3.1 NPI Supply Chain: Consignment, Kitting and Attrition

NPI Supply Chain involves more than just logistics; it functions as a detailed audit of incoming components. During the prototype phase, materials often arrive as “Consignment” (customer-supplied), which typically includes loose cut tape, non-standard labels, and last-minute BOM changes. Feeding this unfiltered mix directly into the SMT line severely impacts efficiency, forcing operators to perform manual component placement. This section explains 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 therefore shift from a “Box Checking” approach to a focused “Component Verification” process.

1. The “Cut Strip” Risk

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

Inspection Rule: Always verify the component markings directly on the physical chip 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, confirm the tape orientation matches the standard (Pin 1 quadrant). If the strip was manually cut from a larger reel, the orientation within the pocket can be ambiguous or even reversed.

2. Handling Moisture Sensitivity (MSL) in Open Bags

NPI parts often arrive in opened or compromised packaging.

The “Bake-Out” Protocol: If 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 step prevents moisture from rapidly expanding and cracking the component during the reflow process, a defect known as “popcorning.” It is important to avoid assuming that opened parts are safe to solder without this validation.

NPI Attrition: The “Rule of 5”

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

The NPI Overage Standard

Excess material must be provided (or purchased) as a fixed quantity, not a percentage.

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 reliably.
Active ICs (Standard): Build Qty + 5 pieces.
- Reasoning: This allowance covers one or two feeder mispicks and a couple of 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 a “Manual Load” via a Tray feeder or direct hand placement to effectively 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: If 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: Do not tape components to a sheet of paper or use standard office tape to send them to the line. This method cannot be processed by the SMT equipment.

Managing Shortages & DNI (Do Not Install)

NPI BOMs are highly fluid. A “missing” part might be an intentional “DNI” location, or it could be a critical shortage that halts production.

1. The DNI Validation

Action: Cross-reference the Kitting list against the latest BOM revision immediately before it is released to the production floor.
Visual Aid: DNI locations must be clearly 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 governed by the following protocol:

Green Release: The Kit is 100% complete. Proceed with the standard production flow.
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: Proceed with SMT assembly. Label the batch as “Incomplete - Missing [Part#].”
Red Release (SMT Shortage): The missing part is a primary reflow component (like an IC).
- Decision: Hold production. Avoid building “partial” boards with the intention of running them through the reflow oven a second time later. 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, engineering may sign a “Stop-Build” waiver to allow hand-soldering that specific part at a later stage.

Recap: NPI Supply Chain Component Preparation and Verification

Parameter	Condition / Criterion	Requirement / Action	Status / Value
Component Verification	Customer-supplied cut tape or loose parts.	Verify component markings directly on chip against BOM. Confirm polarity/tape orientation.	Mandatory prior to SMT line start.
MSL Component Handling	MSL Level 3+ components in non-vacuum sealed or opened packaging.	Bake components (e.g., 125°C for 24-48 hours) before reflow soldering.	Mandatory to prevent “popcorning”.
NPI Overage (Attrition)	Low-volume NPI builds.	Apply absolute overage: Passives (0402-1206): Build Qty + 50 pcs (or min 100mm strip). Active ICs: Build Qty + 5 pcs. Expensive ICs/BGAs: Build Qty + 1 pc (or 0 with manual placement authorization).	Required buffer for feeder waste and mispicks.
Cut Tape Preparation	Supplied strip shorter than minimum feeder engagement length.	Attach Leader Extender or splice strip onto standard carrier reel. Do not use paper or office tape.	Required for automated feeding.
Shortage Management	Missing component in kit.	Cross-reference kit against latest BOM revision. Mark DNI locations on assembly drawing/AOI. For missing primary reflow component (IC): HOLD production (Red Release). For missing post-process part: Proceed, label batch as incomplete (Yellow Release).	Green (100% complete), Yellow (non-critical shortage), Red (stop for SMT shortage).