lulu@ucrmath.ucr.edu (david lu) (06/01/90)
What does it mean for a motherboard to be "layered"?
I've seen ads for 4-layered motherboards, so I assume
that other n-layered motherboards also exist.
Inquiring minds wants to know.
- David
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- Geoffrey James, _The Tao of Programming_lulu@ucrmath.ucr.edu (david lu) (06/03/90)
What exactly does it mean for a motherboard to be "layered"?
I've heard of "4-layered motherboards", so I assume that there
are other n-layered m/b's as well. Are all m/b's layered?
Just wondering ...
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"After three days without programming, life becomes meaningless."
- Geoffrey James, _The Tao of Programming_woan@peyote.cactus.org (Ronald S. Woan) (06/04/90)
In article <6811@ucrmath.ucr.edu>, lulu@ucrmath.ucr.edu (david lu) writes: > What exactly does it mean for a motherboard to be "layered"? > I've heard of "4-layered motherboards", so I assume that there > are other n-layered m/b's as well. Are all m/b's layered? Layered is just what it implies, several layers of 'glass sandwhiched together to allow more conductor paths in a smaller amount of space. Most motherboards are indeed 3+ layered these days. Personally I have always felt that this is not always a good thing as you have to be aware of possible interference and capacitance effects. Ron -- +-----All Views Expressed Are My Own And Are Not Necessarily Shared By------+ +------------------------------My Employer----------------------------------+ + Ronald S. Woan woan@peyote.cactus.org +
root@kesher.UUCP (Aaron_Schmiedel) (06/04/90)
Actually, layered motherboards have a great propensity AGAINT RFI than to single or double sided motherboards. One of the main reasons is that on most of the multi-layer motherboards one of the layers (in the case of a simple voltage construct of +5vdc and ground), is made up of a ground plane, and another is made up of a vcc plane, which is QUITE effective in eliminating interlayer capacitance and most effectively RFI. Most of today's PC stuff is usually built on a 4 layer motherboard in the process described above. This is in order to help pass the FCC's "B" rating. Some of the motherboards I worked on in the military had up to 12 layers, but this was only on krypto equipment. Multi-layer boards are superior overall to single or double layer boards, and do not have any inherent problems (except more expensive to make and design).
silver@xrtll.uucp (Hi Ho Silver) (06/05/90)
In article <6761@ucrmath.ucr.edu> lulu@ucrmath.UUCP (david lu) writes:
$What does it mean for a motherboard to be "layered"?
This refers to the number of layers of traces on the board. Early
circuit boards used only one layer of connections on a side. Lately,
however, it has become more and more common to put several layers of
traces on the board, each layer being separated by an insulating layer.
Since there are inevitably traces which have to cross paths without
being connected, the use of multiple layers makes circuit board design
a much easier task - otherwise, traces which need to cross would either
have to be run through to opposite sides of the board near where they
cross, or wire jumpers would have to be attached.
For those who don't know quite what the word "trace" means in this
context, it refers to the "wires" that are formed by a thin layer of a
conductor applied to the board - have a look at a circuit board and
you'll see what I mean.
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/Silver: Ever Searching for SNTF \ Life sucks. \ someone buy me a BEER! /brown@vidiot.UUCP (Vidiot) (06/05/90)
In article <6761@ucrmath.ucr.edu> lulu@ucrmath.UUCP (david lu) writes:
<What does it mean for a motherboard to be "layered"?
<I've seen ads for 4-layered motherboards, so I assume
<that other n-layered motherboards also exist.
When you look at a circuit board, you normally see the etched runs that make
up the circuit traces. The two sides that you can see are called layers.
Every double-sided board is considered as having two layers. A four layer
board has two more layers inside the board. Consider it as a sandwich.
A four layer board will have three pieces of board glued together. A four
layer board normally has the signal traces on the outside layers and power
and ground traces in the inner two layers.
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rutgers/ decvax!nicmad/ INET:<@spool.cs.wisc.edu,@astroatc:brown@vidiot>poffen@sj.ate.slb.com (Russ Poffenberger) (06/05/90)
In article <838@peyote.cactus.org> woan@peyote.cactus.org (Ronald S. Woan) writes: >In article <6811@ucrmath.ucr.edu>, lulu@ucrmath.ucr.edu (david lu) writes: >> What exactly does it mean for a motherboard to be "layered"? >> I've heard of "4-layered motherboards", so I assume that there >> are other n-layered m/b's as well. Are all m/b's layered? > >Layered is just what it implies, several layers of 'glass sandwhiched >together to allow more conductor paths in a smaller amount of space. >Most motherboards are indeed 3+ layered these days. Personally I have always >felt that this is not always a good thing as you have to be aware of possible >interference and capacitance effects. > Because layered boards are more complex to manufacture, and defects potentially difficult to fix, having a board with a lot of trace layers is not necessarily the best. Usually you want a 4-layer board because this implies that power and ground are run on separate layers and are usually preferable for maintaining signal integrity on the other two (signal) layers by acting like shields. If you had a choice between a 4 layer and 6 layer board, both of equal functionality, take the 4 layer board. This usually implies that the designer of the board took a little more effort is laying out the board, rather than resorting to more layers to route all the traces, not to mrntion that the 4 layer board would probably be a little cheaper and more reliable. Russ Poffenberger DOMAIN: poffen@sj.ate.slb.com Schlumberger Technologies UUCP: {uunet,decwrl,amdahl}!sjsca4!poffen 1601 Technology Drive CIS: 72401,276 San Jose, Ca. 95110 (408)437-5254
phil@pepsi.amd.com (Phil Ngai) (06/06/90)
In article <509@vidiot.UUCP> brown@vidiot.UUCP (Vidiot) writes: |Every double-sided board is considered as having two layers. A four layer |board has two more layers inside the board. Consider it as a sandwich. |A four layer board will have three pieces of board glued together. A four Actually, I think of a four-layer board as two two-layer boards glued together. You would understand this if you realized that two-layer boards are two sheets of copper glued together. Although your description (three pieces of board) isn't completely wrong, it does give the impression that during assembly, the center part is a rigid object that is glued in when really it is some floppy glass fabric impregnated with goopy epoxy. -- Phil Ngai, phil@amd.com {uunet,decwrl,ucbvax}!amdcad!phil "Separate but equal": bad for blacks, good for women.
rmf@bpdsun1.uucp (Rob Finley) (06/08/90)
In article <838@peyote.cactus.org> woan@peyote.cactus.org (Ronald S. Woan) writes: >In article <6811@ucrmath.ucr.edu>, lulu@ucrmath.ucr.edu (david lu) writes: >> What exactly does it mean for a motherboard to be "layered"? >Most motherboards are indeed 3+ layered these days. Personally I have always >felt that this is not always a good thing as you have to be aware of possible >interference and capacitance effects. I am a pcb designer for Harris Broadcast Products. A multi-layer board usually consists of even numbers of layers. Here is why: The blank PC boards start out with copper on both sides. Our fab house doesn't have single sided stock available. It is just as expensive to do a four layer as a three layer board. Even numbers of layers also control warpage of the finished board over time as copper on both sides exert similar stress. Warped boards will fail eventually and you won't enjoy it! The processing is the same. If you develop one side, you are going to have to put both sides in the solution any way. Multi-layer boards are astronomical in cost compared to two layer boards. For capacitance, the usual stack arrangement is to use one layer to connect all of the grounds together. Another layer can also be used only for the positive (+5V) connections. The capacitance between the two power supply layers actually cleans on the power supply for decoupling some of the noise. Having an entire layer as a conductor can also prevent noise caused by traces that are too small for the current load and cause ringing. I am not going to say that there aren't any transmission line effects due to a ground plane running underneath those signal traces. But, computer similation during the layout process can point out problems (for me, it starts at 25Mhz) and then we remove some of the ground plane underneath that trace. Besides, to get the '386 that I am using to write this on a two layer board, I wouldn't want it. The traces would have to be so small to fit them in that no manufacturing process could cope with them. Multi-Layers are a necessary part of this industry. Between a two and a four, I would ignore the two. There are too many advantages. IMHO of course. I am also speaking for myself (didn't I just mention that...) ----- "Lets go kick some Earthling butt!" -- Spaced Invaders quintro!bpdsun1!rmf@lll-winken.llnl.gov uunet!tiamat!quintro!bpdsun1!rmf