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Property of solder pastes produced from solder powder and flux ing agent. The gel is transformed into liquid solution by simple mixing and kneading, but if stored in this state for a long time, it loses its fluidity reverts into gel. This is especially true for substances whose colloid particles have a plastic anisotropy; only weak bonds connect the particles and readily form gels. The influencing factors are the size and shape of particles, their surface properties and the dispersion medium. Under the action of external forces, the internal cohesion of the gel decreases or gets lost in solder paste, so that it turns into a solution and obtains a higher fluidity. When the external forces cease, the particle bonds regenerate and fluidity decreases. As the fluidity slowly returns to the initial state, the paste shows a large hysteresis. This ratio is used to quantify thixotropy. In some cases, however, only the time required to reach the gel state again is considered (setting time). Accordingly, solder paste should be used as soon as possible after preparation.