3.1 NPI Supply Chain: Consignment, Kitting and Attrition

NPI Supply Chain is more than logistics; it is a detailed audit of incoming components. In the prototype phase, materials often arrive as “Consignment” (customer-supplied), consisting of loose cut tape, non-standard labels, and last-minute BOM changes. Feeding this unfiltered mix into the SMT line severely degrades efficiency, forcing operators to execute manual component placement. This section defines how to transform an “Engineer’s Desk Kit” into a “Production-Ready Kit.”

Consignment Audit: The “Bag of Parts” Verification

Unlike standard mass production inventory, NPI materials often lack factory-sealed traceability. The Receiving Inspection team must switch from a “Box Checking” mentality to focused “Component Verification.”

1. The “Cut Strip” Risk

Customer-supplied cut tape often lacks the leader necessary to feed into the Pick & Place machine.

• Inspection Rule: The component markings on the physical chip must be verified against the BOM, not just the label on the bag. Engineers frequently swap labels during bench testing and sampling.
• Polarity Check: For diodes and ICs on cut tape, the tape orientation must be verified to match the standard (Pin 1 quadrant). If the strip was manually cut from a larger reel, the orientation in the pocket might be ambiguous or reversed.

2. Handling Moisture Sensitivity (MSL) in Open Bags

NPI parts often arrive in opened or compromised bags.

• The “Reset” Protocol: When an MSL component (Level 3 or higher) arrives in a non-vacuum sealed bag or without a valid humidity indicator card, the components must be baked (typically at 125°C for 24-48 hours) before reflow soldering. This prevents moisture from rapidly expanding and cracking the component during the reflow soldering process (“Popcorning”). Assuming opened parts are safe to solder without validation should be avoided.

NPI Attrition: The “Rule of 5”

Standard percentage-based attrition (e.g., a “1% scrap allowance”) is less effective during low-volume builds. 1% of a 10-unit build is 0.1 components. A single component dropped by the Pick & Place nozzle will halt the entire build.

The NPI Overage Standard

Excess material must be provided (or purchased) based on absolute integers, not percentages.

• Passives (0402 - 1206): Build Qty + 50 pieces (or a minimum 100mm strip).
  • Reasoning: Feeders require a section of “waste” leader tape to advance the components to the pick point.
• Active ICs (Standard): Build Qty + 5 pieces.
  • Reasoning: This allowance covers 1-2 feeder mispicks and 1-2 potential QC rework failures.
• Expensive ICs / BGAs: Build Qty + 1 piece (or 0 if manual placement is authorized).
  • The Constraint: If zero overage is supplied, the Project Manager must authorize “Manual Load” via a Tray feeder or direct hand placement to aggressively mitigate the risk of machine attrition.

Making “Cut Tape” Machine Ready

SMT machines cannot pick the very last few inches of a cut strip. Sending raw, short strips to the line forces operators to hand-place the remaining parts, which slows down the cycle time.

The Splicing Guideline:

• Condition: When the supplied strip is shorter than the minimum feeder engagement length, the Kitting Department must attach a Leader Extender or splice the strip onto a standard carrier reel.
• Avoid: Taping components to a sheet of paper or using standard office tape to send them to the line is prohibited. This cannot be processed by the SMT equipment.

Managing Shortages & DNI (Do Not Install)

NPI BOMs are highly fluid. “Missing” parts might actually be intentional “DNI” locations, or they might be critical shortages that halt production.

1. The DNI Validation

• Action: The Kitting list must be cross-referenced against the latest BOM revision immediately before it is released to the floor.
• Visual Aid: DNI locations must be marked on the assembly drawing (or flagged in the AOI machine program) so inspectors do not incorrectly report them as “Missing Components.”

2. The “Risk Release” Protocol

Building a board with missing parts is strictly governed by the following protocol:

• Green Release: The Kit is 100% complete. The standard flow must be proceeded with.
• Yellow Release (Post-Process Shortage): The missing part is non-critical for the initial reflow cycle (e.g., a mechanical screw, a heatsink, or a hand-soldered connector).
  • Action: SMT must be proceeded with. The batch must be labeled as “Incomplete - Missing [Part#].”
• Red Release (SMT Shortage): The missing part is a primary reflow component (like an IC).
  • Decision: Hold. Building “partial” boards with the intention of running them through the reflow oven a second time later should be avoided. Secondary reflow cycles can degrade the PCB laminate and existing solder joints.
  • Exception: If the missing part is a simple 2-pin passive component located on the edge of the board, a “Stop-Build” waiver may be signed by engineering to allow hand-soldering that specific part later.

Final Checkout: NPI supply chain: consignment, kitting and attrition

Control Point	Critical Requirement
Passives Overage	Build Qty + 50 pcs (or ensuring sufficient leader length).
Active Overage	Build Qty + 5 pcs (Minimum).
Zero Overage	Requires Manual Tray/Placement authorization.
Consignment Check	The MPN must be verified directly on the Chip Body, not just the Bag Label.
MSL Reset	All loose/open MSL-sensitive parts must be baked before SMT to prevent Popcorning.
Cut Tape Prep	A Leader Extender/Splice must be included for reliable machine feeding.
DNI Status	Must be clearly marked on the Bill of Materials (BOM) to prevent false shortage alarms during Automated Optical Inspection (AOI).
Partial Build Rules	Allowed only if the missing part is a Hand-Load/Mechanical item; Avoid for Surface Mount Technology (SMT) reflow components.