Problem connecting Power Pads to GND polygon

Travis:

Thank you, you put me on the trail to understanding

the problem. All parts are built with PowerPad Direction

PWR, connected to Pin named PAD, and that Pin is grounded

in the schematic.

An example of a package that will not automatically connect

is a QFN-48, Texas Instruments footprint RGZ, for TLV320AIC33.

In this case, the edge of the power pad is within 18 mils of

peripheral SMTs, and with isolate set to 8 mils, there is

just not enough room for the polygon to get in between

the edge SMTs and the PowerPad, so no connection is made, even

though all are named GND.

The Polygon apparently needs more than double the isolate

number to get in between the edge and center pads.  Or perhaps

there is another setting somewhere I need to adjust.

The only way I have found to get the PowerPad to connect to

the peripheral ground SMTs is to turn off thermals for the

PowerPad.

If, as an exercise, I make the PowerPad smaller, the polygon will

connect to the PowerPad, so it is not the construction of

the part in the library as I first suspected.

This is an example of the tuning necessary for Eagle, where

the Isolate hierarchy, the Wire width of the Polygon, some

unexplained rules as to how Polygons work all interact, that

is not clearly explained anywhere that I have found.

Thank you,

--- Graham

==

Travis G wrote:

On 10/11/2009 10:49 PM, Graham wrote:

I am designing a board that includes several kinds of ICs

with "Power Pads" under the IC package that need

to be grounded. For some of the ICs, the GND polygon

connects to the Power Pad as it should. For other

ICs, the GND polygon is not connecting to the Power Pad.

Examining the devices in the library, they appear to be

constructed and labeled the same way. I can't see

a difference in labeling, pin declaration, or grounding

between the ones that connect to ground and the ones

that don't.

 

Can you suggest what might be different between the

ICs or the libraries to cause this?

 

Thank you,

--- Graham

 

==

My first thought is, do the gnd pads of the package have air-wires in

the PCB editor? If so, check the Isolate property for the polygon to get

them to connect.

 

If there are no air-wires, I'd suggest checking the Direction and Name

properties of the symbol's pin. Make sure Direction = Pwr, and that Name

= GND. That usually does it for me...

 

Travis

Travis:

Thank you, you put me on the trail to understanding

the problem. All parts are built with PowerPad Direction

PWR, connected to Pin named PAD, and that Pin is grounded

in the schematic.

An example of a package that will not automatically connect

is a QFN-48, Texas Instruments footprint RGZ, for TLV320AIC33.

In this case, the edge of the power pad is within 18 mils of

peripheral SMTs, and with isolate set to 8 mils, there is

just not enough room for the polygon to get in between

the edge SMTs and the PowerPad, so no connection is made, even

though all are named GND.

The Polygon apparently needs more than double the isolate

number to get in between the edge and center pads.  Or perhaps

there is another setting somewhere I need to adjust.

The only way I have found to get the PowerPad to connect to

the peripheral ground SMTs is to turn off thermals for the

PowerPad.

If, as an exercise, I make the PowerPad smaller, the polygon will

connect to the PowerPad, so it is not the construction of

the part in the library as I first suspected.

This is an example of the tuning necessary for Eagle, where

the Isolate hierarchy, the Wire width of the Polygon, some

unexplained rules as to how Polygons work all interact, that

is not clearly explained anywhere that I have found.

Thank you,

--- Graham

==

Travis G wrote:

On 10/11/2009 10:49 PM, Graham wrote:

I am designing a board that includes several kinds of ICs

with "Power Pads" under the IC package that need

to be grounded. For some of the ICs, the GND polygon

connects to the Power Pad as it should. For other

ICs, the GND polygon is not connecting to the Power Pad.

Examining the devices in the library, they appear to be

constructed and labeled the same way. I can't see

a difference in labeling, pin declaration, or grounding

between the ones that connect to ground and the ones

that don't.

 

Can you suggest what might be different between the

ICs or the libraries to cause this?

 

Thank you,

--- Graham

 

==

My first thought is, do the gnd pads of the package have air-wires in

the PCB editor? If so, check the Isolate property for the polygon to get

them to connect.

 

If there are no air-wires, I'd suggest checking the Direction and Name

properties of the symbol's pin. Make sure Direction = Pwr, and that Name

= GND. That usually does it for me...

 

Travis