Product Development

5 October 2019 by Phillip Johnston • Last updated 14 June 2023

DVT is a stage in the NPI process. DVT units should represent, as much as possible, the final production-intent design. No major future design changes should be expected at the start of DVT (otherwise, you should have another EVT build).

The goal of the DVT is to validate that the MP-intent production process can build production-intent units at sufficient quality. Unlike EVT, DVT enforces test limits. Fallout rates are often high, especially early in the build, requiring engineering engagement to correct the problems and bring yields. up.

At the end of DVT, you should be confident that any issues causing unacceptable yield losses have been (or will be) corrected. If yields are not at an acceptable level, or resolutions are uncertain, another DVT event is warranted (“DVT-2”).

Qualities of DVT

• Units are produced at “medium” quantities: 2-5x EVT quantities.
  • This often means 250-2500 units are produced (and in larger batch sizes than at EVT).
• Units are produced in fewer configurations than EVT – ideally, one per SKU. This is rarely adhered to, however.
  • There are often challenges such as your production-intent supplier producing lower-than-expected yields, requiring you to evaluate an alternative.
  • Additional configurations may be created as cost-down experiments.
  • Keep in mind that additional configurations add significant costs. You need to build each configuration in sufficient quantity to prove that the design is suitable for production.
    • If you are building multiple small-quantity configurations, you are probably not at the DVT stage.
  • There may be experiments or “DOEs” to evaluate different process parameters: different glue vendors, varied glue curing times, modified assembly orders, etc.
• Production-intent components should be used
  • Devices are all form factor units
  • Components should come from production processes (e.g., using hard tools, not soft tools or prints or mills)
    • This is often the first time that hard tools are used at a build and thus represents qualification for those tools.
    • Economic reasons may still require the use of, e.g., milled parts instead of hard-tooled parts, but this should be minimized, as it represents a significant risk if you see these parts for the first time at PVT.
  • Cosmetics may still not be at the desired quality level from the supplier
  • Capabilities like dust- and water-proofing should work at DVT
• Manufacturing test stations are enforcing realistic limits, allowing you to understand (and improve) actual process yield.
  • Since there is new
  • Failures may still be waived, depending on how egregious the failure is. This often involves setting “continue-on-fail” policies, allowing you to track your true process yield while still producing units that are good enough for development or testing purposes.
• Packaging is typically introduced, and packaging processes evaluated
• Additional checks on the manufacturing line are added: e.g., cosmetic inspection, OQC
  • For cosmetics, there will often be an effort to track down cosmetic fallout introduced on the line, but this is often difficult when input components are not cosmetically sound

Uses of DVT Units

DVT units are used for:

• Development
• Certification efforts (FCC certification, UL certification, Bluetooth certification, etc.)
• Reliability and environmental testing
• Internal and external beta testing
• Test station software and manufacturing firmware validation at the CM

NPI Process Flow

• The DVT stage begins once there is at least one EVT configuration that meets the requirements outlined in the Product Requirements Specification
• The DVT stage is complete when:
  • Yield loss problems have been addressed (or there is high confidence that corrective actions put in place after DVT will address the yield problems)
  • Certifications have passed (design modifications to address certification failures may be significant enough to warrant another DVT event, though some teams plunge into PVT anyway)
  • Reliability and environmental testing have yielded acceptable results (design modifications to address failures may be significant enough to warrant another DVT event, though some teams plunge into PVT anyway)
  • Packaging for the device is finalized
  • As a reminder, the DVT units must still meet the Product Requirements Specification.
• After the DVT stage is complete, PVT begins.

Exit Criteria: high confidence in all corrective actions for any issue that causes unacceptable yields on units using mass production parts made from mass production tools.

Related Concepts

• Manufacturing Test limits are enforced at DVT and used to fail units from the line. However, test limits may still be wider than expected in future build stages.
• Outgoing Quality Control is often introduced at this stage for process development and feedback on manufacturing

References

• Hardware engineers speak in code: EVT, DVT, PVT decoded by Anna-Katrina Shedletsky
  

  The DVT build is supposed to be one configuration of your production-worthy design, made of components from production processes (and hard tools) and on a line following production procedures. I believe very few companies actually stick to this requirement — because even if miraculously there are no outstanding issues, there may be parallel efforts to cut cost or increase yields that create additional configurations to build.

  If you do have functional, performance, or reliability issues that are driving Plan B and Plan C configurations at this stage, it can be costly because each of those alternates needs to be built in “full quantity” to ensure that design can be fully mass-production qualified by the end of the build. I believe that’s the real test for whether you are at DVT or not: if you are running side configurations of 20 units, you are fooling yourself, and should call it EVT2.

  Purpose:

  1. To verify mass production yields with one production-worthy design (one configuration for each shipping SKU)
  2. To qualify the first hard tool for every part in the assembly

  Typical Quantities: 300 to 2000

  • All parts should be from hard tools or mass production capable processes
  • All functional test stations must be present with limits in place to understand true yields

  Things that Go Wrong:

  • High functional fallout rates — requiring the need for fast failure analysis and corrective actions
  • Cosmetic yields are 0% — there may be an effort to try to track down and fix cosmetic aggressors, but it is usually fruitless because your cosmetic part suppliers are likely still shipping scratched parts (and you are having to waive them)
    • DOEs (there’s another one! Design of Experiments, mentally replace with “experiments”) are run with alternate glues or curing parameters
    • there are nightly calls with vendors demanding support or giving updates to hardware company executives

  Exit Criteria: high confidence in all corrective actions for any issue that causes unacceptable yields on units using mass production parts made from mass production tools.

• The different engineering validation stages in a nutshell | EVT, DVT, PVT | by Chris Boucher | Medium
• Overview of the hardware product development stages: POC – EVT – DVT – PVT explained
  

  • The objective of the DVT is to fix the design (i.e. dimensions, weight, materials, finish, moving mechanical parts) and rationalize the final product’s features.
    1. At this stage you should carefully revise and consider features vs product quality/finish vs production and BOM cost vs production volume.
    2. Complete the necessary certifications;
    3. Develop and finalize boxing and packaging
    4. Commence to request RFQs from mass-producers and devise plans for logistics.
  • DVT prototype quantities: typically 20-200 units, depending on the design complexity and BOM cost. The prototypes will be used for various reasons: certification lab tests, “beta tests” with early customers/testers.
  • Technologies: 3D printed + gel-coated enclosures with the finish “as from the factory”, rapidly cut/milled parts; industrial equipment (e.g. injection moulding) and 1st generation tooling (e.g. “quick moulds”).
  • Outputs / Deliverables: a [batch of] functional prototypes ready for mass-production with BOM and a design documentation package. Boxing and Packaging design completed. Estimate mass-production yields
  • Limitations: The DVT prototypes and documentation is nearly final and can be slightly changed further in development. Some mechanical parts and electronic components may not be final due to economic reasons (e.g. it is cheaper to CNC mill some metallic parts instead of using dye casting).