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Special Design Considerations for Small Form Factor PCBs

Small form factor wireless devices are increasingly in demand in all areas of business, healthcare, consumer, and mil/aero among other markets. Products like these are based on compact PCBs with tightly spaced digital and analog circuits placed next to each other. Device complexity substantially increases PCB layer count due to increased product functionality.

These small devices now with advances in technology perform considerably more electronic functions then their previous desktop predecessors. On the other hand, OEMs demand even greater robustness, high quality, increased reliability, and better yields associated with these small form factor designs.

As these portable devices become more complex, the PCB designer must take extra pre-cautions to assure an efficient design with virtually no issues. Here are some tips an OEM can follow to ensure an effective small form factors design.

  • Carefully review first pass yields to determine how many products are passing, whether it be 50, 70 or 90%.
  • DFA takes on greater meaning for small PCB designs. Make sure your EMS provider or CM heavily relies on multiple team interaction. Design, fabrication, assembly, and component procurement teams assigned to a given PCB project must precisely tune into a project’s specifications.
  • Assure adequate test points are deployed at layout across the board to allow complete access and coverage during flying probe or ICT test or for direct probing.
  • At fabrication, make sure your EMS provider or CM uses panelization and not fabricating one board at a time. Panelization increases fabrication speed and product assembly, thereby reducing OEM costs.
  • Equipment-related features and physical tolerances must be carefully monitored. In particular, the meander and wonder of drill machines must be closely and periodically watched to avoid assembly problems.
  • In mixed signal designs, the analog section must be totally isolated in terms of placement, routing, and plane creation.
  • Detailed documentation is of utmost importance to assure all design elements are properly executed at fabrication and assembly.

It’s also important to maintain a different mindset to avoid unforeseen issues when it comes to small form factor PCB designs. OEMs must consider the increasing number of layers required in some designs, for increasing noise suppression. Also, active devices are shrinking in size and are packaged in such advanced packaging as ball-grid arrays (BGAs), microBGAs, quad-flat packs (QFP), and chip scale packaging (CSP), which add to the complexity and issues associated with small form factor PCBs.