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What is a Phantom BOM?

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Phantom BOM Definition

A phantom BOM (or phantom bill of materials) is a specific type of subassembly specification utilized in product structures that is not stocked nor regarded as a distinct inventory item. Rather, its components are directly “blown through” (or detonated) into the parent assembly during production, as if the phantom level does not physically exist in inventory.

A phantom BOM operates in the following manner:

  • It facilitates the aggregation of components into a coherent subassembly, enhancing design clarity, reusability, and modular organization
  • In manufacturing planning (e.g., MRP, job estimation), the phantom is not regarded as an independent build item; rather, its subordinate components are immediately utilized in the parent’s production order.
  • Routing or processing steps can be established at the phantom level; however, these routings are integrated into the parent’s routing upon the phantom’s execution in production.
  • The phantom is generally non-stocked, indicating that inventory of that assembly is not maintained. Only its components are stored and utilized.
  • In many systems, it is possible to configure the utilization of phantom inventory; however, the default approach is to disregard it and consistently “explode through.”

Phantom BOMs facilitate planning and minimize additional transactions (e.g., distinct production orders for subassemblies), making them frequently employed to optimize operations for temporary or internal-only subassemblies.

Synonyms & Related Terms

Phantom Bills of Materials are occasionally referred to as:

  • Transient BOMs
  • Pseudo BOMs
  • Blow-through assemblies
  • Transient subassemblies

These synonyms suggest that the phantom is not intended to remain a permanent fixture, but rather as a structural convenience.

Top 5 BOM Management Mistakes

Read our best practice article to learn common BOM mistakes that might be costing your business and how to reduce BOM mistakes with the help of Cloud PLM.

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Why Phantom BOMs Matter (and When to Use Them)

The utilization of phantom BOMs presents many advantages and disadvantages, rendering them a valuable instrument in specific manufacturing and design scenarios.

Advantages

  • Decreased production orders/transactions – not considering the phantom as an independent build item eliminates additional production tasks
  • Streamlined inventory management – oversee the actual components, excluding intermediary assembly
  • Modular reuse of component groups – create reusable “logical groupings” of components that function as a phantom across several parent products
  • A streamlined design framework free from operational constraints – the phantom BOM provides conceptual organization in the BOM without imposing logistical constraints
  • Routing consolidation – The phantom’s routing functions can integrate with the primary routing, thereby simplifying scheduling.

Trade-offs/Considerations

  • Loss of visibility and context – the explosion of the phantom may obscure the logical association of specific components with a subassembly in the final production view
  • Costing and accounting precision – certain cost systems may categorize phantom costs differently; it is imperative to verify that cost rollups accurately account for phantom levels. The cost components of the phantom are typically incorporated into the parent.
  • Complex routing integration – If the phantom has its own routing activities, merging them into the parent’s routing requires careful oversight (operation sequencing, resource allocation) to ensure the accuracy of the final routing created
  • Inventory exceptions – sometimes it may be necessary to stock phantom inventory (or partially utilize phantom inventory). System setups must allow this.

Phantom BOMs are particularly advantageous when there is an intermediate grouping of components that are not required as distinct inventory items, or when the subassembly notion is rational for design clarity but impractical in reality.

Relationship to PLM, QMS, NPI & BOM Management

Phantom BOM & PLM / Quality / Change Control

In a PLM environment, phantom BOMs are an integral part of the product master definition. The phantom structure is preserved for clarity, version control, and design rationale. Upon the occurrence of changes via ECO/ECN, phantom definitions and their subordinate components are subject to version control. The propagation of changes must guarantee the validity of phantom logic, adherence to component lifecycles, and the accuracy of routing merges. Oversight of the quality management system may be necessary in regulated environments to guarantee that phantom transitions, removals, or alterations are properly documented and auditable.

How Do Phantom BOMs Simplify Product Design and NPI?

Phantom BOMs facilitate the maintenance of organized and manageable BOM structures during the new product introduction (NPI) process. You establish logical groups of components initially (as phantom subassemblies) without necessitating a commitment to distinct production phases or inventories for each subassembly. As the design evolves, these phantom groupings minimize BOM clutter while facilitating the reuse of component sets across variation configurations. In BOM management, phantom BOMs facilitate modular design while eliminating the burden of additional inventory and the intricacies of production planning.

How Are Phantom BOMs Flattened During Manufacturing Execution?

With the use of BOMs in manufacturing systems (ERP, MES), the phantom BOM logic is “flattened” during execution—components are separated, and the phantom is removed from operational processes. As a result, phantom BOMs function as an intermediary between the conceptual BOM structure and the execution-level BOM.

FAQs

Under what circumstances should I utilize a phantom BOM instead of a standard subassembly BOM?

Utilize a phantom BOM when the subassembly does not need to be inventoried or monitored separately, and it is more efficient to integrate its components into the parent manufacturing order. If the subassembly requires autonomous inventory management, cost regulation, or serviceability, a standard bill of materials (BOM) is more suitable.

Does a phantom bill of materials utilize the inventory of the phantom item itself?

Phantom BOMs do not, by default, deplete the inventory of the phantom item. The system bypasses the phantom and solely utilizes its subordinate components within the parent manufacturing order.

How are the routing activities of a phantom bill of materials managed in production?

When the production order is approximated, any routing actions set for the phantom are integrated into the parent’s routing. The operations are renumbered and appended to execute within the overarching parent manufacturing sequence.

Do phantom BOMs influence cost rollups?

Yes. In a cost rollup, phantom assemblies are typically regarded as standard assemblies for their cost contributions; the costs associated with the phantom (such as materials, labor, etc.) are incorporated into the parent item. The phantom’s burden, or overhead, is often set to zero to avoid distorting cost stacking.

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