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Appendix A: A PCB vs. MCM-c Comparison Matrix

November 1, 1997
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Appendix A: A PCB vs. MCM-c Comparison Matrix

Problem

Description

PCB solution

MCM-C solution

Cost

Final design must meet cost targets

Reinforced BT epoxy or GETEK can meet high frequency performance requirements, but costs are higher than for conventional FR4 boards, heat sinks and special wire-bondable conductors add to cost

Ceramic MCM technology facilitates tuning, reduces size and simplifies thermal management, providing an attractive balance of performance and cost

Active device variability

Active devices have broad specifications (wide tolerances)

Potentiometers and variable capacitors used to compensate for variability

Active trimming of printed integral resistors and capacitors on the circuit substrate

Circuit tuning

Obtain precise circuit response

Manual trimming of components, impacted by body (hand) and tool parasitics

Automated hands-off trimming of passive components — no parasitic effects

Reliability

Reliable operation over a broad environmental range for bare chip packaging

Requires costly specialty materials and platings

Proven high reliability processes

Filter response

Passive components have wide tolerances

Potentiometers, precision passives or component selection (swapping)

Active trimming of printed integral resistors and capacitors on the circuit substrate to optimize filter response

Heat dissipation

With inadequate heat dissipation chips run hot, degrading lifetime. Nonuniform heat dissipation causes some parts of the MCM to run hotter than others, changing electrical properties (edge-rate degradation)

External heat management add-ons, such as heat sinks, or forced convection or spreading devices out, which adds cost and makes the design more complex

Unpackaged ICs die mounted directly to a high thermal conductivity alumina substrate provide a less complex solution

Size

Circuit elements must be decreased in size to fit a hand-held probe. Minimum circuit size needed for many RF applications

Discrete adjustable components mounted on a PCB form a large module

Screen-printed thick-film resistors and capacitors adjusted to precise value using a laser trimmer replace large discrete adjustable components and allow size reduction

Tuning passive elements to design specifications

Parasitic capacitive effects of tools and operators' hands degrade precision

Potentiometers and variable capacitors are used frequently to compensate for active device variability in applications where precise circuit performance is required

Filter response can be optimized by actively trimming critical components in the filter

Bare chip assembly

Chip and wire techniques are required to attach bare ICs. Board technology must allow reliable assembly

Plated Cu PCB metallizations require special Au plating for compatibility with chip and wire assembly

Conventional thick-film Au metallizations are compatible with chip and wire assembly. Au thick-film conductors have demonstrated robustness in chip and wire processes

 

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