Hi Satish
Firstly you need to understand how Bom Explodes
Example : Assume you have Material X to manufacture X you required X1 X2,X3 .so now your Bom is 4 level .But you dont want to explode all 4 levels .to avoid this you combine x1,x2,x3 has Y by setting Phantoms assembly off . so now you are explodes in 2 level
If phantoms assembly is OFF (i.e 2 level ) you can go with selection of PDS directly by selecting PPDS
But if you want to explode each component in PDS(i.e 4level) then we will go for BOM
Only activation of integration model does not transfer PDS to APO .After activating PDS in APO yo need to go Initial transfer By using TCODE : Curto_create . you need to insure actvation model is active
and all the BOM and Routing are correctly mantained in material master in ECC
I hope this could help you in understanding
Regards
Virender