Kicad

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RogerClark
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Re: Kicad

Post by RogerClark » Thu Feb 23, 2017 9:33 am

@racemaniac

I see what you mean about not letting you route anything invalid

Its just the board I'm doing is quite complex and I didnt realise what was going on. Sometimes it let me route tracks and sometimes it didnt

Re: vias without holes

I'll see if I can convert the altium design reference files as they appear to have a PCB where some SMD pads are via'ed though to a middle layer on a 4 layer board, without a separate via

I'm not sure how that is physically / mechanically achieved

Here are screengrabs from a ref design

Red is the top layer , yellow is a mid layer
Attachments
pcb_mid_layer.jpg
pcb_mid_layer.jpg (61.81 KiB) Viewed 390 times
pcb_top.jpg
pcb_top.jpg (128.27 KiB) Viewed 390 times

racemaniac
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Re: Kicad

Post by racemaniac » Thu Feb 23, 2017 10:28 am

after some googling, i think what you want is a tented via under your pad (it'll still be a via, but on the surface it is a normal pad)
this page has a nice overview of the kinds of vias that exist: https://www.pcbuniverse.com/pcbu-tech-tips.php?a=5

now only to figure out how to do that in kicad ^^ (and also, if you use that, i don't think that any cheap boardhouse will make the board like that. that's a more expensive procedure than what you'll get from the cheap boardhouses).

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RogerClark
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Re: Kicad

Post by RogerClark » Thu Feb 23, 2017 10:50 am

racemaniac wrote:after some googling, i think what you want is a tented via under your pad (it'll still be a via, but on the surface it is a normal pad)
this page has a nice overview of the kinds of vias that exist: https://www.pcbuniverse.com/pcbu-tech-tips.php?a=5

now only to figure out how to do that in kicad ^^ (and also, if you use that, i don't think that any cheap boardhouse will make the board like that. that's a more expensive procedure than what you'll get from the cheap boardhouses).
Thanks

Sounds expensive.

I will see if I can just route the inner pads to under the MCU but I will need to find what the smallest via that the board house can handle.

Edit.

Via in pad, is what would be ideal.
I will see if kicad has a workaround for this.

Edit 2

possibly this
https://forum.kicad.info/t/how-to-add-v ... nt/3845/10

racemaniac
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Re: Kicad

Post by racemaniac » Thu Feb 23, 2017 1:05 pm

i've read some people advising against via's in pads, since the solder meant for the pad can go into the via, and can result in bad smd soldering. but haven't tried it myself (for that reason i put the vias a bit besides the pad on my board to avoid this from happening).

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RogerClark
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Re: Kicad

Post by RogerClark » Thu Feb 23, 2017 9:39 pm

I will need to find out from the company who will make the board which options are avaialble.

Via size looks to be the critical issue if I have to use vias under the IC. I think normally red block under the IC is VSS, so I will need to find out if thats critical, as its a BLE device and has 2.4GHz on one of the pins, which goes to the antenna

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RogerClark
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Re: Kicad

Post by RogerClark » Fri Feb 24, 2017 10:08 am

racemaniac wrote:i've read some people advising against via's in pads, since the solder meant for the pad can go into the via, and can result in bad smd soldering. but haven't tried it myself (for that reason i put the vias a bit besides the pad on my board to avoid this from happening).
I contacted the company in China who will manufacture the board and they said that they think that it would need to be a 4 layer board

I think they are saying they can do via in pad, but things get a bit lost in translation, and its actually OK because they told me that their smallest via is 0.2mm, which means I can stagger some via's under the MCU and track them to a middle layer

They quoted about 20c extra for blue pill size boards to use 4 layers, but pricing is a bit speculative at the moment.

But either way, they seem to think that 4 layers is advisable for this type of IC package, so I'm going to attempt to use 4 layers in KiCad

However I'm not sure which layers are the inner copper layers are called. From what I've read they were called "inner cu 1" and "inner cu 2" but I don't seem to how those options in PCBNew, so perhaps they have been renamed.

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RogerClark
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Re: Kicad

Post by RogerClark » Fri Feb 24, 2017 10:16 am

Figure out how to turn on 4 layers. in the Design rules -> Layers setup

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Squonk42
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Re: Kicad

Post by Squonk42 » Fri Feb 24, 2017 1:47 pm


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RogerClark
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Re: Kicad

Post by RogerClark » Fri Feb 24, 2017 8:16 pm

Squonk42 wrote:Regarding vias in pads, here is an interesting paper:
http://www.4pcb.com/TechTalk_Highly_Rel ... y_2013.pdf

EDIT: also this blog and video:
http://blog.screamingcircuits.com/2015/ ... d-how.html
https://www.youtube.com/watch?v=HqRVKgPSPkI

Thanks

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RogerClark
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Re: Kicad

Post by RogerClark » Sat Feb 25, 2017 12:21 am

I should probably start a new topic for this, but I just thought I'd post the 3D of the board (still lots of routing to do)

(Pin headers would really be on the bottom, but I'm not sure how to tell the 3D view to do that, and its not important in the board design)
nrf52840.jpg
nrf52840.jpg (84.2 KiB) Viewed 317 times
One thing I need to work out is how to calculate the track length of the antenna on the right. I think KiCad has some track length matching I've not figured out how to use it, or even just to measure the length of a track

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