PCB Component Orientation
At one time, the slower circuitry of older circuit boards allowed PCB designers a lot more latitude in how they placed their components. If we have components that aren’t aligned with the correct orientation, there could be a lot of damage when it comes to getting the board assembled. Here is some more information on those guidelines and how you can ensure you have the correct component orientation on PCB designs. In this passage, we will provide the information of PCB component orientation. If you are searching the knowledge of PCB, check and read the content below to learn more.If you want to order PCB product, please check and custom your order online. What are the main considerations for PCB component orientation? There are three primary goals that your PCB contract manufacturer will focus on when they review your design for manufacturability: · Standardization: By making sure that your PCB design will fit into a standard assembly process, your CM can reduce the labor and time involved, which lowers your cost.· Assembly problems: By eliminating known potential assembly issues, your CM will improve production yields and once again pass on cost savings to you.· Quality: By identifying and replacing parts or materials that could be potentially defective from the assembly process, your CM can once again improve yields. During the DFM review, one of the details of your PCB that will be looked at to achieve these goals is component orientation. The rotation of parts on a PCB can have a great effect on its manufacturability, starting with the soldering process. What are the guidelines of PCB component placement? Before going into the specifics of component placement and orientation, there are several general guidelines to keep in mind: · Orient similar components in the same direction.· Avoid placing components on the solder side of a board.· Try to place all your SMT components on the same side of the board, and all the through-hole components (if mixed) on the top side of the board.· When you have mixed technology components (SMT and PTH), manufacturers might require an extra process to epoxy the bottom components.· You should terminate all lands with only one trace.· When you specify a chip under a device, this can make inspections, rework, and test more difficult.· All components used on the wave solder sides of an assembly should first be approved by your manufacturer for immersion in a solder bath. How component orientations affect PCB? At one time, a circuit board could be laid out with its parts arranged aesthetically and it would perform just as well. However, that is no longer the case—today, PCB quote components must be placed in specific partitions according to their function for optimum performance. They also have to be oriented correctly to satisfy the needs of the signal or power circuitry they are servicing. High-Speed SignalsThere is more to a high-speed circuit than just a single point-to-point connection. High-speed circuitry often consists of multiple nets that together make up one complete signal path. For instance, a signal path may start at a source and then go through a resistor before terminating at its load. Therefore, the signal path consists of two nets with a resistor in the middle, and for the best signal integrity, both nets need to be treated together as one. To accomplish this, the resistor must be oriented to provide the most optimum connection between the signal path’s two nets. High-speed routing also consists of memory and data buses that contain many nets. Not only do these nets need room for their trace routing, but for escape vias as well. This requires that all components connected to these nets be orientated in the most optimum direction for the shortest possible trace routing. In the same way, components that are part of impedance controlled nets must be oriented for the shortest and most direct connections, especially those that need to be routed with differential pairs. Power Supplies Power supply components must also be oriented for the most optimum connection configuration during placement. To reduce the inductance and resistance as well as the noise that can be created in high current power supply traces, the routing must be as short and as direct as possible. This will require a very tight placement of the power supply parts and possibly some unusual component orientations. Additionally, power supply components should also all be placed on the same side of the board to help with the short and direct routing. Satisfying all of these signal and power integrity needs will require some creative placement of the PCB components. Some of these parts may end up having to be orientated at odd angles instead of the usual 90-degree increments to achieve the best signal and power routing. The key is to check first with your manufacturer to see what they can and can’t build before starting your board placement. What are the rules of PCB component placement? Place the main components as per signal flow. Refer to the schematic circuit diagram while placing the components. Identify the main components of the circuit such as microprocessors, Ethernet chips, memories, etc.Place these as per the floorplan and with the shortest traces between these main chips as per the datasheet guidelines and which makes the signal flow smooth and unidirectional as far as possible. Place the associated components near the main componentsNext, place the components associated with the main components such as crystal oscillators, decoupling capacitors, termination resistors.Wanna know PCB knowledge? Check and read for more.
PCB Knowledge ⋅ 08/24/2021 09:27
Test Point PCB Design
The circuit boards we design also have some testing to go through; and, in their case, the testing will determine how well they have been manufactured. In order for this testing to happen, the board must be prepared with specific elements that a test probe can access. These elements are called test points and their inclusion on PCB designs is very important. In this passage, we will focus on the topic and if you are curious about it, please check and read our content below for more information or FOR PCB QUOTE HERE.If you want to order PCB product, please check and custom your order online. Why to process test points on PCB? To verify the integrity of the component assembly process, a completed printed circuit board will go through an automated test cycle. This is designed to find component pins that are not connected to the board with a good solder joint and will use a system of probes to contact the test points designed into the board. There are two different systems that are generally used for this testing: In-circuit test (ICT) This is a system that is designed to test all of the nets on the circuit board simultaneously. To do this, ICT employs the use of a test fixture that is loaded with probes to contact the test points on the board. The fixture will have one probe for each test point on the board, which enables the testing to be conducted very quickly. These test fixtures are usually configured to test the bottom of the board, but they can also test the top or both sides of the board at the same time. Because the ICT fixture is designed to test each circuit together, it is the test method most likely to be used for production runs of a circuit board. Another advantage is that ICT can also conduct some functional testing of the board in addition to the manufacturing tests. The drawback, though, is that ICT fixtures take time to develop and are expensive to build. Alterations to existing fixtures for PCB design revisions can be costly as well. Flying probeThis system differs from ICT in that it only uses between two and six probes to conduct all of the tests on the board. As the name would suggest, these probes fly around the board contacting each specific test point sequentially that they are programmed to test. Due to the more individualistic nature of the testing, the flying probe takes a lot longer to test a board than an ICT will. Flying probes also aren’t able to conduct any functional testing of the board due to the minimum amount of test points that are being probed at one time. The advantage of the flying probe test, however, is that it is very fast and inexpensive to set up and run. Additionally, alterations to the test due to circuit board revisions are easy to incorporate. Flying probe systems can also test larger board sizes than ICT systems can. What are the different types of test points of PCB? There are two main types of test points used on a printed circuit board. The first is an easily accessible point for a technician to access with hand-held testing equipment. To help with this, these points often have a post soldered into them for clipping on a test lead. These test points will be marked with a reference designator and usually the name of the net in silkscreen for easy reference, such as “GND.” The other type of test point is used primarily for automated test equipment. The automated test points on a circuit board are thru-hole pins, vias, or small landing pads of metal that are designed to accommodate the probes of automated test systems. There are three main test systems that will use these test points on the board: Bare board test: This is a test that is run after the circuit board has been fabricated to make sure that all of the nets in the board have electrical connectivity. In-circuit test: ICT is run after the board has been assembled. The board is positioned on the ICT fixture which is filled with probes for each individual net. These fixtures usually test the bottom of the board, but they can also test the top or both sides together if needed. Flying probe: Like ICT, this test is run after assembly on each net of the board by accessing the test points. Where it differs, however, is that the flying probe equipment uses two to six probes that move around to each test point instead of using stationary probes in a fixture like ICT does. How to use test points of PCB? Refresh Yourself on Test PointsThere are two different types of testing that require a PCB test point: bench testing by a technician and automated testing during manufacturing. We will be talking about the latter here, and there are two types of automated tests that use test points: bare-board testing for fabrication and in-circuit testing (ICT) for assembly. The bare-board testing is done prior to assembly and it is to make sure that you have good electrical connectivity between all the nodes. The ICT is a more functional test after assembly to make sure that the components are working as they should. In both cases, probes from a test fixture will come into contact with the test points on the circuit board in order to conduct the tests. Assign a Test Point ManuallyThe general rule of test points on a printed circuit board is that each net needs to have a probeable point to test. These “test points” need to be known and cataloged in the Printed Circuit Board design system for reports to be generated that the manufacturer will use when testing the finished boards. To do this you will create test points on the board by flagging pads or vias as probeable points. Altium Designer has capabilities to do this both manually and automatically. Test Point Design RulesYou can set up design rules in Altium Designer for governing the size, spacing, and clearance requirements of the pads and vias to be used as PCB test points. These setups are in the “PCB Design Rules and Constraints” menu, which can be accessed from the Design > Rules pulldown menu.Wanna know PCB knowledge? Check and read for more.
PCB Knowledge ⋅ 08/23/2021 09:47
PCB Heat Dissipation Calculation
Managing heat is also an important part of printed circuit board design and manufacturing. A board that isn’t designed to dissipate the heat it generates may end up with operational problems or even complete failure. During manufacturing it is also important that the heat be managed in order to withstand the high temperatures applied during the soldering process. In this passage, we will focus on the topic of it. If you are looking for more professional knowledge, please check and read for information of PCB heat. Let’s go!If you want to order PCB product, please check and custom your order online. What are the main technologies of PCB heat dissipation? As electronics become more powerful while PCBs get smaller, heat dissipation techniques are more important than ever. Here are a few proven techniques: 1. Thermal Via Arrays You can turn a PCB into an onboard heat sink by incorporating thermal via arrays over copper-filled areas, as shown above. The idea behind doing so is to have heat flowing from components to the copper area and dissipating through the air from the vias. Usually, thermal via arrays are used for power management modules and components with thermal pads. When implementing thermal via arrays, remember that it needs to have a reasonably large diameter, in the region of 0.1 mm, for the heat to be dissipated effectively. Also, ensure the vias are not thermal-relief pads but padded holes that are connected to the copper area at all sides. Increasing the number of thermal vias further helps with heat dissipation. 2. Use Wider Traces Copper traces that conduct high currents build up heat. Therefore, it is important to increase the width of the trace to maximize heat dissipation to the air. Doing so also reduces the thermal resistance of the trace and reduces heat spots. 3. Use Heatsinks and Cooling Fans Passive heat dissipation techniques like thermal via arrays may not be enough if the PCB quote produces more heat than can be reasonably dissipated. In such circumstances, you’ll need to include heatsinks and fans in the design. Heatsinks are attached to components that generate the most heat, usually voltage regulators, CPUs, MCUs, and power transistors. The heatsinks are either screwed onto the PCB or left exposed to the air. In an enclosed design, a cooling fan is installed to displace that hot air into the environment. To handle the greater thermal problems of high speed and high power boards, here are some design techniques that can help: · Large metal pads under hot parts to act as a “thermal” pad.· Solid filled vias to conduct heat from thermal pads into ground planes.· Heat sinks connected to thermal pads of hot parts.· Using board materials with better thermal properties such as polyimides or metal core boards.· Cooling fans as well as strategic component placement to put hot components into the circulating path of the fan. Why to process PCB heat dissipation? Electronic components are all built to operate within a finite temperature range. If the surrounding temperature exceeds the upper limit, the components can break down. Even if it doesn’t break, the excessive heat will negatively affect the component’s performance. For example, an MCU will consume more power at high temperature compared to room temperature. When electronic components are exposed to excessive heat over a prolonged period, their lifespan shortens. Generally, an increase of 10°C will decrease the lifespan of electronics by half. If you’re negligent in your utilization of PCB heat dissipation techniques, you’ll soon face the issues related to premature component failures. It shouldn’t come as a surprise that electronics that require more power to operate will generate more heat. Components like voltage regulators, microcontrollers, and power transistors are all known to heat up when the load current increases. These are just a few examples but there are many more. Older mobile phones tend to heat up during anything more than short conversations. Remove the cooling fan from a laptop’s motherboard and you can soon fry an egg on the CPU. And, if those electronics are placed in an enclosure that heat can almost double. Wanna know PCB knowledge? Check and read for more.
PCB Knowledge ⋅ 08/23/2021 09:32
PCB Tooling Hole Placement
Tooling holes are probably the simplest feature on a PCB, there are some basic guidelines that should be followed when determining where to place tooling holes. Once you consult with your manufacturer on their panel and tooling requirements, or if you’ve decided to make your own panel, tooling holes can be placed with the standard pad and hole features in your PCB design software. In this passage, we will provide that how this works and some best practices for tooling holes in your design. Please check and read the content below to learn more information.If you want to order PCB product, please check and custom your order online. What is the definition of PCB tooling hole? PCB tooling holes, or mounting holes, are circular openings made at the edge of a PCB. Tooling holes are non-plated, and they are used by machines to hold the PCB down for alignment. During the fabrication process, it’s imperative that the PCB be kept still and properly aligned for drilling. If the PCB is not kept still, it will be impossible to deliver precisely-drilled holes. When the fabricated PCB is sent for assembly, the tooling holes will be needed again if there are SMD components in the design. The machines will use the tooling holes for stencil alignment when applying solder paste and placing SMD components with the pick-and-place machines. It is important to note that PCB tooling holes should not be confused with fiducial markers. Fiducial markers are pads that are created on the PCB quote to provide a reference for optical pick-and-place machines. However, both are equally important when designing a PCB with SMD components. What are the considerations of PCB tooling hole? When adding tooling holes, please keep the following in mind: 1. Two or three tooling holes should be added on the PCB, they should be placed in opposite corners of the PCB and as far apart from one another as practical.2. Tooling holes should be 1.152mm (45.4mil) round non-plated holes with 0.148mm solder mask expansion.3. Tooling holes are only required for SMT assembly orders.4. Please try to add tooling holes on empty space and keep them away from traces. If there is no enough room, you can add them to the copper area. What is the importance of PCB tooling hole? Tooling holes used for attaching hardware, also known as “mounting holes,” can be associated with component footprint patterns or isolated by themselves. PCB footprint creation guidelines In addition to having leads or pins that solder to the circuit board, several components have mounting hardware for added physical support. Connectors often bolt to the board to protect their solder connections from the stress of being plugged and unplugged from their cable. These holes may also need to connect the mounting hardware to electrical ground or conduct heat through the board to be dispersed on interior plane layers. Lastly, to mount a circuit board into its system, mounting hardware or brackets are often attached to the board using isolated holes. PCB tooling holes can be put into the board to assist with the different phases of manufacturing. These holes guide the board through its assembly processes, such as solder reflow, wave solder, and automated optical inspection (AOI). Tooling holes are also used during the testing process if the board needs additional test fixture support. However, most of the tooling holes for production are added to the PCB contract manufacturer’s panel based on their requirements instead of the board. How to work with PCB tooling hole? Tooling holes will probably be one of the simplest features in your PCB, but they are critical for fabrication and assembly. There are three main points to consider when determining where and how to place tooling holes in your PCB: · Placement during panelization· Size and plating· Placement with fiducials How to process the PCB tooling hole? Calculate the size of PCB tooling hole Usually, common sizes like 1mm, 1.5mm, and 2mm are acceptable tooling hole sizes for most manufacturers. If you’re unsure, make sure to consult with your PCB manufacturer. For uniformity, you’ll want to stick with a common size for all tooling holes on a PCB. Besides size, you’ll also need to ensure that the PCB tooling hole isn’t plated. A non-plated hole is better in terms of accuracy compared to a plated one. Also, ensure that there is a solder mask expansion that slightly extends over the hole. Place the PCB tooling hole Placing tooling holes is simple: just use the “place pad” or “place hole” feature in your design software. Great PCB CAD tools will let you define specific holes as plated or non-plated; simply set the hole to non-plated and set the required diameter, and you’re finished with tooling hole design. PCB design software like Altium Designer makes this easy with a complete set of CAD tools for PCB design and layout.Wanna know PCB knowledge? Check and read for more.
PCB Knowledge ⋅ 08/23/2021 09:12
PCB Component to Edge Clearance
Components that are placed too close to the edge of the board run the risk of being damaged or causing problems with other aspects of circuit board manufacturing. The problem, of course, is that some components have to be close to or on the edge of the board in order to perform their function. To place your PCB parts so that they are in the most optimal locations, it is important to understand the concerns of placing components too close to the board edge. In this passage, we will provide you all the details of PCB component to edge clearance, if you are going to learn more knowledge about it please check and read the content below.If you want to order PCB product, please check and custom your order online. What are the considerations of edge clearance on PCB? The general guideline for component clearances around the edge of a printed circuit board is 0.100 inches. This will give an adequate amount of room for the test fixture and most assembly operations. Often this number is reduced by the manufacturer depending on the needs of the design. There are some areas of the board where specific clearances must be adhered to: Panel V-grooves: For circuit board panels that will be scored with a V-grove for breakout, the parts must maintain a minimum of 0.075 inches to the edge of the board. This will give the cutting process enough room without damaging the components. For those parts that are taller, the minimum clearance grows to 0.125 inches to give those components a safe distance to the cutter. Panel breakout tabs: For circuit boards that will be separated from panels using a breakout tab, components next to a tab must maintain a distance of 0.125 inches to the edge of the board. For taller components that minimum clearance grows to 0.250 to protect the components during depanelization. Another edge clearance to remember is the copper to the edge of the board. For those components with larger connection areas, their solder joints may fracture with depanelization as well and must be held further back from the edge than other parts. Special Considerations:· Resistors: The recommended minimum edge clearance is 0.05”.· Capacitors: The nearest point of the capacitor to the board edge should be no closer than 0.119”.· Edge Connectors: If possible, use alternatives, such as connectors placed away from the board edge. If edge connectors are required, a good practice is tab routing or a combination of scored and tab routing. What are the main rules of edge clearance on PCB? Although it would be convenient to state definitively what the required component to board edge clearances should be, the truth is that these values vary between manufacturers. What we can do, though, is to lay out the different categories of clearances to be aware of along with some general values that you can use as a starting point: Physical support: Some circuit boards require additional support during manufacturing due to the overall size, thickness, and weight of their components. Copper: Although not a component, there also needs to be enough clearance between traces and power planes to the board edge. This is to protect the metal from twisting and lifting during depanelization. Panels with V-grooves: Some circuit boards are separated from their panels by cutting V-grooves along the board outline. Panels with breakout tabs: Other circuit boards are routed out of their panels before manufacturing and held in place with small breakout tabs until depanelization. Drilled holes: Holes also are not a component, but they need to observe board edge clearance rules as well. It is recommended to maintain a minimum distance of 0.020 inches between the edge of the hole and the edge of the board. Test points: ICT test points also need to be kept back from the edge of the board by 0.100 inches. This will ensure that there is enough room around the perimeter of the board for the vacuum seal of the test fixture. Copper to PCB edge clearance The minimal clearance between edge of board and pattern is. For routed boards:· 0.25mm (10mil) on outer layers· 0.40mm (16mil) on inner layers For boards with scoring (V-cut):· 0.45mm (18mil) on outer and inner layers If you require a copper area or plane to extend up to the board edge please clearly indicate this in the Mechanical Layer. Copper up to the board edge should only be used where absolutely necessary due to: · There is a risk of a rough board edge as the copper may tear during contour routing (profiling).· The copper can create electrical shorts between layers.· Copper up to the board edge is NOT compatible with scoring (V-cut).Wanna know PCB knowledge? Check and read for more.
PCB Knowledge ⋅ 08/21/2021 10:02
How to Calculate Thermal Conductivity of PCB?
Many mass-manufactured boards will be placed on FR4, which has very low conductivity compared to a number of alternative materials. The thermal conductivity of a PCB substrate is often considered an afterthought. There are a number of design tradeoffs that should be considered when choosing a substrate that spans beyond thermal conductivity, and you might be better off using a substrate with low thermal conductivity alongside some passive or active cooling methods. In this article, we will talk about thermal conductivity of PCB. If you are going to learn more PCB knowledge, please check and read the content we provide for more information.If you want to order PCB product, please check and custom your order online. Why thermal conductivity is important to PCB? Heat management is crucial for PCB performance, reliability, and longevity. Inadequate heat management may lead to delamination, damage, or device failure (Figure 2). Thermal conductivity plays a vital role in heat management, and thus it is a key parameter for PCB design. The C-Therm Trident thermal conductivity platform is a useful tool in obtaining rapid, precise, and accurate measurements of PCB component thermal conductivity. The “hot” topic in PCB design is high-speed signal integrity. But on another front, PCB designers may be interested in how hot (literally) an individual PCB trace becomes. Trace temperature is directly related to reliability. In the extreme, a trace that is too hot can melt the solder or cause a board to delaminate. But generally we want trace temperatures to be a lot lower than that. The trace reaches a stable temperature when the heating of the trace equals the cooling of the trace. The heating of the trace is caused by the I2R (power) drop across the trace. It is only in the last 10 years that the industry has recognized the importance of the dielectric in the trace cooling process. How does thermal conductivity influence PCB? Choosing a substrate with an appropriate thermal conductivity is one of many important aspects of PCB design. Thermal management in PCBs becomes particularly important in smaller boards with active components that switch at high speed. It is also important in boards that will carry high current as resistive losses in a trace will generate heat, which then transfers into the substrate. If you know that your board will generate a large amount of heat during operation, or if your board will operate in a high-temperature environment, then you may need to use a substrate with higher thermal conductivity. You may also need to implement passive cooling, active cooling, or both in order to keep the temperature of important components within their safe operating range. It is also important. Component Size As components become smaller, so does the ability to dissipate heat naturally. For example, a MOSFET with a SOT-23 package will have less area for its heat pad than one in TO-220. Therefore, the size of components mounted on a PCB will influence its ability to propagate heat. Thermal ViasThermal vias are holes intentionally placed to dissipate heat off a component. It’s kind of like providing more opportunity for the steam to escape from your porridge instead of trapping it in a container. So, naturally, this means that the more thermal vias there are in an area, the more they will increase the effective thermal conductivity of a PCB. Internal LayersThe presence of internal copper layers can also change the rate and direction of heat dissipation. The thermal conductivity for copper is 355 W/m-K, while FR-4 is 0.25 m-K. With multiple inner-layers of copper, the effective thermal conductivity of the PCB would decrease. Of course, the presence of thermal vias could help to move the heat to the inner layers more efficiently. How to calculate thermal conductivity of PCB? As a fundamental property of any material, thermal conductivity defines the heat flux between hot and cold regions in your PCB. The thermal conductivity of your substrate material can be found in material datasheets. However, once you have an idea of your stackup and copper weight in your layout, you will want to calculate the effective thermal conductivity of your substrate. Formulas for calculating this directly vary depending on who you ask, although there are a number of lumped models in the literature. The simplest method is to use a weighted average based on the volume of copper and substrate material in your PCB: Effective thermal conductivity estimation Effective thermal conductivity estimate based on a volume weighted average of your PCB material parameters The above equation shows a simple volume weighted average for calculating the effective thermal conductivity, where “s” indicates the substrate and “c” indicates copper. However, this is just a rough estimate, and you’ll get much more accurate results if you use a specialized 3D multiphysics simulator. Once you’ve determined the effective thermal conductivity of your PCB, you’re ready to calculate the thermal resistance in your board, which will give you some idea of how heat will transfer through your stackup. What is effective thermal conductivity of PCB? Effective thermal conductivity refers to the ability of a material to conduct and transfer heat. When we’re talking specifically about a PCB’s effective thermal conductivity, we’re talking about how well the PCB can move the heat generated from its components to its surrounding area. Effective thermal conductivity is represented by the symbol and values are expressed in W/m•K. In PCB design, effective thermal conductivity is an important aspect used in thermal modeling and analysis because it allows engineers to predict how well a populated PCB would conduct heat based on specific assumptions and models. With electronic modules continuing to shrink in size, it is a parameter that deserves attention amongst designers.Wanna know PCB knowledge? Check and read for more.
PCB Knowledge ⋅ 08/21/2021 09:24
PCB DFM Guidelines
Design for manufacturing (DFM) is the practice of optimizing the engineering workflow of producing an electronic device. With this much competition, it isn’t only the latest and greatest designs that will win the day, it is also which circuit boards can be built quickly, efficiently, and for the lowest manufacturing costs. To achieve that goal requires that today’s PCB engineers be well versed in design for manufacturing, or DFM, techniques and methods. In this article, we will analyze the DFM in PCB manufacturing process. Please check and read the content we prepare to learn more professional knowledge about it.If you want to order PCB product, please check and custom your order online. Why DFM in PCB is important? In order to avoid all of these problems, PCB designers need to incorporate good DFM practices during their initial circuit board design. This will reduce the need for changes later on, and preserve the layout of sensitive circuitry that is fine-tuned for performance in the prototype. The first step in understanding DFM in circuit board design is to be aware of the manufacturing problems that can happen without them. When a prototype circuit board is first being developed, the focus is usually on the functionality rather than the buildability of the board. As such the component placement on the board may not be optimized for assembly, which may result in higher assembly costs. Even during limited production runs for prototyping, a lot of manufacturing costs can be saved by designing the board for automated manufacturing. These problems are magnified however when the board is ready to be moved into its production phase. Components that are not optimized for manufacturing will have to be re-positioned to avoid the necessity of manual assembly. Another problem is with components that weren’t selected for long-term production. If their price is too high or their availability is limited, the board will encounter additional manufacturing problems. What are the factors of DFM in PCB? If a PCB is performing appropriately and the design engineer is also satisfied with it. Then why DFM checks for it? There are various reasons: cost of final PCB, design layout, and chances of future design failure. · Theoretically, in cost terms, PCB designs submitted without DFM checks are less expensive than the designs with DFM checks. But it is better to pay a little extra so that the manufacturer could ensure whether the design is manufacturable or not. · To sustain a PCB layout with DFM issues, CAM engineers edit the data to meet the design requirements. This is one primary reason that introduces signal integrity issues and EMI/EMC issues. · PCBs assembled and tested efficiently, still fail. The main reason is that the design data still contained the DFM errors that were resolved in the prototype but were not implemented during the production. What are the guidelines of DFM in PCB？ To get the best results in a prototype build, you need to choose a CM that is fully versed in and ready to help you with DFM requirements. Not all CMs are set up for it, and in the case of CMs, they might not have the capabilities to support any DFM engineering at all. For success, make sure to work with a CM that: · Completely understands all DFM requirements and will work with you during the design phase to help you incorporate those requirements. · Has the engineering staff and facilities to review your design, recommend DFM changes, and even make those changes, if that is in your best interest. · Has the manufacturing proficiency to work with prototype designs that have DFM problems in them to get your product built correctly and returned to you quickly. · Select the right manufacturer and involve them up front: Different manufacturers can have strengths and weaknesses just as any business can. Ensure that you have selected the best manufacturer for building your PCB. Once you have made that choice, it is important to also involve them as early as possible with your design. This way you can design your PCB to their DFM rules, instead of making changes later. · Consider the board form factor: The more complex your board shape is, the more involved it will be for the fab vendor to work with. This also includes cutouts and slots in the board. By keeping the board shape as rectangular as possible, you will save money on your fabrication costs. · Keep the components as uniform as possible: A PCB that has many different-sized components on it will slow down the manufacturing process. Each different component size requires different setups for the assembly line, so reduce these to reduce manufacturing time and expense. How to use PCB DFM Guidelines? Despite how important PCB DFM guidelines are, there are no generic guidelines that apply to every single type of PCB design. This means that designers must often use their best judgment concerning which guidelines to follow. Most of the time, however, designers don’t have to guess, since there are some guidelines that work well for most PCB types. For example, a designer can be confident that a PCB with copper traces should be checked for disconnected traces and trace violations, regardless of that PCB’s application. On the other hand, high-speed digital PCBs have DFM guidelines that don’t apply to other PCB types. If a PCB manufacturer recommends following certain DFM guidelines, designers should be ready to perform those checks.Wanna know PCB knowledge? Check and read for more.
PCB Knowledge ⋅ 08/19/2021 17:23
EMI PCB Design Guidelines
Digital circuits are getting faster and more powerful each year, and as a result, it's more important than ever to utilize proper design techniques and materials to reduce electromagnetic interference (EMI) in our PCB designs. Poor planning can lead to increased and unnecessary radiation, as well as reduced system immunity, which can wreak havoc on our devices. In this article, we will tell you everything about the EMI PCB design details. Please check and read the content we prepare below for more PCB knowledge. Let’s go!If you want to order PCB product, please check and custom your order online. How to optimize EMI PCB Design? As explained in the previous section, the likelihood that your board or the system on which it operates contains components or equipment that can be classified as radiators is very high. Besides, unless your circuit board is a stand-alone device, the power supply is directly or indirectly connected to the power supply, which is also a common source of electromagnetic interference. The purpose of the EMI filter is to reduce the interference introduced into your board from this source. EMI filters can be designed from a single component to a complex network with dedicated circuits to mitigate common-mode and different-mode noise. Some basic types of EMI filter design and how to use them are listed below. Once you have decided on a basic design, it will be necessary to optimize it according to the performance specifications of your circuit and/or board. For example, if your EMI filter is designed to drive other circuits or boards, you may be required to add additional filter elements for isolation, smoothing, or electrical parameter constraints (for example, fixed voltage or current). The extent to which you can meet these circuit requirements depends on the capabilities and capabilities of the PCB design and analysis tools available. What are the guidelines of EMI PCB design? As is the case for all circuit board designs, following good EMI filter PCB layout guidelines is essential for manufacturability. Again, the best design requires the adoption of the proper perspective. 2-D PCB Design Perspective When laying out your board, the first considerations are the locations for component footprints—whether from your design package’s library or uploaded from an external source—trace routing, spacing, or board edge clearance. · Ensure that pads and component libraries are matched.· Maximize spacing between adjacent elements—pads, traces, and annular rings—to minimize interference.· Partition components according to signal types.· Assure that trace widths and sizes are sufficient for the current capacities required.· Ensure that impedance matching is instituted where necessary for differential routing, maximum power transfer, etc.· Follow board clearance rules to facilitate depanelization.· Use shielding for high radiation devices.· Make good use of the silkscreen for component polarities and reference indicators to aid assembly. How to reduce EMI in PCB design? Ground planeThe ground plane is in many ways your first line of defense against the kind of noise produced by EMI, because circuits require at least a floating ground in order to work. In a PCB board, the ground plane is there to provide a 0 volt reference line to the power supply ground terminal for the return path of a circuit. Unlike the basin, however, when “ripples” are made, noise is produced, dipoles can form and the entire board can become an antenna. This is why the ground plane, that copper foil layer in your PCB, takes up as much of the cross-sectional area of the board as possible. Reducing EMI across your board starts with how effectively you utilize the ground plane. Trace layoutTraces are conductive paths on a board, which contain flowing electrons while a circuit is active—that means they are just a bend or cross away from creating a fully radiating antenna. Common best practices for trace layout include: · Avoid sharp right-angle bends. Capacitance increases in the 45° corner region changing the characteristic impedance and leading to reflections. This can be mitigated by rounding right angles.· Keep your signals separate. Keep high speed traces (e.g. clock signals) separate from low speed signals, and analog signals separate from digital signals.· Keep return paths short.· Route differential traces as close as possible. This increases the coupling factor, bringing influenced noise into the common mode which is less problematic for a differential input stage.· Use vias wisely. Vias are necessary because they let you take advantage of multiple layers in your boards when routing. Designers must be aware that they add their own inductance and capacitance effects to the mix, and reflections can occur from a change in characteristic impedance.· Avoid using vias in differential traces. If you must, use an oval anti-pad shared by the two vias to reduce parasitic capacitance.Wanna know PCB knowledge? Check and read for more.
PCB Knowledge ⋅ 08/17/2021 17:25
PCI Express PCB Layout Guidelines
PCI is a popular connection interface used for attaching computer peripherals such as RAM, ethernet, and network cards, I/O cards to a motherboard. It was introduced in 1992 with the aim of supporting complex data transfers and evolved its purpose way beyond the same. The PCI bus was made to be available in 32-bit and 64-bit versions. The PCI technology has undergone various updates to evolve into PCI Express which is still under development.、 In this passage, we will tell you everything about PCI Express and please check and read our content for more professional knowledge.If you want to order PCB product, please check and custom your order online. What is the working principle of PCI Express? PCI Express is a serial connection that works more as a network than as a bus. Instead of one bus handling data from various sources, it includes a switch controlling various point-to-point serial connections. Such connections will spread outward from the switch leading to the devices where the data is required to go. As each device has its own dedicated connection, devices no longer share bandwidth as they do on a conventional bus. What is the evolution of PCI? The PCI specification was utilized by the computer industry from 1992 to 2004 as the primary local bus system within a computer. It standardized how PCI expansion cards ranging from a network card to a modem can be self-installed and exchange information with the CPU. CPU processor frequencies rose from 66MHz in 1993 to well over 3GHz in 2003. The existing PCI bandwidth had trouble keeping up with the I/O processing capabilities of the new processors which is what led to the development of PCI Express spec. From 2004 Intel introduced its PCI express spec which kept the core of PCI’s software infrastructure and wholly replaced the hardware infrastructure that could handle higher I/O requirements of processors. PCI had parallel interconnect whereas the new PCI Express has a serial point-to-point interconnect capable of high bandwidth transfers. What are the guidelines of PCI Express PCB Layout? Given are some PCI Express layout and routing guidelines that enable efficient design. Trace routing specificationsWhen compared to most high-speed devices available, PCIe generations permit longer trace in their layout routing specs. Every generation comes with its own specifications on impedance and maximum trace lengths for varying data transfer rates. These should be closely followed to obtain the required performance. The exact routing specifications will depend on which PCIe generation you are utilizing for your design. Trace lengths in Gen 1 and Gen 2 both let RX (received) and TX (transmitted) signal traces reach up to 21 inches in length. When it comes to Gen 3, trace lengths can only go up to 14 inches on signal trace PCIe planes. While each TX trace pair can have only two vias, RX pairs can include up to four vias to maintain impedance within the required specification. A COM Express carrier board allows for trace lengths of up to 9 inches for Gen 1 and 2 when the traces are being sent to a PCIe slot. The tolerance for differential impedance values also differs among the various PCIe generations and bus standards. The values may be different for each bus and generation combination, but they can be found in the COMCDG Rev. 2.0 specification. When keeping the impedance of microstrip traces within specified tolerances, you need to use PCB design software to include controlled impedance routing features. The interactive routing tool in the software will ensure your traces are spread out with the right spacing and geometry. Stack-up and groundingStandard PCIe boards incorporate a 4-layer stack-up with two interior power planes and two signal layers on each surface. Each power layer can be brought to varying bias levels based on device requirements. Other designs for PCIe boards go for a 6-layer stack-up with two signal layers that run between two power layers. In another scenario, one of the power planes can be replaced with a ground plane. In both cases, you can achieve better immunity to EMI by routing signal traces on the inner layers. You can even route traces with varying data rates on different layers. For instance, in a mixed-signal board such as the ones in a WiFi device on a PCIe card, you can route digital traces on the outer layers and the RF traces on the inner layers. The ground/power planes will effectively block noise from reaching the sensitive analog signal traces. Regardless of the stack-up used, you will need to meet the overall board thickness standard of 1.57 mm or 1 mm for PCIe Mini. You will also need to consider standard high-speed design techniques as the Gen 1 of PCIe operates at 2.5 GHz clock speed with future generations increasing in speed. PCI differential pair routingRouting around obstructions and component placement and via placement on a PCIe board is really important. There needs symmetric routing to pins, pads, and components along with the BGA breakout routing. Differential pairs need to be tightly coupled throughout their entire length, with variations in one trace due to vias, pads, or components being mirrored in the other trace. This ensures crosstalk is minimized throughout the differential pair length. Similar practices need to be applied while routing BGA breakouts or breakouts from other components. As the performance requirements of high-speed PCB design continue to increase, it becomes critical to ensure that your design meets PCIe layout routing specifications. PCB board manufacture for PCI requires a great deal of expertise and experience that only a few manufacturers can provide.Wanna know PCB knowledge? Check and read for more.
PCB Knowledge ⋅ 08/16/2021 17:35
Parasitic Capacitance in PCB
Parasitic capacitance or stray capacitance is the result of a virtual capacitor formed between two traces separated by a dielectric. It occurs due to the potential difference generated when the current-carrying traces run in close proximity. To learn more, read the role of trace current capacity in PCB design. This effect is even possible if the conductors are appropriately insulated. It is not possible to avoid parasitic capacitance since no electrical circuit is ideal. In this passage, we provide all about parasitic capacitance in PCB please check and read the content below.If you want to order PCB product, please check and custom your order online. How to calculate parasitic capacitance in PCB? Parasitic capacitance is an inherent property of the conductors. It is the storage of per unit change in electric potential. The parasitic capacitance is calculated as C= q/v. Where C is the capacitance in farads, v is the voltage in volts, and q is the charge in coulombs. · For a constant electrical signal that does not change over time, dv/dt = 0 which means, no change in potential; hence i =0.· If there is a capacitor in the circuit loop, dv/dt will converge to a fixed value, i.e., change in potential, resulting in a current flow; hence i ≠ 0. Trace capacitance calculationThe capacitance of a parallel plate capacitor is given by C= (kA/11.3d)pF. Where C is capacitance, A is the plate area in cm2, k is the relative dielectric constant of board material, and d is the distance between the plates in cm. What is the effect of parasitic capacitance in PCB? The parasitic capacitance effect is a matter of concern in high-frequency circuit boards. While operating at low frequencies, parasitic elements can be ignored since they do not really impact system functionality. Every pad in a circuit board has its parasitic capacitance, and every trace has parasitic inductance. Pads also add their parasitic resistance that stimulates IR losses. Parasitic capacitance can exist between conductors on PCBs, bare boards, PCBAs, assembled boards, and within component packages, especially surface mount devices (SMDs). Since intrinsic capacitor plates have a potential difference, there is a chance of current flow. It does not matter whether the charges are stored between the capacitor plates; the current will not flow until there is a potential difference. As soon as this potential difference increases, a corresponding decrease in electron flow towards the load can be observed for the desired signal path that negatively impacts signal integrity. What are the differences between parasitic capacitance and stray capacitance? The term stray capacitance is often used interchangeably with parasitic capacitance. However, parasitic capacitance accounts for the fact that it will hamper the circuit operation, while stray capacitance accounts for how unwanted capacitance is introduced. What is stray capacitance?Stray capacitance doesn’t always get induced due to the virtual capacitance formed between two PCB conductors but also due to the effect of the surrounding environment. Hence, it is termed as stray capacitance. What is parasitic resistance in a PCB?Parasitic resistance exists in series along traces or as a shunt between the conductive elements. What is parasitic inductance in a PCB?Parasitic inductance exists along a trace and exhibits the behavior of storing and dissipating electrical energy, like an actual inductor. All conductors are inductive, and at high frequencies, the inductance of even relatively short pieces of wire or PCB traces may be important. Where R is the wire radius, and L is the length. How to find the inductance of a PCB trace?Trace inductance increases with trace length and lack of ground plane. What are the causes of parasitic resistance in PCB? At high-frequency, current flow in a circuit board is affected by the parasitic capacitance. Since capacitors are tend to become conductors when frequency increases. Note that when frequency increases, the capacitor will act as a resistor of very small value (approaches to a short circuit), resulting in excessive current flow. Zc = 1/2πfc ; fc = 1/ωc therefore, as frequency increases, Zc also increases. Parasitic capacitance can give you chills during high-frequency operation since a capacitor acts like a wire at an infinite frequency. This is the reason why it can accidentally connect the reference plane of any PCB board to the chassis. Parasitic capacitance effects could be crosstalk and noise, undesirable feedback from the output, and the formation of resonant circuits. So, it is essential to give attention to the overall PCB design, specifically to the layout. A good layout should take utmost care while placing a conductive body by the side of another conductive body. Parasitic elements include inductors formed by package leads, long traces, pad-to-ground, pad to power plane, and pad to trace capacitors, including interactions with vias, etc. Understand parasitic elements as parasites, a threat to your circuit performance.Wanna know PCB knowledge? Check and read for more.
PCB Knowledge ⋅ 08/16/2021 17:30
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