Moisture Sensitivity Level (MSL) Overview

MSL is the abbreviation of Mositure Sensitivity Level, which is also called moisture sensitivity level. It characterizes the chip's ability to resist humid environments. This is an extremely important parameter that is easily overlooked by electronic engineers.

Usually, when the chip is exposed in an open environment, it will absorb moisture, and the moisture may penetrate into the chip plastic package along the pins. During SMT reflow soldering, the moisture expands due to the instantaneous high temperature, and there is a probability that the so-called "popcorn" (POPCORN) phenomenon will occur.

Moisture Sensitivity Level Classification

According to the JEDEC J-STD-020D standard, there are 8 levels of MSL classification, as follows:

● MSL1 - less than or equal to 30°C/85% RH unlimited floor life

● MSL2 - less than or equal to 30°C/60% RH one year floor life

● MSL2a - less than or equal to 30°C/60% RH four weeks floor life

● MSL3 - less than or equal to 30°C/60% RH 168 hours floor life

● MSL4 - less than or equal to 30°C/60% RH 72 hours floor life

● MSL5 - less than or equal to 30°C/60% RH 48 hours floor life

● MSL 5a - less than or equal to 30°C/60% RH 24 hours floor life

● MSL6 - less than or equal to 30°C/60% RH immediate floor life

(For level 6, components must be baked before use and must be reflowed within the time limit specified on the moisture sensitive warning label)

It is particularly important to note that if the ambient temperature or air humidity is greater than the limited test conditions of the corresponding level, the time the chip can be exposed to the open environment will be shorter than the time given in the standard.

Impact of humidity sensitivity level and protective measures

Once moisture enters the chip, there is a chance that sufficient vapor pressure will be generated during SMT to damage or destroy the component. Common damage situations include separation (delamination) of the plastic from the chip or lead frame, damage to the bonding wires, chip damage, or cracks inside the chip (which cannot be observed on the chip surface). The most serious situation is chip swelling and bursting (the "popcorn" effect).

In addition, when moisture enters the chip, it may also cause electrochemical corrosion. When the water vapor is powered on, it may be ionized to generate hydroxide. The hydroxide reacts chemically with the bonding PAD or even the metal layer inside the chip, resulting in the formation of hydrated oxides. The oxides will absorb some water vapor, resulting in a relatively fragile part at the interface between the encapsulation resin and the metal, leading to bonding failure. If there are potassium, sodium, chlorine and other ions in the moisture, the probability of corrosion of the chip, lead frame and PAD will be greatly increased, resulting in delamination or peeling. When delamination occurs, the difficulty of moisture intrusion is greatly reduced, and the reliability of the chip will also be greatly reduced.

Taking into account the cost and the actual production process control, most chips will choose the MSL3 package humidity sensitivity level and use vacuum sealed bags for packaging, and will also put in desiccant and humidity sensitive cards. After the chip is unpacked, the patch and test should be completed as soon as possible, and then coated with three-proof paint and other coatings for humidity protection. If you find that the vacuum bag is leaking, the humidity-sensitive card is discolored, or it has been left for too long after unpacking, be sure to bake it according to the standard process before use to ensure the safety of the chip.