Howdy,

> 
>       1) Is there a standard or rule of thub that can be applied to the
>       seperation for a split plane ?
> 

I use a 50mil separation everywhere I can unless there are rails over +/-12.  If the 
difference in voltage of the split planes next to each other is over 25V I try to use 
a separation of 100mils.  This is an imperical method and may not be practical in all 
applications.

>
>       2) For plated pads and vias, is hole size in layout before or
> after
>       plating. ie if i set hole size to be 50mil, will it compensate for
> 
>       fact hole will be plated and compensate drill size so hole is
> 50mil
>       after plating?
> 

It can.  I specify "Finished Hole Size" in the drill chart on the fab drawing, and I 
have never had any problems from doing so.  If memory serves, the Copper Connection 
advises against against what I just wrote.  

>
>       3) Is there a standard or rule of thumb for dimensions of pad in
>       relation to hole size ? From most of the library components I
> looked
>       at, it seems hole is about 2/3 pad size.
> 

I use a pad 20mil over drill (10mil annular) for pins unless otherwise specified or 
impractical.

> 
>       4) Is there a standard via size/sizes ?
> 

I use an 11mil drill and a 25mil pad due to the board houses my customers use.  When I 
need to get a 5mil trace between the pads of a fine pitch BGA, I use a 24mil pad.

> 
>       5) For a given size diameter component lead is there a guidline
> for
>       hole size ?
> 

For round leads, I like to use 10mil hole over the lead size.

> 
>       6) for a component with square pins, .025mil (+- .005) mil on a
> side,
>       I was going to use pads of diameter 80, hole 52. This sound
>       reasonable.

For square leads, I like to use 5 over diagonal.  Pythagorean's theorum is a^2 + b^2 = 
c^2.

 |\
a| \
 |  \c
 |   \
 -----
   b

To find the diagonal of a right triangle, c = square root of (a^2 + b^2).

> 
>       7) For a thick track, say 30mil to 50mil, is it normal to use
> multple
>       small vias ?
> 

Absolutely.  I prefer to use multiple small vias rather than one large via for most 
designs.

> 
>       Any other pointers welcome.
> 
>       Any help greatly appreciated.
> 

To save my customer money in the fabrication of the board, I will combine hole sizes 
within 2mils of each other, except for press-fit or other critical applications.

The aspect ratio of drill hole to board thickness is a very important issue and can 
greatly affect the cost of the design.  A hole size that is ten times smaller than the 
thickness of the board may affect the cost of the board more than any benefits gained. 
 Try to stay at or under 8:1.

Cheers!
Drew


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