What conditions are required for lead-free solder paste reflow? What are the requirements?

Lead-free solder pasteWhat conditions are required for reflux?What are the requirements? Lead-free solder paste is a gray or grayish-white paste. During the reflow soldering of lead-free solder paste, many details and factors can cause adverse effects. Now, let's take a look at some explanations about lead-free solder paste provided by the editor of JJY:

Lead-free solder paste is relatively expensive. Meanwhile, in the production process of the electronics industry, solder paste is often discarded for various reasons. These discarded solder pastes are still very valuable and cannot be thrown away casually. After the paste is recycled and processed, it can be applied to industrial production, playing a role in reducing enterprise costs. 

At the same time, from the perspectives of health and environmental protection, the lead-free solder paste currently in use is mainly environmentally friendly solder paste, that is, solder paste with lead removed, also known as lead-free solder paste. Lead-free solder paste must first be able to truly meet environmental protection requirements. It cannot remove lead while adding new toxic or harmful substances;It is necessary to ensure the solderability of lead-free solder and the reliability after soldering, and take into account numerous issues such as the cost borne by customers.

The melting point of lead-free solder paste is low and should be as close as possible63/37The eutectic temperature of cream lead alloy is183℃The eutectic temperature of the new product exceeds183℃It should not be a major issue, but this lead-free cream that meets the soldering requirements has not yet been truly popularized. Additionally, before developing lead-free solder paste with a low eutectic temperature, the temperature difference between the melting intervals of the lead-free solder paste should be reduced as much as possible, that is, the temperature between the solid phase line and the liquid phase line should be minimized. The minimum temperature of the solid phase line is150℃The liquidus temperature depends on the specific application(Wave peak cream:265℃The following cream:37m

Lead-free solder paste should have good wettability;Under normal circumstances, the time that solder stays above the liquid phase line during reflow soldering is30~90The time during wave soldering when the pins to be soldered and the substrate surface of the circuit board come into contact with the wave peak of the solder solution is seconds4After using lead-free solder for about a second, it is necessary to ensure that the solder can exhibit good wettability within the above time range to guarantee a high-quality soldering effect.

What are the general requirements?

1It is important to have sufficient slow heating to safely evaporate the solvent, prevent the formation of solder beads and limit the internal stress of the component caused by temperature expansion, which may lead to reliability issues of cracking.

2The active stage of the flux must have an appropriate time and temperature, and the cleaning stage is allowed to be completed when the solder particles just start to melt.

3The stage of solder melting in the time-temperature curve is the most crucial. It is essential to ensure that the solder particles are fully melted and liquefied to form a metallurgical weld. The evaporation of the remaining solvent and flux residue forms the surface of the solder joint. If this stage is too hot or lasts too long, it may affect the components andPCBCause harm.

4The setting of the lead-free solder paste reflux temperature curve is best based on the data provided by the lead-free solder paste supplier. At the same time, the principle of internal temperature stress changes of the component should be grasped, that is, the heating temperature rise rate should be less than per second3°CThe cooling temperature drop rate is less than5°C. 

Shenzhen JJY Industrial Technology Co., Ltd. mainly operates:LEDType solder pasteThere is lead solder pasteLead-containing silver solder paste, stainless steel plate type solder pasteSMTSolder paste and wire manufacturers of type solder paste, lead-free flux paste, no-clean solder wire, lead-free solder wire, leaded solder wire, lead-free and leaded solder rods, wave solder rods, automatic solder wires, etc.