How ToMake A Custom Pastemask Shape ?

What I am doing is creating a flash file with multiple voids or shapes with outside extents that are the same as the pad that you will be using it with. I make the drawing origin the of the flash file the same reference point as that of the copper pad (typically center). When the flash file is added with padstack editor they should be aligned. I hope this makes sense...  

For a single pad you can always just a custom shape to the padstack editor.  You need to create a drawing called a shape symbol and then make sure your path points to the ".ssm" file.

However, if you want to add multiple custom shapes to pastemask, just blank out the paste (null) in the padstack editor, then add a custom shape to the pastemask layer in the package geometry.

I can post an example if you have any issue with doing that.

Edit ->Z-Copy Shape, Select the "Copy to Class/subclass" and "Expand" value?

If i understand you right , this approach would work well on simple shapes , like rectangles and squares , but complex shape as shown in the image would be hard to do since one can not see the outlines of the thermal pad.

I think what you suggested there , i have done once for a QFN package. It worked fine because i could draw an outline of the square thermal pad of that QFN package and i could see where to place the paste mask segment.

I ended up doing what you suggested. i just created the thermal pad shape in PAD EDITOR and then added the paste mask  in PCB DESIGNER to the package drawing. I wasn't sure if that is the 100% kosher way to do things though. I am sorta newish to ORCAD and still figuring things out.