General Questions for Simple Wire-to-Plug PCB


I’m new to PCB designing and have only just begun to mess about with Kicad v7. My main project is a simple one:

I have a motherboard in an external enclosure for my 3D printer. There are about 40 connections that must be made from the motherboard to the printer (all low power; high power connections such as heating elements are separate). I want to neaten this up by creating a cable harness from the motherboard to a connector.

The female connector is made up of 40 (2x20 rows) pass-through soldering points. I have the footprint of the connector downloaded and imported into kicad. Heres where I began to experience some difficulty.

I imported the footprint and loaded it into the pcb editor. I then created 40 solder pads and routed the wires to each of the connectors pass-thru holes. With the rank-and-file pass-thrus some of the wires follow the same path. I figure at this point something is wrong, I’ve clearly missed a step.

In comes the schematic editor. I figured I could just place my connections here, soldering pads, imported footprint, and then apply those to the pcb editor. Unfortunately that doesnt seem to be the case.

Have I chosen the wrong software for my application? My project is extremely simple, just traces from pads to pass-thru holes.

Apologies for this bear of a question, I’m sure I’ve misunderstood some basics. My electronics skills arent particularly honed but I have taken a course of two in the past and enjoyed it. Never designed my own PCB.

Thanks for any insight! I’ll continue to do research in the meantime and update this post if I come to any sudden realizations.

The normal workflow is to place a symbol for the connector on the schematic, route wires to it, assign a suitable footprint, update the PCB, then the layout editor will allow you to draw tracks between pads that are to be connected.

No matter how simple the board may be, there are benefits to starting with a schematic.

You should be able to find a 40 pin connector symbol in the symbol libraries.

You might want to view or review the documentation at to get acquainted with the workflow.


@retiredfeline is correct. Unless the correct connection is REALLY a slam dunk, you will be surprised at how easy it is to make mistakes. The way to avoid this is to number the pins. Use the schematic (probably with netnames that you assign manually) to make sure that the correct wire goes to the correct pin. The software will mostly eliminate the chance for error.

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Try to show us what you have done.
If you spend some time looking around in forum you will get the right to upload files.

posting some pictures would help too. or you can post your design here and more than likely someone will help you update/clean it up for you.

Right, I’ll start with the schematic.

I think I’m having trouble with the symbol-footprint wording. Since I have the footprint from the manufacturer I figure I can use that as a symbol on the schematic. This is clearly incorrect as I cant find it in the symbol library.

What I’ve done (I’ll document every step, hopefully it’ll help a fellow newbie in the future!) is found a 40 pin connector in the symbol library (Conn_01x40_Pin). I then searched for the connectors that I’ll need for the wires coming from the motherboard (Conn_01x02_Pin, etc.). After labeling each of those, I traced the wires to their respective positions on the 40 pin connector symbol.

I now want to link each connector to the appropriate footprint. To do this, I created three custom footprints, each with one, two, and three solder pads.

For each connector I assigned it the respective footprint. I assume it would have been faster for me to import each connector, assign the footprint, then copy as many as needed. I’ll have to keep that in mind for the future.

From here I transfer the schematic to the PCB editor.

Initially I ran into an error which occurred due to labeling each pad as pad 1. After assigning the pads their correct number I reloaded the schematic from the pcb editor and got no errors! I instead got the following (after some movement):

Now I’m hype; this seems to be going in the correct direction!

Next I have to draw the connections. I’m interested in using multiple layers, how can I get the routing paths to use those extra layers? Can I do this automatically?

I’d like to optimize the connectors to be in certain areas e.g. the fan headers in one area, motors in another, etc. Grouped as they are creates a rats nest of paths. How can my grouping be accomplished? Do I have to go back to the schematic editor and re-arrange the pins?

Hopefully I’ve provided enough detail here. Thanks for everyone’s help! I finally had the breakthrough I was looking for, just need to fine tune!

Edit: I’ve found the freerouting plugin, going to give that a try and see how it goes.

Footprints and symbols are different things. The former is for the layout, the latter for the schematic. Symbols are abstract representations of the part and could be as simple as a rectangle with pins. But sometimes they indicate the function. For instance, op-ams and digital gates. Pins are often grouped by function, and not look anything like the package pinout.

If the spacing is one of the standard ones, you’ll probably find footprints for connectors with various nuimber of pads in the library, and not have to make your own. Even if you make your own, there is a footprint wizard for various regular arrays of pads.

You can set the number of layers in the PCB Editor > File > Board Setup. By default it starts with 2 copper layers, front and back. More layers cost more but prices are coming down for 4 layers.

Connectors are numbered in a standard way. So do not change the pad numbers. Rather, place the parts suitably on the board so that the routing is as natural as possible. There may be constraints on where you can place parts.

Also SMD pads are not the best for soldering wires. Having only one side makes it more likely to delaminate.

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As it stands the freerouting plugin did a fantastic job and managed all my connections with the two layers. My next step is to get the silkscreen to display the labels on the final product.

I’ve gone into each custom footprint that I made and changed the text to be on the F.silkscreen layer. How can I update the rest of the footprints in the pcb editor? I updated them manually but would like to update all automatically in the future.

After manually editing each one this is my new silkscreen layer.

In terms of functionality and design, would pass-thrus be easier to work with vs pads? The wires I’ll be connecting range from 20awg to 22awg. Is there a more ‘proper’ way to attach these to a board? Is it just user preference?

Thanks again for the help, I’ve taken it all into consideration and will apply it in my next project!

One thing I would advise is to learn to use the Net Inspector to highlight wires and tracks on the schematic and layout. Make sure every pin goes to the pad intended, and that you haven’t made any schoolboy mistakes like looking at the connector from the wrong side when placing the footprint.

I don’t know where do you plan to connect that wires. To the holes in this socked like looking footprint or to these SMD pads on the right?
If to these SMD pads then it is generally wrong idea to solder wires to such pads. They will break away.
I see names like ‘motor’, ‘fan’. Do your tracks are wide enough for currents that you have. 20AWG wire has much more cross-section than your tracks. Do you know that copper at PCB has typically only 0.035mm thickness.


I should have clarified: the through holes on the left are for a connector, I downloaded the footprint from the manufacturer. The female connector is going to be soldered into those through holes as its board-mounted only.

I was planning to solder the wires directly onto the SMD pads. The motherboard and connector will both be embedded into a case, movement would be minimal. Regardless I’m sure power cycles over time would weaken solder and cause connection issues. I will always go with better-safe-than-sorry. With the breakaway possibility, I assume it’d be best to switch to a through-hole design with strain relief?

I didn’t even think of this (yikes). The fans are relatively low power:

Noctua NFa12x20 @ 0.6W
Winsinn 5015 @ 2.4W

Based on nothing: I feel that almost the default trace would be adequate to carry those kinds of powers. That being said, the noctua may be swapped for a more power hungry fan in the future. I’m sure it wouldnt hurt to ‘future proof’ my design a bit.

As for the stepper motors, they do consume a bit more. On average around 5-10W. I’ve just emailed the printer company to see if they can give me a more precise number, as the motors themselves are unbranded. Searching around for this printer has also brought up little, the company (AnyCubic) is semi new in the space, and their Kobra Go printer moreso.

Unfortunately my electronics course was a few years ago so I’m a bit lost on how to calculate the appropriate trace thickness. Hopefully some google searching can educate me on this. If you have a good way to do this please let me know!

There are calculator tools built into KiCAD :wink: have a play . . .


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Ah of course my object blindness strikes again! Thanks haha

For my own tracking I’m currently applying 0.550A to all motors save for the extruder which is drawing 0.750A.

Edit: I cant believe Kicad is freeware. I will definitely be making a donation after this project is completed.

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