[time-nuts] PCB design questions
SAIDJACK at aol.com
SAIDJACK at aol.com
Mon Jun 2 17:11:06 EDT 2008
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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Tyler Florence" on AOL Food.
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