The importance of PCBA BOM to products

Now my company is mainly engaged in OEM, but I find that many domestic design companies are unable to establish a reasonable BOM table, which causes a lot of unnecessary trouble when it is transferred to production, so I write this article to let you understand the purpose and methods of the establishment of BOM, and the role it plays in a product life cycle.

Bill Of Material, BOM. As the name implies, the PCBA BOM of a product indicates how many parts are needed to assemble the product.According to BOM, we can only purchase materials and arrange the flow chart of production. The beginning of BOM should be marked with 1. Product model 2.Version number 3.Date of drawing up 4.file number 5.The total number of pages.Every product continues to optimize its design or expand its functionality throughout its life cycle.The version number is used to distinguish each version. Here I would like to emphasize that when a new version is determined, the old version must be marked as expired document sealed and stopped using.If you find that the new version is not as good as the old version, and you want to disable the new version and enable the old version, then identify an updated version number for the old version.For example for version A at the beginning, then upgrade to version B, later found version B is better than A, need to use A, so please send A defined version C, although the content of the A and C is the same, but if not defined as C and is still called A, then do A second design optimization version number could trigger chaos in the management of product PCBA BOM table release must be issued by the research and development department, at least by r&d engineers, research and development department is in charge of signed confirmation per level, in order to ensure the correctness of the PCBA BOM.The relationship between BOM and product can only be that multiple BOMs match with one product, but not one BOM match with multiple products, even if the two products are only different contents of a label.

pcb AOI inspection

Some readers may not understand the difference between the product model and the BOM version. Here I would like to emphasize that the product model is determined by the market demand, while BOM is determined by the product model.For example, a company develops a product to be called “001”, another company asks to help him make a sign too, decide this product as “B word 001”, although “a word 001” and “b word 001” are identical completely, the only difference is the trademark.Then, in production, a BOM table should be built for “a 001” and “b 001” respectively. If company a wants to optimize “a 001” and company b thinks “b 001” is very good and there is no need to change, the BOM version of “a 001” can be easily upgraded, while the BOM version of “b 001” does not need to be changed.If at the beginning, either a or b, are unified as “001” to produce, two products produced dozens of times, the production line will not know which you want to do “a word 001” or “b word 001”, as the difference is not big, the chance of error will increase, once two customers put forward different improvement demand is more chaotic increase.

I have a cell phone client do gave me three versions of the BOM, A is the original version but PCB design is a little small problems, and then go back to B, then one of their customer said they like pull antenna, just changed the original rod antenna to the pull rod and do the antenna matching, changed A few resistance inductance values out of A to C version.Finally they said in the contract to produce 31000 sets, XXX model product requirements according to the B version BOM 20000 sets , 10000 units according to the C version BOM do to finish in front of A version of the remaining 1000 sets (PCB scrap is a kind of waste, although there is small problems, because you couldn’t see abnormal quality in short-term usage process, so they could not bear to throw, it’s visible domestic enterprises still need to strengthen the quality concept).Because factory work according to type and quantity, if need to emphasize the version of BOM, so need another liaison, increased the operation complexity, and the difference between the antenna can only be visible after finishing assembly, if in SMT processing one operator did not see the liaison, in case semi-finished products warehouse dispatch wrong BOM version to the PCBA assembly line and in case assembly operators use version B as C version to do assembly, so it’s too late to regret and cry.So instead of highlighting the version number of the BOM in a single notification, it’s better to  add more models to distinguish them.Finally, they accepted my suggestion and defined the product model as XXX-A, XXX-B and XXX-C respectively. The above described the importance of BOM, the relationship between product model and BOM version.The following two items, “set date” and “total page number”, are also understood. “document number” will be known as long as the enterprise adopts ISO management system.

Now let me talk about content of BOM.

There are seven items. 1. Finished product number, 2. Order, 3. Material number, 4. Product name, specification, 5.Usage 6.DIP location 7.Craft.

Finished product, refers to a number of the end product, this is often associated with product model and version of the BOM, because if shipping in name of product model directly to the customer (OEM manufacturers), the customer can’t control this batch of products and what is the difference compared with the previous batch, usually only show real models in front of the final consumer.The customer can know the difference between this batch and the previous batch by the finished material number, because the relevant information of BOM can be learned from this set of data, and then the specific information of this batch of products can be known by checking the BOM.

Order refers to the affiliation of components. Those directly involved in the assembly of finished products are called order 1, and those directly involved in the assembly of semi-finished products are called order 2.For example, capacitance resistance are second-order material in electronic products, because these components need to pass SMT first and then be made into PCBA before they can be further assembled into products.Then PCBA and shell are called order 1, because these directly assemble to the finished product.The division of this order is to facilitate the division of labor arrangements.For example, if SMT only makes PCBA, it can directly check how many materials and parts are needed in the next order of PCBA, without looking at the whole BOM hardly, and then find out the materials and parts which are needed in SMT production.

PCB SMT processing line

The material number abbreviates as “material number”, which refers to the number of each component, because different materials have different properties, such as DIP resistance and SMD resistance, and SMD is divided into 0402, 0603, 0201 and so on. In order to facilitate rapid identification, the material number is developed.Many companies have coding principles for components. For example, a 7K ohm resistor of 0603 is numbered ES0603702, E means the material is electronic, S means SMD component, 0603 is the volume of the material, and 702 means the resistance value of the component.However, many companies do not have their own coding principles, but directly adopt the component manufacturer’s material number, such a drawback is, if you go to an OEM factory to produce, the factory has two customers at the same time, just the two customers use this material, but also use the same component manufacturer’s material number.So the material mixed together, if produce for a first, the quantity of the material is not enough, so take b’s to use.When produee for b, b cries on the side hopelessly.This cries anyway also just delay a few days more, in case the component of a is saved inappropriately, damaged, the component of b was taken again when producing for a, next when producing b, used the component of a, that can only ask god to help .

The name and specification are the specification of the components. Although it is not commonly used in production, it needs to be checked during IQA inspection of incoming materials to ensure  no wrong parts are sent.

Dosage, indicating that in a product, the usage quantity of components can be easily carried out data statistics in the procurement of materials .

Plug-in location, usually used to indicate the position of electronic components on the PCB, for easy verification to ensure that there is no SMT misaligned components.



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