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How to create library part with thermal pad?

e14 Contributor

Hi there,

 

I was hoping someone could give me the recommended flow for creating a

library package with a thermal pad.  I'm using an LME49600TS/NOPBLME49600TS/NOPB which has 5

pins and a thermal pad.  The pad is electrically connected internally

to Vee.

 

I initially tried just marking a tStop region in the shape of the pad

hoping that if I just drew a polygon over it in the layout editor and

hit ratsnest, all would work out.  All I got was a polygon around the

pad not connected to it.

 

I then tried to draw a polygon in the package and name it something but

I discovered you can't name polygons.  A square pad would work I guess

but this isn't the shape of the pad which is in the shape of a 'T'.

 

Any pointers on the correct way of doing this?  The demo board doesn't

have the pad polygon connected to the Vee pin so that shouldn't be an

issue.

 

Thanks, Shareef.

 

 

Parents

  • Well Mr Pearce,

    as much as I thank you for your help, I must admit that I am not as

    knowledgeable using Eagle as you might have thought I was. That is why I

    didn't understand (and still don't) why there are supposed to be holes in

    the tStop layer, what they do, nor how come it is one of the only two

    layers that are generated automaticall for a SMD pad. there might be

    something (or more than one thing) that I don't understand, that's obvious,

    but if I did know, then I obviously wouldn't be posting on this forum, eh?

     

    So, no need to insinuate something by saying that I need less syllables in

    order to understand, or telling me to read the help file when I don't even

    know specifically what to look for... It is hard to know what to look for

    when you think you've looked at everything you could think of, and then

    there's the things one doesn't think of...

     

    In any case your explanation did help me out. I shall try this polygon

    perimeter-delimitation method with the tRestrict layer.

     

    sincerely,

     

    Redcutlass

    --

    Web access to CadSoft support forums at www.eaglecentral.ca.  Where the CadSoft EAGLE community meets.

     

Reply

  • Well Mr Pearce,

    as much as I thank you for your help, I must admit that I am not as

    knowledgeable using Eagle as you might have thought I was. That is why I

    didn't understand (and still don't) why there are supposed to be holes in

    the tStop layer, what they do, nor how come it is one of the only two

    layers that are generated automaticall for a SMD pad. there might be

    something (or more than one thing) that I don't understand, that's obvious,

    but if I did know, then I obviously wouldn't be posting on this forum, eh?

     

    So, no need to insinuate something by saying that I need less syllables in

    order to understand, or telling me to read the help file when I don't even

    know specifically what to look for... It is hard to know what to look for

    when you think you've looked at everything you could think of, and then

    there's the things one doesn't think of...

     

    In any case your explanation did help me out. I shall try this polygon

    perimeter-delimitation method with the tRestrict layer.

     

    sincerely,

     

    Redcutlass

    --

    Web access to CadSoft support forums at www.eaglecentral.ca.  Where the CadSoft EAGLE community meets.

     

Children
  • in reply to e14 Contributor

    On Wed, 30 Mar 2011, Owen wrote to us saying :

    >Well Mr Pearce,

    >as much as I thank you for your help, I must admit that I am not as

    >knowledgeable using Eagle as you might have thought I was.

     

    >So, no need to insinuate something by saying that I need less syllables in

    >order to understand

     

    I apologise for being snarky. However, please do not try to suggest that

    your inexperience with Eagle was under attack. I am actually very

    tolerant of "newbies". What set me off was that I was repeating Olin's

    earlier answer. I have less tolerance than I should of people who need

    to be told things twice. Sorry.

    --

    Rob Pearce                       http://www.bdt-home.demon.co.uk

     

    The contents of     | All power corrupts, but we need electricity.

    this message are    |

    purely my opinion.  |

    Don't believe a     |

    word.               |

     

  • in reply to e14 Contributor

    Redcutlass wrote on Wed, 30 March 2011 12:29

    That is why I didn't understand (and still don't) why there are

    supposed to be holes in the tStop layer, what they do, nor how come it is

    one of the only two layers that are generated automaticall for a SMD pad.

     

    It seems now the real problem is not as much your understanding of Eagle,

    but that you don't understand how PC boards work and how they are made.  If

    you did, it would be intuitive how some of the Eagle layers map to layers

    of a PCB.

     

    Briefly, a PCB can the thought of as a sandwich of layers.  For simple

    double sided boards from top to bottom these are the top silkscreen, top

    soldermask, top copper, the PCB material itself (usually FR4 fiberglass),

    bottom copper, and bottom soldermask.  You might also have a bottom

    silkscreen for a more complicated board.

     

    Go read up on PCB construction, then how the Eagle layers map to that will

    make sense.

    --

    Web access to CadSoft support forums at www.eaglecentral.ca.  Where the CadSoft EAGLE community meets.

     

  • in reply to e14 Contributor

    On 3/30/2011 12:29 PM, Owen wrote:

    Well Mr Pearce,

    as much as I thank you for your help, I must admit that I am not as

    knowledgeable using Eagle as you might have thought I was. That is why I

    didn't understand (and still don't) why there are supposed to be holes in

    the tStop layer, what they do, nor how come it is one of the only two

    layers that are generated automaticall for a SMD pad. there might be

    something (or more than one thing) that I don't understand, that's obvious,

    but if I did know, then I obviously wouldn't be posting on this forum, eh?

     

    So, no need to insinuate something by saying that I need less syllables in

    order to understand, or telling me to read the help file when I don't even

    know specifically what to look for... It is hard to know what to look for

    when you think you've looked at everything you could think of, and then

    there's the things one doesn't think of...

     

    In any case your explanation did help me out. I shall try this polygon

    perimeter-delimitation method with the tRestrict layer.

     

    sincerely,

     

    Redcutlass

     

    Hi Redcutlass,

     

    I'm sure Mr. Pearce didn't mean anything by it. To understand what the

    tStop and bStop layers do you need to look at a PCB. Whenever you have

    smd components, the pads of the components need to remain exposed once

    the board is manufactured, otherwise they'll get covered with

    soldermask(this is gives PCBs their classic green color) and you won't

    be able to solder parts to the board.

     

    The function of the tStop and bStop is to indicate what areas need to be

    void of soldermask so that the copper pad can show through. This is why

    features are automatically drawn on the tStop layer whenver you create

    an smd pad for your package. These voids are what Olin referred to as

    "holes", though I could see how that term could be confusing to a new user.

     

    If you want the autorouter to avoid a certain area then as already

    mentioned you would draw features in the appropriate restrict layer.

     

    hth,

    Jorge Garcia