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- When using a solder wick, you should add some flux to the solder joint you want to desolder.
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Intermetallic Layer
The goal of optimal soldering is to create an intermetallic layer (the layer of bronze between the copper and the tin) of the optimal thickness. This has been empirically determined to be around 1μm. For most applications, this will be achieved when the solder is heated to the correct temperature, the solder flows across the copper to cover all the areas of the joint ("wetting"), and the joint is heated for around 2-5 seconds. Heating the joint for too long will result in an intermetallic that is too thick.
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Wetting is a the ability of the liquid solder to flow over and cover the desired surfaces of the components, wires and PCB pads. Good wetting is achieved when the solder is heated to the correct temperature, there is sufficient active flux and the surfaces to be soldered are not contamined with dirt, fat or oxides.
Flux
Flux is a chemical cleaning agent, flowing agent, and/or purifying agent (Wikipedia article). One of the roles of flux is soldering is to prevent and remove copper oxides on components and PCBs. Tin based solder attaches very well to copper, but poorly to the various oxides of copper, which form quickly at soldering temperatures. By preventing the formation of metal oxides, flux enables the solder to adhere to the clean metal surface, rather than forming beads, as it would on an oxidized surface. There are various types of flux:
- Resin based:
- Synthetic
- Water based
Reflow Soldering
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