Phantom Bill of Material
Definition
A phantom bill of material defines a subassembly that exists in the product structure but is never stocked — it is built and immediately consumed in the parent, so MRP plans through it directly to its components.
In Practice
Phantoms represent transient states: a wiring harness assembled on the line and installed minutes later, or a kit grouping that exists only for engineering clarity. The phantom item carries zero lead time and a lot-for-lot policy; when MRP explodes the parent, it blows through the phantom and places requirements directly on the phantom's components, creating no planned orders or stock records for the phantom itself.
The structure keeps engineering truth without operational overhead — no work orders, no receipts, no put-aways for something that never sits in a bin. If some phantom stock does exist (from a canceled order, say), standard MRP logic nets it first before passing requirements through. Phantoms are also the standard mechanism behind sellable kits and flattened lean BOMs.
Frequently Asked Questions
When should a subassembly be a phantom?
When it is built and consumed in the same flow without ever being stored — line-side subassemblies, transient groupings, engineering-convenience levels. If the item is sometimes stocked, sold as a spare, or built ahead in batches, it needs to be a real planned item instead.
How does MRP treat a phantom BOM?
It plans through it: requirements for the parent pass directly to the phantom's components with zero lead-time offset, and no planned orders are created for the phantom. Any residual on-hand phantom stock is netted first, then the remainder flows to components — standard phantom netting logic in ERP systems.
Related Terms
A multilevel bill of material is the complete product structure showing every level of assembly — from the finished item through subassemblies down to purchased components and raw materials — with quantities linking each parent to its children.
KitA kit is a grouped set of components picked and issued together as one unit — either staged for a production order or sold as a bundled item — so everything needed for assembly or use arrives complete.
Planning Bill of MaterialA planning bill of material is an artificial BOM that groups items for forecasting rather than building — typically a product family parent whose components are options and common parts weighted by their expected percentage of total demand.
Manufacturing OrderA manufacturing order (production order or work order) is the authorization to produce a specific quantity of an item by a due date, carrying the bill of material and routing that define the components and operations required.