Cofired multilayer ceramic substrates

H. Mandai, K. Sugoh, K. Tsukamoto, H. Tani, M. Murata, A Low Temperature Cofired Multilayer Ceramic Substrate Containing Copper Conductors , IMC 1986 Proceedings, May, (1986), pp. 61-64. 

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. 

Master, R.N., Herron, L.W., and Tummala, R.R., Cofiring process for glass-ceramic/ copper multilayer ceramic substrate, IEEE Transactions on Components, Hybrids, and Manufacturing Technology, Vol. 14, 780-783, December 1991. 

The lead-on-substrate MCP could also be implemented using a cofired ceramic package with the leads brazed on and finished by cover coating with a suitable encapsulant or hermetic seaUng of the assembled ICs. Chapter 7 of Ref. 7 gives a detailed discussion of the cofired multilayer ceramic package manufacturing processes. 

Figure 16. Cross section of thin-film multilayer interconnections on a pinned cofired ceramic substrate, with face-up tape-automated-bonded chip and thermal vias. (Reproduced with permission from reference 79. Copyright 1988 Materials Research Society.)...

The development of multilayer ceramics was first demonstrated in the preparation of capacitors in the late 1940s [1]. Over the following 10 years, the techniques necessary to produce multilayer high-temperature cofired ceramics (HTCC) substrates [2] were developed at American Lava and RCA, culminating in the first comprehensive description of this technology in 1961... 

HTCC is an all-inclusive term to describe ceramic substrates that are consolidated at temperatures above about 1000°C. Applied to electronic packaging, this descriptor includes aluminum oxide, aluminum nitride (AIN), and a variety of other developmental or seldom-used materials. Until recently, discriminating between HTCC and low-temperatme cofired ceramics (LTCC) was elementary, as the firing temperatures differed by roughly 600°C. To confoimd that difference, an intermediate-firing multilayer ceramic, or medimn-temperature cofired ceramic (MTCC), has recently been introduced. Details on the processing and properties of this material will be discussed in Section 6.2 and Section 6.4. 

The multilayer systems use low-dielectric-constant materials similar to traditional ceramic substrates for dielectric layers and an internal circuit metallization designed to be cofired with the ceramic dielectric. Cofiring of metallization with a ceramic dielectric required development of compatible systems which would have matching shrinkage onsets, shrinkage rates, and total volumetric shriiikage. Since the metal thermal expansions are... 

MCM-C interconnect substrates are produced from either low-temperature cofired ceramic (LTCC) or high-temperature cofired ceramic (HTCC). Either process can produce multilayer substrates having high numbers of conductor layers (up to 100), although for most applications 2-20 layers are sufficient. The fabrication of MCM-C involves thick-film processes that have wider lines and spacings (5-20 mils) than MCM-D, but are lower in cost. 

High-temperature cofired ceramic (HTCC) packages make use of thermal vias in the same manner as in multilayer thick-film substrates. The via-fill material used in HTCC packages is a refractory material such as tungsten or moly-manganese. 

Substrates made by the multilayer process from tape cast alumina have received considerable attention in recent years for multichip module (MCM) applications. An MCM consists of an array of closely packed chips on an interconnect board several inches on a side. Cofired ceramic is attractive relative to organic laminates because its thermal conductivity is almost 2 orders of magnitude higher, an important consideration in high-density circuitry. In addition both alumina and aluminum nitride ceramics are more closely matched to silicon in CTE than are organic boards. For similar reasons, alumina and AIN are attractive for ball grid array (EGA) mounting of chips. ... 

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