What files are included in a complete PCB assembly file packages?

Before PCB assembly, we will check all the files from customers carefully to make sure the products can be produced correctly from the first time. The files include PCB Gerber files, BOM list, Coordinate file for component pick & place, notes and specifications, testing process etc. Here we do not talk too much about PCB file check. Please view the other page for Free PCB File Check. The complete PCBA file includes the following items.

BOM list

BOM is known as the Bill of Materials, often called the bill of materials. It tests the quality of PCBA processing standard documents and production procedures documents.

BOM records all the electronic materials needed in the PCBA processing, including the brand, model, usage, description, bit number and other information. The electronic materials required in the entire PCBA board will be reflected in the BOM list, so the existence of the BOM list in the PCBA processing is the most crucial part.

The following diagram shows the standard BOM. If the situation allows, customers must provide the BOM in excel format. Other formats of the BOM have to be converted to excel format, which facilitates the engineering and production operations.

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    Coordinate file

    The coordinates file is a standard the processing equipment program uses to locate the coordinates of the PCBA mount components. Automation equipment (such as placement machine, SPI, the first piece of inspection instrument, AOI and other equipment) used for PCBA processing almost always requires the positioning point coordinates. The coordinate file is mainly to locate the coordinate of the component. When the engineers do the program, they need to use this file. 

    Coordinate files can also be exported from the PCB file. The following figure is the standard coordinate file. Coordinate files are usually called Pick & Place files, mostly in txt format.

    Samples provided by the customer (not always required)

    The samples provided by customers are generally used as a reference basis for PCBA processing factories, such as the polarity direction of components, the amount of solder on the solder joints, spray codes, marking, three-proof paint and some other process references. If there is no sample, you can also do a few PCS samples for testing first, especially when there is a batch order.

    Process guidance document

    To control the critical quality of the PCBA processing program, the customer will generally provide some guiding documents for the PCBA processing factory. These guiding documents contain special requirements and particular design points. Some customers will make a note in the BOM file if their unique requirements are not many. For example, the product in the following figure has noted the processing requirements of solder lines and the conformal coating process.

    Test documentation

    After the completion of all the processes of PCBA processing, customers generally have various test project requirements, including test project parameters and technical indicators. In addition, test guidance documents are usually provided by the customer, which contains the guidance and technical requirements of the professional parameters required by the customer regarding the test.

    The following is a functional test file for a power supply circuit board. When designing and making test racks, the product must pass all the tests according to the test documentation to be considered functionally qualified.

    What free checks do we do to make sure assembly your PCBs correctly?

    We focus on the BOM file when matching the above documents and PCB processing requirements.

    BOM is the essential reference document for material procurement and product production (including the model, brand, description, package, bit number, dosage, circuit board version, auxiliary supplies, particular components of the notes and production notes and other information). Its accuracy directly affects product quality.

    A complete and detailed BOM can make the quotation fast and accurate, ensure there are fewer mistakes in the procurement of components and production processes and significantly improve product delivery. The following are the main steps of checking and analyzing BOM.

    Step 1

    Engineers first confirm whether the component model is complete the model and whether the package brand description is consistent (such information can be verified by checking the specifications). Engineers also need to confirm whether the corresponding models and bit numbers are compatible, primarily capacitors, resistors, diodes and transistors of these components. As the amount of these components increases, it is easier to be ignored by engineers, resulting in the appearance of mismatched quantities and bringing trouble to the actual procurement work. 

    For example, the following screenshot shows that the actual bit number is 26, while the BOM shows only 25. In this situation, we usually must inform the customer and operate according to the primary bit number chart.

    At the same time, the engineer has to confirm that there is no duplication of the bit number and the circuit board has this bit number. So all these cases should be verified individually in the first piece inspection.

    There are also some aspects to be ignored easily. For example, the specific model of some resistors is not shown in the BOM. There is only a description of the parameters, and the content description is inconsistent, which can lead to PCB factories buying the wrong materials or causing disturbance to the production line. The following figure shows the conflicting description of the capacitance values.

    Among the inconsistent information, the most significant impact on production is the conflicting information on the material package and board layout.

    To prevent such problems in the actual production process, usually, after the warehouse staff check the parameters of the essential passive parts consistent with BOM, in the final stage of incoming inspection, we need to get the circuit board and materials, place the material on the blank circuit board to check the package size issues. 

    Suppose there is found inconsistency between the material size and the bare board. In that case, we need to promptly propose and communicate with the customer to deal with the proposal, subsequently change the board if the customer needs to change the board, and update the material if the customer needs to find other replacement materials. For example, in the picture below, the size of the cement resistor is too large, and the spacing of the circuit board is too small, resulting in an unreasonable installation in place.

    At the same time there are more hidden problems, that is, the material pin size and the size of the circuit board hole are not consistent, resulting in the component can not be inserted into the PCB board. All these details must be eliminated one by one before starting the machine in the factory. If these problems are not eliminated before production, it will lead to production line stoppage and seriously affect efficiency and progress.

    Step 2

    Check whether the actual incoming material and the parameters of the passive parts are consistent, which requires using multimeters, bridges and oscilloscopes to measure the resistance, capacitance, inductance and other passive components. The usual problems are resistance value mismatch. Capacitance voltage is not enough, etc. The main reason for these problems is that the incoming materials from the component suppliers are not well classified and controlled.

    The following figure shows the measurement and verification of capacitance values.

    Step 3

    Handle specific notes in the BOM, such as component program burn-in, particular component installation, etc.
    For example, in the following screenshot, the BOM clearly states that the single-sided machine DD2 Firstly needs to download the file. Therefore, we need to download the program file first and then do the next step of the testing process.

    Also shown below, the mounting requirements for D1 LEDs specify the mounting height of the LEDs and require that the LEDs be flush with the board edge.

    Step 4

    Confirm auxiliary materials and consumables, such as three-proof paint, dotting red glue, soldering connection wire, labelling, additional materials and consumables for production assembly, etc.

    Three-proof paint is shown in the figure below.

    Dotting red glue and soldering connection wire are shown in the figure below.

    Labelling is shown in the figure below.

    Advise in PCB components sourcing as BOM

    After checking the complete BOM list, we enter the material procurement stage, which usually starts with confirming the market inventory of active components, especially the new main ICs, MCUs, etc., of big brands. Due to the active components’ irreplaceable nature, the component factory’s long delivery time, and the high value of individual products, material procurement plays a pivotal role in the overall project delivery and cost control.

    Problem 1: Component market shortage, the long delivery time of component factories

    Suggestions: The out-of-stock of new materials within three years is normal, and we can try to use the material within five years. We can use the materials within five years if they are in unopened original packaging and stored in a good environment. However, it is prudent to make samples first to see if the tinning condition is good. After ensuring the samples are OK, we can do mass production.

    Problem 2: The material is obsolete products which are very early projects

    Suggestions: Compared to obsolete products, component factories have newer materials. New components can replace outdated products in function and have lower power consumption and more powerful performance. In addition to reading the specification, we can browse some website information. For example, DIGIKEY, MOUSER and other official websites have a lot of updated material tips corresponding to the product.

    Problem 3: components are out of stock, and the prices are increased

    Suggestions: For the procurement of active and passive parts when encountering this problem, we need to deal with them separately. If we encounter this problem when we purchase active components, the customer generally needs to cooperate with the PCBA manufacturer to provide alternative components or modify and adjust the program.

    • Suppose we encounter this problem when we purchase passive components. In that case, we can provide a variety of prominent brands of passive components with the same parameters as a substitute, such as resistors, capacitors and inductors. As for connectors, many of our domestic Chinese connectors can also meet the needs of customers' products, reducing procurement costs, accelerating delivery time, and stabilizing product availability.
    • At the same time, in the process of continuous communication with customers, we can give customers advice according to the customer's future order needs and prepare a part of the components in advance, as a response to the shortage of goods and materials brought about by market fluctuations and other situations.
    • Finally, as engineers who deal with BOM and purchase components, we must have basic knowledge of relevant electronic components to be patient and understand the local components market situation. When purchasing components, we must take the initiative as much as possible. We need to adopt different negotiation strategies for different unit prices and different quantities of components and continuously accumulate quality supply channels.
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