40pin-6 board

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tooly
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Re: 40pin-6 board

Post by tooly »

hi,

on monday morning i will order some pcbs
and i will order 2 pieces of this pcb
first one for me and one for you fred

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Fred
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Re: 40pin-6 board

Post by Fred »

tooly wrote:is it possible to use a cj125 ic in future?
Yes, though afaik, it's not that great.

Triple decouple is now OK.

I look forward to playing with it :-)

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Re: 40pin-6 board

Post by tooly »

here are the first 2 pcbs Image
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Re: 40pin-6 board

Post by Fred »

Cool! :-)
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Re: 40pin-6 board

Post by Ned »

I havent actually read this thread, and i'm not at all very active here so i feel bad for commenting, but Fred linked me here so i think he wants me to.

Quick little background so i hopefully wont get flamed, i'm from NZ and have been doing embedded software for 6+ years now and also do some electronic engineering (schematic design, board design, populating etc etc) but thats not my main focus, software is but i've designed more boards than i care to count and got taught under very strict rules/guidelines

anyway, enough rambling, here is my critique (to be taken lightly as in general i'm impressed and the PCB looks good)

1) the main thing i would change, is the pad sizes on the TH connectors. There is plenty of room to make them bigger, which make them easier/better to solder and will provide more mechanical strength as well in automotive applications. Making them oval is always good to still be able to rout tracks between pins, but also having more room to solder etc.
2) silk screens are great. It's somewhat annoying to findwhat pad is for what component when you have a bunch of 0603s packed in a tight cluster. I understand not putting it on when making a couple boards to save money etc.
3) spending the extra to have boards that arent hot air leveled (like gold plating) is worth it when you have IC with a large number of pins, or small components. Hot air leveling leaves fairly uneven solder on the pads, and when placing components, they can easily slide off or not sit level when you go to solder/reflow the components. Not a big deal for some people, but it's easier and often worth the extra little bit of money IMHO
4) theres a few places where there is uneven track spacing. No big deal but like in the middle of the board, those 4 tracks is an easy example.
5) coming out of pads/vias on angles. Kinda like the via directly to the right of IAC1? pin on the bottom layer. and the track coming out of the bottom right pin of the xtal for example.
6) it looks like that bottom right xtal pin also has a track with a 90 degree bend? thats def a big no-no. And the 5V line from the BDM connector has a track that splits off it on a strange angle
7) tenting all vias is always a nice idea. Boards look so much nicer with tented vias and then its also harder to accidentally short stuff out when youre soldering and have a component close to a via etc.

a quick reasoning for not having strange angle tracks or tracks coming away from components on angles is that you never want a sharp corner on a track. One of the reasons (that i was taught and is probably not even a big deal but worth sticking with anyway) is that when they etch the board, etchant can pool in those areas for longer. It could then either over etch (from pooled etchant sting 'trapped' there) or even under etc (because it doesnt 'drain' well and doesnt get a lot of fresh etchant in that area)

I've done the same things as well on occasion BTW, im not trying to say you're way is wrong but fred asked for opinions, and i'm always happy to give them. Just like i always ask someone to look over my work and tell me what they dont like about it. A lot of the points i made have little/nothing to do with the quality of the board or design, just minor aesthetic changes.

again, i hope this doesnt offend, as i like the board in general and i hope some of the points were useful to anyone reading this. And i'm not perfect, and board design isnt what brings home the bacon for me normally, so dont take anything i say as absolute fact/law/whatever because i'm still learning myself
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Re: 40pin-6 board

Post by Fred »

Great post, Ned! I asked for opinions, but what I was thinking was "thoughts on using freeems on ms hw", however your comment was by far the most useful.

If tenting vias == covering them with solder mask, then I'd be against that on a dev version, and likely against it in general, as vias are very convenient places to stick a DMM and test shit.

I can't find your square corner, so good spotting! :-)

Cheers!

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Re: 40pin-6 board

Post by Ned »

Yeah, thats what tenting is.
Vias are great as test points or for hacking up a board when you've made a fuck up and need to re-route something, but you should have test points on things that you wanna test anyway :P
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Re: 40pin-6 board

Post by Fred »

I mean users, testing down the road to figure stuff out, or diagnose, or repair. This isn't a commercial manufacturing project, Dorothy :-)

You can't go putting test points on everything. It'd be half the board. Vias are there anyway and very useful. Hiding them is a mistake IMO. Chances of shorts on them are slim to none.
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Re: 40pin-6 board

Post by DeuceEFI »

Ned wrote:1) the main thing i would change, is the pad sizes on the TH connectors. There is plenty of room to make them bigger, which make them easier/better to solder and will provide more mechanical strength as well in automotive applications. Making them oval is always good to still be able to rout tracks between pins, but also having more room to solder etc.
Unfortunately bigger pad == more heat to solder the pins on the connectors. This leads to melted plastic on the connectors, not good.
Ned wrote: 2) silk screens are great. It's somewhat annoying to find what pad is for what component when you have a bunch of 0603s packed in a tight cluster. I understand not putting it on when making a couple boards to save money etc.
I agree, with the number of companies that can make a 2-sided PCB with free white silkscreen on both sides (see https://www.seeedstudio.com/depot/fusio ... ?cPath=185 as one example) for little money these days I always recommend having the component outlined and the schematic reference near the component as part of the silkscreen.
Ned wrote: 7) tenting all vias is always a nice idea. Boards look so much nicer with tented vias and then its also harder to accidentally short stuff out when youre soldering and have a component close to a via etc.
I'm with Fred on this one, for a development board this is unnecessary. While it looks good for a production board nobody is going to have to troubleshoot or can send in for repair this would be good, but this is DIY and the vias make excellent places to place probes or to solder jumper wires to when a routing mistake is found, see my various Jaguar threads for examples.

Just my $0.02
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Re: 40pin-6 board

Post by Fred »

DeuceEFI wrote:Unfortunately bigger pad == more heat to solder the pins on the connectors. This leads to melted plastic on the connectors, not good.
Only if you're doing it wrong :-) Seriously, though, you have to keep the heat on for a long time to melt plastic parts. A solder joint like those should be over in a flash if done right. Also only dirty cheap connectors have low-melting point plastic on strips like that.
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