Browse Prior Art Database

THERMAL INDICATING PACKAGE

IP.com Disclosure Number: IPCOM000038445D
Original Publication Date: 1987-Jan-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Mok, LS: AUTHOR [+3]

Abstract

Thermal analysis and fault detection for low-end packages is accomplished using inexpensive liquid crystal temperature indicators. Low-end packages are required to withstand large temperature excursions and many more temperature cycles than high-end systems. Despite this, the packages must still be reliable and low cost. This article describes an inexpensive system for temperature monitoring for production packages. This system may also be used to provide high spatial resolution and fine temperature definition for research and development on thermal characteristics of new packaging methods, such as Tape Automated Bonding (TAB) and Surface Mounted Technology (SMT). This system utilizes the selective color scattering of chiral nematic liquid crystals (LC) resulting from the temperature variations of the chiral pitch.

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THERMAL INDICATING PACKAGE

Thermal analysis and fault detection for low-end packages is accomplished using inexpensive liquid crystal temperature indicators.

Low-end packages are required to withstand large temperature excursions and many more temperature cycles than high-end systems. Despite this, the packages must still be reliable and low cost. This article describes an inexpensive system for temperature monitoring for production packages. This system may also be used to provide high spatial resolution and fine temperature definition for research and development on thermal characteristics of new packaging methods, such as Tape Automated Bonding (TAB) and Surface Mounted Technology (SMT). This system utilizes the selective color scattering of chiral nematic liquid crystals (LC) resulting from the temperature variations of the chiral pitch. In a chiral nematic liquid crystal, the pitch is a decreasing function of the temperature. Thus, using chiral nematics having the pitch of the order of the wavelength of visible light in the temperature range of interest, small or large variations of temperature are shown up as changes in the color of the scattered light. The materials show a continuous color corresponding to a continuous temperature variation in both heating and cooling cycles, as shown in Fig. 1. Fig. 1 shows the color of the chiral nematic liquid crystal as a function of temperature. At present, chiral nematics with material properties for which the color changes from red to blue in a temperature range of 0.lOEC up to 100OEC are available. This can be achieved by preparing suitable chiral nematics single component or eutectic mixtures [*]. Thus, the chiral nematics permit immediate, reproducible visualization of the temperature distribution in colors of operating devices. The results can be recorded photographically or video taped for quantitative analysis. The method can be used for both static observation of thermal mapping and dynamic observation of rapid temperature changes.

Since the surface alignment and anchoring conditions do not affect the color of the materials for the case in which we are interested
[*], the operation is simple and the cost in time and equipment is minimal. The sensitivity can be improved by use of monochromatic light and changing the response ranges within wh...