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4.3 The Incoming Inspection Plan (IQC)

Incoming Quality Control (IQC) is the financial firewall of the EMS factory. Once a defective component is soldered onto a PCB, the cost of rejection increases by factor of 10 (rework) to 100 (scrap).

We do not inspect quality into the product; we verify that the supply chain has delivered the quality promised. This plan defines the logic for accepting materials into the warehouse.

Risk-Based Inspection Logic

Inspecting 100% of incoming resistors is an operational failure. Use a risk-based approach to allocate IQC resources where failure is most likely and most costly.

Class A: High Risk (Critical / Custom)

  • Items: PCBs, Custom Mechanicals (Plastics, Metals), Cables, Displays, Batteries, Safety Critical Parts.
  • Logic: These have high variability or severe impact on safety.
  • Action: AQL 0.65 or 1.0 (Level II). Mandatory dimensional and visual checks.

Class B: Medium Risk (Active Components)

  • Items: ICs, Connectors, LEDs, Transistors, expensive Modules.
  • Logic: Manufacturing defects are rare, but handling/packaging errors (MSL, ESD) are common.
  • Action: AQL 1.0 (Level I). Verify Labels, Packaging, and Lead Condition.

Class C: Low Risk (Standard Passives)

  • Items: Resistors, Capacitors, Screws, Washers (Standard Catalogue parts).
  • Logic: Production processes are automated and highly stable.
  • Action: Dock-to-Stock (DTS). Verify Manufacturer P/N and Quantity only. No physical inspection unless flagged by production failures.

The Golden Rules of Verification

Before opening a reel or box, perform the "Label vs. System" triangular check. 90% of IQC escapes are administrative errors, not physical defects.

  1. MPN Match: Does the Manufacturer Part Number on the label match the ERP system exactly? (e.g., ATMEGA328P-AU ≠ ATMEGA328P-MU ).
  2. AVL Verification: Is this manufacturer on the Approved Vendor List for this specific project?
  3. Date Code: Is the component within the allowable age window (typically < 2 years)?
    • If Date Code > 2 years -> Block and request Solderability Test.

Component-Specific Inspection Criteria

Apply these specific checks based on the component family.

A. Bare PCBs (The Foundation)

The PCB is the most complex component. If it fails, the PCBA is scrap.

  • Warpage: Place on a surface plate. Bow and twist must be ≤ 0.75% of the diagonal dimension (unless IPC-6012 Class 3 requires tighter tolerance).
  • Solder Mask: Check for peeling or blistering.
  • Pads/Finish: Verify ENIG/HASL finish is not oxidized. Discoloration = Reject.
  • Dimensional: Measure critical cutouts and mounting holes against the drawing.

B. Moisture Sensitive Devices (MSDs)

ICs and modules packaged in moisture barrier bags (MBB) are time-bombs if mishandled.

  • Humidity Indicator Card (HIC): Open the outer box. Check the HIC through the bag (if visible) or immediately upon opening.
    • If 10% spot is pink -> Reject or Bake immediately.
  • Bag Integrity: Check for punctures or loss of vacuum. If the bag is not tight, the part is compromised.

C. Custom Mechanics (Enclosures / Metal)

  • Fit Check: Perform a mating test with a Golden Sample counterpart.
  • Cosmetic: Inspect under standard lighting (800-1000 lux) at arm's length (40-50cm).
    • Scratches: None allowable on Class A surfaces (user-facing).
    • Flash/Burrs: Must not interfere with assembly or risk operator injury.
  • Color: Compare against the signed "Limit Sample" or Pantone swatch.

D. Connectors & Electro-Mechanical

  • Pin Condition: Inspect for bent pins (coplanarity). If pins are not flat, they will cause open circuits during reflow.
  • Plating: Check for signs of oxidation or exposed base metal on contact surfaces.

Sampling Strategy (AQL)

Use ANSI/ASQ Z1.4 (ISO 2859-1) standard for sampling.

  • Normal Inspection: Start here for all new vendors/parts.
  • Reduced Inspection: Switch to this if the vendor passes 10 consecutive lots.
  • Tightened Inspection: Switch to this if 2 out of 5 consecutive lots are rejected.

Scenario:

You receive 500 units of a Custom Plastic Case (Class A).

  1. Look up Table: Lot size 281-500 -> Sample Size Code H.
  2. Sample Size: Inspect 50 units.
  3. AQL 1.0:
    • Accept: 1 defect.
    • Reject: 2 defects.
  4. Action: If you find 2 bad units, reject the entire shipment. Do not sort them yourself unless explicitly authorized and charged back to the supplier.

Non-Conformance Management (MRB)

When a lot fails inspection, it moves to the Material Review Board (MRB) cage. It must be physically segregated in the ERP system (Status: BLOCKED).

Dispositions:

  1. RTV (Return to Vendor): Standard procedure for defects.
  2. UAI (Use As Is): Requires Engineering Approval. Used only if the defect is cosmetic and does not affect form, fit, or function (e.g., wrong label font).
  3. Sort/Rework: EMS performs sorting/rework at the supplier's expense. Requires written agreement on hourly rates ($) before work begins.

Pro-Tip: If you accept a "marginal" lot to keep the line running, you own the risk. If the yield drops at SMT, the customer will not pay for the scrap. Always get a concession number from the customer/supplier before using marginal parts.

Final Checklist

Parameter

Specification

Action Owner

Inspection Standard

ANSI/ASQ Z1.4, Level II (Default).

IQC Lead

Critical Metric: PCB

Bow/Twist ≤ 0.75%; Solderability pass.

IQC Inspector

Critical Metric: MSL

HIC Card check mandated for all Bagged ICs.

IQC Inspector

Documentation

CoA (Certificate of Analysis) required for Chemicals/Plating.

Supplier

Rejection Trigger

AQL Threshold Reached -> Stop -> Notify Purchasing.

Quality Engineer

Date Code Limit

Max 2 years from seal date (unless specified otherwise).

ERP System

ESD Control

IQC Station must be grounded; Wrist straps mandatory.

Safety Officer


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