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Old 17th October 2010, 11:04 PM   #1
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Default Some PCB Tips?

Hey guys, can someone please tellme some tipbs about how design my first PCB?

i want to know at least minimun space between components, minimun signal copper width, minimun power copper width. and if is possible other ones. mainly my first design will be an LM3886 PCB, dual layer.

Thanks for your support.
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Old 17th October 2010, 11:15 PM   #2
cuibono is offline cuibono  United States
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What software are you using? I use Eagle. All I can say is, it takes a while to figure out what works for you. It took me a few years.

Two layer boards are especially difficult to fabricate oneself. Are you making the board, or a professional house. If it is a house, they will state their minimum distances. Some even have a file containing all their rules, you can use to check your boards with (called DRC in Eagle).

I guess in general, things look bigger on the computer screen than in real life - so I'd suggest making things bigger than you think.

And really, I'd suggest just using someone elses board design - I've done a number of designs, and they are really time consuming - particularly, once the board is made, there can be many many revisions till things work well.
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Old 18th October 2010, 12:17 AM   #3
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There is no minimum spacing between components (but see individual board manufacturers, who may have rules), but obviously they can't overlap, and you should bear in mind that some may be hot, and some may not, and you may wish to manage this.

Here's a trace width calculator, ANSI PCB Track Width Calculator, there are loads of them, or you can look on a table of values. Just google pcb trace width. In many cases the trace width is met and surpassed without problem. It's unlikely that you will need track spacing less that 10thou. If higher voltages are involved traces need to be spaced adequately, again you can find minimum spacings using google.

Traces should run horizontally, vertically and at 45 degrees, not just any old angle they come out when you join 2 pins together. Don't create included angles less than 90 degrees at junctions, these can create problems in both etched and routed boards.

Where 4 layers or more are used for increased connectivity, it is customary to run e.g. all the traces on the 2nd layer horizontally, and all the traces on the 3rd. layer vertically. This eases the placement of subsequent links (they don't cross one another.) In any case, if you are just routing on 2 layers by all means allow one layer to wander willy-nilly, but most of the links on the second layer should be straight lines, as would be wire links. This will make the placement of later traces less problematic.

Lay out the components following a straight line from input to output where possible, keeping high power away from low power. Route the signal traces first and the power last. Obviously sometimes all the I/O are placed on one side of the board and there may be other constraints, such as heatsink positions or controls, such as pots. In this case take the signal path round in a horseshoe, don't just give up and adopt a random arrangement. When drawing the schematic keep an awareness that some components are associated with others. Refer to the schematic while routing in order that e.g. decoupling caps are placed to keep the traces to their associated IC power pins as short as possible. Try to avoid routing high power in parallel with low power, cross the traces at right-angles.

In the case of digital circuits it can be difficult to organise components to produce a coherent signal path. Keep the traces that make up a bus organised together, however. In order to avoid crossing tracks in a bus, re-assign the pins as necessary either on the originating components or on the receivers, such as latches or bus buffers which have multiple functionally-identical sub circuits. This may require quite a lot of work and thought to preserve the correct organisation and may leave the original schematic looking disorganised, but it results in a better board. Modification of the schematic will be necessary where the layout software works on a netlist exported from a schematic capture program. Some software permits back-annotation from the layout to the schematic capture modules.

Avoid taking traces between the pins of ICs, although this is not always possible. Learn to set up and use the design rules and checkers which are built into most layout software.

w

Last edited by wakibaki; 18th October 2010 at 12:21 AM.
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Old 18th October 2010, 12:39 AM   #4
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thanks too much for your support guys. Any other tip will be welcomed
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Old 19th October 2010, 12:50 AM   #5
jimbo51 is offline jimbo51  Australia
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Excellent tutorial for free download here:

PCB Design & Layout Tutorial - Learn how to design a professional PCB!
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Old 20th October 2010, 01:07 PM   #6
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thanks

exist some resource where i can get defaul size and pin space of the default components?

i want something that say for example

cap 50v 10uf - diameter 5mm, Lead Spacing:2mm, Lead Diameter:0.5mm.

another question...
if i have for example the cap that i show before (50v 10uf) and datasheet say 0.5mm lead diameter, when i make the board, i need to use 0.5 hole and is better to make it a little bigger? (0.6mm for example).
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Old 20th October 2010, 01:33 PM   #7
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Try this one

DIY Audio Amplifier Blog: Making Gainclone PCB at Home.

DIY Audio Amplifier Blog: Make@home PCB drill.
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Old 26th October 2010, 12:47 PM   #8
marce is offline marce  United Kingdom
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PCB Via Current | PCB Trace Width | Differential Pair Calculator | PCB Impedance

one of the best toolkits.

If you go above 50V (SELV) then creepage and clearances come into play.

Look for IPC related stuff, ie IPC-7351 for surface mount footprints.

Hole sizes depend on whther your using plated or non-plated holes.
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