4.3 The incoming inspection plan (IQC)

Incoming Quality Control (IQC) acts as a critical financial and operational firewall for the entire EMS factory. Once a defective component is permanently soldered onto a PCB, the cost of resolving that issue increases by a factor of 10 for rework, and up to a factor of 100 if the board must be completely scrapped.

We cannot inspect quality into a product at our receiving dock; instead, the role of IQC is to thoughtfully verify that the supply chain has delivered the quality we require. This plan defines the structured logic for safely accepting incoming materials into the warehouse.

Risk-based inspection logic

Inspecting 100% of every incoming reel of resistors is an inefficient use of our quality resources. Instead, we recommend a risk-based approach to allocate IQC bandwidth where failure is most likely—and financially most costly.

Class a: high risk (critical / custom)

• Items: Bare PCBs, Custom Mechanicals (like Plastics and Metals), Complex Cables, Displays, Batteries, and safety-critical parts.
• Logic: These physical components naturally exhibit higher manufacturing variability, or they carry a severe impact on product safety and function if they fail.
• Guideline: Utilize an AQL 0.65 or 1.0 (Level II) plan. Mandatory dimensional and detailed visual checks should be performed.

Class b: medium risk (active components)

• Items: Integrated Circuits (ICs), High-Pin-Count Connectors, LEDs, Transistors, and expensive active modules.
• Logic: While intrinsic silicon manufacturing defects from the component maker are rare, mishandling, packaging errors, MSL violations, or hidden ESD damage are far more common in the supply chain.
• Guideline: Utilize an AQL 1.0 (Level I) plan. Focus heavily on verifying supplier labels, packaging integrity, and the physical condition of the fragile leads.

Class c: low risk (standard passives)

• Items: Standard Resistors, Capacitors, Screws, and Washers (Common commercial off-the-shelf catalog parts).
• Logic: The production processes for these passive components are highly automated worldwide and statistically very stable.
• Guideline: Place these on Dock-to-Stock (DTS) status. The dock team only needs to verify the Manufacturer Part Number and Quantity. Physical inspection is usually suspended unless flagged by subsequent process failures on the floor.

The golden rules of verification

Before ever opening a sealed reel or a boxed shipment, the inspector should perform the “Label vs. System” triangular check. The vast majority of IQC escapes are actually administrative mismatches, not physical component defects.

1. MPN Match: Does the Manufacturer Part Number on the physical label match our ERP system exactly? (For example, an ATMEGA328P-AU behaves differently than an ATMEGA328P-MU, and the letters matter).
2. AVL Verification: Is this specific manufacturer actively listed on the Approved Vendor List (AVL) for this particular project build?
3. Date Code Review: Is the component within the allowable age limit (typically < 2 years from date of manufacture)?
   • If the Date Code is > 2 years, it is best practice to temporarily block the material and request a fresh Solderability Test to ensure the leads haven’t oxidized.

Component-specific inspection criteria

Apply these focused checks based on the specific component family being evaluated.

A. bare PCBs (the foundation)

The bare PCB is an incredibly complex component. If it is flawed, the entire PCBA built on top of it becomes expensive scrap.

• Warpage: Place the bare board on a verified, flat surface plate. Any natural bow and twist must be ≤ 0.75% of the diagonal dimension (unless IPC-6012 Class 3 dictates a tighter tolerance for the build).
• Solder Mask: Carefully visually check for any signs of peeling or blistering mask.
• Pads/Finish: Verify that ENIG or HASL finishes are clean and not oxidized. Any notable discoloration or dullness is usually grounds for rejection or further evaluation.
• Dimensional: Always measure the critical housing cutouts and mounting holes against the engineering drawing.

B. moisture sensitive devices (MSDs)

ICs and modules packaged in moisture barrier bags (MBB) are highly sensitive variables if mismanaged during transit.

• Humidity Indicator Card (HIC): Open the outer cardboard box. Check the HIC through the bag (if the bag is transparent) or immediately upon carefully opening the seal.
  • If the 10% spot is pink, the internal environment is wet. Reject the lot or mandate a proper, controlled Bake cycle immediately to recover them.
• Bag Integrity: Inspect closely for punctures or loss of vacuum. If the aluminum bag does not tightly conform to the reels inside, the internal dry environment has been compromised.

C. custom mechanics (enclosures / metal)

• Fit Check: Always perform a quick physical mating test with a validated Golden Sample counterpart.
• Cosmetics: Inspect the surfaces under standard, bright lighting (800-1000 lux) at roughly arm’s length (approx. 40-50cm).
  • Scratches: Generally, none are allowable on Class A (user-facing) aesthetic surfaces.
  • Flash/Burrs: These must not interfere with assembly fit, nor should they present any scratch or injury risk to the operator.
• Color: Compare the plastic color directly against the signed “Limit Sample” or the officially specified Pantone swatch.

D. connectors & electro-mechanical

• Pin Condition: Inspect the connector closely for bent pins or poor coplanarity. If surface-mount pins are not entirely flat and parallel, they will almost certainly cause open solder joints during the reflow process.
• Plating: Check for obvious signs of tarnish, oxidation, or exposed base metal on the critical friction contact surfaces.

Sampling strategy (AQL)

We recommend utilizing the ANSI/ASQ Z1.4 (ISO 2859-1) standard to maintain disciplined sampling across the team.

• Normal Inspection: Start at this level for all new vendors and new part numbers.
• Reduced Inspection: Safely switch to this level if a vendor successfully passes 10 consecutive lots without issue.
• Tightened Inspection: Escalate to this level if 2 out of 5 consecutive lots are rejected.

Example Scenario:

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

1. Reference the Table: A lot size of 281-500 maps to Sample Size Code H.
2. Determine Sample Size: Carefully inspect exactly 50 units.
3. Apply AQL 1.0 Criteria:
   • Accept: If you find 1 defect.
   • Reject: If you find 2 defects.
4. Action: If you find 2 non-conforming units, it is generally best to reject the entire shipment. We strongly advise against sorting parts in-house unless explicitly authorized by management, and the sorting cost is formally charged back to the supplier.

Non-conformance management (MRB)

When a lot fails incoming inspection, it should be moved to the secured Material Review Board (MRB) cage and must be digitally segregated in the ERP system (marked as BLOCKED).

Standard Dispositions:

1. RTV (Return to Vendor): This is the standard, expected procedure for non-conforming material.
2. UAI (Use As Is): This disposition requires formal Engineering and Quality Approval. It is typically only used if the defect is purely cosmetic and has Zero impact on form, fit, or function (e.g. an incorrect font used on an internal, hidden label).
3. Sort/Rework: In this scenario, the EMS performs sorting or rework at the supplier’s expense. This requires a written commercial agreement on hourly billing rates established before the extra work begins.

Pro-Tip: Be cautious about accepting a “marginal” lot just to desperately keep the production line running. If you do, you effectively assume ownership of the risk. If the yield subsequently drops at the SMT process due to those parts, the customer will likely not absorb the cost of the scrap. Always secure a formal concession from the appropriate engineering authority before releasing marginal parts to the floor.

Final Checkout: The incoming inspection plan (IQC)

Parameter	Guideline / Standard	Action Owner
Inspection Standard	ANSI/ASQ Z1.4, Level II (Default base).	IQC Lead
Critical Metric: PCB	Verify Bow/Twist is ≤ 0.75%; confirm solderability.	IQC Inspector
Critical Metric: MSL	HIC Card check should be mandated for all bagged ICs.	IQC Inspector
Documentation	A CoA (Certificate of Analysis) is required for Chemicals.	Supplier
Rejection Trigger	AQL Threshold Reached -> Stop -> Notify Purchasing.	Quality Engineer
Date Code Limit	Generally max 2 years from seal date (unless extended).	ERP System / IQC
ESD Control	Ensure the IQC Station is grounded; wrist straps worn.	Safety Officer