FR-4 Material Details for PCB Design

Design Rules define the design requirements and establish the instructions for Altium Designer’s PCB Editor. Using Design Rules allows you to address every aspect of your design and to complete the design according to varying design requirements. Monitoring the rules with Design Rule Checker allows you to successfully implement your FR4 layers.

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Your PCB design begins with an insulating substrate—typically made from a material called FR4—as its core. The designation “FR4” refers to the flame-retardant properties of the dielectric material and type 4 woven glass-reinforced epoxy laminate used for the substrate. This type of laminate material has high mechanical and high electrical insulating properties regardless of humidity and works as the ideal choice for many electronic component applications. Using the FR4 minimizes the production cost for PCBs.

Select the Correct FR4 Thickness for Your Application

Despite its overall reliability and wide-spread use, standard FR4 has characteristics that limit its selection for specific applications. As you work on your PCB design, you also need to determine the correct FR-4 thickness. Altium Designer provides the tools needed for making the right decision about FR4 within your design. You can use Altium’s Design Rules along with these tools when considering basic material properties, circuit fabrication reliability, and end-use performance.

Issues with standard FR4 substrates can have a dramatic impact on your design. Those issues occur because of the thermal, electrical, chemical, and mechanical properties of FR4. For example, high-temperature applications push the FR4 Coefficient of Thermal Expansion (CTE) to levels that exceed the glass transition temperature (Tg). As the CTE continues to rise, a mismatch grows between the glass transition temperature and the coefficient. When this mismatch occurs, thermal cycling causes the board to become electrically and mechanically unstable. In turn, the instability allows plating damage to through-hole vias to occur, pads to lift, and cracks to appear in surface resin.

Knowing FR-4 necessities for RF Applications

The limitations also become apparent when using standard FR4 with RF applications. On one hand, dielectric stability may suffer across the higher frequencies. Along with a higher dissipation factor (Df) and higher insertion losses at microwave frequencies of 1 GHz to 15GHz, traces used on FR4 have a larger attenuation at RF frequencies. Further, the FR4 thickness affects the effective dielectric constant of the PCB and…the greater impedance matching required for RF circuits. When working with RF circuits, the selection of high-performance FR4 that can handle multiple lamination cycles and has good reliability characteristics works as a solution for those problems.

• Learn more about how FR4 thickness affects your designs.
• Learn more about manufacturing costs for including FR4 in your PCBs.
• Learn more about material selection for RF and high-frequency designs.

Altium Designer’s PCB Editor Assists with the Three-dimensional Design Process

Every use of FR4 affects the electrical performance of a PCB. In turn, your decision to select the board and layer thickness also affects the operation of the PCB. Altium Designer simplifies the process of creating multi-layer boards by designating the type and thickness of the insulating substrate. By providing an end-to-end design platform that includes integrated tools, Altium Designer allows you to address questions about the form factor of your PCB project or the impact of component selection on board thickness.

Altium Designer has the right resources for building FR4 into your complex rigid-flex design. You can build the three-dimensional electromechanical requirements that ensure that your finished board fits within the folded location within the enclosure. Translating those requirements into a mechanical mockup gives you an accurate, realistic view of all the mechanical and hardware elements. Altium Designer gives you the tools for analyzing the assembly-time phase as well as the finished assembly.

Because PCB Editor supports up to 32 signal layers and 16 plane layers, you can define the insulating layers across the entire PCB for traditional rigid designs. While these rigid designs usually use FR4, Altium Designer provides the flexibility to choose from a variety of materials or to use one high-frequency laminate with the combination of many layers of FR-4 laminate and prepreg. With the availability of PCB editor and other tools, Altium Designer meets the demands of different applications.

Define board shapes in Altium Designer.

Use Altium Designer to Define Board Shape

Altium Designer’s PCB Editor and Layer Stack Manager also support rigid-flex designs that do not have a consistent set of layers across the PCB design by supporting multiple layer stacks. With this approach, you can use the master layer stack to define the total set of available layers—along with the sub-stacks--for the design. Altium Designer establishes the definition and naming of each sub-stack and assigns a layer sub stack to a specific region of the board shape.

You can use the Board Shape command to define the board space for your design. Altium Designer’s Design Rule Checker, Autorouter, and other intelligent analysis engines work within the board shape.

• Learn more about how to define board shape from a step model.
• Learn more about changing board sizes within Altium Designer.
• Learn more about how to change and edit board shape within CircuitStudio.

Use the Layer Stack Manager in Altium Designer to Define Layer Stacks

Because thicker FR4 layers have more thermal mass and can dissipate more heat from components, the possibility of thermal expansion causing damage exists. Altium Designer’s PCB Editor includes the signal, power plane, solder mask, silkscreen, and physical layers necessary for fabrication of your physical board. You can use the Layer Stack Manager to add and remove dielectric layers, select FR4 as a dielectric material, and set the thickness of the FR4 layer. In addition, PCB Editor also allows you to set the dielectric constant for the substrate.

PCB Editor allows you to the dielectric properties needed for the signal integrity analysis. Altium Designer’s friendly interface allows you to simply double-click in a cell to configure the setting. Because PCB Editor offers the advantage of working within a rules-driven environment, Altium Designer Design Rule Checker monitors each action, checks for compliance with design rules, and flags any design errors. All this allows you to focus on your design.

Your work with FR4 begins with the Layer Stack Manager in Altium Designer. The Layer Stack Manager assists you with defining the board structure in the vertical, or Z direction, as well as the board shape. Altium Designer provides the resources needed to respond to the demand for complex PCB designs.

If your design requires a multi-layer rigid-flex board, Altium Designer’s easy-to-use Layer Stack Manager allows you to design PCBs with more than 30 layers. By simply pointing and clicking on menu choices, you can:

• Add layers
• Delete layers and
• Move layers

When working with the FR4 dielectric layer, you can specify a name for the layer, show the type of layer, establish the layer thickness in either millimeters or mils, set the dielectric constant, and even select the thickness of a custom coverlay.

Manage your layers more efficiently with Altium Designer’s Layer Stack Manager.

Document Your Layer Stack with Altium Designer

Altium Designer’s Draftsman provides the documentation tools that you need for your complex designs. You can create high-quality documentation that includes dimensions, notes, layer stack tables, and drill tables. Draftsman provides automated extraction of drawing data from the source PCB document and the capability to create multi-page assembly and fabrication documents. You can use Draftsman to access common and additional drawing views such as the Assembly View, Fabrication View, Section View, and Drill Drawing View and use a broad assortment of manual drawing tools to add details to your drawings. Draftsman outputs files to the .pdf format or as documentation output for Outjobs.

Altium Designer uses the Layer Stack Manager dialog and the Layer Stack Legend within Draftsman to document complex layer stack structures. Draftsman’s Layer Stack Legend view shows detailed descriptions and information—such as Gerber files--for each layer in the stack. You can use the Layer Stack Legend command or select an icon from the Additional Views on the Altium Designer Active Bar.

The information for each layer associates with attributes found in the Board Layer Stack. You can use Table Commands and options found in the Table’s properties to build custom tables that show information. For example, you can build a table that shows the FR-4 material used for the dielectric layers.

• Learn more about Altium Designer's native 3D design engine.
• Learn more about Altium Designer's Unified Design Environment.
• Learn more about global editing within Altium Designer.

FR4 remains as the substrate choice for many applications because of its low cost and mechanical properties. Although design teams always seek to minimize cost, Altium Designer’s Unified Platform allows teams to consider all the issues associated with FR4. You can use Altium’s Design Rules, PCB Editor, and Layer Stack Manager to guide your decisions about the proper materials for your board design.