EP0123457B1

EP0123457B1 - Filter connector

Info

Publication number: EP0123457B1
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: 1987-12-09
Also published as: BR8401386A; DE3468079D1; JPH0695464B2; KR840008227A; AU565595B2; MX159641A; KR890004204B1; ATE31372T1; JPS59184479A; CA1216033A; EP0123457A1; AU2628484A

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

Field of the Invention

This invention relates to an electrical filter connector for reducing electromagnetic interference in electrical devices.

Background of the Invention

Filter connectors for attenuating high frequency interference from electrical devices are well known, e.g., US-A-3538464, US-A-4079343, US-A-4126840, US-A-4144509 and US-A-4187481. In these known filter connectors, a capacitor employed with the filter is a series of ceramic layers forming a monolithic structure. Thick film capacitors are also well known e.g. US-A-4274124. Although monolithic capacitors are currently used in filter connectors, it has not been practical heretofore to substitute thick film capacitors for 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 personal computers. Furthermore, such structures have a low strength and frequently crack or fracture during fabrication or installation and even in use. There is thus a need for an improved filter connector employing thick film capacitors.

Summary of the Invention

As is known, the present invention relates to a filter connector of the type comprising a conductive housing, a filter element enclosed within the housing and electrically conductive pins mounted within the filter element. In known filter connectors such as US-A-4079343 the filter element is composed of respective capacitor plates and dielectric members for each pin which form monolithic structures. In contrast and in accordance with the invention the filter element is composed of an alumina substrate containing holes through which the pins extend and a planar array of closely spaced thick-film capacitors, one for .each pin, the capacitors being formed by screen printing multiple layers onto the substrate, a first of said layers being a metallization layer which is continuous except for holes through which the pins extend without contact; said first layer providing a ground electrode in electrical conduct with the housing, a second of the layers being another metallization layer provide discrete pin contacting electrodes and a third of the layers being disposed between the first and second layers and providing an insulative dielectric.
The invention provides a cost effective filter connector for filtering a wide band of frequencies. A filter element in accordance with the invention comprises a multiplicity of closely spaced thick film capacitors, each having one conductive pin mounted in a hole through the capacitor. The capacitors are formed by 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 which is grounded to the connector housing. It is substantially coextensive with an 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 discrete pin electrodes, 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 can substantially overlap a horizontal surface of the ground electrode when this is applied direct to the substrate 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 the 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 further layer providing a nonconductive encapsulant for excluding moisture preferably covers all layers, except electrical contacting or soldering areas, and has a coefficient of thermal expansion compatible with the other components.
A filter connector constructed in accordance with the invention exhibits low inductance and is capable of attenuating electromagnetic signals by at least 30 dB in the UHF range up to 1000 MHz.

Brief Description of the Drawings

The present invention may be 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:

Figure 1 is an isometric view of an assembly, partially sectioned, of a filter connector constructed in accordance with the invention;
Figure 2 is a partial elevational view of the filter connector in section;
Figure 3 is a transverse sectional view along lines 3-3 of the filter connector of Figure 1;
Figure 4 is a section through a single capacitor unit of a filter element assembled to a pin of the further connector;
Figure 5 is an exploded view of the filter element containing multiple capacitor units shown in Figure 4;
Figure 6 is a perspective view of the filter element shown in Figure 5;
Figure 7 is an enlarged. view in cross section along line 7-7 of Figure 6;
Figure 8 is a partial sectional view of a modified filter connector having a ferrite sleeve around each pin; and
Figure 9 is a graph showing an attenuation curve a) for a filter connector where the ground electrode does not cover the substrate compared with an attenuation curve b) for connectors shown in Figures 1 to 7.

Description of the Invention

Referring first to Figures 1 to 3, a filter connector 8 includes a conductive housing 10 having a top shell 12 and a bottom shell 14. Housing 10 encloses two rows of pins 1 amounted on a filter element 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 inserts 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 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 as shown at 34 in Figure 3. Holes 31 in the bottom insulator 38 provide bottom exits for the pins 18 while holes 30 in the filter element 16 provide passage for the pins 18 and the location of the solder joints 22.
The filter element 16 employs a planar array of thick-film capacitors for the pins 18. There is one such capacitor for each pin 18 and, as shown in Figures 4 and 5, the pins 18 project from the solder joints 22 through holes 41 in a relatively thick alumina substrate 42 having opposed parallel surfaces.
A common ground electrode in the form of a first metallization layer 44 is screen printed on the substrate 42 so as to be co-extensive therewith. The layer 44 can cover the entire upper.s.urface of the substrate 42 except for the holes 24 which are larger than the pins 18 to provide clearance therefor. The metallization layer 44 is soldered at 36 to the shell 14.
The ground electrode 44 is partly covered by a screen printed layer of dielectric 46. Although a single layer of dielectric can be used in practice two layers of dielectric 46 and 48 are screen printed over the layer 44 to provide more than adequate protection against shorting between electrodes. As seen in Figure 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 surface of the electrode 44 except for exposed longitudinal borders 43 and 45 which are soldering at 36 to the shell 14. The dielectric 46/48 overlaps and covers the vertical edges of the ground electrode 44 in the holes 24 as seen in Figure 4.
Further metallization layers 50 are screen printed intermittently in a regular pattern, typically arrowhead shaped, over the dielectric layer 46/48 to complete the capacitors. This forms a series of pin electrodes 50, each of which is in electrical contact with a pin 18 through one of the respective solder joints 22. These electrodes 50 are screen printed in such a manner as to form rows of discrete spaced arrowhead-shaped layers distributed over the surface of the dielectric 46/48 as seen in Figures 5 and 6. Each electrode 50 covers the substrate 42 around, and extends through, one of the holes 41 (Figures 5 and 7) to the lower surface of the substrate 42. The thus- lined holes provide rugged mechanical connectors for the solder joints 22 with the pins 18. A final layer in the form of an encapsulant such as a glass (Figures 4 and 5) covers the electrodes 50 and dielectric 46/48. Although one encapsulant layer 52 (Figure 5) can be used it is preferred to have two such layers 52 and 54 which are screen printed over the electrodes 50 for added safety and to match the temperature coefficient of expansion of the layers 42, 46, 48. The arrowhead design of the electrodes 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 the invention are made from pastes 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. Such a paste is applied by screen printing methods and the vehicle is removed subsequently from the applied composition by firing the screened-on layer by conventional techniques. Particularly preferred is a palladium/silver alloy metallization. -The dielectric employed can be any type commonly used in capacitors. However, barium titanate paste is preferred.
The encapsulant can be any one of the types used in capacitors provided it has a coefficient of expansion compatible with the other components employed.
A ferrite sleeve 19 also can be attached to each pin 18, as seen in Figure 8. Such sleeves are well known (US―A 4144 509).
Although Figures 4 and 5 depict the ground electrode 44 as being applied as the first metallization layer and the pin electrodes 50 as the third layer, this can be reversed. Therefore, the pin electrodes 50 can be screen printed directly to the alumina 42 around and in each hole 41. The layers 46 and 48 are then applied to overlap the electrodes 50 except for the annular area around each hole 41 (Figure 5). The ground electrode 44 would then be screen printed over the layers 46 and 48 and all exposed surfaces of the alumina substrate 42. The encapsulant 52/54 is applied in the same manner as in Figure 4. The encapsulant covers all exposed surfaces except for the longitudinal borders 43 and 45 which are the soldered areas (36).
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 a pin, the attenuation curve (a) of Figure 9 results. This curve shows a reduced attenuation and hence reduced filtering 200 MHz in the ultra high frequency range, particularly above 200 MHz and more particularly about 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 44 extends to the periphery of the substrate 42 and is continuous except for the holes at the location of the pins the current flow from the pin can be divided 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 Figure 9.

Claims

1. An electrical filter connector for attenuating electromagnetic interference (8) having a conductive housing (10), a filter element (16) enclosed within the housing and electrically conductive pins (18) mounted within the filter element (16); characterized in that the filter element is composed of an alumina substrate (42) containing holes (41) through which the pins (18) extend and a planar array of closely spaced thick-film capacitors, one for each pin, the capacitors being formed by screen printing multiple layers (44, 46, 50) onto the substrate (42) a first (44) of said layers. being a metallization layer which is continuous except for holes through which the pins extend without contact; said first layer providing a ground electrode in electrical conduct with the housing (10), a second (50) of the layers being another metallization layer provide discrete pin contacting electrodes and a third (46) of the layers being disposed between the first and second layers and providing an insulative dielectric.

2. A filter connector according to claim 1, wherein said first layer (44) providing the ground electrode is applied direct to the substrate (42), the third layer (46) is applied over the first layer adjacent each substrate hole (41) but spaced therefrom and the second layer (50) is applied over the third layer (46) around and within each substrate hole (41).

3. A filter connector according to claim 1, wherein said second layer (50) providing the pin electrodes is applied direct to the substrate (42) to extend around and within each substrate hole (41), the third layer (46) is applied over the second layer (50) adjacent each substrate hole but spaced therefrom and the first layer (44) providing the ground electrode is applied over the third layer (46).

4. A filter connector according to claim 2, wherein the third layer (46) substantially covers the first layer (44) except for exterior contact zones forming electrical connection with the housing and the third layer (46) annularly overlaps the first layer (44) around each hole (41).

5. A filter connector according to claim 4, wherein the second layer (50) annularly overlaps the third layer (46) around each hole and extends within each hole.

6. A filter connector according to any one of claims 1 to 5, wherein the pins (18) are mounted with solder joints (22) in the substrate holes (41).

7. A filter connector according to any one of claims 1 to 6, wherein the layers further comprise at least a fourth layer (52) forming a non-conducting encapsulant having a compatible coefficient of expansion to the other components.

8. A filter connector according to claim 7, wherein the fourth layer (52) covers all exposed layers except for electrical contact-zones.

9. A filter connector according to claim 7 or 8, wherein the layers further comprise an additional layer (54) applied over the fourth layer and also forming a non-conducting encapsulant.

10. A filter connector according to any one of claims 1 to 9, wherein the layers further comprise an additional layer (48) providing an insulative dielectric applied over the third layer (46).

11. A filter connector according to any one of claims 1 to 10, wherein at least one of the metallization layers is a noble metal metallization.

12. A filter connector according to any one of claims 1 to 10, wherein at least one of the metallization layers is palladium/silver alloy metallization.

13. A filter connector according to any one of claims 1 to 10, wherein at least one of the metallization layers is a copper metallization.

14. A filter connector according to any one of claims 1 to 13, wherein the discrete pin electrodes (50) each have the shape of an arrowhead.

15. A filter connector according to any one of claims 1 to 14, wherein a ferrite sleeve (19) encloses each conductive pin (18).

16. A filter connector according to any one of claims 1 to 15, wherein the pin electrodes (50) extends within and adheres to each substrate hole (41).

17. A filter connector according to any one of claims 1 to 16, wherein an electrical connection is made between the first layer (44) forming the ground electrode and the housing (10) at borders of the substrate (42).

18. A filter connection according to claim 17, wherein the electrical connection between the first layer (44) and the housing (10)-is established with soldered zones (36).