Consider replacing them with 74HC or 74HCT or 74AHC or 74AHCT serie. You will get zero, zero, nothing current.
should the power, positive and negative be layed out first?
Not necessarily. Everyone develops their own technique. Here’s mine:
- Identify the “critical” tracks. These are usually high speed or analog tracks that need to be carefully routed and wont tolerate a lot of meandering. But for the same reasons they could be high current tracks, including power, if your board requires them.
- Plan your stack up. If it’s a 2 layer board, then generally you’ll make the top your signal layer because it’ll have most of the components. The bottom will then be your power layer, consisting mostly of a ground pour.
- Divide your board into power domains - where is everything that requires a 3V3 rail? An analog supply? A higher power 5V rail? Work very hard to make these domains neat by arranging the components.
- Once all the components are placed, and only when you’re sure they’re placed in a way that makes the most sense from a routing perspective, start by routing the critical tracks identified in step 1.
- Then route the less critical tracks.
- Finally, place the power pours - they should make up the remainder of the required connections - grounds often go straight from the IC, through a via into a big ground pour. Power rails find their best path to a power pour. Because you’ve taken the time to think through the power domains, everything will hook up like magic
In practice, knowing you’re at Step 4 requires having been to Step 6 a few times - ideally unsuccessfully. That’s when you really learn what getting to Step 4 looks like!
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This point regularly appears from time to time (especially when the topic of auto-routing comes up):
- Component placement is often more critical, and usually more difficult, than trace routing.
Like @Heath_Raftery said, in the course of laying out a board you will probably rip up traces several times as you shuffle components around to find an effective placement. As a corollary to his last comment, knowing when to drop back from Step 5 or Step 6, to Step 4 (and adjust component placement), is an ability you develop with practice.
(And, on my machine, it leaves behind a stack of files with names like “Big_Job_RevB_bak1.kicad_pcb”, “Big_Job_RevB_bak2.kicad_pcb”, etc, which document my wrong-turns and dead-ends. On rare occasions I revert to one of those prior attempts, but more often I open them up to refresh my memory of exactly what the problem was that brought me to the dead end, or to remind me of some snippet of placement and routing that seemed to work especially well.)
Dale
@ Heath_Raftery Good list. I do something similar. Basically:
- place the components so it is fairly easy to route.
- put vcc 30 mil traces on the top layer for all power connections. I run them around the edge of the board to keep the interior free for signals. do “drop-downs” as needed (T off the outside edge)
- run signal traces (10 mil) as needed. This is where the component placement really helps. Sometimes I need to go back to step 1 & 2
- I run the DRC until the only errors are unconnected GND
- bottom layer is for ground plane. I do the “add fill zones” with the B.Cu specified.
- before I do the DRC, I do the “remove filled zones”, fix what is needed, then run DRC. The DRC will automatically fill in the ground plane.
Note sometimes I need to re-route things because the fill zone is blocked from reaching a ground point/pin because traces forming a “dam”.
Also: I am not doing anything fancy - no high-speed, matched impedance, RF designs. YMMV
My PCBs uses AtXmega microcontrollers. I go with VCC through corner of TQFP64 or TQFP44 under it and connect to all its VCC pins from there. Then I go out through other corners to circuits surrounding µc. In rare occasions I can also go out through VCC pins existing at all sides. So I rather have VCC in star configuration. In most cases I have 100% connections at top (only GND at bottom). Flexibility to select pins to which I can connect signals helps a lot. For example if at A3U I need to connect to UART I can chose from 7 locations.
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