Desco TB-2031 Service Manual

TB-2031 November 2008 Page 1 of 3

TECHNICAL BULLETIN TB-2031

Statshield®Moisture Barrier Bags
Application Instructions

DESCO WEST - 3651 Walnut Avenue, Chino, CA 91710 • [phone] • Fax [phone]

DESCO EAST - One Colgate Way, Canton, MA02021-1407 • [phone] • Fax [phone] • Web Site: http://www.desco.com

Figure 1. Desco Statshield® Moisture Barrier Bag

Introduction

Corrosion and thus moisture protection is becoming
increasingly important. From ESD Association 22nd
EOS/ESD Symposium Proceedings*, “As electronic
components use less material they become more
sensitive to voltage and current variations. This
increases their operational speed and functionality.
Corrosion that was heretofore inconsequential now
becomes a major factor in the current electronic

components. . . . This underlines the importance of

protection from angstrom level corrosion of surfaces
beyond the normal solderability level problems on
circuitry.” Statshield®EMI/RFI ESD Moisture Barrier
Bags addresses this concern providing physical, ESD,
EMI/RFI, and moisture protection.

"...it is important to take possible temperature exposure into
account when shipping electronic parts. It is particularly
important to consider what happens to the interior of a
package if the environment has high humidity. If the
temperature varies across the dew point of the established
interior environment of the package, condensation may
occur. The interior of a package should either contain
desiccant or the air should be evacuated from the package
during the sealing process. The package itself should have a
low WVTR." (ESD Handbook ESD TR20.20 section 5.4.3.2.2)

Description

Desco Statshield®Moisture Barrier Bags combine the
properties of a MOISTURE BARRIER constitution with
EMI-RFI-ESD shielding. Statshield®Moisture Barrier
Bags meet the electrical and physical requirements of
ANSI/ESD S541, EIA 583, EIA 541, EIA 625, and MIL­PRF-81705D, Type I. All Statshield®Moisture Barrier
Bags are amide and amine free and pass outgassing
and corrosion tests. All bags are printed with ESD and
moisture warning symbols and are dated and lot coded
for ease of traceability.

Desco offers three styles of Moisture Barrier Bags. The
first is a .0065” (.1651mm) thick heavy-duty bag with
EMI shielding, the second is a .0040” (.1016mm) thick
foil bag with EMI/RFI shielding, and the third is a
.0035” (.0889mm) bag with EMI/RFI shielding
properties. All three bags are available in a wide range
of sizes. Also, custom sizes and custom imprinting are
available.

Construction

Desco Statshield® Moisture Barrier Bags are
manufactured out of a laminated film which features
static dissipative surfaces. The configuration is similar
to the metal-in shielding material, but with two metal
layer being placed between layers of dissipative film. A
polyester layer provides pull strength and heat seal
capability. The metal layer is approximately ten times
thicker than that of traditional static shielding material
and provides the EMI attenuation and moisture barrier
properties.
The metal layer within the Moisture Barrier Bag is
vacuum deposited rather than being a foil layer. This
difference allows the bag to be much softer and
flexible, therefore the metal portion of the bag is less
likely to tear or rip providing a more reliable barrier
against moisture and static electricity.

Made in America

Static Dissipative
Polyester

Aluminum
Shielding
Layer

Polyester Layer
Aluminum Shielding Layer
High Performance Static

Dissipative Polyethylene

*Paper entitled “Corrosion Induced Electrostatic Damage” by
John P. Franey of Lucent Technologies Bell Labs

© 2008 DESCO INDUSTRIES INC.

Employee Owned

Figure 2. Statshield® MBB bag construction.

TB-2031 Page 2 of 3

DESCO WEST - 3651 Walnut Avenue, Chino, CA91710 • [phone] • Fax [phone]

DESCO EAST - One Colgate Way, Canton, MA02021-1407 • [phone] • Fax [phone] • Web Site: http://www.desco.com

General Information

Failures in certain electronic devices and microcircuits
have been linked to the rapid expansion of internally
absorbed moisture during the soldering process.
Moisture absorption into these devices has been
traced to have taken place primarily during shipping
and storage in non-humidity controlled environments.
Additionally, “Dry Packaging” is usually required for
electronic assemblies or devices that are to be placed
into long term storage or for use in military
applications.

The Statshield®Moisture Barrier Bag, Desiccant Packs
and Humidity Indicator Cards have been developed for
use in “DRY PACKAGING” applications. In order for
the MBB bag and its accessories to perform properly,
Desco recommends the user follow procedures
defined in IPC/JEDEC J-STD-033B.

DESICCANT

Desiccant is a drying agent used to lower the moisture
content of air inside a closed space, such as an
Moisture Barrier bag. Desiccant is packaged in
fractional units in order to facilitate its usage with a
variety of bag sizes. One full “unit” of packaged
desiccant will absorb the following quantities of water
at equilibrium with air at 77°F (25°C): 3.00 grams @
20% rH and 6.00 grams @ 40% rH, when tested to
MIL-D-3464.

Desiccant packs are available from Desco in the
following unit sizes and standard packages:

ITEM # UNIT SIZE STANDARD PKG.

13840 1/2 unit - 1.5" x 3" Box of 700
13842 1 unit - 3" x 4" Box of 500
13850 1/2 unit - 1.5" x 3" Pail of 550
13852 1 unit - 3" x 4" Pail of 300

Desiccant packs sold by Desco meet the requirements
of MIL-D-3464. For more detailed information, see
Drawing 13850.

HUMIDITY INDICATOR CARDS

Another integral part of a moisture barrier packaging
assembly system is the Humidity Indicator Card. The
Indicator Card contains chemically impregnated,
humidity sensitive, indicating spots that will change
color with moisture. The comparison bar is used to
determine relative humidity of air. Select the indicating
spot that most closely matches the color of the
comparison bar. The measured relative humidity is the
percentage indicated on the matching spot. The
chemical reaction of the indicating spots is completely
reversible; the spots will continue to change color as
the moisture levels change.

INTERIOR BAG NUMBER OF DESICCANT UNITS
SURFACE AREA *MIH <20% MIH <30% MIH < 40%

100 sq. in. 1.5 1.0 1.0
130 sq. in. 2.0 1.5 1.0
160 sq. in. 2.0 1.5 1.5
200 sq. in. 2.5 2.0 1.5
240 sq. in. 3.0 2.0 1.5
290 sq. in. 4.0 2.5 2.0
340 sq. in. 4.5 3.0 2.5
390 sq. in. 5.0 3.5 2.5
450 sq. in. 5.5 4.0 3.0
510 sq. in. 6.5 4.5 3.5
580 sq. in. 7.5 5.0 4.0
650 sq. in. 8.0 5.5 4.0
720 sq. in. 9.0 6.0 4.5

© 2008 DESCO INDUSTRIES INC.

Employee Owned

13868 13869 13870

Figure 3. Desiccant packs.

In order to provide a moisture barrier packaging
assembly system, desiccant must be inserted into the
bag, prior to having the bag vacuum sealed. The
recommended amount of desiccant is dependent on
the interior surface area of the bag to be used. Figure
4 is a reference table indicating recommended
minimum amounts of desiccant that should be used
with Moisture Barrier Bags.

Figure 4. Table for recommended desiccant usage.
Information taken out of EIA-583, Table 1, Page 8.

Figure 5. Humidity Indicator Cards