18
Storage Condition
Packages described in this document must be stored
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.6.
Out-of-Bag Time Duration
After unpacking the device must be soldered to the PCB
within 168 hours with factory conditions <30°C and 60%
RH as listed in the Table 5-1 on the J-STD-020D p.6.
Baking
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 condi- Baking must be done if at least one of the condi-Baking must be done if at least one of the condi- one of the condi-one of the condi-
tions above has not been satisfied. The baking conditions
are listed in the Table 4-1 on the J-STD-033 p.8.
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).
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.
Removal for Failure Analysis
Not following the above requirements may cause moisture/
reflow damage that could hinder or completely prevent
the determination of the original failure mechanism.
Baking of Populated Boards
Some SMD packages and board materials are not able 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 capacitors are
also temperature sensitive. With component and board
temperature restrictions in mind, choose a bake tem- mind, choose a bake tem-mind, choose a bake tem-
perature 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.
Derating due to Factory Environmental Conditions
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 table of Moisture Classification Level
and Floor Life. 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 address-
ing 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.
Table on follwoing page lists equivalent derated floor lives
for humidities ranging from 20-90% RH for three tempera-
ture, 20°C, 25°C, and 30°C.
This table is applicable to SMDs molded with novolac,
biphenyl or multifunctional epoxy mold compounds.
The following assumptions were used in calculating this
table:
1. Activation Energy for diffusion = 0.35eV (smallest
known value).
2. For ≤60% RH, use Diffusivity = 0.121exp (-0.35eV/kT)
mm2/s (this used smallest known Diffusivity @ 30°C).
3. For >60% RH, use Diffusivity = 1.320exp (-0.35eV/kT)
mm2/s (this used largest known Diffusivity @ 30°C).
