four layer PCB

[Guillermo Parada M]

Why I should design a PCB for a low speed embedded system using more than
two layers, ei four layers.



There are reasons for design a four layer PCB to a low speed embedded
systems?



Thanks.

 

[Tim Wescott]

"Guillermo Parada M" <gapm@vtr.net> wrote in message
news:c3lr32$6pa$1@news1.nivel5.cl...

Why I should design a PCB for a low speed embedded system using more than
two layers, ei four layers.



There are reasons for design a four layer PCB to a low speed embedded
systems?



Thanks.

Board size.

 

[CBarn24050]

There are reasons for design a four layer PCB to a low speed embedded
systems?

the usual reason is that you can't route it on 2 layers.

 

[Mac]

On Mon, 22 Mar 2004 00:48:36 +0000, Guillermo Parada M wrote:

Why I should design a PCB for a low speed embedded system using more than
two layers, ei four layers.



There are reasons for design a four layer PCB to a low speed embedded
systems?



Thanks.

Well, if you need the things that a four-layer board provides.

1) A four-layer board could be easier to route, since VCC and GND don't
have to be routed.

2) Better EMI/EMC performance if the board could be exposed to
interferrence or if it has to pass FCC emission levels or is part of a
low-noise or high-gain system.

3) Traces on a board with power planes have a well-defined impedance based
on trace width and distance to the plane. This can be important for
incoming or outgoing signals which have to match to controlled impedance
cables.

There are probably other benefits, but these are the ones I can think of
right now. Any board with a clock or clocks in the MHz range might benefit
from power planes. Most boards without routed clock signals (i.e.,
combinatorial logic only) probably don't need to worry about 2) and 3).

regards,
Mac

 

[Ban]

CBarn24050 wrote:

There are reasons for design a four layer PCB to a low speed
embedded systems?


the usual reason is that you can't route it on 2 layers.

If you use a BGA-housed component, you will know why you need *at least* 4
layers. And most modern DSPs and parallel flash memory just come in BGA. If
you do not need these, you might as well try to route a dual layer, but
"embedded systems" seems to indicate quite a lot of connections....
--
ciao Ban
Bordighera, Italy

 

[Robert Lacoste]

"CBarn24050" <cbarn24050@aol.com> a écrit dans le message de
news:20040322013353.09957.00000142@mb-m05.aol.com...

There are reasons for design a four layer PCB to a low speed embedded
systems?


the usual reason is that you can't route it on 2 layers

.... in particular when using high density packages (BGA, etc)

Another usual reason is if you don't comply with FCC/CE regulations with a
two-layers design (for example when using a plastic enclosure : A full
ground plane is often helpful...)

Friendly,

Robert Lacoste - ALCIOM : The mixed signals experts
http://www.alciom.com

 

[Frank Bemelman]

"Ban" <bansuri@web.de> schreef in bericht
news:Qvw7c.84385$z23.3615621@news3.tin.it...

CBarn24050 wrote:
There are reasons for design a four layer PCB to a low speed
embedded systems?


the usual reason is that you can't route it on 2 layers.

If you use a BGA-housed component, you will know why you need *at least* 4
layers. And most modern DSPs and parallel flash memory just come in BGA.
If
you do not need these, you might as well try to route a dual layer, but
"embedded systems" seems to indicate quite a lot of connections....

I often open my new 'consumer' electronics (curiosity), and more
often than not it contains single layers PCB's, even when there are
TQFP packages used. It's truly amazing that were able to produce
layouts for that. Even the number of jumpers is quite reasonable.

--
Thanks, Frank.
(remove 'x' and 'invalid' when replying by email)

 

[George]

"Ban" <bansuri@web.de> wrote in message news:<Qvw7c.84385$z23.3615621@news3.tin.it>...

CBarn24050 wrote:
There are reasons for design a four layer PCB to a low speed
embedded systems?


the usual reason is that you can't route it on 2 layers.

If you use a BGA-housed component, you will know why you need *at least* 4
layers. And most modern DSPs and parallel flash memory just come in BGA. If
you do not need these, you might as well try to route a dual layer, but
"embedded systems" seems to indicate quite a lot of connections....

A lot of the stuff that comes in BGA is also available in QFP or
TSOP, though, so you can go surface mount instead.