Microcircuits substrates

Shores AA. Adhesive Bonding Hybrid Microcircuit Substrates with PEEK Thermoplastic Film. ISHM Proc. 1988 1(2). 

Shores AA. Adhesive bonding hybrid microcircuit substrates with a thermoplastic film. SAMPE Quarterly. Apr. 1988 19. 

Buried layers are important parts of microcircuits. TXRF is a sensitive microanalyti-cal tool for inspection of buried layers (Fig. 4.14). On a thick substrate, the angle characteristics are a function of layer thickness. [4.59, 4.60]. 

Fig. 4.5 Film devices and circuits (a) thin-film resistors on glass and steatite substrates (b) thick-film resistor networks on snapstrate alumina substrate (c) various thick-film resistors (d) hybrid microcircuits. (Components kindly supplied by General Hybrid, C-MAC and...

The fabrication of the super alloys of today and those of the future requires improved molds, cores, and binders. Chemical processes and oil refining require catalysts with improved activity, selectivity, and mechanical properties. Classic ceramics and the new ceramics for electronic microcircuits (microelectronics) require purer and more reliable precursors and processes. Chromatographic processes require substrates with improved physical, mechanical, and surface properties. And there is an ever-increasing need of better absorbents, binders, and pigments. 

A microcircuit may be described as a collection of devices each consisting of an assembly of active and passive components, interconnected within a monolithic block of semiconducting material [4]. Each device is required to be isolated from adjacent devices in order to allow for maximum efficiency of the overall circuit. Furthermore within a device, contacts must also be electrically isolated. While there are a number of methods for isolating devices in a circuit (reverse-biased junctions, mesa isolation, use of semi-insulating substrates, and oxide isolation), the isolation of active components of a single device is almost exclusively accomplished by the deposition of an insulator. 

In assembling hybrid microcircuits or multichip modules, ceramic interconnect substrates fabricated using thin-film 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 1-inch square) while either paste or film adhesives may be used for smaller substrates. Substrates may be alumina, beryllia, aluminum nitride, or silicon. 

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. 

Of the mass-transfer dispensing methods, screen printing and stencil printing are the oldest and most widely used. Screen printing has been used for over 40 years in the electronics industry to apply thick-film conductors, resistors, and dielectrics in fabricating circuits on ceramic and plastic-laminate substrates. Screen printing is also used as a batch process for depositing electrically conductive and insulative adhesives to interconnect devices on thin-film and thick-film hybrid microcircuits. 

Poor adhesion and delamination can also result from dispensing insufficient adhesive to cover the entire bond line (Fig. 6.2). Generally, a minimum thickness of 2 mils is required. A visible fillet around two or more sides of an attached die or substrate provides assurance that sufficient adhesive has been used and has spread and covered the bond line. In fact, the appearance and extent of fillet are inspection criteria for the acceptance of high-reliability circuits as defined in MIL-STD-883, Method 2010 for monohthic ICs and Method 2017 for hybrid microcircuits. According to these methods, at least 75% of the fillet should be visible along each side of the device. Applying a uniform thickness is also important. Nonuniform thicknesses result in tilted devices with the potential for cracking and separation. 

The first specifications for adhesives were generated by the staff of NASA and the DoD who were prompted by the high reliability that was required of microcircuits used in aerospace programs. These specifications covered primarily die and substrate attachments for hermetically sealed integrated circuits, hybrid microcircuits, and multichip modules. Subsequently, with the increased use of surface-mount adhesives in the assembly of commercial printed-wiring boards and underfills for flip-chip devices, industry associations took the lead in generating the requirements and test methods. 

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