Micro-charges were a type of explosive used by Starfleet and possessed by Ferengi merchant, Ulis, during the mid-22nd century.
In 2151, Lieutenant Malcolm Reed of the Enterprise NX-01 suggested using two micro-charges to blow open the airlock of an Axanar cargo ship. (ENT: "Fight or Flight")
When the Ferengi raiders who raided Enterprise in the same year believed they had discovered the ship's vault, which was actually sickbay's imaging scanner, it was suggested that they use micro-charges to blow it open, as a means of circumventing what they believed to be a magnetic seal. (ENT: "Acquisition")