topic Re: Create a new board for Cree SMD LEDs in EAGLE Forum

Create a new board for Cree SMD LEDs

Anonymous — Sat, 28 Mar 2020 15:49:05 GMT

Dear community,

I'd like to create a board for some special Cree SMD LEDs. The board should consist of a metal core board, on which the layout board should bear on.

Now first of all, I have to create a library file for the LEDs, as there doesn't exist such a file for this kind of LED.

Here is my first question regarding the creation of the library file, particularly the footprint:

The solder pad for the LED should consist of three pads: cathode, anode, thermal (non-conducting) pad.

I managed to create both the cathode and the anode pad. However, I don't know how to efficiently create the middle thermal pad. As you can see in the first picture, it is in "Z-form". So I created 3 thermal pads in rectangle format and appended them in a very circumstantial way:

Therefore, I drew a symbol with 3 connections, as you can see in the second picture.

"C" for "Cathode", "A" for "Anode", and "TH" for Thermal. Then, while connecting both footprint and symbol, I was able to connect "TH" to TH1 and append TH2 and TH3 with it.

Coming to my question: is there a more efficient and less pedestrian way to create one coherent middle thermal pad in Z-form?

I'm looking forward to hearing from you, Thanks in advance for any help!

Kind regards,

Chris

Re: Create a new board for Cree SMD LEDs

jltharin — Mon, 30 Mar 2020 11:37:11 GMT

Hi @Anonymous

You can create only one pad (example smaller as TH1) and you use polygon to draw the Z shape all around....
You can connect the polygon to pad and it will make only one. (copper I mean)

BTW: you also need to create the soldermask, solderpast, etc layers polygon over the copper polygon...
They aren't create automatically as for the pad...

PS/Tips: Don't make the polygon with a too small thickness otherwise you GERBER files will take a long time to be generated.

I'm not 100% that it's less pedestrian way to create like this way but it works...

Good luck and have a nice day!
jltharin

Re: Create a new board for Cree SMD LEDs

Anonymous — Mon, 30 Mar 2020 11:45:55 GMT

Hey @jltharin,

Thanks for your reply!

How can I connect the pad with the polygon as you mentioled in your advice?

Kind regards,

Chestal

Re: Create a new board for Cree SMD LEDs

jltharin — Mon, 30 Mar 2020 11:53:31 GMT

Hi @Anonymous

It automatically connected if the pad is inside the polygon.

Good luck and have a nice day!
jltharin

Re: Create a new board for Cree SMD LEDs

jltharin — Mon, 30 Mar 2020 12:02:40 GMT

Hi @Anonymous

here an example of footprint with custom shape

Hope it can help...

Good luck and have a nice day!
jltharin

Re: Create a new board for Cree SMD LEDs

Anonymous — Mon, 30 Mar 2020 12:17:10 GMT

Hey @jltharin,

Thanks for your example!

However, I don't see, how you connected a small pad with the whole polygon. There is only one coherent upper and lower area.

So, following your advice, I put a small SMD pad and will then draw a polygon around it.

But how can I connect both?

Kind regards,

Chestal

Re: Create a new board for Cree SMD LEDs

jltharin — Mon, 30 Mar 2020 12:30:20 GMT

Hi @Anonymous

When you create a polygon around the pad (in a copper layer) it will be automatically connected.

See picture below:

I highlighted the pads and you can see the polygon around. As my pad is inside the polygon, the copper of polygon becomes automatically the custom pad... Don't need to do anything special!
When you will be in PCB editor, you will should route the signal to the middle of the pad (highlighted in picture)

Good luck and have a nice day!
jltharin

Re: Create a new board for Cree SMD LEDs

Anonymous — Tue, 31 Mar 2020 12:23:07 GMT

Thanks @jltharin jltharin for your help!

Kind regards,

Chestal