WO2014173514A1

WO2014173514A1 - Circuit board and method for producing a circuit board

Info

Publication number: WO2014173514A1
Application number: PCT/EP2014/001038
Authority: WO
Inventors: Lutz Rissing
Original assignee: Gottfried Wilhelm Leibniz Universität Hannover
Priority date: 2013-04-24
Filing date: 2014-04-17
Publication date: 2014-10-30
Also published as: DE102013007042A1

Abstract

The invention relates to a circuit board having a substrate (2) made of an electrically insulating substrate material or an electrically conductive substrate material having a coating made of an electrically insulating material, at least one electronic component (28) and/or at least one electrical conductor (8) for electrically contacting the at least one electronic component (28), wherein the at least one electrical conductor (8) is disposed in a conductor recess (6) which extends in a surface (4) of the substrate (2).

Description

title

Printed circuit board and method for producing a printed circuit board Description

The invention relates to a printed circuit board with a substrate made of an electrically insulating substrate material or an electrically conductive substrate material with a coating of an electrically insulating material, at least one electronic component and / or at least one electrical conductor for electrically contacting the at least one electronic component. The invention also relates to a method for producing such a printed circuit board.

Such circuit boards have long been known from the prior art and are used in particular for so-called high-temperature electronics. This includes circuits whose service operating temperature exceeds the usual range of up to 125 ° C continuous temperature load. Of course, such printed circuit boards are also suitable for conventional electronic components that are not operated in this extreme temperature range.

Insofar as the substrate material is an electrically conductive material, it is insignificantly soft with this electrically conductive substrate material

CONFIRMATION COPY a coating of the electrically insulating material is provided. It is only important that the substrate material is electrically insulated against the at least one electronic component and against the at least one electrical conductor in order to avoid short circuits. It is also irrelevant which electrically insulating material is used and which thickness has the applied coating. The choice of both the materials used and the required layer thickness is easily possible for a person skilled in the art on the basis of his specialist knowledge, so that further explanations are dispensed with. If an electrically insulating substrate material is mentioned below, this also means an electrically conductive substrate material with an electrically insulating coating.

High-temperature electronic components can be divided into two categories. On the one hand there are sensors and logic modules which are supposed to record local states of larger systems and process them by signal technology. They are used on site in a hot environment and must function properly at the prevailing temperature. For example, such sensors and logic devices in the powertrain of a car, which may have up to 175 ° C, on the exhaust of a car whose temperature can reach up to 650 ° C or used for example in throttle valves, which can reach up to 200 ° C.

On the other hand, high-temperature electronic components include power modules that generate high power losses from their own function and thus are heated to high temperatures. In particular, these components are now increasingly used in the form of modular systems in which the individual functional units are integrated into subsystems. Intelligent modules also contain, for example, control, monitoring and protective electronic components. Among other things in these applications, the printed circuit boards described here can be used. On the substrate of the electrically insulating substrate material while the electronic components used are arranged, which are contacted by corresponding conductor tracks or conductors. For this purpose, a full-surface layer of an electrically conductive material, for example copper, is conventionally applied to the substrate, with the individual conductor tracks subsequently being etched out of the full-area copper layer. This results in a comparatively cost-intensive production process, in which case additionally the etching solutions used have to be disposed of, whereby the cost expenditure is again increased. From DE 24 51 299 A, therefore, a method for producing such printed circuit boards is known, in which the division of the closed, electrically conductive surface in ducts and connection surfaces takes place mechanically. This happens, for example, by a machining.

As an alternative, the individual electronic components may also be provided, for example, by means of soldered connections in which the electrical contacting is effected by the solder, or by so-called bonding wires which are fastened to both points to be connected, for example by soldering. An overview of corresponding production processes and their weaknesses can be found, for example, in the journal "Microelectronics Reliability" 49 (2009), 1250-1255.

The contacting of the individual electronic components represents one of the main problems in generic printed circuit boards. The heat, which is produced in particular with power components, must be dissipated in order to avoid overheating of the electronic component. Since the printed circuit boards conventionally consist of a large number of very different materials, such as, for example, metals, ceramics, thermal compounds and cooling elements, some of which have very different thermal expansion coefficients, load also to mechanical stresses in the component. However, it should be noted that even a component made of only a single material is subjected to mechanical stresses caused by the temperature gradient occurring during the dissipation of the resulting heat. In addition to the high thermal load and the mechanical stress can lead to a breakage of solder joints or the tearing off of bonding wires. In this case, the corresponding electronic component is disabled and must be replaced if necessary with high cost and effort.

From DE 196 42 488 A1, therefore, a method for producing flat multi-chip modules and thin-film circuit boards is known, in which the electronic components are characterized by a very flat design. These particularly flat components are embedded in special sinks flush in synthetic resin plates, which form the substrate. The contacting of these elements takes place at contact points that point to the top of the substrate and thus can be contacted from above. For this purpose, an insulating layer is first applied to the sunk electronic components, which consists of a UV-structured dry solder mask. This contact holes are made possible to the chip contacts, so that the contacting of the recessed chips is made possible by a subsequent full-surface metallization.

From DE 26 36 408, however, a printed circuit board with conductor tracks made of an insulated wire is known whose geometric position is defined and permanent to each other. In this case, insulated wires are used, wherein penetrated at the contact points, the insulating layer and a gas-tight electrically conductive connection between the wire conductor and the associated component is formed.

DE 101 34 562 B4 also deals with a system and a method for electrical contacting and mechanical fastening of printed circuit boards. Again, cutting or insulation displacement elements are used.

All of these methods have in common that first a full-surface, conductive layer is applied, and then the areas that should not be available as a conductor, are removed again. This results in a complicated and expensive production process. Due to the different height profiles of the individual components or the bonding wires used for contacting occurs due to the mechanical stress caused by the thermal stress, often to functional failures due to broken solder joints, torn wires or other errors in the contact.

The invention is therefore based on the object to present a printed circuit board and a cost-effective method for producing such a circuit board in order to inexpensively realize a variety of materials for producing a thermally and mechanically stable circuit board with integrated conductors of large cross-sections while allowing contacting at least one electronic component ,

The invention solves this problem by a printed circuit board according to the preamble of claim 1, which is characterized in that the at least one electrical conductor is arranged in a conductor recess extending in a surface of the substrate. This has the advantage on the one hand that no full-area electrically conductive, for example metallic, coating has to be applied to the substrate made of the electrically insulating substrate material, which subsequently has to be structured or removed such that the desired printed conductors remain on the substrate layer. The complex structuring process of the full-surface conductive coating is thus eliminated. On the other hand, these countersunk electrical conductors can also be used for contacting the electronic components, so that the conductors are designed in this way can be sufficiently dimensioned for the large electrical power consumed by particular power devices.

With the present invention, it is possible to further develop a printed circuit board so that a contacting of the at least one electronic component is easily possible and this contacting withstands the occurring mechanical and thermal stresses particularly well.

Advantageously, the at least one electronic component is also arranged in a component recess in the surface of the substrate.

The electronic component advantageously has at least one contact point with which the at least one electrical conductor is connected for electrical contacting. Preferably, a depth of the conductor recesses and a depth of the component recess are coordinated so that the electrical conductor and the at least one contact point are positioned at the same height relative to the surface of the substrate. This means that no height difference must be overcome for contacting the at least one electronic component, as is conventionally the case with electronic components which are arranged on the surface of the substrate. Such differences in height lead in the electrical conductors in particular in the corners and creases, which are required by the difference in height, particularly strong mechanical and thermal stresses, which are a frequent source of error. In addition, in this embodiment, the electrical conductor and the electronic component together are almost completely surrounded by the electrically insulating substrate material. A movement of the individual components relative to each other due to the mechanical stress caused by the different thermal expansions is therefore almost impossible, so that a breakage of the joints due to these mechanical movements can be almost certainly excluded. Advantageously, the upper side of the at least one electrical conductor is flush with the surface of the substrate. In a particularly preferred embodiment, this also applies to an upper side of the at least one electrical component. This means that no or only very small three-dimensional structures or elevations are present on the surface of the substrate, so that, for example, further necessary coatings in the form of insulating or electrical layers can be applied particularly easily. For this purpose, the surface can be ground or polished after the introduction of the at least one electrical conductor and / or the at least one electronic component. In this way, the individual circuit boards are good and easy to stack, so that they can be arranged on or one above the other and are thus used in a particularly space-saving manner.

Preferably, the substrate has at least one channel in which a cooling element is arranged. As already stated, in particular in power electronics, immense electrical power is sometimes converted into thermal energy. To avoid overheating of the components, this heat must be dissipated. Conventionally, the substrate is placed on a cooling element for this purpose. In order to improve the thermal contact here, a thermal paste or a sintered layer can be used. If conventionally the electronic components are placed on the surface of the substrate, the heat must first be passed through the substrate before it can be fed to the actual cooling element via the thermal paste or the sintered layer. However, if, as in the present case, the at least one electronic component and / or the at least one electrical conductor are recessed into the surface of the substrate, the thickness of the substrate naturally decreases at this point. For this reason alone, better heat dissipation is possible, as this route takes the heat through the substrate must pass through, is less than is the case with printed circuit boards of the prior art. In addition, however, it is possible to arrange at least one channel in the substrate, which extends, for example, between the respective component recess or conductor recess and the opposite surface of the substrate. If a cooling element is introduced here which has good thermal conductivity, the removal of the heat from the power component can be further accelerated and improved.

The cooling element is not limited to solid elements, such as metal wires, such as copper, limited, which can be used as cooling elements due to their good heat transfer property. Also, liquids or gases which are used as cooling fluid are understood in the present case as a cooling element in the context of the invention. These can flow or be pumped through the respective channel and thus also provide for heat dissipation. Of course, the individual measures can be combined to ensure the best possible heat dissipation.

Advantageously, the at least one channel is part of a refrigeration cycle system in which a liquid or gaseous cooling medium is circulated. Since it can be a closed system, despite the high electrical power and water as a coolant quite possible, which makes a particularly simple and inexpensive design possible. The heat can be conducted, for example, to a heat pipe, in particular a copper heat pipe, via the cooling element.

In a printed circuit board according to an embodiment of the present invention, the at least one conductor recess may also be formed so as not to be opened to the top of the substrate. In this case, it may be, for example, a tunnel or channel, in for example, can be introduced from a side surface of the substrate from the at least one electrical conductor. Again, for the purposes of the present invention, this is a conductor groove that extends in the surface of the substrate, even if there is no direct access from the surface of the substrate.

An inventive method for producing such a printed circuit board comprises the following steps: a) introducing the at least one conductor recess in the surface of the substrate of the substrate material, b) introducing the at least one electrical conductor in the at least one conductor recess.

First, therefore, the required conductor recesses and, if desired, the required component recesses for the respective electronic components can be introduced into the substrate material. This happens, for example, by machining. The at least one electrical conductor and the possibly present electronic components can be used in particular subsequently in the wells thus created. This ensures that the often sensitive components are not damaged or destroyed during the optional machining for the desired wells.

Advantageously, the at least one electrical conductor is positively inserted into the at least one conductor recess. For this he is in particular clipped or inserted. If the conductor recess is, for example, a rectilinear depression, the at least one electrical conductor can also be introduced from a side surface of the substrate into the groove-shaped depression, for example. However, such positive and / or non-positive connections are not limited to substrates made of a ceramic material. Sub- Polymer-based or other electrically insulating materials are conceivable. By inserting or clipping the electrical conductors in the respective conductor recess a simple and environmentally friendly and therefore cost-effective connection between the substrate and the electrical conductor is achieved. In particular, the cross section of the conductor recess is chosen so that a clip connection can be made. Such a connection refers to a compound in which at least one of the two components to be connected is elastically deformed during connection and later recoils into the original shape. The two components jam, for example, geometriebedingt. In particular, rounded, elastic deformation regions are to be favored in order to avoid mechanical stress peaks and thus to reduce the probability of breakage.

As a particularly advantageous embodiment of the conductor recess has a achtförmig in cross-section groove has been found. Such grooves can be introduced with a corresponding form cutter in a single operation in the substrate. By segmented embodiments of these grooves, in which the individual conductors are formed overlapping at their ends, it is also possible to provide non-linear conductor tracks, which consequently do not run along a straight line in the substrate.

For example, silicate compounds are suitable as spanable ceramics which are used as the preferred substrate material, since they have a comparatively high modulus of elasticity combined with high temperature resistance.

The introduction of the at least one electrical conductor into the at least one conductor recess can be done particularly advantageously by pouring liquid conductor material into the already existing conductor recesses. This is the material from which the electric Conductor should exist, for example, copper, melted and introduced in the liquid state in the existing conductor wells. Subsequently, the liquid conductor material is cooled and solidified. This results in a particularly good and easy to manufacture fixation of at least one electrical conductor in the corresponding Leitervertie- tion. Alternatively, of course, an already introduced in the solid state in the conductor recess electrical conductor, for example, be melted, so that here comes the subsequent cooling the particularly good and easy to produce fixation and attachment of the electrical conductor in the conductor recess to conditions.

Advantageously, the at least one electrical conductor is fastened in the conductor recess, in particular adhesively bonded. In addition, it is possible, for example, to arrange an intermediate layer of a polyimide between the at least one electrical conductor and the conductor recess or the substrate material. This has an increased flexibility, so that the thermal expansion of the at least one electrical conductor can be at least partially absorbed. This also reduces the mechanical stresses in the circuit board and thus increases the temperature resistance. Of course, it is also possible to glue, solder or otherwise secure the at least one electrical conductor in the conductor recess.

In a further advantageous embodiment, the at least one electrical conductor is introduced into the at least one conductor recess before the ceramic substrate is fired.

This is particularly advantageous if it is not necessary to use straight-lined conductor depressions into which the respective electrical conductor can not be inserted from the side in a particularly simple manner. For this case, for example, an eight-shaped groove in cross-section has proved to be advantageous as a conductor recess. In Different ceramic green sheets are each provided with straight depressions into which the respective individual segments which are to form the electrical conductor later are already inserted. Due to the eight-shaped cross-section of the recess and an electrical conductor can be used, which also has an eight-shaped cross-section. Here, the lower area serves as a stabilizing foundation, which centers the electrical conductor in the recess and locked in a form-fitting manner. The individual segments may be formed overlapping so that the protruding upper portion of one segment of the electrical conductor builds up pressure on the adjacent lower portion overlapped by it so that upon firing of the ceramic material a connection is created between the two conductor segments , so that an electrical conductor is created. For this purpose, it is possible to cover the individual overlapping surfaces, for example with a solder, so that it comes here to intermetallic phases between the individual segments, while at the same time the individual ceramic green sheets are joined during firing into a single ceramic component.

In addition, when burning the ceramic material with the introduced electrical conductor, for example, a direct bonded copper (DBC) are generated, so that a particularly stable connection between the ceramic and the copper is achieved.

Tests have shown that when using temperature-resistant polymer substrates an intermetallic compound of the individual conductor segments is not necessary. Just by the mechanical tension of the individual segments to each other and the pressure applied to each other thereby there is sufficient electrical contact between the individual conductor segments, so that an electrical conductor is formed. The segmentation of the electrical conductors also has the advantage that at higher temperatures, the expansion of substrate and electrical conductor caused by the different coefficients of thermal expansion can be compensated by the provision of expansion joints.

In the same method step, in which the conductor recesses and / or the component recesses are introduced into the substrate, the channels and other depressions for cooling elements and other components to be arranged on the substrate can also be introduced.

The invention also achieves the stated object by a method for producing a printed circuit board described here, comprising the following steps: a) positioning the at least one electrical conductor in a desired position,

b) wrapping the at least one electrical conductor with the substrate material,

c) forming the substrate with the at least one conductor recess by curing the substrate material.

First, therefore, some or all of the electrical conductors and / or some or all of the electronic components are positioned as they are to be located later in the finished substrate. In this case, the particular desired three-dimensional shape and optionally designed in three dimensions course of individual electrical conductors can be specified and realized particularly simple, since initially no conductor recesses must be introduced into an already existing substrate. In particular, in the case of winding, bent or otherwise complicated electrical conductors, this represents a significant advantage. Only in the next method step, the so arranged at least one electrical conductor is coated with the substrate material. This can be done in different ways and with different materials. Thus, liquid or powdery substrate material can be used as well as kneadable and moldable solid substrate material. In particular, for liquid and powdery substrate material, it is advisable to use an enveloping mold, within which the at least one electrical conductor is arranged and into which the substrate material is now introduced in the second method step.

Only in the third step, the thus introduced substrate material is cured, so that the substrate is formed, which now completely or at least partially surrounds the electrical conductor positioned in the first step and so to a particularly easy to produce, yet solid connection between the substrate and the electrical conductors leads.

Suitable substrate materials are liquid or liquefiable materials, such as, for example, plastics or epoxy resins, which, for example, cure in a reactive manner in the last process step. This curing can be done by supplying heat or UV radiation. Other, in particular, inorganic liquids such as, for example, melted aluminum oxide can also be used. Particularly in the case of liquid or liquefied substrate materials, it makes sense to encase the electrical conductor which has been arranged in the desired position in the first method step, for example by injection molding with the liquid material. As already explained, it is also possible to use other materials, for example ceramic materials, which may be present in liquid or liquefied form.

When a powdery substrate material is used, the curing may be performed, for example, by sintering or by complete fusion the introduced powder, which envelops the at least one electrical conductor, happen by subsequently curing this molten powder again. Particularly in the case of ceramic materials, it makes sense to use wrought and moldable materials which cure even without further external influence, for example without the supply of heat or UV radiation. This has the advantage over curing by sintering or melting and subsequent cooling of an introduced powder that no additional energy is needed. Such a manufacturing process is therefore inexpensive and environmentally friendly.

Of course, in addition to the at least one electrical conductor, all other devices and elements to be arranged in or on the substrate can also be positioned in the first method step. This includes in addition to the electrical conductors and electronic components or cooling elements, such as cooling channels. The fact that all these elements can be positioned before the substrate material is arranged, a free positioning and a complicated route for both the electrical conductors and for cooling channels and cooling elements in a particularly simple manner can be produced.

In an advantageous embodiment of the method described here, the substrate material is a ceramic material which is fired after the introduction of the at least one conductor recess, after the introduction of the at least one electrical conductor or for forming the substrate. In particular, in cases where the substrate material is fired together with the electrical conductor, there is a particularly intimate connection of the two materials together, so that a particularly stable shape of the circuit board is formed. In the event that the at least one electrical conductor is introduced into a conductor recess of an already existing substrate, consequently, the conductor recesses and / or the component recesses can be introduced into the corresponding ceramic green sheet from which the substrate is to be formed, before it is burned achieved its final stability and strength. This can be done for example by machining in a known manner.

The inventive method for producing the printed circuit board, the number of required process steps is greatly reduced while reducing the susceptibility to failure of the electrical connection produced.

The present invention thus provides a printed circuit board which is inexpensive to produce and allows both integrated cooling and the generation of strong conductor cross-sections. At the same time, rapid mechanical structuring and transfer to low-temperature substrates is possible. The method enables the use and processing of materials suitable for high temperatures, whereby a high thermal load capacity of the printed circuit board is achieved.

With the aid of a drawing, an embodiment of the present invention will be explained in more detail below. It shows:

FIG. 1 shows a substrate and an electrical conductor of a printed circuit board according to a first exemplary embodiment of the present invention;

FIG. 2 shows a substrate according to a second exemplary embodiment of the present invention,

Figure 3 - the schematic representation of conductor segments and Figure 4 - a sectional view through a printed circuit board according to another embodiment of the present invention.

FIG. 1 shows a substrate 2, which is produced from an electrically insulating substrate material and has a surface 4. In this surface 4 is a conductor recess 6, which is formed in the embodiment shown in Figure 1 in the form of a groove with an eight-shaped cross-section.

Above the substrate 2 is an electrical conductor 8, which has the same cross section as the conductor recess 6. The electrical conductor 8 can be introduced into the conductor recess 6 in various ways. First, it can be clipped from above into the conductor recess 6. Since both the electrical conductor 8 and the conductor recesses 6 have a waist 10, there is a positive connection between the electrical conductor 8 and the conductor recess 6. Alternatively, the electrical conductor 8 through an opening 12, through which the conductor recess 6 ends in a side surface 14 of the substrate 2, are inserted. This is particularly useful for the case shown in Figure 1, when the conductor recess 6 and the electrical conductor 8 extend along a straight line.

FIG. 2 shows the substrate 2 with the surface 4 in which the conductor recess 6 is located. This now has a branch 16, which leads to a component recess 18. In the conductor recess 6 and the associated branch 16 electrical conductors 8 can now be introduced, by which it is possible to electrically contact a component not shown in Figure 2, which is inserted into the component recess 8, electrically. By way of example, this component can be a power component that develops a large amount of heat during operation. In order to be able to dissipate these, a channel 20 is located in the substrate 2 through which a cooling medium or a cooling element can be passed.

FIG. 3 shows the schematic representation of two segments 22, which each have an upper portion 24 and a lower portion 26.

If the two segments 22 are pushed together so that the upper part 24 of the right-hand segment 22 in FIG. 3 comes to rest on the lower part 26 of the left-hand segment 22 in FIG. 3, an electrical conductor 8 can be produced by connecting the two segments 22 , This is of particular interest in the case when segments 22 already introduced into corresponding conductor recesses 6 are to be connected to an electrical conductor 8, for example, when a ceramic substrate material is fired.

FIG. 4 shows the sectional representation through the substrate 2 with the surface 4. The conductor recess 6 and the component depression 18 can be seen. The electrical conductor 8 is located in the conductor recess 6, while a component 28 is arranged in the component recess 18. The respective depth of the conductor recess 6 and the component depression 18 is adapted to one another such that the upper sides of the electrical conductor 8 and the component 28 terminate flush with the surface 4 of the substrate 2 on the one hand, and the electrical conductor 8 and the component 28 on the other hand can be arranged so that the electrical conductor 8 is arranged at the same height as a contact point 30 of the component 28. Thus, a contact of the component 28 by the electrical conductor 8 is possible without a height difference must be overcome, which leads to kinks and curves and thus to increased mechanical and thermal loads.

Below the component recess 18 are three channels 20 through which a coolant can be passed. Alternatively, they may also be filled with a cooling element, such as a copper wire, which due to its good thermal conductivity dissipates the heat emitted by the component 28 heat.

LIST OF REFERENCE NUMBERS

2- substrate

4- surface

6-conductor recess

8- electrical conductor

10- waist

12 - opening

14- side surface

16- branch

18-component recess

20-channel

22 segment

24- upper part

26- lower share

28- component

30- contact point

Claims

claims:

1. PCB with

a substrate (2) made of an electrically insulating substrate material or an electrically conductive substrate material having a coating of an electrically insulating material,

at least one electronic component (28) and / or at least one electrical conductor (8) for electrically contacting the at least one electronic component (28),

characterized in that the at least one electrical conductor (8) is arranged in a conductor recess (6) which extends in a surface (4) of the substrate (2).

2. Printed circuit board according to claim 1, characterized in that the at least one electronic component (28) in a component recess (18) in the surface (4) of the substrate (2) is arranged.

3. Printed circuit board according to claim 2, characterized in that the at least one electronic component (28) has at least one contact point (30) to which the at least one electrical conductor (8) is connected for electrical contact, wherein a depth of the conductor recess (6) and a depth of the component recess (18) are coordinated so that the electrical conductor (8) and the at least one contact point (30) are positioned at a same height relative to the surface of the substrate.

4. Printed circuit board according to one of the preceding claims, characterized in that an upper side of the at least one electrical conductor (8) with the surface (4) of the substrate (2) terminates in alignment. Printed circuit board according to one of the preceding claims, characterized in that the substrate (2) has at least one channel (20) in which a cooling element is arranged.

Method for producing a printed circuit board according to one of the preceding claims, comprising the following steps:

a) introducing the at least one conductor recess (6) into the surface (4) of the substrate (2) from the substrate material,

b) introducing the at least one electrical conductor (8) into the at least one conductor recess (6).

A method according to claim 6, characterized in that the at least one electrical conductor (8) is arranged in a form-fitting manner in the at least one conductor recess (6), in particular clipped into it.

Method according to one of claims 6 or 7, characterized in that the at least one electrical conductor (8) in the conductor recess (6) attached, in particular glued.

A method of manufacturing a printed circuit board according to any one of claims 1 to 5, comprising the steps of: a) positioning the at least one electrical conductor (8) in a desired position,

b) wrapping the at least one electrical conductor (8) with the substrate material,

c) forming the substrate (2) with the at least one conductor recess (6) by curing the substrate material. Method according to one of claims 6 to 9, characterized in that the substrate material is a ceramic material which, after the introduction of the at least one conductor recess (6), after the introduction of the at least one electrical conductor (8) or for forming the substrate (2 ) is burned.