which is ubiquitous in our lives ,engineers also need a precise:”recipe”-this recipe is the”Bill of Materials,or BOM”
Today,let’s unveil the mystery of the mystery of the PCB BOM and see how this seemingly dry list becomes the”lifeline”of electronic product manufacturing.
1.What is printed circuit board assembly BOM List?
Bom(short for Bill of Materials) is a document in PCB design and manufacturing that details all the components,meterials,and quantities required to assemble a circuit board.
IF the PCB design drawing(Gerber file)is the “architectural blueprint”of the circuit board,defining the placement of components and electrical connections,then the BOM is the “procurement list”and “assembly guide”for that blueprint.
Without a Bill of Materials(BOM),even with the most perfect design,a factory cannot know what to buy or use to transform a blank circuit board into a powerful core component.
2.What information Does a BOM contain?
A professional PCB BOM is far more than just a list of part name.It’s typically a well-structures table containing the follwing core information:
（1）Item/Serial Number:A unique number assigned to each component for easy searching and tracking.
（2）Component Name/Description:A simple description of the component,such as”100uF 16V electrolytic capacitor”or STM32F103C8T6 microcontroller.
（3）Component Model/Part Number：This is the“most critical”information;it is the component unique “identity card”with the manufacture.For example,
GRM21BR61A226ME44L(Murata capacitor model). The model number must be absolutely accurate; even a slight difference can render the entire board unusable.
（4）Package:Describe the physical form and pad size of the component on the PCB, such as”0805″(Resistor/capacitor package)or QFP-48(Chip package).It ensures the component can be soldered precisely to the correct location.
（5）Component Designation: Corresponds one-to-one with the markings on the PCB design drawing such as “R1,R2,C5,U3″It tells the assembly worker’which part should be placed where.
（6）Quantity:The number of this component required per circuit board.This is the direct basis for calculating costs and procurement quantities.
（7）Supper/Manufacturer:Recommended or specified component sources.This helps ensure consistent quality and stable supply.
（8）Remark:Some special requirements,such as “specific brand only.””lead-free process requirement””alternative material information”etc.
In the design phase:It summarizes the engineers’selection,aiding in cost estimation and feasibility analysis .
In the procurement phase:The procurement department uses the BOM to request quotes from suppliers and place orders,ensuring the correct materials are purchased.
An incorrect BOM can lead to the purchase of a large number of faulty components,resulting in significant economic losses.
In the production phase:The production line uses the BOM to requisition and prepare material,and SMT Placement machines and operators perform precise assembly based on the Component identification information in the BOM.
In the testing and repair phase:Repair personal use the component identification numbers and model numbers in the BOM to quickly locate and replace faulty components.
In the product lifecycle management phase:When a component is discontinued (EOL),the BOM is used to quickly locate affected products and find alternative solutions.
In short,the accuracy of the BOM directly determines the success or failure of product manufacturing.”Garbage in ,garbage out”-if the BOM is wrong,the manufactured product will inevitably be wong as well.
Creating and maintaining a perfect BOM is no easy task.Common challenges include:
Incorrect or Incomplete information:Incorrect model numbers,mismatched reference numerals,incorrect package designs,etc,are the most common and fatal problems.
Component Discontinuation or Shortage:The electronic component market changes rapidly.A critical chip in the BOM may suddenly be discontinued,causing production interruptions .
Disorganized Alternative Material management:A component may have alternative materials from multiple suppliers.If this not clearly indicated in the BOM, it may lead to inconsistencies in materials used in different batches,affecting performance consistency.