Based on the provided information, a primary reason your solder paste isn't melting is that your soldering iron is not hot enough.
Insufficient Soldering Iron Temperature
As the reference notes, If the soldering iron isn't hot enough, then the solder won't melt as it should. Solder paste contains tiny particles of solder mixed with flux. For the solder within the paste to melt and flow properly, it needs to reach its specific melting point. This heat is typically supplied by a soldering iron.
If the iron's tip temperature is below the melting point of your solder paste, it simply won't provide enough energy to transition the solder from a solid to a liquid state.
Practical Considerations:
- Heating Time: Ensure your soldering iron has had ample time to reach its target temperature. It's crucial to warm up your soldering iron before you start.
- Temperature Setting: If your soldering iron has an adjustable temperature control, verify that it is set appropriately for the type of solder paste you are using. Different solder alloys have different melting points.
- Tip Contact: Make sure the soldering iron tip makes good contact with the area you are trying to solder (e.g., the pad or component lead where the solder paste is applied) to efficiently transfer heat.
- Tip Cleanliness: A dirty or oxidized soldering iron tip can significantly hinder heat transfer, making it difficult to melt solder paste even if the iron's internal temperature is correct.
Ultimately, for solder paste to melt and facilitate a good connection, the heat source, usually a soldering iron, must be sufficiently hot. It needs to be hot enough to help flow the molten solder through the seams or onto the pads.
