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As with traditional tin/lead welding processes, many metals will dissolve in lead-free alloys. This dissolution rate is determined by the matrix material, solder composition, solder temperature, and solder flow rate. Depending on the metal plating on the circuit board, silver (silver-plated) or copper (copper bare or with an OSP layer) may actually leach into the solder bath. Adding pure tin or Sn-Ag alloy to the solder bath can control the alloy. You may need to monitor impurities such as copper, lead, and silver, as they raise the melting point of the alloy. For example, for every 1% increase in copper in the solder alloy, the melting point of the lead-free alloy increases by 25°C. For lead-free solder, the three main contaminants are lead, copper, and iron. 1) Lead contamination: The surface coatings of components and boards contain lead. The result may lead to excessive lead levels, and even cause different melting points for the solder. When the lead content in tin/silver solder reaches 1.5%, the melting point of the tin/silver alloy rises from 221°C to the range of 228–231°C for the \"new\" tin/lead/silver alloy. Lead contamination can only be reduced by replacing the solder or adding new material to dilute it. 2) Iron contamination: Iron dissolves slowly in tin/lead solders. And the amount of lead-free solder that dissolves is about 10 times that of tin/lead solder. This is mainly due to the high tin content and high operating temperature, which cause the dissolution of iron in the solder tank. It would be better to use a titanium alloy tank. 3) Copper contamination: Controlling the copper content in the wave soldering bath is crucial for achieving low-defect soldering during the welding process. Due to the dissolution of copper in the boards and components, there is a tendency for the copper content in the solder in the tin furnace to increase. This is particularly evident when using OSP bare copper sheets. Studies show that the typical dissolution rate is an increase of 0.01% Cu per 1,000 plates (each process has its own characteristics; here it merely refers to the dissolution rate). High-tin alloys absorb copper more rapidly than low-tin alloys, and the amount of copper in the lead-free alloy determines how much copper will be dissolved. From the tin/lead welding process, we know that a copper content of 0.2% or higher causes problems such as an increase in tin bridges. The maximum allowable copper contamination in tin/lead is generally specified at 0.3%. In the soldering process of lead-free copper circuit boards and copper pins, the copper content is usually kept below 1.0%. An increase in copper levels mainly leads to an elevation in the alloy’s melting point, reduced fluidity, and more slag formation. The alloy can be controlled by adding pure tin or Sn-Ag alloys to the solder bath. However, at low temperatures and without stirring in the solder bath, alloys of tin and copper such as Cu6Sn5, Cu3Sn, and Ag3Sn tend to precipitate at the edges of the bath and at the bottom of the solder. These are alloys with relatively high melting points, and dissolving them requires relatively high temperatures and longer times; even higher temperatures are needed to melt them. For the SAC3005 alloy, it is recommended to keep its copper content between 0.3% and a maximum of 0.7%. If the copper content is higher than 1.0%, it will increase the liquid temperature. This means that the temperature of the solder bath must be increased accordingly to ensure good welding quality. The copper content in the solder bath can be diluted by adding YW9-3005. Sometimes we can also achieve a balanced copper content by simply adding SA30. However, each process has its own unique characteristics; we recommend conducting regular tests on the solder bath to better control the copper content. This post was last edited by yutr on 2009-2-26 16:06.]