Enhanced Gallium Nitride Transistors (eGaN)

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EPC_Appnote_GaNassembly_fig3_flip_chip_490x193.jpg

Innovations in transistor switching has brought improved speed and thermal efficiency in field-effect switching and a high-power capacity of gallium nitride transistor technology. As much as 12 volts per nanosecond slew is available in some devices. The GaN is not packaged, rather, the silicon die is the package. The largest of a product line, the EPC1015, is 4.1mm long, 2.3mm wide, and 1.6 mm high. Solder-bumps are applied to the die at the factory, with assembly to a circuit board accomplished by reflow soldering[1]


In June 2009 Efficient Power Conversion Corporation (EPC) introduced the first enhancement mode gallium nitride on silicon power transistors designed specifically as power MOSFET replacements. These products were developed to be produced in high volume at low cost using standard silicon manufacturing technology and facilities. The initial product family consists of 10 part numbers ranging from 40V to 200V and from 4 milliohms to 100 milliohms. Table 1 lists the devices and their basic characteristics.

For more information about EPC’s GaN transistors, go to www.epc-co.com.

The Two Key Differences

Between Using Power MOSFETs and Enhancement Mode GaN (eGaN™) FETs
Source: http://epc-co.com/epc/MOSFETUsers.aspx
  1. Do not exceed gate drive maximum ratings
  2. Layout considerations resulting from enhancement mode GaN’s very high frequency response.


How2 Get The Most Out Of GaN Power Transistors

by Johan Strydom, Efficient Power Conversion, El Segundo, Calif.
June 2010
PDF: http://www.how2power.com/newsletters/1006/articles/H2PowerToday1006_design_EPC.pdf


Advantages of eGaN characteristics

  1. Negative thermal-curve current-response, as the GaN transistor gets hotter, it conducts less (resistance increases), unlike the MOSFET which conducts better as it warms. This enables shared current loads, rather than an individual transistor die drawing more current on a destructive run-away.
  2. Superior performance over Silicon MOSFETs eGaN FET-Based Synchronous Rectification
    (EEPower.com) https://eepower.com/power-converters/egan-fet-based-synchronous-rectification-efficient-power-conversion-1148

Omega Micro Technologies awarded SBIR

March 15, 2011

Omega Micro Technologies, Inc. has been selected for award of N111-034 'Thermally Efficient Gallium Nitride Power Amplifier and Transmit / Receive Module Packaging (TEATRM)'.

'The objective of this SBIR is to demonstrate innovative cost effective packaging for high power Gallium Nitride(GaN) Power Amplifiers (PAs.) for Navy Shipboard Radars and Electronic Warfare (EW) Systems.'

Retrieved 07:27, 29 May 2014 (MDT) from http://www.omegamicrotech.com/news.html

High Thermal Performance Gallium Nitride Power Amplifier and Transmit/Receive Module Packaging

Navy SBIR 2011.1 - Topic N111-034

Opens: December 13, 2010 - Closes: January 12, 2011

N111-034 TITLE: High Thermal Performance Gallium Nitride Power Amplifier and Transmit/Receive Module Packaging

TECHNOLOGY AREAS
Sensors
ACQUISITION PROGRAM
NA, IWS 2.0 will transition technology into developing Radar and EW systems
OBJECTIVE
Demonstrate innovative cost effective packaging for high power Gallium Nitride(GaN) Power Amplifiers (PAs.) for Navy Shipboard Radars and Electronic Warfare (EW) Systems.

DESCRIPTION: Gallium nitride power amplifiers have demonstrated state-of-the-art performance levels with respect to devices currently used in most Department of Defense (DoD) systems.1 In particular, the relatively higher power and efficiency levels achieved with GaN PAs can be used to enable significant improvements in radar system range, weight, cooling, and cost. The reliability of GaN devices has also been established through the Defense Advanced Research Project Agency (DARPA) Wide Bandgap Semiconductor (WBGS) program.2

System insertion of GaN PAs still faces challenges related to affordable high performance packaging of GaN PAs. In particular cost effective thermal management is a key challenge for GaN PAs due to their relatively high RF power density and its corresponding high power dissipation density. To this end, solutions are sought with respect to the cost effective packaging of GaN PAs. Examples of representative solutions include (1) the development of high thermal conductivity PA heat spreaders and package base materials that address issues of mechanical damage and piezoelectric effects associated with coefficient of thermal expansion match differences between spreaders and GaN devices, plating compatibility with production eutectic solder process, and cost effectiveness. Heat spreaders should have a thermal conductivity greater than 250 W/mK that are compatible with AuSn or similar eutectic solder processes and that possess a coefficient of thermal expansion that matches silicon carbide. (2) The development of relatively high thermal conductivity solders and epoxies appropriate for attachment of GaN PAs to thermal spreaders or for attachment of transmit/receive modules to phased array cold plates. These thermally conductive interface materials shall have a thermal conductivity in excess of 25 W/mK, they shall be reworkable and suitable for low cost manufacturing processes and they shall also be able to satisfy the power dissipation levels anticipated during GaN PA operation without degradation. Finally, (3) development of affordable Transmit/Receive (T/R) module packaging technologies that provide a relative cost reduction are also sought. The technologies developed shall provide reliable life cycle operation of GaN T/R modules and reduce cost by 50%.


Retrieved 07:27, 29 May 2014 (MDT) from http://www.navysbir.com/n11_1/N111-034.htm

Master The Fundamentals Of Your Gallium-Nitride Power Transistors

Source: http://electronicdesign.com/article/power/master_the_fundamentals_of_your_gallium_nitride_power_transistors.aspx
CGS is small when compared with silicon MOSFETs, giving them very short delay times as well as excellent controllability in low-duty-cycle applications. A 48- to 1-V buck regulator has been demonstrated at 1 MHz using 100-V GaN transistors from EPC. Drain-to-source capacitance (CDS) is also small versus silicon. Capacitance curves for GaN are similar to those for silicon except that with a similar resistance, its capacitance is significantly lower.


EPC GaN transistor product listing

Efficient Power Conversion (EPC)
URL: http://epc-co.com/epc/ToolsandDesignSupport/DeviceModels.aspx

Digikey info

eGan(TM) Basics

URL: http://dkc1.digikey.com/us/en/tod/EPC/eGaN-Basics_NoAudio/eGaN-Basics_NoAudio.html


eGan Power Transistor Characteristics

URL: http://dkc1.digikey.com/us/en/tod/EPC/eGan-Power-Transistors_NoAudio/eGan-Power-Transistors_NoAudio.html


Fujitsu GaN HEMT

Fujitsu reveals GaN transistor for power supplies
Steve Bush, Thursday 02 July 2009 16:18
Fujitsu Laboratories has developed a GaN power transistor for mains PSUs, claiming it to have the highest current density yet.


Fujitsu reveals power GaN transistor

GaN is inherently a fast technology, and the material withstands voltages better than both Si and GaAs.
Source: http://www.electronicsweekly.com/Articles/2009/07/02/46422/fujitsu-reveals-gan-transistor-for-power-supplies.htm


MIT research

Sept. 2010
Improving the transistor: Small device, big energy savings
Source: http://web.mit.edu/mitei/research/spotlights/improving-transistor.html


App Note –EFFICIENT POWER CONVERSION

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Assembling EPC GaN Transistors
Source: http://epc-co.com/epc/documents/product-training/Appnote_GaNassembly.pdf



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See also

Electronics_101@yahoogroups.com —mailing list:

Re: [Electronics_101] Noob on GaN transistors

Reflow that small is tricky, but possible at home, especially if you go the tacky-flux route so you don't have to deal with solder paste stencils.

I use a $20 hotplate, fine tweezers, and a magnifying visor.

If the part is placed no more than 25% off-pitch (0.1mm for the small pitch, 0.15mm for the large) it tends to self-center due to surface tension. The tricky part is getting them there in the first place. Me, I'd just buy a bigger part ;-)

http://www.delorie.com/pcb/hotplate/


With the fine pitch components, I have found it helps sometimes to poke at them with tweezers while they are reflowing[1] on the hotplate. It's usually very easy to push them on the right position because the surface tension makes them snap in pitch sized increments.

I don't use care when applying the paste or placing the components, because I know I can poke them into place on the plate. Much quicker that way, as long as the design is small. You can also poke solder balls towards pads if you have been really messy with the paste.

I think this hands on approach is a great advantage of the hotplate over the oven.

ST


http://www.walmart.com/ip/Aroma-Single-Burner-Portable-Electric-Range-Hot-Plate/5871070

I use the same model, but for larger boards I put an aluminum slab (1/4" thick) on top to spread the heat evenly.


That's crazy, man. Get a copper heat spreader and a damned light dimmer!!

I did get an alumimum plate to put on that, it works quite well. As for a light dimmer, it's not needed - the cast iron gives the hotplate a nearly perfect reflow curve.


Reply by D.J. Delorie:


DEM wrote:

Q1: Assuming the surface tension you mention caused by the liquid solder, does one have a short window of time before the solder begins to get crusty from oxidation?


The solder will last far longer than anything else on the board, at those temperatures.


Q2: Does the hot plate temperature need adjusted below a critical temp? (per device specs?) verses keep it hot for optimum reflow and get in and out fast?


My technique is to put the pcb on a *cold* hotplate, *then* turn it on. Having the PCB go through the warm-up gives it a pretty good heat curve, and you just take it off the hot plate as soon as all the solder melts.


Q3: Does the circuit card need to be lifted off the hot plate "just in time" to avoid damage?


Yes.


It sounds like the GaN die will stay where it is supposed to after wetting...


Oh yeah. Most people underestimate the surface tension of LIQUID METAL.


Q4: So, can the card be handled before the solder sets to get it off of the hot plate?


Carefully. I have a metal power supply lid next to the hotplate, which happens to be the same height, so I can gently slide the pcb off the hotplate onto the "cooling rack".


Q5: Can the itty-bitty GaN transistor dies be reliably cleaned with solder wick for a second (third, forth) attempt while mastering the technique?


Not likely. They come with solder balls pre-attached; the wick would remove those. Your only choice is to switch to solder paste and hope it gets up into the die.


Please throw in any more juicy info that comes to mind! Oh, I'm also assuming that the board must have a solder mask between the fine-pitch circuit traces.


Nope. Most fabs can't do mask that fine anyway, and end up removing it. Any mask "bridges" less than about 6 thou (0.15mm) risk breaking, floating around, and just messing things up.


Biq Q1: Is it practical to attempt etching one's own sub-millimeter circuit traces? (Say no say no!)


I've done 5 mil traces at home with photomask, or 8 with toner. That's 0.2mm. It takes a while to get reliable results at those sizes, though.


Big Q2: Are there prototype boards one can purchase to affix these little no-see-ums (at my age) onto?


There are a few fabs that specialize in small one-off boards, like http://batchpcb.com, where you can have one made if you like. It will take time though.


I put a sample breakout at http://www.delorie.com/electronics/adapters/


Another option is to use the breakout PCB as a poor-man's SMT, instead of adding the inductance of all those leads and things.


I really want close to a perfect square edge as this is the point and purpose of the design.


Then you need to stop thinking about breakout boards, and design a pcb that will hold the whole circuit ;-)


You'll probably have to learn more than I know about transmission lines and microstrip traces to get it right, though.


next




  1. 1.0 1.1 reflow soldering: parts are aligned for soldering, and the solder bump on the silicone die is caused to melt with external heat, and reflow occurs as the wetting of melted solder to the micro-fine circuit-board-copper-traces aligned under the solder-bump.