![]() This is a highly simplified look at acids. Numbers smaller than 7.0 (higher concentrations of H +) are acidic and greater than 7.0 are basic. The pH scale runs from 0 to 14 with 7.0 being neutral. The H + concentration is expressed as pH, the negative log of the hydrogen ions per liter – pH =−log 10 where represents the hydrogen ion concentration in moles (M). Solutions containing more H + than H 3O + are acids and solutions with fewer relative hydrogen ions are basic. The hydrogen ions are highly reactive and can be donors of protons or recipients of electrons in chemical reactions. The hydrogen ion (H +) is just a proton (and is often referred to as a proton rather than hydrogen ion). A hydrogen atom (H) consists of one proton and one electron. It’s mostly about hydrogenĪqueous solutions contain hydrogen in two forms: hydrogen ions and hydronium ions. This special terminology causes considerable confusion for non-chemists when laboratories testing cleanliness of circuit assemblies report that failures are due to excessive amounts of weak acid residues. Weak acids do not ionize completely while strong acids do. To them, strong acids are those that break into their constituent parts (“ionize”) when added to water. But chemists don’t think of potency when classifying acids as strong or weak. For our purposes, we can think of “strong” acids simply being more powerful than “weak” acids. Let’s pause to apologize to chemists for our use of the words “strong” and “weak” in referring to acidity. The greater attraction means stronger acids have greater deoxidizing ability (able to remove greater amounts of oxide faster than weaker acids and able to remove oxides from a greater range of metals than weaker acids). Stronger acids, in general, attract oxygen with more force than weaker acids. During deoxidation (the interaction of the acid with the metal oxide, a base), hydrogen from the acid combines with the oxygen stripped from the oxide to form water while the other elements of the acid combine with the metal to form metallic salts. Inorganic acids in the form of halides (discussed below) are found in some electronics fluxes but in very low concentrations and only supplemental to the greater amounts of organic acid.Īcid strength is determined by its hydrogen ion content more hydrogen ions equate to greater acidity. Inorganic acids (compounds of hydrogen with non-metals) such as hydrochloric or hydrobromic have exceptional oxide removal properties but not compatible with electronic reliability they leave highly conductive and corrosive residues that can cause electrical failures. The term used to describe flux acidity is “activity.” Most often, the acids are organic (meaning they contain carbon). (Jim) Smith, PhD ABD, President, Electronics Manufacturing Sciences, part of the flux that removes oxides, which the industry for reasons lost in antiquity insists on calling “activators,” is almost always acid, either directly or in a compound that releases acid when heated. Removal of oxides and prevention of reoxidation is the role of flux. With the exception of gold, all component surfaces are oxidized and that oxide must be completely removed and the deoxidize surface protected from reoxidizing before application of the solder. Oxidized metal lacks that energy, however, and does not allow wetting. Elemental metal is unstable and has energy to draw the solder (interatomic attraction). Solder flow is known as wetting and occurs only if the solder is applied to a pure elemental metal surface. If you haven’t read Part 1 of soldering flux, that really is the best place to start. If you read Part 1, you know the fundamentals of flux and are ready for the specifics of how to pick the flux that will make your soldering life very easy. This is the second of a three-part explanation of fluxes: what they do, how they do it and which one is best for various applications. However, fluxes are complex and making the right choice involves navigating a chemical minefield complicated by occasionally bizarre terminology and, too often, shady marketing practices by some well-known flux manufacturers. The right flux can save immense costs including but not limited to solder defects, cleaning and product failures. Liquid flux is just those same ingredients in a solvent.įlux selection may be the most important decision any electronics assembly business will ever make. ![]() RLC Resonant Frequency and Impedance Calculatorįlux consists of two basic ingredients: acids to remove oxides and a substance or substances (“solids”) to coat the surface and prevent oxygen from reaching the surface after oxides are removed.Bandwidth Rise Time and Critical Length Calculator.Transmission Line Reflection Calculator.Trace Width and Current Capacity Calculator.
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