Storage Condition
Baking of Populated Boards
Packages described in this document must be stored Some SMD packages and board materials are not able
in sealed moisture barrier, antistatic bags. Shelf life in a
sealed moisture barrier bag is 12 months at <40° C and
90% relative humidity (RH) J-STD-033 p.7.
to withstand long duration bakes at 125° C. Examples
of this are some FR-4 materials, which cannot withstand
a 24 hr bake at 125° C. Batteries and electrolytic capaci-
tors are also temperature sensitive. With component and
board temperature restrictions in mind, choose a bake
temperature from Table 4-1 in J-STD 033; then determine
the appropriate bake duration based on the component
to be removed. For additional considerations see IPC-7711
andIPC-7721.
Out-of-Bag Time Duration
After unpacking the device must be soldered to the PCB
within 168 hours as listed in the J-STD-020B p.11 with
factory conditions <30° C and 60% RH.
Baking
Derating due to Factory Environmental Conditions
It is not necessary to re-bake the part if both conditions
(storage conditions and out-of bag conditions) have been
satisfied. Baking must be done if at least one of the con-
ditions above have not been satisfied. The baking condi-
tions are 125° C for 12 hours J-STD-033 p.8.
Factory floor life exposures for SMD packages removed
from the dry bags will be a function of the ambient envi-
ronmental conditions. A safe, yet conservative, handling
approach is to expose the SMD packages only up to the
maximum time limits for each moisture sensitivity level
as shown in next table. This approach, however, does not
work if the factory humidity or temperature is greater
than the testing conditions of 30° C/60% RH. A solution
for addressing this problem is to derate the exposure
times based on the knowledge of moisture diffusion in
the component package materials ref. JESD22-A120).
Recommended equivalent total floor life exposures can
be estimated for a range of humidities and temperatures
based on the nominal plastic thickness for each device.
CAUTION
Tape and reel materials typically cannot be baked at the
temperature described above. If out-of-bag exposure
time is exceeded, parts must be baked for a longer time
at low temperatures, or the parts must be de-reeled,
de-taped, re-baked and then put back on tape and reel.
(See moisture sensitive warning label on each shipping
bag for information of baking).
Table on next page lists equivalent derated floor lives for
humidities ranging from 20-90% RH for three tempera-
ture, 20° C, 25° C, and 30° C.
Board Rework
Component Removal, Rework and Remount
If a component is to be removed from the board, it is
recommended that localized heating be used and the
maximum body temperatures of any surface mount
component on the board not exceed 200° C. This method
will minimize moisture related component damage. If any
component temperature exceeds 200° C, the board must
be baked dry per 4-2 prior to rework and/or component
removal. Component temperatures shall be measured at
the top center of the package body. Any SMD packages
that have not exceeded their floor life can be exposed to
a maximum body temperature as high as their specified
maximum reflow temperature.
Table on next page is applicable to SMDs molded
with novolac, biphenyl or multifunctional epoxy mold
compounds. The following assumptions were used in cal-
culating this table:
1. ActivationEnergyfordiffusion=0.35eV(smallestknown
value).
2. For ≤60% RH, use Diffusivity = 0.121exp (-0.35eV/kT)
2
mm /s (this used smallest known Diffusivity @ 30° C).
3. For >60% RH, use Diffusivity = 1.320exp (-0.35eV/kT)
2
mm /s (this used largest known Diffusivity @ 30° C).
Removal for Failure Analysis
Notfollowingtheaboverequirementsmaycausemoisture/
reflow damage that could hinder or completely prevent
the determination of the original failure mechanism.
12
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