Anywhere between 2–40. You can choose the number of layers. There are at a minimum two layers to a PCB, the conducting layer (usually copper but others can be used), and the insulating layer. With modern Photography methods, the lines that form the conductors can be made very thin. This can make them susceptible to ungluing themselves from the insulating material with excessive amounts of heat. Along with the insulation or substrate layer, additionally can be the solder mask layer, and finally can be a opaque silk screening on top with the components identified, component layer), also on the back can be another silk screening of paint for the SMT layer. Then comes multi-layer PCB assignment, and depending on layers complexity goes up. As explained under point 4, the PCB is defined as a number of copper layers in a well-defined sequence. Copper layers are usually just named layers or also called SIGNAL layer. However, to define the complete PCB, other layers are required. they are usually named by their functionality and position. Examples: TOP solder mask layer, TOP paste layer, TOP legend layer, BOTTOM peel-off layer etc… In general, a PCB assembly is classified by the number of copper layers. Boards that consists of 1 or 2 layers are often called:1-layer PCB = single sided PCB2-layer PCB = double sided PCBBoards with no copper layers or with more than 2 copper layers are defined and called by the number of copper layers.
PCB Glossary ⋅ 03/11/2021 11:01
PCB design is a main function in any electronic product development process. For a PCB to perform reliably and within its specification, the PCB design process is critical and must follow an effective process. PCB Design SoftwareFor both large companies and self-employed PCB designers, there are many computer aided design (CAD) software packages available. The most commonly used CAD tools are Altium Designer, PADs, Allegro, and OrCAD. For students and hobbyists, there are free CAD tools available such as Eagle and KiCad, although their functionality is somewhat limited. The PCB design software capabilities vary quite a bit. The basic software tools provide the simpler functions, while the pay-for tools enable more facilities such as complex routing and simulation. With the increased complexity and requirements in newer technologies, using a higher end software tool is often required.Schematic CaptureOnce a design specification is complete and creates a clear list of requirements for the PCB, the first stage is schematic capture. Although it is possible to draw a schematic manually, most schematics are captured on a computer using PCB design software. The schematic is a 2D rendering which serves as a blueprint for placing the components and laying out the traces on the PCB. Schematic symbols are created and linked to a PCB footprint which defines each component’s physical dimensions and placement of the copper pads or through holes.Component PlacementThe next stage in PCB design is component placement. For components to be incorporated into the PCB design, they must have all of the relevant information defined in their footprints. Also, the board size and shape, any drilling information, keepouts, critical component locations, etc. must be defined. Before getting into the detailed PCB design, it is important to get a rough idea of where the components will be located on the board and to determine if there is enough space on the board to contain all of the required circuitry. This process will also help determine how many layers will be needed. Once a rough placement has been completed, a more detailed component placement can begin. This can take into account things such as the proximity of devices that may need to communicate with each other or may affect the speed of certain signals, and other information such as RF considerations.RoutingOnce component placement is complete, the next stage of PCB design is to route the connections (traces) between all the components. First, if the design is more complex, a set of rules is input into the PCB design software which will trigger an error message if broken. Next, a netlist will be generated from the schematic, which shows all of the traces between all components. Critical routes are completed first, where size and length of the trace is critical. Then the remaining routes are completed, often moving up and down through multiple layers of the PCB.Manufacturing OutputsThe information for the photo plots of the PCB design are output in the form of Gerber files. This is the standard format PCB manufacturers use and are a form of numerical control files used by a photo plotter. In addition to Gerber data, drill information is generated along with the screen print and photo-resist information. Pick and place data is generated, which manufacturers use to program the machines that actually affix the components to the PCB.
PCB Glossary ⋅ 03/11/2021 10:57
Soldermask protects all the circuits on the outerlayers of the PCB, where we do not intend to attach components. But we also need to protect the exposed copper holes and pads where we plan to solder and mount the components. To protect those areas, and to provide a good solderable finish, we usually use metallic coatings, such as nickel, gold, tin/lead solder, silver and other final finishes designed just for PCB manufacturers.This page will discuss some of the materials most commonly used to construct printed circuit boards, the characteristics of those materials, and What are Printed Circuit Boards Made Of?Here are a few of the most popular materials used in the fabrication of printed circuit boards:FR4 epoxy laminate and prepreg: FR4 is the most popular PCB substrate material in the world. FR4 laminates and prepreg are made from glass cloth, epoxy resin, and are usually the lowest cost PCB material available. It is especially popular for PCBs with lower layer counts – single, double sided into multilayered constructions generally less than 14 layers. Additionally, the base epoxy resin can be blended with additives that can significantly improve its thermal performance, electrical performance, and UL flame survival/rating – greatly improving its ability to be used in higher layer count builds, higher thermal stress applications, and greater electrical performance at a lower cost for high speed circuit designs. FR4 laminates and prepregs are very versatile, adaptable with widely accepted manufacturing techniques with predictable yields.2.Polyimide laminates and prepreg: Polyimide laminates offer higher temperature performance than FR4 materials as well as a slight improvement in electrical performance properties. Polyimides materials cost more than FR4 but offer improved survivability in harsh and higher temperature environments. They also are more stable during thermal cycling, with less expansion characteristics, making them suitable for higher layer count constructions.3.Teflon laminates and bonding plies: Teflon laminates and bonding materials offer excellent electrical properties, making them ideal for high speed circuitry applications. Teflon materials are more expensive than polyimide but provide designers with the high-speed capabilities that they need. Teflon materials can be coated onto glass fabric, but can also be manufactured as an unsupported film, or with special fillers and additives to improve mechanical properties. Manufacturing Teflon PCBs often requires a uniquely skilled workforce, specialized equipment and processing and an anticipation of lower manufacturing yields.4.Flexible laminates: Flexible laminates are thin and provide the ability to fold the electronic design, without losing electrical continuity. They do not have glass fabric for support but are built on plastic film. They are equally effective folded into a device for a one-time flex to install application, as they are in dynamic flex, where the circuits will be folded continuously for the life of the device. Flexible laminates can be made from higher temperature materials like polyimide and LCP (liquid crystal polymer), or very low-cost materials such as polyester and PEN. Because the flexible laminates are so thin, manufacturing flexible circuits also can require a uniquely skilled workforce, specialized equipment and processing and an anticipation of lower manufacturing yields.5.Others: There are many other laminates and bonding materials on the marketplace including BT, cyanate ester, ceramics, and blended systems that combine resins to get distinct electrical and/or mechanical performance characteristics. Because the volumes are so much lower than FR4, and the manufacturing can be much more difficult, they are usually considered expensive alternatives for PCB designs.Careful laminate selection is important to ensure the PCB has the right electrical, dielectric, mechanical and thermal properties for the end application.PCBBUY specializes in manufacturing flexible and rigid flex printed circuit boards. We carefully select materials to ensure that the PCBs we manufacture will offer ideal performance in critical applications and extreme environments. Contact our team today to learn more about our PCB manufacturing services.
PCB Glossary ⋅ 03/11/2021 09:30
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