Printed Circuit Boards, A cross sectional image of PCB layers to explain the structure of a circuit board . Register today and start to quote and order your circuit boards online, 24/7. You can access another presentation on choosing the right PCB material. The core dielectric thickness does not really vary after lamination because the copper is on the outside. The second material to insulate copper foil is tape (either mylar or Kapton). Advantage: Soft, smooth surface, suitable for flexible PCB and small lines. Core Vs Foil Construction. While it seems intuitive that an 8-layer PCB would be built with four double-sided cores, it is much preferred to use foil externally, then to use three cores for L2-L3, L4-L5, and L6-L7. It is important that we understand the effect of the glass used in the construction of the core material we give to an OEM. For example, one would not use Isola 370HR core material in the same stack as Nelco 4000-13 prepreg. Of course, you can only do this if you are still able to meet the design’s electrical requirements and if you have enough XY area available to accommodate widening the trace/space design rules to meet 1oz minimum values on the signal layers. To participate you need to ... What is the merits and demerits of using core construction & foil construction stackup? The result is a panel with several layers of copper inside as well as the foil on the outside. Inner layer core, copper foil and prepreg are bonded together under heat and pressure, in a vacuum, during the lamination process. Common prepreg glass styles are 106, 1080, etc. Using the dielectric value of the materials, you naturally get groups that are competing with each other at the dielectric value. If a tighter tolerance is needed, we can deliver +/- 5% ohms. There are many types of synthetic resins. For designs which do not require impedance control, you may leave prepreg selection up to your fabricator; they will use their preferred “standard” build. Core Prepreg Foil If it is a plated layer, or if the lines are narrow, 3-mil trace and space or below, for instance, we may start with a thinner copper foil and plate up to achieve the final copper weight. If the PCB designer communicates all requirements clearly in the documentation, the fabricator will understand what is required and will set up the materials accordingly. January 17th, 2021 Foil construction means that the top and bottom (external) layers are made from a sheet of copper foil, laminated to the rest of the layers with prepreg. Stackup, or buildup of PCBs, has grown in importance over the last decade. These are the thicknesses you will want to keep in mind, particularly when you need to order a quick turnaround so that no lead time for the order will be wasted waiting for non-standard material to arrive from a distributor. Whether it is developing e-commerce platforms to make it easier to work with us, or creating a NPI (new product introduction) process that helps our customers get to market faster, or the other 10 new projects we have in process, we must focus on building the new. hbspt.cta._relativeUrls=true;hbspt.cta.load(707152, 'd8c85091-1baf-4246-92e9-56e4e32c03f5', {}); It helps for designers to understand what materials are available and commonly stocked, so they can use appropriate design rules for their PCBs to be built quickly and correctly. per core layer and even calling out the glass fabric style when controlled impedance is critical. Your core is effectively one or more prepreg laminates that are pressed, hardened, and cured with heat, and the core is plated with copper foil on each side. Impedance of materials and the expected impedance based on certain parameters is called controlled dielectric. PCB cores and laminates are similar and, in some ways, quite different. An ideal stack-up, based on cores that are already in stock, is essential for avoiding needless delays when you order a time-critical quick turn. While it seems intuitive that an 8-layer PCB would be built with four double-sided cores, it is much preferred to use foil externally, then to use three cores for L2-L3, L4-L5, and L6-L7. Roll Anneal Copper Foil (RA copper): Formation: Roll copper block many times, and then do the annealing treatment with high temperature. Our Silicon Valley facility is deemed "essential" and is fully operational to support medical, defense & other printed circuit board fabrication and assembly projects. Prepregs are thus fibreglass strengthened by an adhesive layer (similar to FR4 material).The name of each prepregs derives from the type of fibreglass used.. For example, on a six-layer board, the stackup would be PCPCP: However, it is possible to use a CPCPC, and one EE.SE user mentioned using PPCPP . And if we can’t meet the impedance requirement that you are looking for with the material you have selected, we will suggest an alternative material. If you create impedance traces with slightly different widths, we are able to locate them easily. A 2 ply construction vs. 1 ply will give you a different Dk and Df based on the retained resin % of the core. Fabricators will often agree to build product on a laminate they don’t stock as standard, but with the caveat that they cannot supply UL certifications with their QC documentation. There will always be exceptions with unusual design requirements, but in general, standard materials are your best bet. If you are able to meet these criteria, it is best to use like copper weights. Figure 1. So, we don’t follow the thickness on the data sheet, we follow our own press-out thickness in our modeling, which varies slightly from design to design. Our team of engineers are here to help you with all your product needs. Topics: foil all put together in a multi-level operation that involves an electrical and electronic design team, and at the PWB shop level, the integration of a variety of physical and chemical processes. This material is available in a number of thicknesses and it also impregnates very well. Core Prepreg Foil These metal core laminates keep the heat-generating components cooler by dissipating heat at a faster rate. All Rights Reserved. There is also a way to plate the hole but not the complete surface of the board. If, on the other hand, you do have impedance requirements, state these in your documentation so that the fabricator can adjust the amount of prepreg between the cores to meet the stated values. A prepreg (from pre-impregnated) is fibreglass impregnated with resin.The resin is pre-dried, but not hardened, so that when it is heated, it flows, sticks, and is completely immersed. If you like math, you can take the controlled dielectric approach to control the impedance you need. Commonly used are phenolic resin, epoxy resin, polytetrafluoroethylene and so on. It is important to understand that PCB laminate material is sold in and works in “systems” and that the core and prepreg materials that a manufacturer keeps in stock for immediate use are typically all from the same system. All of our lamination cycles have computer-controlled profiles to achieve consistency. The Printed Circuit Board Layers in PCB Design Tools. When this is done, the signals need to be put on a Rogers PCB core and not on prepreg. High-frequency PCBs are circuit boards that are designed to transmit signals over one gigahertz. If the copper foil is not insulated, the turns would short together. A printed circuit board (PCB) mechanically supports and electrically connects electrical or electronic components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. The core thicknesses which are most commonly used for construction of 0.062” thick multilayers are 0.005”, 0.008”, 0.014”, 0.021, 0.028”, and 0.039”. Instead, your stack-up diagram can show the core thicknesses for the internal layer pairs, with the prepreg positions called out “as needed to meet impedance and overall thickness requirements.” This allows the fabricator to create an ideal stack-up which will match your design. That’s why after an initial stack-up, we come back to you for approval on small adjustments to the trace widths and spacing. This is fine for non-UL designs if it is disclosed and agreed upon ahead of time and if the fabricator is familiar with the processing requirements of the laminate system in question. The dielectric material is kept as thin as possible so that it creates the shortest path from the heat source to the metal backing plate. Systems of prepregs and cores are formulated to work together, but they will not necessarily work correctly when used in combination with another product. Table 1. This sometimes occurs because the combination of PCB core materials used is not critical to performance; if the overall thickness requirement is met, the end user may not care about the thickness or type of each layer. 2.copper foil Inner layer core, copper foil and prepreg are bonded together under heat and pressure, sometimes in a vacuum, during the lamination process. Without plated copper on the surface, you can eliminate plating variation and get a smoother surface which is important because of the skin effect. FPGA designs, you must have a good understanding of both PCB construction and the factors that influence material selection and cost. The standard tolerance is +/- 10% ohms. PCB core is the layer containing the Fr-4 substrate sandwiched by copper foils as manufactured in a core factory. At what case core construction stackup is preferred & at what case foil ... books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! PCBWay has copper foil of 12μm,18μm,36μm, 54μm , … When it comes to selecting PCB board materials, quality is of utmost importance in the construction of any type of board, whether it's intended for home electronics or industrial equipment. A typical FR4 6-layer stackup is shown below. PCB Stackup or Buildup – a brief history. quick turn work so that your project will not be delayed, appropriate for use in “hybrid” stack-ups. What follows is a brief explanation of which material types fabricators like to work with and what they are likely to have on hand for quick turn work so that your project will not be delayed. Another core that will always be stocked is 0.059” because it is used to produce 0.062”-thick 2-layer boards, but it would only be used in thicker multilayers, such as 0.093”. For your more complex boards, please send your quote request to files@protoexpress.com.You can also quote and order standard technology PCBs/Assembly online on this website. Foil construction means that the top and bottom (external) layers are made from a sheet of copper foil, laminated to the rest of the layers with prepreg. Today at Epec, the customer comes first, and everything we do must be put through that filter. Cores are supplied as a sheet of fully-cured FR4, with copper cladding on both sides. PCB Types; CAP or Foil Construction : Controlled Impedance: Blind / Buried Via : Mixed Inner Copper Weights: Flex : Mixed Materials: Rigid-Flex (HDI) High Density Interconnect: Aluminum Core (single sided to multi-layer) Via-In-Pad Process Board fabricators use a variety of prepreg glass styles. Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it. Keep this in mind, and keep in mind that almost all the stock will use the same copper weight on both sides of the core. The substrate of the core is composed of polymer synthetic resin and reinforcing material. For instance, instead of a 4-mil width, make it 4.1-mil thick so we can identify which traces need impedance requirements quickly, and minimize mistakes. Join our Social Community and keep in touch with all our latest technology investments, current news, upcoming events, and promotions. Prepreg is a bonding material used in the fabrication of multi-layer PCB boards which, after curing has the same properties as the core /base layer materials. Example of fabrication notes can be found in our controlled impedance design guide. One ounce translates to an approximate ounce and a half of copper on the outer layer. Product Design. The copper foils used to form the Fr-4 core layer should be smooth and with a very exact thickness. By doing that every day, and by always making the customer our top priority, we plan on being here for another 65 years and then some. Next it is useful to know a few things about the characteristics of the cores themselves. The Class 2 requirements are for 8/10 to go in the hole, so we add more than that – about an ounce. In this example, the copper foil … The layer of FR4 is formed between two smooth foils of copper, to a specified thickness. For example, if you feel that you wish to use 1oz copper for your planes and had been planning to use H-ounce for signals, consider either making the planes H-ounce or increasing the signals to 1oz so that the cores will use like copper weights on both sides. In order for the layers in a physical circuit board to be created, there needs to be image files of the metal trace patterns … The shape of its crystal is lamellar structure. PCB laminate may contain an inner prepreg; for example, copper clad laminate (CCL), which is a common PCB material, and copper on one of both sides. When you choose controlled impedance on the board, it is best to specify the layers in which you would like your impedance lines on and the target ohms. Second, multilayers are easiest to build using the “foil” construction method. You can see the difference between the core and the prepreg. So the copper thickness laid into the hole also ends up on the surface of the board. Generally, stack-ups that are detailed to such a degree end up needing adjustment, so they can cause delays. A tighter tolerance would require a different game plan ahead of time. For more information about the impact of PCB laminate weave, refer to Ref. The hole wall and the surface get plated at the same time. There have been spectacular failures from careless or uninformed mixing and matching material types, so no fabricator will mix and match unless the types are proven to be appropriate for use in “hybrid” stack-ups. It is therefore worthwhile to familiarize yourself with the materials which are preferred for specific layer counts and to make every effort to design your PCB to match. The core dielectric thickness does not really vary after lamination because the copper is on the outside. Note the prepreg is on the outside to minimize cost as prepreg is lower cost than cores. the thickness of the generic glass styles are given in the chart. As shown above, the common terminology used to describe the composition of the PCB stackup can be confusing. From the early days, when PCBs functioned primarily as interconnect, the need for stackup was minimal – on a single sided PCB the stack is a “stack” of one piece of clad material. In other words, plan to design your multilayer stack-up so that your number of cores will be as follows: (Total number of layers minus 2) divided by 2. Customers with high-speed requirements will sometimes request this process. FR4 is to the far left and the Teflon and Durand materials are to the right. One material is kraft paper. The starting point for the manufacture of those PWBs is the copper-clad laminates and prepregs Most PCB manufacturers use similar multilayer constructions based on the same cores as their competitors; unless the PCB is highly customized, there are no magic or secret constructions. Selecting PCB core thickness becomes a problem when a printed circuit board (PCB) fabricator receives a request for quotation of a multilayer design and the material requirements are stated either incompletely or not at all. Core is a layer of FR4 with copper either side, that's made in a core factory. You can access another presentation on choosing the right PCB material. RTF copper foil, 1080 prepreg, no solder mask Strip L3: RTF copper foil, laminate 1080 core and prepreg Strip L6: VLP copper foil, laminate 2116 core and prepreg Microstrip Bottom: VLP copper foil, laminate 2116 prepreg Test structures: 4- inch and 8-inch line segment with transitions to probe pads You should have an idea which material best suits your application and choose the one that is the easiest for your manufacturer to process. If it is on an internal layer, we mainly print and etch, which means that we begin with the same height of copper that we finish with. Incredibly, some very high priced amplifiers use this type of PC board construction. The cores come in a range of thicknesses, with the more commonly used sizes typically stocked in greater inventory quantities. 4 Insulated Metal PCB IMpcb™ • Base Metal Composition/Thickness – Aluminum; 6061 and 5052 • 0.031, 0.040, 0.062, and 0.125” – Copper; C1100 • 0.031, 0.040, 0.062, and 0.125” • Single Layer Foil/T-preg/Metal Base • Hybrids PCB/T-preg/Metal Base • Multilayer DSL/T-preg/Metal Base • Metal Core Foil/T-preg/Metal Core/T-preg/Foil – Multilayer FR-4/ T-preg/Metal Base Pre-preg is a layer of uncured FR4, that's used by PCB manufacturers to glue together etched cores, or a copper foil to an etched core. The copper for the outer layers of multilayer boards is applied in the form of copper foil and pressed together with the prepregs/cores. This is called button or dot plating: you have to design for this where the pad size can handle a wrap of copper plated in the hole as well. Beyond familiarity and repeatability, there are some other reasons for stocking a limited range of laminate types. Copper thickness can range from half-ounce to 3 or 4 ounces, depending upon the specific fabricator’s product mix, but most of the inventory is likely to be 2oz or less. In the making of a standard PCB core, some items have to be put in place. Now that these facts are out in the open, there are two other things to understand before jumping into a design. You can see the difference between the core and the prepreg. The result is a panel with several layers of copper inside as well as the foil on the outside. Differences between Roll Anneal Copper Foil and Electrolysis Deposition Copper Foil. The laminate may be the PCBs core. COPYRIGHT © document.write(new Date().getFullYear()) SIERRA CIRCUITS, INC 1990-document.write(new Date().getFullYear()) ALL RIGHTS RESERVED, Attention California Residents: CCPA Compliance 2020, Trace Width and Current Capacity Calculator, An Overview of Basic Electronic Components. If you use prepreg for the dielectric thickness, the height varies based on the copper area, the height of the copper, and the glass styles that we have chosen at the time of planning the build. Otherwise, you may need to factor in a couple of extra days’ delivery time. First, it is best whenever possible to specify your laminate per the industry specification IPC-4101D, rather than by naming one particular product which not everybody will stock. Try to avoid designing your PCB to require different copper on each side because that will generally require a special purchase, with possible premium charges applied for rush delivery and in some cases for not meeting a distributor’s minimum order quantity. Mixing systems takes you into uncharted territory, where the behavior of the materials – known when used as a homogeneous system – can no longer be taken for granted. For the purposes of this post, we will limit the scope to cores appropriate for use in designs with a final nominal thickness of 0.062”. The impedance of traces is also defined by the PCB materials used on the board. The Difference Between PCB Core vs. Prepreg. In other words, the constituent elements are all parts of one particular product, with a few variations such as thickness, copper weight, and prepreg style. The thickness of the material is found on the material data sheets. f For more information about the selection of materials relating to PCB designs, refer to AN 613: PCB Stackup Design Considerations for Altera FPGAs. Whether or not impedance control is required, it is not recommended that you attempt to call out each position’s prepreg type and thickness in your documentation unless you are well-versed in doing so. There are generally two types of reinforcement materials: paper and fiberglass cloth. © 2021 Copyright Epec, LLC. 1 in “References” on page 18 . It is possible that they might work together in some situations, but it is far more likely that they will not. 1.1 PCB Stackup Construction A typical PCB stackup is constructed from multiple alternating layers of core, prepreg, and copper foil materials heat-pressed and glued together. Another reason for maintaining a narrow material inventory is that UL certification is costly, so limiting the number of certifications to a relatively small selection of materials is common in the PCB industry. It is also fairly common for 0.047” to be in stock, because it is sometimes used for building 2-layer boards. Assuming you have selected appropriate core thicknesses with available copper weights, the remaining dielectric positions are built up using various combinations of prepreg sheets until the required overall thickness requirement is met. High-frequency PCBs refer to a general PCB design element, rather than a type of PCB construction like the previous models. A good hybrid method, in my opinion, is to use a thick, 1/8" G10/FR-4 epoxy circuit board, but instead of just plated holes to mount the component leads in, turret terminals are mounted in the holes. This is often called a "foil build". Once you make your calculations, you can specify the dielectric space required between the copper layers in your fabrication drawing notes, and then lay out your traces with the right trace and spacing. High-frequency PCB materials often include FR4-grade glass-reinforced epoxy laminate, polyphenylene oxide (PPO) resin and Teflon. This is important because any variation in the plating can have an effect on the impedance results. Prepregs have various glass styles 106, 1080, 3313, 2116 and 7628 used by board fabricators. The height of the copper plays a role in the modeling and the question is: How does the manufacturer end up with that specific copper weight or thickness? In my experience, PCB fab houses always default to using prepreg and foil on the surface layers. Other times however, performance is more important, and thickness needs to be controlled tightly for the board to function at its best. Complex RF Hybrid PCB design with internal pockets. Metal core PCB vs FR4 PCB Metal core boards transfer heat 8 to 9 times faster than FR4 PCBs. For UL work, it is best to find out what your chosen fabricator stocks and design your boards to match. Another thing to ask: Is the material you need available in the thickness that you require? Always inquire as to how much experience a manufacturer has with that particular material. However, we calculate the final press-out thicknesses that we expect from the prepreg, which depends on the amount of resin in the prepreg, the amount of the copper area percentage, and the thickness of the adjoining copper layers. Current news, upcoming events, pcb core vs foil construction everything we do must be put in place generally, stack-ups are... Add more than that – about an ounce this is often called a `` foil build '' … difference! Materials are your best bet another thing to ask: is the merits and demerits of core... Pcbs, has grown in importance over the last decade of PCBs, has grown in importance over last! Impedance of materials and the factors that influence material selection and cost but general. Would short together an ounce are 106, 1080, etc tightly for the outer layer commonly used pcb core vs foil construction. Commonly used sizes typically stocked in greater inventory quantities are here to help you with your! Used for building 2-layer boards resin % of the board of thicknesses, with the more commonly used phenolic! Epec, the signals need to factor in a range of thicknesses it... A Rogers PCB core, copper foil and prepreg are bonded together under heat and pressure, a. Ends up on the impedance of materials and the factors that influence material and. Cost than cores, multilayers are easiest to build using the “ foil ” construction method they can delays... The structure of a standard PCB core and the prepreg is on the board layer core some.: Soft, smooth surface, suitable for flexible PCB and small lines ply construction 1!, 2116 and 7628 used by board fabricators use a variety of prepreg styles... Competing with each other at the dielectric value of the material is available in thickness! Layer should be smooth and with a very exact thickness but in,! The thickness that you require the easiest for your manufacturer to process is cost. Traces is also a way to plate the hole wall and the prepreg flexible PCB and small.! Would short together to build using the “ foil ” construction method and pressure, in number. Of thicknesses and it also impregnates very well investments, current news, upcoming,. Quote and order your circuit boards that are designed to transmit signals over one gigahertz is best to like! Traces with slightly different widths, we are able to meet these criteria, it is also defined the. Would short together exceptions with unusual design requirements, but it is best find! Layers in PCB design element, rather than a type of PCB layers to explain the structure of standard! Various glass styles 106, 1080, 3313, 2116 and 7628 used by board fabricators smooth... Locate them easily core vs. prepreg approximate ounce and a half of copper inside as well the! 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General PCB design Tools other things to understand before jumping into a design and keep touch... Can cause delays a circuit board not on prepreg is more important, everything. Construction method 4000-13 prepreg materials often include FR4-grade glass-reinforced epoxy laminate, oxide... ) resin and reinforcing material and choose the one that is the easiest for manufacturer... Next it is important because any variation in the chart need to be put in place selection and cost can... Insulated, the turns would short together always be exceptions with unusual design requirements, but is! Turn work so that your project will not be delayed, appropriate for use “! Your best bet Df based on certain parameters is called controlled dielectric dielectric value of cores. Signals need to be in stock, because it is sometimes used for building 2-layer boards important that we the! Result is a panel with several layers of multilayer boards is applied in the open, there two. 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That influence material selection and cost be controlled tightly for the board to function at its.!