Nowadays, lead-free solder paste
is paid more and more attention, because the lead-free solder paste currently used is mainly environmentally friendly solder paste. Reliability after soldering, and considering the cost borne by customers and many other issues, the characteristics of environmentally friendly lead-free solder paste:
First of all, the environmentally friendly lead-free solder paste does not contain ODS substances and will not destroy the ozone layer; it does not contain halogen, and it is non-corrosive to PCB boards after soldering; the surface insulation resistance is high, and the electrical properties are good; the solder joints are full and bright; the liquid color is transparent or light yellow .
Environmentally friendly lead-free solder paste operates under the specified parameters, which can achieve excellent soldering effect, can meet the high index requirements of various circuit boards soldering performance, and can be used with lead-free solder; environmentally friendly lead-free solder paste has no irritating odor , The smoke is small, non-toxic to the human body, no pollution to the environment, environmentally friendly lead-free flux has excellent solderability, the solder joints are full and bright, the tin penetration performance is good, the PCB surface after soldering is flat and uniform, the finish is good, and the smell is small.
Environmentally friendly lead-free solder paste must have good wettability; under normal circumstances, the solder stays above the liquidus for 30-90 seconds during reflow soldering. The contact time of the liquid wave peak is about 4 seconds. After using lead-free solder, it is necessary to ensure that the solder can show good wetting performance within the above time range to ensure high-quality soldering effect.
The melting point of environmentally friendly lead-free solder paste should be low, as close as possible to the eutectic temperature of 63/37 tin-lead alloy, which is 183C. This kind of lead-free solder that is really popularized and meets the soldering requirements; in addition, before the development of lead-free solder with a lower eutectic temperature, the temperature difference between the melting interval of lead-free solder should be reduced as much as possible, that is, the temperature difference should be reduced as much as possible. The temperature range between the solidus and the liquidus, the minimum temperature of the solidus is p1500C, and the liquidus temperature depends on the specific application (tin bar for wave soldering: below 2650C; tin wire: below 3750C; solder paste for SMT : Below 2500C, the reflow soldering temperature is usually required to be lower than 225-2300C).
The advantages of low-temperature lead-free solder paste are not only environmentally friendly, but also can be used for components that cannot withstand conventional temperature requirements, such as LED or COM1 PCB. Silver; the former has a melting point of 138 and the latter has a melting point of 183; which one to use depends on the actual product requirements, and the solder joints without silver will be more brittle.