I'm designing an MCU card for a 64-pin dsPIC, something like this:
I have several questions regarding MCU card design (two-layer board):
Is it enough to place only one bulk 10uF/6.3V capacitor (tantalum), instead of 4 of them? These little buggers are quite expensive, and I've read somewhere that it is perfectly fine to use only one. I also plan to put a tactile switch on MCLR (reset) pin, and a LED indicator for power supply - both of these components would go in separate corners, leaving no space left for bulk capacitors.
Is it OK to place traces under a crystal? When it comes to crystal soldering, should I leave some space between the bottom of the crystal and the board (let's say 1-2 mm), or this does not matter?
The dsPIC has power supply pins on all 4 sides. Is it ok to connect these pins under the microcontroller? Something like this:
- I plan to use a combination of 100nF/1uF ceramic capacitors between Vdd and Vss, placed on a bottom layer. Is it enough to use only one pair, or should I use 4 pairs of capacitors - one pair for each Vdd/Vss pair? If it is OK to connect Vdd and Vss under the microcontroller (see Q3), I suppose that it is OK to use only one pair of capacitors.