What Exactly Needs to be Included on Your Bill of Materials?

As with any PCB assembly facility, Bittele electronics requires a complete Bill of Materials (or BOM) in prior to the commencement of any assembly order. The BOM is an essential part of the assembly process, as it is basically equivalent to an electronic shopping list; it is on the BOM where we determine all the relevant information regarding the parts that are needed to be assembled on any given order. What items are required, how to obtain them, their price, quantity availability, as well as relevant assembly instructions are all examples of what a complete BOM should entail.

There are about 10 crucial parts that all BOMs must have. Providing all the required information helps to ensure that your account manager can easily and quickly have your BOM fully priced, and in turn, your quote finished in a timelier fashion. Missing information can lead to delays by the way of needing to communicate back and forth for the required information.

1 – Item Number

The first column of any BOM should simply be the BOM item number. Each unique part number should have a unique item number. The number of BOM lines will have a direct correlation to the assembly cost. It is wise to group parts with the same part numbers all together on single lines as this will help to reduce some of the assembly costs. It also affects the total BOM cost because of how price breaks work when buying in bulk online. For example, if line 4 has a certain part number, requiring 100 pieces, while line 7 has the same part number requiring 10 pieces, if left separated the total BOM price would have taken the price break for 100 pieces and added it to the price break of 10 pieces. Depending on the price breaks involved with that part number, you could end up paying more than double the price-per-unit for those extra 10 pieces, whereas if they had all been listed together under line 4 as a total quantity of 110, you would be paying for all 110 pieces at the lower price-per-unit break point.

In order to serve you better, Bittele always points out these BOM line situations to our clients to make them aware and may assist in taking the steps to reduce BOM lines by combining like part numbers.

2 – Reference Designator

The reference designator column is necessary for assembly. A reference designator must be present for every item the will be present on the board itself. Even items with the same part numbers, if they have more than one of that part number present on the board, they must all have unique reference designators (for example, Part number XXXXX has 3 total parts-per-board, labelled as C1, C2 and C3).

The reference designators on the BOM must match the reference designators given on your Gerber files.

3 – Description

This column is important to have as it gives us quick information about the part at a glance. It will also allow Bittele to cross check your description with the datasheet, to help eliminate any errors that were made when you generated the BOM.

4 – Quantity

This column indicates the total number of parts for any given BOM line that will be present on a single board. This number must always match the number of reference designators for that line (for example, if a line has a part number with three reference designators, C1, C2 and C3, then the total quantity for that line should be 3).

5 – Manufacturer

This column indicates the manufacture of the given part number on that specific BOM line. Some different manufacturers may have similar or partially matching part numbers, and this information allows us to select the correct manufacture with certainty.

6 – Manufacturer Part Number (Mfg. P/N)

This column is very important as it is where you will list the exact part number of the item you want to be placed on the board. It is highly recommended to always provide a part number, even for passive resistor or capacitor parts. In order to avoid all possibilities of the wrong parts being used, Bittele requires complete part numbers to eliminate any uncertainties. If a part number appears to be only partially complete, we will confirm the exact part number with you before production. Not providing a valid part number may lead to delays in finalizing your quote.

7 – Package

This column is not a firm requirement, however, it is very helpful for our account managers in completing your quote. Certain packages, such as BGA and QFN parts, incur additional charges, so having that information easily viewable helps us to be sure we account for every part concerning your order. Having this information ready helps to speed up the quoting process, and also provides another level of verification when cross-checked against the part number.

8 – Type

Like package, this column isn’t required, but it does help us to quickly calculate the total number of pads and through-holes present on your board. The assembly price is affected by these numbers, so being able to quickly identify part types also help to speed up the quoting process.

9 – Your Instructions

This column is where you can put down any special instructions regarding that BOM line item number. Instructions such as “Do Not Install” or “Consigned” are commonly used here. Also, instructions for buying parts but not placing them (hence shipping them back with the completed boards) can also be put in here.

10 – Alternate Part Numbers

This column can be very critical towards aiding the speed and full completion of your quote. Part stock is constantly changing every hour of every day, and while a part may be in stock at the time of you creating your BOM, there’s no guarantee that it will remain in stock by the time we complete your quote. Providing alternate part numbers for substitution in case of stock issues helps us to finish pricing your BOM without having to send emails back and forth for suggestions. By default, Bittele will always list suggested part substitutions for passive resistor and capacitor parts in the case of any stock issues.