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86 SMT007 MAGAZINE I NOVEMBER 2025 defect screening), especially for pass/fail decisions or supplier qualification. For stringent requirements, include environmental preconditioning (e.g., steam aging or controlled storage) and, where appropri- ate, destructive analysis (cross-sections, X-ray) to correlate wetting data with joint integrity. Additional Testing for High-reliability Applications Many sectors—industrial, automotive, medical, and aerospace and defense—expect devices to remain serviceable for years, which often means long- term component storage. In these contexts, engi- neers should verify solderability, a leading indica- tor of interconnect reliability, beyond basic incom- ing inspection. This matters because long storage and harsh environments promote oxidation, contamination, and intermetallic growth on terminations, which slow or prevent wetting. Supplemental testing helps confirm that finishes (including re-tinned surfaces) still deliver robust joints at end-of-life storage. Stressing for Shelf-Life: Steam Aging Steam aging accelerates natural aging by expos- ing components to elevated humidity and tempera- ture under controlled conditions. The goal is to sim- ulate years of shelf life in days or hours, then mea- sure whether the finish still wets promptly and com- pletely under your standard test method. In practice, teams should apply steam aging to representative lots or post-re-tin samples, follow the relevant standard's time/temperature/humidity profile and handling steps, and immediately evalu- ate solderability after aging to minimize confound- ing re-oxidation. Recommended Supplemental Regime A comprehensive evaluation strategy combines complementary methods to deliver both qualitative insights and quantitative data. The primary screen- ing step should use a dip-and-look test to quickly assess visual indicators such as overall coverage, non-wetting or de-wetting, pinholes, and other sur- face defects. This rapid inspection provides an immediate go/no-go assessment and helps flag potential issues early in the process. Next, a quantitative wetting balance test should be performed to measure key parameters such as wetting time, peak wetting force, and the shape of the wetting curve. These results can then be com- pared against your established baselines to detect subtle performance shifts and confirm whether the soldering process is meeting expected standards. When deeper insight is needed, correlation meth- ods such as cross-sectional analysis, X-ray, or CT imaging to evaluate voiding, and shear or pull tests should be employed. These techniques help link observed wetting behavior directly to joint integrity, providing a more complete understanding of how surface interactions affect mechanical reliability. For re-tinned components, it is important to con- duct testing both before and after the re-tinning pro- cess, as well as following steam aging. This ensures that any observed improvements in wetting perfor- mance are long-lasting and robust, rather than tem- porary enhancements that degrade over time. Interpreting Results When interpreting results, treat wetting-balance metrics as engineering data; use control limits derived from known-good parts/finishes rather than universal pass/fail numbers. Use replicates and report the full context (finish, flux, alloy, bath tem- perature, immersion rate, preconditioning). If dip- and-look passes but force/time metrics trend worse, investigate bath cleanliness, flux activity, or surface contamination; conversely, strong force data with visual defects still warrants fail and rework. F i g u re 3 : Wet t i n g - b a l a n c e c u r ve c o m p a r i n g c o m p o n e nt s b efo re a n d af te r re -t i n n i n g . ▼ K N O C K I N G D OW N T H E B O N E P I L E