2 layer and 4 layer pcb

[Rajinder]

Hi all
I am starting to get familar with schematic capture using Eagle PCB.
I am now ready to do some simple pcb designs. I am looking st a 7 segment pcb as a starting project. This fits into a microchip development board that i have. So it will be a small module pcb. The bosrd will plig into I/O lines from a header, where then it will have a 4 x 7 segment display and transistors to select each digit, transistors driven from seperate i/o lines.

I wanted to ask the advantages of 2 layer v 4 layer for this design. As far as i am aware 4 layer gives a solid ground plane and vcc. Also allows tracks to be in the inner layers and is better from a emc prospective.
I am looking at a 2 layer pcb for my design above. My other questions are
1. I will be using tracks on both sides of the pcb. Can i still fill the remaining of the bottom layer as gnd?
2. Top layer will have vcc, components, decoupling caps and signal tracks. Any recommendations on calculating track widths and lengths?
3. It is not high speed stuff so i presume a 2 layer pcb fill be sufficient.

Thanks in advance.

 

[(*steve*)]

2 layer will also be substantially cheaper than 4 layer.

Settle on a track width that you will normally use -- say 0.8mm and stick to that unless you need thicker traces for high currents or finer traces to fit between pads etc.

Thinner traces increase the likelihood of broken traces, although with modern manufacturing that's not likely going to be an issue until you go really fine.

Flood filling parts of the board is great for making boards at home because it uses less etchant. Unless you have a specific need, there is no particular point for commercial boards. One potential purpose is to reduce the impedance of your ground wiring.

 

[BobK]

Settle on a track width that you will normally use -- say 0.8mm

That's huge. Would not work well with the 0.65 mm pitch PICs I am using now!

For DIP work, I typically use 15 mils (about 0.4 mm), and I go down to 12 or 10 mils to sneak lines between pins on a DIP. And, of course, wider if more than a few hundred mA of current.

M