[time-nuts] PCB design questions

[SAIDJACK at aol.com]

HI Dave,
 
for quick and inexpensive one-off designs, you may try a "one-layer"  PCB.
 
Basically mounting all the parts onto an FR4 clad with Copper on one or two  
sides (BTW: 5-layer boards don't exist as far as I know).
 
Use SMD parts, and bend-up the ground pins. Then solder these parts  
backwards onto the Copper plane, with all pins connected to ground directly  soldered 
onto the plane.
 
Use 0603 caps between the Copper plane and the power pins. Route the traces  
with thin wire (for example transformer wire etc), and tape them onto the 
Copper  plane, or glue them down.
 
Place 0603 or 0805 parts onto the bottom of the IC's (which is now the  top 
of course since we mounted them backwards), one leg soldered to the IC  pin.
 
You can cut small local planes with an exacto knife if necessary, for  
example to generate heatsinks for regulators, or pads for larger  components etc.
 
Once debugged, you can use a hot-glue gun to ruggedize everything.
 
This works extremely well, very good isolation, great grounding and heat  
dissipation due to the Copper plane, no degradation due to vias, and it is quite  
fast, especially when working under a microscope, and as cheap as it  get's.
 
bye,
Said
 
 
In a message dated 6/2/2008 11:22:31 Pacific Daylight Time,  
david.partridge at dsl.pipex.com writes:


1.  Surface mount or through hole?  I don't have a re-flow oven (or even  a
hot air soldering system), so my inclination is to use through hole  CMOS
(74HC163s with 74AC glue logic and flip-flops), with the surface  mount
restricted to the clock shaper using a BAV99 and either an ADCMP600  or
MAX999 and surrounding components.   Will using through hole  cause me grief?

2. How many layers?   In an ideal world with  money no object, if I
understand the current art correctly, I think I'd  probably aim for a five
layer board with Vcc, Digital Ground and Power  Ground being separate
internal planes, and trace routing on the top and  bottom of the board with
as few vias between top and bottom as  possible.  Does that sound right?

Do you think I can safely  restrict myself to two layers, and if so does it
make most sense to make  one side of the board digital ground, and route
everything else (Vcc,  Power/Analogue Ground, and signals) on the other side.
Or is there a better  approach (always assuming that a two layer board is a
viable  option).

Cheers
Dave  Partridge





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