Why is acid not a desirable flux to use in soldering small connections?

Using acid as a flux in soldering small connections is not advisable primarily because it is corrosive. Acidic flux can lead to the degradation of metal surfaces and the solder joint over time, creating potential reliability issues in electrical connections.

When soldering, the flux's role is to facilitate the flow of solder and ensure a clean joint by removing oxides and other contaminants. However, if the flux is corrosive, it can continue to react with the metal after the soldering process is complete, which can weaken the connection and lead to failure. Once the solder joint is made, a non-corrosive flux is preferred, as it will not adversely affect the components over time.

Other factors such as evaporation rate, solidification speed, or ease of cleaning might apply to different types of fluxes, but they do not fundamentally address the key concern associated with acid flux—its long-term corrosive effects on electrical connections. Therefore, the corrosiveness of acid flux is the most significant reason why it is undesirable in soldering small connections.