The components of lead-free solder paste are: Sn, Ag, Cu, Bi, and the main components of leaded solder paste are: Sn, PB. We cannot directly distinguish this alloy with the naked eye. It needs to be detected by a spectral analysis instrument. detection.
Leaded solder paste is divided into: 6337 leaded solder paste, LED special solder paste, stainless steel special solder paste, high-temperature high-lead solder paste, the alloy composition of these solder pastes is also different, different manufacturers have different ratios and production processes difference.
Lead-free solder paste is roughly divided into: high-temperature lead-free solder paste (alloy composition: Sn/Ag/Cu), medium-temperature lead-free solder paste (Sn/Ag/Bi), low-temperature lead-free solder paste (Sn/Bi), alloy The distinction of components requires professional testing equipment to analyze, which is invisible to the naked eye.
That is to say, the amount of solder with lead is much higher, so the soldering temperature will have different requirements. The soldering temperature of lead-free is higher than that of lead, and lead-free solder paste has strict temperature requirements. The soldering effect is the best at a certain temperature, and the minimum peak temperature should be in the range of 200-205°C. The highest peak temperature should be 235°C. This upper temperature limit of 235°C coincides with the maximum component temperature values of most component manufacturers. Therefore, the temperature control of lead-free reflow soldering is much stricter.
The earlier reflow ovens used a temperature curve of five temperature sections, so that the temperature goes straight up and down, the soldering effect is not very good and it is not conducive to the production of PCB, and it may damage the entire PCB. The current reflow ovens generally have 20 temperature curves, so that the welding curve is smoother and the welding effect is more perfect.
Leaded solder paste and lead-free solder paste are different in color. Leaded solder paste is gray-black after opening, and lead-free solder paste is gray-white.
The finished paste of lead-free solder paste is grayish, and the color of finished paste with lead solder paste is black.
In addition to our introduction above, lead-free solder paste and leaded solder paste have different activity of solder paste. In contrast, the activity of lead-free solder paste is stronger, regardless of lead-free solder paste or leaded solder paste. The most important thing in the application is the temperature curve. According to the reference provided by the manufacturer, plus your own experiments, you can achieve good results by adjusting the process window.
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