With the miniaturization of artificial intelligence, the Internet of Things, and wearable electronic products, the international microelectronics and semiconductor packaging industry and even the military industry have higher requirements for lead-free products. This is the reason why high-lead solder pastes are still exempted in some areas when the global solder has been lead-free for 20 years. If the components are soldered on the circuit boards by secondary reflow, whether using SAC305 lead-free solder paste, Sn63Pb37 leaded solder paste, or Bi58Sn42 low-temperature lead-free solder paste, the peak reflow temperatures will not exceed the melting point of high-lead solder paste. The traditional solder for secondary reflow is high-lead solder paste, such as Pb92.5Sn5Ag2.5, with the first reflow soldering temperature of 290-310℃. However, they should have the same or similar soldering strength. The problem is that the solder pastes used for secondary reflow soldering cannot have the same soldering temperatures. In addition, after some components are soldered on one side of the circuit board, other components must be soldered on the other side, which should perform secondary soldering. For example, after the chip or component is packaged and soldered, the components need to be connected to the circuit boards by the second reflow soldering. Many components and circuit boards encounter problems during secondary reflow when using solder paste in the microelectronics and semiconductor packaging industry. S econdary r eflow p rocess puts forward requirements for l ead- f ree s older p aste Secondary reflow soldering, lead-free solder paste, high-strength low-temperature lead-free solder, reflow profile & solutionġ. Similarly, it is a perfect solution for circuit boards that require double-sided secondary reflow. The strength of the solder joint is similar to that of the SAC solder paste series alloy, which perfectly solves the problem of the lead-free solder paste alloy selection for the secondary reflow of components and circuit boards. FL series low-temperature high-strength solder paste is used at the second soldering of secondary reflow soldering. It is designed to use ordinary SAC305 solder paste or SAC0307 solder paste at the first soldering of secondary reflow soldering. If the board is simple and there are no complex components such BGAs or big components on the board, the slumping type profile will be the better choice.Fitech proposed a new secondary reflow solution for microelectronics and semiconductor packaging based on the company's patent. The Soaking type is similar to a trapezoidal shape while the slumping type has a delta shape. There are two different profiles involved in the reflow process – soaking type and slumping type. The maximum allowable cooling down slope needs to be considered in order to avoid any defect from occurring. ![]() Cooling zone: In the cooling zone, the temperature is gradually decreasing and makes solid solder joints. ![]() A common peak temperature is 20–40 ☌ above liquidus.
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