AVL (Approved Vendor List) Best Practices: How to Build One That Actually Works

AVL (Approved Vendor List) Best Practices: How to Build One That Actually Works

An AVL (Approved Vendor List) is how you keep production moving without breaking your design. A good AVL prevents the two worst manufacturing problems:
1. line stoppage (no parts available)
2. silent reliability failures (bad substitutions that “fit” but don’t perform)

This guide explains how to build an AVL that is practical, fast for purchasing, and safe for engineering.

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What an AVL really is (not just “a list of brands”)

A working AVL includes:
• approved manufacturers (and sometimes distributor channels)
• approved part numbers or approved spec windows
• substitution rules (what’s allowed, what needs approval)
• required documentation (CoC, traceability)
• testing/validation requirement when substituting

If your AVL is only “Vendor A/Vendor B,” it’s not enough—because specs can still change silently.

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Step 1: Classify your BOM parts into control tiers

Use the substitution categories from #24 and turn them into AVL tiers:

Tier A (strict): engineering approval required

Examples:
• MCU/MPU/FPGA, memory
• RF modules
• power ICs (buck/boost/LDO controllers, chargers, PMICs)
• ESD/TVS on high-speed ports
• safety isolation parts

AVL format:
• approved exact MPNs only
• no “equivalents” without approval

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Tier B (controlled): substitute within locked specs and approved list

Examples:
• MLCCs used in power rails
• inductors for DC-DC converters
• MOSFETs and diodes in power paths
• connectors
• crystals/oscillators

AVL format:
• approved MPNs + locked key parameters
• substitution allowed only if all parameters match

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Tier C (flexible): substitute freely within spec

Examples:
• many resistors
• many non-critical capacitors
• indicator LEDs (with defined brightness range)
• common hardware (screws, standoffs) if standardized

AVL format:
• define spec window and footprint
• allow multiple brands and MPNs

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Step 2: Define “critical parameters” for each Tier B class

This is the core of a good AVL. Without this, purchasing will accidentally break your design.

MLCC (ceramic caps)

Lock:
• capacitance, dielectric (X7R/X5R/C0G), voltage rating, package
• for power rails: minimum effective capacitance under DC bias (if you can)

Inductors (for DC-DC)

Lock:
• inductance, Isat, Irms, DCR max, footprint, height

MOSFETs

Lock:
• Vds rating, Rds(on) at your gate voltage, package thermal, Qg (if PWM)

Diodes

Lock:
• reverse voltage, current, Vf at operating current
• for TVS: VRWM, clamping, capacitance, IEC rating

Connectors

Lock:
• mating type, latch type, plating, mating cycles, current rating, wire gauge

Crystals/oscillators

Lock:
• frequency, tolerance/ppm, load capacitance (crystal), ESR, package, startup/jitter (if needed)

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Step 3: Specify sourcing channels and traceability requirements

For Tier A parts (and many Tier B):
• preferred: authorized distributors
• require lot tracking on incoming
• require CoC for high-risk parts when buying outside authorized channels

If you allow brokers:
• define when it’s allowed (shortage only)
• require inspection/testing plan
• quarantine + sampling policy

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Step 4: Set a substitution approval workflow that is fast (and doesn’t block production)

A simple workflow that works in real companies:

Tier C

Purchasing substitutes freely within spec → records MPN and lot.

Tier B

Purchasing can substitute only from AVL-approved list and must confirm locked parameters.
If substitution is new (not already on AVL), engineering approves once and adds it.

Tier A

Always engineering approval before purchase/assembly.

Key point:
The workflow must be fast. If engineering approval takes a week, production will bypass the process.

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Step 5: Keep the AVL “alive” (maintenance rules)

An AVL is not a one-time document.

You should update it when:
• a part goes NRND/EOL
• repeated shortages occur
• you find better-cost equivalents (validated)
• quality problems occur (remove vendor/MPN)
• your product moves to higher volume (add second sources)

Simple maintenance habit:
• review Tier A parts quarterly
• review Tier B parts every 6 months
• Tier C can be updated as needed

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Step 6: AVL template structure (copy this format)

You can use this structure in Excel/Notion/ERP:

Columns that make AVLs useful
• BOM Line / Ref Designator group
• Function (e.g., “buck output inductor”, “USB ESD”)
• Primary MPN
• Approved Alternates (MPNs)
• Tier (A/B/C)
• Locked Parameters (must not change)
• Package/Footprint
• Notes (special handling, MSL, testing)
• Approved by / Date
• Supply risk notes (lead time trends, last buy, etc.)

If you keep these fields consistent, purchasing can act quickly and safely.

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Step 7: Most common AVL mistakes (and how to avoid them)

Mistake 1: Too strict → production gets stuck

Fix:
• expand Tier B/C alternates
• pre-approve multiple sources for common passives and magnetics

Mistake 2: Too loose → silent failures

Fix:
• lock critical parameters
• require approval for Tier A always

Mistake 3: No traceability

Fix:
• lot tracking for Tier A/B
• incoming inspection for high-risk parts

Mistake 4: AVL not updated

Fix:
• schedule regular review
• assign an owner (purchasing + engineering)

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A simple “starter AVL” strategy (fast and practical)

If you’re starting from zero, do this:
1. Build Tier A list first (top 20 critical active parts)
2. For each, add at least one alternate (same family/pin-compatible if possible)
3. Build Tier B rules next (power passives, TVS, connectors)
4. Make Tier C broad (resistors/caps) with locked basic specs
5. Add traceability rules for anything bought outside authorized channels

This gives maximum protection with minimal bureaucracy.