Short checklist compiled from these posts

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Short checklist compiled from these posts

Postby bamboosamurai » Wed Mar 21, 2012 10:39 am

I am starting my first PCB design that will be a little complicated for a first design, so I've read through these forums and made some notes and thought I would share it. Maybe noobs like my self could find this useful.



EagleCAD NOTES for xxx

* Decoupling capacitors needed as clost to 1284p as possible where ever Vcc & Grn pinnned out
* Smaller = quicker responce
* Pick the largest capacitance in the smallest package
* 1 10uF tantalum cap per major IC microcontroller
* 0.1uF and a 10nF cap at every power pin on every IC
* The 10nF caps need to be small, preferable 0402 or at most 0603 sized to avoid the lead inductance
from the package nullifying the effect of the capacitor.

* Traces should not connect at acute angles; "can form acid traps" (No less than 45 degrees)
* Route critical nets like supplies first, with wide tracks
* No 90 degree angles for professionalism
* "Mitre" 90 degree bends in tracks
* Traces should run straight into pads to avoid acid traps
*OK'ed examples:
* http://jila1.nickersonm.com/thermmeas_all_1.1.png
* http://desmond.imageshack.us/Himg705/sc ... res=medium

* Wide Vcc line
* Use more direct and wider (lower impedance) Vcc trace
* On a standard PCB allowing 10°C temperature rise, an external 16mil trace will carry ~1.2A
* Vcc trace should go to the cap first and then to the chip through a short wide trace
* Trace calculator: http://circuitcalculator.com/wordpress/ ... alculator/

* Ground
* Make to bottom copper pour ground and connect all to this pour.

* Diodes
* Normal diode for the batteries, which will match all the supplies when tied together at just below 5V

* Resistors
* Atmel recommends a 4k7 - 10k pullup resistor on ~RESET

* Crystals
* The caps for the crystal need to be right next to the crystal

* May need to tie the unused inputs either high or low
* The Arduino and other micros have multiple ground pins; I would tie them all to ground;

*Auto routing is not a good idea:
* Forget autorouting - manual route it, unless you have an outorouter that costs >10k

*Great Tutorial someone posted: http://www.alternatezone.com/electronic ... alRevA.pdf

*Dont know how true this is but: "With BatchPCB, they usually send twice as many boards as you order."

*On average:
Traces: 16mil (32mil for power)
Spacing:10mil
Minimum drill: 20mil (vias)
Primary grid: 10mil
Alt grid: 5mil

If it's a more complex, tight board you might want to use something like this

Traces: 10mil
Spacing: 10mil
Minimum drill: 15mil (IF you can)
Primary grid: 5mil
Alt: 2.5mil
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Re: Short checklist compiled from these posts

Postby bamboosamurai » Wed Mar 21, 2012 10:41 am

*at the top 1284p is just the micro I am using
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Re: Short checklist compiled from these posts

Postby langwadt » Thu Mar 22, 2012 11:33 am

I'd say don't bother with both 10nf and 100nf decoupling, 100nf alone will do just as good. and I'd use ceramics for the larger capacitor too, tantalum has a bad habit of catching fire at the slightest abuse.

If a part has multiple gnd pins (vcc too) they MUST be connected, the datasheet will normally say so too
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Re: Short checklist compiled from these posts

Postby Bryan Tong Minh » Wed Apr 04, 2012 1:04 pm

I've never exactly understood why 90 degrees angles are a bad idea. Can anybody explain this a bit?
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Re: Short checklist compiled from these posts

Postby macegr » Wed Apr 04, 2012 3:35 pm

Bryan Tong Minh wrote:I've never exactly understood why 90 degrees angles are a bad idea. Can anybody explain this a bit?


It's mainly just acid traps, really, unless you're designing a circuit over 30GHz. Vias are an example of an extreme right angle and they don't affect radiated emissions at the operating frequencies that hobbyists will use.

And really, acid traps are not actually a concern until you use very small traces. A normal trace won't trap enough etchant to react with enough copper to affect the circuit. Modern etch and rinse processes also make it much less likely of an occurrence.

So, this is why I still avoid 90 degree angles...it looks nicer, and usually results in a slightly shorter signal path. However I don't worry about it too much if I have to make a 90 degree angle.

There's one more reason to do it: it's such a common rule of thumb, that regardless of actual impact on the circuit, other engineers will think less of you for having lots of 90 degree traces. Use 45 degree traces so other, less informed engineers will think you know what you're doing :)
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