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Checklist: Evaluating electronics product design for manufacturing (DfM) services

By Mark Zetter

Product design for manufacturing considerations can culminate into an exhausting list of items depending on the electronics product and product requirements.

Taking measures to consider as many aspects of a product’s design requirements as early as possible during the product development phase can help companies save time and money.

Contract manufacturers with experience in product design can be an OEM’s best source for helping to put together a checklist of product design considerations.

Below are some items broken out by activity or process companies should consider.

 

Design, component selection

  • Verify components are available in production quantities
  • Minimize number, and number of, different components
  • Confirm no end-of-life (EOL) components designed in
  • Minimize sole-source devices, components
  • Multiple, alternative manufacturers specified for all components
  • Second sources checked for mechanical and electrical fit
  • Component tolerance issues identified and evaluated
  • Component temperature ranges considered
  • BGA vs fine-pitch QFP considerations
  • Trim pots eliminated where possible
  • Design for environment: for recycle, re-use, repair

 

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General board layout considerations

  • Visible orientation marks on silkscreen layer for all polarized components
  • Polarized components in proper directions
  • Layer numbers visible on PCB or break-offs
  • Names on artwork

 

Board assembly manufacturing processes

  • Workmanship requirements established (e.g., IPC, military, aerospace)
  • Number of processes identified and minimized
  • Hand soldering minimized
  • Hand insertion and assembly minimized

 

Through-hole components

  • Non-plated tooling holes for through-hole automation
  • Drill sizes: lead diameter + X for auto-inserted through-hole (may suggest size of ‘finished hole’ instead so design house can determine which size drill to use to allow for plate up)
  • Dual in-line package (DIP), axial and radial inserted components (note some exceptions on non-plated, single-sided boards)
  • Customary for DIP socket drill holes to be 0.040″
  • Orientation of auto-insert components at 0°, 90°, 180°, and 270°
  • DIP components oriented same way on volume boards
  • Axial components oriented same way on volume boards
  • Transistor lead layouts spaced properly, in-line, pad-to-pad
  • No stand-up axial components
  • Minimum annular rings on through-hole pads

 

SMT land patterns

  • Fine-pitch land patterns at 60% pad width/pitch
  • Land patterns match to actual physical components
  • Use of land patterns fall in with DFM optimization
  • No natural bridges on fine-pitch SMT
  • Non-solder mask defined pads for BGAs

 

Wave-soldered bottom side SMT components

  • Confirm lower-yielding process required
  • Bottom-side SMT wave land patterns optimized
  • Component orientation optimized for waved SMT components
  • 4-sided SMT and fine-pitch SMT not soldered
  • Minimum component-to-component spacing equal to height of tallest of two components
  • Other wave solder shadowing considerations to prevent ‘skips’ (solder surface tension does not break when waving, therefore solder cannot properly wet the interface to form a solder joint)
  • No SMT components on bottom within clinch head footprint on mixed-technology PCBs

 

Hardware

  • PCB includes stainless steel to prevent rusting, repel solder
  • Tinned, plastic encapsulated microcircuits, etc…will solder to board
  • Phillips or allen-head screws for ease of assembly
  • Silpad washers on power devices where required
  • Identify rivscrew use, where possible
  • Non-plated mounting holes, without pads, where/if possible

 

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Board mechanicals

  • Three (3) fiducial marks 0.060″ on each side with SMT via-holes covered with soldermask (normal strategy except for certain ICT-enabled designs)
  • Layer stack-up identification on board or break-off tabs
  • Component-to-edge-of-board considerations identified
  • Panelization or break-offs discussed with ODM or contract manufacturing partners

 

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