Firstly, Manufacturing > Variants > Create Assembly Drawing is used in conjunction with the Variant Editor used by Allegro Design Entry HDL (Variant Editor will generate the variants.dat file). Basically, it generates the appropriate assembly views in Allegro based on the population status defined in Variant Editor and that is all it does. (effectively deleting the outlines of unpopulated components and pushes the view to a different subclass)
You can create your PCB assembly drawings in Allegro and do not need to export it to an external CAD tool to generate them. The only real issue is that to generate a Bottom Assembly drawing you will need to create a plot file and load it back into Allegro mirrored so you can see the assembly text right reading. The main issue is the Bottom Assembly view can become out of date if you make placement changes and will have to regenerate the plot and load it back into Allegro mirrored.
By “create plot a plot file” I mean use File > Export > IPF that generates a Cadence intermediate plot file of what is displayed than it can be loaded back into Allegro at different a scale, different class/subclass or mirrored for assembly documentation. Using Manufacturing > Dimension/Draft > Create Detail can do the job as well but the Text Strings will get exploded in the resulting Assembly view which will make any resulting PDF not text searchable.
The purpose of the assembly drawings is to provide the assembly machine operator with enough information to check that the assembly rotation of each assembled component is correct and every component is on its correct position as specified by the customer. The file can be, for example, as.jpg or .pdf format.
The drawing should clearly indicate pin 1 position of each IC and the reference designator of each component. Other types of common polarity markings are positive terminal marking for tantalum capacitors and cathode marking for diodes.
The assembly drawing is typically made by exporting a image file of the silkscreen layer of the PCB (PADS Layout: File CAM…). The file should include the options that are shown in image 2.
Image 2. Assembly drawing document options in Pads Layout
Image 3. Example Assembly Drawing