Hi Thangam,
BOM is master data. Once created you can use the same BOM for all sales order provided there is no change required for the components. If you want BOM to be specific to sales order then use tcode CS61 enter the sales order number, item no, material number , usage as 5 and click on Copy Material BOM. Enter the material BOM number from which to be copied.
If production derived based on sales order, suggest to follow the below process:
Suggest to use strategy 20 for the FERT Material for which BOM is required. So when ever sales order is created RUN MRP against sales order in MD50. Convert planned to production orders. Now production orders and BOM in production order overview is specific to sales order. No need to maintain seperate BOM for different sales order when there is no change in Material BOM components.
Thanks & Regards,
Ramagiri