S2080 Datasheet, PDF (1/2 Pages) M/A-COM Technology Solutions, Inc. – Moisture Effects on the Soldering of Plastic Encapsulated Devices

Application Note
S2080
Moisture Effects on the Soldering of Plastic Encapsulated
Devices
Rev. V5
Introduction
Improper packaging, storage, and handling of plastic
encapsulated devices (PED’s) can trap moisture within
the devices and lead to damage during reflow soldering
to printed circuit boards. As part of reliability qualification
and testing, M/A-COM tests and classifies all
semiconductor devices for moisture sensitivity to assure
long term reliability. This application note briefly
describes the moisture-induced soldering failure
mechanism and test procedures, and moisture
sensitivities of M/A-COM’s plastic packaged
semiconductors.
Moisture Induced Soldering Failures
Moisture inside a plastic package turns to vapor and tries
to expand when the package is exposed to rapid high
temperatures during soldering. The internal vapor
pressure can cause separation of the plastic encapsulant
from the semiconductor chip or lead frame, internal and
external cracks, and damage to thin films and wire
bonds. In severe cases, soldering may cause an
integrated circuit to bulge and then explode with an
audible pop. Compared to through-hole devices, surface
mount devices (SMD’s) have thinner plastic capsules
and come into more intimate contact with high
temperatures. Therefore, measures to limit and reduce
the ingress of moisture during handling and storage of
SMD’s are generally more critical for SMD’s than for
through-hole devices. To reduce the effects of moisture-
induced stress during soldering, M/A-COM recommends
bake-out of some of its most moisture sensitive devices
before reflow soldering according to standard industry
procedures.
Moisture Test Methods
M/A-COM tests its PED’s according to the procedures
outlined by the standards organization JEDEC. We will
briefly summarize the procedures here, but we
recommend that the reader consult IPC/JEDEC J-STD-
020, J-STD-033 and JESD22-A113 for detailed
explanation of test procedures and failure criteria. For
information on surface mounting consult application note
M538 or S2083.
As recommended by JEDEC, we start with a sample of
known good parts and subject the parts to a 24-hour
bake-out at 125°C to remove all moisture. Next we place
the parts in a moist, warm environment for a prescribed
period of time, as outlined in Table 1 under “soak
requirements”. Within four hours of removing them from
the soak, we then subject the parts to three cycles of
convection reflow with the temperature profile
recommended by JEDEC. The tin-lead eutectic solder
profile includes a preheat to 150°C, followed by 60 - 150
seconds above 180°C with a maximum temperature of
240°C, followed by a ramp-down back to room
temperature. The lead-free/RoHS solder profile includes
a preheat to 200°C, followed by 60 - 150 seconds above
217°C with a maximum temperature of 260°C. Please
consult JEDEC for the complete profile.
After the convection reflow procedure, we examine the
devices for failures. JEDEC defines moisture-induced
solder stress failures as any external cracks visible with a
40X optical microscope, DC electrical or functional
failures, and most internal cracks, especially those that
intersect a bond wire or ball/wedge bond. M/A-COM also
examines the devices for any delaminating associated
with moisture sensitivity.
M/A-COM performs these tests on any devices with
different package type, mold compound, or die pad area
relative to devices that we have already tested.
Moisture Absorption and Floor Life
After bake-out for removal of moisture, all PED’s
eventually reach a condition of humidity equilibrium
between the inside and outside of the package. JEDEC
defines the time at which the moisture inside the package
reaches a level likely to induce failure as the “floor life”.
The rate of moisture absorption depends upon ambient
temperature and humidity conditions, so JEDEC defines
the floor life under specific ambient conditions. Devices
stored beyond the floor life require a bake-out before
reflow soldering to avoid possible damage. M/A-COM
includes moisture sensitivity labels with all PED’s that
have a limited floor life and might need bake-out.
Moisture Sensitivity Ratings
Devices with sensitivity to moisture-induced solder stress
should be shipped and stored in sealed, dry containers
with a desiccant. As explained above, sensitive devices
require a bake-out to remove moisture prior to reflow
soldering if stored in typical ambient conditions beyond
the floor life, or damage could result.
Based on the floor life, JEDEC outlines six levels of
moisture sensitivity as shown in Table 1. Level 1 devices
are considered not sensitive to moisture, and have an
unlimited floor life. These devices do not require dry pack
shipping, and do not require bake-out prior to reflow
soldering. Devices above level 2 are considered moisture
sensitive, and require dry pack shipping and bake out.
Level 6 devices are considered extremely moisture
sensitive. The JEDEC guidelines specify that the user
should reduce or eliminate reflow heating by mounting
these PED’s on sockets or by performing a bake-out on
the devices immediately before reflow soldering.
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