IPC/JEDEC Moisture Sensitivity Levels

IPC/JEDEC Moisture Sensitivity Levels (MSL)

Different package types exhibit different sensitivity levels to moisture ingress and its effects. The older, through-hole, bulkier packages absorb moisture per volume at a slower rate than the thinner, surface-mount packages of recent times.

The problem with moisture absorption and retention inside the package is that the trapped moisture will vaporize and exert tremendous internal package stresses when the device is subjected to sudden, elevated temperature, such as during board mounting. Package cracking due to such moisture-induced stresses is known as popcorn cracking.

In general, surface-mount devices (SMD's) are more prone to popcorn cracking because: 1) they are thinner and therefore has lower fracture strength; 2) they absorb and retain moisture more easily; and 3) SMD board mounting also subjects the molding compound to the high temperature experienced by the leads.

In recognition of the varying degrees of popcorn cracking tendency of various package types, IPC/JEDEC defined a standard classification of moisture sensitivity levels (MSL's). The MSL's are expressed in numbers, with the MSL number increasing with the vulnerability of the package to popcorn cracking. Thus, MSL1 correspond to packages that are immune to popcorn cracking regardless of exposure to moisture, while MSL5 and MSL6 devices are most prone to moisture-induced fracture.

Table 1 below presents the MSL definitions per IPC/JEDEC's J-STD-20.

Table 1. IPC/JEDEC J-STD-20 MSL Classifications

			Soak Requirements
	Floor Life		Standard		Accelerated
Level	Time	Cond degC/%RH	Time (hrs)	Cond degC/%RH	Time (hrs)	Cond degC/%RH
1	unlimited	<=30/85%	168+5/-0	85/85	n/a	n/a
2	1 year	<=30/60%	168+5/-0	85/60	n/a	n/a
2a	4 weeks	<=30/60%	696+5/-0	30/60	120+1/-0	60/60
3	168 hours	<=30/60%	192+5/-0	30/60	40+1/-0	60/60
4	72 hours	<=30/60%	96+2/-0	30/60	20+0.5/-0	60/60
5	48 hours	<=30/60%	72+2/-0	30/60	15+0.5/-0	60/60
5a	24 hours	<=30/60%	48+2/-0	30/60	10+0.5/-0	60/60
6	TOL	<=30/60%	TOL	30/60	n/a	60/60

1) TOL means 'Time on Label', or the time indicated on the label of the packing.

2) The standard soak time is the sum of the default value of 24H for the semiconductor manufacturer's exposure time (MET) between bake and bag and the floor life or maximum time allowed out of the bag at the end user or distributor's facility. For example, an MSL 3 package will require a standard soak time of 192 hours, which is 168 hours of floor life plus 24 hours between bake and bag at the semiconductor manufacturer.

Solder Heat Resistance Test (SHRT)

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