Spacing is a function of position and distance. Space matters, whether in the laws of physics or the imaginary lines that separate states, personal property, and even countries. Actually, space governs nearly every aspect of human life. However, spacing guidelines aren’t just arbitrary rules, and in some cases, they impact safety as well. In printed circuit boards, distance and placement, which are closely related, are paramount considerations. The spacing guidelines governing design for manufacturing (DFM) and design for assembly (DFA) aim to preserve the functionality, performance, and even the overall safety of the PCB.
Why is Component Spacing Important for SMDs?
Like most areas within the field of electronics, PCB design and assembly are always evolving and becoming more complex. In terms of PCBs, this development involves increased precision, greater design accuracy, and maximization of board space. As a result, good spacing between SMD components is an absolute priority.
Increased precision and accuracy, along with the requirement to accommodate more components while following DFM and DFA guidelines, thoroughly tests both the designer's and manufacturer's abilities. However, adhering to these strict requirements is a genuine necessity. For instance, the guidelines governing the minimum spacing between SMD components in your design ensure both the operational integrity of the surface mount technology (SMT) and the manufacturability of the board, while avoiding issues with PCB pads, such as shorting. In general, component spacing principles, when applied properly to the design process, can elevate the PCBA design quality, aid assembly and improve board performance and functionality.
SMD Component Spacing Considerations
Because the overall design of every PCB is unique, the essential requirements to optimize the functionality and performance of each board are unique as well. Even so, maximizing efficiency and component density are typically at or near the top of the list of development goals for electronics. To achieve this aim, designers and engineers alike recommend that you utilize certain basic guidelines for component placement and spacing in all PCB designs. Although trade-offs in any design are inevitable, following the proper guidelines will produce plans that shift from design through manufacturing with greater ease. Here are some considerations to incorporate into your design when the objective is to minimize the distance between components and make the best use of board space.
Design Considerations for SMD Spacing
- Component size is important as large components tend to release more heat which will affect the adjacent component's performance and functionality.
- Package type should also be considered as SMDs with fanout require more surface area and therefore must be positioned farther away from other components than packages, such as BGAs.
- Via type will undoubtedly be a major concern. Not only does this impact your stackup and board space, but also the complexity of the assembly process.
- PCBAs use a wide range of connectors to interface with other boards or devices. Spacing for these PCB connectors must be considered as it must be adequate to allow for the connections to be made.
- If your design includes design for testing (DFT), there may be a need to add test points or allow space for test fixture connections.
Assembly Considerations for SMD Spacing
- Component orientation is an often overlooked consideration. However, like components should be commonly arranged to facilitate good solder flow.
- The shadow effect occurs during the process of reflow and describes how SMD components, which are more significant in size, tend to cast a shadow over smaller components if the spacing between them is minimal. This can prevent smaller component pads from reaching the necessary temperature for solder paste melting as quickly as their larger counterparts.
- Rework, unfortunately, is often required during assembly. As technicians manually perform various activities on the board, such as repositioning and hand soldering, adequate spacing must be allotted.
- Board edge clearance is also a major consideration as it can negatively impact the depanelization process.
- Tooling holes in PCB laminates permit quick and accurate stacking for drilling. These same tooling holes also facilitate proper positioning when dispensing solder paste, as well as for board positioning when mounting SMDs (pick-and-place machines). Therefore, this is a determining factor in the minimum spacing between SMD components during the design process.
When it comes to PCB assembly, the following factors related to component spacing should be considered.
Designing for Minimum Distance Between SMD Components
Component minimum spacing rules may vary, depending on your CM’s capabilities. However, these must be followed as do creepage and clearance standards. Along with these, there are design measures one can take to minimize spacing between SMDs and promote ease of assembly, as listed below.
How to Design for Minimum Distance Between SMD Components
- Follow creepage and clearance standards.
- Follow your CM’s DFM spacing rules and guidelines.
- Minimize trace widths to maximize routing channels between components.
- Route on inner layers only.
- Use via-in-pad.
- Choose a green solder mask to minimize spacing requirements.
- Avoid placing fiducials between adjacent components, as much as possible.
- Orient plugin connectors so as not to increase SMD spacing, if possible.
As always, it is an excellent idea to work closely with your CM, as they are familiar with various DFM techniques and can make the proper recommendations for spacing to facilitate good assembly.
Absolutes in terms of minimum distance specifications for SMDs are debated by designers and engineers alike. As there is no definitive specification that fits all spacing demands for the various PCBAs or SMD placement configurations, the best option is to work closely with your CM and follow the guidelines provided above.
|Tempo's Custom PCB Manufacturing Service
Minimum spacing and proper placement are crucial considerations that can impact PCB quality, manufacturability, performance, and functionality. At Tempo Automation, we closely collaborate with you from day 1 of design to ensure your design follows spacing specifications for SMD components and adheres to minimum distance requirements for assembly.
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 want more information on how to design for minimum distance between SMD components, contact us.