In PCBA processing, under normal circumstances, the lead-free printing process will not be greatly affected. Mainly due to the physical characteristics of lead-free alloys compared with Sn-Pb alloys, they have the characteristics of low density, high surface tension, and poor wettability, so there are some requirements in terms of template opening design and printing accuracy. So when we understand the difference in physical properties between lead-free solder paste and leaded solder paste, we can easily make certain improvements to the PCB soldering process.
The difference in physical properties of lead-free solder paste and lead solder paste
1. The wettability and spreadability of lead-free solder paste is far lower than that of lead solder paste. Where the solder paste is not printed on the PCB pad, the molten solder cannot be spread. Then, after the PCBA circuit board proofing and soldering, the bare copper pads that are not covered by solder will be exposed to the air for a long time. Under the harsh environment of moisture, high temperature, corrosive gas, etc., the solder joints will be corroded and become invalid, affecting the product life And reliability.
2. In order to improve the wettability, the flux content of lead-free solder paste is usually higher than that of lead solder paste.
3. Due to the lack of lead lubrication, the filling and mold release properties of solder paste are poor when brushed.
Therefore, when we consider the lead-free printing process, we must consider the manufacturability of the template opening and lead-free placement.
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