Incoming Inspection for Electronic Components: A Practical SOP

Incoming Inspection for Electronic Components: A Practical SOP

Incoming inspection is how you catch problems before they enter production: counterfeit parts, wrong substitutions, damaged reels, moisture exposure, mixed date codes, and parts that look fine but are not what your BOM requires.

You don’t need a giant lab to do this well. You need a repeatable SOP, a clear risk tier system, and basic tools.

This guide gives a practical incoming inspection process you can use in a factory or sourcing team.

⸻

Step 1: Classify parts by risk (so you don’t waste time)

Tier A — High risk / High impact (inspect every lot)

Examples:
• MCU/MPU/FPGA, memory
• power ICs, chargers, PMICs
• RF modules
• ESD/TVS for external ports
• safety-related parts

Tier B — Medium risk (inspect by sampling)

Examples:
• inductors and magnetics
• MOSFETs and power diodes
• connectors used by customers
• crystals/oscillators
• key MLCCs on power rails

Tier C — Low risk (basic checks only)

Examples:
• standard resistors
• non-critical capacitors
• simple LEDs
• common hardware

You can tune this by experience, but having tiers is mandatory—otherwise inspection becomes expensive and slow.

⸻

Step 2: Required tools (minimal but effective)

You can do strong inspection with:
• 10×–40× microscope (or good inspection camera)
• digital caliper
• precision scale (optional but useful)
• multimeter / LCR meter (for passives)
• ESD-safe workstation (wrist strap + mat)
• camera for recording evidence
• label scanner or manual log system

Optional (for high-risk lots):
• X-ray service (for BGA/QFN internal checks)
• decapsulation service (very high value or suspicious lots)

⸻

Step 3: Incoming inspection flow (use this every time)

Step A — Paper check (before you open the bag)
1. Confirm PO matches delivery:
• manufacturer name
• exact MPN including suffix
• quantity and packaging (T&R, tray)
2. Check documentation (if required):
• CoC, traceability info
• distributor invoice/packing list
3. Verify lot/date code consistency and labels

Fail here → quarantine immediately.

⸻

Step B — Packaging and handling check

Look for:
• intact reels/trays (no re-taping, no mixed packaging)
• moisture barrier bag (for MSL parts)
• desiccant + humidity indicator card (HIC) where expected
• no broken seal or punctures

Red flags:
• resealed bags with no humidity card
• inconsistent labels across reels
• tape splices not documented (splices are sometimes normal but must be controlled)

⸻

Step C — Visual inspection (microscope)

Sample parts and check:
• top markings: font consistency, laser quality, alignment
• surface condition: sanding marks, resurfacing, scratches
• leads/pads: oxidation, re-tinning signs, bent pins
• contamination: residue, foreign particles
• for connectors: latch integrity and plating consistency

Typical counterfeit signs:
• uneven marking depth
• glossy “painted” look on top surface
• evidence of resurfacing
• mixed date codes in same reel
• inconsistent mold marks

⸻

Step D — Dimensional check (caliper)

Check package dimensions vs datasheet for suspicious lots:
• body size
• pin pitch
• overall height

This catches “wrong package” mistakes fast.

⸻

Step E — Electrical spot checks (by part type)

For resistors/capacitors/inductors (Tier B/C)
Use LCR meter to verify:
• resistance value within tolerance
• capacitance value (be aware MLCC value depends on test conditions)
• inductor value and basic DCR (if supported)

Important for MLCC:
• A quick LCR check won’t reveal DC bias behavior, but it can catch totally wrong values.

For MOSFETs/diodes (Tier B)
Spot checks:
• diode mode checks for body diode behavior
• gate threshold sanity (basic)
• Rds(on) spot check if you have fixture (optional but powerful)

For ICs (Tier A)
Spot checks:
• marking/label verification is primary
• if possible: simple functional test on a test board
• power-up current draw
• basic communication (I2C/SPI/UART)
• ID readout or programming (MCU)

If you can’t test, rely more heavily on authorized supply + documentation.

⸻

Step 4: Sampling plan (simple and practical)

You don’t need complicated statistics at first. Use a risk-based approach:

Tier A
• inspect every reel/tray lot visually
• sample: 5–10 parts per reel (more if suspicious)
• quarantine if any red flag appears

Tier B
• sample by quantity:
• small lot: 3–5 pcs
• medium lot: 5–10 pcs
• large lot: 10–20 pcs
• inspect packaging + basic electrical checks

Tier C
• packaging + label verification
• random spot checks occasionally

If your volumes are high, you can later adopt AQL sampling formally, but this tier method works well in practice.

⸻

Step 5: Moisture sensitivity handling (MSL parts)

For QFN/BGA and many ICs, moisture control matters.

If bag is opened:
• track floor life
• reseal properly with desiccant
• bake if required (follow manufacturer guidelines)

Common failure from poor MSL handling:
• “popcorning” during reflow (internal cracking)

Incoming inspection should record:
• whether MSL bag is intact
• HIC status (humidity indicator color)
• date opened and storage condition

⸻

Step 6: Quarantine and disposition rules (no confusion)

If any of these happen, quarantine immediately:
• wrong MPN/suffix
• missing or inconsistent labels
• suspicious marking/resurfacing
• moisture bag compromised for MSL parts
• mixed date codes without explanation
• obvious damage to leads/pads

Disposition options:
• return to supplier
• send for third-party analysis (X-ray/decap)
• allow use only after engineering sign-off and additional testing

⸻

Step 7: Recordkeeping (this makes you faster over time)

Log the following:
• supplier and channel (authorized/broker)
• purchase order and invoice
• MPN and quantity
• lot/date codes
• inspection results + photos
• disposition (accepted/quarantined/returned)
• which production batches used which lots

This is what lets you isolate problems later instead of recalling everything.

⸻

Common incoming inspection mistakes
• Only checking quantity, not MPN suffix
• Skipping moisture control checks for QFN/BGA
• No photos or records → impossible disputes later
• No tiering → inspection becomes too slow and expensive
• Letting “urgent production” bypass quarantine rules

⸻

Quick one-page SOP checklist (what your team should follow)
1. Verify PO/MPN/suffix/quantity/packaging
2. Check labels + traceability documents (Tier A)
3. Inspect packaging integrity + MSL bag/HIC
4. Microscope check markings and leads (sample by tier)
5. Dimensional checks for suspicious lots
6. Electrical spot checks by part type
7. Log results + photos
8. Quarantine if any red flags
9. Release to stock only after pass