in EOS/ESD Technology Dec/Jan 1990
Over the past twenty years, MIL-B-81705
has helped shape static-control products and methodologies. Here's
how this key military specification has grown and changed with time.
(View Part II
of this article)
Charles R. Hynes,
ESD Consultant, Contributing Editor, Minnetonda, MN
MIL-B-81705 is a specification
for barrier materials (not bags) from which sleeves, tubes, and
Class -A or F, Style 1 or 2 MIL-B-117 bags are fabricated. (There
is no such thing as a Type-I or Type-II 81705 bag, despite frequent
references to the contrary.)
The development of
81705 makes an interesting story. The original version of this specification
was dated July 14, 1969, as MIL-P-81705 (AS). Unfortunately, my
files do not contain a copy of that document. If someone still has
a copy, I'd like to see it.
As is the case with
all Mil-Specs, the letter offset by hyphens relates to the first
word in the title of the document. Thus, the "P" in the
original version, and the "B" in the current document
indicate a title change. The "(AS)" suffix indicates that
the Navy (NAVSEA in this case) was the custodian of the document;
it still is. The suffix further indicates that the specification
was originally intended for Navy procurement.
On February 2, 1972,
the specification's first revision become effective. The number
changed to MIL-B-81705-A. The title was:
BARRIER MATERIALS, FLEXIBLE, ELECTROSTATIC-FREE, WATER-VAPORPROOF,
Only two classes of materials were shown: Class 1-Oil resistant
and Class 2-Nonoil resistant.
No reference was made
to MIL-STD-1686 because it didn't exist is 1972. It appeared eight
years later, when 81705 lost its (AS) suffix and became applicable
to "all departments and agencies of the Department of Defense."
The scope of the document
covered "barrier materials for the packaging of missiles, explosive
powder, and electrosensitive devices, micro circuits, semiconductors,
thin-film resistors and associated airborne components."
At this point, we referred
to Paragraph 6.1, Intended use.
6.1 Intended use. It is intended
that these barrier materials be used to fabricate enclosures primarily
for missiles stored, handled, and transported in cradles and subjected
to a small during logistic flow. These barrier materials are especially
formulated to prevent the buildup or retention of electrostatic
potential under any atmospheric conditions, the objective being
to maximize explosive safety and to preclude ignition of stray flammable
materials. The finished enclosure is to provide protection from
Under Paragraph 6.3,
we find a footnote:
6.3 The relationship between the classification of materials in
earlier issues of this specification and of this specification is
(*Because of the unavailability
of the Type I Transport material, it has been deleted from the specification.
There is a continuing need for an electrostatic-free transparent
material and for this reason industry is encouraged to develop such
As of February 2, 1972,
a transparent, electrostatic-proctective material had not yet been
approved, although industry was at work on what was to become pink
From Table 1, we find
that the only electrostatic property test that was required was
a static-decay test per FedSTD 101, Method 4046 and a maximum 2-sec
decay rate was established.
A test for electromagnetic
protection was not included. MIL-P-116, MIL-P-17555, and MIL-STD-794,
while they existed, were not referenced.
last long. Revision B became effective two years later, August 15,
1974. The first amendment came on March 19, 1989. The second amendment
came April 21, 1982, and the third came June 9, 1983. In May 1987,
Revision C was approved for public release and became effective
January 25, 1989.
(When there is no effective
date on a copy of a standard or specification, anything contained
in that draft remains subject to change. Unless you see a release
date on a copy of a specification in the upper-right-hand corner,
don't let anyone tell you that the document has been approved for
procurement purposes. Until a new revision is approved and dated,
the most recent existing revision, with amendments, is operative.)
With approval of the
81750's B revision in 1974, we find a change in the language of
This specification covers opaque and transparent heat-sealable,
electrostatic-free, flexible, barrier materials for the packaging
of missiles, explosive powered and electrosensitive devices, microcircuits,
semiconductors, thin-film resistors, and associated airborne components,
in addition to the Type I opaque material provides for the attenuation
of electromagnetic radiation (see 6.1).
The barrier materials shall be of the following types as specified.
When no type is specified Type I shall be furnished (see 6.2).
Type I- Opaque. Type
of the materials specified in earlier issue of this specification
is detailed in Section 6.
In paragraph 1.2, we
see "Type I- Opaque" and "Type II- Transparent"
classifications. Pink poly was born! We are immediately referred
to Paragraph 6.1.
use. It is intended that these barrier materials be used
to fabricate enclosures for electrostatic sensitive equipment and
components. These barrier materials are especially formulated to
prevent the buildup or retention of electrostatic potential, the
objective being to maximize explosive safety, to protect miniature
electronic parts, and to preclude ignition of stray flammable materials.
The finished enclosure is to provide protection from corrosive environments.
I barrier materials. Type I barrier material is intended
for use for the watervaporproof electrostatic and electromagnetic
protection of microcircuits, certain semiconductor devices (such
as microwave diodes and field-effect transistors, thin film resistors,
and other miniature electronic parts requiring this protection)
barrier material. Type-II barrier material is intended
of ruse where transparency is required and contact with oil or grease
is not contemplated. The transparent material is also intended for
level C or commercial packaging use where a waterproof, electrostatic-free,
barrier is needed. For level-A requirements use is limited to interior
wraps or bags [sic].
For the first time,
we see a distinction between electrostatic an electromagnetic protection.
In paragraph 6.1.2, we can see MILP-116 begin to emerge, although
it is still not referenced. Levels C and A refer to these levels
as used in 116. Also not that Type II (pink poly), when used for
level "A," is restricted to interior wraps on bags. Those
who would have you believe that double wrapping is something new
are incorrect; however, we must be more precise about when double-wrapping
Paragraph 6.1.1 of
this document is one of the earliest references to distinguish between
electrostatic and electromagnetic protection, and from this document
and others, it becomes obvious that double-wrapping was mandated
to provide a combination of water vapor, electrostatic, and electromagnetic-varrier
The definitions of
Type-I and Type-II materials appear in Paragraph 3.3, Construction.
I. Type I barrier material shall consist of aluminum
foil and other laminates constructed in any manner which will ensure
compliance with the performance requirements of this specification
and which will be suitable for the purpose intended. Butting of
component materials or the finished product is not permitted except
in the direction perpendicular to the rolling direction. The areas
shall be plainly externally flagged to prevent use of that portion
of the roll when a butt weld is made on the finished product or
II. Type II barrier material shall consist of a transparent,
unsupported, nonlaminated plastic sheet both surfaces of which shall
be chemically neutral and identical, extruded from a homogeneous
antistatic resin mix. The material shall be unprinted and have no
ink, talc, cornstarch, metallization or other foreign matter applied
to the surface after extrusion.
The basic definition
of a Type I material did not change from Revision A. However, the
definition of Type-II was completely new. Among key words introduced
were "transparent," "unsupported," "nonlaminated,"
"chemically neutral," "homogeneous," "antistatic,"
and "resin mix." Each of these terms plays a vital role
in controversies that developed later.
In Paragraph 3.6 Identification
of Material, we find that Type I material was to be printed with
designated information using a water-resistant ink that approximated
Color #27038 of Fed. Std. 595. What was that color? Black.
In Paragraph 3.6.2,
for Type II we find the following words: "Type II barrier materials
shall be of uniform color, approximating the lusterless red (pink)
which conforms to color number 31668 of Fed. Std. 595." As
we will show later, identification of this material created numerous
problems, some of which remain unresolved.
The next section of
MIL-B-81705-B is perhaps the most important part of ht document
because it lists all of the physical properties and test methods
used to quantify those properties. Table 1 of this article is a
complete reprint of Table 1 as it originally appeared in MIL-B-81705-B.
The next item a vendor
hands you a piece of product literature that says, "meets requirements
of 81705-B," don't be misled into the belief that the product
meets all requirements of 81705-B. Likewise, anyone who published
a statement that says "meets or exceeds static decay requirements
of Fed. Std. 101, Method 4046" should become suspect.
Method 4046 does not
include any pass-fail criteria; it is simply a test method used
to establish a value. Whether or not that value is acceptable is
governed by the maximum 2.0-sec. decay rate given in Table 1 of
I have never been able
to determine why or how the 2.0 sec limit was established. The closest
I ever came was during a roundtable discussion at NAVSEA headquarters
in Washington, DC. When the question came up, someone said, "It
takes more than two seconds for someone to pick up a package (or
bag), open it, and touch what's inside the package." If someone
can shed light on this, I'd like to see the item study or other
justification for the time limit. For 15 years, we have accepted
this value as gospel without any concrete rationale to support it.
This is just one of
the questions that a historical review of this document asks. The
static-decay test in Method 4046, of Fed. Std. 101, has been the
only approved test for the electrostatic-protective property of
a barrier material since 1974. None of the three amendments added
any new tests, nor did the maximum decay rate change.
Since it was the only
approved test, it was applied to nearly every conceivable static-control
product, either on the market or developed subsequent to 1974. We
suddenly saw product literature for totes, table mats, smocks, DIP
tubes, foam, and even aerosol cans that met the "requirements
There was a second
criterion and test method included in 81705-B, but it only applied
to Type I material. The property to be tested was called "Electromagnetic
interence attenuation frequency range 1 to 10 GHz." The requirement
was "25 decibels (minimum) attenuation...limited to the 1 to
10 GHz frequency range." A series of tests was mandated at
500 MHz intervals between 1.0 and 10.0 GHz- the frequency range
did not begin at 500 MHz as some misunderstood it.
Table 1, we are directed to Paragraph 4.8.6 for the test method,
and that paragraph says, "EMI ATTENUATION. This measuring technique
is intended for determining RF attenuation characteristics of the
Type I material."
As I see it, EMI is
a three-legged monster. It can include field effects from a statically
charged object. As long as the charge remains dormant, the primary
field is considered a pure "E" field. This is the first
leg of the monster. The second leg is the pure magnetic field, or
"H" field found around a common magnet. The third leg
is the RF energy associated with the entire radiant energy spectrum.
The spectrum is well-defined by frequency and wavelength.
Those who are familiar
with the RF spectrum will recognize the 1 to 10 GHz range as beign
associated with microwave and radar transmission. It was already
known that the radiant energy created during a thunderstorm or an
ESD event covered a wide frequency range. In the same roundtable
discussion at NAVSEA where I raised the question about the 2-sec
decay time, I asked, "Why is the RF frequency range limited
to 1 to 10 GHz?" The answer, again, was quick and simple. The
Navy had documented failures of components subjected to the radiant
energy of its high powered radar units.
Thus, if the sensitive
component was wrapped in a Type II material, which provided electrostatic
protection and this, in turn, was overwrapped with a Type I material
which would provide electromagnetic protection, the problem of protecting
static-sensitive devices from "field forces" was solved.
It looked good on paper, and in theory, but technology refused to
As noted in an earlier
article, the definitions of electrostatic and electromagnetic have
yet to be clearly defined. Lack of precise definition left a great
deal of latitude for those who were to develop new static-protective
barrier materials, and some raging battles ensued.
One school of though
said that use of a Type II material was sufficient to prevent damage
to static-sensitive devices. If no charge accumulated on the material,
no E-field would exist around the packaged device, and if a charged
person or object touched the outside of the barrier layer, even
when grounded, no spark would occur.
The other school of
though pointed out that Type II material was not conductive enough
to form an effective Faraday Cage when a device surrounded by this
material moved though an E-field strong enough for polarization
to take place.
As will we see in future
articles, test methods came under scrutiny. Our entire understanding
of ESD phenomena grew dramatically. Devices that had been packaged
to level C of MIL-P-116 began to fail as sensitivity levels dropped.
New forces of destruction were identified. And, above all, an explosion
of static-safe products hit the market.
In 1979, the EOS/ESD
Assn. was formed, and from the very first symposium, responsible
investigators began to report the results of their work. At about
the same time, the Electronics Industry Assn. formed a committee
to begin development of an ESD-protective packaging standard. These
two organizations were to have a profound impact on 81705 and other
Charles Hynes concludes
his exploration of MIL-B-81705 in the next issue of EOS/ESD Technology.