3.3 Process materials change control

Changing a chemical consumable in electronics manufacturing is rarely a simple commercial substitution; it represents a structural change to the manufacturing baseline. A new flux formulation might appear acceptable initially but could introduce long-term reliability issues like electromigration in the field. Therefore, changing any process material—such as solder paste, adhesive, or cleaner—requires thorough engineering validation, not just a procurement assessment.

The substitution protocol

The Standard: Procurement should not authorize or purchase a substitute process material without formal engineering approval or an Engineering Change Order (ECO).

The Rationale: Chemical interactions are complex. A substituting cleaner might react negatively with specific component coatings. Procurement generally relies on Engineering to assess these technical risks.

The Guidance: If a distributor offers a “direct replacement” for a discontinued product, it must not be accepted automatically. The suggestion must be routed to Process Engineering for review.

The change approval workflow

Changing a production chemical typically follows a standardized qualification path, with Procurement managing the commercial aspects and Engineering managing the technical validation.

Phase 1: risk assessment & approval

The Trigger: A Vendor Product Change Notification (PCN), an End-of-Life (EOL) notice, or a process improvement initiative.
The Input: Review of the Technical Data Sheet (TDS) and Safety Data Sheet (SDS).
The Gate: Engineering leadership reviews the proposed change to determine if formal qualification testing is warranted.

Phase 2: validation trial

The Action: A small, controlled sample lot must be procured.
The Protocol: A defined Design of Experiments (DOE) must be executed.
- E.g. for Solder Paste: Print volume repeatability, slump, and voiding (via X-Ray) must be evaluated.
- E.g. for Chemistries: Surface Insulation Resistance (SIR) testing must be performed to validate electrical cleanliness.
The Criteria: The new material should meet or exceed the performance metrics of the current baseline process.

Phase 3: pilot run (production beta)

The Action: A limited, controlled batch of PCBAs should be run through the line using the new material.
The Scope: Typically a small run (e.g. 50–100 units).
The Monitor: First Pass Yield (FPY) and specific defect rates must be closely tracked to identify any process shifts.

Phase 4: final sign-off & system update

The Document: A Final Qualification Report (FQR) must be compiled to authorize the change.
The Output: The Approved Process Materials List (APML) must be updated and a new internal ERP Part Number assigned if the change warrants it.

The rollback strategy

Every chemical change process should include a contingency plan.

The Guideline: A sufficient buffer stock (e.g. 2 weeks’ worth) of the old material must be retained before fully transitioning to the new material in production.
The Rationale: If unforeseen issues (like unexpected test probe contamination) arise during the initial high-volume run of the new chemistry, the production can quickly revert to the old, validated chemistry to maintain production while investigating the issue.

Inventory disposition

When transitioning to a new chemistry, the remaining inventory of the old material must be managed carefully.

If the Change is a Process Upgrade (Hard Cut):

The Action: The old inventory must be scrapped and safely disposed of.
The Financial Impact: The cost of scrapping the old inventory must be ensured to be factored into the ROI analysis for the process change.

If the Change is a Commercial Substitution (Soft Transition):

The Action: The old stock must be consumed using strict FIFO before introducing the new stock.
The Constraint: Mixing different chemistries on the same physical assembly must be avoided unless Engineering has explicitly proven their compatibility.

Documenting the change

Clear records of chemical changes within the PLM or ERP system must be maintained for traceability and audit purposes.

Data Field	Description	Example
Change ID	The unique Engineering Change Order (ECO) or change identifier.	ECO-901
Material Details	Explicit naming of the Old vs. New Material.	Solder Paste A → Solder Paste B
The Reason	Motivation for the change (e.g. Cost, End of Life (EOL), Quality).	EOL Replacement
Validation Proof	Link or reference to the formal Qualification Report.	Doc-1234
Effectivity	Identification of where the change applies (e.g. SMT-01).	All SMT Lines
Cut-In Point	The planned date or lot code for the transition.	Target: Nov 1st
Disposition	How the old inventory will be handled (Scrap or Use-Up).	Exhaust old stock
Approvals	Required signatures from Engineering and Quality.	[Digital Signatures]

Final Checkout: Process materials change control

Control Point	Engineering Requirement	Target Goal
Approval Authority	Chemical substitutions require engineering sign-off.	Enforced
EHS Compliance	New chemicals undergo full SDS and EHS review.	Mandatory
Validation Data	Empirical data (e.g. SIR testing) supports the swap.	Documented
The Pilot Run	System changes are preceded by limited pilot runs.	Standard Practice
The Backup Plan	Buffer stock of old material is retained for safety.	Maintained during cut-in
Traceability	The cut-in lot is tracked in product history records.	Executed