Hi Max, Multi-point grounding of PCB to metal chassis is a good idea.
The beneficial effect of the multi-point connection of the PCB to a metal chassis is to reduce the net impedance associated with the return currents for signals flowing on the PCB. The impedance decrease provides a lower voltage generated across the printed circuit board, thus reducing the common mode present on the various circuit nodes on the board. This is especially critical as frequencies rise, regardless of the concern often raised about (the red herring of) "ground loops". In fact, one of my pet peeves, as it were, are "low noise designs" that use "isolation"--segregated Vcc/0V structures--to keep noise from coupling between areas of the circuitry. It is common to see high frequency circuits on PCBs separated with ferrite beads and having isolated, DC-coupled 0V planes. Often, the oscillator is designed with its own Vcc/0V island. The fallacies of this approach are as follows: 1. Intentionally segregating the Vcc/0V structures drives up the impedance in return paths, creating RF voltages at the isolation element (be it a ferrite bead in Vcc or a 'necked down' area in the 0V plane). The net effect is to produce a common mode voltages in series with every signal line that is associated with "isolated" area. When you route a conductor off of the isolated area, this common mode voltage is a high frequency "ripple" on the conductor. 2. At RF, the circuits are coupled anyway! The parasitic capacitance between circuits negates the notion of high frequency isolation. Of the sixty or so examples of this "design" implementation we have seen over the past year or two, the performance during radiated emissions is always troublesome. I'd welcome comments on this subject.
