In this video, you will see how the assembly BOM in Business Central works – from setting up the BOM on an item card to linking assembly orders to sales.
An assembly BOM is the recipe for a product bundle. It tells Business Central which parts go into a finished item you sell. If your business sells kits or packages, you need to know how the assembly BOM works. Of course, this guide covers setup, sales order options, and nested BOM structures.
What Is an Assembly BOM?
A Bill of Materials defines the parts that make up a finished product. Think of it as a recipe. You list every item and resource needed, and then Business Central uses that list to drive fulfillment. Some people call this kitting – putting parts into a pack and selling it as one unit.
Two types of BOMs exist in Business Central: Assembly BOMs and Production BOMs. Production BOMs belong to the manufacturing module. They handle routings, costing, and subcontracting. Assembly BOMs, however, are simpler. They gather parts into a finished item for sale, without the full manufacturing engine.
An assembly BOM can include two types of lines:
- Items – physical parts pulled from stock, such as tables or chairs
- Resources – labor or services needed to finish the build, for example an install resource
So in short, an assembly BOM is a flexible list. You can mix items and resources freely to match how your team builds and sells.
Items Inside Items: Nested BOMs
A part on an assembly BOM can itself be a BOM. Consequently, this creates a multi-level structure. Some people call this a phantom BOM – a box inside a box. One item number stands for a group of other item numbers, each of which may also be a group.
Business Central also supports up to 50 levels. In practice, however, most businesses use two or three. Beyond that, it gets hard to manage. The good news is that you can build these structures entirely within the assembly BOM framework. So there is no need to switch to the manufacturing module.
Setting Up an Assembly BOM on the Item Card
To check if an item has an assembly BOM, open the Item List in Business Central. The list has an Assembly BOM column and a Production BOM column. These are separate fields, so check the right one.
Open an item where Assembly BOM shows Yes. Next, go to Related, choose Assembly, and pick Assembly BOM. This opens the BOM lines. Each line shows the part number, name, quantity, and unit of measure. You can add or remove lines right here as your product changes over time. Also, each line can point to a resource, not just an item.
The Show BOM button at the top gives you a single view of the item and all its parts. For items with nested BOMs, you can expand each level to see every part in the full recipe.
Replenishment Policy: Assemble to Stock vs. Assemble to Order
On the item card, go to the Replenishment section. First, set Replenishment System to Assembly. Then set the Assembly Policy field. This field controls how Business Central handles demand for this item:
- Assemble to Stock – the planning system includes this item in replenishment runs. Reorder points and min quantities apply. The team builds the bundle before orders arrive.
- Assemble to Order – the planning system skips this item. Instead, an assembly order is created only when a customer orders it. This works well when parts are shared across many bundles.
In short, Assemble to Stock suits fast-moving bundles. Assemble to Order, however, suits custom or low-volume kits where pre-building stock does not make sense.
Using Assembly BOMs on Sales Orders
When you add an assembly BOM item to a sales order line, Business Central acts based on the assembly policy. However, the exact behavior depends on which policy you have set. There are two main options to know.
Explode BOM on the Sales Order
The Explode BOM function breaks the bundle line into its component lines. Select the bundle line, go to Functions, then choose Explode BOM. Business Central then swaps the bundle line for individual lines – one per part and resource from the BOM.
After that, you are selling each part on its own. Also, the original bundle line turns into a comment. For example, this is useful when you want to price parts one by one. It also works well when the customer needs to see exactly what they are getting on the order.
Quantity to Assemble to Order
If the item is set to Assemble to Stock but you need to start a build right now, enter a number in the Quantity to Assemble to Order field on the sales line. Business Central then creates a linked assembly order right away.
This is a handy manual override. The planning cycle does not need to run first. If the item is already set to Assemble to Order, however, Business Central creates the assembly order for you as soon as you add the line.
The Assembly Order
An assembly order is the work order for the team. Specifically, it shows the finished item, the quantity, and all the parts from the BOM. When it is linked to a sales order, both documents show that link clearly.
The team gathers the parts and does the work. Then, when they are done, posting the order creates two types of entries:
- Negative adjustments for each part used
- One positive adjustment for the finished item
After that, the finished item is ready to ship from the sales order. Therefore, the whole process – from order creation to shipment – is linked and traceable at every step.
Visualizing Multi-Level Assembly BOMs
When parts on an assembly BOM are also BOMs, the structure grows quickly. However, Business Central has a tree view to help you see everything at once.
First, go to the item card. Then open Assembly, pick Assembly BOM, and click Show BOM at the top. The tree opens with the finished item at the top. If a part has its own BOM, you can expand that line to reveal its sub-parts. In addition, click Expand All to open every level at once. This shows every part and resource that goes into the final product, across all levels.
This view is most useful during product design. In practice, you want to confirm the recipe is correct before you start selling or assembling.
Wrapping Up: Why Assembly BOM Mastery Pays Off
Understanding the assembly BOM in Business Central gives you full control over parts and fulfillment. Whether you choose Assemble to Stock, Assemble to Order, or use Explode BOM to sell parts one by one, the process is clear and traceable from order to shipment.
In addition, nested BOMs let you model complex product structures without leaving the assembly framework. Start with a solid recipe on the item card, pick the right assembly policy, and Business Central does the rest.
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