Touch sensor: pad and airwires

On 02.08.2016 14:45, Marco Trapanese wrote:

Hello,

I'm designing a common touch sensor: a circular pad with a small hole at

the center to allow back-lighting from the bottom side.

 

I placed a square smd pad with roundness 100% to make it circular.

Then I placed a hole at the center.

 

I was expecting the DRC complaining about dimensions, but the weirdest

thing is there is always an airwire to the center.

Of course I connected the pad to the front-end in another point, because

the center will be cut.

 

I guess the dimensions layer surrounding the hole prevents EAGLE to

understand I've already connected that pad.

 

Is there a better way to do this or I must accept these drawbacks?

Thanks

Marco

Instead of hole, use a pad. If the device in lib editor have both the

pad and smd, make sure they are both merged to the same pin symbol.

Your hole may efficiently prevent the copper from reaching the center of

the smd pad.

On 02.08.2016 14:45, Marco Trapanese wrote:

Hello,

I'm designing a common touch sensor: a circular pad with a small hole at

the center to allow back-lighting from the bottom side.

 

I placed a square smd pad with roundness 100% to make it circular.

Then I placed a hole at the center.

 

I was expecting the DRC complaining about dimensions, but the weirdest

thing is there is always an airwire to the center.

Of course I connected the pad to the front-end in another point, because

the center will be cut.

 

I guess the dimensions layer surrounding the hole prevents EAGLE to

understand I've already connected that pad.

 

Is there a better way to do this or I must accept these drawbacks?

Thanks

Marco

Instead of hole, use a pad. If the device in lib editor have both the

pad and smd, make sure they are both merged to the same pin symbol.

Your hole may efficiently prevent the copper from reaching the center of

the smd pad.

Il 02/08/2016 15:20, Morten Leikvoll ha scritto:

Instead of hole, use a pad. If the device in lib editor have both the

pad and smd, make sure they are both merged to the same pin symbol.

Ok, I removed the hole, created the pad and appended both pad and smd to

the same pin symbol.

But it still shows the unconnected airwire:

http://oi65.tinypic.com/14nojr.jpg

anyway they ARE connected, as you see using the show command:

http://oi63.tinypic.com/33wmcck.jpg

instead it works (of course I'd say) if I route directly to the

"non-existing" center:

http://oi64.tinypic.com/2psiwde.jpg

I'm not sure if it's the best way.

The connection should be ok because the pad is connected to the smd and

to the track.

By the way, the pads always have plated hole, right? In my case I need

to reduce the smd size of the bottom led.

On 03.08.2016 07:49, Marco Trapanese wrote:

Il 02/08/2016 15:20, Morten Leikvoll ha scritto:

 

Instead of hole, use a pad. If the device in lib editor have both the

pad and smd, make sure they are both merged to the same pin symbol.

 

Ok, I removed the hole, created the pad and appended both pad and smd to

the same pin symbol.

 

But it still shows the unconnected airwire:

 

http://oi65.tinypic.com/14nojr.jpg

 

anyway they ARE connected, as you see using the show command:

 

http://oi63.tinypic.com/33wmcck.jpg

 

instead it works (of course I'd say) if I route directly to the

"non-existing" center:

 

http://oi64.tinypic.com/2psiwde.jpg

 

I'm not sure if it's the best way.

The connection should be ok because the pad is connected to the smd and

to the track.

 

By the way, the pads always have plated hole, right? In my case I need

to reduce the smd size of the bottom led.

 

 

I see you got another via inside the pad. That will probably not

connect, and cause DRC errors. I am not sure if that is ok or not. You'd

be better off only using the PAD in the device, and add the large circle

(wich is not a smd pad is it) to the board level as a polygon, and

rename it to the signal. Making a cicle with polygons is possible, but a

bit awkward. You may start with a square and use split to make it round,

one quadrant at a time.

Il 03/08/2016 09:08, Morten Leikvoll ha scritto:

I see you got another via inside the pad. That will probably not

connect, and cause DRC errors. I am not sure if that is ok or not. You'd

be better off only using the PAD in the device, and add the large circle

(wich is not a smd pad is it)

I'm not sure what you mean here. Yes, the large circle is an smd "pad".

to the board level as a polygon, and

rename it to the signal. Making a cicle with polygons is possible, but a

bit awkward. You may start with a square and use split to make it round,

one quadrant at a time.

Unfortunately is not acceptable because I want a complete device, with

different packages (i.e. different sizes and with or without the

backlight led) in my library.

Your solution will work, of course, but every time I need to place such

a component I must to manually redraw and reposition everything!

On 03.08.2016 15:48, Marco Trapanese wrote:

Il 03/08/2016 09:08, Morten Leikvoll ha scritto:

 

I see you got another via inside the pad. That will probably not

connect, and cause DRC errors. I am not sure if that is ok or not. You'd

be better off only using the PAD in the device, and add the large circle

(wich is not a smd pad is it)

 

I'm not sure what you mean here. Yes, the large circle is an smd "pad".

Well, maybe its ok like it is now, but you have a small via inside the

smd, wich is normally not allowed since its supposed to open the solder

mask (wich I guess you have disabled for this pad). This will create a

DRC but will also work if you justdraw a wire from the via to the touch

pad center and ignore the error.

Looking at your layout, you could probably improve it slightly and avoid

this extra via. Wire the upper led pad over the resistor(?) under the

via and put the resistor between the IC and LED. Then you got direct

access to the center from that resistor.