IEC 60749-20-2020 Semiconductor devices – Mechanical and climatic test methods – Part 20: Resistance of plastic encapsulated SMDs to the combined effect of moisture and soldering heat.
4 General description
Package cracking and electrical failure in plastic encapsulated SMDs can result when soldering heat raises the vapour pressure of moisture which has been absorbed into SMDs during storage. These problems are assessed. In this test method, SMDs are evaluated for heat resistance after being soaked in an environment which simulates moisture being absorbed while under storage in a warehouse or dry pack. Moisture sensitivity level (MSL) ratings generated by this document are utilized to determine the soak conditions for preconditioning in accordance with IEC 60749-30.
5 Test apparatus and materials
5.1 Humidity chamber The humidity chamber shall provide an environment complying with the temperature and relative humidity defined in 6.3.
5.2 Reflow soldering apparatus The infrared convection, the convection and the vapour-phase reflow soldering apparatus shall provide temperature profiles complying with the conditions of soldering heat defined in 6.4.2 and 6.4.3. The settings of the reflow soldering apparatus shall be adjusted by temperature profiling of the top surface of the specimen while it is undergoing the soldering heat process, measured as shown in Figure 1 .
Unless otherwise detailed in the relevant specification, any board material, such as epoxy fibreglass or polyimide, may be used for the holder. The specimen shall be placed on the holder by the usual means and in a position as shown in Figure 1 . If the position of the specimen, as shown in Figure 1 , necessitates changing the shape of terminations and results in subsequent electrical measurement anomalies, a position that avoids changing the shape of terminations may be chosen, and this shall be specified in the relevant specification.
5.4 Wave-soldering apparatus
The wave-soldering apparatus shall comply with conditions given in 6.4.4. Molten solder shall usually be flowed.
5.5 Solvent for vapour-phase reflow soldering
Perfluorocarbon (perfluoroisobutylene) shall be used.
Unless otherwise detailed in the relevant specification, the flux shall consist of 25 % by weight of colophony in 75 % by weight of isopropyl alcohol, both as specified in Annex B of IEC 60068-2-20:2008.
A solder of the composition as specified in Table 1 of IEC 60068-2-20:2008 shall be used.IEC 60749-20 pdf download.