During the soldering process, there are occasional situations where a low solder temperature is needed. This happens in the manufacture of microcircuits or in cases where there is a risk of overheating of microelectronic elements, but high strength is not required. Rose alloy is the most suitable for these purposes.
At a Glance
Roze alloy contains:
- bismuth 50%;
- lead 25%;
- tin 25%.
Tolerance for component proportions is ±0.5%. In terms of physical parameters, this solder is close to Wood's alloy, but has less toxic properties due to the absence of cadmium in its composition, therefore it is more suitable for home use. It does not require any equipment with a fume hood at the workplace.
The melting point of the Rose alloy is +94 °C. It hardens already at +93 °C. Such a temperature regime is successfully used for tinning boards with Rose alloy. At home, this process can be carried out in boiling water. But it should be remembered that this alloy is sensitive to overheating, in addition, itfragile enough.
Rose alloy, what is it and why is it called that? The solder is named after the famous German chemist Valentin Rose, Sr., it is a small silver-colored granules or rods.
What materials are used for soldering?
Soldering with a similar composition facilitates the connection of temperature-critical contacts of radio components and elements in microelectronics due to the low melting temperature. It is applied in the industry as solder of the POSM-50 brand. This material successfully soldered copper, its alloys with aluminum, nickel, brass, silver-plated surfaces of ceramic elements, precious metals.
Boiling water tinning technology
Due to the unique temperature characteristics at home, the following technology for tinning printed circuit boards using Rose alloy has been developed. What is it and how does it work?
First of all, you need to clean the etched copper surface of the PCB.
Then heat a small enameled metal container filled with water (bowl or pan) to boiling point. A large can is also suitable. Throw a small amount of citric acid into boiling water.
After that, gently lower the printed circuit board to the bottom of the container with the tin surface up. The required number of granules of the Rosé alloy falls behind her. After that, in boiling water, the molten granules are distributedevenly with a wooden stick or rubber spatula on the copper surface of the board. In this case, the tinning process takes place.
Excess solder is removed with a swab or spatula. After that, the tinned board is removed from the container and allowed to cool. The result is a bright, almost mirror-like tinned surface that is as good as the industry standard.
In order for subsequent soldering with Rose alloy to have sufficient strength and not be brittle, it is necessary to achieve a minimum thickness of the tinning layer. After that, it is necessary to thoroughly rinse the surface of the board with water to remove acid residues. To further reduce oxidation, it is desirable to cover it with a layer of an alcohol solution of rosin. It will prevent the access of oxygen to the metal surface and will act as a flux during the soldering process, ensuring an impeccable quality of the connection.
Technique for working with glycerin
There is a way of tinning in glycerin with Rose alloy. What is it and how to organize the process? For tinning, it is desirable to use an enameled metal container, for example, a bowl. It is half-filled with glycerin from the nearest pharmacy and heated to a temperature of about 200 ° C. Add a few drops of soldering acid to the liquid. Further, the board is lowered into the heated glycerin with a stripped copper layer up. From above, pellets of Rosé's alloy are thrown. Then, with a rubber spatula, melted metal ballsrubbed on the copper surface of the board. After that, the workpiece is carefully removed with tweezers and thoroughly washed with running water from acid and glycerin. The shiny tinned surface is covered with a layer of alcohol-based rosin solution. After that, the board is ready for use.
Simplified tinning technology
With no desire to mess around with metal containers, boiling and acid, a radio amateur can tin a printed circuit board in the simplest way. Tinning in this case is also carried out with Rose alloy. What is it and how is it performed? The copper foil of the printed circuit board is cleaned with sandpaper and coated with an alcohol solution of rosin, the so-called liquid flux. After that, it is necessary to put the required amount of Rosé alloy granules on the copper tracks of the board and use a low-power soldering iron to carry out the tinning process through the fluffy braid of the coaxial cable. Then wash off the remnants of the spent flux with alcohol and cover with an alcohol solution of rosin as a kind of protective varnish.
Advantages and disadvantages of tinning technologies
Each of these methods has its pros and cons. Tinning in boiling water is preferable because of the low operating temperature (up to +100 °C). It gives a high quality tinned surface, does not damage thin traces of boards and etched inscriptions.
When working in glycerin heated to 200 ° C, a similar quality of coating is obtained. But at the same time there is a danger of getting burned by an oily heated liquid. Vapors of glycerin also do not contribute to improving the he alth of a radio amateur. ExceptIn addition, it should be remembered that when dehydrated glycerin is overheated, acrolein appears, which belongs to the 1st class of harmful effects and has strong carcinogenic properties.
Tinning with a soldering iron is easier and faster, but there is a risk of overheating with peeling of foil tracks and etched inscriptions on the printed circuit board.
Making Rosé Alloy DIY
It is not always possible to purchase the necessary materials. In this case, you should try to make them yourself. To obtain an alloy, it is necessary, first of all, to purchase bismuth. Instead of pure tin, you will have to use tin-lead solder, since pure metal cannot always be obtained. Normal solder is about 40% lead and 60% tin. It is necessary to take a piece of solder and a piece of bismuth exactly the same in volume. Mix all components in a crucible and melt with the addition of rosin flux. Then gently pour the molten solder into a container of water in a thin stream. Rose alloy granules will form at its bottom. Of course, this method is not entirely accurate, so the percentage correspondence of metals will not be quite up to par, as well as the melting point. For a more accurate alloy, Rose will need chemically pure tin, lead and bismuth.
Safety and Precautions
Although Rose alloy does not contain cadmium, its components (lead and bismuth) can cause an allergic reaction or intoxication. Therefore, it is better to keep the alloy in a tight sealed package. The shelf life of the composition is about 3 years. When soldering and tinningsafety precautions must be observed. Work in a ventilated area. Avoid breathing vapors of lead, tin and bismuth. The fumes of rosin and glycerin are also harmful. When working with a heated crucible, protective equipment is required in the form of thick gloves and goggles.
