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.
Ce qu'il faut savoir
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.
Pourquoi vous devez savoir
La concentration d'halogénures est contrôlée parce que les halogénures ont le potentiel de corroder la soudure, ce qui peut conduire à une croissance dendritique en présence d'un biais électrique appliqué et d'humidité. Lorsque les produits non nettoyés passent les tests J-STD-004 SIR et ECM et sont utilisés correctement, ce problème ne se pose pas. Pour les résidus de flux qui doivent être nettoyés (solubles dans l'eau), l'utilisation d'un processus de nettoyage complet et efficace devrait empêcher toute corrosion. Il est essentiel de rappeler qu'un flux contenant des halogénures n'est pas intrinsèquement nocif pour un assemblage. La présence d'halogénures doit simplement être caractérisée pour favoriser la conception et l'assemblage d'un dispositif électrochimiquement fiable.
En revanche, la décision d'un fabricant d'utiliser exclusivement des produits sans halogène est motivée par des considérations environnementales. Les halogènes utilisés dans la chimie d'un flux sont généralement des halocarbures, qui peuvent polluer l'environnement lorsque les assemblages contenant des résidus de flux halogénés sont éliminés de manière inappropriée. Bien que les flux contenant des halogènes soient utilisés tous les jours dans le monde entier, une entreprise peut choisir d'imposer elle-même des réglementations qui rejettent l'utilisation de flux contenant des halogènes afin d'éviter complètement ce problème. Il n'existe aucune réglementation gouvernementale interdisant purement et simplement l'utilisation de tous les matériaux de soudure contenant des halogènes dans l'électronique. Étant donné qu'il n'y a pas de nécessité technique de caractériser la teneur en halogène, le test d'halogène est facultatif.
Où la confusion s'installe
Pour ceux qui sont plus curieux sur le plan technique, voici une exploration plus approfondie :
- 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.
Pour en savoir plus
Pour plus d'informations sur la caractérisation des flux selon la norme J-STD-004, n'hésitez pas à consulter ces articles :
