<title>Inspection of high-performance peltier coolers using lock-in thermography</title>

Abstract

Peltier cooling devices are used on the Hubble Space telescope for temperature control of various detector packages. A typical construction of these devices involves sandwiching an array of Bismuth-Tellurium (Bi<SUB>2</SUB>Te<SUB>3</SUB>) posts between two ceramic plates. When a DC current is applied to the device heat is moved from one side of the device to the other, depending on the polarity of the current. Because these devices can change temperature very rapidly, there is the potential for damage due to thermal expansion and contraction of the constituents. A failure in the bonding of the Bi<SUB>2</SUB>Te<SUB>3</SUB> to the ceramic sheet can lead to reduced efficiency or failure of the device. NASA Langley Research Center has developed a nondestructive thermal imaging technique to determine the integrity of the Bi<SUB>2</SUB>Te<SUB>3</SUB> posts through the ceramic surface of the peltier device. By driving the peltier device with a time varying DC current, a corresponding temperature rise and fall can be observed on the surface of the device using a commercial infrared camera. Lock-in thermography can then be used to construct both phase and amplitude images of the front surface temperature. It has been found that failure of Bi<SUB>2</SUB>Te<SUB>3</SUB> posts results in a measurable change in both the amplitude and phase. This paper will describe an inspection method that has been developed and show results of the inspection of the extremely small Bi<SUB>2</SUB>Te<SUB>3</SUB> posts whose dimensions are 0.81mm by 0.81mm and approximately 1.45mm tall.