Bernd Gromoll

Micro cooling systems for high density packaging

Abstract Future 3D electronics packaging systems will require micro cooling systems that can be integrated and permit the continued use of air as a coolant. To achieve this, new types of silicon micro heat exchangers were made using an anisotropic etching process. Various heat exchanger configurations and sizes were made using sandwich and stacking techniques. They can be used either as a heat exchanger for direct cooling with compressed air or as a heat pipe and thermosyphon for indirect cooling with fan-blown air. The performance characteristics of the various cooling systems are stated. The micro-heat-pipe can be used for power loss densities of up to 3 W·cm −2 , the direct air cooling up to 15 W·cm −2 and the thermosyphon up to 25 W·cm −2 . Cooling performances are achieved that are otherwise only possible with liquid cooling. The practical application of the micro cooling system is demonstrated using the example of the Pentium processor. With a power loss of 15 W, the high-performance micro cooling system is able to limit the increase in operating temperature to 15 K. The volume of the micro heat exchanger is 2.5 cm 3 and therefore considerably smaller than that of standard heat sinks.

Thermosyphon Cooling System for the Siemens 400kW HTS Synchronous Machine

A commercial GM cryocooler is employed to cool the rotor of the first Siemens 400 kW HTS machine. Excellent thermal connection between cold head and rotor is achieved using a thermosyphon. At the rotor’s inner surface the required cooling power is provided by evaporating fluid, that is recondensed at the coldhead. Our configuration allows an easy mechanical decoupling of the stationary cold head and the rotor, using a magnetic liquid rotary seal. In order to shorten cool‐down time, a precool to 70 K is done with a thermosyphon filling of nitrogen, while a motor operating temperature of 25 K is reached using neon. Temperature difference between the thermosyphon’s cold and warm ends is below 1 K for a heat transfer of 40 W. During operation, a temperature controller stabilizes condenser temperature and hence rotor temperature. The self‐regulating cooling system has been operated continuously and without problems since Spring 2001. The machine was also operated with newly developed pulse‐tube cryocoolers, th...

Development of a 25 K Pulse Tube Refrigerator for Future HTS‐Series Products in Power Engineering

Demands are made on refrigerators for future HTS‐series products like generators, motors, transformers, which are only partly fulfilled by commercially available refrigerators. Based on the experiences with HTS‐prototypes, pulse tube refrigerators (PTRs) are considered to have the highest potential to fulfill the identified requirements. Siemens have therefore started the development of a high‐performance PTR together with TransMIT Giessen. Design target is a PTR with a cooling power of 80 W near 25 K based on an oil‐free CFIC — linear compressor with a power input of 2 × 5 kW. The initial tests on the first single‐stage laboratory version of this PTR with stainless steel mesh regenerator revealed high regenerator losses from circulating mass flow that manifests itself in form of an azimuthal temperature asymmetry in the regenerator. The circulating flow can be greatly reduced by increasing the transverse heat conductance of the matrix by use of stacks of different materials. So far, the minimum no‐load temperature of the PTR is 35 K and a cooling power of 75 W is available at 50 K with a compressor efficiency of about 80 %. Further optimization of the regenerator matrix appears to be possible.Demands are made on refrigerators for future HTS‐series products like generators, motors, transformers, which are only partly fulfilled by commercially available refrigerators. Based on the experiences with HTS‐prototypes, pulse tube refrigerators (PTRs) are considered to have the highest potential to fulfill the identified requirements. Siemens have therefore started the development of a high‐performance PTR together with TransMIT Giessen. Design target is a PTR with a cooling power of 80 W near 25 K based on an oil‐free CFIC — linear compressor with a power input of 2 × 5 kW. The initial tests on the first single‐stage laboratory version of this PTR with stainless steel mesh regenerator revealed high regenerator losses from circulating mass flow that manifests itself in form of an azimuthal temperature asymmetry in the regenerator. The circulating flow can be greatly reduced by increasing the transverse heat conductance of the matrix by use of stacks of different materials. So far, the minimum no‐load t...

Trends in cooling technology for high-density packaging

A general look at the development of cooling systems for multichip modules over the last few years reveals a clear increase in the levels of power dissipation. Heat transfer and cooling methods for multichip modules are considered. The extremely high demands placed on cooling systems are leading to increasingly cost-intensive technical solutions. Microcooling systems must be capable of integration in order to cool the 3D computer structures of the future. A microcooler produced in Si etched technology is presented as the foundation of this type of cooling system.<<ETX>>

Application and Performance of Si-Microcooling Systems for Electronic Devices

A silicon-etched type of microcooler has been developed which, it is hoped, will form the basis of an integrated design of microcooling systems for electronic components. A number of different versions of the microcooler have been made to suit different coolants and different applications. The performance that has been achieved so far using air and water and employing natural and forced convection is described. The initial results of using the microcooler as the evaporator of a thermosyphon circuit show promise for other possible applications.