3.3 Process Materials Change Control

In electronics manufacturing, "Process = Chemistry + Physics." Changing a consumable is not a commercial swap; it is a fundamental alteration of the manufacturing baseline. A new flux formulation can pass visual inspection today but cause electromigration failures six months later. Therefore, changing any process material—solder paste, adhesive, cleaner, or coating—is a Critical Process Change that requires rigorous validation, not just a price comparison.

The "No Silent Substitutions" Rule

Rule: Procurement is strictly Forbidden from authorizing a substitute process material without a signed Engineering Change Order (ECO).

Why: A "better" cleaner chosen for cost might react with the potting compound to create conductive residue. Procurement lacks the technical visibility to assess this risk.

The Trap: If a Distributor says, "Product A is discontinued, here is the direct replacement Product B," Stop. Do not accept it. Flag it to Engineering immediately.

The Change Approval Workflow

Changing a chemical involves a standardized qualification path. Procurement drives the timeline; Engineering drives the data.

Phase 1: Risk Assessment & Approval

• Trigger: Vendor PCN, End-of-Life (EOL), or Cost Reduction initiative.
• Input: Technical Data Sheet (TDS) + Safety Data Sheet (SDS).
• Gate: Process Engineering Manager must approve the intent to test.

Phase 2: Validation Trial (The "DOE")

• Action: Purchase a sample lot (Small Qty).
• Protocol: Run a controlled Design of Experiments (DOE).
  • Solder Paste: Print volume repeatability, Slump test, Solder ball test, Voiding analysis (X-Ray).
  • Chemistries: SIR (Surface Insulation Resistance) testing to validate cleanliness.
• Criteria: New material must meet or exceed the CpK (Process Capability) of the current baseline.

Phase 3: Pilot Run (Production Beta)

• Action: Run a limited batch of non-critical or "internally used" boards.
• Scale: 50 – 100 units.
• Monitor: First Pass Yield (FPY) and specific defect rates.

Phase 4: Final Sign-off & Cut-In

• Document: Final Qualification Report (FQR) attached to the ECO.
• Output: Update APML (Chapter 3.1) and issue new internal Part Number (if applicable).

Rollback Strategy

Hope is not a strategy. Every change must have an "Undo" button.

Requirement: Retain at least 2 weeks of stock of the Old material before switching fully to the New material.

Why: If the new flux causes massive probe contamination at In-Circuit Test (ICT) after 3 days of running, you must immediately revert to the old chemistry to keep the line running while you investigate.

Inventory Disposition Logic

When the switch is flipped, the old chemistry becomes a liability.

If Change = Performance Upgrade (Hard Cut):

• Then Dispose of Old Stock immediately.
• Action: Scrapping cost must be calculated into the ROI of the change.

If Change = Commercial/Second Source (Soft Transition):

• Then Consume Old Stock to zero (FIFO).
• Constraint: Do not mix chemistries on the same board (e.g., do not rework a board with Flux A if it was screened with Paste B, unless compatibility is proven).

The Change Record

Documentation is the only defense against liability. A Change Record must exist for every swap.

Field	Description	Data Type
Change ID	Unique ECO identifier	String (ECO-901)
Material	Name of Old vs. New Material	String
Reason	Cost / EOL / Quality Improvement	Enum
Validation	Link to Qualification Report (SIR/Cross-section)	URL / Doc ID
Affected Lines	SMT-01, SMT-02, Wave-01	List
Cut-In Date	Date/Lot Code of first production use	Date
Disposition	Plan for old inventory (Scrap/Use)	Text
Approver	Process Engineering Mgr & Quality Mgr	Signatures

Final Checklist

Control Point	Requirement	Critical Threshold
Authority	Procurement cannot approve subs	Forbidden
Safety	SDS Review & Safety Sign-off	Mandatory
Testing	SIR / Compatibility Data	Required
Pilot Run	Limited production batch	Min 50 units
Backup	Old stock retention	2 Weeks Supply
Traceability	Cut-in Lot recorded in History	100%