Electronics Protection - May/June 2013 - (Page 8)

Feature A Little Diamond Goes a Long Way: Overcoming Thermal Limitations to Enable Next Generation Technology Mario M. Pelella, PhD VP of Engineering, Technology and Process Solutions Sp3 Diamond Technologies Today’s power devices face significant thermal management challenges, tomorrow’s devices even more so. The 2011 NRC/CSTB study, “The Future of Computing Performance” indicated that the growth in the performance of computing systems, even if they are multiple-processor parallel systems, will become limited by power consumption within a decade. Accordingly, historical trends show that the gap in single-processor performance is expected to grow from a factor of 10 in 2010 to 1,000 by 2020, due in large part to thermal management constraints. Today, the use of chemical vapor deposition (CVD) diamond segments for both industrial and electronic applications is accelerating, driven largely by higher heat flux devices. The buildup of heat can severely limit or impair the performance of electronic devices. Manufacturing costs are driving the use of CVD diamond to applications where its highly desirable attributes can solve thermal management problems while avoiding other, more complicated solutions that add weight and increase the size of the package. There are many applications that can benefit from the thermal properties of diamond, including high-performance heat spreaders for wide bandgap power amplifier semiconductor devices in transmit/receive modules for phased array radar systems, laser diode submounts, RF and wide bandgap semiconductor devices in telecom for radio systems, power amplifiers and related systems and thermal submounts for extremely high heat flux components in laser-guided munitions and directed-energy weapons. The bottleneck for thermal management of junction temperature within optoelectronic and electronic devices is at the heat spreader assembly. The ability of the heat spreader to conduct heat away from the laser chip or electronic chip ultimately determines the device’s performance and reliability. The thermal “pinch” of cooling capability of the assembly is at the heat spreader. Therefore, successful device manufacturers pay special attention to materials choice and assembly design of the heat spreaders. Industry Needs A heat spreader is typically positioned between the electronic device and a larger heat sink. The heat generated within the electronic device is most often concentrated in a small area and temperatures in this region rise much higher. By spreading the localized heat generated by the device, a CVD diamond heat spreader can improve the cooling capability of laser die in assembled devices by 30 to 100 percent. How Much Diamond? Understanding Thermal Management Needs for Each Application Heat spreader size and thickness may be optimized for each application using thermo-mechanical modeling of the assembly, such as finite element modeling (FEM). Optimal CVD diamond heat spreader thickness is about 400 μm, based on improved performance and cost. A rule of thumb for sizing of heat spreaders is 2.5 times the lateral dimension for edge mounted chips, such as edge emitting laser chips, and five times the lateral device dimension for chips mounted in the center of the heat spreader, such as for RF power transistor chips. In the case of lower thermal conductivity head spreaders, such as AlN and BeO, the heat spreader thickness 8 contributes significantly to assembly thermal resistance, and heat spreader thickness is usually chosen to be between ¼ to ½ the thickness of the chip. Heat sink dimensions are on the order of 10 times or more the size of the chip in lateral and depth directions. Figure 1. Typical package stack with heat spreader Potential users of diamond heat spreaders should model the thermal behavior of their application from the die, this is primarily what dictates the size of the diamond. Often unrealized when considering CVD diamond is that a little goes a long way. It’s not tied to device size, but rather to the thermal behavior of the application. The largest CVD diamond heat spreader commonly manufactured is one inch square, which is a full coupon, enough for a device that is 0.2 inches (5.08 mm) square. Although rule-of-thumb guidelines for determining how much diamond an application will require are outlined above, only thermal modeling will give the best accuracy. Then, within the model, a potential user should also take into account (from the top down) their attachment method. A typical attachment is an 80/20 AuSn preform (sometimes AuGe) used to attach the metallized diamond heat spreader to the copper heat sink on the bottom (See Figure 1). Diamond heat spreaders configured for integration in standard electronic and optoelectronic device assembly processing are used in device applications and provide dramatic device power and reliability performance improvements at a small fractional increase in total device bill of materials (BOM) cost. Copper is Common and Conventional, but it’s Not Insulating CVD diamond exhibits exceptionally high thermal diffusivity and greater thermal conductivity than other material choices. It’s three times greater than copper, five times greater than aluminum nitride or beryllium oxide and five times greater than refractory metals like copper tungsten or molybdenum copper. Electrically conductive materials such as copper, aluminum, molybdenum, copper, and copper tungsten are not well suited as heat spreaders for signal lasers and RF devices due to the complexity of adding signal trace patterning on the heat spreader. While the cost for CVD diamond is higher on a volume basis than Cu, AlN, BeO or refractory metals such as WCu and MoCu, the cost for CVD diamond heat spreaders is small compared to the device BOM cost. Its use also enables an increase of device optical power of up to 300 percent at the same device junction temperature and device reliability. The cost increase for replacement of copper heat-spreaders with diamond is also relatively small as the CVD diamond heat-spreaders have an unmetallized price of about $1.5 per cubic millimeter. May/June 2013 www.ElectronicsProtectionMagazine.com http://www.ElectronicsProtectionMagazine.com

Table of Contents for the Digital Edition of Electronics Protection - May/June 2013

Electronics Protection - May/June 2013
Newer Technology Releases Next-Generation Power2U AC/USB In Wall Charging Solution
Raritan Boosts its DCIM Leadership Position with dcTrack 3.0
Specifiers of Enclosures for Components in Outdoor Applications: Be Aware of Material Selection Issues
Realizing the Many Benefits of Power System Relay Upgrades
How to Protect Electronic Circuits from Power Surges
A Little Diamond Goes a Long Way: Overcoming Thermal Limitations to Enable Next Generation Technology
Hardware Technology Eliminates Problems Caused by Using Traditional Captive Screws
Managing Lithium-Chemistry Batteries: It’s Mostly About Their Temperature
Protecting and Improving Electronic Components Performance
Advancements in Thermal Management Conference Preview
One Stop Systems Introduces nanoCUBE Desktop Expansion
Select-A-Shield RF Shielded Tent Closure System Is Non-Radiating
Thermoelectric Air Conditioner Delivers Maximum Cooling Regardless of Power Supply
On-line, Double-Conversion UPS from Emerson Network Power Earns Energy Star Qualification
Dirak Introduces a New Swinghandle
Dual-Cure Conformal Coating Eliminates Need for Additional Processing
Industry News
Calendar of Events

Electronics Protection - May/June 2013