Sierra Circuit Certification

What is design for assembly?

Design for assembly, or DFA, is a systematic process that is used to reduce the assembly costs of a product by simplifying its design. This is done by reducing the number of components or parts in the product design and ensuring the parts are easily assembled. DFA techniques are intended to arrive at a simpler product structure and assembly system.

Design for assembly includes a distinct design methodology that considers product functionality along with the cost and efficiency of the product assembly process. Design choices go a long way in ensuring the quality and reliability of the end product.

The objectives of design for assembly

The objectives of DFA are as follows:

  • 1) The components selected in the BOM are available and not obsolete or end-of-life products.
  • 2) The components’ manufacturing part numbers (MPN) must match with the footprint of the PCB.
  • 3) The component placement, sizes, and distances between the components are compatible with the assembly       manufacturing processes.
  • 4) The solder mask and solder paste layers are correct and meet the production requirements.
  • 5) The DNI (do not include) components are correctly marked and verified.

Recommended layout for components

The land pattern design and spacing for each component package will affect the comprehensive reliability and timeline requirements for the PCBA along with the repairability of the board. Sufficient spacing between components on the board guards against possible faults such as solder-bridging while enabling easier manual soldering or rework.

While greater spacing facilitates greater ease of assembly, some applications need close spacing to accomplish a smaller form factor.


Common PCB assembly defects

Understanding assembly defects and their root causes can help a fabricator in enhancing the quality of the PCBA and boosting manufacturing yield. The most common board assembly defects are as follows:

  • Open solder joints (opens)
  • Solder bridges (shorts)
  • Component shift

Factors that impact the cost of the PCB assembly

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    Component packages

    As electronic components are available in different packages, assembly costs might also depend on the component packaging. BGAs and QFNs come with a higher cost due to the electrical connections beneath the components that require a higher level of accuracy for component placement. They also need X-ray inspection to look for voids and short circuits between the pins.

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    Board assembly volumes

    The assembly cost for boards depends on various factors such as initial setup costs, stencil cost and programming. Economies of scale come into play here, as high-volume production runs will bring down one-time set-up costs. Prototype boards might need a different set-up for each run or even each board, which will add to the cost of the boards manufactured.

Take a peek at what’s inside the design guide

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"Sierra makes it easy to place orders and offers quality and quick turn for our prototype boards."

Bruce Feige

CAD Operator/Supervisor, Ohio Semitronics, Inc
"You guys have the DFM checks that are really handy."

Herbert Gass
Design Engineer, Winduracnce LLC
"From getting a quote to placing an order, it was all very easy. The DFM/DFA check-in system worked pretty well."

Ryan Tullius
Design Engineer