What Should We Know about “Tinning Rods”

Preparation and quality requirements of tinning rods/strips

Tin rod, as the name implies that is rod solder, is referred to as tin rod industry. Mainly used for wave soldering and immersion welding, is currently the largest consumption of electronic solder variety; a small amount is also used for flame brazing or soldering iron welding of large structural parts and long welds. It is the most important and essential connecting material for all electronic and electrical products and the global annual consumption is about 100,000 tons. 

The preparation process of tin strip is simple, including batching, melting and casting, and the degree of oxidation and the content of metal and non-metal impurities are strictly controlled. The melting temperature and casting temperature have great influence on the quality of tin. The preparation of tin strips is simple and the technical threshold is low, so the competition is extremely fierce. The current pricing only adds a meager processing fee to the cost of raw materials. Once the price of raw materials tin fluctuates sharply in the short term, the meager profit may be wiped out, or even a loss.

The main requirements for the quality of tin strip are as follows: 

(1) The surface of tin strip is smooth; 

(2) Good fluidity and wettability during welding; 

(3) Good mechanical properties; 

(4) Bright solder joint;

(5) Less oxidation residue.

The common defects on the surface of tin strip are flower spots and bubbles. These defects are caused by the manufacturing process and the use of molds. For example, there is no scraping surface during manufacturing, the cooling system is not good, and the molds are not smooth, which will lead to the above problems. The cause of the blistering is related to the weather in which it was made. Production workers take the tin bar, do not directly use the hand, the moisture in the hand will affect the brightness of the tin bar, tin bar version of the best use of plastic paper, both can see the brightness, and not damp. When the storage time is long or the storage place is too damp, there will be a layer of oxide on the surface of the tin strip, which will also make the brightness of the tin strip fade, but it has little effect on the use effect.

The classification of tin strips:

Tin strips are classified by environmental protection, including leaded tin strips and lead-free tin strips. 

At present, the commonly used lead-free tin strips are: tin copper lead-free tin strip (Sn99.3Cu0.7), tin silver copper lead-free tin strip (Sn96.5Ag3.0Cu0.5), 0.3 silver lead-free tin strip (Sn99Ag0.3Cu0.7), high temperature type lead-free tin strip (SnSb). 

The commonly used lead tin electrode mainly includes: 63/37 solder bar (Sn63/Pb37), 60/40 solder bar (Sn60/Pb40) and high temperature solder bar (400 degrees above welding). 

In addition to the main elements of tin, lead, copper, silver, often contain a small amount of other elements, such as nickel, antimony, bismuth, in, rare earth and so on.

These micro alloy elements in tin strip have great influence on the physical and mechanical properties of tin strip: bismuth can reduce the melting temperature of tin strip and improve the wetting and spreading property, but too much bismuth will reduce the fatigue life and plasticity of solder joints, and the appropriate amount of bismuth is about 0.2~1.5%. Ni can improve the mechanical properties and fatigue life of solder joints by changing the microstructure and refining the grain. In the systematic design of chemical composition, the designer obviously hopes that the tin strip can achieve an optimal balance in various aspects of performance, such as welding performance, melting temperature, strength, plasticity and fatigue life, etc.

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