This means that, when used directly as a soldering aid, a small amount of solder paste flux can be used in place of a relatively large amount of liquid flux. Solder paste flux gel can be brushed on where needed and, unlike liquid flux, will not flow away from the application area. A slow rise in temperature is necessary to prevent solder balling, but must be great enough to activate the flux, then melt the solder itself, and recool quickly enough to retain the desired shape. Once printed, the circuit board forming process is followed by pre-heating and reflow (melting).įor the flux, the temperature and rate of change in temperature are key in the reflow process. The solder paste flux component must have enough tackiness to secure the components while the fixture is processed through the manufacturing line. Paste is spread over a stencil in the pattern required on the final end product, a printed circuit board. 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. Rheology Modifiers – any of a variety of compounds that allow a liquid to display Non-Newtonian properties that is, to change viscosity as pressure is variedįlux is nearly inert at room temperature but becomes strongly reducing when its temperature is increased.Activators – chemicals disrupting/dissolving metal oxides, typically acids of various corrosivity.Surfactants – a detergent used to lower the contact angle of the flux with the surface its applied to, allowing greater coverage.Rosins/Resins – high-temperature tolerant, non-volatile chemicals, most commonly forms of glycol.Solvents – liquid used an inert medium to combine the active ingredients, such as water.Use as many hot deionized water rinses as necessary.Solder paste flux has a very complex chemical composition. Rinse in hot water containing 2% HCl solution. Remove any oil, grease, or other contaminants from the surface to be soldered. However, the following cleaning steps must be followed in critical applications. For most applications, the residues can be removed with a damp rag. Although the flux is self-cleaning, it is recommended taht the parts first be cleaned with a rough surface. The flux is active between 93-315 degrees Celsius/200-600 degrees Fahrenheit. Procedure: Weldcote Soldering Paste Flux is generally applied using an acid rush.It is not recommended for aluminum and magnesium. It is employed mainly in pumbing and maintenance applications. Weldcote Soldering Paste Flux is useful on most common metals.The petrolatum helps protect the solder joint against corrosive attack and the paste form insures that the flux stays put until soldering.Weldcote Soldering Paste Flux is a Petrolatum-based soldering paste that contains zinc chloride and ammonium chloride.
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