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78 SMT007 MAGAZINE I FEBRUARY 2019 To avoid the damage of microcracks and de- lamination during the processing of electronic components, appropriate environmental stor- age is essential. The introduction of lead-free soldering and the associated higher processing temperatures involved makes moisture man- agement even more important. Lead-free re- flow increases the consequent saturated vapor pressure within components considerably (up to 30 bars). The same component that could be safely processed before lead-free becomes a moisture sensitive device with limited floor life. The difference is often two moisture sen- sitivity levels (MSLs) higher in classification, and shorter allowable exposure time (floor life). Component suppliers should deliver these moisture sensitive components in effective protective packaging to avoid absorption of humidity during transport and storage. These moisture barrier bags (MBBs) are made from multiple layers of plastic and aluminum. Prop- erly prepared and sealed, they are also a protec- tive packaging that can prevent oxidation. ESD bags or zippered plastic bags do not protect against moisture. After opening the package, the time begins during which the components absorb humidity. Depending on ambient hu- midity and temperature, the components can be safely used only within a limited time pe- riod. This time period is classified by the IPC/ JEDEC J-STD-033D. When a component has exceeded the al- lowed exposure time, the component can be dried and made safe again through a baking process, traditionally done at 125°C. The com- ponent should be processed especially careful- ly after that. Repeated absorption of humidity Controlling Oxidation and Intermetallics in Moisture-sensitive Devices More Than Just Dry Air by Richard Heimsch, SUPER DRY TOTECH

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