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This paper presents the design and performance of a leadless IMCM-D electronic package with the following attributes: (1) 432-pin land-grid VO array, (2) mountablddemountable to its printed circuit board by means of a soiderless socket, (3) signal speeds above 1 GHz, and (4) up to 25 W dissipated using forced-air cooling. I. 1NTROI)UCTIONThe on-going increases of circuit density and speed in microchip technology are pushing electronic packaging to accommodate higher pin counts, higher signal speeds, and higher power than ever before. These trends pose a number of problems: large (expensivle) packages, long (inductive) leads, closely spaced leads (contributing to crosstalk and board noise), difficulties in package attachment (and/or repair) to the circuit pack, complexities in signal routing and parts placement on the circuit pack, and concentrated thermal loads that are difficult to handle. This paper discusses the design and performance of a leadless electronic package that successfully addresses most of these problems. The package has a pin count of 432 and is used to deliver ECL-level 622 MHz clock and 622 Mb/s data streams to/from a single, high-power GaAs gate array. In addition, the gate array also communicates Yo eight nearby SRAMs by means of' 78 Mb/s bidirectional Tnlevel signals. XI. DESIGN OF THE PALCKAGE AND SOCKETA sketch of the package, with lid removed, is shown in Fig. I(a). There 432 gold-covered YO contact pads with diameters of 0.75 mm, arranged in three concentric rows at a pitch of 1.27 mm (0.050"). 'The innermost row of pads is devoted exclusively to power and ground connections, while the outer two rows are used mainly for U 0 signals. The package is based on the ATCIrT POLYHIC interconnection technology [ 1 -21, in which multilayer hybrid circuits are fabricated on alumina substates. For the package discussed in this paper, a die cavity is laser-milled into the substrate, such that both the substrate and the GaAs die are attached directly to a heat sprender. :LS illustrated in Fig. I(b). In addition to its thermal role, the heat spreader serves as the stiff mechanical member of package, protecting the alumina substrate from excessive flexure. The package is nonhermetic, as epoxies are used throughout its assembly. T h e hybrid circuit is fabricated from pattemed 12 p m thick metal layers separated by 50 pm thick dielectric layers of 0-7803-3034-X/95/$4.00 0 1 9 9 5 IEEE 149

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