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 )33 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.
6()33 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.