3.1 Approved Process Materials List (APML) + Specifications

A Bill of Materials (BOM) defines the components, but the Approved Process Materials List (APML) defines the chemistry that holds them together. Solder paste, flux, adhesives, and cleaning agents are not generic commodities; they are critical process variables. Changing a flux brand without validation can alter wetting characteristics, causing dendrite growth or voiding that fails months later in the field. The APML is a closed ecosystem: if it is not on the list, it does not enter the factory.

APML Architecture & Attributes

The APML serves as the "BOM for the Process." Every chemical consumable must be defined with the same rigor as an electronic component.

Required Data Attributes

• Material ID: Internal Part Number (e.g., CHE-0045).
• Mfr Part Number: Exact Vendor Reference (e.g., Indium 8.9HF).
• Category: Solder Paste / Flux / Adhesive / Cleaner / Conformal Coating.
• Storage Class: Temperature requirement (e.g., Refrigerated 2–8°C).
• Shelf Life: Definition of "Use By" window (e.g., 6 months from Mfg Date).
• Process Compatibility: Links to specific reflow profiles or wash processes.

Sourcing & Substitution Logic

Chemicals interact. A "better" cleaner might dissolve the ink on a capacitor. Substitution requires engineering validation, not just a price check.

If Purchasing Requests a New Source:

• Condition: Same Manufacturer, Different Distributor.
• Action: Approved.
• Constraint: Distributor must adhere to "Cold Chain" logistics if material is temp-sensitive.

If Manufacturer Changes Formulation (PCN):

• Action: Stop. Treat as a new material.
• Requirement: Process Engineering must run a qualification lot (shear test, SIR testing) before release.

If Purchasing Suggests an "Equivalent" Alternate:

• Action: Forbidden.
• Reason: "Generic" solder paste does not exist. Flux rheology dictates print speed and voiding rates.
• Exception: Only permissible if the alternate is already fully qualified and listed as "Alt-1" in the APML.

Storage & Handling Controls

Chemistry is perishable. The Warehouse team is the guardian of shelf-life and environmental integrity. Failure here turns liquid cash into hazardous waste.

Inbound Cold Chain (Receiving Protocol)

• The Risk: Solder paste exposed to >10°C separates and fails.
• Rule: Priority Intake. Shipments marked "Refrigerated" bypass standard queue.
• Verification: Inspect the included temperature logger or chemical indicator dot immediately.
  • If Indicator = Red/Tripped: Quarantine immediately and notify Buyer for RMA. Do not receive into ERP.
• Storage: Transfer to cold storage (+2°C to +10°C) within 15 minutes of dock arrival.

Shelf Life & FIFO Discipline

• Rule: Strict FIFO. The ERP must auto-allocate the oldest active lot first.
• Control: Warehouse software (WMS) must block the picking of expired Material IDs.
• Prohibition: Never "re-label" or extend the expiration date of chemical consumables without a written waiver from the Process Engineering Manager.

Ownership & Governance

The APML is not a suggestion box. It is a controlled document owned by Process Engineering, not Procurement.

Ownership Roles:

• Process Engineer: Owns the technical specification. Sole authority to Add/Remove items.
• Procurement: Owns the commercial negotiation and stock levels. Cannot substitute brands.
• Quality: Audits expiration dates and storage logs.

Review Cadence:

• Event: Annual APML Review.
• Action: Remove obsolete materials. Update Safety Data Sheets (SDS). Verify RoHS/REACH compliance.

The APML Table Structure

Implement this structure in your ERP or Document Control System.

Material ID	Category	Manufacturer	Mfr P/N	Approved Alt	Storage	Shelf Life
SOL-001	Solder Paste	Indium	8.9HF Type 4	Alpha OM-338	0–10°C	6 Mos
FLX-002	Rework Flux	Kester	959T	None	Ambient	2 Yrs
ADH-055	Underfill	Loctite	3513	None	-40°C	12 Mos
CLN-101	PCB Wash	Kyzen	Aquanox 4625	Zestron FA+	Ambient	5 Yrs

Final Checklist

Control Point	Requirement	Critical Threshold
Definition	All process chemicals listed	100% Coverage
Substitution	Procurement auto-swap	Forbidden
Receiving	Temp Log check for Cold Chain	Mandatory
Expiry Control	System block on expired lots	Active
Traceability	Lot # recorded to Batch ID	100%
Ownership	Engineering Sign-off	Required for Adds