DIN EN 61760-4:2016-03

This part of IEC 61760 specifies the classification of moisture sensitive devices into moisture sensitivity levels related to soldering heat, and provisions for packaging, labelling and handling. This part of IEC 61760 extends the classification and packaging methods to such components, where currently existing standards are not required or not appropriate. For such cases this standard introduces additional moisture sensitivity levels and an alternative method for packaging. This standard applies to devices intended for reflow soldering, like surface mount devices, including specific through-hole devices (where the device supplier has specifically documented support for reflow soldering), but not to - semiconductor devices, - devices for flow (wave) soldering. Due to the higher temperature profiles of reflow soldering processes for tin-silver-copper or other lead-free solder alloys with higher melting temperatures than eutectic Sn-Pb solder, the sensitivity of pre-solder moisture-stressed components to solder heat is becoming increasingly important. Currently available component moisture sensitivity classification standards are applicable to plastic molded semiconductors and similar solid state packages (for example IEC 60749-20), but not to other types of components. This part of IEC 61760 also extends the classification and packaging procedures of J STD 020 and J STD 033. It is intended for use with component types for which J STD 020 and J STD 033 are not required or not suitable. Certain materials, polymer plastics and fillers are hygroscopic and may absorb moisture depending on time and storage climate. The absorbed moisture evaporates during rapid heating during reflow soldering and causes pressure in the material, deformation, and swelling, delamination, cracking and weakening of internal interconnection structures. Moisture generally penetrates absorbent material when exposed to ambient air. Absorption of moisture or penetration of moisture into voids can lead to moisture concentrations within the component that are high enough to cause cracking and/or delamination during the soldering process (for example, the "popcorn effect"), which can adversely affect reliability. Moisture can also affect the bonding strength of adhesives, seals, potting compounds, plastics with electroplated coatings, and so on. Exposure to moisture can also cause the transport of ionic contaminants into the component, increasing the potential for circuit corrosion failures. It is therefore necessary to dry moisture-sensitive devices, to seal them in moisture protection bags and remove them only immediately before soldering them onto printed circuit boards. The permissible time from opening the moisture protection bag until the last soldering process, during which a component may be exposed unprotected to a climate that corresponds approximately to the real ambient conditions, is a measure of the sensitivity of the component to the ambient moisture. This time is designated as floor life. The moisture sensitivity level (MSL) is determined at the classification temperature, which is higher than the applied soldering temperatures. Therefore, the actual soldering temperature determined at the surface of the component shall be lower than the classification temperature. Packaging, storage, floor life, and pretreatment of moisture-sensitive components prior to reflow soldering are indicated by the moisture sensitivity class. In humidity tests, such as according to IEC 60068-2-78, components are stressed in their original state (unmounted) or in the assembled state, for example soldered to a test PCB. These tests determine the influence of adsorbed or absorbed moisture on the behavior of the component, for example, electrical properties, corrosion effects, but they cannot determine the influence of absorbed moisture on the sensitivity to the heat load during soldering processes. The aim of the test method described in this standard is to test the resistance of components to the heat of soldering in conjunction with the moisture load during pretreatment. Further moisture effects such as the impairment of the electrical characteristic values or the insulating properties are not covered by this standard and shall be tested separately. The symbol identifies moisture-sensitive components and is applied to all warning labels regarding moisture sensitivity. The responsible committee is DKE/K 682 "Montageverfahren für elektronische Baugruppen" ("Electronics assembly technology") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.