6 Bill of Substances

The Bill Of Substances (BOS) is a way to manage compliance information-gathering with regard to the parts and materials used in the manufacturing process.

To understand the BOS and how it is ”derived” from the BOM in Agile PLM, let us first look at what a Bill Of Material is.

6.1 BOM Lists Parts that become Products

The Bill Of Material (BOM) is the list of all parts and subassemblies that are assembled into the manufactured product. The BOM is central in Agile PLM's Product Collaboration solution, and is fully documented in Product Collaboration User Guide.

This is a simple list of BOM levels from the top-level assembly down.

Levels of the BOM

First or top level: Top-Level Assembly (TLA), the ultimate product being manufactured
Second level: Assemblies and sub-assemblies
Third level: Items (parts and documents; these are manufactured at your company)
Fourth level: Manufacturer Parts (these are parts from companies on the Approved Manufacturer List, or AML)

Although we are introducing the Bill of Substances by reviewing the Bill of Materials, it is important to understand that the BOM and the BOS list different kinds of entities. Therefore, the "levels" in the BOM and the "levels" in the BOS do not correspond with each other: both lists are, however, organized as a hierarchy.

There is a relationship between the BOM and the BOS: anything on the first four levels of a BOM - any kind of part or assembly - can be the origin of a Bill Of Substances.

6.2 BOS Lists Substances contained in Parts that require Compliance

The Bill Of Substances is a hierarchical list of substances that are contained in the parts and assemblies that make up a BOM. This is a list of BOS hierarchical levels from any composition of a part or part group or subassembly or TLA:

Levels of the BOS

First or top level: the Composition of a part or assembly
Second level: Subpart
Third level: Homogeneous Material
Fourth level: Substance Group
Fifth level: Substance

You may recognize the 2nd-5th levels are the Substances classes. This order of this hierarchy is particularly important in compliance rollups, which are documented in Rolling Up Compliance Data. Note that the top level of a BOS is the Composition.

While the purpose of the BOM is to assemble parts into a sensible sequence so that the product works, the purpose of the BOS is to assemble data about substances contained in products so that the substances can be analyzed and evaluated and your company's products can be in compliance. An example follows.

6.3 Rationale for the BOS

Depending on the type of specification with which you need to be compliant, you will need more or less information from your suppliers. For example, the RoHS legislation wants parts to be compliant at the homogeneous material level. This means that you might require your component manufacturer to specify how much lead it contains per homogeneous material within the component.

Unfortunately the sub-units (subparts) of a component (say, the packaging around a chip) are not always homogeneous, but they may consist of a coated material. For the RoHS legislation, this means that such a subpart consists of two homogeneous materials, each of which must be compliant.

This creates a tree structure called the Bill of Substances. Suppliers need to provide information at each of the levels of the BOS.

Depending on the type of specification involved, levels in the above list may be omitted.

Figure 6-1 Schematics of Bill of Substances

6.4 Summary of BOS Structures

The rules relating to the type of substances that can be added to the Composition tab are:

A subpart can contain a material and a subpart at the same level. A subpart cannot contain all four types of substances at the same time.
A material can contain only substances and substance groups. A material cannot contain a subpart or a material.

Here are the valid structures of the Substances classes:

For Subparts:

Subpart > Substances AND/OR

Subpart > Substance Groups AND/OR

Subpart > Substance Groups >Substances

Subpart > Homogeneous Materials AND/OR

Subpart > Subpart AND/OR

Subpart > Subpart > Homogeneous Material

For Homogeneous Materials:

Homogeneous Material > Substances AND/OR

Homogeneous Material > Substance Groups AND/OR

Homogeneous Material > Substance Groups > Substances