A preform is material that has undergone preliminary shaping but is not yet in its final form.
In fiber optics, a preform is a piece of glass used to draw an optical fiber. The preform may consist of several pieces of a glass with different refractive index, to provide the core and cladding of the fiber. The shape of the preform may be circular, although for some applications such as double-clad fibers another form is preferred. In fiber lasers based on double-clad fiber, an asymmetric shape improves the filling factor for laser pumping.
Due to the surface tension, the shape is smoothed during the drawing process, and the shape of the resulting fiber does not reproduce the sharp edges of the preform. Nevertheless, the careful polishing of the preform is important, any defects of the preform surface affect the optical and mechanical properties of the resulting fiber. In particular, the preform for the test-fiber shown in the figure was not polished well, and the cracks are seen with confocal optical microscope.
In archeology, a preform is the rough, incomplete and unused basic form of a stone tool formed by lithic reduction. Typically, a preform is the shaped remnant of a lithic core. Larger and thicker than the intended tool, it lacks the final trimming and refinement that is present in the completed artifact. Sometimes basic features such as stems and notches have been initiated. In most cases, the term refers to incomplete projectile point.
A solder preform is a specially designed shape of solder adjusted to the application where it is used. Although there are many methods that are used to manufacture the solder preform, stamping is probably the most common method. The solder preform can be manufactured including the solder flux needed for the soldering process. This can be an internal flux, inside the solder preform, or external, where the solder preform is coated.
A Brazing preform is a high quality, precision metal stamping used for a variety of joining applications in manufacturing electronic devices and systems. Typical brazing preform uses include attaching electronic circuitry, packaging electronic devices, providing good thermal and electrical conductivity, and providing an interface for electronic connections. Square, rectangular and disc shaped brazing preforms are commonly used to attach electronic components containing silicon dies to a substrate such as a printed circuit board.
Rectangular frame shaped preforms are often required for the construction of electronic packages while washer shaped brazing preforms are typically utilized to attach lead wires and hermetic feed-throughs to electronic circuits and packages. Some preforms are also used in diodes, rectifiers, optoelectronic devices and components packaging.
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