Along with that comment: your names are confusing to anyone who is not real familiar with the process (or maybe even just the db itself) so it's hard to offer any direction beyond maybe uncheck "Require Referential Integrity" on the join to shipping table. You can still have a relationship regardless.
Product Lookup suggests it's about the many products offered yet you say it's about orders. Product Build suggests it's about what sub items go into a product for sale/shipment but you say it's about orders too.
the order (Product Build Table)
the Order (Product Lookup Table)
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.