The main difference between high-temperature solder paste
and low-temperature solder paste is that the temperature of some chips cannot be high when passing through the furnace, and bubbles will form when the temperature is high, but the low-temperature solder paste may cause problems with some vibration pins after the temperature is generated (higher). , High temperature solder paste is generally used in SMT components with large heat generation. Some components generate large heat and can withstand high temperature, while low temperature solder paste contains bismuth element, which is relatively brittle. If the components need to move or vibrate, it is not recommended to use Low temperature solder paste.
The melting points of lead-free high-temperature solder paste and low-temperature solder paste are different. High-temperature solder paste is composed of tin-silver-copper alloy. The high temperature is 217, so if you want to distinguish between these two kinds of furnace temperatures, you can pass both solder pastes through the furnace, and set the temperature profile of the reflow soldering to the low-temperature solder paste, if one of them is dropped after the furnace If it is very strong or cannot stick, it is high temperature solder paste, because the melting point of high temperature solder paste is 217 and the maximum temperature of low temperature solder paste may be 220, which just reaches the melting point of high temperature, so failure to melt tin will cause parts to drop.
Therefore, in our SMT chip processing, we generally choose 6337 leaded solder paste or lead-free high-temperature solder paste.
The problem of low temperature solder dropouts is a common problem encountered with low temperature solder products. The main reason is that its solder metal composition is a tin-bismuth alloy. More bismuth in solder paste can reduce the melting point, but the same solder joint is very brittle, which makes it easy to drop parts.
So how to avoid such problems? Let's talk about it below:
① The cooling speed should not be too fast, and do not move it until it reaches room temperature.
②In the selection of solder paste, tin-bismuth-silver solder paste containing silver with a higher melting point can be used instead. Although the melting point of tin-bismuth-silver solder paste is higher, the solder joints are much firmer.
③ When dividing the board, pay special attention to the best use of the board machine to minimize the generation of stress and reduce the deformation of the machine board.
④Check the temperature curve, pay attention to the cooling slope.
⑤ This kind of board is usually an aluminum substrate, so pay attention to the cooling treatment after reflow. After coming out of the oven, add cold air to cross the bridge.
⑥Reflow oven is protected by a fixture.