Today, electronic circuit boards are virtually everywhere. Any device or system that utilizes electricity, especially from a standalone or off-grid source like a battery, will likely also contain a PCBA for signal processing, power distribution, control or some other functionality. In fact, the leading technologies driving the current Industry 4.0 revolution are based on leveraging the wide range of capabilities that PCBAs make possible.
With such a wide range of utilizations and applications, designing a new PCBA may seem like starting a painting from a clean canvas. Creating a custom PCB architecture is certainly artistic, as each design reflects the idiosyncrasies of the designer; however, a well-defined palette, or set of PCB manufacturing steps, exists that your CM follows to create the physical embodiment of your design.
Just as each design is unique, so too may be the board itself. For example, applications can require unusual shapes, such as the small boards that are deployed in wearables like watches and fitness monitors. One of the best ways that you can aid your CM in building your board is to know and use standard PCB sizes and specifications for your design whenever possible—even when your application necessitates a non-standard PCB form factor.
Standard PCB Drill/Hole Sizes
For most PCB specifications, the designer has a great deal of leeway in determining parametric values. This includes one of the most important specifications, PCB drill hole sizes. However, some considerations will limit a designer’s range of choices, and those considerations fall into one of the following categories:
PCB Size Constraint Types
- Industry Standard limits
Publications such as IPC A-600 Acceptability of Printed Boards, IPC-6011 Generic Performance Specification for Printed Boards and IPC-6012 Qualification and Performance Specification for Rigid Printed Boards include limitations on the size of drill holes and annular rings (the copper area that surrounds plated through holes, or PTHs). These regulatory limits are set to define the minimum hole diameter and annular ring size that board fabricators must meet to satisfy the three IPC board classifications and associated performance expectations.
- CM DFM limits
In addition to the regulatory limitations placed on drill hole size, your drill hole specifications must fall within the capabilities of your CM’s drill equipment and processes. These DFM limits should extend to or beyond the requirements defined by published standards. Adhering to these requirements helps ensure that your boards can be built.
PCB drill holes are most often used for vias that enable trace routing from the surface to other layers of the board, as well as between layers within the board structure. Other uses include thermal vias to aid with heat dissipation and mounting holes to secure the board’s installation. Regardless of drill hole type, you should consult the appropriate performance specification standard and IPC-2221 Generic Standard on Printed Board Design, as well as your CM, for guidance in drill hole design. Doing so can also help you ensure that regulatory mandates are met and that your CM can actually produce the hole size you want.
In addition to the standard minimum size requirements and range of capability for your CM’s drilling equipment, other considerations include aspect ratio (the ratio of drill bit diameter to drill hole depth), drill hole type, current ampacity requirements and pad size (for vias), component density level (defined in IPC-7351) and minimum hole size, as specified from equations given in IPC-2221 Generic Standard on Printed Board Design. Although there is no fixed hole size that must be used, there is a definable range of standard PCB drill hole sizes to guide your selection. By choosing a hole size between 5 mil (0.13 mm) to 20 mil (0.51 mm), your CM should be able to accommodate your design, although the smaller sizes may cost more.
Standard PCB Screw Size
Depending on how your board will be deployed and if support, such as fasteners, is needed, you may need to base some of your PCB drill hole selections on the size of the screw used for mounting. For screws, non-plated through holes (NPTHs) are used to avoid any unwanted conduction, and they can be selected from standard screw sizes that fall within your CM DFM limits. Some common sizes are:
PCB standard screw sizes
Standard PCB Panel/Board Sizes
As shown in the sections above, selecting the right PCB drill hole can be an involved process. Fortunately, not all specifications require you to consider as many variables. Two such cases are your board and panel sizes. Your PCB size—horizontal length x width—must provide sufficient surface area to accommodate your components, traces and connections, clearance requirements, including board edge clearance, and connector spacing. It is a good practice to avoid very small board sizes—below 75 mil x 75 mil, if possible—as these may be challenging for your CM to process. Your board size will also define how many PCBs can be included on each panel, as your CM’s method of depanelization, routing or scoring, which is much simpler for rectangular boards as opposed to odd-shaped ones, must be accounted for as well.
Panelization should be considered during design, as it determines how many panels are needed and the amount of waste per panel; however, you should consult with your CM or allow your CM to design the panel layout. Although PCB panel size can be used to assist you in defining the board size and the number of layers for your PCB stackup, your CM will typically determine which of the standard PCB panel sizes, which include 9 in x 12 or 24 in and 18 in x 12 or 24 in, will optimize your manufacturing process.
DFM for HDI Printed Circuit Boards
Standard PCB Thickness Sizes
It is almost universally accepted throughout the industry that the standard PCB thickness is 1.57 mm, or approximately 0.062 in. In many cases, opting for this board thickness will meet your needs. However, there are factors that may necessitate that you choose a smaller—0.031 in (0.78 mm ), for instance or larger—0.093 in (2.36 mm)—standard alternative. Contributing factors are design complexity, component density, copper width and matching impedance requirements. Again, working with your CM can help you determine the best standard PCB thickness to select for your design.
Standard PCB Core Sizes
A design specification that impacts your stackup layer and overall board thickness is your choice for core size. The PCB core, along with substrate, prepreg and laminate refers to basic material sections within your board’s construction. The core differs from a substrate in that a substrate has copper attached on one side while the core has copper on both sides. Additionally, all PCBs have a core, even single-layer boards. Depending upon your PCB thickness, you may opt to use one of the commonly used or PCB standard core sizes that range from 0.005 to 0.039 in (.0127 to 1 mm). It is also advisable not to use prepreg dielectric layer thickness below 3 mil. Also, you are better served by choosing 2-ply for prepreg layers.
Knowing standard PCB sizes for the board parameters discussed above can aid you in designing boards that can be readily built with a high yield rate, especially if you consult with your CM to ensure manufacturing regulations and DFM guidelines are adhered to. At Tempo Automation, the industry leader for fast, high-quality PCBA prototypes and low-volume manufacturing, we will work with you from Day 1 of design to ensure that your boards incorporate your design intent and are first-time right manufacturable.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel. If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you would like more information on standard PCB sizes and how utilizing them improves your board build, contact us.
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