PCB Spacing requirements

[Moustache_Bash]

For chemical etching for DIY (like, doing at home not a board house), what would you guys recommend for the minimum trace width and minimum spacing between traces?

[eatyourguitar]

0.050 space between everything is a good choice. I used 0.032 here for my first etch and I almost did not get a working board. when I have 2 layer boards made in china 0.008 is all I need for min trace width and space between traces although I usually bump it up to 0.012 or more between traces with 0.024 or more trace width and 0.016 trace width if it goes between pads on the same part.

[Moustache_Bash]

I'm having problems using .05" spacing. I'm using KiCad (I don't know if you're familiar with that program at all), and in it you can set "Design Rules" for Clearance and Track Width. I've set those parameters to .05", and I can't lay down some tracks because the spacing of say a DIP-8 is .04". Do you think I should just make all connections going to DIPs, like .035?

[Mike]

I use 0.025" traces, and try to leave 0.025" spaces around everything I can. I try to lay everything out on a 0.1" grid. The lowest reliable etch I can get is 0.008" using dollar store photo paper, a Samsung printer, and HCl+H2O2.




I'm confused about what you are saying, though. A DIP-8 is not 0.04" in any dimension. The pins are 0.1" apart, and the rows are 0.3" apart.

I know you didn't ask, but... give ExpressPCB a shot. The learning curve is very small, and the software is very robust. Even if you want to switch to a more advanced program later on, I think ExpressPCB is a great starting point. The drawback is that they want you to order boards from them. You either have to print straight onto your transfer medium, or, if you need to manipulate the layout, print your design into a PDF, and then manipulate that PDF in the image program of your choice.

Mike

[eatyourguitar]

I think express PCB is really easy to use but really expensive to use to get PCB's made. the service costs $130 for something that costs $10 somewhere else. thats why the software is **FREE**. I investigated all the ways to actually get any gerber files out of it and while it is possible, it is really really not worth it for the extra effort. eagle was not that hard. I learned by watching videos. now I can make anything I want within 160mm x 100mm %100 for free. good for 2-layer gerber files and also good for making PDF's or etching 1-layer boards. I can export to PDF at 1000 dpi and print at a copy center at 1000 dpi. that should help with the detail if I can get the rest of the etching stuff tweaked a little better.

[Moustache_Bash]

I use 0.025" traces, and try to leave 0.025" spaces around everything I can. I try to lay everything out on a 0.1" grid. The lowest reliable etch I can get is 0.008" using dollar store photo paper, a Samsung printer, and HCl+H2O2.

I'll have to experiment and see what my printer is capable of.

I'm confused about what you are saying, though. A DIP-8 is not 0.04" in any dimension. The pins are 0.1" apart, and the rows are 0.3" apart.

I was just using TI's datasheet of an LM386 as reference.

I know you didn't ask, but... give ExpressPCB a shot. The learning curve is very small, and the software is very robust. Even if you want to switch to a more advanced program later on, I think ExpressPCB is a great starting point. The drawback is that they want you to order boards from them. You either have to print straight onto your transfer medium, or, if you need to manipulate the layout, print your design into a PDF, and then manipulate that PDF in the image program of your choice.

Mike

I'll look into it.

Thanks for your help, guys.

[Mike]

OK, I got it now. You only really need to be concerned with the pin spacing-- the distance between the center of one pin and the center of the next. For DIP, it is 0.1".

The 0.040" that you see there is actually the space between pins for the portion of the IC that is above the board. That is not the measurement you need.

Look at the drawing below what you outlined in red. The actual part of the pins that goes through the board is much narrower than the part that sits above the board. The drawing lists it as 0.018±0.003. That would put the actual space between the pins somewhere around 0.082".

Mike

[eatyourguitar]

OK, I got it now. You only really need to be concerned with the pin spacing-- the distance between the center of one pin and the center of the next. For DIP, it is 0.1".

The 0.040" that you see there is actually the space between pins for the portion of the IC that is above the board. That is not the measurement you need.

Look at the drawing below what you outlined in red. The actual part of the pins that goes through the board is much narrower than the part that sits above the board. The drawing lists it as 0.018±0.003. That would put the actual space between the pins somewhere around 0.082".

Mike

the drills for that are usually like 0.032 on most pcb's but I use 0.029 when I drill it in my basement and it still fits. therefor the widest spacing you could have with a hypothetical pad +0.000 is 0.1 - 0.032 = 0.068. the elongated pads work much better than the round pads if you are trying to get between the pins but I usually avoid it completely for 1-layer boards. on my 1-layer boards, the DIP8 has a 0.05 pad with a 0.05 trace running into it. this gives me exactly 0.05 empty space which is my preference and requirement. I can still run two traces under the DIP8 just not between pins.