IEC 60749-20-2020 pdf free download

IEC 60749-20-2020 pdf free download.Semiconductor devices — Mechanical and climatic test methods — Part 20: Resistance of plastic encapsulated SMDs to the combined effect of moisture and soldering heat
Dispositifs a semiconducteurs — Méthodes d’essais mécaniques et climatiques — Partie 20: Résistance des CMS a boItier plastique a l’effet combine de l’humidité et de Ia chaleur de brasage.
A.1.2 Considerations on which the condition of moisture soak is based A.1.2..1 General description of moisture soak
The presence of moisture in SMDs is caused by diffusion of water vapour into the resin. The moisture content of the resin needs to be examined, since package cracking during soldering emanates from near the die pad or the die. Examples of characteristics for moisture soak at 85 °C, 85 % relative humidity, are shown in Figure A.1. In the case where the resin thickness from the bottom surface of the package to the die pad is 1 mm, Figure A.1 indicates that over 168 h are needed for saturation to take place.
Moisture soak characteristics, such as that of the resin in Figure A.3, show a slow moisture soak speed which is nevertheless considered significant. Figure A.1 and Figure A.4 to Figure A.8 represent moisture soak characteristics of the resin.
Saturation is needed for soldering heat tests in order to simulate long-time storage of, for example, one year which occurs when SMDs are dry-packed or warehoused. The diffusion speed of water vapour into resin depends only on temperature. Given the resin thickness as defined in Figure A.2, saturating moisture time at 85 °C depends on the resin thickness as shown in Figure A.3. It would appear that, for a normal SMD whose resin thickness is from 0,5 mm to 1,0 mm, 168 h of moisture soak time are required.
The saturated moisture content of resin depends on temperature and relative humidity as shown in Figure A.4. The relative humidity required for moisture soak can be determined from Figure A.4 (for example, so that the content of moisture at 85 °C can be made to correspond with the content of moisture at 30 °C, the actual storage temperature). Conditions of moisture soak for soldering heat tests are derived from Figure A.4 as shown in Table A.1.
Figure A.5 shows the moisture content in resin at the first interface (top surface of die or bottom surface of die pad) under conditions of moisture soak and real storage conditions.IEC 60749-20-2020 pdf free download.