Lead-free solder bars have a high melting point and can damage components or assemblies. According to the concept of lead-free soldering, the melting point temperature of SnAgCu is increased from 183°C to nearly 217°C, and the peak temperature is as high as 260°C. After a long period of preheating, the high temperature can be properly reduced. Trim temperatures are also affected, with some components reaching up to 280°C. Components used at such higher temperatures must undergo qualification certification, and uncertified components need to be assembled manually.

Optical inspection questions

Testing lead-free solders is essentially the same as testing conventional leaded solders. The solder joint appearance of lead-free soldering looks very similar to traditional tin-lead solder joints. To detect which type of welding it belongs to, the key is to find a detection mechanism that correctly distinguishes the visual characteristics of each shape. However, the solder joints of lead-free and lead-based soldering still have some differences in appearance and affect the accuracy of the AOI system. The streaks of lead-free solder joints are more pronounced and rougher than corresponding lead solder joints due to the phase transition from liquid to solid. As a result, such solder joints appear rougher and uneven. In addition, the surface tension of lead-free solder is high, it is not as easy to flow as lead solder, and the shape of the rounded corners formed is also different. These visual differences require recalibration of AOI equipment and software. For example, the "automatic pass values" set in some lead solder AOI systems may be slightly different than lead-free solder.