Hybrid or multichip modules

Substrate attachment. In assembling hybrid or multichip modules, ceramic intercoimect substrates fabricated using thin-fihn or thick-film processes are attached to the inside base of a ceramic or metal package. Generally, film adhesives that have been cut to size are used to attach large substrates (greater than one-inch square) while either paste or film adhesives may be used for smaller substrates. Substrates may be alumina, beryllia, aluminum nitride, or silicon. 

Some adhesive materials and processes are used across many applications. For example, adhesives used to attach bare die and substrates in hybrid or multichip modules may be used for a wide variety of ground-based military... 

Qualihcation tests for adhesives are dehned in Method 5011 of MlL-STD-883 and requirements for qualifying sealed hybrid microcircuits or multichip modules that contain adhesives are specihed in MlL-PRF-38534. Space, automotive, and medical applications generally use the military specihcations, but are modihed or supplemented with additional tests and requirements for their particular application. 

Complex Electronic Hardware All devices that are not simple are considered to be complex. See the definition of Simple Hardware [EASA CM-SWCEH-OOl]. Complex Electronic Hardware Includes custom micro-coded components (such as ASICs, PLDs and associated macro functions) and integrated technology components (such as hybrids and multichip modules). RTCA-DO-254 (para 1.6) advises that hardware should be examined hierarchically at the levels of integrated circuit, board and LRU for complexity, including addressing functions that may not be testable, such as unused modes in multiple usage devices and potentially hidden states in sequential machines . An item constructed entirely from simple items may itself be complex. Complexity is an attribute of systems or items which makes their operation difficult to comprehend. Increased system complexity is often caused by such items as sophisticated components and multiple interrelationships. 

A wide variety of ceramic or alumina substrate materials have been developed for use in hybrids and multichip modules. These materials are the subject of specialized manufacturing processes beyond the scope of this handbook. The reader needing information on this group of materials is advised to contact a major manufacturer of ceramic materials. 

Multichip packaging involves the attachment and interconnection of a variety of chip devices on an interconnect substrate that may be single layer or multilayer. There are two basic types of multichip packaging hybrid microcircuits and multichip modules. 

Figure 33 Hybrid multichip module stmcture with five copper conductor levels and six polyimide insulating films deposited by spin coating onto a doped silicon wafer. In this process, the integrated circuits are inserted in cavities that are created by laser drilling or anisotropic chemical etching of the silicon substrate. IC chips are bonded to the substrate by means of a heat-resistant insulating adhesive.

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