How to create library part with thermal pad?

Olin wrote on Thu, 31 March 2011 07:27

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.

euh, no. I am quite aware of how a PC board is made, be it single

double-sided, or multi-layered. I know what the solder mask does and what

delimitation it is supposed to have around the components. This is not my

first succesfully-manufactured board I've designed...

Funny enough,I asked a co-worker if he would refer to the Stop layer (he

doesn't use Eagle) as having "holes" in it, and he looked at me with

question marks in his eyes..

He then suggested that maybe the person who said that meant "openings"...

Then suddenly it all made sense.

You see, it isn't a question of my lack of knowledge, it is a question

using the correct word to describe the Stop layer. when I read holes I

thought to myself: round small openings. That's a hole. Not, "a perimetric

delimitation around an area", which opening would have suggested.

I was hoping not to have to defend myself in such a manner but it seems as

though people would rather assume that I lack knowledge.

anyway, another reader on another related topic has found a solution. I

shall go try that out now.

anyways, thanks for your replies, I hope I don't come off as too defensive.

--

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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.

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

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.

On Tue, 29 Mar 2011, Owen wrote to us saying :

>Actually I don't understand why you say it generates holes...

>I might need to read the help section on tStop, but I know that there were

>no holes generated in our boards on the tStop layer...

Try reading what he said:

>Things drawn in the tStop and bStop layers make

>holes in the top and bottom solder mask, respectively.

So there's no mention of holes in the board, nor of holes "generated in

the tStop layer". It's quite simple, so let's try fewer syllables:

The tStop and bStop layers define where the SOLDER MASK is NOT present.

That is, they define the HOLES in the SOLDER MASK. Please note that this

is the SOLDER MASK. It has ABSOLUTELY NOTHING to do with board holes or

copper traces.

If you want to keep a polygon (or the autorouter) away from somewhere,

you need the tRestrict layer. This is all explained in the help, so

perhaps you should read it.

--

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.               |

On 3/29/2011 3:10 PM, Owen wrote:

Actually I don't understand why you say it generates holes...

I might need to read the help section on tStop, but I know that there were

no holes generated in our boards on the tStop layer...

 

I looked in the pdf Manual and they donT' mention much detail about the t

and b Stop layers...

maybe you are confusing *Stop ( negative solder mask) with *Restrict (

negative copper in fills) ???

Actually I don't understand why you say it generates holes...

I might need to read the help section on tStop, but I know that there were

no holes generated in our boards on the tStop layer...

I looked in the pdf Manual and they donT' mention much detail about the t

and b Stop layers...

--

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

Redcutlass wrote on Tue, 29 March 2011 15:42

Actually that seems to be exactly the problem: Even if I place a pad,

the copper ploygon I place around it,

That makes no sense.  If you place another copper polygon completely over a

pad, of course you won't get thermals.  The pad itself will generate copper

gaps for the thermals, but your explicit polygon will put copper there

anyway.

Quote:

IsnT' that what the tStop (or bStop) layer does?

It's not clear what you think they are supposed to do.  The layers are well

documented in the help.  Things drawn in the tStop and bStop layers make

holes in the top and bottom solder mask, respectively.  I can't even guess

why you think this has anything to do with thermals.  You really need to

read the help for layers.

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Olin wrote on Tue, 29 March 2011 13:46

Redcutlass wrote on Tue, 29 March 2011 13:13

but in the component editor, it simply ignores my NAME request!

 

I think you mean the package editor?

 

That will result in the right copper, but the DRC will give you lots

of overlap errors.

Yes, sorry, I meant package editor.

Actually that seems to be exactly the problem: Even if I place a pad, the

copper ploygon I place around it, to mold to the shape I desire, does not

"connect" to the polygon. I wish I could explain it better... When I fill

my layout with ratsnest, it just goes all over the GND area, totally

ignoring the tStop layer I made for it. IsnT' that what the tStop (or

bStop) layer does? At least, that's how the SMD pads are treated...

thanks!

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Redcutlass wrote on Tue, 29 March 2011 13:13

but in the component editor, it simply ignores my NAME request!

I think you mean the package editor?

It would be nice if you could draw arbitrary stuff and have that be part of

a pad such that the DRC doesn't create a flood of errors.  However, you

can't.  Any time you want a connection point you have to start with a pad.

You can then add copper to it as you like.  That will result in the right

copper, but the DRC will give you lots of overlap errors.

--

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