3.1 The Virtual Build: DFM + Sourcing + Data Freeze

Before a single dollar is spent on silicon or a single stencil is cut, the product must be built virtually. The "Virtual Build" is the rigorous simulation of the manufacturing process using data alone. This is the financial firewall of the project. Once you proceed past this gate, every error costs hard currency to fix. In the virtual phase, fixing a mistake costs zero dollars—only time. This stage transforms a design from "theoretical intent" into "executable instruction."

The Data Freeze: Locking the Target

Manufacturing cannot hit a moving target. A common failure mode in NPI is the "Rolling Change," where engineers try to slip in a new resistor value or a layout tweak after the quoting process.

The Engineering Reality

An EMS line is programmed based on a specific checksum of files. If you change one file, the entire validation set (Sourcing, Pick & Place Data, Stencil Design) becomes void.

• If you change the BOM after the "Freeze" date → Then the procurement team must cancel orders, pay restocking fees, and re-quote, delaying the launch by weeks.
• Rule: Declare a "Data Freeze." Any change after this point requires a formal Engineering Change Order (ECO) and a restart of the DFM process.

Deliverable 1: The DFM Report (Design for Manufacturing)

The DFM Report is not a critique of your design skills; it is a compatibility check between your PCB layout and the factory's machines. It highlights features that are physically impossible or statistically risky to build.

Typical DFM Flags

1. Acid Traps: Acute angles in traces that trap etching acid, eating away the copper over time.
2. Solder Mask Slivers: Narrow strips of mask that will flake off and cause bridges.
3. Thermal Imbalance: A small pad connected to a massive ground plane without "thermal relief" spokes.
   • If thermal relief is missing → Then the pad will not get hot enough to melt the solder, causing a "Cold Solder Joint."

Pro-Tip: Do not ignore "Yellow Flags" (Warnings) in a DFM report. A Red Flag means "Cannot Build," but a Yellow Flag means "Will Build with Low Yield." Fix the Yellow flags to save money.

Deliverable 2: Sourcing Risk & Alternates

The BOM must be scrubbed against the global supply chain. This is not just checking price; it is checking "Lifecycle Status."

The AVL (Approved Vendor List) Strategy

You must define who is allowed to manufacture your components.

• If you specify "Murata GRM155..." (Specific MPN) → Then the factory can only buy that exact part. If it is out of stock, the line stops.
• If you specify "10uF 0603 X5R 10V" (Generic Spec) → Then the factory can switch between Samsung, Yageo, or TDK based on availability.

The "Risk List"

The Virtual Build produces a list of "High Risk" parts:

• NRND (Not Recommended for New Designs): The manufacturer plans to stop making this soon.
• Obsolete: It is already gone; you are buying leftover stock.
• Allocation: The part is being rationed globally (common for chips).

Deliverable 3: The Assembly Array (Panelization)

You rarely build one board at a time. You build a "Panel" (or Array) containing multiple boards connected by tabs or V-scores.

The Engineering Reality

The machine speed is determined by how many boards travel into the zone at once.

• If you do not define the panel drawing → Then the factory will optimize for their material usage, which might make the panel too floppy for your testing fixture.
• Critical constraint: The panel rails (waste edges) must be at least 5 mm wide to fit the conveyor belts.

Final Checklist