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