Managing DDR3 Thermal Challenges

Date: 2/3/2009

Managing DDR3 Thermal Challenges

Its standard industry practice is to include heat spreaders in DDR3 x4 DIMMs only when the modules contain 36 or more x4 DRAMs, but should you assume that you’re achieving  optimal performance?

Engineers at SMART Modular Technologies decided to check it out and their results indicated that the number, density, speed, and type of DDR3 module used should, in fact, determine the use of heat spreaders or heat sinks. In addition, the positioning of the socket(s) in relation to the airflow and other heat-generating components on the board was an important consideration.

SMART conducted analysis on two industry-standard 4GB DDR3-1333 RDIMMs: a dual-rank 4GB RDIMM using 256Mx4 components and a quad rank 4GB RDIMM using 128Mx8 components. Testing included inserting one to six modules systematically into the Intel® Thurley development platform (Nehalem CPU, Tylesburg Chipset). Measurements were made in different areas using a thermal imaging camera to detect hotspots. A Flukemeter with thermocouples was used for localized temperature measurements and High-Performance Linpack (HPL) test software helped achieve ~90%+ memory utilization.

Notes:
Under all conditions, the register and memory case temperatures shown in the table do not approach the maximum allowable case temperature of 106ºC at 1333MHz for the register or 85ºC for the memory, as specified in the datasheets. Interestingly, as additional DIMMs are added, the application appears to even out the memory usage among the six DIMMS, reducing the power draw of a single DIMM insertion.

When using the Intel platform and running the HPL software, it was observed that an average power draw for this x4 based DIMM is 5W rms (root mean square). The thermal image in Figure 1 with a six DIMM insertion shows that the registers, in fact, are the main hot spots.

In this preliminary study, the data captured are limited in sample size with less than optimal open-cover airflow measurements. (A spot check measurement with a closed cover indicated that the cooling might actually improve.) SMART is working with OEMs on a wide variety of DDR3 implementations, including ATCA telco, blade servers, and networking.

SMART already has several different types of standard, very low profile (VLP), and small form factor heat sinks available that can be implemented into a system design to help manage DDR3 thermal concerns. In addition, SMART engineering support is ready to assist OEMs who have concerns on the best methods to maximize system cooling for new DDR3-based system designs.

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