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By ginkgo | 03 September 2022 | 0 Comments

Five basic requirements for reflow soldering technology

The main technical features of reflow soldering are: use flux to purify the metal surface to be soldered (remove oxides), so as to have good wettability to the solder; supply molten solder to wet the metal surface; form an intermetallic compound between the solder and the soldering metal ; In addition, micro welding can be realized. In order to achieve ideal reflow soldering, the five basic requirements of reflow soldering technology must be met. 
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1. Appropriate heat. Appropriate heat means that for the materials on the reflow soldering surface, there must be enough heat to melt them and form an inter-metal interface (IMC). Sufficient heat is also one of the basic conditions for wetting. On the other hand, the heat must be controlled to a certain extent to ensure that the material in contact (not just the solder ends) is not thermally damaged and that the IMC layer is not formed too thick.

2. Good wetting. In addition to being a symbol of better solderability, wetting is also an important condition for forming the shape of the final reflow solder joint. Poor wetting often indicates suboptimal solder joint structure, including incomplete formation of the IMC and poor solder joint fill. These problems will affect the life of reflow solder joints.

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3. Appropriate size and shape of solder joints. To have sufficient life of reflow solder joints, it is necessary to ensure that the shape and size of solder joints meet the requirements of solder end structure. Solder joints that are too small have insufficient mechanical strength to withstand the stress in use, and even the internal stress that exists after welding. And once fatigue or creep cracking begins to occur during use, the fracture speed is also faster. The poor shape of the reflow solder joints can also lead to the phenomenon of overweight and shorten the life of the solder joints.

4. Controlled tin flow direction, controlled tin flow direction is also an important part of the reflow soldering process. The molten solder must flow in the desired direction to ensure controlled solder joint formation. The phenomenon of tin absorption in the reflow soldering process is the technical details related to the control of the tin flow direction.

5. The soldering surface does not move during the reflow soldering process. If the soldering end moves during the soldering process, it will not only affect the shape and size of the solder joints, but also may cause false soldering and inner holes, depending on the movement and time. This will affect the quality life of solder joints. Therefore, the design and process of the entire product must take care that the welding end remains stationary during the welding process.

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In the reflow soldering process, in addition to the above general soldering conditions, there is a special point, that is, the chemical components in the solder paste that have no effect after the printing process must be volatilized in time. This is especially strict on the first side in the double-sided welding process.

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