Radio Frequency Integrated Circuit Design - Webs

The Use and Design of Passive Circuit Elements in IC Technologies
as shown in Figure 5.42. This results in low inductance (a few tenths of a
nanohenry) and very little extra capacitance. One disadvantage is that the pads
must be further apart; however, the patterning of the PCB is still very fine,
requiring a specialized process. Once flipped and attached, it is also not possible
to probe the chip.
When using chip-on-board packaging, the chip is mounted directly on
the board and bond wires run directly to the board, eliminating the package,
as shown in Figure 5.43. The PCB may be recessed so the top of the chip is
level with the board. This may require a special surface on the PCB (gold, for
example) to allow bonding to the PCB.
Packaging has an important role in the removal of heat from the circuit,
which is especially important for power amplifiers. Thermal conduction can be
through contact. For example, the die may touch the metal backing. Thermal
conduction can also be through metal connections to bond pads, wires to
package, or directly to PCB for chip-on-board. In the case of the flip-chip,
thermal conduction is through solder bumps to the printed circuit board.
Figure 5.42 Flip-chip packaging.
Figure 5.43 Chip-on-board packaging.
References
[1] Abrie, P. L. D., RF and Microwave Amplifiers and Oscillators, Norwood, MA: Artech
House, 2000.
[2] Barke, E., ‘‘Line-to-Ground Capacitance Calculations for VLSI: A Comparison,’’ IEEE
Trans. on Computer-Aided-Design, Vol. 7, Feb. 1988, pp. 195–298.
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