Note: Descriptions are shown in the official language in which they were submitted.
6~33
TITLE
FILTER CONNECTOR
~aclc~round oE the Invention
1. Field of the Invention
~ his invention relates to a filter connector
for reducing electroma~netic interference in
electrical devices. ~tore particularly, it refers to
a filter connector having a series of thick film
capacitors ~ith holes within the various elements of
the capacitors, each accommodating an electrically
conductive pin and attenuating various frequencies
applied to the pinO
2. Background of the Invention
Filter connectors for attenuating hi~h
~requency interference from electrical devices are
well known Erom several patents; e.g., U.S. Patent
3,538,464, U.S. 4,126,840, U.S. 4,144,509 and
U.S. 4,187,481. In each of these paten~s, a
capacitor employed ~ith the filter is a series of
2D ceramic layers ~orming a monolithic structure. Thick
film capacitors are also we}l known from U.S. Patent
4,274,124. Although monolithic capacitors are
currently used in filter connectors, i~ has not been
- practical heretofore to substitute thick fil~
capacitors such as shown in U.S. 4,274,1~4 for ~hese
monolithic capacitors. ProbleMs have occurred in
designing a thick film capacitor for a filter
connector which has a low enough inductance to
attenuate high frequencies.
In recent years, the common usage of
computers and particularly home computers has
resulted in the generation of significant additional
amounts of high frequency electromagnetic signals
in~erfering with other electrical deYices. ~or the
EL-4218 35 purpose of reducing the output of such signals, the
~2~6~)3~
United States Federal Communications Commission (~CC)
has promulgated regulations requiring attenuation at
their source. See 47 CFR 15, Subpart J.
Available monolithic capacitor structures
us~ in ~ilters are not cost e~fective f~r use in
low-cost electronic equipment such as the ~ersonal
computer. Since the cost of producing a filter
connectox can be ~reatly diminislled hy usin~ thick
film capaci~ors, a filter connector employin~ such a
~0 thick film capacitor with a low inductance is
needed~ A useful commercial filter attenuates the
electromagnetic signal at least 30 decibels (d~) at a
lOOn me~aher~z (Mllz) frequency.
9b~:~
This invention is a cost effective
electrical filter connector for filterin~ a ~ide band
of frequencies up to 1000 ~z using a particular
de~i~n of thick film capacitor in rel~eating scquenc~
to form the filter element. The filter element
comprise~ a multiplicity of closely spaced thick film
capacitors, each one having a conductive pin mounte~
in a hole through a capacitor, The capacitor has
multiple layers of screen printed materials over an
alumina substrate having two horizontal surfaces and
~hich is generally rectangular in shape, One layer
is a metallization forming a ground electrode. This
electrode is grounded to the connector housing. It
substantially covers an entire horizontal surface of
the alumina substrate and has holes sufficient in
si2e to accommodate the conductive pins but without
touching any of the pins.
Another layer is a metallization forming a
pin electrode, but its area is limited to a portion
around a given hole in the substrate~ This la~er is
in electrical contact with the pin throu~h a solder
~2~ 33
joint, In between the two electrodes is a layer,
dielectric in nature, applied directly over one of
tlle e~ectrodes. Thi~ layer substantially overlaps a
horizontal surface of the ground electrode when it is
the first layer l~ut allows the two l~n~est ~ es on
each side o~ the ground electrode to remain ex~osed.
This la~er also has holes barely sufficient to allow
con~uctive pins to pass throu~h witltout touchiny the
dielectric material. The Zielectric material also
covers the vertical surface of the ground electrode
which is nearest each ~lole.
A fourth and last layer is a nonconAuctive
enca~slllant for excludin~ moisture coverin~ all
layers except electrical contac~ing or solderin~
areas. This filter connector maintains a substantial
attenuation in the ultra high frequency ran~e up to
at least 1000 ~Hz.
~he present invention may be best understood
by those having ordinary skill in the art by
reference to the followin~ detailed description when
considered in conjunction with the accompanying
drawings in which:
FIG. 1 is an isometric view of an assembly,
partially sectioned, of the filter connector;
FIG. 2 is a partial elevational view of the
filter connector in section;
FIG. 3 is a transverse sectional view along
lines 3-3 of the filter sonnector of FIG. l;
FIG. 4 is a section through a single
capacitor unit of a filter element assembled to a pin;
FIG. 5 is an exploded vie~ of a filter
elemen~ containing multiple capacitor units shown in
FIG. 4;
FIG. 6 is a perspective view sf the filter
element member shown in FIG. 5;
1~6~)~3
FIG. 7 is a magnified view in cross section
alon~ lines 7-7 of FIG; 6;
l~IG. 8 is a partial sectional view of the
~ilter connector having a ferrite sleeve around each
S pin; an(l
FIG. 9 is a graph showing an attentuation
curve for a rilter connector wllere the ~round
electro~e does not cover the substrate colnp~red Witi
one shown in FIGS. 1-7.
D=~
Referring first to FIG. lf filter connector
comprises a llousing lO havin~ a top shell 12 an~ a
bot~oln shell 14. ~lousing lO encloses two rows of
pins 18 mounted on a filter member 16. The interior
of connector 8 is protected by a top lnsulator 20 an~l
a bottom insulator 38. Pins 18 are individually
mounted on filter element 16 by solder joints 22.
Threaded insert 28 can be inclu~e~ in the
connector optionally to provide a moun~ing fixture to
2n a ca~inet. Ground contacts 32 are made available on
the top shell 12 to provide a ground contact for a
female plug (not shown) inserted over the pins 18.
The two shells 12 and 14 are crimped together by a
tah 40. Pins 18 can ~e either straight or
right-angled 34 as shown in FIGS. 1-3. FIGS. 2-4
show the solder joints 22 where the pin 18 is
attached to the filter element 16. ~oles 31 in the
bottom insulator 38 provide bottom exit for pins 18.
Hole 30 in the filter member 16 provides the means
for passage of pins 18 through the filter member and
the location of solder joint 22.
The structure of filter element 16 is seen
by reference to FI~S. 4 and 5. PIG. 4 shows only one
capacitor unit within the filter element 16 for
illustration purposes. The filter element comprises
~Z ~603~
s
an alumina subs~.rate 42 which has screen printed on
one hoeizontal surface a metallization ~4. ~his
metalliza~ion forms a ~round electrode that is
sui~sequently soldered 36 to the shell 1~. The ground
electro(~e covers substantially the ~ntire surface of
the alumina substrate 42. It has holes 24, seen in
! FIG~ 5, ~hich are large enou~h to accommodate the
pins 18 without touching the pins.
The ground electrode 44 is par~ially covere~
by a screen ~rinted layer of dielectric 46. For
; purposes of this specification, a single layer of
dielectric is mentioned although in practice two
l~ers of dielectric ~6 and ~ are screen }~rin~ed
over the ground electrode to provide more than
adequate protection against shorting between
electrodes. As seen in FIG. 5, the dielectric laye~
46~48 also has holes 26 which are sli~htly larger
than the diameter of the ~ins 13. The dielectric
46/48 covers the horizontal surface of the electrode
4~ except for the edges 43 and 45 whi~h are soldering
areas used for the ground to the shell 14. ~he
dielectric ~6/48 also is~applied on the vertical edge
of the ground electrode 44 t~hich is contiguous with
the holes 24 as seen in FIG. 4.
A second metallization la~er 50-is scre~n
printed intermitt~n~ly in a regular pattern usually
- arrowhead shaped over the dielectric layer. This
forms a series of pin electrodes 50, each of ~hich is
in electrical con~act with a pin 1~ through solder
~oint 22. This electrode is screen printed in such a
manner as to form a series of discrete spaced apart
arrowhead-shaped layers distributed over the surface
o dielectric 46/48 as seen in FIGS. 5 and 6. There
is one electrode 50 contiguous with each hole 26 and
3S also annularly surrounding ~he holes 41. ~he last
~2~L6~33
layer, glass encapsulant: 52/54, covers both the
electrodes 50 and dielectric 46/48. Altllou~h only
one layer is shown i~ FIG. 5, in practice two layers
of encapsulant are usually screen print~d over the
electro~]e 50 for added safety. For }~url~oses of this
speciEication, when talking about a layer of
encapsulant, one or more layers OL encapsulant is
Ineant. The arrowhea(3 desi~n of the elec~rocle 50
provides a means for closely spacing ~he car~acitors
used in the filtex connector and, hence~ increasin~
tlle area 5~ the capacitor and there~ore i~s
capacitance value. of course, other designs cou~d be
used which sa~is~y the ~urpose of producing
capacitors of the type employed in this invention.
It is preferred that the metallizations used
in layers one and three be a noble metal or an alloy
of a noble metal. However, copper metallization
compositions could be employed. Particularly
preferred is a palladium/silver alloy metallization.
Each layer is applied using conventional screen
printing methods. The dielectric employed can be any
type commonly used in capacitors. However, barium
titanate is preferred.
The glass encapsulant can be any one of the
types used in capacitors having a coerficient of
expansion compatible with the other components
employed.
A ferrite sleeve 19 also can be attached to
the pin 18, as seen in FIG. 8. Such sleeves are well
kno~m as seen in U.5. Patent 4,1~4,509. The use of
the particular filter member of this invention will
increase the filtering action of filter connectors
employing ~errites,
Metallizations used in this,invention are
made Erom compositions containins a finely divided
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metal powder of either a noble metal or copper, a
binder for ~he metal and a vehicle to disperse the
powders evenly. The com~osition is applied ~y screen
printing methods and the vehicle is removed from the
applie~ composition ~y ~irin~ the screen~ on layer
by convent ional techniques .
Although the drawings FIGS. ~-5 depict the
~roun-3 electrode 44 as l~eing applied as ~he Eirst
metalli2ation layer and the pin electrode 50 as the
third layerl this can he reversed. Therefore, pin
electrode 50 can be screen printed directly to the
alumina 42 around each hole 41. The layers 46 and 4
are then applied to overlap the layer 50 exce~t ~or
the solder area 22. The ~round electrode 44 would
then ~e screen printed over the layers 46 and 48 and
all exposed hcrizontal surfaces of ~he alumina
substrate 42. The encapsulant 52/54 is applied in
the same manner as in ~IC. 4. The enca~sulallt covers
all exposed surfaces except for edges 43 and 45 whicl
are soldex areasr
The low inductance at hi~h ~requencies
achieved by this invention is a direct result of the
geometry of the ground electrode as related to the
pin electrode. If the ground electrode and
dielectric are placed only to one side of the pin,
the attenuation curve ~a) of PIG. 9 results. This
curve shows a reduced attenuation and hence reduced
filtering action in tne ultra high frequency range,
par~icularly above 200 ~1Hz and more particularly
above 700 ~z. The reason for this reduced
attenuation is that the capacitor has a series
resonance around 200 M~z ~shown by the sharp peak in
curve (a)) caused ~y the inductance of the electrodes
of the capacitor.
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When ~he ground electrode extends
substantially over the entire suhstrate and the
dielectric surrounds the hole, the current flow fro~
the pin can divide into ti~o components, each flo~in~
to~ar(~ a ~roun(l connection on each 5ide 0~ t~le filter
element 16. This results in a decreased effective
electrode inductance by providing two parallel
current paths. The decreased inductance results in
an increased series resonant frequency and an
increased attenuation such as is shown in curve ~b)
of FIG. 9.
