WO2023075652A1

WO2023075652A1 - A method of producing a printed circuit board, and a printed circuit board

Info

Publication number: WO2023075652A1
Application number: PCT/SE2021/051080
Authority: WO
Inventors: Tony JOSEFSSON; Torbjörn DAHL; Tomas Bergsten
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2021-10-28
Filing date: 2021-10-28
Publication date: 2023-05-04

Abstract

The present invention relates to a method (100) of producing a printed circuit board (200;400;600), wherein the printed circuit board (200;400;600) comprises a first substrate (201;601) comprising a first surface; at least a second substrate (202) comprising a second surface; and the method comprises a step of laminating, which comprises: providing (S10) a conductive paste pattern (302) to one of the first and second surface; providing (S20) an adhesive pattern (301) to one of the first and second surface; joining (S30) the first substrate (201) and the second substrate (202). The conductive paste pattern (302) and the adhesive pattern (301) are positioned between the first substrate (201) and the second substrate (202),and the adhesive pattern and the conductive paste are in a non-solidified state; and solidifying (S40) the adhesive pattern and the conductive paste pattern. The present invention also relates to a printed circuit board.

Description

A METHOD OF PRODUCING A PRINTED CIRCUIT BOARD, AND A PRINTED CIRCUIT BOARD

TECHNICAL FIELD

The present disclosure relates to a method for producing a printed circuit board. More particular, the invention relates to a method of producing a printed circuit board comprising a step of laminating.

BACKGROUND

In order to facilitate increased circuit density on printed circuit boards (PCB) an increased number of layers in the PCB are used. Commonly, the top and bottom surface of the PCB are used to mount components often in the form of soldered surface mounted components. In some scenarios such as for example systems on a chip (SoC), complete circuits with a dedicated PCBs are used and the SoC is mounted on the main PCB using technologies such as flip-chip or ball grid arrays. There is also an increased interest in embedding components within the PCB to further increase miniaturization and integration. This embedding is associated with a number of challenges such as for example efficient cooling of the embedded components. In modern telecommunication equipment it is often desired to minimize the amount of wave guides used to connect a circuit to an antenna or an amplifier for example. This means that the antenna must be mounted as close as possible to the circuit and in a modern PCB design one side of the PCB is often used as an antenna substrate with antennas connected to the circuit on the other side by means of via holes. This often limits the design of the PCB since only one side of the PCB is available for mounting components. It is a great interest within the industry to have more options for integration at their disposal and especially options that allows efficient embedding of circuits in the PCB, while simultaneously provide efficient cooling.

It is therefore an object of the present disclosure to suggest an improved PCB lamination method and a PCB. SUMMARY

An object of the present disclosure is to provide a method for producing a PCB which seeks to mitigate, alleviate, or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and to provide an improved method for producing a PCB which allows dense packages of components and embedded components.

This object is achieved by means of a method of producing a printed circuit board, wherein the printed circuit board comprises a first substrate comprising a first surface, and at least a second substrate comprising a second surface. The method comprises a step of laminating, which comprises: providing a conductive paste pattern to one of the first and second surface; providing an adhesive pattern to one of the first and second surface; joining the first substrate and the second substrate, wherein the conductive paste pattern and the adhesive pattern are positioned between the first substrate and the second substrate, and the adhesive pattern and the conductive paste are in a nonsolidified state; and solidifying the adhesive pattern and the conductive paste pattern.

According to an aspect a printed circuit board is provided, wherein the printed circuit board comprises: a first substrate comprising a first surface; at least a second substrate comprising a second surface; a conductive paste pattern bonded to each one of the first and second surface; an adhesive pattern bonded to each one of the first and second surface; wherein the first substrate and the second substrate are joined, by the conductive paste pattern and the adhesive pattern.

An advantage of the present invention is that components and circuits may easily be embedded in the PCB. This is due to the fact that the formation of the PCB does not require high pressure for lamination. The first substrate and the second substrate may each be formed by conventional lamination which utilizes high pressure.

A further advantage of the present disclosure is that pressure sensitive components may be embedded in the PCB, since the laminating process is performed at low pressure and cavities with openings to the ambient air pressure may be formed. Furthermore, this allows SoC circuits to be easily embedded in a PCB according to the present disclosure.

Further objects and advantages may be found in the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particular description of the example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the example embodiments.

Figure 1 is a flowchart illustrating a method for producing a printed circuit board according to the present disclosure;

Figure 2 is a first example of a printed circuit board according to the present disclosure;

Figure 3 illustrates the conductive paste pattern and the adhesive pattern for the first example of a printed circuit board according to the present disclosure;

Figure 4 is a second example of a printed circuit board according to the present disclosure;

Figure 5 illustrates the conductive paste pattern and the adhesive pattern for the second example of a printed circuit board according to the present disclosure; and

Figure 6 is a third example of a printed circuit board according to the present disclosure. DETAILED DESCRIPTION

Aspects of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. The apparatus and method disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.

The terminology used herein is for the purpose of describing particular aspects of the disclosure only, and is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

In this disclosure the term 'solid body' should be interpreted as a body firm and stable in shape, not a liquid or fluid.

Some of the example embodiments presented herein are directed towards a method for laminating a printed circuit board (PCB). As part of the development of the example embodiments presented herein, a problem will first be identified and discussed. This problem is associated with embedding a circuit in a PCB. This circuit may for example be a pressure sensor with integrated electronics and for integration reasons the designer considers to embed the pressure sensor in a cavity of the PCB. Since the conventional formation of the PCB involves lamination under pressure the pressure sensor may easily be destroyed. This limits the designer options to place the pressure sensor on the PCB, and the conventional placement of the pressure sensor is on an outer side of the laminated PCB in order to avoid the pressure sensor from being destroyed during lamination.

Figure 1 is a flowchart illustrating a method 100 of producing a printed circuit board according to the present disclosure.

The method 100 comprises the step of laminating a printed circuit board 200;400;600, which are described in more detail in connection with figure 2-6. The printed circuit board 200;400;600 comprises a first substrate 201 comprising a first surface 205. The first substrate may be a conventional PCB with multiple layers, and the first side 205 may be a layer with a trace i.e. electrical path on the PCB. The printed circuit board further comprises at least a second substrate 202 comprising a second surface 206 which may be a layer with a trace, similar to the first surface 205.

The step of laminating comprises the following steps disclosed below:

In step S10 there is provided a conductive paste pattern 302 to one of the first surface 205 and the second surface 206.

In step S20 there is provided an adhesive pattern 301 to one of the first surface 205 and the second surface 206.

In step S30 the first substrate 201 and the second substrate 202 are joined. The conductive paste pattern 302 and the adhesive pattern 301 are positioned between the first substrate 201 and the second substrate 202, and the adhesive pattern and the conductive paste are in a nonsolidified state.

Finally, in step S40, the adhesive pattern 301 and the conductive paste pattern 302 are solidified. This may be achieved by providing heat to the printed circuit board.

Optionally, prior to the step S20 of providing the adhesive pattern 301 onto the surface. Spacer fillers 203 will be mixed into an adhesive 204 for the adhesive pattern 301. A spacer filler 203 is a solid body with a defined dimension. In other words, the spacer filler is firm and stable in shape, not a liquid or fluid. The spacer filler has a higher mechanical strength than the surrounding material. This way the distance between the first substrate and the second substrate will be set to the dimensions of the spacer filler and the first and second substrate will be parallel to each other. For example spherical spacer fillers may be used.

The step S40 of solidifying the adhesive pattern and the conductive paste pattern, may involve applying a pressure typically smaller than 0.1 N/mm2 to the printed circuit board. This pressure is significantly lower than the conventional pressure used for lamination of printed circuit boards. The step S30 of joining the first substrate 201 and the second substrate 202, may further comprise aligning the first substrate and the second substrate by means of guiding elements. These guiding elements may for example be guiding pins with corresponding guiding holes. This allows precise mounting of the first substrate relative the second substrate.

The method disclosed herein allows the step S10 of providing the conductive paste pattern such that air gaps 304 may be formed between the first substrate and the second substrate. This allows air to flow from regions between the first and the second substrate. Hence, no pressure build-up will occur during lamination of the printed circuit board due to heat.

The step S20 of providing (S20) an adhesive pattern 301 further comprises providing the adhesive pattern 301 such that air gaps 303are formed between the first substrate and the second substrate. This will enable air to flow from regions between the first substrate and the second substrate.

The step S10 of providing the conductive paste pattern may comprise printing, or dispensing, the conductive paste.

The step S20 of providing the adhesive layer may comprise printing, or dispensing, the adhesive.

According to some embodiments, the first substrate, or the at least second substrate, is provided a recess 401,602 for an embedded component 603 or for flow of a coolant such as air, prior to the step of joining S30 the first substrate and the second substrate. The recess may be located between the first substrate and the second substrate.

Figure 2 is a cross sectional view of a first example of a printed circuit board according to an embodiment of the present disclosure. The printed circuit board, generally designated 200, comprises a first substrate 201 with a first surface 205, and at least a second substrate 202 comprising a second surface 206. The printed circuit board further comprises a conductive paste pattern 302 bonded to each one of the first 205 and second surface 206. The conductive paste pattern 302 is formed by discrete regions of conductive paste 207. The printed circuit board further comprises an adhesive pattern 301 bonded to each one of the first surface 205 and second surface 206. The adhesive pattern 301 is formed from an adhesive 204 mixed with spacer fillers 203 , the spacer fillers 203 are solid bodies with defined dimensions. In other words, the spacer filler is firm and stable in shape, not a liquid or fluid. The spacer filler has a higher mechanical strength than the surrounding material. The first substrate 201 and the second substrate 202 are joined, by the conductive paste pattern 302 and the adhesive pattern 301.

Figure 3a discloses the adhesive pattern 301 from above. The cut line shown in the Figure 3a as A-A' indicates the cross sectional view illustrated in Figure 2. As seen in Figure 2 the adhesive pattern 301 is applied as discrete regions separated with air gaps 303 between the regions. The adhesive pattern may be applied by means of printing or dispensing. Similarly, in Figure 3b the conductive paste pattern 302 is shown from above and the conductive paste pattern is applied as discrete regions of conductive paste 207 separated with air gaps 304. This allows the conductive paste pattern to be configured for power or signal transmission without short circuits between neighboring conductive regions. Furthermore, it allows air flow through regions with conductive paste patterns.

Figure 4 is a cross sectional view of a second example of a printed circuit board 400 according to an embodiment of the present disclosure. The second example differs from the first example disclosed with reference made to Figure 2, and 3, in that a third substrate 402 is provided with a recess 401 that is a through hole through the third substrate 402. The third substrate 402 is arranged between the first substrate 201 and the second substrate 202. This way a circuit may be arranged in the recess 401. For example a pressure sensor may be arranged therein and the air gaps 303, 304 allow the ambient air pressure to act on the pressure sensor. Furthermore, the recess 401 may in some embodiments be used as a flow channel for a coolant such as air. Figure 5a discloses corresponding adhesive patterns 301 for the printed circuit board, and Figure 5b discloses the conductive paste pattern 302 for the second example.

Figure 6 is a cross sectional view of a third example of a printed circuit board 600 according to an embodiment of the present disclosure. The third example differs from the first example disclosed with reference made to Figure 2, and 3, in that a recess 602 is formed in the first substrate 601. This recess 602 is configured to hold a circuit 603 which is arranged therein. Optionally, the circuit 603 may be connected with a further conductive paste pattern 604 to the second substrate 202.

This disclosure relates to a method of producing a printed circuit board, wherein the printed circuit board comprises: a first substrate comprising a first surface; at least a second substrate comprising a second surface; and the method comprises a step of laminating, which comprises: providing a conductive paste pattern to one of the first and second surface; providing an adhesive pattern to one of the first and second surface; joining the first substrate and the second substrate, wherein the conductive paste pattern and the adhesive pattern are positioned between the first substrate and the second substrate, and the adhesive pattern and the conductive paste are in a non-solidified state; and solidifying the adhesive pattern and the conductive paste pattern.

According to some embodiments, prior to providing the adhesive pattern onto the surface, mixing spacer fillers into an adhesive for the adhesive pattern.

According to some embodiments, the step of solidifying comprises applying heat to the printed circuit board.

According to some embodiments, the step of solidifying comprises applying a pressure typically smaller than 0.1 N/mm2 to the printed circuit board.

According to some embodiments, the step of joining further comprises aligning the first substrate and the second substrate by means of guiding elements.

According to some embodiments, the step of providing further comprises providing the conductive paste pattern such that air gaps are formed between the first substrate and the second substrate. According to some embodiments, the step of providing further comprises providing the adhesive pattern such that air gaps are formed between the first substrate and the second substrate.

According to some embodiments, the step of providing (S10) the conductive paste pattern comprises printing, or dispensing, the conductive paste.

According to some embodiments, the step of providing (S20) the adhesive layer comprises printing, or dispensing, the adhesive.

According to some embodiments, the first substrate, or the at least second substrate, is provided a recess for an embedded component or flow, prior to the step of joining (S30) the first substrate and the second substrate.

According to some embodiments, the recess is located between the first substrate and the second substrate.

This disclosure also relates to a printed circuit board, wherein the printed circuit board comprises: a first substrate comprising a first surface; at least a second substrate comprising a second surface; a conductive paste pattern bonded to each one of the first and second surface; an adhesive pattern bonded to each one of the first and second surface; wherein the first substrate and the second substrate are joined, by the conductive paste pattern and the adhesive pattern.

In the drawings and specification, there have been disclosed exemplary embodiments.

However, many variations and modifications can be made to these embodiments. Accordingly, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the embodiments being defined by the following claims. The description of the example embodiments provided herein have been presented for purposes of illustration. The description is not intended to be exhaustive or to limit example embodiments to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various alternatives to the provided embodiments. The examples discussed herein were chosen and described in order to explain the principles and the nature of various example embodiments and its practical application to enable one skilled in the art to utilize the example embodiments in various manners and with various modifications as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products.

It should be appreciated that the example embodiments presented herein may be practiced in any combination with each other. It should be noted that the word "comprising" does not necessarily exclude the presence of other elements or steps than those listed and the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, that the example embodiments may be implemented at least in part by means of both hardware and software, and that several "means", "units" or "devices" may be represented by the same item of hardware.

In the drawings and specification, there have been disclosed exemplary embodiments. However, many variations and modifications can be made to these embodiments. Accordingly, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the embodiments being defined by the following claims.

Claims

1. A method (100) of producing a printed circuit board (200;400;600), wherein the printed circuit board (200;400;600) comprises: a first substrate (201;601) comprising a first surface (205); at least a second substrate (202) comprising a second surface (206); and the method comprises a step of laminating, which comprises: providing (S10) a conductive paste pattern (302) to one of said first and second surface; providing (S20) an adhesive pattern (301) to one of said first and second surface; joining (S30) said first substrate (201) and said second substrate (202), wherein the conductive paste pattern (302) and the adhesive pattern (301) are positioned between said first substrate (201) and said second substrate (202), and the adhesive pattern and the conductive paste are in a non-solidified state; and solidifying (S40) the adhesive pattern and the conductive paste pattern.

2. The method according to claim 1, wherein, prior to providing said adhesive pattern (301) onto said surface, mixing spacer fillers (203) into an adhesive (204) for the adhesive pattern (301).

3. The method according to any one of the preceding claims, wherein the step of solidifying comprises applying heat to the printed circuit board.

4. The method according to any one of the preceding claims, wherein the step d) of solidifying (S40) comprises applying a pressure to the printed circuit board.

5. The method according to any one of the preceding claims, wherein the step of joining (S30) further comprises aligning the first substrate and the second substrate by means of guiding elements.

6. The method according to any one of the preceding claims, wherein the step of providing (S10) further comprises providing the conductive paste pattern (302) such that air gaps(304) are formed between the first substrate and the second substrate.

7. The method according to any one of the preceding claims, wherein the step of providing (S20) further comprises providing the adhesive pattern (301) such that air gaps (303) are formed between the first substrate and the second substrate.

8. The method according to any one of the preceding claims, wherein the step of providing (S10) the conductive paste pattern comprises printing, or dispensing, the conductive paste.

9. The method according to any one of the preceding claims, wherein the step of providing (S20) the adhesive layer comprises printing, or dispensing, the adhesive.

10. The method according to any one of the preceding claims, wherein the first substrate, or the at least second substrate, is provided a recess (401,602) for an embedded component (603) or for a flow of air, prior to the step of joining (S30) the first substrate and the second substrate.

11. The method according to claim 10, wherein the recess is located between the first substrate and the second substrate.

12. A printed circuit board (200;400;600) comprising: a first substrate (201;601) comprising a first surface; at least a second substrate (202) comprising a second surface; a conductive paste pattern (302) bonded to each one of said first and second surface; an adhesive pattern (301) bonded to each one of said first and second surface; wherein said first substrate (201) and said second substrate (202) are joined, by the conductive paste pattern (302) and the adhesive pattern (301).