Once mixed, solder paste is most commonly used in a stencil-printing process. Its tacky nature holds components together until the heat of the soldering process melts the solder and the parts are fused together. Solder paste flux can also act as a temporary adhesive. While the main use of solder paste flux is in the creation of solder paste, it is also sold directly as a gel or tacky flux. There are three types of solder paste flux: The J-STD-004 standard for electromigration and surface insulation resistance is >100 MΩ after one week at elevated temperature and humidity with a DC bias applied. The principal standard is J-STD-004, which categorize fluxes by composition, activity (strength), the presence or lack of halide activators, and reliability from electromigration standpoint and surface insulation resistance (SIR). Standards and DefinitionsĪ number of standards exist to define the various flux types. However, the non-metallic ingredients of the flux, due to their lower density, result in their comprising of nearly half the paste volume. Solder paste flux typically contains 60-80% by weight active ingredients, compared with liquid flux’s 2-25%.īy weight, a mixed solder paste commonly consists of 90% metal. Solder paste flux is different than liquid flux in both physical form and activity level. It also prevents the beading of the applied solder, facilitating easy flows and application. This prevents the formation of metal oxides on both the base and filler materials to which it is applied.
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