Guidelines for making layouts of dual layer boards

[iceblu3710]

I have recently migrated from PTH to SMT technologies as my designs become more complex however I am have an horrible time trying to layout me components so that I can route the boards.

I imagine that layout is something that trial and error and practice makes perfect but are they any pointers for dual layer boards?

For example I have a small 2x3" board with 4-10pin, 1-12pin, 1-14pin soic chips, a 2-FPC connector, pinheaders, v-reg, and all the resistors and caps to go with it and on a 4 layer board layout is a breeze but on dual layer its tooth an nail.

I sent it to my friend to use his copy of the Spectra Autorouter on and its worked pretty well but both Eagle and Pulsonix leave airwires.

In general are their layout guidelines you guys follow or will it just eventually come with practice?

 

[6BaMe]

Re: Parts Layout

I have recently migrated from PTH to SMT technologies as my designs become more complex however I am have an horrible time trying to layout me components so that I can route the boards.

I imagine that layout is something that trial and error and practice makes perfect but are they any pointers for dual layer boards?

For example I have a small 2x3" board with 4-10pin, 1-12pin, 1-14pin soic chips, a 2-FPC connector, pinheaders, v-reg, and all the resistors and caps to go with it and on a 4 layer board layout is a breeze but on dual layer its tooth an nail.

I sent it to my friend to use his copy of the Spectra Autorouter on and its worked pretty well but both Eagle and Pulsonix leave airwires.

In general are their layout guidelines you guys follow or will it just eventually come with practice?

I never use Spectra to lay-out my board because it takes longer time to clean it up compare with manually routing.
If I was you, I will lay-out this board from fresh and it takes me about 10-15 minutes to finish your board without any problem.
So forget about short cut or looking for easiest way to do the job but go with the professional way instead.

 

[iceblu3710]

Re: Parts Layout

It takes you 10-15min to manually route a board... It takes me a whole day IF i'm lucky...

I only use the auto router when I am in a pinch and cannot do it by hand or its just a prototype and I do not care. I am trying to do everything by hand but this is a bloody art form and I just plain suck.

Do you use any layout conventions or rule of thumbs when you do your boards?

I usually create the pcb outline then place and lock my connectors where they need to be and then it takes 4 or 5 renditions of relocating parts until everything is routable.

I remember a windows alpha program from a while back that the traces followed the mouse and other traces and parts bumped and wiggled out of the way to maintain clearances. was like wiring in alphabet soup but looked promising.

 

[keith1200rs]

Parts Layout

I remember using a package a while ago that showed connection density which was handy when placing components to avoid bottlenecks. I almost never autoroute and unless you are really packing stuff in would not expect to pens more than a couple of hours on a small circuit like you describe.

My suggestions:

Don't fix things which don't need to be fixed. So, have the flexibility to move things right until the end. The same is true of the board outline - fix it at the end if you can.

Placement is the most important so try to place things so tracking is minimal.

Placement should follow through schematic flow, provided the schematic is drawn logically.

I often layout small groups and bring them together a bit at a time. So, I might layout an opamp with associated discretes first. Then the next, and then bring them together.

Try to decide on which side is for vertical and which side is for horizontal tracks, but often you have to ignore this most of the time.

Lay some decent width power and ground tracks early on.

Don't be afraid of ripping bits up or moving parts/tracks after you have routed them.

Keith