DE19613587C2 - Arrangement for blocking the electromagnetic radiation in printed circuit boards and integrated circuits - Google Patents

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 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 of 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.

DE 195 07 124 A1 covers the conductor tracks from Printed circuit boards and IC with spaced conductive Known areas.

The substrate and the conductive layer have a mass electrode connected, d. H. there is only a limited one Contact with the mass system.

DE 43 26 825 A1 describes a solution for HF shielding of circuits or circuit elements on printed circuit boards where the elements to be shielded are covered with an over train will be boarded. The circuit or Isolate circuit element in a 1st step with one the layer and in a 2nd step with an electrical conductive layer coated.  

Essential feature of those presented in DE 43 27 766 A1 Circuitry is that at ground potential lying conductor track rings a separation point for the Have conductors of the conductors. But there is only a connection to the mass system, which has the effect of Reduction of electromagnetic radiation from PCBs severely restricted.

The object of the invention is therefore to provide effective means Reduction of electromagnetic radiation from PCBs, IC and PCB housings for the IC Propose structure.

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

When examining the cause-effect relationships the following phenomenon was found:

A complete shielding of the bus line system is not mandatory. A one-sided approximation is sufficient a (conductive surface) metal surface to the interference reduce emissions! When approaching a distance of The effect is already effective at 1.5 mm. A high impact brings the approximation to approx. 0.2 mm. The metal surface should te at least at their corner points with the GND system of associated module. If not all Key points are contacted, the effectiveness is reduced speed.  

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. 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.

Based on this, the essence of the invention is that the bus conductor tracks of printed circuit boards and IC, but also in analogously the fine conductor tracks (and bond wires) of a chip or printed circuit board housing by spaced Arrangement of conductive strips and / or surface elements ten are covered, these covers at least cover a surface side of the conductor tracks and min at least at their corner points or on their side edges are connected to the GND system of the associated module.

Taking into account the mechanism of action and the manufacturer technology is used for the distance of the conductive Areas preferably selected a size up to 1.5 mm.

For the bus coverage of printed circuit boards with surface (SMD) or push-through assembly 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 covers consist of rectangular metal plates in different, the geometry of the conductors to be covered card areas or IC and an automatic assembly adapted dimensions, which are referred to below as bridges be drawn. The bridges are so on the surface the printed circuit board that they on both sides Bus overlap. The corner points or side edges of the Bridges are e.g. B. using the reflow soldering process rens connected to the GND system of the circuit board. Two Further soldering areas can be arranged between the corner points his. To cover a larger length and width of the Bus line system can seal multiple bridge elements to be strung together. (Favorable dimensions for SMD assembly are z. B. 20 × 5 mm, 25 × 7.5 mm or 10 × 30 mm.)

Instead of or next to covers in the form of a closed thin metal plate are also covers in the manner of a Short-circuit ring applicable.

The bridge covers according to the invention can also be Arrange inside IC as well as external cover for IC. The dimensions of the cover are the geometric Ab measurements of the IC adjusted.

To the bridge covers within IC:

The bus system of the circuit card can continue in the IC or under the IC on the PCB. The same principles are used to solve the emissions problem pien, as explained above, in modified technical  Execution applicable.

The bridge covers can be provided 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 only from a bridge cover or from two bridge covers are taken over.

With a bridge covers in the lower part of the IC masters both cases. A metallic layer is conceivable in the IC, which at the corner points in in the corner points of the Housing IC pin is guided and over this corner points is connected to the GND of the circuit board (claim 11). The chip's GND system can use this metallic Layer connected via bond wires in the same way who the. Furthermore, a metallic one can also be in the chip Layer can be formed as a cover, the bond wires at the corner points to the GND corner connections becomes.

If the chip is placed too high in the IC, u. U. two covers needed. For IC, whose case after PCB technology are manufactured and consequently there are many, if you have a small printed circuit board possible applications for bridge covers.

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 placed on a bridge cover applied to the bus of the chip and the bond wires covers one side. The cover is over at the corner points Vias and IC pin with GND of the circuit board (Assembly) connected. The vias of the bus (IC connectors) can be on the B side of a short be surrounded by the ring. Located on the L side of the IC another cover, one on the circuit board (Module) under the IC area through Applying the IC covers. The connection of the cover with the GND system of the circuit board (module) the corner points in the same way as the connection the top (B-side) cover 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 bridge covers for IC:

Common IC packages have no internal covers. In order to achieve an effect according to the invention for these components can achieve Ab or under the IC package covers are arranged, see p. Claims 5 to 10.

To the emergence of edge fields from the edge of the ladder ICs on the card are metallic (conductive) clasp-shaped bridge covers on the Edges of the printed circuit board pushed on. These covers are contacted with the GND system of the circuit board and tongue-like overlap the IC located on the edge  on the top of the housing. The IC must not overlap completely towards the center of the circuit board. However, there must be a clear mark in the edge area of the circuit board overlap, cf. Claim 16.

The bridge cover can have a grained surface be provided to make it flexible and adaptable surface unevenness (assembly) of the assembly 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 variants of the bridge covers,

Fig. 3 two versions of bridge covers (flat and bent) in the assembly position,

Fig. 4 IC structure with bridge covers, 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 bridge covers, which are used as external covers for IC; Arrangement of the cover below the IC,

Fig. 7 as Fig. 6; Arrangement of the cover above the IC and

Fig. 8 bridge covers for blocking marginal fields.

Fig. 1 shows a basic arrangement for the invention. A cover 2 lies on a printed 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 cover 2 formed from a conductive surface are chosen in the dimensions of, for example, 20 × 5 × 0.2 mm so that the bus conductors 1 are covered.

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

Fig. 2 illustrates different variants of bridge covers and connection options with the circuit board on the corner points or side edges of the covers 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 the setting of the preferred distance of up to 1.5 mm is carried out 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 cover 2 ( FIGS. 2.2 and 3.2),
• 3. by an insulating coating 9 of the cover 2 , the surfaces 6.2 must be left blank for contacting GND 3 .

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

Instead of closed bridge covers, 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 pin of components can be ge leads. This type of cover 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 bridge covers.

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

In the embodiment of FIG. 3.2 is a Brückenab cover 2 is inserted with spacing nubs 8. As a result, an insulating gap 7 is set to exposed parts (through contact 15 ).

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

The printed circuit board housing 21 contains the upper side of the printed circuit board 21.1 (printed circuit board, upper printed circuit board) and the lower side of the printed circuit board 21.2 (lower printed circuit board). The chip 23 is glued to a bridge cover 2.1 located under the bus conductor runs of the chip and covers the bus conductor runs and the bonding wires 22 . At the corner points, the cover 2.1 is connected via vias 15 and IC pin 19 to GND of the circuit board (assembly) 20 .

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 .

On the underside 21.2 , a second bridge cover 2.2 is arranged, which covers a bus located on the circuit board (assembly) 20 below the IC area 21 by mounting the IC 21 . The covers 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 as a conductor pattern, a bridge cover 2.2 and the IC pin 24 in the corners of the cover for connection to the printed circuit board (assembly group) 20 . The lower surfaces (outer sides) of the connections 24 act as an IC pin in order to serve as soldering surfaces on surface cards 20 on circuit boards 20 . The inside 19 serve as contact surfaces of the bond wires 22 which lead to the chip 23 . The cover 2.2 is accordingly located under the bus area of the chip 23 and above the bus area of the underlying circuit card (module) 20 .

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 on the outside to the underside of the bridge cover 22 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 cover 2.1 would be arranged in the IC circuit board housing 21 according to FIG. 5 on the upper side (B side) 21.1 . This cover is not absolutely necessary. If available, it can be connected at the corner points via plated-through holes 15 to the lower GND pad 24 .

In FIG. 6 bridge covers are shown, which are installed prior to the insertion of the IC, that is, are arranged under the IC. IC 14 and cover 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 cover's soldering points are adapted for through-mounting. In Fig. 6, corresponding covers for SO housing ( Fig. 6.1, 6.2, 6.3, 6.4) and for QFP and PLCC housing ( Fig. 6.6, 6.7) are shown for surface mounting.

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

The bridge cover 2 can be extended with short-circuit rings 12 (FIGS . 6.5, 6.7) which enclose the pin areas of the IC. This type of cover 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.

Bridge covers 2 , which are arranged above IC 14 , are shown in Fig. 7.2, 7.3, 7.4. The covers have a GND connection IC pin 19 (for surface and push-through installation; in the picture surface assembly), which are arranged at the corner points or other points distributed on the outer edges and which are connected on the circuit board 20 to GND.

The bridge cover 2 of FIG. 7.4 consists of several ren short-circuit rings 12 whose conductors are connected nodular at the center 12.1 and which are closed on the GND-system of the circuit board (module) 20.

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

In Fig. 8 different embodiments of Kan tenbrückenabdeckungen 2.3 are shown. Call clamps 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 cover 2.3 , but several times between the ends.

Reference list

1

- bus ladder trains

2nd

- conductive surfaces, covers, bridge covers

3rd

- GND (ground)

4th

- pin-shaped GND connections

2nd

5

- solder resist

6

- opening in the solder resist,

6.1

GND connections of the PCB,

6.2

GND connections of the bridge

7

- Air gap / isolation gap

8th

- Spacer knobs on the bridge

2nd

9

- Insulating cover

10th

- solder joint

11

- backing material

12th

- short-circuit ring

13

- capacitors

14

- IC package

15

- plated-through hole

16

- PIN area

17th

- Edge of the short-circuit ring

18th

- IC connections of the IC lying over the bridge

19th

- IC PIN

20th

- PCB

21

- PCB housing for IC construction

21.1

- PCB, top conductor pattern

21.2

- PCB, lower circuit diagram

22

- bond wires

23

- Chip

24th

- Bridge connection to circuit board

25th

- contact springs

26

- Top contacting

26.1

- Top

27

- Pads

28

- metal foil

Claims (16)

1. Arrangement for blocking the electromagnetic radiation in printed circuit boards, IC and printed circuit board housings for the IC construction, in which the conductor tracks ( 1 , 22 ) are covered and this cover in the form of conductive strips and / or surface elements ( 2 , 12 ) in a distance of up to about 1.5 mm is arranged, and these covers ( 2 , 12 ) cover at least one surface side of the conductor tracks ( 1 , 22 ), and at least at their corner points or on their sides with the GND system ( 3 ) of the associated module are connected. 2. Arrangement according to claim 1, characterized in that the application of the covers ( 2 , 12 ) is carried out as an SMD component in surface mounting, or in the case of push-through mounting the covers ( 2 , 12 ) have pin-shaped GND connections ( 4 ). 3. Arrangement according to claim 1 or 2, characterized in that the covers are designed as bridges ( 2 ) made of one or more 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,

consist. 4. Arrangement according to claim 1 or 2, characterized in that the cover is designed as a closed thin metal plate in the manner of a short-circuit ring ( 12 ), the opening width of the ring transverse to the conductor track ( 1 , 22 ) being less than 3 mm. 5. Arrangement according to one of claims 1 to 4, characterized in that for conventional IC housing ( 14 ) the covers ( 2 , 12 ) are arranged externally above or below the IC housing ( 14 ). 6. Arrangement according to claim 5, characterized in that the bridge cover ( 2 ) arranged under the IC housing ( 14 ) is expanded with short-circuit rings ( 12 ). 7. Arrangement according to claim 5 and 6, characterized in that the short-circuit rings ( 12 ) enclose 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 6 or 7, characterized in that the short-circuit ring ( 12 ) is guided separately around one or more IC ( 14 ). 9. Arrangement according to claim 5, characterized in that the above the IC housing ( 14 ) arranged bridge cover ( 2 ) as a GND connection ( 6.2 ) IC PIN ( 19 ) for a surface and Durchsteckmon days. 10. The arrangement according to claim 5, characterized in that the cover consists of a plurality of short-circuit ring segments ( 12.1 ), the conductors of which are connected in the form of a node in the middle, 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 4, characterized in that for the execution of covers ( 2 , 12 ) within printed circuit board housings ( 21 ) for the IC structure at least one metallic layer ( 2.2 ) in the IC or in the chip ( 23 ) is introduced, which is guided at the corner points or in the case of a metallic layer in the chip via bonding wires to the IC pin ( 19 ) lying in the corner points of the housing ( 21 ) and via these corner points with GND ( 3 ) of the circuit board ( 20 , 21.2 ) is connected. 12. The arrangement according to claim 11, characterized in that the chip ( 23 ) is applied to a bridge cover ( 2.1 ) which covers the bus conductor runs ( 1 ) of the chip ( 23 ) and the bonding wires ( 22 ) on one side and the cover ( 2.1 ) at the end points via plated-through holes ( 15 ) and IC-PIN ( 19 ) to GND ( 3 ) of the circuit card / module ( 20 ), as well as the plated-through holes of the bus conductor cables ( 1 ) / IC connections on the top ( 21.1 ) of a short-circuit ring ( 12 ) is surrounded and on the underside of the IC ( 21.2 ) there is another bridge cover ( 2.2 ) which covers a bus located on the circuit card / module ( 20 ) under the IC area by applying the IC. 13. An arrangement according to claim 11, characterized in that the chip (23) is arranged inside the circuit card housing (21) for the IC structure on a bridge cover (2.2) and the printed circuit card housing (21) of a small square or rectangular two-sided There is a printed circuit board ( 21.1 , 21.2 ), the underside ( 21.2 ) having the IC-PIN ( 19 ), a bridge cover ( 2.2 ) and the IC-PIN ( 24 ) in the corners of the cover as the conductor pattern, and the lower surfaces of the Cover connections ( 24 ) serve as IC PIN for surface mounting on printed circuit boards ( 20 ) and the inside of the IC PIN ( 19 ) represent contact areas for the bond wires ( 22 ) leading to the chip ( 23 ). 14. Arrangement according to claim 11, characterized in that the chip ( 23 ) is externally applied to the underside of the bridge cover ( 2.2 ) and bonded from the outside, the layer of the underside ( 21.2 ) being arched out into the interior of the printed circuit board and the chip ( 23 ) is arranged sunk. 15. An arrangement according to claim 13, characterized in that a second bridge cover (2.1) is net angeord in the PCB housing (21) on the top (21.1) and this cover (2.1) at the corner points by vias (15) with the lower GND Pad is connected. 16. The arrangement according to claim 1, characterized in that for blocking the edge fields of printed circuit boards ( 20 ) metallic clasp-shaped bridge covers ( 2.3 ) on the edge of the printed circuit board ( 20 ) are attached, which with the GND system ( 3 ) of the printed circuit board ( 20 ) are in contact, the actual cover tongue-like overlapping the IC ( 14 ) located in the edge area close to the top of their housing.