Solder Paste Incoming Inspection Checklist

Upon receipt of Solder Paste, immediately verify the manufacturer’s label against the purchase order to confirm alloy composition, particle size distribution, and expiration date, while cross-checking the lot number with the supplier’s CoC and internal ERP system to ensure full traceability and compliance with IPC-J-STD-005 requirements. Store unopened containers at 0–10°C without temperature fluctuation exceeding ±2°C per hour, and log ambient conditions in the receiving area using a calibrated data logger that records time-stamped readings every 15 minutes throughout the entire unloading and staging process.

Before opening, inspect each sealed tube or jar for physical damage, bulging, leakage, or discoloration of the outer packaging, and reject any unit showing signs of frost formation inside the cap seal or condensation on the inner lid, because moisture ingress during cold-chain interruption promotes premature oxidation of tin particles and degrades Flux activity. Once opened, assign a unique inspection ID and record the exact time of first use, since solder paste must be brought to room temperature for 2–4 hours under controlled humidity below 60% RH before stirring, and any deviation risks phase separation between metal powder and vehicle matrix.

Perform manual stirring for exactly 3 minutes using a dedicated non-metallic spatula rotating at 60 rpm to avoid air entrapment, then load a 2g sample into a Brookfield viscometer spindle SC4-21 and measure viscosity at 25°C with shear rate ramped from 0.5 to 50 rpm over 60 seconds, accepting only values within ±15% of the certified baseline specified on the CoA. Simultaneously dispense 0.5g onto a pre-weighed glass slide, dry at 105°C for 90 minutes, cool in a desiccator for 20 minutes, and calculate metal content gravimetrically as (dry_weight / initial_weight) × 100%, rejecting batches falling outside the 88.5–90.2% range for SAC305 formulations.

Use a digital microscope at 200× magnification to scan three random 1mm² fields across a freshly printed test pattern on FR-4, evaluating particle agglomeration, flux bleeding, and edge definition, where bridging width exceeding 25µm or void density above 8% per square millimeter indicates inadequate rheology control or aging-related degradation. Conduct slump testing by depositing a 0.3mm-diameter dot onto a heated ceramic plate at 25°C, imaging after 10 minutes and calculating spread ratio as final_diameter / initial_diameter, discarding material if ratio exceeds 1.42 due to excessive vehicle fluidity compromising stencil release.

Run differential scanning calorimetry on a 10mg sample from the same container used for viscosity testing, heating from 25°C to 250°C at 5°C/min, and compare onset melting point against the spec sheet; deviation beyond ±1.8°C suggests flux decomposition or unintended alloy segregation. Visually assess post-reflow residues under 50× white-light illumination for halos, cracking, or hygroscopic tackiness, because such anomalies correlate strongly with chloride ion contamination above 0.055 µg/cm² as measured by ion chromatography, which accelerates electrochemical migration in high-humidity environments. Document all measurements in the centralized QA database within 90 minutes of completion, attaching raw instrument files and signed technician verification before releasing the batch to production.