![]() ![]() ![]() Residue may be removed with an appropriate solvent. Assemblies sensitive to corrosion or the possibility of electrical conduction through the residue should be cleaned as soon as possible after assembly. In the absence of testing to prove otherwise, RA flux residue is assumed to be corrosive. IPC classification is usually ROM0, ROM1, ROH0, or ROH1. RA flux has similar and higher activity than RMA for moderately and highly oxidized surfaces. Rosin activated flux consists of rosin, solvent, and aggressive activators. Many RMA fluxes pass SIR testing as a NC flux. Most are non-corrosive and non-conductive. IPC classification is usually ROL0, ROL1, ROM0, or ROM1. Most RMA flux is fairly low in activity and best suited to easily solderable surfaces. Rosin mildly activated (RMA) flux consists of rosin, solvent, and a small amount of activator. Some, but not all, NC fluxes are more difficult to remove than RMA fluxes. NC residue is clear, hard, non-corrosive, non-conductive, and designed to be left on many types of assemblies. IPC classification is usually ROL0 or ROL1. NC flux typically has low-to-moderate activity and is suited to easily solderable surfaces. No clean flux consists of rosin, solvent, and a small amount of activator. R residue is hard, non-corrosive, non-conductive, and may be left on. Rosin flux has very low activity and is suitable only for easy-to-solder surfaces. Rosin flux consists of rosin and solvent. Note overlap of activity levels between flux groups. Each is available with a variety of activity levels, physical qualities of their residue, and cleaning methods required.įlux Comparison chart shows relative activity ranges of each flux category. There are five main categories in QQ-S-571E. Using a smaller powder will just cost more.įlux categories are defined by Military Specification QQ-S-571E as well as the IPC flux rating system. Using too large a powder will cause printing and dispensing difficulties, compromising quality. If the feature is smaller, the application requires the next smaller powder size. Dimensions listed for gullwing, square/circle, and dispense dot sizes represent the smallest feature recommended for that size powder. The Powder Size chart (Figure 2) cross-references particle size to typical printing and dispensing requirements. Having selected the best alloy, particle size is next. If a solder joint needs to retain physical integrity during a later operation, such as a second reflow process, the peak temperature of the later operation needs to be below the solidus temperature of the alloy. While wetting begins at the solidus temperature, best wetting is achieved at a peak temperature 15º C or more above the liquidus. Alloys are called eutectic when the solidus and liquidus are equal.In between the solidus and liquidus, a region called the plastic range, some portion of the alloy is solid but the majority is liquid.Below the solidus, an alloy is 100% in a solid state.The phase change from the solid state to the liquid state begins upon reaching the solidus and ends upon reaching the liquidus. *Eutectic – Solidus and Liquidus are equal **MP – Melting pointĮach alloy has temperatures at which it changes from solid to liquid ( Figure 1). Some applications that fall under the RoHS directive are exempt from being lead-free because the reflow temperature requirements can only be met with high-lead solder alloys which are exempt under RoHS regulation.įigure 1. Sometimes this is due to the product falling under the RoHS (Restriction of Hazardous Substances) directive and sometimes it is a corporate directive. Many applications have a requirement for use of lead-free solder alloy. What type/size does the power need to be for the smallest feature in the application?.Is there a reflow temperature requirement or limitation?.When choosing a solder alloy, there are a few questions that need to be answered. ![]() It is always worth a call to your Nordson EFD solder sales specialist to review requirements to ensure you are using the best solder paste for the job. There are additional details of alloy and flux performance not covered that can be very important in the selection process. This guide covers the most significant steps in selecting a solder paste. ![]()
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