What are the causes of wave solder dross oxidation?
In the working condition of wave soldering, lead-tin and lead-tin tapes are made of tin alloy. During continuous contact between tin and air, a chemical reaction occurs to form tin dross oxide. During the soldering process, the tin rod is transformed from a solid state to a liquid state through high temperature, which will greatly increase the oxidation rate of tin and lead to the generation of tin dross. For excessive tin dross in the wave soldering process, it is necessary to distinguish whether the dross is normal or not. Generally speaking, black tin dross normal, tofu tin dross abnormal.
Wave soldering impurity content is too high resulting in excessive tin slag causes:
1. Boise furnace tin in copper and trace elements content exceeds the standard. Copper, iron content exceeds the standard is the main reason for the generation of slag. Circuit board circuit is made of copper, most of the electronic feet are made of iron. In the operation process, more or less copper and iron elements will fall into the tin furnace, over time will cause copper and iron elements exceed the standard. When the copper is greater than 0.8%, iron is greater than 0.05%, will produce a large number of tin slag, the impact of poor quality tin on the circuit board.
2. Wave furnace operating temperature is too high. High temperature is also the reason for the generation of slag. If the temperature is too high, copper and iron is easy to exceed the standard.
3. Usually clean the furnace is also important. If not cleaned for a long time, the furnace impurity content is too high, is also the reason for too much tin slag.
The causes of wave soldering generated tin oxide:
1. At present, the design of some wave furnace on the market is not ideal. The wave is too high, the platform is too wide, the double-wave oven is too close, the choice of rotary pump. When the wave is too large, when the solder off, the temperature reduction deviation is relatively large. Solder mixes with air and rushes into the furnace, leading to oxidation and semi-dissolution, producing dross. The rotary pump does not take precautions to press the dross into the furnace continuously, and the cyclic chain reaction stimulates the generation of dross.
2. Wave soldering temperature is generally controlled in the lower range, generally 280 ℃ ± 5 ℃ (lead tin cu0.7 tin bar), which is the basic temperature required by the welding process. The low temperature of tin can not achieve good dissolution, indirectly leading to excessive tin dross.
3. The larger the contact area of tin liquid and air, the more tin dross. If the melted tin falls directly into the tin furnace, it is easy to bring the air into the melted tin, so that the tin and air combined to form tin oxide.
4. Whether the tin slag is often cleaned up so that the falling tin can enter the furnace as soon as possible, rather than staying on the slag, and uneven heating, which can also cause too much tin slag.
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