Electronics > Beginners
Getting a PCB right the first time
Bassman59:
Also, after you've gotten the footprints and pinouts all correct, you'll still screw up the mechanical part. Does it fit into the box? Are the mounting holes and connectors and such in the right place? Did the mechanical drawing of the enclosure front panel make any sense? Did you pay attention to the keepouts so that parts aren't butting up against the metalwork?
tszaboo:
It doesnt need to be perfect as first try. That's what the prototype is for. I always schedule a prototype into the project plan, no matter how much management is screaming because of it. In fact, you should make a huge bone-headed mistake that ensures that they dont send the prototype into production, so all the other small mistakes can be corrected. If you dont have one, they will send it into production, the first time they see an LED blink on a board.
djacobow:
--- Quote from: NANDBlog on July 12, 2019, 08:39:59 pm ---It doesnt need to be perfect as first try. That's what the prototype is for. I always schedule a prototype into the project plan, no matter how much management is screaming because of it. In fact, you should make a huge bone-headed mistake that ensures that they dont send the prototype into production, so all the other small mistakes can be corrected. If you dont have one, they will send it into production, the first time they see an LED blink on a board.
--- End quote ---
Yeah, I'm happy if my prototype can be *made* to work, or at least prove out the parts of the design that had "worried me." If that means some cut traces, added bodges, and parts flipped upside down, that's fine.
When I make a board and find lots of errors and things I want to fix to make the board better, more manufacturable, etc, it doesn't upset me too much. When my board has ONE such error, that actually ticks me off more. I guess that may or may not be logical, depending how how much time I spent on the board trying to get it "perfect". :-//
KL27x:
--- Quote ---the footprints are of the correct dimensions
--- End quote ---
Recommended footprint mechanical drawings are almost always included in the datasheet for a component.
--- Quote ---maybe its inverted/mirrored and that renders the pcb useless.
--- End quote ---
I don't think there's a cure for dyslexia. >:D
There are only a couple or regular gotcha's I can think of that are always on my checklist for Eagle, aside from obvious ERC and DRC's.
View the unrouted signals layer by itself (to make sure it's completely empty, of course) in case there are any almost-connected signals that leave tiny gaps.
Check clearances and soldermask to make sure vias are tented/untented as intended.
tautech:
All of the above plus a few little things gleaned from many SS home etched PCB's without overlays.
Component orientation markings.
Amend IC and active component footprints for the copper to show pin 1 or add an adjacent copper dot as a pin 1 signifier.
Same for polarized caps, make one pad square and/or add a + into the copper closeby.
Diodes often have a polarized footprint but adding a K in copper closeby never hurts.
Mark polarized headers, just a + and GND/Neg/- is plenty.
Unconnected copper = No Net.
Measurements
Double check scaling of prints and final artwork is correct, if you haven't got calipers......GET SOME !
Don't skimp on TH drill hole size, anyone that reworks your board will thank you.
Annular rings, make them as large as is practical and when clearance is a problem elongate them.
Watch for insufficient trace clearances when using elevated voltages....overlays and conformal coatings can help manage this.
Always consider rework when laying out a PCB so that some poor bugger doesn't have to remove 1/2 the components from the PCB to remove just the one they want. Particularly important for SMD PCB's !
Use medium or low density class passive footprints for anything that might be hand soldered or reworked.
Finally, does the PCB make sense in that are polarities to each and every polarized component are correct.
Oh, and DRC !
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