MIL- STD-883F 2004 TEST METHOD STANDARD MICROCIRCUITS - 第389页

MIL-STD-883F METHOD 2026 25 August 1983 1 METHOD 2026 RANDOM VIBRATION 1. PURPOSE . This test is c onducted f or the pur pose of det ermining t he abili ty of t he micr ocir cuit; to wit hstand t he dynamic s tres s exer…

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MIL-STD-883F
METHOD 2025.4
19 August 1994
2
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MIL-STD-883F
METHOD 2026
25 August 1983
1
METHOD 2026
RANDOM VIBRATION
1. PURPOSE
. This test is conducted for the purpose of determining the ability of the microcircuit; to withstand the
dynamic stress exerted by random vibration applied between upper and lower frequency limits to simulate the vibration
experienced in various service-field environments. Random vibration is more characteristic of modern-field environments
produced by missiles, high-thrust jets, and rocket engines. In these types of environments, the random vibration provides a
more realistic test. For design purposes, however, a swept frequency sinusoidal test may yield more pertinent design
information.
2. APPARATUS
.
2.1 Vibration system
. The vibration system, consisting of the vibration machine, together with its auxiliary equipment
shall be capable of generating a random vibration for which the magnitude has a gaussian (normal) amplitude distribution,
except that the acceleration magnitudes of the peak values may be limited to a minimum of three times the rms (three-sigma
(α) limits). The machine shall be capable of being equalized so that the magnitude of its spectral-density curve will be
between specified limits (for example, see figures 2026-1 and -2). When the test item, or a substitute equivalent mass, is
appropriately secured to the vibration machine. The equalization of an electrodynamic vibration machine system is the
adjustment of the gain of the electrical amplifier and control system so that the ratio of the output-vibration amplitude to the
input-signal amplitude is of a constant value (or given values) throughout the required frequency spectrum.
2.1.1 Control and analysis of vibration
.
a. Spectral-density curves. The output of the vibration machine shall be presented graphically as power-spectral
density versus frequency. 1
/ The spectral-density values shall be within +40 and -30 percent (±1.5 dB) of the
specified values between a lower-specified frequency and 1,000 Hz, and within +100 and -50 percent (±3 dB) of the
specified values between 1,000 and an upper-specified frequency (2,000 Hz). A filter bandwidth will be a maximum
of one-third-octave or a frequency of 25 Hz, whichever is greater.
1
/ Power-spectral density is the mean-square value of an oscillation passed by a narrow-band filter per
unit-filter bandwidth. For this application it is expressed as G
2
/f where G
2
/f is the mean-square value
of acceleration expressed in gravitational units per number of cycles of filter bandwidth. The
spectral-density curves are usually plotted either on a logarithmic scale, or in units of decibels (dB).
The number of decibels is defined by the equation:
The rms value of acceleration within a frequency band between f
1
and f
2
is:
where G
r
2
/f is a given reference value of power-spectral density, usually the maximum specified value.
dB = 10
G
/f
G/f
= 20
G/ f
G
/f
2
2
r
r
log log
rms
1/2
f
f
G
= G f df
1
2
∫
⎡
⎣
⎢
⎤
⎦
⎥
2
/
MIL-STD-883F
METHOD 2026
25 August 1983
2
b. Distribution curves. A probability density-distribution curve may be obtained and compared with a
gaussian-distribution curve. The experimentally-obtained curve should not differ from the gaussian curve by more
than ±10 percent of the maximum value.
2.2 Monitoring
. Monitoring involves measurements of the vibration excitation and of the test-item performance. When
specified, the device shall be monitored during the test. The details of the monitoring circuit, including the method and
points of connection to the specimen, shall be specified.
2.2.1 Vibration input
. The vibration magnitude shall be monitored on a vibration machine, on mounting fixtures, at
locations that are as-near as practical to the device mounting points. When the vibration input is measured at more than
one point, the minimum input vibration shall be made to correspond to the specified test curve (see figures 2026-1 and
2026-2). For massive test-items and fixtures, and for large-force exciters or multiple-vibration exciters, the input-control
value may be an average of the average magnitudes of three or more inputs. Accelerations in the transverse direction,
measured at the test-item attachment points, shall be limited to 100 percent of the applied vibration.
3. PROCEDURE
. The device(s) shall be rigidly fastened on the vibration platform and the leads adequately secured.
The vibration machine shall then be operated and equalized or compensated to deliver the required random frequencies and
intensities conforming to the curves specified in test condition I, figure 2026-1 or test condition II, figure 2026-2. The
device(s) shall be subjected to a random vibration specified by the test condition letter (see tables I and II) for a duration of
15 minutes in each of the orientations X, Y, and Z. Where this test is performed as part of a group or subgroup of tests, the
post-test measurements or inspections need not be performed specifically at the conclusion of this test.
3.1 Examination
. After completion of the test, an external visual examination of the marking shall be performed without
magnification or with a viewer having a magnification no greater than 3X and a visual examination of the case, leads, or
seals shall be performed at a magnification between 10X and 20X. This examination and any additional specified
measurements and examination shall be made after completion of the final cycle or upon completion of a group, sequence,
or subgroup of tests which include this test.
3.2 Failure criteria
. After subjection to the test, failure of any specified measurement or examination (see 3 and 4),
evidence of defects or damage to the case, leads, or seals, or illegible markings shall be considered a failure. Damage to
marking caused by fixturing or handling during tests shall not be cause for device rejection.
4. SUMMARY
. The following details shall be specified in the applicable acquisition document:
a. Test condition (see 3).
b. Measurements after test (see 3 and 3.1).
c. Test condition I or II and letter (A-K).
d. Test duration if other than specified.
e. Requirement for test to be conducted with device powered up, when applicable.