Keep Solder-Paste Replenishment Visible in the Production Record

Adding paste to a stencil creates a material-history boundary even when the printer recipe stays unchanged. Fresh material may mix with paste that has already experienced printing, idle time, and ambient exposure. A container label alone therefore cannot identify the condition of every deposit printed afterward.

State the permitted material combination

Begin with the paste supplier’s handling instructions and the qualified line procedure. Verify formulation, alloy, powder classification, lot, and relevant time limits before replenishment. Do not assume that two products can be combined because their alloy names match. AIM’s Line-Down technical series includes the question of mixing old and new paste, illustrating why this should be a specific process decision.

The production record should distinguish adding unused paste, transferring paste between containers, and returning material recovered from a stencil. Those operations have different histories. If reuse is allowed by a validated procedure, identify its conditions and approval; a general instruction to conserve paste is insufficient.

Link additions to boards

• Record the active stencil, printer, assembly revision, and paste roll already in use.
• Identify the added container and its opening and preparation history.
• Record addition time and a defensible quantity estimate or measurement.
• Mark the first board printed after the addition and any recovery strokes.
• Preserve the inspection results immediately before and after replenishment.

Use the container-time record for the incoming material and a separate line event for its introduction. For intermittent production, connect the event with the restart-print review. This avoids attributing a pause effect to a new material lot.

Define the traceability boundary honestly

Consider a printer that adds paste from lot B while lot A remains on the stencil. Boards produced afterward may contain both lots until the roll is replaced and the equipment is prepared under the defined changeover procedure. Assigning the very next board exclusively to lot B would overstate traceability. Record the overlap population and the event that establishes a clean boundary.

Smaller controlled additions can improve operational consistency but create more events to record. Larger additions reduce handling frequency while changing the amount of material exposed on the stencil. Choose the practice through print-performance evidence and supplier guidance, then make its records practical for operators.

When investigating an excursion, retain both container identities, addition times, and affected board ranges. This supports a targeted review without pretending that physical mixing produces an exact lot transition at a single serial number.