Contents
A bill of materials (BOM) defines the components a product requires. An approved vendor list (AVL)—often called an approved manufacturer list (AML)—defines which manufacturers or approved component alternatives may satisfy those requirements. A separate approved supplier list may control which distributors, independent suppliers or other purchasing sources can sell the parts. These records answer different questions and should not be treated as interchangeable.
Terminology varies among companies, so the controlled documents must state what “vendor,” “manufacturer” and “supplier” mean. For PCB assembly, the practical objective is to give purchasing enough approved flexibility without allowing an unreviewed component or source into production.
| Item | Main purpose | Typical content | Main owner |
|---|---|---|---|
| BOM | Define required parts | MPN, value, package and quantity | Engineering |
| AVL / AML | Define approved manufacturers or alternatives | Approved MPNs and makers | Engineering / Quality |
| Approved supplier list | Define approved purchasing sources | Distributor or vendor | Procurement / Quality |
| Assembly BOM release | Control production data | Released part and revision data | NPI / Manufacturing |
What is a BOM?
A BOM is a controlled product record that identifies the items required to build an assembly. A sourceable electronic BOM normally includes the complete manufacturer part number, description, quantity, reference designators and package. It should also identify do-not-install or do-not-populate positions where relevant.
The BOM tells the manufacturer what the design requires, but it does not automatically explain whether multiple manufacturers are acceptable. An incomplete MPN may omit temperature grade, finish, tolerance, speed or packaging suffixes. The BOM risk analysis guide explains how lifecycle, lead time, MOQ and single-source exposure affect the complete parts list.
What is an AVL or AML?
An AVL or AML is a controlled approval record that identifies which manufacturers, manufacturer part numbers or component alternatives may be used for a defined BOM requirement. Some organizations use AVL for manufacturers, others for suppliers, and some distinguish AML from AVL. The label matters less than a clear definition inside the quality system.
An entry should show the approved part identity, approval status, product or BOM scope, restrictions and responsible owner. Approval may be unconditional for that defined use or conditional on a product revision, manufacturing site, qualification result or customer authorization. Listing a candidate is not the same as approving it.
What is the practical difference between a BOM and an AVL?
The BOM answers, “What part does the design require?” The AVL answers, “Which approved manufacturers or component alternatives may satisfy that requirement?” One BOM line can therefore point to one approved MPN or several controlled choices.
For example, a BOM line may require a 10 kΩ resistor in a specified package, tolerance, power rating and temperature coefficient. The AVL can name manufacturer MPNs that engineering has accepted for that position. It must not reduce the requirement to “10 kΩ, or equivalent” if voltage rating, construction or pulse capability matters.
Why does an AVL matter for PCB assembly?
An AVL creates sourcing flexibility while preserving engineering control. Approved alternatives can reduce dependence on one manufacturer, support continuity planning and allow quotation against known options. At the same time, the approval boundary prevents purchasing or an assembler from choosing a superficially similar part without authorization.
A formal AVL is not mandatory for every small experiment. A prototype may use a tightly controlled single BOM choice. As a product moves toward repeat production, clearer approval data improves repeatability, change control and communication among engineering, quality, procurement and the PCBA supplier.
Manufacturer approval and distributor approval are different
Manufacturer approval concerns the company and MPN that produce the component. Distributor or supplier approval concerns the commercial channel from which the component is purchased. An approved manufacturer does not make every seller an approved source, and an approved distributor cannot turn an unapproved component into an engineering-approved substitute.
Authorized distribution, independent supply and contract-manufacturer sourcing may carry different documentation, warranty and risk conditions. Define permitted channels separately and apply risk-based controls. The component traceability and counterfeit-prevention guide covers provenance, receiving evidence and inspection without replacing engineering approval.
How should alternate components enter the AVL?
An alternate should enter the AVL through a controlled engineering decision, not a catalog suggestion. First identify the sourcing need and the original part’s critical function. Compare specifications, verify package and pinout, review relevant performance, test or qualify where needed, approve the result and release updated controlled data.
The approval record should identify the original and alternate MPNs, affected references or BOM line, comparison evidence, validation performed, limitations, approver and effective revision. The alternate-component evaluation guide covers electrical, thermal, mechanical and firmware review in detail; the AVL records its approved outcome rather than repeating the analysis.
How can an AVL govern passive components?
A passive-component AVL may permit multiple manufacturers when engineering defines the relevant limits. For a resistor, those limits can include resistance, tolerance, power, voltage, temperature coefficient, construction, package and pulse capability. For a capacitor, capacitance, effective bias behavior, dielectric, ESR, voltage, tolerance and package may be material.
Some organizations approve named MPNs; others approve a controlled specification plus qualified manufacturers. Either model must make the boundary auditable. An unrestricted “or equivalent” note transfers an engineering decision to purchasing and should not be used as a substitute for criteria.
Why are IC and complex-semiconductor approvals often restrictive?
IC approval is often restrictive because two devices with similar descriptions can differ in pinout, startup behavior, timing, analog performance, package, register map, firmware support or lifecycle. A manufacturer-documented second source may still require application-specific review.
The AVL can identify whether an IC is approved as a true drop-in option, approved only with firmware, approved for a later product revision or not approved. That status prevents production from combining incompatible hardware and software baselines.
How should connectors and electromechanical parts be controlled?
Connector approval must preserve the mating interface, pin assignment, keying, dimensions, mounting, retention, ratings and mechanical envelope. Tooling, contact plating, insertion cycles and product lifecycle may also matter. The same board footprint alone does not prove compatibility.
Record the mating part or family where it constrains approval. A substitute that solders correctly but does not fit the enclosure, cable or service tooling is not equivalent for the finished product.
How does revision control apply to an AVL?
AVL approval should be linked to the product and BOM revision for which the evidence is valid. An engineering change order or engineering change notice can release a newly approved option, withdraw an outdated part or add restrictions. The manufacturing release should use the same approved baseline.
Revision control prevents an alternate qualified for one design from silently spreading to another. It also preserves the reason for a decision when an old manufacturer part is later removed. This article does not prescribe a specific PLM system; a controlled spreadsheet, ERP field or database can work if ownership, status and revision are unambiguous.
How does a clear AVL affect PCBA quotation?
A clear AVL lets a quotation state which approved options and sources support its material assumptions. The supplier can identify lines with flexibility, lines restricted to one MPN and lines requiring customer approval before an alternate is priced. That can improve the quality of lead-time and cost discussions without guaranteeing a fixed result.
The quoted source, packaging and validity period still need confirmation. An AVL does not prove inventory availability or reserve stock; those questions belong in the project’s current sourcing review. Excel Circuit’s component sourcing service can review BOM and approval constraints before PCBA quotation.
What are common AVL mistakes?
- Ambiguous “or equivalent” wording: no measurable approval boundary is defined.
- Incomplete MPNs: package, grade or finish differences remain unresolved.
- Outdated alternatives: lifecycle or qualification changes are not reviewed.
- Unapproved vendor substitution: a seller or assembler makes an engineering choice.
- Package-only matching: pinout and performance are assumed from body style.
- No revision scope: an approval is applied to products it was never evaluated for.
- Mixed ownership: manufacturer approval and purchasing-source approval are recorded in one unclear field.
A useful approval record also distinguishes a temporary deviation from a permanent AVL addition. A one-build authorization may solve a specific shortage without approving that part for every future order. Record quantity, lot or build scope, expiry condition and customer disposition so the exception does not become an undocumented standard.
Conditional approvals need machine-readable restrictions where practical. A note such as “approved only for product revision C after firmware 2.4” is actionable; “approved with conditions” is not. Purchasing and manufacturing should see the restriction before an order or work order is released, not after material arrives.
How do you build an AVL for PCB assembly?
- Normalize the BOM and resolve incomplete part identities.
- Identify critical, custom, single-source and lifecycle-sensitive parts.
- Record existing approved manufacturer choices.
- Define the electrical, mechanical and process limits for possible options.
- Route candidates through engineering review.
- Validate alternatives at a level appropriate to the design risk.
- Assign approved, conditional, pending or rejected status.
- Document approved or restricted purchasing sources separately.
- Release the AVL with the correct BOM, product and ECO/ECN revision.
- Review entries when the design, lifecycle evidence or sourcing conditions change.
Periodic review should follow program exposure rather than an invented universal interval. A lifecycle notice, supplier problem, new product revision or qualification result can trigger review even when a calendar date has not arrived. If an approved option becomes obsolete, use the obsolete-component response guide to assess stock, replacement and redesign paths.
AVL checklist
- Part identity: BOM line, references, description and complete original MPN are clear.
- Manufacturer: legal maker and approved manufacturer MPN are recorded.
- Alternate status: approved, conditional, pending or rejected status is explicit.
- Sourcing source: allowed distributors, independent-source restrictions and customer-supplied rules are separate from component approval.
- Qualification: comparison, tests, limitations and evidence location are retained.
- Lifecycle: status source and review date support the decision.
- Revision: BOM, product and ECO/ECN applicability are identified.
- Approval owner: engineering, quality, procurement and customer responsibilities are named.
Before release, test the record with one real purchase scenario. A buyer should be able to select an approved MPN and permitted source without interpreting design intent. If two reasonable readers could reach different choices, the item needs a clearer part identity, restriction or approval owner.
Information required from the customer
Provide the current BOM, approved manufacturers, approved alternates and any restricted manufacturers. Include approved distributors or source restrictions, a customer-supplied AVL/AML, lifecycle requirements, production quantity, qualification requirements and the active product, BOM and ECO/ECN revision.
Identify whether an entry is a candidate or a released approval. If Excel Circuit may propose alternatives, define who can approve them and what comparison or validation evidence the project expects.
Review the AVL before PCBA quotation
Send your BOM and approved manufacturer requirements if you need the AVL, alternates and sourcing constraints reviewed before PCBA quotation. Clear approval ownership allows sourcing flexibility without turning procurement into uncontrolled design change.
