Component-attach materials: thermal

Table 5.17 Thermal characteristics of component attach materials ...

In order to predict temperature rises in electronic components, a thermal model needs to be created, which shows all of the dissipating elements and the entire heat path. Starting at the junction of each dissipating semiconductor, the model needs to include all layers in the thermal path the die attach, substrate (if used and its attachment), package, thermal interface materials (if used), heat sink and circuit card assembly (CCA). The heat dissipated in each component, physical layout, and availability of cooling air are required to calculate the temperature-rise predictions. 

Ivan, J. Gonzales, J. Mena, M.G. Moisture and thermal degradation of cyanate-ester-based die attach material. Proceedings of the 47th Electronic Components and Technology Conference, San Jose, CA, May 1997 525-535. 

Whatever the technology used to create an optical interconnection system it must be capable of forming an effective fully interconnected stable system. An effective practical system requires a balance of material properties for a broad thermal operating range, ease of optical coupling to sources, detectors, optical fibers with industry compatible connectivity and acceptable total optical loss. Practical applications also require capability for versatile configurations and be process forgiving. For example, compatibility with common industrial assembly processes like solder reflow for electronic or E/0 component attachment and interfaces. 

Plastic products are often constrained from freely expanding or contracting by rigidly attaching them to another structure made of a material (plastic, metal, etc.) with a lower coefficient of linear thermal expansion. When such composite structures are heated, the plastic component is placed in a state of compression and may buckle, etc. When such composite structures are cooled, the plastic component is placed in a state of tension, which may cause the material to yield or crack. The precise level of stress in the plastic depends on the relative compliance of the component to which it is attached, and on assembly stress. 

The primary advantage of CD complexation is to stabilize and protect sensitive host molecules, such as flavors, odors, or pharmaceuticals. CDs sharply reduce the volatility, chemical, thermal and photo reactivity of guest moleciiles. More recently, CDs have been used for separation of components in solution. For example, CDs can remove reactive components from fhiit juices to prevent oxidation or eUminate bitterness. Attachment of CDs to chromatographic supports provides chiral separation, selective component removal and modified chemical reactivity. A number of modified and pol3nnerized CD materials have gained acceptance as separation media (9). 

One problem which arises when a detector array is attached to the face of a multi-layer module is the inability of the detector material to absorb forces generated by a mismatch of coefficient of thermal expansion between the detector array material and the module. Furthermore, it is difficult to isolate a fault that may be attributable to either the detector elements, module wiring or processing elements. A buffer board is introduced in WO-A-8807764 (Grumman Aerospace Corporation, USA, 06.10.88) which facilitates electrical communication between the detector elements and the module and conductive patterns formed on the module layers, and also enhances the structural characteristics and separate testability of the system components. 

Thermally conductive adhesives may be filled with metal, ceramic, or inorganic particles. Silver-filled epoxies have high thermal conductivities, but may not be used where there is a risk of electrical shorting. In such cases, epoxies or other polymers filled with electrically resistive, but thermally conductive materials such as aluminum nitride, boron nitride, alumina, or beryllia must be used. Some applications for thermally conductive adhesives include attachment of power devices, heat sinks, large components such as capacitors and transformers, large ceramic substrates, and edge connectors. 

Mechanical attachment of components, devices, and other parts of an electronic assembly is the prime function of adhesives. Although adhesives are expected to bond a wide variety of materials for electronic applications, they do not need to be structural. They should, however, meet minimum tensile and shear strengths in order to withstand mechanical shock, thermal shock, thermal cycling, and vibration as specified for the intended application. For consumer and commercial products, these stresses may be minimal. For high reliability aerospace and medical systems, more severe tests as defined in MIL-STD-883 and other documents must be used. 

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