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Method for a thermocouple attachment to a metallic surface using solder

IP.com Disclosure Number: IPCOM000007596D
Publication Date: 2002-Apr-08
Document File: 5 page(s) / 120K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a thermocouple attachment to a metallic surface using solder. Benefits include improved thermal performance.

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Method for a thermocouple attachment to a metallic surface using solder

Disclosed is a method for a thermocouple attachment to a metallic surface using solder. Benefits include improved thermal performance.

Background

              Typical processor package thermal performance is assessed using the metric Rjc, which is the thermal resistance between the die and the integrated heat spreader. This metric is expressed by

an equation (see Figure 1) where Tj is the maximum temperature of the die. The value Tc is the temperature of the integrated heat spreader. The value P is the power input to the die. The value Adie is the cross-sectional area of the die through which the heat is transferred.

              The challenge is developing a metrology to measure this parameter. A metrology is deemed capable of measuring a parameter if the precision to tolerance (P/T) ratio is less than 30%. The value of P/T can be expressed by an equation (see Figure 2) where sms is the measurement system variation in measuring Rjc. USL is the upper specification limit. The value xbar is the process mean. The value Rjc is a function of Tj, Tc, and power (see Figure 1). Therefore, reducing the variation in any of the three input parameters Tj, Tc, or power reduces the variation in Rjc. The disclosed method reduces the variation of the parameter Tc.

              The conventional solution (see Figure 3) utilizes a K-type thermocouple to measure the integrated heat spreader temperature (Tc). This K-type thermocouple is attached to the integrated heat spreader using a two-part epoxy that is cured at room temperature for 8 hours or alternatively at 65°C for 1 hour. The epoxy has a relatively low thermal conductivity (approximately 1 W/m-K) but can be used to attach the thermocouple to many types of surfaces such as metals, ceramics, plastics, wood, and paper products. An accurate heat spreader temperature is attained if the thermocouple bead contacts the heat spreader. If any epoxy is located between the thermocouple bead and the heat spreader, the thermocouple reads a lower temperature because the heat is not transferred through the much lower thermally conductive (relative to heat spreader) epoxy. As the input power and the heat flux increases, the thermocouple attachment becomes more critical. Larger temperature gradients exist through the die, heat spreader, thermocouple bead, and epoxy.

General description

              The disclosed method utilizes solder to securely attach a thermocouple to a nickel-plated copper surface. The key elements of the method include:

§         Type T thermocouples

§         Tin-indium solder with low liquidus temperature (between 100°C and 150°C)

§         Solder flux

§         Heating plate capable of temperatures above 150°C

Advantages

              The disclosed method reduces the variability of the Tc measurement compared to the conventional epoxy thermocouple attachment. The solder used to attach the T-type thermocouple to the integrated heat spreader has a much greater thermal conductivity than the epoxy. The thermal conductivity of...