Components of PCB machining requirements include manufacturing instructions, drilling files, dimensional files, laminated drawings and assembly files. But what are the processing requirements? Why processing requirements? PCSPCB will disassemble all the points about PCB board processing documents and provide best practice cases.
Unlike components welded to a PCB, a PCB is a fixed product that takes time and effort to design and manufacture according to a specific product. The more complex the PCB, the more processing requirements are required. Regardless of the complexity of the PCB, these documents can provide clarity to PCB suppliers, thus speeding up the manufacturing process. The supplier will use the processing requirements in conjunction with the actual PCB production data to verify the accuracy of the production.
The purpose of the processing requirement is simple: it defines a PCB. There is no such thing as a "standard" PCB solution because it is designed according to the product required to serve. Each PCB has its own unique manufacturing and quality requirements, which are set by the user. In addition, machining requirements are also used for verification, as CAD systems sometimes generate incorrect data that are not easily detected until the manufacturing design is analyzed in the factory. At the same time, the processing requirements are also used for subsequent quality inspection, and the quality inspector needs to ensure that the PCB meets all IPC specifications during the final inspection.
The processing specification is a document that PCB design engineers define the specifications, appearance and functions of the finished product, and can also be used as a communication tool between PCB designers and manufacturers. Engineers can use machining instructions to control PCB quality. PCB processing instructions should accurately define the specifications of the finished PCB. In order to maximize the usefulness of processing instructions, PCB design engineers should be familiar with IPC specifications. The Rigid PCB Board Quality and Performance Specification in IPC-6012 provides design engineers with a number of options that they can use to define a finished PCB.
When specifying the surface treatment process, the engineer can also specify the durability of the surface treatment. In this way, you can ensure that the PCB can withstand long-term storage, as well as sufficient support for the thermal cycle required for assembly. This example also illustrates the comprehensiveness of the IPC specification, as IPC-6012 references J-STD-003. Another way to control quality and cost is to specify the quality level of the PCB. For example, high-reliability PCBS may need to refer to IPC-6012 Level III standards because there are fewer control points for quality in IPC Level I and Level II standards. In addition, the overall manufacturing cost of Class I and II standards is lower. In the PCB industry, PCBS generally need to meet IPC Level II standards, but certain processes need to meet Level III standards, such as electroplating.
A good way to specify plates is to look at IPC-4101 and IPC-4202, which use the "/ number" to specify PCB material classification based on material grade.
When writing processing instructions, try to be concise and clear, vague words are easy to produce ambiguity or errors, resulting in unnecessary cost and time loss.
The board processing document is also used in quality control to ensure that the PCB complies with all IPC specifications.
The drilling table is one of the machining requirements used for design verification. It lists all boreholes that match the borehole drawings, including hole dimensions, number, tolerances, and identifiers. These marks indicate the location of each hole on the PCB, and designers can also add additional information, such as blind and buried hole information, to minimize misunderstandings. Sometimes, the CAD system will produce some unknown errors, so in this regard it takes a little more time to ensure its accuracy.
Part of the processing requirements is the PCB profile drawn to scale. The drawing should provide accurate PCB profile requirements. A simple, scale-drawn PCB profile is suitable for many design areas, but more details are needed to produce the most accurate manufacturing drawings. In addition to the appearance, it should also be added to the size line drawn to scale, a good manufacturing drawing should also include an origin for the manufacturer's reference.
While working in the factory, I realized the importance of checking the scale first. Often, the customer's CAD system configuration outputs incorrect Gerber files, resulting in a different scaling of the physical layer than the drill file. If PCB dimensions are included, I can quickly figure out what the problem is. Although this is only a small reference point, it is very useful.
It should be noted that adding too many size lines will disturb the line of sight and make it impossible to read the drawing. I once saw a drawing of a circular PCB with so many dimensions and angles added to it that our engineers couldn't read it. Therefore, it is best to include only the overall dimensions and the key dimensions.
A laminated file (or simply "laminated") is a detailed cross-sectional image of the PCB. Not every PCB requires a laminated file, but some designs require specific information. For double-layer PCBS, designers can list the finished board thickness and tolerances in the manufacturing instructions, but some designs require a laminated diagram with specific details.
PCB design engineers can specify the laminated structure, but in my experience, it is still limited in practice.
PCB design engineers can specify the finished copper thickness of each layer, as long as the data is accurate, this will be a good processing description. However, I have seen laminates with specified inner copper thickness where the thickness requirements do not match the standard manufacturing thickness. This is acceptable if the customer and the supplier agree. Requiring an unconventional laminated structure without a reason can cause problems and lead to an extended EQ time, as unconventional manufacturing increases PCB delivery times and costs.
PCB designs with blind, buried, and/or backdrilled holes may have complex drilling sequences. Drawings showing the sequence of all drilling allow PCB suppliers to specify the number of decompression and drilling cycles. Although suppliers can be determined based on PCB drawings, there is still a risk of misunderstanding.
The laminated drawing should also include the material type of the PCB material and the dielectric thickness of the finished product. This information is usually only required for PCBS that require impedance control. Material type and dielectric thickness contribute to impedance control. With careful layout, engineers can minimize electromagnetic interference (EMI) and crosstalk through the reference plane.
Laminated structural drawings are a good way to document impedance control specifications. The correct impedance line is marked to determine the impedance line on each layer. The table should also include the track width, position, target impedance value, and reference layer for each impedance line.
Some PCBS have thermal management specifications, such as insulated metal substrate (IMS) or buried copper block technology. Copper blocks and metal substrates come in a variety of shapes and sizes. Laminated drawings are a good way to show the thickness and shape of the copper blocks, as well as IMS technical details such as thermal media and metal substrate thickness.
NCAB's detailed lamination drawings specify the layering sequence, copper thickness and drilling sequence to ensure that the PCB meets impedance control requirements. Learn more about impedance control and download our PCB Lamination & Impedance Design guide to ensure your design is accurate.
A Mosaic file is a drawing drawn to scale that shows the number of PCBS in each work board. The assembly file should indicate the size, and the spacing between each PCB should be accurate. The edge of the plate should have at least 3 available fixture holes to ensure accurate alignment during assembly. If a more uniform plating of the entire board is required, the edge of the board is a good place to add plated copper without affecting the board.
Patchwork helps to control cost and quality, while ensuring consistency across batches and being more cost effective on a unit basis. Optimizing the assembly method can improve material utilization, reduce waste and reduce costs, but it still needs to be treated with caution, because too much or too little PCB on a single work board will make the entire work board unstable and easy to spread before assembly. The optimization of the assembly method can achieve efficient assembly and reduce costs and waste. If you don't know how to do this, don't worry, NCAB can give you effective advice.
Boards for different applications also have their own version update needs, and updated processing requirements can reduce front-end EQ time. Many engineers and purchasers have reflected that PCB takes too long to EQ in the early stage. In addition to updating machining requirements, care should also be taken when specifying redundant information for different drawings. Too much redundant information increases the risk of missing information when updating data, leading to more problems and longer lead times.
When the PCB processing requirements are completed, it feels great. Documents and drawings should be concise and contain all relevant information. If there are details that interfere with the machining instructions or drawings, it is best to clarify them further. PCB is a definite product, PCB suppliers know how to produce PCB, but they may not have produced your PCB. Therefore, in order to ensure the accuracy of production, they will ask various questions about your documents, and the purpose of PCB processing requirements is to minimize these problems. Optimizing this part of the design is time-consuming, but it's worth the expense for better quality, cost, and delivery.
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