Fans of soldering electronic circuits and experienced professionals pay great attention to the correct choice of solder for printed circuit boards. Both the quality of the soldering and its accuracy and aesthetics depend on the correctness of this decision. Therefore, it is so important to familiarize yourself with the known types of solders and their characteristics. This will help you select the appropriate type of brazing alloy for your application.
What it is
Alloys of tin are called solders with the addition of a number of impurities, which make it possible to obtain the desired parameters in terms of melting temperature, as well as in fluidity and other important indicators. The known types of solder are divided into two main modifications: low-melting or soft and refractory (hard). Since the second category is used only for industrial brazing of metals, we will be mainly interested in soft solders.
They are in demand when working with electronic boards that are part of radio equipment (the maximum melting temperature is no more than 450 degrees). These solders are designated by three letters POS, and the following numbers indicate the tin content. That is, POS-40 means that the alloy contains 40 percent of it, and the rest is lead. For a product brand POS-61, for example, the content of components will be 61 and 39 percent, respectively.
Areas of use of POS solder
Let's consider where different grades of POS solder are used from the range from 30 to 90.
The table shows that the POS-90 alloys with the richest tin content are used mainly for repairing food utensils.
The rest of the brands were distributed as follows:
- POS 40 is used in the repair of radio and electronic equipment (it is often used for soldering radiators).
- POS 30 is in demand for the production of cables, as well as for tinning and soldering zinc sheets.
- POS 60 is used in the installation of printed circuit boards and is the main working material of the radio amateur.
Note:POS 60 and 61 (which is practically the same) melt already at 183 degrees with a gradual increase in temperature to 190 degrees.
For all other types of solder, this indicator varies from 220 to 265 degrees. These alloys are sold in the form of fine wire (or in small tubes).
Low temperature mixes and pastes
When soldering boards containing parts and elements sensitive to overheating, it is not safe to use the previously discussed brands of solders. The relatively high melting temperature can easily damage the part to be soldered. For these cases, special low melting point alloys have been developed (photo below)
Of the refractory types of solders of this class, POSK-50-18 with the addition of cadmium stands out.
However, even more popular among amateurs and professionals is a special alloy called "ROSE" (or POSV-50). Its main purpose is soldering non-ferrous metals (copper and brass parts). In addition, it is ideal for
tinning of printed circuit boards. In conclusion, let us recall the special pastes used for soldering CMD elements and miniature microcircuits.
These substances consist of very small balls based on the Sn62Pb36Ag2 alloy and a special flux. Due to the fact that such a mixture dries quickly when open, it is stored and sold in small tubes. Solder pastes are in demand when repairing smartphones and similar devices and are very expensive due to the silver they contain.