Ceramic packaging technology

The substrates carrying the circuits shown in Fig. 4.5 are a 95-96% alumina. This ceramic has been adopted for its combination of physical and chemical characteristics and, importantly, low cost. It offers a combination of mechanical, thermal and electrical properties which meet the in-service requirements, and compositional and microstructural characteristics suited to thick film printing (see Section 4.2.2). Alumina substrates are manufactured on a very large scale making the unit costs a small fraction of the total circuit cost. 

Over the past two decades MLC technology has been progressively developed for advanced packaging, especially by main frame computer manufacturers, and it is increasingly exploited for microwave communications. Especially significant is the emergence of low temperature co-fired ceramic (LTCC) technology. 

In the manufacture of the multilayer structure for the TCM, square sheets are stamped from a roll of green tape loaded with a debased alumina powder. Many small (about 150 /im diameter) holes ( vias ) are punched through the tape at predetermined positions. Electrical wiring patterns with line widths and 

In the TCM removal of heat is effected directly from the back of each semiconductor chip through a spring-loaded piston, assisted by immersing the multilayer structure in helium gas and by flowing water in the top cover. 

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The most advanced implementation of cofired-ceramic-packaging technology is the thermal conduction module (TCM) used in large-scale computers (IBM) (4, 72, 74). This package can accommodate over 100 flip-chip-bonded ICs on a 90 by 90 mm cofired ceramic substrate. The multilayer ceramic substrate contains 33 metal layers for chip pad redistribution, signal interconnection, and power distribution (Figure 14). Each chip contains 120 bonding pads, and 1800 pins are brazed to the bottom of the substrate for connection to a PWB. 

Briefly trace how the demands of electronic circuit technology have impacted on the development of ceramic packaging technology. 

Adhesives are also tailored to meet specific requirements of the packaging or assembly technology used (Table 5.9). Thus, the requirements for single-chip packaging in hermetically sealed ceramic packages such as CERDIPs will be somewhat different from those of plastic dual-in-line packages (PDIPs) and plastic-encapsulated microcircuits (PEMs). 

The original multilayered ceramic packages were developed around what is today known as a high-temperature cofired ceramic (HTCC). In this technology the ceramic was primarily an alumina-based... 

G. Zablotny, Improving Yields in Cofired Ceramic Packages An Examination of Process and Equipment, Hybrid Circuit Technology, 9 [2] 33-35 (1992). 

The method of deposition is what differentiates the hybrid circuit from other packaging technologies and may be one of two types thick film or thin film. Other methods of metallizing a ceramic substrate, such as direct bond copper, active metal brazing, and plated copper, may also be considered to be in the hybrid family, but do not have a means for directly fabricating resistors and are not considered here. Semiconductor technology provides the active components, such as integrated circuits, transistors, and diodes. The passive components, such as resistors, capacitors, and inductors, may also be fabricated by thick- or thin-film methods or may be added as separate components. 

The discussion of lead properties of course does not apply to leadless devices such as leadless ceramic chip carriers (LCCCs). Design teams using these and similar packages must understand the better heat transfer properties of the alumina used in ceramic packages and must match coefficients of thermal expansion (CTEs or TCEs) between the LCCC and the substrate since there are no leads to bend and absorb mismatches of expansion. Use of ceramic devices may lead the design team to consider the use of Low Temperature Co-fired Ceramic (LTCC) substrates and assembly technologies XXX. 

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