Blackening of solder joints often occurs after Reflow Soldering, and the direct cause is incomplete volatilization of Solder Paste Flux or inadequate cleaning.

Flux residue is mostly caused by excessive Solder Paste usage or improper reflow soldering temperature curve settings, which prevent the active substances from fully decomposing.

When using solder paste, take only the required amount to avoid excess, and ensure reasonable pad design to facilitate flux escape.

During reflow soldering, the temperature curve must be strictly monitored, especially the preheating zone and peak temperature, to ensure full volatilization of the flux.

If residue problems are found, try adjusting the reflow soldering time or lowering the peak temperature, but take care to avoid affecting solder joint formation.

The cleaning process is a key step; select a suitable cleaning agent and control the cleaning time and pressure properly.

In daily production, regularly check the usable time limit of solder paste after opening to avoid aging and deterioration that would impair flux performance.

When purchasing, prioritize high-quality solder paste products with low flux residue and good volatility.

Operators must master correct solder paste printing and reflow soldering parameter setting methods.

Establish a sound process record system to facilitate quick identification of problem sources.