WO2003069966A1

WO2003069966A1 - Method for the production of a semi-finished product for a printed board, semi-finished product, and printed board

Info

Publication number: WO2003069966A1
Application number: PCT/EP2003/000410
Authority: WO
Inventors: Udo Bechtloff; Johannes Schauer
Original assignee: Ksg Leiterplatten Gmbh
Priority date: 2002-02-11
Filing date: 2003-01-16
Publication date: 2003-08-21
Also published as: DE10205592A1; AU2003205619A1; DE10205592B4

Abstract

Disclosed is a method for producing a semi-finished product (30) for a printed board comprising strip conductors having different thicknesses. The inventive method consists of the following steps: a metal layer (2) is applied on a substrate (1); a face (4) of the metal layer (2) is thinned in a surface (3) area thereof in order to configure a sector (5) receiving strip conductors with a metal layer having a first thickness and another sector (6) receiving strip conductors with a metal layer having a second thickness, the two thicknesses being different; and an essentially even outer surface is formed on the face (4) of the substrate (1) by applying an insulating substrate layer (7) on the metal layer (2), which at least partly covers both the sector (5) receiving strip conductors with a metal layer having a first thickness and the other sector (6) receiving strip conductors with a metal layer having a second thickness.

Description

Process for producing a semi-finished product for a printed circuit board, semi-finished product and printed circuit board

The invention is in the field of printed circuit boards.

The increasing variety of electronic assemblies that are created with the help of printed circuit boards places high demands on the complexity and variability of the printed circuit boards used. There is an increasing need for printed circuit boards which have conductor tracks with different conductor track thicknesses. Conductor paths with differing conductor path thicknesses expand the assembly options of the circuit boards.

In known methods, in order to produce the different conductor track thicknesses, additional conductor track material is applied galvanically to a part of existing conductor tracks which originally have a uniform thickness. The conductor material is usually copper. As a result of the galvanic application of the additional conductor material, unevenness occurs on the surface of the circuit board to be assembled, so that the planarity of the circuit board surface desired for the assembly is lost.

The object of the invention is to provide an improved method for producing a semi-finished product for printed circuit boards and a printed circuit board, which (which) enables the formation of a planar assembly surface.

The object is achieved according to the invention by a method for producing a semifinished product for printed circuit boards with conductor tracks of different thicknesses, the method comprising the following steps: providing a substrate with a metal layer; Thinning out the metal layer in the area of a surface on a front side of the metal layer to form a partial area for conductor tracks with a first metal layer thickness and another partial area for conductor tracks with a second metal layer thickness, the first metal layer thickness being smaller than the second metal layer thickness; and forming a substantially flat outer surface on the front side of the substrate with the aid of the application of an insulating substrate layer on the metal layer, which at least partially covers the partial region for conductor tracks with the first metal layer thickness and the other partial region for conductor tracks with the second metal layer thickness. According to a further aspect of the invention, the semi-finished product thus created is used to produce a printed circuit board.

According to another aspect of the invention, a printed circuit board with a plurality of conductor tracks of different thickness is created, with a height of the plurality of conductor tracks of different thickness, in which the plurality of conductor tracks extend above an outer surface formed by an insulating substrate layer, for all of the plurality of conductor tracks in the is essentially the same.

An essential advantage which results from the invention compared to the prior art is that a semi-finished product is produced which, on the one hand, has regions for printed conductors of different thicknesses, but on the other hand has an outer surface which, when the semi-finished product is used for producing a printed circuit board despite the creation of conductor tracks with different thickness when structuring allows the formation of a planar assembly surface. This is achieved in that the substrate layer is applied to the thinned and therefore uneven surface on the front of the substrate used. The surface of the metal layer of the semi-finished product opposite the thinned surface is flat and is available for structuring the conductor tracks. The areas created here for conductor balm structures have the same height above the substrate layer of the semifinished product, but extend at different depths into the substrate layer of the semifinished product, so that areas for conductor track structures with different thicknesses are created.

An expedient development of the invention provides that portions of the surface on the front side of the metal layer which are covered by the insulating substrate layer are surface-treated before the application of the insulating substrate layer in order to improve the adhesion of the insulating substrate layer. This improves the properties of the semi-finished product, in particular sufficient strength, for further processing.

A preferred embodiment of the invention can provide that the portions of the surface on the front side of the metal layer are subjected to a treatment for roughening the surface. In this way, the adhesion of the insulating substrate layer is effectively improved. According to one embodiment of the invention, a semi-finished product preferred for producing printed circuit boards is formed by using a metal foil as the substrate with the metal layer.

In order to be able to produce a semifinished product for a copper-based printed circuit board, it can be provided in a practical embodiment of the invention that the metal foil is a copper foil.

A preferred development of the invention can provide that the insulating substrate layer comprises a mouldable material, and that in order to form the essentially flat outer surface on the front side of the substrate, the insulating substrate layer comprising the mouldable material is pressed with the substrate, so that part of the malleable material is pressed into a space above the other portion with the second metal layer thickness. This makes it possible, even in the case of semifinished products which have a multiplicity of partial areas with different metal layer thicknesses, to create surfaces which enable the semifinished product to be used for producing printed circuit boards. The mouldable material penetrates into the spaces above the partial areas with the smaller metal layer and essentially fills them up completely, so that the semi-finished product fulfills the requirements with regard to the mechanical and electrical properties for a printed circuit board.

In a preferred development of the invention, the creation of the essentially flat outer surface on the front of the substrate is made possible in a simple manner and by means of known technologies in that an adhesive film based on a glass fabric impregnated with uncured epoxy resin is used as the insulating substrate layer.

For pressing the insulating substrate layer with the substrate, a pressing means is expediently used on a side of the insulating substrate layer facing away from the substrate, so that the insulating substrate layer can be adequately adhered to.

A preferred embodiment of the invention can provide that the metal layer for thinning is etched in the area of the surface on the front. This makes it possible to use the usual etching technique in connection with the method for producing the semi-finished product. When producing a printed circuit board using the semifinished product, the semifinished product is expediently pressed with at least one further substrate layer, the essentially flat outer surface on the front of the substrate facing the at least one further substrate layer during the pressing. In this way, the back of the substrate, which is planar, is available for structuring conductor tracks.

The invention is explained below using an exemplary embodiment with reference to a drawing. Here show:

Figure 1A is a schematic representation of a substrate with a metal layer from the side; Figure IB shows the substrate of Figure 1A with a thinned metal layer;

Figure IC is a schematic representation of a substrate layer from the side;

Figure 1D is a schematic representation of a semi-finished product with the substrate of Figure

IB and applied substrate layer according to Figure IC from the side;

Figure 1E is a schematic representation of a circuit board based on the semi-finished product of Figure 1D from the side;

FIG. 2 shows a schematic illustration of a multilayer printed circuit board after pressing using the semi-finished product according to FIG. 1D; and

3 shows the multilayer printed circuit board according to FIG. 2 after the structuring of conductor tracks.

FIGS. 1A and IB show a schematic illustration of a substrate 1 with a metal layer 2 in an initial state and after the metal layer 2 has been thinned out in a side view. The substrate 1 is, for example, a copper foil. For thinning, the metal layer 2 is processed in the area of a surface 3 on a front side 4 by means of etching, so that partial areas 5 with a first metal layer thickness and partial areas 6 with a second metal layer thickness are created, the first metal layer thickness being less than the second metal layer thickness.

The substrate 1 with the thinned-out metal layer 2 is then connected according to FIG. 1D to an insulating substrate layer 7, which is shown in an initial state in FIG. The insulating substrate layer 7 is pressed onto the surface 2 on the front side 4 of the metal layer 2. The insulating substrate layer 7, which has an adhesive film, for example The base of glass fabric impregnated with uncured epoxy resin (“prepregs”) is deformed when pressed on, so that spaces 8 in the area of partial areas 5 are filled with the first layer thickness , 10, which are placed on a front side 11 and a back side 12. The pressing plates 9, 10 are removed again after pressing in. The arrangement of insulating substrate layer 7 and metal layer 2 shown in FIG. 1D between the pressing plate 9, 10 forms a semifinished product 13 for the production of printed circuit boards with regions 14 for conductor tracks with a first conductor path thickness and regions 15 for conductor tracks with a second conductor path thickness which is different from the first conductor path thickness.

The semifinished product 13 is processed for the production of a printed circuit board 16 according to FIG. 1E. In this case, the metal layer 2 is structured to form conductor tracks 17, 18 of different thicknesses, for example by means of etching. The height at which the conductor tracks 17, 18 rise above an outer surface 19 of the printed circuit board 16 formed by the insulating substrate layer 7 is, however, essentially the same for the conductor tracks 17, 18.

Figure 2 shows a schematic representation of a circuit board 20 using the semi-finished product 13 from the side. The printed circuit board 20 is a multilayer printed circuit board which, in addition to the metal layer 2 of the semifinished product 13, has further conductor track layers 21, 22 and 23 and further substrate layers 24, 25. The arrangement of the conductor track layer 23 and the further substrate layer 25 is formed in the same way as the semifinished product 13. Known technologies can be used to produce the printed circuit board 20, for example the tendon technology or the metal resist strip technology. The use of the semi-finished product 30 shown in FIG. 2 for a multilayer printed circuit board is exemplary. The semifinished product 13 can be used for printed circuit boards of any kind which comprise one or more conductor track layers of different thickness.

The printed circuit board 20 is structured in order to form conductor tracks in the metal layer 2, for example by means of etching, so that printed conductor structures are formed, as is shown schematically in FIG. 3. In this way, conductor tracks 26, 27 with different thicknesses are created. However, the height at which the conductor tracks 26, 27 rise above an outer surface 28 of the printed circuit board 20 formed by the insulating substrate layer 7 is essentially the same for the conductor tracks 26, 27. In this way, one is used for the assembly of the printed circuit board 20 created suitable planar surface 29 with electronic components. The conductor tracks 26, 27 are shown enlarged in FIGS. 2 and 3 to explain the principles of the invention, and have thicknesses of approximately 18 μm to 35 μm and approximately 400 μm, for example, in conventional circuit boards. The described method enables the formation of very fine conductor track structures with a conductor path width of, for example, 120 μm.

The features of the invention disclosed in the above description, the claims and the drawing can be of importance both individually and in any combination for realizing the invention in its various embodiments.

Claims

Expectations

1. A method for producing a semi-finished product (13) for a printed circuit board with conductor tracks of different thicknesses, the method comprising the following steps: - providing a substrate (1) with a metal layer (2);

- Thinning of the metal layer (2) in the area of a surface (3) on a front side (4) of the metal layer (2) to form a partial area (5) for conductor tracks with a first metal layer thickness and another partial area (6) for conductor tracks with a second Metal layer thickness, wherein the first metal layer thickness is smaller than the second metal layer thickness; and

- Forming a substantially flat outer surface on the front side (4) of the substrate (1) by means of the application of an insulating substrate layer (7) on the metal layer (2), which is the partial area (5) for conductor tracks with the first metal layer thickness and the other Partial area (6) for conductor tracks with the second metal layer thickness is at least partially covered in each case.

2. The method according to claim 1, characterized in that portions of the surface (3) on the front side (4) of the metal layer (2), which are covered by the insulating substrate layer (7), before the application of the insulating substrate layer (7) for the improve the adhesion of the insulating substrate layer (7) are surface-treated.

3. The method according to claim 2, characterized in that the portions of the surface (3) on the front (4) of the metal layer (2) are subjected to a treatment for roughening the surface (3).

4. The method according to any one of the preceding claims, characterized in that a metal foil is used as the substrate (1) with the metal layer (2).

5. The method according to claim 4, characterized in that the metal foil is a copper foil.

6. The method according to any one of the preceding claims, characterized in that the insulating substrate layer (7) comprises a moldable material, and that for forming the substantially flat outer surface on the front side (4) of the substrate (1), the insulating substrate layer comprising the moldable material (7) is pressed with the substrate (1), so that part of the moldable material is pressed into a space (8) above the partial area (5) with the first metal layer thickness.

7. The method according to claim 6, characterized in that as the insulating substrate layer (7) is an adhesive film based on an impregnated with uncured epoxy resin

Glass fabric is used.

8. The method according to claim 6 or 7, characterized in that for pressing the insulating substrate layer (7) with the substrate (1) pressing means (9, 10) are used.

9. The method according to any one of the preceding claims, characterized in that the metal layer (2) for thinning in the region of the surface (3) on the front (4) is etched.

10. The method according to any one of the preceding claims, characterized in that the first metal layer thickness is in a range of about 18 to 35 microns, and the second metal layer thickness is about 400 microns.

11. A method for producing a printed circuit board (16; 20), wherein a semi-finished product (13) produced according to one of claims 1 to 10 is used.

12. The method according to claim 11, characterized in that the semi-finished product (13) with at least one further substrate layer (21, 22 or 24, 25) is pressed, wherein the substantially flat outer surface on the front (4) of the substrate ( 1) the at least one further substrate layer (21, 22 or 24, 25) faces during pressing.

13. The method according to claim 11 or 12, characterized in that a multilayer printed circuit board (20) is formed.

14. Semifinished product for a printed circuit board with conductor tracks of different thickness, in which in a metal layer (2) on an insulating substrate (7) a partial area (5) for conductor tracks with a first metal layer thickness and another partial area (6) for conductor tracks with a second metal layer thickness are formed, the first metal layer thickness being different from the second metal layer thickness, characterized in that an essentially planar surface, which can be structured to form the conductor tracks of different thicknesses, is formed on a rear side (12) and which covers the partial area (5) for conductor tracks with the comprises the first metal layer thickness and the other partial area (6) for conductor tracks with the second metal layer thickness.

15. Printed circuit board (16; 20) with a plurality of conductor tracks (17, 18; 26, 27) of different thickness, a height of the plurality of conductor tracks (17, 18; 26, 27) of different thickness in which the plurality of conductor tracks (17, 18; 26, 27) extend above an outer surface (19; 28) formed by an insulating substrate layer (7), which is essentially the same for all of the plurality of conductor tracks (17, 18; 26, 27).