ASTM D748-00(2005)
(Specification)Standard Specification for Natural Block Mica and Mica Films Suitable for Use in Fixed Mica-Dielectric Capacitors
Standard Specification for Natural Block Mica and Mica Films Suitable for Use in Fixed Mica-Dielectric Capacitors
SCOPE
1.1 This specification covers natural block mica and mica films (cut and uncut) suitable for use in the manufacture of fixed mica-dielectric capacitors, based on electrical, visual, and physical properties as determined by tests specified herein.
1.2 The values stated in inch-pound units are to be regarded as the standard.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
An American National Standard
Designation: D 748 – 00 (Reapproved 2005)
Standard Specification for
Natural Block Mica and Mica Films Suitable for Use in Fixed
Mica-Dielectric Capacitors
This standard is issued under the fixed designation D 748; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope become available. Natural block mica and mica films that do
2 not conform to the requirements of this specification for
1.1 This specification covers natural block mica and mica
capacitor use may well be capable of meeting the requirements
films (cut and uncut) suitable for use in the manufacture of
for other critical electrical insulation purposes.
fixedmica-dielectriccapacitors,basedonelectrical,visual,and
4.2 The system of classifying electrical quality of natural
physical properties as determined by tests specified herein.
block and mica films (cut and uncut) covered by this specifi-
1.2 The values stated in inch-pound units are to be regarded
cation is based on a combination of electrical and physical
as the standard.
properties,andvisualqualitiesspecifiedherein,whichthemica
2. Referenced Documents
must possess. This system differs radically from past practices
and previous concepts of mica quality for capacitor use. The
2.1 ASTM Standards:
electrical classification system does not discriminate against
D 149 Test Method for Dielectric Breakdown Voltage and
the presence of spots and stains in even first quality electrically
Dielectric Strength of Solid Electrical Insulating Materials
selected mica, provided the mica conforms to specific and
at Commercial Power Frequencies
physical requirements. Appreciable amounts of air inclusions
D 351 Classification for Natural Muscovite Block Mica and
and waviness also are permitted in all electrical quality classes,
Thins Based on Visual Quality
provided the mica meets specific electrical and physical
D 1082 Test Method for Dissipation Factor and Permittivity
requirements. Mica meeting these requirements is acceptable
(Dielectric Constant) of Mica
without regard to color or origin. However, mica meeting these
3. Terminology
electrical and physical requirements but having lower visual
qualitythanthatmeetingtherequirementsforthevisualquality
3.1 For definitions pertaining to this specification see Clas-
classification is not considered generally as desirable.
sification D 351.
4.3 In capacitor fabrication, one or more pieces of cut film
4. Significance and Use
or block mica having lower than required electrical and
physical properties may prevent meeting the end requirements
4.1 The properties included in this specification are those
ofthecapacitor.Itisthereforerequiredthateachpieceofblock
required to identify the types of natural block mica and mica
(cut) or film (cut or uncut), or both, be tested for the electrical
films (cut and uncut) suitable for use in the manufacture of
requirementsandinspectedforthevisualrequirementslistedin
fixed mica-dielectric capacitors. There may be other require-
this specification.
ments necessary to identify particular characteristics. These
will be added to the specification as their inclusion becomes
5. Forms
generally desirable, and the necessary test data and methods
5.1 This specification covers the following three forms of
natural mica, suitable for use in the manufacture of mica-
This specification is under the jurisdiction of ASTM Committee D09 on
dielectric capacitors:
Electrical and Electronic Insulating Materials and is the direct responsibility of
5.1.1 Form1—Full-knife trimmed natural block mica 0.007
Subcommittee D09.19 on Dielectric Sheet and Roll Products.
to 0.035 in. (0.18 to 0.89 mm) in thickness.
Current edition approved Sept. 10, 2000. Published November 2000. Originally
{1
approved in 1943. Last previous edition approved in 1994 as D 748 – 71 (1994) .
NOTE 1—Acertain percentage of block mica thinner than 0.007 in. may
Coutlee, K. G., “Electrical Quality Classification of Raw Mica by a Rapid,
be accepted under this specification, upon agreement between the pur-
Direct-Reading Test Method,” Proceedings, ASTM, Vol 46, 1946, p. 1486.
chaser and the manufacturer.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
5.1.2 Form 2—Half-knife trimmed natural block mica
Standards volume information, refer to the standard’s Document Summary page on
0.007 to 0.035 in. in thickness.
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 748 – 00 (2005)
5.1.3 Form 3—Films (cut or uncut) split or manufactured and coupling purposes where high Q value, high stability, and
from natural block mica in any range from 0.0008 up to and low temperature coefficient are not required.
including 0.006 in. (0.020 to 0.15 mm).
NOTE 3—Experience has shown that silver electrode molded capacitors
made with Class C-3 mica which contained slightly conducting spots and
6. Grades (Sizes)
stains but contained“ very slight” air inclusions and “nearly flat” waves,
had temperature coefficient and capacitance stability characteristics just as
6.1 For grades see Classification D 351.
good as that obtained with capacitors made with the best Class C-1 mica.
7. Classes
8. Electrical and Physical Properties, and Visual
7.1 This specification covers the following four classes and
Qualities
subdivisions of natural block mica or mica films. The class of
8.1 Natural block mica and mica films shall conform to the
mica desired shall be specified by the purchaser. Block mica or
requirements as to electrical and physical properties and visual
mica films shall conform to all of the requirements of its
qualities as prescribed in Table 1. Visual qualities not covered
respective class, unless otherwise specified by the purchaser.
in this specification are permitted provided mica meets the
7.1.1 Class C-1 Special—Class C-1 special mica films, in
electrical and physical requirements.
addition to having the highest Q obtainable for mica in the
megacycle range also have the highest Q generally obtainable
9. Test Methods
for mica in the audio frequency range (1000 min at 1 kHz).
Such mica therefore is particularly suitable for capacitors 9.1 The properties enumerated in this specification shall be
which must meet highest Q requirements at both high and low determined in accordance with the following:
frequencies.
9.2 Grading According to Size—Classification D 351.
7.1.2 Class C-1—Class C-1 block mica or mica films have
9.3 Electrical Conductivity—See Annex A1.
the highestQ value obtainable for mica (2500 min at 1 MHz in
NOTE 4—Forthepurposeofthisspecification,electricalconductivityin
capacitors)andissuitableforuseinallsizesandtypesofsilver
spotted and stained areas of block mica is revealed when visible sparking
and foil electrode, molded and clamped unit capacitors, includ-
or glowing takes place inside or on the surface of the mica in the vicinity
ing the most critical types, for use in high stability tuned
of the test probe and not by actual puncture of the mica by the
circuits,aswellashighcurrentradiofrequencycapacitorsused high-potential current. If actual puncture of the test specimen does take
place this indicates the presence of mechanical faults, such as pinholes,
in radio transmitter circuits.
tears, or cracks which extend completely through the mica.While this test
NOTE 2—Based on commerical experience Class C-1 block mica or
method had been found suitable for controlling conductivity in spots and
micafilmsaresatisfactoryforthemanufactureofallofthesetypesofmica
stains and dielectric weakness due to mechanical faults in block mica, an
capacitors.However,ithasbeenfoundthat“mediumtoheavy”air-stained
even greater factor of safety will be realized if this flash test is applied
mica may produce a slightly lower yield of highest stability and high
directly to capacitor films. In this instance the purpose of the test is to
current radio frequency types of capacitors as well as a somewhat lower
detect dielectric weakness due to any cause.
yieldofsatisfactorysilverelectrodemicalaminations.Likewise,“medium
9.4 QValueorDissipationFactor—TestMethodD 1082at
to heavy” wavy mica may also adversely influence the application of
silver electrodes. In addition, there is some possibility that excessive
1 MHz, or by the rapid, direct-reading method described in
waviness may cause cracked laminations in molded capacitors due to the
Appendix X1.
high molding pressures employed and it may be less suitable from a
NOTE 5—IncasesofdisputearisingfromborderlinecasesofQvalueor
stacking standpoint. Similarly, some reduction in unit volume capacitance
dissipationfactoranddielectricstrength,thetestspecimensshallbebaked
offoilelectrodecapacitorsmayresultfromexcessiveamountsofeitherair
for a minimum period of2hata temperature of 121 °C (250 °F), and
inclusions or waviness.
tested immediately upon cooling to room temperature.
7.1.3 ClassC-2—Class C-2 block mica and mica films have
a high order of Q value (1500 min at 1 MHz in capacitors) and 9.5 Dielectric Strength—Test Method D 149, using the
are suitable for use in all sizes and types of silver and foil short-time test with ⁄4-in. (6.4-mm) diameter electrodes in oil.
electrode molded and clamped unit capacitors similar to those 9.6 Weight Loss on Heating—Preheat the test specimens in
specified for Class C-1 mica. However, a certain percentage of an oven at 121 °C (250 °F) for a minimum time of 2 h and then
capacitors made with Class C-2 block mica and films may weigh.Thenheatthespecimensintheovenat600°C(1110°F)
show a somewhat higher temperature rise in transmitter types
for 5 min and reweigh. Calculate the percentage loss in weight
than capacitors made with Class C-1 block mica or mica films. after heating based on the weight of the specimen at the end of
7.1.4 ClassC-3—Class C-3 block mica and mica films have
the 2-h preheating period.
the lowest Q value (200 min at 1 MHz in capacitors) of the
9.7 Thickness [Uniformity(Films)]—Judgesplittingquality
three classes covered by this specification. Such Q value,
by the uniformity of thickness of films split from mica by
however, is sufficiently high to permit this mica to be classed
viewing between crossed polaroids.
as a low-loss insulating material. This mica is particularly
9.8 Visual Qualities—See Classification D 351.
suitable for use in foil electrode molded and clamped type
9.8.1 Air Inclusions—Reflected daylight or equivalent.
capacitors (Note 3) used in less critical circuits for blocking
9.8.2 Waves,Buckles,Ridges,etc.—Reflecteddaylightorits
equivalent where distortion of parallel and vertical lines of
reflected image, such as a window frame, can be judged.
9.8.3 Cracks, Tears, Pinholes, and Stones—Determine the
Coutlee, K. G., “Judging Mica Quality Electrically,” Transactions, Am. Inst.
Electrical Engrs., Vol 64, 1945. presence of such mechanical defects as cracks, tears, pinholes,
D 748 – 00 (2005)
TABLE 1 Electrical, Physical, and Visual Quality Requirements of Natural Block Mica and Mica Films for Use in Capacitors
Class C-1 Class C-2 Class C-3
Electrical Properties:
A
Conducting paths none none none
B B B
Q value or dissipation factor at 1 MHz E-1 E-2 E-3
Dielectric strength, min average 1000 1000 1000
H
single
V/mil at 60 Hz 850 850 850
CCC
Dielectric constant
Physical Properties:
Weight loss on heating (5 min at 600 °C), max % 0.2 0.2 0.2
D
Thickness uniformity (mica films) best best intermediate
EE
Temperature coefficient of capacitance and retrace
F
Visual Qualities:
H H H
Air very slight very slight very slight
A
G I F I
B
inclusions slight slight slight
H
J J J
C
medium medium medium
nearly nearly nearly
A
B flatslight flatslight flatslight
C
medium medium medium
K D
Waves heavy heavy heavy
Cracks none none none
Tears none none none
Pin holes none none none
Stones none none none
Buckles none none none
Ridges none none none
A
This applies to the conductivity of visible spots and stains only and excludes air stains or air inclusions.
B
The Q values or dissipation factor Q = of block mica or mica films suitable for use in capacitors shall fall within specified electrical quality groups,
S D
dissipation factor
based on end-use requirements, designated E-1 Special, E-1, E-2, or E-3. These quality groups shall conform to the Q or dissipation factor values prescribed in Table 2
or the corresponding scale readings of the vacuum-tube voltmeter when tested by the rapid, direct-reading method described in Appendix X1.
C
As the dielectric constant of natural block mica suitable for use in capacitors is fairly uniform, no value is specified.
D
Until definite values can be specified, the permissible amounts of such defects shall be agreed upon between the purchaser and the manufacturer.
E
It has been found that the temperature coefficient of capacitance and retrace of capacitors made with Classes C-1, C-2, and C-3 mica are more dependent on such
factors as electrical and mechanical design and manufacturing technique than on any differences in the mica itself.
F
See Classification D 351.
G
The amount of air inclusions shall not exceed the specified limits for each subclass. The permissible amount of air inclusions shall be stated by suffixing the letter A,
B, C, or D as the case may be, to the required electrical quality class.
H
Few and tiny in one fourth of usable area (must not contain air chains, etc.).
I
In one half of usable area (must not contain air chains, etc.).
J
In two thirds of usable areas.
K
The waviness shall not exceed the specified limits for each subclass. The permissible amount of waves shall be stated by suffixing the letter A, B, C or D, as the case
may be, to the letter denoting the amount of permissible air inclusions. For example, Class C-1 B A block mica or mica films denotes:
C-1 B A
Best electrical quality slight air inclusion in one half usuable area nearly flat waves
and stones by the spark coil test as prescribed inAnnexA1,or a statement of precision or bias. No activity has been planned
by visual inspection as judged by transmitted daylight or its to develop such information.
equivalent.
11. Keywords
10. Precision and Bias
11.1 block mica; capacitor; classes; dielectric strength; elec-
10.1 Thistestmethodhasbeeninuseformanyyears,butno trical conductivity; form; grades; mica; mica films; Q value;
information has been presented to ASTM upon which to base visual quality; weight loss
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.