Manufacturers of electronic equipment in North America use hybrids extensively and continue to find new applications, among these are:
• copper motherboards for military applications
• telephone line interface circuits in telecommunication switching systems
• engine control hybrids in automobiles
Hybrid manufacturers are responding to the increased complexity of IC's and the variety of new opportunities.in a number of specific ways. General trends are:
• Jarger area substrates - For many years hybrid manufacturers have used master substrates to take advantage of economies of scale and have manufactured several circuits at once. With the decrease in the cost of ceramic in the late 70's and increase in quality (particularly with respect to camber) larger substrates are being more widely used. Five years ago circuits of 2.5×5 cm were standard, today substrates of at least 10×12.5 cm are used by most hybrid manufacturers.
The size of individual circuits is also increasing. Some military circuits are routinely designed and manufactured at sizes up to 15×20 cm. Telecommunications and automotive circuits have not yet reached these extremes, but many new circuits for these applications are as large as 7.5×10 cm.
• Greater Print Density. As feature size of add-on components and semiconductor ICs have been reduced, hybrid manufacturers have followed suit and designed circuits with finer lines. 500 micron lines and spaces were commonly used five years ago, but again the high reliability segment took the lead and developed finer line capability in conjunction with the paste suppliers. 125 micron lines are now considered the norm for this segment. The commercial segment routinely uses 250 micron lines and is moving toward the 125 micron resolution achieved by the high reliability segment.
• Multilayers - Many of the new applications place a premium on small size. This challenge is being addressed by multilayer technology. Today almost all new designs in the military and data processing segments use multilayer technology (typically six or more metal layers) either in precious or base metals. Telecommunication and Automotive circuits are still primarily single layer, however many new designs are moving from one-to-two layers with extensive crossovers to full multilayers with as many as four metal layers.
• High Conductivity Conductors - The increase in semiconductor IC speed has placed a premium on conductivity for hybrid circuits. Within precious metal conductors, there has been a move towards lower palladium and platinum content materials, and there is a parallel move towards copper conductors.
• High Thermal Conductivity Substrates - Again advances in ICs have created new needs in hybrids. The increased heat generated by the more complex ICs is becoming a general concern, rather than the specialized problem of a few very advanced designs. There is as yet no clear trend as to how this problem will be solved, but there is a great deal of activity investigating alternate substrates, chief among these being Aluminum Nitride.
• Polymeric Thick Film - Traditionally thick film has been a cermet technology. However, as designers search for lower dielectric constant K and lower cost processes, polymeric technologies are being explored.
The North American hybrid market is large, vigorous and growing. It continues to be dominated by the high reliability applications, both in terms of dollar value of circuits produced and leadership in development of new technology. The commercial segment represents an area of considerable growth and opportunity today, and a number of advanced hybrid designs are being introduced in both telecommunications and automotive applications.
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