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Apparatus and Program for Measuring Thermal Interface Material Thickness Using High Pulsed Ultrasonic Waves

IP.com Disclosure Number: IPCOM000031046D
Original Publication Date: 2004-Sep-08
Included in the Prior Art Database: 2004-Sep-08
Document File: 4 page(s) / 79K

Publishing Venue

IBM

Abstract

An apparatus and program are described to calculate thermal interface material thickness using ultrasonic waves. It has been shown that this method can be performed in dynamic and static mode.

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Apparatus and Program for Measuring Thermal Interface Material Thickness Using High Pulsed Ultrasonic Waves

Static and dynamic measurement of thermal interface during actuation of area array module is an important parameter is evaluating the thermal efficiency of the processor. Any gap or discontinuity between the heat sink and processor will result in non-uniform pressure distribution across the thermal interface resulting in degradation of thermal efficiency. No known solution exists to measure thermal interface gap nondestructively in static or dynamic mode of operation.

     Heat dissipation of semiconductor packages has become one of the limiting factors in miniaturization. The thermal issue consists mainly of three parts:
1. The heat transfer to the outside world to be improved by better heat sinks, higher air velocity's and liquid cooling
2. The thermal resistance of the package itself, and
3. The interface resistance that is defined as the sum of the thermal resistance of the interface material plus both contact resistances.

     A recent article shows that when the thermal interface material (TIM) that is used for the Pentium* 2 is also used for the Pentium* 4, its thermal resistance account for 80% of the total resistance. To enable an optimum choice, the thermal performance of the TIM is critical. One of the critical aspect of providing a lower thermal resistance is to have no air gaps between the heat sink and TIM and/or between TIM and processor. The thermal interface gap or non-uniform distribution is usually caused one of the following parameters and are usually application specific.

Screw Torque

Clip installation
Time-dependent phenomena; e.g., reduction in clamping force, warpage, and aging Flatness of both heat sink and processor
Non-uniform heating

     The consequences of above parameters results in higher thermal resistance and hence decreasing the thermal performance of the processor.

     In this publication, a nondestructive method to characterize thermal interface gap is described. Figure 1 shows a schematic diagram of how the transducer/receiver are placed on the heat-sink, and Figure 2 shows the flowchart used to calculate dynamic thermal interface material thickness.

     Initially, a high-pulsed ultrasonic wave is introduced into the heat sink assembly (as shown in Figure 3), and it's back reflection from each interface are received. The signals are then fed to a signal processor which analyzes the signals for peak in energy due to change in material density. The signal obtained at a certain delta time are collected and a cepstrum analysis is performed. Cepstrum analysis helps establish periodicity of a signal and keeps only the family of harmonics with uniform spacing. At this point, the signal is clus...