Why Holes have stop layer traces ?

Georges Palauqui wrote:

Dear all,

 

I wonder why placing a hole in the Layout (manually or by a component

which have one (like some connectors)) make a trace in the Stop Layer

?

 

This stop layer is generally used by Gerber file to make the Solder

Mask, right ? So why do we need some solder paste inside the PCB hole

?

 

Georges

The stop layers are used to define the Stop Mask. Currently with Eagle it

automatically applies a solder mask over a regular hole so the solder stop

material is kept back from the hole edges. As the Solder stop material is

not very strong this prevents chipping / uplifting of the material around

the hole circumference. The precision with which the solder mask can be

placed comes into play a little as well and so this is the industry

practice.

That said, Eagle should now make that practice an option of each hole. This

mainly applies to packages but having the option in the board editor would

not hurt.  With the reducing scale of devices there is an immediate need to

be able to define a raw hole and not be committed to Eagle /DRC

defaults/automatic additions. This change must also include preventing  a

calculated polygon stand back from a hole (distance from shape in dimension

layer).  Recently the footprint for a MEMS microphone could not be correctly

created because of this limitation with holes.

The solder paste placement is defined from the Cream layers which are used

to form the Gerber file for the stencil. Hence, solder paste will not be

applied to the holes.

I hope this helps

Warren

--

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Dear Warren,

this is very detailled answer and I didn't catch everything (because english is not my native language), but I get my important information : Stencil Gerber file should be done using Cream Layer, not Stop Layer....

Thanks a lot,

Georges

On 02/18/2012 01:46 AM, Georges Palauqui wrote:

Dear Warren,

 

this is very detailled answer and I didn't catch everything (becasue

english is not my lative language), but I get my important

information : Stencil Gerber file should be done using Cream Layer,

not Stop Layer....

That is correct.  Stencils are produced from the Cream layers.

What may be confusing you is that the stop layers are photographic

negatives.  That is, stop mask will be everywhere except where traces

(and circles, and polygons, etc) appear in the on-screen image.  So if

you see a circle around a hole, that indicates where the solder mask

will NOT be applied.

Hope this helps.

    - Chuck