Military EMI/RFI Filters
MIL-PRF-28861 is approved for use by all departments and
agencies of the Department of Defense. Like the earlier
15733, it defines filters for EMI applications. However, it goes
into detailed requirements for a number of attributes such as
baseline control, capacitor dielectrics, filter inductors, case
and lead finishes, potting/impregnants, X-ray, DPA, SLAM
and soldering methods.
and the measurement of basic electrical parameters for the
filter. It also defines visual and radiographic inspections.
All filters in a lot are 100ꢀ tested, when Group A per MIL-
PRF-28861 is performed. Sample inspection of a filter lot is
performed when Group A per MIL-PRF-15733 is specified.
Group A per MIL-PRF-28861 stipulates that up to 10ꢀ of
tested Class B filters can be defective, and are simply
removed from the lot. Failure rates in excess of 10ꢀ will
cause the entire lot to be rejected.
Quality conformance inspection (QCI), or “Group A” testing,
is performed on 100ꢀ of the filters for each production lot
with limits on the number of failures allowed. For Class S filters,
baseline documentation is required to track the major
process steps and inspection points in manufacturing and
quality assurance. This baseline also “locks” in the design
through configuration control. Changes to the product
design, or the process steps for defined areas, can only
be done with formal government approval. Class “S” devices
are qualified on a lot-by-lot basis, with Group A and B
screening and testing documented on each manufacturing
lot.
Class S filters are only allowed PDA rates ranging from 2 to
3ꢀ on individual tests. If the combined total failures exceed
10ꢀ, then the lot must be scrapped.
Group B screening defines environmental tests on samples
from the production lots. Some of these tests are destruc-
tive, including Destructive Physical Analysis (DPA). These
tests permit a percentage of failure for each sampling of
Class B Filters. No failures are permitted for Class S filters.
DPA – Destructive Physical Analysis to RS-469 is a quality
assurance technique that involves taking lot samples
and cross-sectioning them for internal inspection. A filter is
sectioned and then polished for microscopic examination.
This is used to detect specific filter defects, such as flawed
interconnects, capacitor voids, improper margins, dielectric
separation (delamination), and improper dielectric grain
growth. For detailed information see DPA Criteria section.
All AVX Filters internal design standards reflect these three
standards of performance and reliability. For detailed informa-
tion on these standards, see Filter Design Guide, M28861
Screening and R-Level Screening sections of catalog.
Group A, B Tests – These tests or inspections are typically
defined by MIL-PRF-15733. The Group A screening test
sequence will include thermal shock, voltage conditioning,
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