EP0838136A1

EP0838136A1 - Conductive connection and process for producing it

Info

Publication number: EP0838136A1
Application number: EP96914834A
Authority: EP
Inventors: Kurt Etter
Original assignee: Optiprint AG
Current assignee: Optiprint AG
Priority date: 1995-07-07
Filing date: 1996-05-28
Publication date: 1998-04-29
Also published as: WO1997003544A1

Abstract

A conductive connection with a first and a second conductive layer (1, 2) provides for the electrical and mechanical connection of spatially separate connection regions. Thus, the juts (4) from at least one conductive layer (2), which are preferably arranged in a grid, establish the conductive connection between the layers (1, 2) through their contact with the surface of the opposite conductive layer. For the mechanical connection at least one partial layer is formed between the juts (4) as a bonding layer (3). Conductive connections as per the invention are used preferably to enlarge the earthing layer in high-frequency switches. Thus, the first conductive layer (1) is mounted on the back side of a carrier plate (10) and connected on its side opposite the carrier plate (10) to a second conductive layer (2) of great thickness.

Description

Conductive connection and method of making the same

The invention relates to a connection according to claim 1 and a method according to claim 8.

Printed circuit boards for high-frequency circuits require earthing or ground surfaces which, in addition to their electrical compensation function, usually also have to dissipate heat generated in high-frequency parts. For this purpose, such a grounding surface is designed as an electrically conductive and preferably also a heat-conducting layer, which is arranged on the back of a printed circuit board or on the side of an insulating carrier plate facing away from the conductor tracks. Through holes are provided in the insulating carrier plate to connect this conductive layer with conductor tracks. The dimensioning of the grounding and / or heat dissipation surface strongly depends on the circuit connected to it and sometimes also on the design of the housing accommodating the circuit. Particularly in the case of earthing surfaces of great thickness, it is expedient to use them as a carrier part of the circuit and thus to arrange the circuit in a holder for the earthing surface. Since the requirements for the design of the earthing surface are often application-dependent, the earthing surface is formed in two parts according to a known solution.

In the known two-part grounding surfaces, a first conductive layer adhering to the back of an insulating carrier plate is conductively connected to a second conductive layer. The first conductive layer has only a small, essentially the same thickness for all applications, preferably consists at least partially of copper, chemical nickel-gold, or galvanic gold and serves primarily as a contact surface with the second conductive layer. The second conductive layer has a shape or thickness that is adapted to the respective application or circuit. For different high-frequency circuits, a grounding surface with a large thickness is required. So that the second layer, even with larger activity is light, inexpensive and easy to work with, an aluminum plate is used in particular.

In order to mechanically connect the two conductive layers to one another, they are screwed together according to a known embodiment. At least in the area of the screws used, the two layers lie close together and are thus conductively connected to one another. The screwing of the two layers with up to twenty screws is complex and leads to high production costs without ensuring a constant connection quality. If the screw connection is inadequate, changes in the contact resistance or, depending on the compositions of the conductive layers, such as oxidations and / or intermetallic changes, can occur in particular in the case of strong weather influences in parts of the contact area. In the case of carrier plates with a high population density, the space for attaching a sufficient number of screws is sometimes lacking.

According to a further known embodiment, the two layers are arranged between the layers by means of one

Adhesive layer made of silver conductive paint or silver conductive paste joined together. The silver conductive paint connects the two layers both mechanically and electrically. However, it has been shown that this type of connection has numerous disadvantages. For example, this connection is not sufficiently temperature and moisture resistant, so that it cannot be used in devices that must be weather-resistant. The absorption of moisture by the silver conductive paint leads to changes in the distance, or the mechanical connection, and the contact resistance between the two conductive layers. Depending on the compositions of the conductive layers, oxidations and / or intermetallic changes may occur. In addition, the processing of the silver conductive paint is complex and, together with the high price of the silver conductive paint, leads to high manufacturing costs without ensuring a constant connection quality. The object of the invention is to describe a mechanically stable and conductive connection between two conductive layers, the conduction properties of which are independent of weather influences and which can be produced easily and with constant quality.

In a first inventive step, it is recognized that when an adhesive layer is used, it must be selected so that the mechanical connection is optimal. When choosing the adhesive, a compromise between adhesive and conduction properties should not be sought because, as the example of the silver conductive paint shows, an adhesive with inadequate mechanical bonding properties is found. By ensuring the conduction property of the connection regardless of the choice of the adhesive by at least one conductive connecting part between the two conductive layers, an adhesive with adhesive properties optimally matched to the two conductive layers can be selected.

In a second inventive step, it is recognized that for the preferred creation of the line connection between the two layers as a connecting part, at least one of the conductive layers should include at least one protrusion projecting against the other layer, the projecting contact area of which is in conductive contact with the other layer occurs. By forming the at least one connecting part, preferably as a projection of a conductive layer - that is, already connected to it - the assembly of the connection is facilitated. In addition, the surface of a layer can be structured as desired, or can be provided with a plurality of projections, which are arranged in a grid-like manner in particular. In order to produce the surface provided with projections, for example a flat surface can be processed with material-lifting processes such as knurling, creasing, milling, planing or chemical processing processes such as etching. If necessary, conductive layers with protrusions are produced by casting in molds with depressions forming the protrusions. In a preferred embodiment, the projections form a type of nail bed, the nails starting from a first conductive layer, penetrating the adhesive layer and connecting with their tips or contact areas to a second conductive layer. The term nail bed is not to be understood as a restriction to projections provided with tips. The projections can also be rib-shaped or burr-shaped. These ribs or ridges are arranged approximately in a grid-like manner and are designed in a cutting shape, so that they can pierce a glue film in a linear manner. A preferred rib grid comprises ribs arranged in parallel, which are preferably arranged in two different directions, in particular rotated by 90 ° to one another.

By providing a close-meshed projection grid, a small-scale connection structure with many conductive connection areas and one or more adhesive connection areas arranged in the same area can be achieved. In the case of electrically conductive and / or thermally conductive projections and layers, this ensures that an essentially uniform current and / or heat conduction density can be achieved in the connection area. Electrical, thermal or other energy flows originating from components do not go through distant connecting bridges, but flow essentially as they would flow with layers lying flat against one another. This is particularly important in the case of earthing surfaces for high-frequency circuits.

Tests with conductive connections according to the invention have shown that the gluing and the conduction properties withstand extreme temperatures and moisture. The manufacture is simple, inexpensive and provides connections of constant quality.

Another advantage of the nail bed connection is that the connection density, or the surface distribution of the projections, can be adapted to the individual needs of a circuit. One that varies across the interface Connection density can be used, for example, in high-frequency circuits for generating a desired electrical oscillation behavior, or also for adapting the heat conduction capacity to individual heat sources or for optimally guiding the heat flow. In the known solutions with layers screwed together or connected by means of an essentially homogeneously conductive adhesive layer, no specific variation in the connection density is possible.

By omitting projections in a partial area of the interconnected layers, a connection-free area is created there, which can be used, for example, to interrupt the first conductive layer, which is arranged approximately on the back of a printed circuit board, and one of form a separate line area for the earthing surface. The second conductive layer can be continuous and nevertheless does not lead to a conductive connection of the separated line area to the grounding surface. This option is particularly advantageous for printed circuit boards with a high density of components, because this also means that the back of the printed circuit board from the

Earthing surface separate conductor tracks can be formed.

Another advantage of the nail bed connection is that the mechanical connection strength that can be achieved by the adhesive layer is increased by the projections. The projections increase on the one hand a second adhesive surface between the adhesive layer and the second conductive layer and on the other hand this second adhesive surface extends along the projections to the first conductive layer, that is to say up to a first adhesive surface between the adhesive layer and the first conductive layer. The projections take on a reinforcing or stiffening function in the adhesive layer. Since various adhesives, even in the solid state, have an increased elasticity compared to metals or other solid bodies, the connection according to the invention can be used in particular to reduce the elasticity of an adhesive connection due to the adhesive. This is important for sound or ultrasound conduction. In addition to the mechanical connection function, the adhesive layer preferably also performs a sealing function for the line connection through the projections. Since, for example, waterproof adhesive completely surrounds a projection and in particular its contact area with the opposite layer, the contact surface is tightly sealed and there is no danger of oxidative or intermetallic changes due to external influences or substances coming from outside. In embodiments with ribs, in substantially orthogonal

Directions, it is possible that the entire adhesive layer is laterally surrounded by four extremely arranged ribs. These ribs are in contact with the other conductive layer and thus, in the sense of sealing lips, protect the glue layer from environmental influences.

Various approaches are possible for assembling a conductive connection according to the invention. For example, a film, preferably made of acrylic, is placed on at least a portion of a conductive layer, and a further conductive layer is placed thereon. By pressing the two conductive layers against one another and optionally by applying heat or some other form of energy, the two conductive layers are mechanically adhered to one another by the adhesive layer, while the contact areas of the projections have pierced the film and are connected to the opposite one conductive layer are in conductive contact.

During the pressing, the time profile of the contact pressure and / or the temperature profile can be selected, in particular by supplying and possibly by removing heat. The adhesive layer essentially does not change its extent during hardening.

The thickness of the film is chosen so that the space between the projections or in the recesses between the compressed conductive layers can accommodate the film volume. If the film thickness is too large or If the film volume is too large, the two layers could not be brought into conductive contact, or only with difficulty. So it will always remain, at least a small part of the free space, glue-free. However, because the projections are pressed through the film, a pressing pressure necessary for the gluing occurs on the film, at least in the area of the projections.

Instead of the film, a liquid, preferably an acrylic, adhesive can also be used. Liquid adhesives are applied using a brush, roller or roller, but preferably also using screen printing. Applying the adhesive by means of screen printing has the great advantage that the adhesive can be applied specifically to partial areas of at least one conductive layer. Especially in the case of projections thereof

Contact areas can not displace the adhesive when pressing the contact areas against the opposite conductive layer, it is expedient if no adhesive is applied to these contact areas or to the locations on the opposite layer assigned to them.

Advantageous embodiments are also possible in which the arrangement or configuration of the conductive and adhesive connections are essentially inverse to the nail bed connection described. The adhesive connections are arranged at grid points, preferably in depressions of at least one conductive layer. The layer surface arranged around the depressions forms at least one projection area which is in contact with the other conductive layer.

The creation of depressions, the total cross-sectional area of which is smaller than half the layer surface, may be less complex than the production of a nail bed-like projection grid. Such depressions can be pressed into a conductive layer using an embossing process, for example. According to the recesses, the adhesive must be grid-like on at least one conductive layer, especially in the recess. exercises to be applied. The quantities applied must be selected such that adhesive connections are formed when the conductive layers are pressed together, without adhesive being pressed into the contact area of the conductive connections.

The conductive connection developed for the expansion of the grounding surface of a printed circuit board is by no means restricted to this application. It can be used as an inexpensive and permanent electrically conductive and / or heat-conducting and / or possibly also sound-conducting connection for a wide variety of connection or power line problems. In particular, the heat flow, which is impaired by a continuous adhesive layer, from an electronic component into a cooling element adhered to it can be increased through the use of a connection according to the invention with layers or protrusions of high thermal conductivity.

The drawings explain the invention on the basis of possible embodiments, to which the invention is, however, not restricted.

Fig. 1: cuts through differently executed conductive

Connections Fig. 2: Perspective representations of projections Fig. 3: Section through a conductive layer with projections

Fig. 4: Top view of a conductive layer with projections Fig. 5 and 6: Section through a conductive connection with two conductive layers, one of which is arranged on the back of a circuit board

1 shows six different variants of a conductive connection with a first, upper conductive layer 1 and a second, lower conductive layer 2. At least one adhesive layer 3 is arranged at least in a partial area between these two conductive layers 1 and 2. The at least one adhesive layer 3 adheres to mutually facing regions of the first and second conductive layers 1, 2 and forms a firm connection between the two conductive layers 1, 2. In order to also ensure a conductive connection between the two layers in addition to the mechanical connection, at least one connecting part 4 ′, as shown in illustration d), is arranged between the two layers 1, 2. In this case, the at least one connecting part 4 'with a first and a second contact region 5a and 5b must be in conductive contact with the first and second conductive layers 1, 2, respectively.

In order to be able to correctly insert the connecting parts 4 'into the region of the adhesive layer, these are preferably introduced into the through holes provided for this purpose in an adhesive film, so that the adhesive film with the connecting parts 4' can be placed on the second conductive layer 2. The first conductive layer 1 is then placed on the adhesive film and pressed against the second layer 2 and, if necessary, preferably treated with heat to solidify the adhesive connection. In order to avoid problems with the connecting parts 4 'when establishing the connection, these are preferably formed, as in the representations a), b), c), e) and f), as projections 4 of at least one conductive layer 1, 2.

The representation a) shows a projection 4 which projects from the second layer 2 against the first layer 1 and is in conductive contact with the latter via a flat contact region 5. The at least one adhesive layer 3 is preferably placed in a ring around the projection 4, so that the projection 4 and thus the contact area 5 are tightly enclosed. In order to obtain a good adhesive bond, the thickness of the adhesive layer 3 before pressing is somewhat greater than the height of the projection 4.

The representation b) shows, starting from the second layer 2, in the contact area 5 pointed projections 4, which penetrate through a continuous adhesive layer 3, in particular a film when pressed together, and in particular somewhat enter the first conductive layer 1. When entering the first layer 1, the adhesive layer is displaced so that the two conductive layers 1 and 2 come into conductive contact. The illustration c) shows a second conductive layer 2 produced by die casting. The contact areas 5 are approximately rounded due to the manufacturing process, but can nevertheless penetrate the adhesive layer 3. In individual applications it can be expedient if projections 4 start from both conductive layers, as can be seen in illustration e). This design results in a very high strength against shear forces acting between the two conductive layers. Representation f) shows an embodiment in which the surface area of the projections 4 is greater than the surface area of the adhesive layers 3. The adhesive layers are essentially arranged in depressions of at least one conductive layer.

2 shows protrusions 4 of different designs, or end regions of protrusions 4, which enable the adhesive layer to be pierced. The end face that comes into contact with the other layer has at least one contact area in the form of a tip (illustration a), optionally at least one ridge line (illustration b), an arched one (illustrations c and g), or one flat (illustrations e and f) contact area, the projection edge adjoining the at least one contact area preferably tapering towards the contact area, in particular being conical or pyramid-shaped. It has been shown that the projections with flat contact areas, if they are sufficiently small, displace the adhesive layer in such a way that they connect tightly or without adhesive to the opposite layer. According to illustration d), curved and / or cruciform ridge lines are also expedient if appropriate. As already mentioned above, the ridge lines can form a ridge grid extending over large parts of the second conductive layer.

3 shows a conductive layer 2 with truncated pyramid-shaped projections 4. The distances 6 between the central regions of the next adjacent projections 4 are at least 0.1 mm, but are preferably in a range from 0.2 to 0.8 mm, possibly substantially 0.4 mm. The projections 4 project by a height 7 of at least 0.02 mm, but preferably from 0.03 to 0.3 mm, in particular from 0.1 to 0.2 mm. In the embodiment shown, the angle of inclination 8 of the surface areas to the surface normal is preferably essentially 45 °.

FIG. 4 shows a grid-like arrangement of the projections 4 according to FIG. 3, the distance 6 being between the central regions of the next adjacent projections 4. The contact surfaces 5 of the projections 4 are preferably square and have a side length 9 of at least 0.01 mm, but preferably the side length 9 is in a range from 0.01 mm to 0.3 mm, in particular from 0.015 mm to 0.2 mm.

5 shows an embodiment in which at least the first conductive layer 1 is arranged on the back of a printed circuit board or on the side of an insulating carrier plate 10 facing away from the conductor tracks 11. The first conductive layer optionally comprises several, in particular two, an inner and an outer, conductive sub-layers la and lb, the inner (la) approximately a copper layer and the outer (lb), for example, a thin chem. Nickel-gold layer, or a galvanic gold layer. The surface of the first layer 1 facing the second conductive layer 2 is preferably essentially flat. The second conductive layer 2 preferably consists essentially of aluminum and comprises a plurality of protrusions 4 in the form of a truncated pyramid, which are in particular arranged in a grid-like manner. An adhesive layer 3 is arranged between the projections 4. The second layer, together with the first layer, forms a layer with increased earthing and, in particular, heat capacity.

6 shows a conductive connection between a first conductive layer 1 and a second conductive layer 2, which two layers together form a grounding surface of a printed circuit board 10 '. At least one conductor track Ila is through the Plated through to the first conductive layer 1 by means of a conductive connection 13. In the second conductive layer, in particular at least one recess 15, which is accessible through an opening 14 in the carrier plate 10 and in the first layer 1, is provided, in which a component 16 connected to the circuit board 10 'can be arranged in order to to ensure optimal cooling by the second conductive layer 2. Optionally, the second conductive layer 2 has at least one partial region 17 without projections, in relation to which a conductor region 18 which is separate from the first conductive layer 1 but is located in the same plane is arranged in isolation.

It goes without saying that all features of the described embodiments can be combined as desired.

Claims

claims

1. Conductive connection with a first conductive layer (1), a second conductive layer (2) and an intermediate adhesive layer (3) forming at least one partial layer, characterized in that in the area between the two conductive layers (1, 2) at least one connecting part (4, 4 ') connecting the two conductive layers (1, 2) is provided.

2. A conductive connection according to claim 1, characterized in that the at least one connecting part (4 ') is formed as a projection (4) of one conductive layer (1, 2), protrudes against the other conductive layer (1, 2) and is in direct contact therewith, the adhesive layer (3) adhering at least partially around the at least one projection (4) to the mutually facing surfaces of the first and second conductive layers (1, 2).

3. Conductive connection according to claim 2, characterized in that at least one conductive layer (1, 2) has a plurality of projections (4), preferably arranged in a grid-like manner on the layer surface, in particular at least one of the following features being provided, a ) the distances (6) between the central areas of the next adjacent projections (4) are at least 0.1 mm, but are preferably in a range from 0.2 to 0.8 mm, possibly at substantially 0.4 mm, b) the projections (4) are at least around 0.02 mm, but preferably by 0.03 to 0.3 mm, in particular by 0.1 to 0.2 mm, and c) the projections (4) have at least one contact area (5) on their projecting end face that comes into contact with the other layer (1, 2) ) in the form of a point, or possibly a ridge line, or an arched or in particular flat, in essentially parallel to the adjoining layer surface, the edge of the projection adjoining the at least one contact area (5) preferably tapering towards the contact area, in particular being conical or pyramid-shaped.

4. Conductive connection according to one of claims 1 to 3, characterized by the fact that the adhesive layer (3) completely encloses at least one connecting part (4, 4 ') laterally and thus the at least one contact point between the connecting part (4, 4') and a region of the one conductive layer (1, 2) adjoining it tightly.

Conductive connection according to one of Claims 1 to 4, characterized in that the adhesive layer (3) optionally consists of conductive material, but preferably non-conductive material, in particular acrylic.

6. Conductive connection according to one of claims 2 to 5, characterized in that at least the first conductive layer (1) on the back of a printed circuit board (10 '), or on the side of an insulating carrier plate facing away from the conductor tracks (11) (10) and in particular has a substantially flat surface facing the second conductive at least one projection (4), but preferably a plurality of grid-like projections (4), facing layer (2), preferably at least one of the following features being provided , a) the conductive layers (1, 2) are electrically conductive and / or thermally conductive, b) the first conductive layer (1) is a copper layer and / or possibly a chem. Nickel-gold layer, but in particular around a galvanic gold layer, c) the first conductive layer (1) is at least one conductive due to the carrier plate (10) Connections (13) to at least one conductor track (11) are plated through and, in particular in the case of high-frequency circuits, serves as a grounding surface, d) the second conductive layer (2) forms, together with the first conductive layer (1), a layer with an increased Earthing and in particular heat capacity, e) the second conductive layer (2) is designed as an aluminum plate and in particular has a substantially greater thickness than the first layer (1), and f) the second conductive layer (2) is designed as a cooling element.

7. Conductive connection according to claim 6, characterized in that one of the following features is provided, a) in the second conductive layer (2) is at least one recess (15) accessible through an opening (14) in the first layer. provided, in which a component (16) connected to the printed circuit board (10 ') can be arranged, and b) the second conductive layer (2) has at least one partial area (17) without projections (4), which is insulated from the one first conductive layer (1) separated but lying in the same plane

Conductor area (18) is arranged.

8. A method for producing a conductive connection according to claim 1 with a first conductive layer (1), a second conductive layer (2) and an intermediate adhesive layer (3) forming at least one partial layer, characterized in that a) in one first step on at least one of the two conductive layers (1, 2) at least one projection projecting against the other conductive layer (1, 2)

(4) is generated, b) in a second step at least one layer of the adhesive layer (3) at least with a partial area a conductive layer (1, 2) is brought into contact and c) in a third step the two conductive layers (1, 2) are pressed against each other so that the adhesive layer (3) with both at least in a partial area of the surfaces facing each other Surfaces come into adhesive contact and at least one contact area (5) of a projection (4) of one conductive layer (1, 2) comes into conductive contact with the surface of the other conductive layer (1, 2) without adhesive.

9. A method for producing a conductive connection according to claim 8, characterized in that at least one of the following features is provided, a) for producing at least one projection (4) is approximately the conductive layer (1, 2) in a die-casting mold with at least one recess forming the projection (4), or else a substantially flat surface of the conductive layer (1, 2) is formed by stamping, or rolling or pressing with a

Embossing tool and / or grooves and / or milling and / or planing and / or knurling and / or possibly processed by chemical treatment, b) the adhesive layer (3) is placed as a film on at least a portion of a conductive layer (1, 2) , c) during pressing, at least one contact area (5) of a projection (4) passes through the adhesive layer (3), d) the adhesive layer (3) is applied to at least a portion of the surface of a conductive layer (1, 2) by means of screen printing , e) during pressing, the time profile of the contact pressure and / or the temperature profile can be selected, in particular by supplying and possibly removing heat, f) the adhesive layer (3) essentially does not change its extent during hardening.