Recently, I’ve fielded several requests to clarify the distinction between “halide-free” and “halogen-free.” Both terms apply to the composition of soldering fluxes in the electronics assembly industry. While some may use the terms interchangeably without any repercussions, the definitions are not synonymous. This topic can get a bit confusing, so in this article, I’ll outline the difference between halides and halogens in the context of both industry standards and general chemistry.
Lo que hay que saber
Understanding these terms in the context of industry standards is crucial. For a standardized definition of “halide-free,” we refer to J-STD-004 (Rev. C). J-STD-004C defines “halide-free” as a flux that contains less than 0.05% of combined halide ions (F-, Cl-, Br-, I-) as a weight percentage of the solid portion of the flux. The analytical test method “ion chromatography” is performed on flux in the unheated state. The halide content of a flux is designated by the final character in the flux classification: 0 for halide-free, 1 for halide-containing.
On the other hand, IEC 61249 defines “halogen-free” as a material with residue that contains less than 0.09% of chlorine (all forms), less than 0.09% of bromine (all forms), and less than 0.15% of chlorine and bromine combined. The analytical test method (per J-STD-004C) “bomb calorimetry,” followed by ion chromatography, is performed on flux residue in the final reflowed residue form. The halogen test is optional, and there is no standardized character designation.
Por qué debe saberlo
La concentración de haluros se controla porque los haluros tienen el potencial de corroer la soldadura, lo que puede provocar un crecimiento dendrítico en presencia de una polarización eléctrica aplicada y humedad. Cuando los productos no-clean superan las pruebas J-STD-004 SIR & ECM y se utilizan correctamente, esto no es motivo de preocupación. Para los residuos de fundente que deben limpiarse (solubles en agua), el uso de un proceso de limpieza exhaustivo y eficaz debería evitar cualquier corrosión. Es crucial reiterar que un fundente que contiene haluros no es intrínsecamente dañino para un ensamblaje. La presencia de haluros simplemente debe caracterizarse para promover el diseño y montaje de un dispositivo electroquímicamente fiable.
En cambio, la decisión de un fabricante de utilizar exclusivamente productos sin halógenos obedece a consideraciones medioambientales. Los halógenos en la composición química de un fundente suelen ser halocarbonos, que pueden contaminar el medio ambiente cuando los conjuntos con residuos de fundentes que contienen halógenos se eliminan de forma inadecuada. Aunque los fundentes que contienen halógenos se utilizan a diario en todo el mundo, una empresa puede optar por autoimponerse normas que rechacen el uso de fundentes que contengan halógenos para evitar por completo este problema. No existen normativas gubernamentales que prohíban totalmente el uso de materiales de soldadura que contengan halógenos en la electrónica. Dado que no existe una necesidad técnica de caracterizar el contenido de halógenos, la prueba de halógenos es opcional.
Donde la cosa se complica
Para los más técnicos, he aquí un análisis más profundo:
- In general chemistry, halogens are the elements in group 17 of the periodic table. A “halide” is any halogen-containing compound. Halides can be broken down into two main categories: ionically bonded and covalently bonded. In ionically bonded compounds, atoms with opposing charges (positive and negative) attract each other. If the negatively-charged atom is a halogen, it’s considered a “halide ion.” However, in the electronics industry and its standards, the term “halide” technically refers to a “halide ion.” The ion chromatography analysis does not detect the concentration of all halide species, only ionic halide species.
- Based on standard definitions, a flux could technically be classified as both “halide-free” and “halogen-containing.” Activators, one of the primary components of fluxes, are the chemicals that dissolve and remove oxides to enable soldering. Typically, activators are halocarbons or organic acids, and halocarbons are particularly effective at removing oxides. If a flux is formulated with halocarbons, halide ions can form within the flux due to side reactions. This is why many flux-containing products, notably solder paste, will be halide-containing if they are halogen-containing. However, it shouldn’t be assumed that a halide-free flux is also halogen-free.
- Using the same analytical method for halogen content, J-STD-004 defines flux residues as “low halogen” if Br ≤ 0.1% and Cl ≤ 0.1%. Yet, it’s uncommon to see a flux-containing material labeled as “low halogen.”
- A common question I get asked is, “What does the ‘HF’ in [product name] stand for?” Indium Corporation offers many solder pastes and fluxes with “HF” in the title (like Indium8.9HF, for example). The HF stands for halogen-free. However, not all halogen-free products have “HF” in their name. If a product is halogen-free, it will be noted on it’s product data sheet.
While this is a lot of information to digest, it’s important not to overthink it. For many assemblies, choosing between halide-free and halide-containing, or halogen-free and halogen-containing, is not going to make or break the device. There are many more factors to consider when selecting the optimal solder material. If you’re in the market for flux and solder, we encourage you to have a conversation with a member of our technical support team. We’ll be happy to discuss your project and help you navigate our portfolio of electronics assembly materials.
Lecturas complementarias
Para obtener más información sobre la caracterización de fundentes según J-STD-004, no dude en consultar estos artículos:
