First Published in EOS/ESD Technology Aug/Sept
Part II: From
Over the past twenty years, MIL-B-81705 has helped
shape static-control products and methods. Here's part two of the
story of how this key military specification was itself shaped and
(View Part I of this Article)
Charles R. Hynes
ESD Consultant, Contributing Editor, Minnitonka, MN
(Editor's Note: In the December/January
issue, Chuck Hynes began his exposition of MIL-B-81705, a specification
for the barrier materials from which sleeves, tubes, and Class-A
or F, Style 1 or 2 Mil-B-117 bags are fabricated. The original version
of this specification dates back to 1969 as MIL-P-81705 (AS). In
Part 1, the author brought us up to the early 1970's; this month,
his review continues from that point.)
We left MIL-B-81705 at Revision B,
dated 15 August 1974. Since then, the specification has been amended
three times. When Amendment Two was released, all changes made in
Amendment One were repeated and some additional ones were added.
In Paragraph 1.1 SCOPE, "opaque" was dropped and "associated
airborne components" became "associated higher assemblies."
This last change broadened the applicability of MIL-B-81705.
The titles of Type-I and Type-II materials
in Paragraph 1.2 were changed. Under Type I, the word "opaque"
was dropped and "watervaporproof," and "greaseproof"
were added, Type-I material was still designated electrostatic and
electromagnetic protective. Type-II material changed from being
simply "transparent" to "transparent, waterproof,
The color specification (Federal Standard
595) was dropped from Paragraph 2.1, and two new documents appeared:
DOD-STD-1686 and DOD-HDBK-263. Refereeing to these two documents
would have a major impact on MIL-B-81705. As we will see later,
the material-classification system (Antistatic-Static Dissipative-Conductive)
was born in those two documents.
In Paragraph 3.3.1, covering Type-I
materials, the word "aluminum" was changed to "metal."
That change opened the door to using nickel, stainless steel, copper,
and possibly gold or silver.
In Paragraph 3.3.2, covering Type-II
materials, "any tinted color" became acceptable, and words
like "unsupported," "nonlaminated," "chemically
neutral," and "homogenous antistatic resin mix" disappeared.
With the color identifier gone, it
became mandatory in paragraph 3.6 to mark the materials. Type-I
material was to be marked "EMI/STATIC SHIELD," and Type-II
material was to be marked "ANTISTAT." The paragraph read,
"markings (for Type II) shall be embossed," and "markings
shall be printed" in groups that are one inch apart, on the
length of the material, and every six inches across the width of
Emboss or Paint?
The firms that began producing Type-II
materials were faced with a production problem. If embossing was,
indeed, a requirement, they would have to purchase costly embossing
equipment and install it on every extrusion line that produced Type-II
Surface printing the material was a
much less-expensive alternative; however, it had some problems,
too. Waterproof inks that would adhere to the surface were available;
however, the hygroscopic nature of the material and the migration
of the antistatic additive caused the bond between the ink and the
surface of the material to weaken. In less than a month, some of
the printing could be obliterated in normal handling.
When changing from a color identifier
to embossing or printing, the specification writer faces several
problems. No one can think of everything, and no one can be an expert
in every facet of life. The identification of Type-II material is
a classic example of what can happen when good Government-Industry
communications are lacking.
Another critical aspect of Paragraph
3.6, Amendment Two, was including the word "antistat."
This term took on new meaning when DOD-STD-1686 and DOD-HDBK-263
were released. In Paragraph 18.104.22.168 of HDBK-263; an antistatic protective
material was defined as follows:
"Antistatic materials are those
materials having surface resistivities equal to or grater than 109
and equal to or less than 1014 W/sq. These materials
include hygroscopic antistatic materials such as MIL-B-81705, Type
Surface resistivity, as measured by
ASTM D-257, was introduced as another test for Type II materials,
and a range was defined; however, this test was not included in
either Amendment Two or Three. Until the "C" revision
of MIL-B-81705 is approved and released, surface-resistivity measurements
are not part of qualification testing required for approval of an
MIL-B-81705, Type-11 material, except by reference to a definition
in HDBK-263. This is another example of the chain reactions that
occur when documents are interrelated.
Another important point should be made.
When MIL-B-81705 began, the title contained the words "Electrostatic-free."
Those words still appear in the title of Amendment Three; however,
the term "Electrostatic protective" was taken from the
text of Amendment Two. With the advent of the term "anti-static,"
definitions of these terms became more important.
The terminology became even more complex
with the introduction of triboelectrification in HDBK-263. Here
is a complete reprint of Paragraph 7.1.4 of HDBK-263, dated 2 May
"7.14 Triboelectric properties.
Many antistatic materials such as MIL-B-81705 Type II, virgin cotton,
unfinished wood, and some paper products provide good protection
against generation of static electricity from triboelectric effects.
As described in 4.2, the amount of charge created by triboelectric
effects is dependent upon factors such as surface smoothness, lubricity,
contact area, pressure, and speed of rubbing. Hygroscopic-type antistatic
materials processing sweat layers have good lubricity and generally
are poor generators of static.
"Many conductive and static-dissipative
materials also provide protection from triboelectric generation.
Some metals, however, will create significant charges from triboelectric
generation as indicated in the triboelectric series. Aluminum, for
example, when rubbed with a common plastic, can generate substantial
electrostatic charges. Although a conductive material distributes
a charge over its surface, the other substance with with it is rubbed,
or from which it is separated, especially if it is insulative, can
become highly charged."
If you have followed this series of
articles, you can understand the difficulty we had with the definitions
of "electrostatic protective" and "electromagnetic
protective," which we encountered in MIL-P-116 and MIL-O-17555.
Clearly defining these terms is an extremely difficult task.
Let's begin with "electrostatic
free." This term can only apply to the material itself. It
implies that the material will not hold a static charge. If we define
a static charge as an excess or deficiency of electrons on or in
a material, the definition is meaningless unless we use the term
relative to ground or atmosphere.
Even a metal object can become electrostatically
charged when isolated from the ground in a dry environment. While
the charge may eventually dissipate, during the period of time that
the object remains charged, it cannot be "electrostatic-free."
This concept probably led to the use of the static-decay test in
Method 4046 of Federal Standard 101. Thus, for a number of years,
a material that could meet the two-second decay limit was considered
When the term changed to "electro-static
protective," it could apply to more than the material itself.
The term now implied that Type-II material had a relationship to
whatever it contacted and would also provide barrier properties
to external electrostatic charges. But that was already a function
of the Type-I, electromagnetic-protective material. Coincidentally,
the inclusion of a metal layer in the Type-I material, providing
25 decibels of attenuation for RF energy, automatically made Type-I
material an effective Faraday cage, which also would act as an electrostatic
The interior surface of MIL-B-81705
Type-I material was a static generator. A paper presented at the
First Annual EOS/ESD Symposium, by J. R. Huntsman and D. M. Yenni,
entitled "The Deficiencies in Military Specification MIL-B-81705..."
pointed out the shortcomings of MIL-B-81705 Type-I material.
On the Inside
Triboelectric tests showed that sensitive
components could become charged if they contacted the "inside"
surface of the material. How could this be? When tested by Method
4046 of Federal Standard 101, Type-I materials showed extremely
fast decay times. Even buried conductive grid bags (then newly developed)
and other metallized laminates that were transparent tested extremely
Investigators began to look at the
interrelationship of triboelectrification, resistivity, static decay,
electrostatic shielding, and electromagnetic shielding. The situation
was confusing and became even more so when vendors with vested interests
began using favorable test data to convince users that their products
If the surface resistivity of a specimen
indicated that the material was insulative but a static-decay test
showed that the specimen would drain a charge in 0.02 sec, the product
was released for sale. Conversely, if a material had a relatively
low resistivity number, some claimed that their material provided
electrostatic shielding, even though static-decay test data did
not reflect performance equal to that of a Type-I material.
The EIA forms PEPS
Because of the confusion, the Electronics
Industry Association formed the Packaging of Electronic Parts and
Supplies Committee and the EIA's PEPS Committee, as it became known,
began to wrestle with the problems. It took over seven years to
produce the new ANSI/EIA 541 Standard. During its development, the
standard was referred to an Interim Standard No. 5 (IS-5).
Chronicling the history of IS-5 and
541 would make a separate book. The final contents of that document
represent the combined thinking of 100 or more people who participated
in it's drafting.
A list of PEPS committee members reads
like the "Who's Who" of the EOS/ESD world; many of these
individuals were also members of the EOS/ESD Association. In the
beginning, representation came from users, vendors, and the military,
with vendors dominating. Those vendor representatives, however,
were extremely responsible. The voice of vested interests was tempered
and, in some cases, rejected by those who wanted to end the confusion.
One of the most important statements
to hit the ESD world is contained in paragraph two of the foreword
to the document. It reads as follows:
" 'Antistatic' no longer refers
to a resistivity range. In this standard, 'Antistatic' refers to
a material's ability to resist triboelectric charge generation.
A material's propensity depends upon the nature of the material
itself and the material with which it is in contact also with the
means of surface separation. The antistatic property is not a dependent
function of material resistivity. Material resistivity is an intrinsic
property used to define its degree of conductivity without regard
to other materials. Resistivity measurements depend on the apparatus,
sample size and shape, and voltage used. Not all materials are ohmic
(linear) in their resistivity."
Suddenly, "antistatic" took
on a whole new meaning. The classification system in HDBK-263 conflicted
with this new definition. In addition, the term "anitstatic,"
when applied to MIL-B-81705, created problems. The development of
ANSI/EIA 541 will be the topic of a future article, so for now,
let's return to MIL-B-81705.
On December 1, 1982, a triservice meeting
was held at the US Naval Air Development Center (Warminster, PA)
to discuss updating of MIL-B-81705. A result of that was the definition
of an effort to compare the following three test procedures for
use in evaluating the electrostatic properties of materials:
The then-current static-decay test for evaluating the electrostatic
properties of materials,
Surface and volume resistivity,
Triboelectric test method. (NASA developed the original "tribo"
Specimens from no less than six different
MIL-SPEC Barrier materials were to become part of the test. Two
of the six, of course, were MIL-B-81705 Type-I and Type-II materials.
On June 18, 1983, a contract was awarded
to a private contractor for the services and equipment needed to
run the tests. They completed the work and submitted a final report
on March 28, 1984. The report, along with supporting data, is over
150 pages long, and, to my knowledge, has never been made public.
To paraphrase key sections of the report:
All three tests can, to some degree, provide useful information
about the antistatic properties of homogeneous MIL-B-81705, Type-II
materials (for example, pink poly).
On the other hand, none of the test
methods, as configured in 1983, could adequately evaluate the antistatic
properties of homogeneous MIL-B-81705, Type-I material or any other
laminated, nonhomogeneous material.
Laminates with buried, highly conductive
layers behave differently from homogeneous materials.
When a nonconductive surface is backed
by a more conductive surface, the nonconductive surface takes on
the apparent decay characteristics of the most conductive layer
when monitored by a field meter. The phenomenon of voltage suppression
was apparently involved.
If a sample had an antistatic path
as long as the specimen, a static decay test would reveal the existence
of "dead spots" in the material but a surface resistivity
test might indicate that the material was a good antistatic material.
The NASA triboelectric test was found
to have some inherent problems; it was not reliable in all cases.
The dielectric constant of a material
was found to have a major effect on the decy-time characteristic
of that material. If a material's dielectric constant varies from
sample to sample, capacitance and decay time will vary, even if
the surface resistance is the same.
When attempting to correlate surface-resistivity
test results with results from other methods, such as static decay,
it is the measured resistance value and not the normalized resistivity
value that must be used.
The report stated that none of the
test methods, as configured in the early 1980s could be relied upon
to test both Type-I and Type-II MIL-B-81705 materials.
The contractor developed some new fixtures
and procedures that eliminated the voltage-suppression effects of
laminated Type- I material and provided evidence that with modifications
to Method 4046 of Federal Standard 101, static-decay testing would
do everything that the NASA tribo test would do. However, the NASA
test could not do everything that the modified Method 4046 test
The individuals responsible for revising
MIL-B-81705 after receiving this report must have felt like tennis
balls in a doubles match. The materials in question were used to
package millions of dollars worth of high-reliability items. Changes
made to test methods for MIL-B-81750 materials would create a tremendous
chain reaction throughout the entire world of ESD protection.
Industry investigators suggested new
tests for buried conductive layered laminates. NASA felt that its
tribo/decay test was still a good one, and ASTM D-257 surface resistivity
tests came under fire. Method 4046, as configured, was not the whole
The EIA PEPS Committee has clearly
changed the entire meaning of the word "antistat." Industries
were using new, transparent, buried-conductive-layer materials.
Vested interests pressed the ESD community to buy products that
"met the requirements of MIL-B-81705."
Electrostatic protection is only one
of the material properties listed in the specification's table of
properties, shown in the December/January issue. We have yet to
deal with EMI protection, corrosion, water-vapor properties, or
The next article in this series will
deal with ANSI/EIA 541, including some of the issues raised in this
article, and we will examine its impact on military specifications
and standards. [EOS/ESD Technology Editor's correction:
Part one of this article stated that "the Navy (NAVSEA)...(was)
the custodian of (the specification)." The Navy is the custodian,
but NAVAIR is the correct command. We regret the error.]