How-ToFinance & Operations

How to Set Up and Use Assembly BOMs in Business Central

Learn how to create assembly BOMs in Business Central, configure assembly policies, and post assembly orders for both stock and order-based assembly.

Stein Sæstad
8 min read

Assembly BOMs define which components go into an assembled item. Unlike production BOMs, which are tied to a manufacturing routing and require production orders, assembly BOMs are lighter-weight and intended for kitting and simple assembly work. You can assemble items to stock in advance or build them directly against a sales order, with the assembly order created automatically when the sales line is saved.

Assembly BOMs vs Production BOMs

Both define components for a parent item, but they are used in different contexts.

Assembly BOMProduction BOM
Document typeAssembly OrderProduction Order
Routing supportNoYes
ComplexitySimple kittingMulti-stage manufacturing
Triggered by salesYes (Assemble-to-Order)No (demand-driven via planning)
Capacity planningNoYes

Use assembly BOMs for items where assembly is straightforward, does not require a work center, and can be described entirely in terms of components and quantities.

Creating an Assembly BOM

  1. Search for Items using Alt + Q and open the item that will be the assembled parent.
  2. On the Item Card, go to the General tab and verify the Replenishment System field is set to Assembly.
  3. Select Assembly > Assembly BOM from the action bar (or navigate to Bill of Materials depending on your layout).
  4. In the Assembly BOM page, select New Line for each component.
  5. For each component line, set:
    • Type, Item or Resource
    • No., the component item number or resource code
    • Description, filled automatically from the component record
    • Quantity per, how many units of this component are needed per one assembled item
    • Unit of Measure Code, defaults from the component
  6. Close the BOM. It is active immediately.

Assembly Policies

The Assembly Policy field on the Item Card controls how assembly orders are created.

Assemble-to-Stock

The assembled item is built in advance and held in inventory. Assembly orders are created manually or through planning.

Use when: The item is stocked, demand is predictable, and you want to have finished units on hand before orders arrive.

To create an assembly order manually:

  1. Search for Assembly Orders using Alt + Q.
  2. Select New.
  3. Set the Item No. to the assembled item.
  4. Set the Quantity to Assemble and the Due Date.
  5. The component lines populate automatically from the BOM.
  6. Post the order when assembly is complete (see posting steps below).

Assemble-to-Order

The assembly order is created automatically when a sales order line is added for the item. Assembly happens specifically to fulfil that sales order.

Use when: The item is not stocked, is customised per order, or lead time is short enough to build on demand.

When a sales order line is saved for an assemble-to-order item:

  • Business Central creates a linked assembly order automatically
  • The assembly order quantity matches the sales line quantity
  • You can view and modify the linked assembly order from the sales line using Line > Assemble-to-Order Lines or the Assembly-to-Order link in the fact box

To change the policy on an item:

  1. Open the Item Card.
  2. On the General tab, change the Assembly Policy field to Assemble-to-Stock or Assemble-to-Order.
  3. Save.

Modifying Components on a Specific Order

For assemble-to-order scenarios, you may need to adjust components on an individual assembly order, for example, a customer requests a different colour option.

  1. Open the linked assembly order (from the sales line or from Assembly Orders).
  2. On the component lines, change quantities, swap items, or add/remove lines as needed.
  3. Changes apply to this order only and do not affect the BOM.

Posting an Assembly Order

Posting consumes the components and adds the finished item to inventory.

  1. Open the Assembly Order.
  2. Verify the Quantity to Assemble and component lines.
  3. If you want to post a partial quantity, change Qty. to Assemble to a lower number.
  4. Select Post from the action bar.
  5. Confirm the posting.

Resulting Ledger Entries

Posting an assembly order creates the following entries:

  • Item Ledger Entries, Output: A positive entry for the assembled item (Entry Type: Assembly Output)
  • Item Ledger Entries, Consumption: Negative entries for each component consumed (Entry Type: Assembly Consumption)
  • Value Entries: Cost entries for both the output and the consumed components, based on each item’s costing method

For assemble-to-order items, posting the assembly order and shipping the sales order are linked, when you post the shipment on the sales order, Business Central automatically posts the assembly output at the same time.

To review the entries after posting:

  1. Search for Item Ledger Entries using Alt + Q.
  2. Filter by Order Type = Assembly and the relevant Order No.

Checking Component Availability

Before posting, check whether all components are available:

  1. Open the Assembly Order.
  2. Select Assemble > Check Availability from the action bar.
  3. Business Central shows any component shortfalls and the dates they are expected to be available.

If components are short, you can create purchase orders from the availability check or adjust the due date.

To set up the replenishment and stocking rules for your assembly components, see How to Set Up Reordering Policies and Planning in Business Central.