[kicad-users] Problem with TSSOP footprints

[Dave Instone [e-mail] [kicad-users]]

I'm running Kicad 4.0.6 Win32 version.

As the library didn't have that footprint I created one using the soic
wizard

The pin pitch is 0.65mm and the recommended PCB pad width is 0.45mm .
Fine, all looked well until I tried to connect to the pads. Clicking on
the pad highlighted the net but the trace wouldn't start. Starting from
the end point the trace refused to go anywhere near the pad it was if
there was a wall there. In default canvas mode the trace would go into
the pad but 'end' didn't end it!

Then I noticed that in the default mode the pads were fenced in by thin
red lines. Obviously some sort of clearance allowance but no mention of
it in the wizard. To cut short the history of the head scratching SMD
pads done by the wizard seem to have a rectangle drawn round them with
the width being about twice the width of the pad itself. Take a line
of pads, if the rectangles touch you can't get a trace in. Note that
from the pin data above the rectangle would come out at 0.9mm wide and
the spacing pin to pin is only 0.65!

I've temporarily got over it by reducing the width of the pad until I
could connect tracks. I also found if I ran track in with the narrow
pads and then swapped the footprint for one with the correct pad widths
the connection remained.

Any thoughts on how to resolve this?

Regards

Dave

[yann jautard [e-mail] [kicad-users]]

I did not used kicad since a while, but IIRC the red line around pads
and tracks is to show the clearence zone. The value for that is defined
somewhere in your design rules

I'm running Kicad 4.0.6 Win32 version.
As the library didn't have that footprint I created one using the soic
wizard
The pin pitch is 0.65mm and the recommended PCB pad width is 0.45mm .
Fine, all looked well until I tried to connect to the pads. Clicking on
the pad highlighted the net but the trace wouldn't start. Starting from
the end point the trace refused to go anywhere near the pad it was if
there was a wall there. In default canvas mode the trace would go into
the pad but 'end' didn't end it!
Then I noticed that in the default mode the pads were fenced in by thin
red lines. Obviously some sort of clearance allowance but no mention of
it in the wizard. To cut short the history of the head scratching SMD
pads done by the wizard seem to have a rectangle drawn round them with
the width being about twice the width of the pad itself. Take a line
of pads, if the rectangles touch you can't get a trace in. Note that
from the pin data above the rectangle would come out at 0.9mm wide and
the spacing pin to pin is only 0.65!
I've temporarily got over it by reducing the width of the pad until I
could connect tracks. I also found if I ran track in with the narrow
pads and then swapped the footprint for one with the correct pad widths
the connection remained.
Any thoughts on how to resolve this?
Regards
Dave

[Pedro Martin [e-mail] [kicad-users]]

Hi,

You should reduce the clearance, under Design Rules menu, not the size
of the pad.

Pedro.

Post by yann jautard ***@free.fr [kicad-users]
I did not used kicad since a while, but IIRC the red line around pads
and tracks is to show the clearence zone. The value for that is defined
somewhere in your design rules

I'm running Kicad 4.0.6 Win32 version.
As the library didn't have that footprint I created one using the soic
wizard
The pin pitch is 0.65mm and the recommended PCB pad width is 0.45mm .
Fine, all looked well until I tried to connect to the pads. Clicking on
the pad highlighted the net but the trace wouldn't start. Starting from
the end point the trace refused to go anywhere near the pad it was if
there was a wall there. In default canvas mode the trace would go into
the pad but 'end' didn't end it!
Then I noticed that in the default mode the pads were fenced in by thin
red lines. Obviously some sort of clearance allowance but no mention of
it in the wizard. To cut short the history of the head scratching SMD
pads done by the wizard seem to have a rectangle drawn round them with
the width being about twice the width of the pad itself. Take a line
of pads, if the rectangles touch you can't get a trace in. Note that
from the pin data above the rectangle would come out at 0.9mm wide and
the spacing pin to pin is only 0.65!
I've temporarily got over it by reducing the width of the pad until I
could connect tracks. I also found if I ran track in with the narrow
pads and then swapped the footprint for one with the correct pad widths
the connection remained.
Any thoughts on how to resolve this?
Regards
Dave

[Pedro Martin [e-mail] [kicad-users]]

There is also a local clearance related to each individual pin.
Check whether this clearance is zero.

The clearance can be set in 3 places: general, local to a footprint or
local to a pin.

If pin clearance is zero, the program takes the footprint clearance. If
footprint clearance is also zero, the general clearance is applied.

Pedro.

Post by Pedro Martin ***@yahoo.es [kicad-users]
Hi,
You should reduce the clearance, under Design Rules menu, not the size
of the pad.
Pedro.

Post by yann jautard ***@free.fr [kicad-users]
I did not used kicad since a while, but IIRC the red line around pads
and tracks is to show the clearence zone. The value for that is defined
somewhere in your design rules

I'm running Kicad 4.0.6 Win32 version.
As the library didn't have that footprint I created one using the soic
wizard
The pin pitch is 0.65mm and the recommended PCB pad width is 0.45mm .
Fine, all looked well until I tried to connect to the pads. Clicking on
the pad highlighted the net but the trace wouldn't start. Starting from
the end point the trace refused to go anywhere near the pad it was if
there was a wall there. In default canvas mode the trace would go into
the pad but 'end' didn't end it!
Then I noticed that in the default mode the pads were fenced in by thin
red lines. Obviously some sort of clearance allowance but no mention of
it in the wizard. To cut short the history of the head scratching SMD
pads done by the wizard seem to have a rectangle drawn round them with
the width being about twice the width of the pad itself. Take a line
of pads, if the rectangles touch you can't get a trace in. Note that
from the pin data above the rectangle would come out at 0.9mm wide and
the spacing pin to pin is only 0.65!
I've temporarily got over it by reducing the width of the pad until I
could connect tracks. I also found if I ran track in with the narrow
pads and then swapped the footprint for one with the correct pad widths
the connection remained.
Any thoughts on how to resolve this?
Regards
Dave