These reflections are referred to as ringing. Simulated traces and PCB stack-up. Impedance Calcuator PCB stackup, signal integrity and controlled impedance: Signal integrity tools: Stackup design. The microstrip is a very simple yet useful way to create a transmission line with a PCB. Controlled Impedance PCB Parameters and Stackup. 19 mm, a difference from the 0. In both cases, you’ll need to enter your stackup information into the calculator to get accurate results. Reduced space and weight. Some fabricators can advise on track geometries if you supply them with your preferred stackup. It's important to know what a differential impedance calculator won't tell you, as well as what you need to account when designing your PCB stackup: Propagation Constant and LossesPCB impedance calculation and Track geometry design Example of Microstrip (the tracks on TOP and BOTTOM layers) impedance calculation 90 Ohms Differential / 55 Ohm Single ended for: Track width: 11mil / Copper foil 18um (0. Designers can utilize layer stack management and routing to control board impedance. Always measure the bend radius from the inside surface of the bend. 11. It is tough to find and fix every single fault in a circuit board. Enable the Stack Symmetry option in the Properties panel. $egingroup$ @EricMatevosian JLCPCB does 4-layer boards very cheaply, with two choices of impedance controlled stackup (7628 and 3313 prepreg) at no extra cost. Defining Microvia Structures. Learn more about the rules-driven design engine in Altium Designer. Planes, in Multilayer PCB’s, provide significant reduction in radiated emission over two layer PCBs. It provides vital information like material thickness and copper weights. Below is an example of an impedance. Link to PCB stackup Speedstack enhanced with Projects; Via stub checks; Via pad/antipad coaxial calculation . Speedstack PCB stackup design tool is a packaged combination of the Si8000m field solving impedance calculator and the Speedstack professional layer PCB stackup design system. Contents. Just Try "Saturn PCB Design" tool (FreeWare). Stack-ups, also known as build-ups, carry the details of trace width for different controlled impedance traces such as 50 ohms or 100 ohms differential. The two conductors are separated by a dielectric material. Layer 5 - Ground. Figure 2. Every board designer would require supporting PCB design tools to simplify the design process. In a 4-Layer PCB board, You have to insert the parameters, depending upon the capabilities of the manufacturer of your liking; Thickness of the PCB (Combining all the layers) – Can be from 0. Dielectric material (partially cured) is used to bond copper cores and copper foil in the layer stack-up. For an embedded (internal) microstrip, the formulas provided in paragraph 4. This decision is based on the type of stack-up used in the PCB design. It covers both single-ended and differential traces and is based on the. A typical value of 1/7 Lambda has been set by default. Stack Exchange Network. g. 2. PCB stack-up with controlled impedance requirements. An RF PCB design is a bit different from a conventional board. So you computed a 100Ω impedance and it gave you 6/9mil for a differential pair. The cost index provides a relative idea of the cost compared to another layer order. 2116 Prepreg 4. 8-layer PCB stackup question. This integrated pcb stackup calculator streamlines impedance optimization for high-speed designs. My problem is to calculate overall impedance (independent of layer stackup topologies). Converts short and long line . core materials is easiest when you use PCB design software with an integrated stackup and impedance calculator tool. Below is an example of HDI stack-up generated using the Stackup Designer. 0+N+0. It defines the acceptable variation between the maximum and minimum limits. ALTIUM DESIGNER. We will show you how our Stackup Designer, Impedance Calculator, and Material Selector work. Add a damping resistor near the source. Stick to these design rules when you’re designing your stack-up. It renders accurate results suitable for use in circuit board manufacturing and. 6 layer rigid-flex PCB stack-up with air gap 8 layer rigid-flex stack-up with air gap. PCB Stackup or Buildup – a brief history. You will then be presented with a table representing the suggested stack-up for that type of substrate. Speedstack PCB stackup design tool is a packaged combination of the Si8000m field solving impedance calculator and the Speedstack professional layer PCB stackup design system. Once you enter the values of all the required. Use an impedance calculator when planning out your stackup to set up fixed impedance controlled trace widths later on. PCB Impedance-Calculation: Help with the dimensioning of the impedances of your circuit board. PCB stackups are created by using combinations of the aforementioned four types of transmission lines. The copper and dielectric fabrication layers are configured on the Stackup tab of the Layer. A stack-up describes the construction of a multilayer board in sequential order. Stackups must be kept symmetrical, so there must also be 4 mils of dielectric between layers 7 – 8. The thicker the PCB stiffener is, the more support it will offer. 1. g. I cut the side of the PCB to verify the material thickness and measured 0. 1 mil when tracks are inside. IPC 6012 CLASS 2. Make sure you understand the factors that influence transmission line impedance , and. The material thickness between layers 1 – 2 should be 4 mils, max. One thing is for sure: When you are routing a high-speed PCB design you are going to be working with. There are some advantages to using a. This is an 8-layer HDI PCB with a 48 mil total thickness. 5. @ahbushnell The main calculation I used is the one from Saturn PCB Toolkit, and the result is largely similar in "coplanar wave" with the gap used, or "miscrostrip" configuration. The Altium Stackup Manager not only allows you to define the stackup, but you can also create impedance profiles for various SE and DIFF impedances. 9 is an example of the amount of information that must be included in the stackup drawing to insure the PCB is correctly fabricated. This simple impedance calculator had a number of limitations, including requiring return paths to be implemented by plane layers, only supporting symmetrical stripline board structures and no support for differential impedance calculations. 01) and dielectric constant (3. An ideal 6-layer stack-up is shown in. L1 and L4 are the outer layers, L2 and L3 are the inner layers. Now I'd like to get into this topic and the first task would be to create a ~ 10cm board to board interconnect flex PCB with 90 ohm (USB) and 100 ohm (LVDS) controlled impedance traces on it. I used the KiCAD PCB calculator, asked the PCB manufacturer about the tangent loss (0. 24 hours a day, 7 days a week. 87 mil) is nominal thickness of 7628 prepreg. Cross-hatched copper plane in a flex stack-up for controlled impedance. In air gap construction, the flex layers are kept as several independent sets of no more than three layers per set. PCB stack-up design. 25. RLC Resonant Frequency and Impedance Calculator. Advanced PCB transmission line design and stackup. Enter the relative permitivity, width of the trace, the ground plane spacing, and the substrate thickness to calculate the characteristic impedance. 0994mm vs. Following images present PCBWay's default layers stack. Polar UK: Speedstack PCB – PCB stackup / Impedance field solver package. 4+6+4 HDI stackup Layer buildup/stackup reference. Bittele Electronics Achieves ISO 13485 Certification; Bittele speeds up its quick-turn pcb assembly service;This calculator uses the frequency, either entered or calculated from risetime, to find the full wavelength in air and divide from that. Here’s a PCB design for assembly checklist you can refer to before you proceed with the assembly process. L1=Ground, L2=signal/transmission lines, L3=Power, L4=signal or. Linked to our 2D field solver-based impedance calculator to design high-speed traces; See what Laurent Nicolet has to say about the future of PCB etching. Hot Network Questions Fixing wrong ideas about coefficients (e. where Z 0,surf can be computed as specified in Eq. Blind vias exist from: Layers 1 to 3; Layers 1 to 4; Layers 5 to 8 Stackup Editor Zoom: Hybrid Design Shield: Mask:. This will help you get better electrical continuity. Since it directly references the stackup information and has a. It is performed to achieve maximum power transfer and reduce the signal reflections from the load. Good tensile strength: Even though they are flexible, polyimide board materials have commendable tensile strength. Altium Designer provides you with much more than just an impedance calculator for PCB stackup design. Panasonic Megatron 6 and Rogers 4350B laminates are more widely used in the industry due to their high-speed reliable characteristics. Si9000e – PCB insertion loss field solver. JLC's [url=. HDI stack-up: 16-layer board with through-hole, buried and staggered blind vias ITEQ Stackup Pro TM. Note: The results are only for approximation and rough estimation, the final values and the. 2 The PCB stack-up design 2. ) Hide We may add extra cost for these special options which will be confirmed after review. 8-layer HDI stack-up generated using Stackup Designer. But if your stackup is such that one signal and one plane layer are a pair on either side of one of the original thin panels. One: A quick solving calculator lets you seek a target impedance by varying any one parameter, it could be line width, stack height or Er; you choose the variable and set the goal seek. How do you calculate PCB trace impedance? PCB trace impedance depends on trace width, trace thickness, substrate material (e. It is the ratio of voltage and current amplitudes of a single wave propagating along the line in the absence of reflections from other directions. As you route traces on a real board, they can couple to other traces and conductors capacitively or inductively. The toolset that is used to create the stackup then uses Maxwell’s equations to precisely calculate parasitic inductance and parasitic capacitance. 15 mm min track/clearance/annular ring and 1. The elastic nature of flexible PCBs allows for placement around edges and folds. Stack-up is an arrangement of board materials in sequential order. 6-layer rigid-flex stack-up: 6 layers with 3rd and 4th layers as flex. In this phase, the design is entered into the schematic tool (Altium, Allegro, etc). 1 of the Microstrip Calculator using H2 in place of h, εr,eff can be computed as specified in Eq. But in general do these things: Use a Sig/Gnd////Gnd/Sig stackup for more consistent impedance at top and bottom. Calculation of impedance and trace width. Used interchangeably with controlled dielectric by some PCB designers. Similar to the Saturn tool, this capability allows you to experiment with the stackup and track dimensions to estimate impedances. 125. Freedom of design. The build-up provides the following information: The copper thickness and weight. For Si engineers & PCB technologists. GND L3. 6- layer PCB stack-up. 05 vs 4. 6 for 7628) 3313 thinner prepreg between top layer and inner layer (0. You will then be presented with a table representing the suggested stack-up for that type of substrate. The side and top view of a dense PCB layer stackupThe flexible PCB stackup drawing will give the thickness of each layer including the copper thicknesses of the conductive layers. In this article, we will demonstrate controlled impedance routing using Altium Designer. mm. Also impedance have often a 10% margin to take into account manufacturing process. For your convenience, we have designed an Impedance Calculator to help you calculate the impedance and the trace width you require. I'hv already checked on Saturn PCB Design tool. To validate the trace width and spacing in your design, use the Better DFM tool. If you require a controlled impedance PCB, you should discuss this with your PCB fabricator. HDI PCB stackup with staggered microviasSignal Integrity (SI) in High-Speed PCB Designs. Off the top of my head, I can think of Polar and z-calc but I never liked these. 5 oz) and 1. thanks to 6 layers I am now pretty confident that I can place all diff pairs on top and bottom layers, directly above the ground planes. The dielectric constant of air is 1,and the dielectric constant inside the pcb stackup is usually 1. Best schematic design practices. Signal layer. Introducing the industry's first 3D web-based printed circuit board stackup design tool. 293, 50% of the copper removal can be achieved. A PCB transmission line is a type of interconnection used for moving signals from the transmitters to the receivers on a circuit board. According to the Altium Designer, stack-up tool’s impedance calculator, the impedance of trace 3 is 50Ω. The stripline impedance calculator provided below is useful for gaining an initial estimate of trace impedance for striplines. Aggressive gold baths, as well as high gold thickness, can increase the corrosion to a level approaching black pad. It also has an integrated impedance calculator to get the desired impedance and trace/space values on any signal layer. 4mm to 3. Using the built-in Simbeor ® impedance calculator, the PCB editor's Layer Stack Manager calculates the trace width needed to deliver the specified impedance. You can then use a stripline or microstrip impedance calculator to estimate your line impedance. Dimension:If you require a controlled impedance PCB, you should discuss this with your PCB fabricator. To open the Layer Stack Manager select Design » Layer Stack. Turnkey PCB manufacturing services involve: Fabrication solutions: Design review, sourcing dielectric materials, and bare-board manufacturing. Damping resistors help achieve a critical damping state. Here’s what Rick Hartley had to say. Coplanar Waveguide Calculator. This PCB has 4-mil vias. 4 GHz antenna (50 ohms single ended). Stress Vs. 53 mm thick dielectric with 4. The first goal in stackup design is to determine the number of signal layers you'll need to support high speed routing for all your interfaces. The differential one makes sense, but it looks like for single ended 50 ohms, their calculator only suggests a trace width. There are a few methods for calculating trace impedance in a circuit board as long as the dielectric constant and trace geometry are known: Use the IPC-2141 equation for microstrip or stripline impedances. 2 (double-sided) Flex thickness x 12. For PCB fabricators, Speedstack PCB interfaces with the industry standard Polar Si8000m PCB Controlled Impedance Field Solver. He added, “Designers today understand why controlled impedance really matters. 01) Speedstack PCB Layer Stackup Design Software bundles – Please note the following packaged software combinations: Speedstack PCB 2022. Reflections, ringing, and overshoot result from traces on the PCB without effective impedance controlling routing. Board thickness (h) = 50 micron. Note that the built-in impedance calculator does not account for the affect of vias, it assumes lossless transference from one signal layer to the next. Let’s discuss the need for impedance. Released in 2009, it considers the impact of thermal conductivity, board thickness, dielectric material, and the presence. The purpose of filling vias is to: Avoid the entry of any impurities. Speedstack PCB Stackup Design and Documentation . 2. If a signal encounters impedance discontinuity, it will generate jitters in PCBs and hampers the signal integrity. The stack-up should be symmetrical on either side of the metal core in a multilayer board. You can also calculate the accurate drill diameter, via to via spacing, and the thermal vias that. An impedance table should also be included in the fab drawing. Based on my understanding of a 4-layer stack-up, one of the best set-up I chose is 8 mil trace space and 10 mil trace thickness. But I'm unsure if the Height I entered is. 29 relative dielectric constant. Planning the multilayer PCB stackup configuration is one of the most important aspects in achieving the best possible performance of a product. 3. Learn more about stackup design in Altium Designer. This new release builds on the familiar ease of use of the popular In-Circuit Design online Impedance Calculator that has been utilized by tens of thousands of Engineers and PCB Designers world wide since 1996. Historically, the primary electrical requirements have been a controlled impedance in the signal layers and enough copper in the plane layers to deliver DC power to the circuits mounted on the PCB. The PCB stackup is the substrate upon which all design components are assembled. The most common problems seen in Gerber files include design mismatch, insufficient clearances, obsolete file formats, unregistered layers, and incomplete files. We will assume here that both of the lines of the pair are identical and uniform. For a Dk = 4. Flex thickness x 6. 3 How to calculate the average effective. [2] Calculate the top layer signal end impedance: Two tools are giving Zo=48 and Zo=47. 008” to 0. Stackup design is the arranging of the signal and power layers of a PCB to meet the electrical and mechanical performance needs of a specific design. Dimension:There are many calculators available online, as well as built into your PCB design software. Many of the design choices PCB designers make are in order to maintain good signal integrity. This will leave the rest of the signals which are rather non-critical like I2C, power good signals, etc. Place SMT. Controlled differential impedance starts with characteristic impedance. 1 mil as the thickness when the controlled impedance tracks are on top/bottom, use 8. Start Building Your Stack-Up With PCBWay impedance calculator, you can calculate the approximate impedance of your PCB / high frequency circuit board. Changing the stackup and copper ground plane location will change the trace geometry required to maintain the right impedance value during routing. In other words, for proper impedance control, the load impedance must be equal to the characteristic impedance. HDI also results in a lesser number of PCB layers. PCB Trace Impedance Calculations. Typical 12 layer PCB stack-up. Repeat #1 for differential impedance. Planning Your High Speed PCB Stackup and Impedance. These diff pair are going to be routed in the top layer. Signal integrity is about the quality of the signal passing through a transmission line. I'm avoiding a 4-layer PCB stackup. Sierra Circuits’ Via Impedance Calculator uses the physical dimensions of a via to calculate its capacitance, inductance, and impedance. These are precisely the characteristics of a pair of lines to be designated as a differential pair. 4. = room temperature (25⁰C) L= Length of trace. Layer 2 - Ground. • Ground planes must not be broken in the GND reference layer immediately beneath he transmission line. We started offering design layout services because, for our customers, it comes down to completing the project onIn terms of how these calculators work, the impedance of a transmission line in a PCB can be calculated in four ways: Use the R, L, C, G parameters from the Telegrapher’s equations to calculate the impedance of the transmission line. PCB Coplanar Waveguide Calculator RF. 2. Stack-up for FPC. Stack-ups, also known as build-ups, carry the details of trace width for different controlled impedance traces such as 50 ohms or 100 ohms differential. The design engineer must take charge of the design to mitigate the above issues. Select the number of substrate layers. 5 techniques to reduce ringing in PCB designs. The microstrip is a very simple yet useful way to create a transmission line with a PCB. 9 is an example of the amount of information that must be included in the. I used the KiCAD PCB calculator, asked the PCB manufacturer about the tangent loss (0. While this calculator will provide a baseline, any final design considerations should be made towards loss, dispersion, copper roughness, phase shift, etc. The differential tracks should match this impedance. The stackup drawing must contain more information than in the past, and the fabrication notes will need to be expanded. PCBCart's Standard PCB Layer Stack-up. Loss planning, including copper roughness — Layer by layer calculation of loss as a function of geometry, Df, copper roughness on both sides and frequency. Once you know the characteristic impedance, the differential. Learn More about using the Altium Designer’s impedance calculator in this brief tutorial. (Sorry guys, I live and I have grown up in a metric world ) With these values, Saturn PCB's off-line calculator gives 57 Ohm differential impedance. Critical Length. Polar Instruments (Asia Pacific) Pte Ltd . Type of PCB Differential Impedance (Ohms) Standard PCB: 100: PCI-SIG bus Gen 1: 85: PCI-SIG bus Gen 2: 85:. Flex circuit’s polyimide material is lighter than FR4. PCB stackup calculator. Use impedance calculation tools for specific dimensional values based on your design requirements. When selecting a multilayer stackup we should consider the following: • A signal layer should always be adjacent to a plane. You will then be presented with a table representing the suggested stack-up for that type of substrate. Email: [email protected] is the allowed diversion/variation from a specific dimension. The ICD Stackup Planner calculates characteristic impedance plus edge coupled and broadside coupled differential impedance. 0. 5oz to 6oz), inner layer copper thickness from 18μm to 70μm (0. A well-designed PCB stackup can maximize the electrical performance of signal transmissions, power delivery, manufacturability, and long-term reliability of the. 24 hours a day, 7 days a week. 0 HUB. Z-planner Enterprise is a stackup planning tool that includes a PCB stackup calculator focused on electrical impedance and signal integrity that helps you manage and optimize your PCB stackup design. 5oz to 6oz), inner layer copper thickness from 18μm to 70μm (0. Let us explore the different file types and the methods to generate PCB assembly files. A copper of a specific weight is rolled on one square foot area of a layer in the board. The iCD Stackup Planner features a precision 2D Boundary Element Method (BEM) Field Solver providing customers with the accuracy and simulation speed they need for high-speed PCB Design. As an example, If I want to meet the 80Ω diff/ 40Ω single impedances, taking the first inner signal layer, and using the Saturn Edge Coupled asymmetric calculator, the input would be: H2= 180um H1= 176um w = 0. Controlled impedance. Saturn PCB - Toolkit for Impedance Calculation. Formulas from IPC-2141A Design Guide for High-Speed Controlled Impedance Circuit Board. Developing an efficient stackup is a complicated process championed by innovative companies such as Candor, a leading PCB manufacturer. Ideal board stackup from top to bottom is shown in Table 1. Good stackup management allows you to obtain excellent products. For example, in the image above, layer L10 in the stackup is enabled for impedance calculations, with the Top Ref set to 9-L9, which is a Plane layer,. Si9000e – PCB insertion loss field solver. On a multilayer PCB this only works when the signal is also on an inner layer-- making it difficult to have the proper impedance AND capacitance on an outer layer. Z-planner Enterprise contains a stackup calculator which ensures signal integrity across a PCB for various controlled impedance models to quickly. 7 design rules to reduce crosstalk in your PCB designs. Stripline and microstriplines are calculated individually. PCB Multi-Layer Stack-Up; PCB Design and Layout Guidelines; Basics of Control Impedance; Search articles: « Older Posts. I'm designing a custom PCB around the Raspberry Pi RP2040 MCU. Max. Depending on the requirements you can generate a stack-up. More reliability: The improved signal integrity and power distribution make the 8-layer PCB more reliable than its lower-layer counterpart. PCB. A few of them are summarized below. 4mm to 3. JLCPCB Impedance Calculator. To mitigate these factors, first determine the loss budget for your targeted protocol. A hybrid stackup construction enhances your PCB’s performance and cost-effectiveness by combining different materials or technologies. Modern applications demand high-speed, high-density, complex stack-up design. The impedance calculator in the Allegro stack-up editor uses a static 2D field solver by default (bem2d). 5 oz) and 1. 727 3. Use a field solver that can account for dispersion and copper roughness. The tool used 0. • The typical PCB stack-up uses a signal layer on the top (component side) layer, a solid, contiguous ground plane. Accurate impedance calculations require accounting for differences between edge-coupled, embedded, and offset trace topologies. There are many factors that go into calculating the width of an impedance controlled trace. Since it directly references the stackup information and has a. Most CAD systems provide an impedance. Notice that there is no impedance information on the stackup drawing. Consider High-Speed Signal Frequency Range in PCB Stackup Design. Note that the built-in impedance calculator does not account for the affect of vias, it assumes lossless transference from one signal layer to the next. Using the built-in Simbeor ® impedance calculator, the PCB editor's Layer Stack Manager calculates the trace width needed to deliver the specified impedance. In particular, we looked at some of the basic stackup and routing rules needed to support a digital interface like I2C or SPI. PCB Laminates & Materials Quick Turnaround Program; Why. For example, if you are using 1 oz of copper for a 1 sq ft area, the thickness of copper is 1 oz. Use 3. 05 (Compatible with Atlas versions up to v19. Vias (plated holes) are used to route electrical signals among different layers of a multilayer layer PCB. subtract 3 from 3x to isolate x)1,370. It also has a major impact on the EMC performance of a product. 05. Talk to a Sierra Circuits PCB Expert today. Note that they have other board thickness and copper thickness variants available. The best PCB stackup design tools will account for dispersion in your board laminate material and will include it in impedance calculations. It is relevant when high-frequency signals are propagating on the PCB transmission line. 1. 0. PCB manufacturing materials and the configuration of the board layer stackup will have a major effect on your impedance and PCB etching. For example, for a simple coated microstrip with a target impedance of 75Ω it would not be unusual to specify a tolerance of ± 5%; typically, though, impedance is more often specified with a tolerance of ± 10%. PCB layer count estimation is a vital process in board manufacturing and cost. eu. Achieving a critically damped state in the transmission line is crucial to achieving the fastest settling time without overshoot or oscillation. Trace width and spacing depend on your PCB stackup. Call us: +1 (800) 763-7503. 4mm to 3. 679 nH/inch. Using the built-in Simbeor ® impedance calculator, the PCB editor's Layer Stack Manager calculates the trace width needed to deliver the specified impedance. PCBCart's Standard PCB Layer Stack-up. 010" to get a ratio of 0. We recommend the software from Polar Instruments if you want to get exact impedance calculation. Si8000m . You can see for example, Matthew K. The IPC-2141 trace Impedance calculator will help make initial design easier by allowing the user to input basic parameters and get a. The PCB layer stack-up calculator is a powerful tool for modern electronics design. Using an impedance control PCB calculator, the engineer determines that 50-ohm single-ended traces require a width of 6 mils and a spacing of 10 mils. Follow IPC-2220, IPC-2226 standards if you. The stackup defines what layers are in your PCB, what thickness each layer of copper is, and what the thicknesses of the cores or substrates between the copper layers are. The copper thicknesses of the inner and outer layers are 0. The lowest possible cost of circuit board can only be achieved by adopting accurate PCB design and the right engineering tactics. You should check their website out if your application uses a non-standard stackup for thin or high power applications. By leveraging mathematical precision and providing ease of use, it adds tremendous value to the field, facilitating innovative and efficient designs. Calculating Impedance in PCB Stackups. P = placement tolerance. If the PCB stackup is done differently, where the signal layer is closer to the power/gnd plane, then the trace can be thinner while still having the proper impedance. 2 of the Microstrip Calculator, h=H1 and b=H2-H1. The grid of layers is divided into 2 regions, the layers in the stackup are displayed on the left, then for each signal layer in the stackup there is a layer displayed in the. But this needs to be done in a proper way, according to the stack-up that contains certain requirements like impedance, number of layers, thickness of the PCB, etc. Board designers can focus on reducing via diameter to enhance routing. 0mm, copper thickness from 1oz to 4oz, inner layer copper thickness from 1oz to 2oz, and minimal spacing between layers to 4mil. Here is my layer stack up image with thickness of dielectric between the copper layers. Here is the 6 Layer stack up I would prefer. By leveraging mathematical precision and providing ease of use, it adds tremendous value to the field, facilitating innovative and efficient designs. Technical Report. The following is the usual FPC stackup information. Currently, the PCB stackup contains two metal layers (Top and Bottom) and a default dielectric layer (FR-4) between them. Step 1: Inner layer core selection. When defining reference planes, both with impedance controlled routing and in managing return paths, your stackup might force return currents to pass into a PCB power plane before being coupled back to a.