Multichip Module Technologies:Choosing Substrate Technologies and Assembly Techniques.

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Choosing Substrate Technologies and Assembly Techniques

The MCM designer has the freedom of choosing/identifying substrate and assembly technologies [13–15] from many sources [16,17]. If you are about to start a design and are looking for guidelines, finding a good source of information could be Internet access. In addition to designing to meet specific performance requirements, it is also necessary to consider ease of manufacture. For example, Maxtek publishes a set of design guidelines, that inform the MCM designer of preferred assembly materials and processes, process flows, and layout guidelines.

Substrate Technologies Assembly Techniques

Chip-on-board Surface mount

Chip-on-flex Chip-and-wire Thick-film ceramic Mixed technology Cofired ceramic Special module Thin-film ceramic Under Substrate Technologies and Assembly techniques it will be very informative to look at some pictorial examples, a primary source of which is Maxtek. The pictorial examples, followed by a brief description of technology or assembly technique shown, will serve as a quick guideline for someone who would like to get a feel of what technologies are viable in the MCM technology domain. Here, it is important to mention that a lot of current space electronic flight projects use MCM technologies for their final deliverables. Project Cassini, for example, used MCM hybrids in telecommunication subassemblies. On this note, take a look at some of the examples of MCM technologies currently on the market.

Chip-on-Board

Chip-on-board substrate technology (Figure 9.1) has low set-up and production costs and utilizes Rigid FR-406, GETEK, BT Epoxy, or other resin boards [3]. Assembly techniques used are direct die attach/ wire bonding techniques, combined with surface-mount technologies.

Chip-on-Flex

Chip-on-Flex substrate technologies [18,19] (Figure 9.2) are excellent for high-frequency, space-constrained circuit implementation. In creating this particular technology, the manufacturer needs Kapton or an equivalent flex-circuit base material with board stiffeners. Here, the die can be wire-bonded, with “glob- top” protection, while other discretes can be surface mounted. Integral inductors can be incorporated (e.g., for load matching).

Thick-Film Ceramic

This technology is the most versatile technology, with low-to-medium production costs. The 1-GHz attenuator above demonstrates the versatility of thick film on ceramic substrate technology (Figure 9.3), which utilizes both standard and custom ICs, printed resistors and capacitors actively trimmed to 0.25% with extremely stable capacitors formed between top plate and ground plane on the other side of substrate. Thick-film thermistor here senses overheating resistor and protects the remainder of the circuit.

Multichip Module Technologies-0134Multichip Module Technologies-0135

Co-Fired Ceramic

Co-fired ceramic MCM substrate technologies (low- or high-temperature co-fired multilayer ceramic) (Figure 9.4) are particularly suited for high-density digital arrays. Despite its high set-up and tooling costs, up to 14 co-fired ceramic layers are available from this particular manufacturer. In this technology, many package styles are available, including DIP, pin-grid array, and flat pack.

Thin-Film Ceramic

For thin-film ceramic technologies (see Figure 9.5), here is the outlined technology features include:

• High-performance MCMs, offset by high set-up and tooling costs

Multichip Module Technologies-0136

• Alumina or BeO (as shown here) substrate

• Both sides of substrate can be used, the back side typically being a ground plane, with access through plated-through holes

• Chip-and-wire assembly with epoxied capacitors

• Many packaging styles available, including Kovar or ceramic package and lid

• Primarily used for high-frequency circuits requiring thin-film inductors or controlled impedance lines For quick reference, some specifications and MCM technology information are summarized in Tables 9.3 and 9.4.

Other thick-film components are available, such as thermistors and spark gaps. In many applications, both sides of a substrate can be used for printed components.

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