Thermocouple Attachment Methodology for Memory

The importance and memory cooling has increased dramatically due to higher thermal design power coupled with narrowed module pitch. The ability to accurately predict and validate memory cooling capabilities has therefore become more and more critical in system thermal design.When DRAM case temperature is measured with thermocouple, due to the low conductivity of the DRAM surface material and thermocouple attachment process, significant measurement variation of up to ±20% has been observed even from a single operator. In this paper, a measurement capability analysis is performed to identify an optimal temperature measurement method for better repeatability and reproducibility. Multiple thermocouple attachment methods are investigated including epoxy (OMEGABOND™ 101 Two Part Epoxy), super glue, Kapton tape, and copper tape. Wire gauge and thermocouple type sensitivity are also analyzed.The testing results show that the most consistent method for measuring DRAM package temperature is to use copper tape to attach a thermocouple. The measurement variation is <; 5% among four different operators with ten thermocouple attachments each. However, the temperature measurement is consistently lower than the highest reading of other methods due to the higher contact resistance between the Thermocouple and the DRAM surface. The proposed optimal methodology is to: (1) Measure the DRAM temperature with the most consistent and easy-to-instrument method, which is to use copper tape to attach 30-gage Type-J thermocouple wire. (2) Apply a correction factor to come up with the actual DRAM case temperature. The correction factor comes from a calibration curve obtained with a more accurate attachment method that is however difficult-to-instrument and suffers from low reproducibility. With this methodology, a consistent DIMM cooling prediction could be obtained across sites which enables optimal system thermal design that supports different types of memory modules accordingly.The same methodology could be applied to other electronic devices which have similar low-conductivity surfaces.