EP0123457A1

EP0123457A1 - Filter connector

Info

Publication number: EP0123457A1
Application number: EP84302143A
Authority: EP
Inventors: Thomas Douglas Linnell; Arthur Thomas Murphy; Frederick John Young
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1983-03-30
Filing date: 1984-03-29
Publication date: 1984-10-31
Also published as: DE3468079D1; MX159641A; EP0123457B1; AU2628484A; BR8401386A; KR890004204B1; JPS59184479A; CA1216033A; ATE31372T1; AU565595B2; KR840008227A; JPH0695464B2

Abstract

A filter connector (8) for attentuating electromagnetic interference up to 1000 MHz having a housing (10), a filter element (16) enclosed within the housing (10) and electrically conductive pins (18) mounted within the filter element (16). The filter element (16) contains an alumina substrate (42) with thick film layers (44, 50) of a metallization forming pin and ground electrodes, and a dielectric layer (46, 48) separating the electrodes screen printed over the substrate and a glass encapsulant (52, 54). The ground electrode (44) substantially covers a horizontal surface of the substrate (42).

Description

Background of the Invention

1. Field of the Invention

This invention relates to a filter connector for reducing electromagnetic interference in electrical devices. More particularly, it refers to a filter connector having a series of thick film capacitors with holes within the various elements of the capacitors, each accommodating an electrically conductive pin and attenuating various frequencies applied to the pin.

2. Background of the Invention

Filter connectors for attenuating high frequency interference from electrical devices are well known from 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 patents, a capacitor employed with the filter is a series of ceramic layers forming a monolithic structure. Thick film capacitors are also well known from U.S. Patent 4,274,124. Although monolithic capacitors are currently used in filter connectors, it has not been practical heretofore to substitute thick film capacitors such as shown in U.S. 4,274,124 for these 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 interfering with other electrical devices. For the purpose of reducing the output of such signals, the United States Federal Communications Commission (_FCC) has promulgated regulations requiring attenuation at their source. See 47 CFR 15, Subpart J.
Available monolithic capacitor structures used in filters are not cost effective for use in low-cost electronic equipment such as the personal computer. Since the cost of producing a filter connector can be greatly diminished by using thick - film capacitors, a filter connector employing such a thick film capacitor with a low inductance is needed. A useful commercial filter attenuates the electromagnetic signal at least 30 decibels (dB) at a 1000 megahertz (MHz) frequency.

Sumnary of the Invention

This invention is a cost effective electrical filter connector for filtering a wide band -of frequencies up to 1000 MHz using a particular design of thick film capacitor in repeating sequence to form the filter element. The filter element comprises a multiplicity of closely spaced thick film capacitors, each one having a conductive pin mounted in a hole through a capacitor. The capacitor has multiple layers of screen printed materials over an alumina substrate having two horizontal surfaces and which 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 size 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 layer is in electrical contact with the pin through a solder joint. In between the two electrodes is a layer, dielectric in nature, applied directly over one of the electrodes. This layer substantially overlaps a horizontal surface of the ground electrode when it is the first layer but allows the two longest edges on each side of the ground electrode to remain exposed. This layer also has holes barely sufficient to allow conductive pins to pass through without touching the dielectric material. The dielectric material also covers the vertical surface of the ground electrode which is nearest each hole.
A fourth and last layer is a nonconductive encapsulant for excluding moisture covering all layers except electrical contacting or soldering areas. This filter connector maintains a substantial attenuation in the ultra high frequency range up to at least 1000 MHz.

Brief Description of the Drawings

The present invention may be best understood by those having ordinary skill in the art by reference to the following 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 connector of FIG. 1;
FIG. 4 is a section through a single capacitor unit of a filter element assembled to a pin;
FIG. 5 is an exploded view of a filter element containing multiple capacitor units shown in FIG. 4;
FIG. 6 is a perspective view of the filter element member shown in FIG. 5;
_FIG. 7 is a magnified view in cross section along lines 7-7 of FIG. 6;
_FIG. 8 is a'partial sectional view of the filter connector having a ferrite sleeve around each pin; and
FIG. 9 is a graph showing an attentuation curve for a filter connector where the ground electrode does not cover the substrate compared with one shown in FIGS. 1-7.

DESCRIPTION OF THE INVENTION

Referring first to FIG. 1, filter connector 8 comprises a housing 10 having a top shell 12 and a bottom shell 14. Housing 10 encloses two rows of pins 18 mounted on a filter member 16. The interior of connector 8 is protected by a top insulator 20 and a bottom insulator 38. Pins 18 are individually mounted on filter element 16 by solder joints 22.
Threaded insert 28 can be included in the connector optionally to provide a mounting fixture to a cabinet. 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 tab 40. Pins 18 can be 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. Holes 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 FIGS. 4 and 5. FIG. 4 shows only one capacitor unit within the filter element 16 for illustration purposes. The filter element comprises an alumina substrate 42 which has screen printed on one horizontal surface-a metallization 44. This metallization forms a ground electrode that is subsequently soldered 36 to the shell 14. The ground electrode covers substantially the entire surface of the alumina substrate 42. It has holes 24, seen in FIG. 5, which are large enough to accommodate the pins 18 without touching the pins.
The ground electrode 44 is partially covered by a screen printed layer of dielectric 46. For purposes of this specification, a single layer of dielectric is mentioned although in practice two layers of dielectric 46 and 48 are screen printed over the ground electrode to provide more than adequate protection against shorting between electrodes. As seen in FIG. 5, the dielectric layer 46/48 also has holes 26 which are slightly larger than the diameter of the pins 18. The dielectric 46/48 covers the horizontal surface of the electrode 44 except for the edges 43 and 45 which are soldering areas used for the ground to the shell 14. The dielectric 46/48 also is. applied on the vertical edge of the ground electrode 44 which is contiguous with the holes 24 as seen in FIG. 4.
A second metallization layer 50.is screen printed intermittently in a regular pattern usually arrowhead shaped over, the dielectric layer. This forms a series of pin electrodes 50, each of which is in electrical contact with a pin 18 through solder joint 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 of dielectric 46/48 as seen in FIGS. 5 and 6. There is one electrode 50 contiguous with each hole 26 and also annularly surrounding the holes 41. The last layer, glass encapsulant 52/54, covers both the electrodes 50 and dielectric 46/48. Although only one layer is shown in FIG. 5, in practice two layers of encapsulant are usually screen printed over the electrode 50 for added safety. For purposes of this specification, when talking about a layer of encapsulant, one or more layers of encapsulant is meant. The arrowhead design of the electrode 50 provides a means for closely spacing the capacitors used in the filter connector and, hence, increasing the area of the capacitor and therefore its capacitance value. Of course, other designs could be used which satisfy the purpose 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 coefficient 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 known as seen in U.S. Patent 4,144,509. The use of the particular filter member of this invention will increase the filtering action of filter connectors employing ferrites.
Metallizations used in this.invention are made from compositions containing a finely divided metal powder of either a noble metal or copper, a binder for the metal and a vehicle to disperse the powders evenly. The composition is applied by screen printing methods and the vehicle is removed from the applied composition by firing the screened on layer by conventional techniques.
Although the drawings FIGS. 4-5 depict the ground electrode 44 as being.applied as the first metallization layer and the pin electrode 50 as the third layer, this can be reversed. Therefore,.pin electrode 50 can be screen printed directly to the alumina 42 around each hole 41. The layers 46 and 48 are then applied to overlap the layer 50 except for the solder area 22. The ground electrode 44 would then be screen printed over the layers 46 and 48 and all exposed horizontal surfaces of the alumina substrate 42. The encapsulant 52/54 is applied in the same manner as in FIG. 4. The encapsulant covers all exposed surfaces except for edges 43 and 45 which are solder areas.
The low inductance at high frequencies 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 FIG. 9 results. This curve shows a reduced attenuation and hence reduced filtering action in the ultra high frequency range, particularly above 200 MHz and more particularly above 700 MHz. The reason for this reduced attenuation is that the capacitor has a series resonance around 200 MHz (shown by the sharp peak in curve (a)) caused by the inductance of the electrodes of the capacitor.
When the ground electrode extends substantially over the'entire substrate and the dielectric surrounds the hole, the current flow from the pin can divide into two components, each flowing toward a ground connection on each side of the 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.

Claims

1. In an electrical filter connector for attenuating electromagnetic interference having a housing, a filter element enclosed within the housing . and electrically conductive pins mounted within the filter element, the improvement whereby the filter element comprises a multiplicity of closely spaced thick film capacitors formed by screen printing multiple layers over an alumina substrate having two flat horizontal surfaces containing holes and electrically conductive pins mounted thereon, one layer being a thick film metallization forming a ground electrode in electrical contact with the connector housing and substantially covering one horizontal surface of the substrate and having holes within the ground electrode sufficient in diameter to allow the conductive pins to pass without touching the electrode.

2. A filter connector according to claim 1 wherein the ground electrode layer is the first layer applied to the substrate, a second layer being an insulating dielectric material applied over the ground electrode at least in the area surrounding each substrate hole but exclusive of an electrical contacting area and a third layer being a thick film metallization forming a discrete pin electrode applied over the second layer in the area surrounding each substrate hole thereby being in electrical contact with a pin and insulated from the ground electrode.

3. A filter connector according to claim 2 wherein a fourth layer is a nonconducting encapsulant having a compatible coefficient of expansion covering all exposed layers exclusive of electrical contacting areas.

4. A filter connector according to claim 3 wherein the first layer of the filter element is a. noble metal metallization.

5. A filter connector according to claim 3 . wherein the first layer of the filter element is a palladium/silver alloy metallization.

6. A filter connector according to claim 3 wherein the third layer of the filter element is a noble metal metallization.

7. A filter connector according to claim 3 wherein the third layer of the filter element is a palladium/silver alloy metallization.

8. A filter connector according to claim 3 wherein the first layer of the filter element is a copper metallization.

9. A filter connector according to claim 3 wherein the third layer of the filter element is a copper metallization.

10. A filter connector according to claim 2 . wherein the third layer metallization is in the shape of an arrowhead.

11. A filter connector according to claim 1 wherein a ferrite sleeve encloses each conductive pin.

12. In an electrical filter connector for attenuating electromagnetic interference having a housing, a filter element enclosed within the housing and electrically conductive pins mounted within the filter element, the improvement whereby the filter element comprises a multiplicity.of closely spaced thick film capacitors, each one accommodating a pin within holes in an alumina substrate having two flat horizontal surfaces and having multiple layers screen printed over the substrate, a first layer being a noble metal metallization forming an electrode grounded to the connectot housing and substantially covering one horizontal surface of the substrate, the first layer having holes therein sufficient in diameter to allow the conductive pins to pass without touching the first layer, a second layer being a dielectric insulat-ing material, the second layer substantially covering the first layer except for exterior electrical contacting areas and annularly overlapping the first layer around each hole, a third layer being a metallization forming a discrete pin electrode surrounding each substrate hole and applied to annularly overlap the second layer, and a fourth layer being a nonconducting encapsulant having a coefficient of expansion compatible with the other layers together with substrate and covering all exposed layers exclusive of electrical contacting areas.

13. A filter connector according to claim 12 wherein the pin electrode metallization extends within and adheres to each substrate hole.

14. A filter connector according to claim 1 wherein the ground electrode is a third layer applied over a second layer and substantially all the horizontal surface of the substrate, a first layer being a metallization forming a discrete pin electrode applied_over the substrate to surround each substrate hole and the second layer being a dielectric material applied over each pin electrode.

15. A filter connector according to claim 14 wherein a fourth layer is a nonconducting encapsulant having a coefficient of expansion compatible with the other layers together with substrate and covering all exposed layers exclusive of electrical contacting areas.

16. A filter connector according to claim 15 wherein the first layer of the filter element is a noble metal metallization.

17. A filter connector according to claim 15 wherein the first layer of the filter element is a palladium/silver alloy metallization.

18. A filter connector according to claim 15 wherein the third layer of the filter element is a noble metal metallization.

19. A filter connector according to claim 15 wherein the third layer of the filter element is a palladium/silver alloy metallization.

20. A filter connector according to claim 15 wherein the first layer of the filter element is a copper metallization.

21. A filter connector according to claim 15 wherein the third layer of the filter element is a copper metallization.

22. A filter connector according to claim 14 wherein the first layer metallization is in the shape of an arrowhead.

23. In an electrical filter connector for attenuating electromagnetic interference having a housing, a filter element enclosed within the housing and electrically conductive pins mounted within the filter element, the improvement whereby the filter element comprises a multiplicity of closely spaced ' thick film capacitors, each capacitor accommodating a pin within holes in an alumina substrate having two flat horizontal surfaces and having multiple layers screen printed over the substrate, a first layer being a noble metal metallization forming a discrete pin electrode applied over the substrate around and within each hole, the first layer being in electrical contact with a conductive pin passing through the substrate hole, a second layer being a dielectric insulating material overlapping the first layer except for electrical contacting areas, a third layer being a noble metal metallization forming a ground electrode and overlapping the second layer and substantially all of one horizontal surface of the substrate, and a fourth layer being a nonconducting encapsulant having a coefficient of expansion compatible with the other layers-together with substrate and covering all exposed layers exclusive of electrical contacting areas.

24. A filter connector according to claim 23 wherein the pin electrode metallization extends within and adheres to each substrate hole.

25. A filter connector according to claim 1 wherein an electrical connection is made between the ground electrode and the conductive housing on one horizontal surface of the substrate.