Eagle - Double sided PCB - Vias on top but soldering on bottom

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#1

Hi there! I am new in Eagle software and its quite amazing. I've spent about 40 hours on the program and I am experiencing a major problem. I am making homemade double sided PCBs , but the problem is that I need the top layer just for vias. I don't want to solder anything from the top layer, except SMD Leds. How do i force Eagle to autoroute my board, with only routing vias on top? All the soldering should be from the bottom layer.

So all i want is to autoroute from eagle and having just vias and smds to be soldered on top and all the other components from bottom.

Please help!

#2

That doesn’t really have to do with the autorouter, it has to do with your component placement. If you put through-hole parts on the top side, you will solder them on the bottom. If you put SMD components on the top, you will solder them on the top.

My guess is you are trying to avoid vias in general because you are making a homemade PCB without through-hole plating. The question you are probably asking is how to avoid vias altogether, except at component pads, where you can use the component lead as a via by soldering top and bottom.

One way to do this is to draw a rectangle on the vRestrict layer that covers your entire board. Eagle will not place any vias in a board area that is covered by vRestrict objects.

–
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#3

I dont want to avoid any vias. The autorouter decides to route some pads from the top layer and some other pads from the bottom. I just need it to route them all from bottom. I want just to solder vias and then all the pads from bottom.

I think that what you are saying will help me... But i dont know how to make scripts (or whatever) in Eagle. I just know to design boards by mouse.

#4

If you could help me I would appreciate it...

#5

I'm not sure what you're trying to achieve. If you're not avoiding vias then you're OK with making "homemade vias" on a homemade PCB, which will require either rivets or inserting a wire into a via and soldering its top and bottom. If you're willing to do that, which does require soldering on the top, then I don't see why you wouldn't want to solder the tops of through-hole wire leads either.

Or maybe I'm just missing the point.

If you really just want to prevent routing away from pads on the top you can draw rectangles over each pad on the tRestrict layer.

No need to write scripts in Eagle. Just a bit of tedious work.

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#6

Thats nice.... Now I can see what some of the layers do... I am using vias by cutting wires and soldering them from top to bottom. Its impossible to solder relays, and things like it from the top. Vias are possible in homemade PCBs but they are still a bit long, so you can put devices on top of them.

Etc... If I need to make vias on the relay pads, then the relay pins wont be long enough so they can reach the bottom layer, because vias are homemade and they have about the double length of the PCB width. Hope I made it clear enough now...

Its the second time I am making a homemade PCB, and maybe i am using a stupid method for making a PCB. But vias work well for me. The PCB is impossible to be made in just a single layer.

#7

1)This thing doesn’t help me when the autorouter routes the pads to components.
The problem is that it routes them on top and they are difficult to reach with the soldering iron to solder them. Thats why I need them all in the bottom layer.
Now i am just talking about the routes that need to be soldered in pads that are underneath the component, like a relay, an ic socket, a trasformer, a large electrolytic capacitor, a set of pin headers etc.

2)The tRestrict layer excludes only vias?

  1. How can I found out some more things like layers and stuff about eagle?
#8

Have you used the [ | ] mirror command to have your components placed on the bottom layer? Maybe that is where you are having trouble.

Sparkfun.com has a set of tutorials on Eagle.

If you post your schematic & board here, we can see the problem more clearly to help.

#9

I managed to find out how to use the trestrict an dautoroute…

I now need another solution to a problem… In home made PCBs it is good to have the same spacing everywhere so it takes about the same time for the whole copper to be wiped out.
with t restrict there wont be any copper under the components and it takes too much time for whole areas of copper to be wiped out. I need to add a copper inside every component but with no ground or anything. Just to add copper so I guarantee I wont burn any routes when I’m etching the PCB.

example:
I need the black square under the relay, to be filled in with red but with no connection ro something. Just to avoid etching for more time.

eagle.png

#10

Use the Polygon and add it that way. Right hand column, 5th from the bottom, looks like a square with a piece missing.

Can also out a polygon on the whole board, name it GND, and use it a ground plane to make routing easier. Use on both sides.

#11

Look at the big pane on the left side of the autorouter dialog labelled "preferred direction". Click on "top" and select "N/A". This tells the autorouter to keep off the top layer.

-j

#12

The tRestrict was what I needed to know.

Now something else...How can I set the width of the space between routes? Or between route and Ground? For the autorouter...

#13

Under Tools:DRC, you can define the spacings that are used.

#14

Tools -> DRC tells the design rule checker what spacing to complain about.

On the autorouter main dialog, look at "grid spacing" to adjust the minimum distance between autorouted traces.

If by "ground" you mean ground plane, look at the properties (the "i" button on the top left) and adjust "spacing" and, IIRC, "isolate" parameters. Hit ratsnest to see changes.

-j

#15

I thought that the routing grid in autorouter settings is for the width of each route... I have it 0.127mm is it safe for AC & DC? small currents of course

#16

Is it safe to use the above route spacing settings or should I consider to increase it a bit more?

#17

That's like 0.033", very very thin. Change the grid view to inch, and make the traces at least 0.1".

0.127mm = 0.00127cm x 2.54"/cm = 0.0032"

Go with 0.16" or 0.2" for power traces.

#18

CrossRoads: Go with 0.16" or 0.2" for power traces.

CrossRoads, just laughed out loud... I use 0.15-0.16" for signal traces, and 0.24" minimum for power... One of my boards features a +5V ring around the perimeter that is about 0.5" wide... keeps losses low! Probably overkill.

#19

Actually I think I was off by a factor or 10. I design with 0.02" (20 mil) for power, and 0.01" (10mil) for signal traces.

#20

CrossRoads: Actually I think I was off by a factor or 10. I design with 0.02" (20 mil) for power, and 0.01" (10mil) for signal traces.

Whoops, me too. 15-16mil and 24 mil respectively, it is.