DE19613587A1 - Arrangement for reducing electromagnetic radiation with circuit boards and other electronic circuit carriers - Google Patents

Abstract

The arrangement involves covering the conductive tracks or buses. This covering is arranged in the form of conductive strips and/or flat elements at a spacing of approx. 1.5 mm. The covering covers both sides of the bus. The respective component groups are connected at least at their corner points or their side edges, ti the GND system. Preferably the covering is provided as SMD components using surface mounting technology or using plug assembly the covers have pin type GND terminals. The covers may be formed as bridges made of several rectangular thin metal plates.

Description

The invention relates to the reduction of electromagnetic Radiation from printed circuit boards or other carriers electro African circuits through measures on the layout.

Printed circuit boards or other carriers of electronic circuits conditions due to the switching processes of your digital electronic circuits high frequency electromagnetic Blast waves. The frequency of the radiation lies in MHz to GHz range. Particularly high radiation values generate fast, high frequency (MHz) periodically working digital circuits, in particular circuits, which contain microcomputers.

Through regulations on electromagnetic compatibility (EMC) limits are set for devices. To the of Legislators are required to comply with the limit values Device manufacturers determined on the devices or assemblies EMC measures required.

There are a variety of shielding and protection measures Filtering known. Measures taken directly on circuit boards specifically applied to the layout are still on the Beginnings.

One measure that is carried out on printed circuit boards is the sheet-like formation of mass (M), supply voltage (V) and shield (S) conductors (hereinafter MVS ladder tracks). By using wide conductor strips the resistance and inductance decrease for  the switching processes of the nanosecond range digital integrated circuits (IC). With that the high-frequency interference voltages along the MVS system, are the source of the electromagnetic radiation, decreased.

The widespread use is for one or two-layer printed circuit boards MVS lines set practical limits. The available area of the circuit board must be between signal line lines and MVS lines. In places higher Signal conductor tensile densities, such as microcomputer IC, are mostly only narrow lines for MVS possible.

In practice, this can be achieved through closer internal meshing the MVS conductor tracks with the help of wire jumpers an improvement can be achieved. Further measures can be taken according to the state of the art only at the interfaces to PCB (filter) or outside the PCB e.g. B. be carried out as shielding.

The object of the invention is therefore to provide effective means Preference to reduce electromagnetic radiation propose that have a reduced space requirement and Can be used directly on circuit boards and especially on the layout are.

An inventive solution to this problem is in the patent claim 1 specified. Developments of the invention are characterized in the subclaims.

The surface of bus line systems is particularly strong in the emission of electromagnetic waves leap

The following phenomenon was found when investigating the cause-effect relationships:
Complete shielding of the bus line system is not required. A one-sided approximation of a (conductive surface) metal surface is sufficient to reduce the interference emission! The effect is already effective when approaching a distance of 1.5 mm. The approximation brings a high effect to approx. 0.2 mm. The metal surface should be connected at least at its corner points to the GND system of the associated assembly. If not all key points are contacted, the effectiveness is reduced.

As a rule, this effect can be used for two-layer conductors do not card out solely with means of the layout be used sufficiently. The bus can be covered with a copper surface on the opposite side of the bus Side of the circuit board. Of the The distance is then 1.5 mm for two-layer circuit boards (PCB thickness). At this distance, it unfolds not yet the full effectiveness of the effect. Farther the bus area can be viewed on the other side of the map mostly not completely close lying surfaces. in the Lead the area below the bus crossing lines ben openings that provide full coverage of the busbe prevent rich.

On printed circuit boards that have more than two layers (Multi layer) there may be similar relationships.

Proceeding from this, the essence of the invention resides in one cover the bus from printed circuit boards or integrated circuits (IC) with conductive surfaces (metal or plastic) and their contact with GND on the corner score and possibly other positions, such as B. on the sides  edge.

Taking into account the mechanism of action and the manufacturer technology is used for the distance of the conductive Areas preferably a range from greater than zero to about 0.2 mm and in some applications still up to 1.5 mm selected.

For the bus coverage of printed circuit boards with Surface (SMD) or push-through installation became special components developed. So z. B. assemblies in surfaces assembly with special components that are used in the reflow Process melted together with the other equipment be zen.

The parts consist of rectangular metal plates in different, adapted to the geometry of the printed circuit board areas or IC and an automatic assembly dimensions that are referred to as bridges. The bridges are placed on the surface of the circuit board so that they overlap the bus on both sides. The corner points or side edges of the bridges are z. B. using the reflow soldering process connected to the GND system of the circuit board. Additional soldering areas can be arranged between the corner points. To cover the entire bus area, several bridges (similar to dominoes) can be strung together. (Favorable dimensions for SMD assembly are e.g. 20 × 5 mm, 25 × 7.5 mm or 10 × 30 mm.)
A bridge or a chain of bridges (dominoes) can be applied in the form of a conductive lacquer layer or as a sticker directly on the solder mask on the circuit board (assembly). The corner contact with GND is to be carried out analogously to the domino arrangement of discrete bridges. It must be contacted on the outer edges of the bus at a distance of approx. 20 millimeters.

By placing the bridges directly on the bus the low Ab required for high effectiveness reached about 0.2 mm.

In the solder stop coating of the circuit board, openings for GND system will be provided to the contacting points of the bridge. The bridges can also be used pin-shaped GND connections for push-through installation procedures are carried out.

Instead of or next to closed bridges are also short-circuit ring-like bridges applicable.

The bridges according to the invention can also be used within from IC as well as external bridges for IC. The Bridge dimensions are the geometric dimensions of the IC adjusted.

To the bridges within IC:
The bus system of the circuit card can continue in the IC or can also be routed under the IC on the circuit card. To solve the emission problem, the same principles, as explained above, can be used in a modified technical version.

The bridges can be used for:

• 1. Pin, bond and chip areas, i.e. H. for sources within of the IC,
• 2. For the circuit card bus below the IC.

Both functions can, depending on the arrangement of the conductive Areas of only one bridge or two  Bridges are taken over.

With a bridge in the lower part of the IC, both cases controlled. A metallic layer in the IC is conceivable, those at the corner points on in the corner points of the housing horizontal IC pin is guided and with these corner points GND of the circuit board is connected (claim 11). The The chip's GND system can use this metallic layer Bond wires are connected in the same way.

Furthermore, a metallic layer can also be in the chip are designed as a bridge that is connected to the Corner points to the GND corner connections.

If the chip is placed too high in the IC, u. U. two bridges needed. For IC, whose case after conductor card technology are manufactured and therefore from a small circuit board, there are many Possible applications for bridges.

According to the state of the art for printed circuit board housings on the top (B-side) of the printed circuit board housing Chip (Die) glued and ge on the pad of the top bonded. Vias lead to contact areas of the Underside of the circuit board (L side) as the IC pin nen. The chip and bond wires come with a plop top covered.

According to the invention, the chip is applied to a bridge, the one side of the bus of the chip and the bond wires covers. The bridge is via contact at the corner points tations and IC pin with GND of the circuit board (assembly) connected. The vias of the bus (IC-An short-circuit) on the B-side of a short-circuit ring be surrounded. There is one on the L side of the IC  another bridge that one on the circuit board (assembly) Bus located under the IC area by applying the IC covers. The favorable distance of 0.2 mm can be adhere. The connection of the bridge to the GND system the printed circuit board (assembly) takes place at the corner points the same way as connecting the tops (B-Sei ten) bridge of the IC (claim 12).

The chip can also according to claim 13 in the interior of the PCB housing are integrated.

In a further embodiment (claim 14) the Chip arranged on the underside of the circuit board housing net.

To the external bridges for IC:
Common IC packages have no internal bridges. In order to achieve an effect according to the invention for these components, bridges can be arranged above or below the IC housing, see. Claims 6 to 10.

To the emergence of edge fields from the edge of the ladder ICs on the card are metallic (conductive) clasp-shaped bridges on the edges of the Printed circuit board pushed on. These bridges are with the GND system of the circuit board contacts and overlap tongues shaped the IC located on the edge close to their housing top. The overlap of the IC need not be completely in Towards the center of the PCB. However, it must Edge area of the circuit board a clear overlap are available, cf. Claim 16.

IC can also be used with an adhesive tape-shaped bridge in the design as a conductive film with an insulation layer outside the GND contact areas to the conductor  card (assembly) are covered, see Claim 17.

A modified version of this adhesive bridge can right and left with electrically conductive self-adhesive be provided with the edge contacts. In the middle of Tape is insulated as described and self-adhesive. In this version it is like the reason described Arrangement in the inner areas of the circuit board as a bridge applicable.

The bridge can have a grained surface to be flexible and adaptable Surface unevenness (assembly) of the module to reach.

To further explain the invention reference is made to the Referred claims.

Details, further features and advantages of the invention also result from the following description of Embodiments. In the accompanying drawing gene.

Fig. 1 basic arrangement for covering the bus conductor tracks with conductive surfaces (bridge (n)),

Fig 2 different bridge variants.,

Fig. 3, two bridge designs (flat and bent) in the assembly position,

Fig. 4 IC structure with bridges, wherein the IC from a double-sided circuit card consists,

Fig. 5 IC structure with a built in the printed circuit card housing chip,

Fig. 6 representation of bridges that are used as external bridges for IC; Bridge arrangement below half of the IC,

Fig. 7 as Fig. 6; Bridge arrangement above the IC,

Fig. 8 bridges for blocking edge fields and

Fig. 9 execution of a stick-on band-shaped bridge.

Fig. 1 shows the essence of the invention in a basic arrangement.

A bridge 2 lies on a circuit board, consisting of carrier material 11 , GND 3 , bus conductor lines 1 and solder resist 5 , at a distance of approximately 0.2 mm from the bus conductor lines 1 . The dimensions of the bridge 2 formed from a conductive surface are chosen in the dimensions of for example 20 × 5 × 0.2 mm so that the bus conductor trains 1 are covered.

Openings 6 in the solder resist 5 ensure surface mounting by soldering the bridge 2 to GND 3 of the circuit board.

Fig. 2 illustrates different bridge variants and connection options with the circuit board over the corner points or side edges of the bridges 2 , see. GND connections 6.2 in Fig. 2.3 or pin-shaped connections 4 .

The insulation to the conductor tracks of the bus system and thus setting the preferred distance of 0.2 mm done by:

• 1. the solder resist 5 of the circuit board ( Fig. 1.1 and 3.1) or
• 2. by an air gap 7 , which is predetermined by spacer knobs 8 of the bridge 2 ( FIGS. 2.2 and 3.2),
• 3. by an insulating coating 9 of the bridge 2 , the areas 6.2 must be left blank for contacting GND 3 .

Bridges with pin-shaped GND connections 4 can be used for the push-through assembly method ( Fig. 2.4, 2.5, 2.6).

Instead of closed bridges, short-circuit rings ( Fig. 2.5) can also be used. The opening of the rings across the bus should be kept small (<3 mm). Wider short-circuit rings can be supplemented by one or more longitudinal bars. Through the openings of the short-circuit rings, connection pins of components can be guided. This type of bridge can be used to protect connection areas. In the event that two opposite sides of a short-circuit ring are connected to different potentials, the short-circuit ring can close via capacitors 13 according to FIG. 2.6.

Fig. 3 shows the cross-sectional view of two built-in bridges.

In the embodiment according to FIG. 3.1, the flat bridge 2 rests on the solder resist 5 , which takes over the insulation of the conductor tracks 1 to the bridge 2 . The connection to the GND system 3 is made via the solder joint 10 .

In the embodiment of FIG. 3.2 a bridge 2 is used with distance knobs 8. As a result, an insulating gap 7 to exposed parts (plated-through hole 15 ) is provided.

The IC of FIG. 4 is constructed from a card double-sided circuit and has two bridges 2.1 and 2.2.

The printed circuit card housing 21 includes the ten-top Leiterkar 21.1 (PCB, upper conductive pattern) and the printed circuit card underside 21.2 (lower wiring pattern). The chip 23 is glued to a bridge 2.1 located under the bus conductor tracks of the chip and thereby covers the bus conductor tracks and the bond wires 22 . At the corner points, the bridge 2.1 is connected to the GND of the printed circuit board (module) 20 via plated-through holes 15 and IC pin 19 .

The plated-through holes 15 of the bus conductor tracks (IC connections) are surrounded on the top 21.1 by a short-circuit ring 12 .

A second bridge 2.2 is arranged on the underside 21.2 and covers a bus located on the circuit board (assembly) 20 below the IC region 21 by mounting the IC 21 . The bridges are connected to the GND system of the printed circuit board (assembly) 20 via the IC contact 24 .

FIG. 5 shows an IC, the chip 23 (die) of which has been integrated into the interior of the printed circuit board housing 21 . As in Fig. 4, the housing consists of a small square or rectangular two-sided circuit board. The underside 21.2 has the IC pin 19 , a bridge 2.2 and the IC pin 24 in the corners of the bridge for connection to the printed circuit board (assembly) 20 as the conductor pattern. The lower surfaces (outer sides) of the connections 24 act as an IC pin in order to serve as soldering surfaces when surface-mounted on printed circuit boards 20 . The inner sides 19 serve as contact surfaces of the bond wires 22 , which lead to the chip 23 . The bridge 2.2 is accordingly located below the bus area of the chip 23 and above the bus area of the circuit card (module) 20 below it.

In addition, a short-circuit ring could be provided in the outer region of the lower layer 21.1 , if necessary by metallizing the end faces.

The chip 23 (Die) can also be arranged on the underside of the circuit card housing 21 . It is glued onto the underside of the bridge 22 on the outside and bonded from the outside (below). The chip would protrude beyond the IC pin. In order to prevent this, the layer of the underside 21.2 can be curved into the interior of the printed circuit board, so that the chip can be arranged sunk.

A second bridge 2.1 could be arranged in the IC printed circuit board housing 21 according to FIG. 5 on the upper side (B side) 21.1 . This bridge is not absolutely necessary. If available, it can be connected to the lower GND pad 24 at the corner points via plated-through holes 15 .

In Fig. 6 bridges are shown, which are installed before the IC is populated, that is to say arranged under the IC. IC 14 and bridge 2 are e.g. B. soldered together in a reflow process with the circuit board (assembly) 20 . This variant can be used for surface mounting and if the soldering points of the bridge are adapted for push-through mounting. In Fig. 6 corresponding bridges for SO housings ( Fig. 6.1, 6.2, 6.3, 6.4) and for QFP and PLCC housings ( Fig. 6.6, 6.7) are shown for surface mounting.

On the circuit diagram of the circuit card (assembly) 20 , soldering areas 6.1 must be provided for the connections 6.2 located at the corner points or side edges of the bridge 2 . It is advantageous to provide the bridges 2 on the underside, with the exception of the GND connection points 6.2 in FIG. 6.3, with insulation 9 . The solder connection 6.2 can also comprise an entire side strip ( Fig. 6.4).

The bridge 2 can be extended with short-circuit rings 12 ( Fig. 6.5, 6.7) which enclose the pin areas of the IC. This type of bridge can also be used to protect the connection areas of the IC.

The outer edge 17 of the short-circuit rings 12 can be angled upwards ( FIG. 6.8 in connection with FIGS. 6.7 and 6.5). The bend also blocks fields that emerge from the side of the IC.

The short-circuit ring 12 can be guided separately around an IC 14 ( Fig. 7.1). In Fig. 7.1 a variant for surface mounting with Reflowlötstellen 10 is shown.

Bridges 2 , which are arranged above IC 14 , are shown in FIGS. 7.2, 7.3, 7.4. As a GND connection, the bridges have IC pin 19 (for surface and through-hole mounting; surface mounting in the picture), which are arranged at the corner points or further points distributed on the outer edges and which are connected on the circuit board 20 to GND.

The bridge 2 according to Fig. 7.4 consists of several short-circuit rings 12 , the conductors 12.1 are node-shaped connected in the middle and which are closed via the GND system of the circuit board (module) 20 .

The short-circuit rings 12 mentioned are only completed via the PIN 19 of the bridge 2 and the GND system of the printed circuit board (module) 20 .

In Fig. 8 different embodiments of the Kan tenbrücken 2.3 are shown. Clamping or soldering is conceivable. Surface ( Fig. 8.1, 8.2) and push-through installation ( Fig. 8.3) can be used for soldered connections. The solderless contact can be made with contact springs 25 ( Fig. 8.1, 8.2) or tips 26 ( Fig. 8.4, 8.5), which snap into solder eyes 27 (see 26.1) or press against a metallic GND surface. It should not only be contacted at the ends of the bridge 2.3 , but several times between the ends.

In Fig. 9 a tape-like bridge 2.4 is shown. The bridge is glued on the edge as a conductive film 28 to an open GND surface 3 with conductive adhesive. The bridge 2.4 is thus conductively connected at the edge to the GND 3 of the printed circuit board 20 (assembly). Following the area of the conductive adhesive, the conductive film 28 is insulated on its underside. The insulation 9 is coated with non-conductive adhesive. With this part, IC 14 or conductive patterns in the edge area are pasted over. The short distance to the chip of the IC necessary for the application of the method is ensured by direct gluing. The desired length can be cut from a tape.

Reference list

1 bus ladder trains
2 conductive surfaces, bridges
3 GND (ground)
4 pin-shaped GND connections on 2
5 solder resist
6 opening in the solder resist, 6.1 GND connections on the circuit board, 6.2 GND connections on the bridge
7 air gap / insulating gap
8 spacer knobs of the bridge 2
9 insulating cover
10 solder joint
11 carrier material
12 short-circuit ring
13 capacitors
14 IC package
15 plated-through holes
16 PIN area
17 Edge of the short-circuit ring
18 IC connections of the IC above the bridge
19 IC PIN
20 circuit boards
21 PCB housing for IC assembly
21.1 Circuit board, upper circuit diagram
21.2 Circuit board, lower circuit diagram
22 bond wires
23 chip
24 Bridge connection to circuit board
25 contact springs
26 Top contacts
26.1 top
27 pads
28 metal foil

Claims (18)

1. Arrangement for blocking the electromagnetic radiation in printed circuit boards and IC, characterized in that the cover of the bus conductor trains ( 1 ) of printed circuit boards ( 20 ) or integrated circuits (IC) ( 14 , 21 ) advantageously with a distance of up to approx. 0.2 mm, for some applications sufficient up to 1.5 mm, arranged conductive surfaces (bridges) ( 2 ), the bridges ( 2 ) at least at their corner points with the GND system ( 3 ) of the associated Assembly are connected. 2. Arrangement according to claim 1, characterized in that the bridges ( 2 ) are mounted on the surface of printed circuit boards or on / in IC ( 14 , 21 ) that they cover the bus ( 1 ) on both sides, whereby either the corner points and / or side edges of the bridges ( 2 ) are connected to the GND system ( 3 ) of the circuit board, for example by using the reflow soldering process, or the bridge (s) ( 2 ) pin-shaped GND connections ( 4 ) the push-through assembly process exhibit. 3. Arrangement according to claim 1 or 2, characterized in that the bridges ( 2 ) by one or more than rectangular thin metal plates

• a) with the geometric dimensions of advantageously 20 × 5 mm, 25 × 7.5 mm or 30 × 10 mm or
• b) in dimensions that correspond to the entire or divided bus areas to be covered,

are carried out, bridge elements to cover a greater length and width of the bus line system ( 1 ) can be strung together. 4. Arrangement according to one of claims 1 to 3, characterized in that when the bridge (s) ( 2 ) is placed directly on the bus conductor strip ( 1 ), the distance adjustment and insulation to the conductor strips ( 1 ) of the bus system is carried out by

• a) the solder resist ( 5 ) on the circuit board,
• b) an air gap ( 7 ), which is predetermined by spacer knobs ( 8 ) of the bridge ( 2 ),
• c) by an insulating coating ( 9 ) of the bridge ( 2 ), in which the surfaces ( 6.2 ) are left free for contact with GND ( 3 ).

5. Arrangement according to one of claims 1 to 4, characterized in that instead of the execution of the bridge (s) ( 2 ) as a closed thin metal plate, the bridge (s) in the manner of a short-circuit ring ( 12 ) are ausgebil det, the. The opening of the ring across the bus conductor train ( 1 ) must be kept small. 6. Arrangement according to one of claims 1 to 5, characterized in that for conventional IC housings ( 14 ) the bridges ( 2 ) are arranged externally above or below the IC housing ( 14 ). 7. Arrangement according to claim 6, characterized in that the bridge ( 2 ) arranged under the IC housing ( 14 ) is expanded with short-circuit rings ( 12 ), the short-circuit rings ( 12 ) enclosing the PIN areas ( 16 ) and the outer Edge ( 17 ) of the short-circuit rings upwards, covering the connections, can be angled. 8. Arrangement according to claim 7, characterized in that the short-circuit ring ( 12 ) is guided separately around one or more IC ( 14 ). 9. Arrangement according to claim 6, characterized in that the above the IC housing ( 14 ) arranged bridge ( 2 ) as a GND connection ( 6.2 ) IC-PIN ( 19 ) for surface and push-through installation. 10. The arrangement according to claim 9, characterized in that the bridge ( 2 ) consists of a plurality of short-circuit ring segments ( 12.1 ), the conductors of which are connected in the middle in the form of a knot, the conductors being connected via the GND system ( 3 ) to the circuit board (assembly) ( 20 ) close to short-circuit rings ( 12 ). 11. Arrangement according to one of claims 1 to 5, characterized in that for the execution of bridges ( 2 ) within IC at least one metallic layer ( 2.2 ) in the IC, possibly also in the chip ( 23 ), which is introduced the corner points (in the case of a metallic layer in the chip via bonding wires) is guided on the IC pin ( 19 ) lying in the corner points of the housing ( 21 ) and is connected via these corner points to GND ( 3 ) of the printed circuit board ( 20 , 21.2 ). 12. The arrangement according to claim 11, characterized in that the chip ( 23 ) is applied to a bridge ( 2.1 ) which covers the bus conductor runs ( 1 ) of the chip ( 23 ) and the bonding wires ( 22 ) on one side and the bridge ( 2.1 ) at the end points via plated-through holes ( 15 ) and IC-PIN ( 19 ) is connected to GND ( 3 ) of the circuit board (module) ( 20 ), as well as the plated-through holes of the bus conductor cables ( 1 ) (IC connections) on the top ( 21.1 ) is surrounded by a short-circuit ring ( 12 ) and on the underside of the IC ( 21.2 ) there is another bridge ( 2.2 ) which covers a bus located on the circuit board (module) ( 20 ) under the IC area by attaching the IC . 13. The arrangement according to claim 11, characterized in that the chip ( 23 ) in the interior of the circuit card housing ( 21 ) on a bridge ( 2.2 ) is angeord net and the circuit card housing ( 21 ) from a small square or rectangular two-sided circuit board ( 21.1 , 21.2 ) exists, the underside ( 21.2 ) having the IC-PIN ( 19 ), a bridge ( 2.2 ) and the IC-PIN ( 24 ) of the bridge located in the corners as the conductor pattern, and the lower surfaces (outer sides) of the bridge connections ( 24 ) serve as an IC PIN for surface mounting on printed circuit boards ( 20 ) and the inner sides of the IC PIN ( 19 ) represent contact surfaces for the bond wires ( 22 ) leading to the chip ( 23 ). 14. Arrangement according to claim 11, characterized in that the chip ( 23 ) outside on the underside of the bridge ( 2.2 ) (L-side bridge) is applied and from the outside (bonded below), the layer of the underside ( 21.2 ) in the The interior of the printed circuit board is arched out and the chip ( 23 ) is arranged sunk. 15. The arrangement according to claim 13, characterized in that a second bridge ( 2.1 ) in the printed circuit board housing ( 21 ) on the upper side ( 21.1 ) is angeord net and this bridge ( 2.1 ) at the corner points via vias ( 15 ) with the lower GND Pad is connected. 16. Arrangement according to one of claims 1 to 5, characterized in that to block the edge fields of printed circuit boards ( 20 ) metallic clasp-shaped bridges ( 2.3 ) on the edge of the printed circuit board ( 20 ) are attached, which with the GND system ( 3 ) the printed circuit board ( 20 ) are in contact, the actual bridge tongue-like overlapping the IC ( 14 ) located in the edge area close to the top of their housing. 17. Arrangement according to one of claims 1 to 5, characterized in that the bridge ( 2.4 ) is applied in a stick-on, band-shaped design, the bridge ( 2.4 ) as a conductive film ( 28 ) on the edge of the circuit board ( 20 ) with the open GND surface ( 3 ) of the circuit board ( 20 ) is contacted and the film ( 28 ) outside the conductive areas on its underside has insulation ( 9 ).