WO2018069319A1

WO2018069319A1 - Method for producing a multi-layered printed circuit

Info

Publication number: WO2018069319A1
Application number: PCT/EP2017/075812
Authority: WO
Inventors: Angelika Schingale; Markus Ochs; Karsten Meier; Mike Röllig
Original assignee: Continental Automotive Gmbh
Priority date: 2016-10-11
Filing date: 2017-10-10
Publication date: 2018-04-19
Also published as: DE102016219733A1

Abstract

The invention relates to a method for producing a multilayered printed circuit, the individual printed circuit layers (3, 7) being provided with metallic conductor structures having contact points (4) that have a uniform thickness of at least 5 µm across the printed circuit surface and at least the first printed circuit layer (3, 7) having bores (5) with metalized walls that are in electrical contact with the contact points (4) of the metallic conductor structure or form such a contact point (4). The method comprises the following steps: a) a structured prepreg layer (1) is applied to a first printed circuit layer (3), said structured prepreg layer exposing the contact points (4) of the metallic conductor structures, b) applying a second printed circuit layer (7) to the prepreg layer (1), c) if necessary, applying additional prepreg and printed circuit layers to the stack formed, d) laminating the at least two printed circuit layers (3, 7) and the at least one prepreg layer (1) such that contact points (4) of the first printed circuit layer (3) and of the printed circuit layer (7) to be connected come into contact, e) heating, during lamination, the stack to a temperature below the melting temperature of the metal of the contact points (4), f) applying a solder resist layer (8) to each outer layer of the stack, and g) subsequently remelting the metal of the contact points (4) at a temperature above the melting temperature thereof.

Description

description

Method for producing a multilayer printed circuit board Printed circuit boards are carriers for electronic components. They serve the mechanical attachment and connection of the electronic components. A circuit board is made of electrically insulating material with conductive connections adhering thereto, the tracks. Fiber-reinforced plastic is common as insulating material. The tracks are usually etched from a thin layer of copper. The components are soldered to solder pads, the so-called contact pads, or in pads. There are a variety of different PCB types. For example, one-sided and two-sided printed circuit boards are known in which electrically conductive connections are applied either only on one surface or on the two opposite surfaces of the printed circuit boards. In so-called multilayer printed circuit boards or multi-layer printed circuit boards Leiterzugstrukturen are arranged in multiple layers both on and inside the circuit board. To produce several thin circuit boards are glued to each other with so-called prepregs. These multilayer printed circuit boards can have up to 48 layers. In the field of automotive applications 4 to 8 layers are common. Connections of the connecting layers between the individual layers are by means of so-called

Realized through contacts. The production of single-sided or double-sided, optionally plated-through, printed circuit boards is usually photochemical. The manufacture of the conductor tracks is performed by photolithography, as a rule, by a thin layer lichtempfind ^¬ union photoresist is applied to the surface of the first fully metallized circuit board. After loading ^¬ clearing of the photoresist through a mask with the desired layout of the trace pattern are depending on the photoresist, either the exposed or the unexposed portions of the lacquer soluble in a suitable developer solution and are removed. If the circuit board thus treated is introduced into a suitable etching solution, only the exposed part of the metallized surface is attacked. The parts covered by the photoresist are retained because the resist is resistant to the etching solution. Subsequently, the copper layers can be galvanically reinforced after etching in order to achieve the desired layer thickness. In addition, metallic protective and contact layers made of tin, nickel or gold can be applied galvanically on partial surfaces or the entire copper surface. Then a solder mask is applied, which covers the tracks and leaves only the solder joints.

The production of multilayer printed circuit boards is also associated with a variety of wet chemical processes. For example, after the pressing of a multilayer layer structure into the outer material layer (s) introduced holes are filled by wet-chemical processes, so as to establish a contact individual conductor or connecting layers. As part of a wet chemical process usually copper is deposited in a galvanic. In addition to high demands on process safety, a wet-chemical process is also associated with many ecological aspects. In these acids, alkalis, toxic chemicals are used. Partly the disposal of hazardous waste is required.

It would therefore be desirable if the production of a multilayer printed circuit board with the least possible number of wet-chemical processes could take place.

DE 694 31 740 T2 discloses the production of a multilayer wiring board in which, according to FIGS. 7 and 8, a plurality of printed circuit board layers are pressed together, wherein contact points of the printed circuit board layers are connected to plated-through holes. The pads are provided with connection pads or bumps, both of which are multilayer coated using electrolytic nickel plating and electrolytic gold plating. Layering and in the case of the connection bumps with additional electrolytic tin plating and electrolytic gold plating are produced in sequence. These are very complicated wet chemical processes.

It is the object of the invention to avoid this disadvantage.

The object is achieved by a method for producing a multilayer printed circuit board in which the individual printed circuit ^¬ tenlagen are provided with metallic conductor structures having contact points, which have a uniform thickness of at least 5ym over the PCB surface, and at least a first printed circuit board layer holes metallized with Has walls which are in electrical contact with the contact points of the metallic conductor structure or form such a contact point, in which

a) a structured pre-preg position is applied to the first printed circuit board layer, leaving the contact points of the metallic conductor structures free,

b) is placed on the prepreg layer, a second printed circuit board layer on ^¬,

c) if appropriate, additional prepreg and printed circuit board layers are applied to this stack,

d) the at least two printed circuit board layers and the at least one prepreg layer are pressed so that contact points to be connected of the first printed circuit board layer and the second printed circuit board layer come into contact,

e) is heated during the compression of the stack up to a temperature below the melting point of the metal of the contact points,

f) a solder stop layer is applied to the outer layers of the stack,

g) and then the metal of the contact points is remelted at a temperature above its melting temperature. Thus, the connections between the printed circuit board layers and possibly their bores for the production of plated-through holes in the printed circuit board are produced by the direct contact of the contact points of the printed circuit board layers. The metal of the contact points is remelted by pressure and heat during pressing, so that the contact points of different circuit board layers connect by forming intermetallic boundary layers, without further material would be necessary.

In this way it is very easy vias through the entire board, or even up to Lei ^¬ terstrukturen realized on an inner layer by only the metal of the contact points generated by the edge of Bohrungswandmetallisierung are pressed by pressure and heat to an intermetallic barrier layer.

In a variant of the method according to the invention, in step e) the stack is heated up to a temperature above the

Melting temperature of the metal of the contact points heated and this remelted, wherein the step g) is omitted.

The pressing and remelting takes place in one operation. In a development of the invention, the holes are filled with a material from the group of materials solder, adhesive, polymer or sintered material after step e) in a step e ^x ) and this then remelted or cured.

If necessary, the holes can be completely filled.

The invention will be described below with reference to exemplary embodiments with the aid of figures. Show

FIGS. 1 to 8 show the individual steps of a first variant of the method according to the invention, FIGS. 9 to 11 show a first alternative to the steps of FIG

FIGS. 7 to 8,

FIGS. 12 and 13 show a second alternative to the steps of FIGS

FIGS. 7 to 8,

FIGS. 14 and 15 show a third alternative to the steps of FIGS

FIGS. 7 to 8. In FIGS. 1 to 8, a first variant of the method according to the invention for producing a multilayer printed circuit board with plated-through holes is shown in a schematic manner. The dimensions of the individual components are not measured ^¬ scale, but should only illustrate the procedure.

1 shows a prepreg layer 1, which is patterned according to FIG. 2, in that openings 2 are introduced into the prepreg layer 1 by drilling, punching, cutting, etc., which provide the connection surfaces required for the vias to be produced on a first structured circuit board layer 3 to share according to FIG. 3. The first printed circuit board layer 3, which is cleaned, etched and dried before laying, has in a conventional manner conductor track structures and contact surfaces and holes 5 with metallized walls.

In accordance with the invention, the edges of the bore wall metallization lying on the printed circuit board outer side and further regions to be connected to other printed circuit board layers are formed as contact points 4 with a minimum thickness of 5ym, so that the two contact points 4 of two adjacent circuit board layers 3, 7 to be joined together have a total thickness of have at least 10ym. The contact points are released 4 on the first printed circuit board layer 3, the prepreg 1 is applied to the first patterned conductor ^¬ board layer 3 of FIG. 3, so that in particular through the holes 2. According to FIG. 4, a second structured printed circuit board layer 7 is positioned on the prepreg layer 1. This stack construction is processed in a subsequent pressing step according to FIGS. 5 and 6 (with vacuum assistance).

According to FIG. 7, a solder stop layer 8 is applied to the surfaces of the stack and optionally structured. Subsequently, as shown in FIG. 8, a remelting of the metal of the contact points 4. If, as shown in FIG. 8 worked with remelting, the

Temperature of the pressed material at the end of the pressing profile, after curing of the prepreg layer 1 and before cooling briefly brought above above the melting temperature of the metal of the contact points 4.

In FIGS. 9 to 11, the process is shown when, prior to the application of the solder stop layer 8 and the remelting of the metal of the contact points 4, a filling material 9 is introduced into the bores 5. The filler 9 may be a solder, an adhesive, a polymer or a sintered material, which is remelted or cured after introduction.

Subsequently, in turn, a Lotstoppschicht 8 is applied to the outer surfaces of the resulting circuit board, which can also be done in a known manner by lamination, spin or curtain coating as in the other variants.

In the figures 12 and 13 a further variant of he ^¬ inventive method is shown in which takes place the remelting of the metal of the contact pads 4 before application of the solder resist layer. 8 Here, the temperature is already increased during the pressing over the melting phase of the material of the con ^¬ tact stations 4, so that the intermetallic boundary layers can arise

Finally, FIGS. 14 and 15 show a third variant of the method according to the invention, which is a combination of the first and the second variant, in which the remelting of the Metal of the contact points 4 takes place during the pressing and then before applying a Lotstoppschicht Füll ^¬ material 9 is introduced into the holes 5. The invention takes advantage provided with bores, ready struc tured ^¬ as mechanically and electrically connecting printed circuit board layers (inner and outer layers) to form throughput contacts in multilayer printed circuit boards. Through the use of structured prepreg layers and sufficiently thick contact points, an electrical connection is created during the pressing of the aforementioned circuit board layers or in a downstream temperature process (soldering or curing) in addition to the mechanical one. It completely eliminates any form of galvanic generation of the electrical feedthroughs.

Claims

claims

A method of producing a multilayer printed circuit board in which the individual circuit board layers (3, 7) are provided with metallic conductor structures having contact points (4) which have a uniform thickness of at least 5 μm over the circuit board surface, and at least a first circuit board layer (3). 3, 7) has bores (5) with metallized walls, which are in electrical contact with the contact points (4) of the metallic conductor structure or form such a contact point (4), in which

a) on the first printed circuit board layer (3) a structured prepreg layer (1) is applied, the contact points (4) of the metallic conductor structures leaves free,

b) a second printed circuit board layer (7) is applied to the prepreg layer (1),

d) the at least two printed circuit board layers (3, 7) and the at least one prepreg layer (1) are pressed so that contact points (4) to be connected come into contact with the first printed circuit board layer (3) and the second printed circuit board layer (7), e) during the compression of the stack is heated up to a temperature below the melting temperature of the metal of the contact points (4),

f) a solder stop layer (8) is applied to the outer layers of the stack,

g) and then the metal of the contact points (4) is remelted at a temperature above its melting temperature.

2. The method of claim 1, wherein in step e) the stack is heated up to a temperature above the melting temperature of the metal of the contact points (4) and this is remelted and the step g) is omitted.

3. The method of claim 1 or 2, wherein after step e) at a step e ^x ) the bores (5) with a material (9) filled from the group of materials solder, adhesive, polymer or sintered material and this subsequently umge ^¬ molten or cured.