DE102021207599A1 - planar transformer - Google Patents

Abstract

The invention relates to a planar transformer which is embedded in a multilayer printed circuit board (1), which consists of printed circuit board layers (5) stacked on top of one another and bonded to one another, each having conductor structures (7, 9), in particular copper conductor tracks, the Planar transformer with a transformer core (17) is formed, which has a bridge part (19) on both sides of the multilayer printed circuit board (1), which merge into one another via at least one transformer core web (15), which passes through an opening (21) in the multilayer Printed circuit board (1) is performed. According to the invention, the transformer core web (15) is provided as an insert part that is separate from the bridge parts (19).

Description

The invention relates to a planar transformer according to the preamble of claim 1 and a method for producing such a planar transformer according to claim 10.

In order to achieve a high power density of voltage converters in the vehicle, planar transformers are often used, which have a low overall height compared to classic wound transformers. In order to further reduce the costs and the installation space of the planar transformers, they can be embedded directly in the printed circuit board. The transformer windings can be etched into the copper foils directly during the manufacturing process of the printed circuit board.

A generic planar transformer can be embedded in a multilayer printed circuit board. This can consist of printed circuit board layers stacked one on top of the other and connected to one another with a material fit, each of which has conductor structures, in particular copper conductor tracks. The planar transformer is formed with a transformer core. This is made up of a bridge part on both sides of the multilayer printed circuit board. The two bridge parts arranged on both sides are connected to each other via three transformer core webs. The transformer core webs are each routed through an opening in the multilayer printed circuit board.

In the prior art, the transformer core is made up of two halves, which are braced against one another using mechanical clamping elements, which is difficult to manufacture. In addition, the transformer core webs are guided through the openings in the multilayer printed circuit board with a larger hole clearance, which may have negative effects on the functionality of the planar transformer and/or lead to relative movements in a vibration test, for example. Furthermore, with the transformer core structure known from the prior art, only a limited number of degrees of freedom can be used in the manufacture of the planar transformer.

From the EP 3 605 564 A1 a planar transformer is known.

The object of the invention is to provide a planar transformer in which the number of degrees of freedom in the production process for producing the planar transformer can be increased in a simple manner and/or the functionality of the planar transformer can be increased.

The object is solved by the features of claim 1 or 10. Preferred developments of the invention are disclosed in the dependent claims.

The invention is based on a planar transformer that is embedded in a multilayer printed circuit board. This consists of printed circuit board layers that are stacked on top of one another and bonded to one another, each of which has conductor structures (i.e. copper conductor tracks). The planar transformer is formed with a transformer core. This has a bridge part on each side of the multilayer printed circuit board. The two bridge parts can merge into one another via at least one transformer core web. This is routed through an opening in the multilayer printed circuit board. According to the characterizing part of claim 1, the transformer core web is provided as an insert separate from the two bridge parts. During the manufacturing process of the printed circuit board, a setting process takes place, in which the insert part, in particular as a material coin, is inserted into the opening in the multilayer printed circuit board independently of the bridge parts. This is followed by a joining process in which the bridge parts are connected to the insert part.

According to the invention, the windings are developed directly onto the printed circuit board, as in a normal planar transformer, when creating the target printed circuit board for, for example, a control or gate driver printed circuit board for a pulse-controlled inverter. The available layers of the printed circuit board are used to integrate the primary and secondary coils (also several secondary coils). An essential aspect of the invention relates to the fact that a recess (or the opening) is provided in the target printed circuit board during the printed circuit board manufacturing process. In the further manufacturing process, the recess is closed by a sheet metal filling, i.e. by an insert part or material coin, which consists of copper, micro sheet metal or transformer sheet metal, for example. It is taken into account that there is a corresponding support surface so that the sheet material coin (e.g. micro sheet metal) can no longer fall out after the surface treatment. This can be done, for example, with a one-sided / partially quilted material coin and copper plating or during a tinning process. The use of an organic passivation at the location of the material coin is not sufficient for a material other than copper, since a tinning process has to take place to fix it.

The printed circuit board is then sealed with the solder resist (recess of the soldering areas, covered areas are insulated with it). The here The printed circuit board provided with the material coins is delivered to the assembler.

The printed circuit board that has been delivered is then further processed by the assembler as follows: The material coins are assembled with the upper and lower bridge parts (in the corresponding process steps one after the other) of the transformer sheet metal. Depending on the material used, the connection technology can be, for example: bonding, vibration welding or soldering. The other SMD or PIP components (i.e. pin-in-paste components) to be assembled on the printed circuit board are also assembled during the soldering process, for example. This means that adjustments to the layout and the use of standard components for the transformer core mean that the transformer core can be sourced from multiple suppliers and faster development can be implemented. In addition, the transformer according to the invention can be used to prevent movements of the transformer core relative to the printed circuit board (e.g. during a vibration test). According to the invention, the center of gravity of the transformer is not outside the printed circuit board, but rather close to the center point of the printed circuit board. Furthermore, the printed circuit board area requirement is insignificantly higher than with an external connection of a planar transformer. The secondary voltages can be routed further to the point to be used in the same circuit board layer. Another important aspect concerns the fact that the material coin is fixed in a metallization process by copper plating or tin plating (depending on the material used and electrochemical compatibility, other materials can also be used). The remaining transformer parts (bridge) are manufactured in the printed circuit board assembly process, for example by soldering, bonding or ultrasonic welding. According to the invention, sensors for detecting, for example, temperature, current, etc. can be integrated directly. In addition, direct routing from the planar transformer to the target circuit board is possible.

Essential aspects of the invention are described in detail below: The transformer core is designed in several parts, that is to say it consists of at least one transformer core web and two transformer core bridge parts. These can be assembled at different points in the process. For example, the insert (that is, the transformer core web) can be preassembled in the printed circuit board by a printed circuit board supplier. The pre-assembly unit formed in this way can be transferred to another plant in which the bridge parts are assembled. These can optionally be made of the same material or of different materials compared to the insert part.

With regard to a process-reliable production process, it is important if the insert part can be preassembled in the multilayer printed circuit board in a secure position. Against this background, the insert part can be glued into the opening or inserted into it with a press fit. In a variant that is preferred in terms of production technology, the following securing means can be provided for securing the position of the insert in the opening in the multilayer circuit board: The securing means can have at least one vertical stop which is formed on the inner wall of the opening in the multilayer circuit board. After the setting process has been completed, the insert part is securely supported on the height stop. In a simple embodiment variant, the vertical stop can be an inner wall step formed in the opening. At the inner wall step, a cross-sectionally enlarged inner wall section on the setting side can merge into an inner wall section of the opening with a reduced cross section. The insert part can be designed with a correspondingly contour-matched insert part section with an enlarged cross section and with an insert part section with a reduced cross section.

Alternatively and/or additionally, the securing means can have a tongue/groove connection. In the case of the tongue/groove connection, the insert part is formed in the circumferential direction with a plurality of material grooves which are spaced apart from one another and extend in the setting direction. In the pre-assembly state, corresponding material projections, which are formed on the inner wall of the opening in the multilayer printed circuit board, protrude into the material grooves of the insert part. It is preferred if the material grooves are formed in the insert part section with the enlarged cross section. In this case, the groove depth can be dimensioned in such a way that the groove bottoms merge into the insert part section with reduced cross section.

Alternatively and/or additionally, the following measure can be taken in the pre-assembly state in order to prevent the insert part from falling out of the opening in the multilayer printed circuit board. The edge of the opening in the multilayer printed circuit board can be surrounded by a potential-free copper conductor. The copper conductor track and an insert end face can be aligned approximately flush with one another. In this case, the setting process can be followed by a metallization process. In the metallization process, a metal layer made of copper or tin, for example, can be applied as a securing means to the front side of the insert part and to the copper conductor track. In common practice, the metallization process is carried out in a galvanic bath, in which, for example, copper is deposited on the multilayer printed circuit board is divorced, with the formation of the metal layer.

In the assembled state, the respective bridge part can be connected to the assigned end face of the insert part via a connecting means. The connection can be made, for example, by soldering, bonding, ultrasonic welding or the like.

In the metallization process, the external conductor structures of the multilayer printed circuit board can also be thickened, which is favorable in terms of production technology. In addition, through-plating can take place in the metallization process, in which the conductor structures of different circuit board layers (that is to say different circuit board levels) are electrically connected to one another. For example, the metallization process can be done with copper. In this case one speaks of coppering.

• 1 und 2 In unterschiedlichen Ansichten einen Planartransformator im Zusammenbauzustand;
• 3 bis 8 jeweils Ansichten, anhand derer ein Zusammenbauvorgang veranschaulicht ist.

An exemplary embodiment of the invention is described below with reference to the accompanying figures. Show it:

• 1 and 2 In different views, a planar transformer in the assembled state;
• 3 until 8th each is a view showing an assembly process.

In the 1 and 2 a finished planar transformer is shown, which is embedded in a multilayer printed circuit board 1 . Its upper side and underside are equipped with further electrical components 3 in an assembly process. The planar transformer is embedded directly into the multilayer printed circuit board 1, so that the transformer center of gravity SP ( 2 ) viewed in the thickness direction of the multilayer printed circuit board 1 is located approximately in the middle of the multilayer printed circuit board 1 . The other electrical components 3 are connected to the multilayer printed circuit board 1 using SMD technology. The multilayer printed circuit board 1 consists of printed circuit board layers 5 ( 2 ), each of which has inner conductor structures 7 and outer conductor structures 9 .

An example is the multilayer circuit board 1 in the 2 made up of a total of seven circuit board layers. Their conductor structures 7, 9 are arranged in a manner known per se with galvanic isolation between the input potential (primary side) and the at least one output potential (secondary side) such that there is generally no electrical connection between the transformer windings. The output potentials can be passed on to other layers (separately from the others) via a plated-through hole (via). If necessary, the different layers can be used for a secondary output. According to the 1 or 2 the upper outer conductor structure 9 is electrically connected to a connection point 11 of the multilayer printed circuit board 1 . A plated-through hole (via) 13 is formed in the connection point 11 .

The formed in the multilayer printed circuit board 1 conductor structures 7, 9 are according to 1 or 2 looped around a central transformer core web 15 of a transformer core 17 out. In addition, the transformer core 17 has two further transformer core webs 15 arranged outside the conductor structures 7 , 9 . The total of three transformer core webs 15 connect two bridge parts 19 to one another, which are arranged on both sides of the multilayer printed circuit board 1 . Each of the three transformer core webs 15 is through a corresponding breakthrough 21 ( 3 ) of the multilayer printed circuit board 1.

It should be emphasized that the 2 until 8th are only roughly schematic representations that only reproduce the structure of a planar transformer to the extent that it is necessary for understanding the invention. Thus, only one wide conductor track is indicated in each of the figures. In fact, however, the wide conductor track consists of a large number of turns. Also tower in the 2 , 7 and 8th the bridge parts 19 the outer insert parts 15 slightly. In an actual embodiment, the bridge portions 19 would terminate directly at the outer insert portions 15 in view of reduced material costs.

In the 2 the via 13 located at the connection point 11 is formed from a drilled hole in the multilayer printed circuit board 1 . The inside of the borehole is metallized in a metallization process with a metal layer 23 made of copper, for example, in order to electrically connect the conductor structures 7 inside the multilayer circuit board 1 to the connection point 11 . In addition, the outer conductor structures 9 are also thickened with a metal layer 23 during the metallization process in order to increase their current-carrying capacity. In addition, contacts (not shown) are also possible, which are implemented as so-called blind vias or as buried vias, which are present, for example, only in the inner layers or in a certain number of layers.

A core of the invention consists in the multi-part structure of the transformer core 17, in which the transformer core webs 15 are each provided as insert parts separate from the bridge parts 19. This results in additional degrees of freedom in the manufacturing process. The manufacturing process is shown below using the 3 until 8th described roughly schematically insofar as it is necessary for the Understanding of the invention is required. So according to the 3 First, the multilayer printed circuit board 1 is still unequipped including breakthrough 21 provided. In a setting process ( 3 ) The transformer core webs 15 are used as inserts, in particular as material coins, independently of the bridge parts 19 in the respective opening 21 of the multilayer printed circuit board 1. The insert parts 15 are dimensioned in such a way that they can be used with almost no play, specifically with the formation of a preassembled unit.

A vertical stop 25 is formed in each of the openings 21 with a view to securing the position of the respective insert part 15 in the opening 21 in the multilayer printed circuit board 1 . After the setting process has taken place, the respective insert part 15 is on the height stop 25 ( 3 ) supported. In the 3 the height stop 25 is implemented as an inner wall step, at which an inner wall section 27 of the opening 21 with an enlarged cross section on the setting side merges into an inner wall section 29 of the opening 21 with a reduced cross section. The respective insert part 15 is contour-adapted to this with an insert part section 31 with an enlarged cross section and an insert part section 33 with a reduced cross section.

How from the 3 or 4 further shows that a tongue/groove connection is realized between the respective insert part 15 and the opening 21 . For this purpose, the respective insert part 15 has a plurality of material grooves 35 spaced apart from one another in the circumferential direction, which extend in the setting direction S. In the assembled state, corresponding material projections 37 formed on the inner wall of the opening 21 in the multilayer printed circuit board 1 protrude into the material grooves 35 of the insert part 15 . The material grooves 35 are in accordance with 3 and 4 formed in the insert part section 31 with the enlarged cross section. The groove depth t is dimensioned in such a way that the bottom of the groove is 39 ( 4 ) merge flatly into the insert part section 33 with reduced cross section.

In order to ensure that the inserts 15 are not lost, the following measures have been taken: the opening edges 41 of each of the openings 21 in the multilayer printed circuit board 1 are each surrounded by a potential-free copper conductor track 43 . The copper conductor track 43 and an insert part end face 45 are aligned approximately flush with one another (when the insert part 15 is in the inserted state). In addition, the outer conductor track 9 is protected between the insert parts 15 at least by an indicated solder resist 10, so that the applied bridge parts 19 do not cause a short circuit.

After the setting process, the metallization process already mentioned takes place, in which the metal layer 23 is applied as a securing means both to the end face 45 of the insert part and to the copper conductor track 43 . Depending on the material of the insert part 15, the metal layer 23 can be copper and/or tin. The tinning takes place after the coppering as a passivation. In the event that the copper conductor track 43 and the insert part 15 have been tinned, the copper plating has been carried out first.

The setting process and the metallization process can take place in a circuit board manufacturing plant, for example. The pre-assembly unit produced ( 5 ) can be transferred to another plant where the assembly of the bridge parts 19 takes place. Depending on the joining process, the metal layer 23 ( 6 ) coated insert end faces 45 a connecting means 24 ( 7 ) are applied. A connection is then made by soldering, bonding, ultrasonic welding or the like ( 8th ). For example, bonding may not require a fastener.

Reference List

1

multilayer circuit board

3

electric components

5

PCB Layers

7

internal conductor structures

9

outer conductor structures

10

soldermask

11

junction

13

via

15

Transformer core web

17

transformer core

19

bridge part

21

breakthrough

23

metal layer

24

lanyard

25

altitude stop

27

cross-section enlarged inner wall section

29

inner wall section with reduced cross-section

31

Cross-sectionally expanded insert section

33

insert section with reduced cross-section

35

material grooves

37

material protrusions

39

groove bottom

41

opening edge

43

potential-free copper track

45

Insert end face

S

setting direction

SP

Transformer Focus

t

groove depth

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 3605564 A1 [0005]

Claims (10)

Planar transformer which is embedded in a multilayer printed circuit board (1), which consists of printed circuit board layers (5) stacked on top of one another and bonded to one another, each having conductor structures (7, 9), in particular copper conductor tracks, the planar transformer having a transformer core (17) which has a bridge part (19) on each side of the multilayer printed circuit board (1) which merge into one another via at least one transformer core web (15) which passes through an opening (21) in the multilayer printed circuit board (1) is guided, characterized in that the transformer core web (15) is provided as an insert part separate from the bridge parts (19), and in that in particular in a setting process the insert part (15), in particular as a material coin, is independent of the bridge parts (19) in the breakthrough (21) of the multilayer printed circuit board (1) can be used, and in a subsequent joining process, the bridge parts (19) to the one spare part (15) can be connected. planar transformer claim 1 , characterized in that the planar transformer has securing means for securing the position of the insert part (15) in the opening (21) in the multilayer printed circuit board (1). planar transformer claim 1 , characterized in that the securing means have at least one vertical stop (25) which is formed on the inner wall of the opening (21) in the multilayer printed circuit board (1), and that after the setting process has taken place the insert part (15) on the vertical stop (25) is supported. planar transformer claim 3 , characterized in that the vertical stop (25) is an inner wall step at which a cross-section-widened inner wall section (27) on the setting side transitions into a cross-section-reduced inner wall section (29) of the opening (21), and in that in particular the insert part (15) it has sections (31, 33) that are contour-adapted in cross-section and have a larger cross-section. Planar transformer according to one of claims 2 , 3 or 4 , characterized in that the securing means have a tongue/groove connection, in which the insert part (15) has a plurality of material grooves (35) spaced apart from one another in the circumferential direction, which extend in particular in the setting direction (S), and that in an assembled state project into the material grooves (35) of the insert (15) corresponding material projections (37) which are formed on the inner wall of the opening (21) of the multilayer printed circuit board (1). planar transformer claim 5 , characterized in that the material grooves (35) are formed in the insert part section (31) with the enlarged cross section, and in that in particular their groove depth (t) is dimensioned in such a way that their groove bottoms (39) penetrate evenly into the insert part section with the reduced cross section (33 ) pass. Planar transformer according to one of claims 2 , to 6, characterized in that an opening edge (41) of the opening (21) of the multilayer printed circuit board (1) is surrounded by a potential-free metal conductor track (43), and that in particular the metal conductor track (43) and an insert end face (45 ) are aligned approximately flush with one another, and that after the setting process a metallization process takes place, in which a metal layer (23), for example made of copper and/or tin, can be applied as a means of security. planar transformer claim 7 , characterized in that the external conductor structures (9) of the multilayer printed circuit board (1) can also be thickened in the metallization process, and/or through-plating (13) takes place in the metallization process, in which conductor structures (7, 9) different printed circuit board layers (5) can be electrically connected to one another. Planar transformer according to one of the preceding claims, characterized in that in the assembled state the respective bridge part (19) is connected to the associated end face (45) of the insert part via a connecting means (24), and that in particular the connection is made by soldering, bonding, ultrasonic welding or the like he follows. Method for manufacturing a planar transformer according to one of the preceding claims.

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