The metal particles in the solder paste are too large, an inappropriate type is used, or the quality of the solder paste is poor. The solder paste may also absorb moisture when exposed to the air for a long time, making the solder joint surface uneven.
The active agent components of the flux in the solder paste chemically erode the surface of the tin powder, causing "oxides" to form on the surface of the tin powder. This "chemical corrosion" reaction not only changes the melting characteristics of the tin powder but also consumes the active components in the flux, making it difficult to effectively and thoroughly remove the oxides on the surface of the tin powder during reflow soldering. The solder joints where the tin powders are not fully melted will have a dull sandy appearance.
If the soldering temperature is too high, the solder will oxidize quickly, resulting in a rough solder joint surface. If the temperature is too low, the solder will not melt completely, and the solder joint surface will also appear rough.
Welding time that is too short or too long will affect the quality of the solder joint. Too short a time may result in the solder not being completely melted, while too long a time may result in solder joint oxidation and welding defects.
If the nitrogen protection in the reflow oven is insufficient or the oxygen content is too high, the solder joint surface may oxidize, resulting in a gritty feel.
Oxide layer, dirt or grease on the substrate surface or component pins may also cause uneven solder joint surface.
Excessive cooling speed may cause the grain structure of the solder joint surface to be rough, thus showing a sandy feel. It is recommended to control the cooling rate according to the process requirements.
上一条:5 Common Types, Allowing You To Quickly Troubleshoot 90% of PCB Failures
下一条:Specifications for Handling Defective PCB Assembly You Should Know