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52 SMT007 MAGAZINE I JULY 2025 K N O C K I N G D OW N T H E B O N E P I L E F i g u re 3 : Re -t i n n i n g w i t h a s i d e wave p ro c e s s c a n e l i m i n ate s u r fa c e ox i d at i o n a n d b r i d g e -f re e s o l d e r j o i nt s . ▼ procedures can distort the wet- ting curves, undermining the reliability of the results. While the wetting balance method provides detailed and quanti- tative insights, it is best used by experienced personnel in a well-maintained testing environ- ment. This is often part of devel- opment or qualification testing, rather than a routine production quality control method. Both methods help ensure that the component's solderable surfaces are properly prepared and meet reliability standards. They are especially useful when switching between solder alloys, from lead-based to lead- free, or changing processing conditions. Note: There are no universally established industry pass/fail criteria based solely on wetting balance measurements. Engineers primarily use these tests for development and qual- ification rather than routine pro- duction monitoring. Verification with visual inspection or addi- tional test methods is often nec- essary to confirm acceptable solderability. Clarifying the Difference: Solderability Testing vs. Re-tinning Although component re-tinning or preconditioning is not a formal solderability test, it is an effective method for reworking compo- nents with poor or degraded sol- derability. Severe oxidation of the component surfaces often causes this degradation, typically from prolonged storage in warehouse environments. Oxidation creates a barrier that hampers proper wetting and joint formation during soldering, thereby compromis- ing reliability. Re-tinning involves applying a fresh layer of solder to restore surface conditions, ensur- ing better wettability and bonding during assembly. This process is particularly valuable for high-reliability or end-of-life product builds, where salvaging existing components can be a cost-effective alternative to discarding and replacing them. For example, with a fine-pitch quad flat package (QFP) device, re-tinning with a side wave pro- cess can eliminate surface oxida- tion and bridge-free solder joints, ensuring the component meets the necessary quality standards (Figure 3). Proper re-tinning not only improves solderability but