Because plastic packaging components can be mass-produced and reduce costs, the ICs used in most pcba products are plastic-sealed devices. However, the plastic packaging device has a certain hygroscopicity, so the plastic sealing devices SOP, PLCC, QFP, PBGA, etc. are all Moisture Sensitive Devices (MSD). Humidity sensitive devices mainly refer to non-hermetic devices, including: plastic packaging; other water-permeable polymer packaging (epoxy, silicone resin, etc.); general IC, chip, electrolytic capacitor, LED, etc.
Both reflow and wave soldering are instantaneously heating the entire SMD. When high temperatures during the pcb soldering process are applied to the housing of the hygroscopic molded device, the resulting thermal stress can cause cracks in the joint between the package and the leads. Cracks can cause shell leakage and slow the chip’s moisture, and can loosen the pins and cause early failure.
Humidity sensitivity level of humidity sensitive devices
The IPC/JEDEC J-STD-020 standard classifies the moisture sensitivity levels of the devices, as shown in Table 1. The on-site service life in this table is for tin-lead soldering. Since lead-free soldering has a higher soldering temperature than tin-lead soldering, according to experience, the humidity sensitivity level of the device is increased by one level for every 10 °C increase in soldering temperature. Therefore, if the device is grade 3 when tin-lead is soldered, then it is grade 4 when using lead-free solder.
|Classification||After unpacking the environment||After the unpacking, the service life on site|
|class 2||≤30℃，60%RH||one year|
|class 2a||≤30℃，60%RH||four weeks|
|class 6||≤30℃，60%RH||According to moisture sensitive label regulations|
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