important.

Blogger

we sputter metal onto the diamond - have to use Ti to bond to diamond  - so typical metallization is Ti/Pl/Au

Newbie

Jian--what is your experience with Intersil as to chip scale packaging with no bond wires?

traditional semiconductor packages add heat spreading, but at the same time add thermal resistance.  The best package is no package.  EPC's die are only limited by how fast we can get the heat out the back or front.  By thinning the die we can get the best power density as long as we have a good thermal connection to a heatsink on the back.

Blogger

How do you grow the metal layer for solder attachment on the diomand substrate? 

 

Newbie

goafrit2--the heat spreader takes heat from a small area to a larger area. The heat sink then takes that heat out to the fins. In some cases, if you just have the heat sink, then the heat is concentrated in the center and cannot make effective use of the fins at the edge of the heat sink.

Newbie

@eGaN FET - and you still need something between the die and the heatsink to transfer with. Is that not what the thermal grease is for - fill in the air gaps to provide better conduction?

Master

All of the CVD diamond we grow is pure diamond, not a compound - but there's different levels of impurities depending on how fast your grow the diamond that impacts thermal conductivity

Newbie

@Scott Elder - Chip industry is not going completely bondwire-less. They are using clips for source connection and the drain is the lead frame. Still a bondwire for the gate. Unless you are talking about going to bumped die like EPC is offering with little in the way of packaged parts.

Master

Yes, but...simple geometry.  Thermal resistance of a rectangular flow is R*d/A where R is the material's thermal resistivity, d is the distance to flow, A the cross section of the flow.  As a die attach, d is small and A relatively large. For lateral flow, d is now large but A small.  How can this help much, even with optimal R?

Blogger

@Bruce--are the lower grades, which grow faster, compounds rather than pure carbon?

Blogger

You still have to get the heat out.  Even with a chipscale device like an eGan FET you can put a heat sink on the backside and increase your power density by more than an order of magnitude.

Blogger

Element Six customers have used synthetic diamond cost effectively for very small, high-power-density GaN devices to enable more power, higher efficiency, and longer lifetimes

Newbie

eafpres - the cvd method for growing diamond places certain constraints on the materials you can grow it on to.  Substrates such as Si and SiC can be used but more commonly the diamond is attached via soldering or metallization post growth 

With the work that Element Six has done over the past many years, the cost of synthetic diamond has come down considerably; and that's why we make different grades of thermal conductivity - we can grow the lower grades faster

Newbie

How relevent is this technology to the future given that the integrated world is moving to chip scale packaging without bond wires?   So there really isn't a die attach.  And there aren't bond wires either.  

Blogger

what is the really the key difference between heat spreader and heat sink?

Master

Barry - I think in part the answer to your question is too fold.  First the diamond is iotropic so heat flow through is same as heat flow in plane.  also a rough rule of thumb to get maximum reduction in junction temperature you want your heat spreader e.g. diamond the thickness of the heat spot, e.g. gate width

The challenge is cost.  If diamond is primarily a heat spreader, it may be less expensive to thin down the die and attach it to the metal heat sink directly.  The result isn't quite as good but you can make a larger die to compensate.  It's all about cost.

Blogger

Is it feasible to grow a "relatively thick" layer of diamond on the bottom of a heatsink and therefore have an integrated heat spreader/heat sink, which would be used in the traditional way but have higher overall thermal performance?

Blogger

yes, diamond is acting as a heat spreader - not heat sink

 

Newbie

Alex - the question about integration with the mosfet, is one ive been keen on.  The challenge has been to address the price point for the area of device they often ask about.  To date diamond has most often been used in small area devices with very high power densities.  It might well be than GaN based devices are beginning to push this need ?

Eventually you have to interface to a piece of metal to get the heat out to the atmosphere.  Doesn't that mean that diamond is acting as a heat spreader more than a heat sink?

Blogger

So if I follow, one topic is using synthetic diamond as a packaging material for ICs or related

Another topic is using it as the top/bottom layer on thermoelectric elements in place of Alumina

 

Blogger

@BB >>2000 W/mK is about 5 times higher thermal conductivity than copper

OK - that puts it in perspective. Now I get it.

Blogger

I don't understand diamond.  As a die attech, it's very thin and wide in the direction of heat flow.  This is an inherently low thermal resistance path, not a big problem.  Yet for heat to flow sideways, we have a very thin cross section in the heat flow thus very much higher thermal resistance path.  It's hard for me to understand how even a diamond spreader could be effective.

Blogger

1000W/mK is about 2.5x copper and closer to five times silicon/ aluminium nitride

The typical alumina ceramic used in TEC's has a thermal conductivity of about 20 W/m/K, so even 1000 W/m/K would be a vast improvement.

Newbie

for reference, what is the thermal conductivity of silicon?

Blogger

2000 W/mK is about 5 times higher thermal conductivity than copper

 

Newbie

I've always wanted to ultimately see synthetic diamond extended to the power element like the MOSFET----Alex Lidow at EPC has a packageless technology for his eGaN MOSFET and with synthetic diamond added to the mix---that could make for a very thermally efficient device---can this be done?

figrue of merit - polyscrystalline diamond can be made with thermal conductivity as high as natural diamond - higher than 2200 W/mK

 

Newbie

@BBolinger - is 1000W/mK considered highly thermally conductive?

Blogger

sorry, that wasn't what i was suggesting - although there has been some research into using diamond as a semiconductor device

Newbie

What is the figure of merit, or better yet, the actual improvement between traditional and synthetic diamond. Also, what price increase is there?

Master

we normally use a Ti/Pl/Au thin metallization to enable soldering to the die

 

Newbie

Bruce--are you suggesting you can make the P/N dice out of diamond?

 

Blogger

the bonding interface has to have as low thermal resistance as possible

 

Newbie

I like that idea Paul! Better thermal conductivity with synthetic diamond enhance the overall circuit

Yes, we've worked with customers to do exactly that - replace AlN with diamond heat spreaders - the key issue is how you bond to the die

 

Newbie

Element Six has engineered CVD diamond at several different thermal grades to try to optimize the cost/performance ratio; we have grades from 1000 to 2000 W/mK

 

Newbie

Getting the heat out of the TEC is just as much of a problem. The heat sink must not only handle the heat the TEC is removing, but it must also handle the heat associated with the power input to the TEC. A bottle neck to the heat transfer can be the ceramics themselves, so perhaps there could be a way to implement synthetci diamond in place of the more typical alumina ceramic.

Newbie

So CVD is chemical vapor deposition?

Just to get started, Element Six has made CVD synthetic diamond for more than 20 years - we've worked with LED's, laser diodes, and RF devices to provide heat spreaders for thermal management of these devices

 

Newbie

Bruce---will you kick off the discussion for synthetic diamond in the IC process---possibilities?

I thought we could begin with a synthetic diamond discussion and then branch off into wherever it takes us

Steve - can you make some opening remarks here with respect to your recent blog?

 

Blogger

Daniel Twitchen - joined.  Works in the area of manufacture of synthetic diamond using CVD techniques for applications that include heat spreaders and high power laser optics.

Many chips these days use the PCB copper planes as heatsinking. Are there recommended ways to model and design such "PCB heatsinks"?

Blogger

Right---getting the heat out of a LED or an integrated IC, same problem

 

Hi Jian - thanks  for joining us. Jian and I crossed paths just a little bit in my previous job as an FAE for Intersil.

 

Blogger

The company also made thermally enhanced PCB prepreg and laminates, some of which were used in LED assemblies.  Getting head out from LEDs is a problem similar to getting heat out of dense ICs/processors.  Limited area, problems of gaps, materials need to be electrical insulators but thermal conductors, etc.

Blogger

Welcome Jian! We appreciate your participation from Intersil

Jian Yin from Intersil Corp here

 

Newbie

Sounds like pretty good background for the discussion at hand.

Blogger

In a past life I worked for Laird Technologies.  The Thermal Solutions Business Unit made and sold thermoelectric elements, modules, and complete cooling assemblies.  I have an engineering background but was involved in strategy and product marketing.  I visited lines making the dice for TECs and the assembly lines for the TE modules.

Blogger

Blaine---what is your experience in TECs?

Welcome Lau. Good to have you here

Master

Welcome Paul---we also have Blaine Bateman online with us who has some TEC background

 

Paul Lau from TE Technology, here.

Newbie

Hi Blaine---thanks for joining us.

Hi, I'm Blaine Bateman (eafpres), a blogger here.  I have some background in thermal including TECs so this should be interesting!

Blogger

Alex---great to have you here with us!

Welcome Bruce! We should begin getting participants on shortly

Alex Lidow from EPC is  here

Blogger

Hi Steve,

This is Bruce Bolliger from Element Six here.

 

 

Newbie

We have some experts on this chat session with us today:

Paul Lau, TE Technology, Inc., Engineering  for thermoelectric coolers

Jian Yin, Intersil, Application engineer

Bruce Bolliger, Sr. Director, Semiconductor Business at Element Six (Synthetic diamonds)

Alex Lidow, CEO EPC, expertise in eGaN MOSFET (packageless technology)

We're having a chat on Tuesday June 25th at 2 PM EDT on integrated analog. Please come join us for the discussion. The topic is Analog integration is increasing: How can we best get the heat out? We will have industry experts discussing the problem that results from packing lots of circuitry onto a small die and methods to keep it cool.

Blogger


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