A Guide to Specifying Rigid PCB Materials in the StackUp
Rigid PCBs are made by layering copper foil and pre-impregnated (prepreg) epoxy-laminate to form the stackup. Use Altium Designer’s Layer Stack Manager together with Board Outline Mode to define and document your intended rigid PCB.
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Rigid boards fit well into product case parts
Rigid PCBs are made by arranging layers of copper foil and pre-impregnated (prepreg) epoxy-laminate. The prepreg forms into rigid material to make insulation layers between conductive copper layers. Vias are drilled to connect copper traces and the final stack of layers is plated before covered with nonconductive mask material. Finally, legends are applied with a technique called silkscreen.
The resulting arrangement of layers is called the PCB stackup. Fabricators produce the stackup by starting with a core. A core is made of substrate from prepreg material with copper foil laminated onto both of its plane surfaces. Using gerber files describing each PCB layer, the fabricator etches the inner copper layers first leaving designed signal traces. This is followed by adding the next insulator layer and so on until the outer layers are applied.
Altium Designer has layer stackup tools to design and display intended PCB layout. The tools include the powerful Layer Stack Manager where conductive and insulation layers are set, drill pairs are defined, materials are specified, and impedance calculations are made. While setting the stack and establishing layers, Altium Designer’s PCB environment provides Board Planning mode for viewing and analyzing the resultant design. Finally, layer definitions are easily ported to output documents for elegant communication with your fabricator.
A rigid PCB transmits electricity using copper. Most present-day designs require several signal layers within your rigid PCB. Thickness of the copper layer is usually specified in ounces. For power and ground planes a 1 oz thickness of copper is usually poured for the plane. For signal layers ½ oz copper is typical. Other copper foil thicknesses are available for specialized design.
Insulator materials in rigid PCBs form the design’s substrate using pre-impregnated epoxy-laminate. The most common rigid insulation material is called FR4. It is an industry designation that represents the ratio of fiber to resin, so materials may vary somewhat to meet FR4 ratio requirements. For specialized applications such as radio frequency or millimeter wavelength other types of material designations are available. Consult IPC-2221 for listing of all material types.
Use the Layer Stack Manager with PCB tool to specify stackup
Specify Layer Materials within Altium Designer’s Configuration Tools
Determine circuit design needs and select layer materials tailored for signal integrity. Specify how many layers will be required to suit design needs. Establish best arrangement of copper and substrate and analyze the type of dielectric. Confirm sourcing for materials and you are ready to go.
- Understand the materials and how they go into supporting your design.
- Consider manufacturing costing when using FR4.
- Choose material that best supports your design.
Once you’ve evaluated materials for use in your layers, it is time to build your stack.
Whether working toward a rigid-flex PCB, if rigid flex is even in your consideration, or if you’re just looking to organize the layer stack of your circuit boards, using strong PCB design software is invaluable for your design process. The base material will challenge your PCB design to accomodate, and you will have to arrange your printed circuit accordingly.
Choosing how to arrange layers for your rigid PCB is important for quiet designs. Part of material selection is knowing how it will impact your signals. Arrangement of layers with selected materials is done to minimize effects of noise. Noise is caused by magnetic flux generated when signals have insufficient referencing.
Design Rigid PCB Layers to Cancel Flux
There are several ways to cancel flux with layer arrangement in a rigid PCB. One is to place power and ground layers adjacent to one another to take advantage of capacitive decoupling. Another is to place high-speed signal layers adjacent to a ground plane. Other techniques using microstrip and stripline along with impedance matching techniques utilize the dielectric properties of the substrate.
- Listen to an expert discuss layering techniques for flux cancellation.
- Take a look at how to choose a stackup for high frequency
- Choose where to locate vias for minimal loop generation
Once you’ve chosen your layer stackup to maximize flux cancellation, use Altium Designer’s unified environment to build and document your stack.
Port stackup information into your panelization and share in the assembly drawing
Circuit boards are significantly more difficult to imagine without a strong PCB design software supporting them. Even if you don’t venture into the realm of flex PCBs, your printed circuit boards can be a bear to design and produce without having the proper tools behind you in development. Rigid PCBs, flex PCBs, or rigid-flex PCBs - you should not be constrained in this choice by your circuit board design software.
Altium Designer has an elegant environment with easily applied tools to specify your rigid PCB. Altium’s unified environment contains a Layer Stack Manager where you can configure the layers of your board. Options include specifying the material and type, its thickness, and for substrates its dielectric constant. Copper layer thickness may be specified here as well. Additionally, Altium provides Board Planning Mode, an environment where viewing the stack defined in the Layer Stack Manager can be viewed in 3D. Here, too, environmental variables may be adjusted to maintain all details relevant to the design.
Rigid PCBs Need Powerful Tools to Detail Quiet Design
To specify and adjust all the details of your layer stackup use Altium Designer’s powerful and intuitive tools. Altium’s Layer Stack Manager is readily accessible from the Design menu pulldown. It is an intuitive tool arranged in tabular form. Each cell acts as a radio button for easy selection and editing. Here is where you will specify core, substrate materials, layer arrangement, and dielectric constants. All that is specified here can be easily viewed in the panelization. From the panelization layering information can be ported to the assembly documents for communication with fabrication houses.
- Use the best EDA tool to make your rigid PCB.
- Discover a mode that allows intuitive interaction with your rigid PCB.
- Ensure signal integrity with thoughtful placement of vias.
Altium Designer’s Layer Stack Manager and Board Planning Mode are powerful and intuitive tools to specify your design. Rigid PCBs are made by arranging layers of copper and pre-impregnated epoxy-laminate that form into thin, solid planes that drive devices within your system. Altium has powerful EDA tools to implement layer stack design requirements. By studying available materials and their industry standards, rigid PCBs can be designed to produce signal integrity for all design considerations.