Electronic miniaturization is not simply a process of making everything smaller. Miniaturization of one phase of a product usually reveals limitations and obstacles in other parts of the overall design and manufacturing process. So progress often comes in uneven spurts, as advances in a specific technology—semiconductor fab, pc board, power, manufacturing, and packaging—leapfrog other technologies. Developments in several areas other than integrated-circuit dies are proving critical to the continued progress of miniaturization.
In the passive-component area, the introduction of the "0201" (20- by 10-mil) form factor for surface-mounted devices (SMDs) is one example. These near-microscopic components occupy 25% of the pc-board area and less than 20% of the volume of previous 40- by 20-mil parts. A related development is the use of adhesives in place of solder to mount SMDs. In addition, phasing out lead-based solder will have far-reaching effects on all of the electronics industry. Even developments in chip technology produce miniaturizing effects elsewhere. The creation of CMOS IC designs that operate on lower supply voltages will enable even greater miniaturization and longer battery life by downsizing power sources.
For some time, the subtractive (etch) process for pc-board fabrication has been seen as a barrier to further circuit miniaturization. As feature sizes shrink, maintaining dimensional tolerances and long-term reliability becomes more difficult because etching tends to undercut metal beneath the trace mask. A new additive process uses electroforming to build up metallic traces on a pc-board substrate and supports fabrication of 25-mm diameter holes and 10-mm wide lines/spaces on pc boards as thin as 12.5 mm. These figures represent 75% to 80% reductions versus etched pc boards. Such techniques as chip stacking further conserve board real estate.
Thermal management also has been identified as an obstacle to miniaturization, especially as device speeds and packaging densities rise. Heat loads are expected to outpace established cooling techniques sometime in 2003 or 2004. Now the focus is shifting to localized, active cooling strategies that provide very low thermal resistance, subambient capability, cost-effectiveness, and reliability for direct, spot refrigeration of high heat-flux regions on IC dies.
The bottom line of most tradeoffs in miniaturization is whether or not the market will support the cost of achieving a given size/performance level. Cutting-edge miniaturization typically becomes more expensive as sizes are reduced. A part of the increased cost results from facilities and placement/bonding machines that can attain higher precision. By some estimates, a yield of at least 98% is necessary to make miniaturized electronic products profitable. More aggressive miniaturization can make such yields more difficult to achieve, driving up cost until manufacturing technology matures. Adding to the problem is the growing impracticality of rework or repair as products shrink. Some miniaturization processes preclude testing until components are committed to final pc-board assembly.
Miniaturization is a strong draw in many types of consumer products, but it can be taken too far. For example, cell phones could be shrunk to the point where keypads and displays would be difficult to use. Increasingly, product designers are challenged to provide easy-to-use man-machine interfaces despite higher product complexity and shrinking control-panel real estate. Many electronic devices have already reached a near optimal form factor. Future miniaturization will focus more and more on increasing a product's sophistication, performance, and market penetration.
Miniaturization typically extracts some cost penalty, so it's most suitable to less cost-sensitive products. Markets like instrumentation, security, military/aerospace, and especially medical electronics can support the cost, whereas current telecommunications products can't. Continued progress now depends on manufacturers and designers solving problems related to electronics and the physics and chemistry of cooling, pc-board production, power distribution, and RF signal transmission.