What are SMT Moisture - Sensitive Devices (MSD) and How to Control Them? (Part 2)

2025-05-26

2.3 MSL ClassifICation Test Soaking Conditions

Before the test, it is necessary to ensure that the MSD is dry (baked at 125℃ for 24 hours). The specific soaking conditions are shown in Table 2:

Table 2. MSL Classification Test Soaking (SOAK) Time

The above test by default includes the maximum exposure time (MET = 24 hours) for the supplier's baked packaging/distributor's unpacking. If MET ≠ 24 hours, the corresponding soaking time can be increased or decreased accordingly (standard conditions: MET ± 1 hour corresponds to soaking time ± 1 hour; accelerated conditions: MET ± 5 hours corresponds to soaking time ± 1 hour).

The activation energy in eV indicates the moisture diffusion ability of different encapsulation materials and represents the equivalent factor between accelerated and standard conditions. There may be potential stress damage risks to the device during the test after soaking under activation energy conditions. Therefore, the eV conditions need to be clarified before the test. If the activation energy of moisture diffusion of the material is not included in the above table, the JESD22 - A120 standard can be referred to for clarification.

2.4 MSL Classification Peak Reflow Soldering Temperature

SMDs with thinner encapsulation and smaller volume have higher requirements for reflow soldering temperature during MSL classification. According to different SMD encapsulation structures and single - board reflow soldering assembly processes, the requirements for peak reflow soldering temperature are shown in Table 3 below:

Table 3. MSL Classification Peak Reflow Soldering Temperature

Note: 2.4.1 The above encapsulation volume does not include the volume occupied by the device's external leads (or terminals/bump balls, etc.) and embedded heat sinks.