During the soldering process, situations periodically occur when a low solder temperature is required. 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. For these purposes, the Rose alloy is most suitable.
brief information
The composition of the Rose alloy includes:
- bismuth 50%;
- lead 25%;
- tin 25%.
The permissible deviation of the proportions of the components is ± 0.5%. In terms of physical parameters, this solder is close to the Wood alloy, but has less toxic properties due to the absence of cadmium in its composition, therefore it is more suitable for working at home. For its use, equipment with an exhaust hood at the workplace is not required.
The melting point of the Rose alloy is +94 ° C. It hardens already at +93 ° C. This temperature regime has been successfully used for tinning circuit boards with a Rose alloy. In domestic conditions, this process can be carried out in boiling water. But it should be remembered that this alloy is sensitive to overheating, in addition, it is quite fragile.
Rosa alloy, what is it and why is it called that? The solder is named after the famous German chemist Valentine Rosa Sr., it is a small granules or rods of silver color.
What materials are used for soldering?
Soldering with such a composition facilitates the connection of temperature-critical contacts of radio components and elements in microelectronics due to the low melting point. It is used in industry as solder grade POSV-50. This material is successfully soldered copper, its alloys with aluminum, nickel, brass, silver-plated surfaces of ceramic elements, precious metals.
Boiling Water Board Tinning Technology
Due to the unique temperature characteristics at home, the following tinning technology for printed circuit boards using the Rose alloy has been developed. What is it and how does it work?
First of all, it is necessary to clean the etched copper surface of the printed circuit board.
Then heat to a boiling point a small enamelled metal container filled with water (a bowl or pan). A big tin can may come up. Throw a small amount of citric acid into boiling water.
After that, gently lower the printed circuit board to the bottom of the tank with the surface for tinning up. The required number of Rosa alloy granules is dropped after it. After that, in boiling water, the molten granules are distributed evenly with a wooden stick or rubber spatula on the copper surface of the board. In this case, the process of tinning occurs.
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, not inferior in quality to an industrial design.
In order for subsequent brazing with the Rose alloy to have sufficient strength and not to be brittle, it is necessary to achieve a minimum tinning layer thickness. After that, thoroughly rinse the board surface with water to remove any 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 during the soldering process it will act as a flux ensuring the perfect connection quality.
Glycerin Technique
There is a method 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, say a bowl. It is half filled with glycerin from the nearest pharmacy and is heated to a temperature of about 200 ° C. It is necessary to add a few drops of soldering acid to the liquid. Next, the plate with the stripped copper layer is lowered into the heated glycerin. Rosa alloy pellets are thrown on top. Then, with a rubber spatula, molten metal balls are rubbed 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. Shiny tinned surface is covered with a layer of alcohol solution of rosin. After that, the board is ready for use.
Simplified tinning technology
If there is no desire to tinker 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 by the Rose alloy. What is it and how is it performed? The copper foil of the printed circuit board is cleaned with sandpaper and covered with an alcohol solution of rosin, the so-called liquid flux. After that, on the copper tracks of the board, it is necessary to put the required number of granules of the Rose alloy and use a small soldering iron through the fluffy braid of the coaxial cable to perform the tinning process. Then, with alcohol, wash off the remnants of the spent flux and coat with an alcohol solution of rosin as a kind of protective varnish.
Advantages and disadvantages of tinning technology
Each of these methods has its positive and negative sides. Tinning in boiling water is preferable due to the low working temperature (up to +100 ° C). It gives high quality tinned surfaces, does not damage the thin paths of boards and etched inscriptions.
When working in glycerin heated to 200 ° C, a similar coating quality is obtained. But there is a danger of getting burns with an oily heated liquid. Glycerol vapors also do not contribute to improving the health of the ham. In addition, it should be remembered that when the dehydrated glycerol is overheated, the substance acrolein appears, which belongs to the 1st class of harmful effects and has strong carcinogenic properties.
Tinning with a soldering iron is simpler and faster, but there is a risk of overheating with peeling of foil tracks and etched inscriptions on the printed circuit board.
DIY rose alloy
It is not always possible to purchase the necessary materials. In this case, it is worth trying to make them yourself. To obtain an alloy, it is necessary, first of all, to purchase bismuth. Instead of pure tin, it is necessary to use tin-lead solder, since pure metal is not always possible to get. In normal solder, approximately 40% of lead and 60% of tin. It is necessary to take a piece of solder and exactly the same volume of a piece of bismuth. Mix all components in a crucible and melt with the addition of rosin flux. Then pour the molten solder carefully into a container of water with a thin stream. Rose alloy granules will form at its bottom. Of course, this method is not entirely accurate, so the percentage compliance of metals will not fully meet the norm, as well as the melting temperature. For a more accurate alloy, Rose will need chemically pure tin, lead and bismuth.
Safety Precautions
Although the 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 tinning, safety precautions should be observed. Work in a ventilated area. Avoid breathing vapors of lead, tin and bismuth. Evaporation of rosin and glycerin is also harmful. When working with a heated crucible, protective equipment in the form of tight gauntlets and glasses is required.