Your Odoo Implementation Consultant or an Odoo Partner can help you here since this is a technical process not yet supported by Odoo Studio.

1. Create a Server Action like this:

action = {
    "name": "Bills of Materials",
    "type": "ir.actions.act_window",
    "res_model": "mrp.bom",
    "view_mode": "tree",
}

Note: After saving this Server Action, take a note of the ID (which you can find in the URL).  In this case it was 1566 but on your database it will be different.

2. Create a View that overrides the standard Sales Order View and adds a button linking to the ID of the Server Action. 

Note: there are several Views with the name sale.order.form, just choose the first one in the list when you search for it.

You then get a button looking like this in the corner of the Sales Order...

... that lets Users click it (after filling at least the Customer) and see all Bills of Materials:

Note:  you need to be in Developer Mode to access the Server Action and Views Menus. This is possible to implement in both of our hosted deployments of Odoo - Online (Saas) and Odoo.sh (Private Cloud).