WO2021190690A1

WO2021190690A1 - Method for producing conductor track structures on a non-conductive carrier substrate

Info

Publication number: WO2021190690A1
Application number: PCT/DE2021/100199
Authority: WO
Inventors: Matthias Hildebrandt; Jan Van Aalst
Original assignee: Lpkf Laser & Electronics Aktiengesellschaft
Priority date: 2020-03-23
Filing date: 2021-03-01
Publication date: 2021-09-30
Also published as: DE102020107904B4; DE102020107904A1

Abstract

The invention relates to a method for producing conductor track structures on a non-conductive carrier substrate (1). In a first method step, an etch-resistant polymeric coating (5) is applied as an electrolytic resist to the respective base layer (2) in the carrier substrate (1) on the opposite outer sides. An electrical reinforcing layer (8) is applied to the base layer (2), in a section that is free of the etch-resistant coating (5), in accordance with the conductor track structure, said electrical reinforcing layer (8) at the same time electrically conductively connecting the opposite base layers as through-hole plating (7) in the region of possible apertures (3). Thereafter, in a manner directly adjoining the reinforcing layer (6) of the conductor track structure, a linear recess (9) is made in the resist coating (5) and the base layer (2) situated therebeneath by means of laser radiation, and the region to be removed is thermally insulated with respect to the adjacent reinforcing layer (6) of the conductor track structures. This is then heated in targeted fashion by a heat source until the adhesion of the base layer (2) on the carrier substrate (1) is significantly reduced, in order to extensively remove the base layer (2) together with the etch-resistant coating (5) from the carrier substrate (1) by way of the pressure difference (Δρ) of a suction-removal means (11) and so to produce the desired conductor track structures on the non-conductive carrier substrate (1).

Description

PROCESS FOR MANUFACTURING CONDUCTIVE TRACK STRUCTURES ON A NON-CONDUCTIVE SUPPORT SUPPORT

The invention relates to a method for the production of conductor track structures arranged in different planes on a non-conductive carrier substrate, which in each case has an electrically conductive base layer on opposite outer sides, at least in sections, an etch-resistant resist coating, in particular a galvanic resist, being applied to the outer sides, then in accordance with the generating conductor track structures on at least one outer side, in particular on both outer sides, the etch-resistant resist coating is partially removed and an electrical reinforcement layer corresponding to the conductor track structure is applied to the areas freed from the etch-resistant coating on the base layer.

The electrical contacting of integrated circuits (IGs, chips) usually takes place via a plastic board coated with a metal. In order to produce complex electronic circuit systems, through-contacts generally have to be implemented in the carrier substrate used. For example, printed circuit boards or stamped-laminated substrates are used as carrier substrates.

The through-plating from the top to the bottom of such a circuit board is often achieved through openings in the carrier substrate. These openings can also accommodate conductive contact pieces from electronic components applied to the circuit board, which contact pieces extend through the openings and thereby provide a side connection between the two outer sides. As an alternative to this, the perforations on other surfaces can also comprise a continuous metallic layer as a through-hole contact. A through-connection of two metal layers is produced to bridge a separating layer of the carrier substrate as an electrical insulator. Such vias can be used, for example, within a carrier substrate made up of several layers (package), which represents an electrical circuit and includes defined connection surfaces on the underside for contacting and receiving electrical components, such as integrated circuits.

To produce the functional conductor track structure, it is necessary in the generic method to remove the resist coating and the underlying base layer after the reinforcement layer has been applied, since this would otherwise lead to a short circuit in the conductor track structure. For this purpose, a further etching resist, for example tin, is first applied galvanically to protect the conductor track in order to protect it from undesired etching removal in the subsequent etching step. Thus, in the subsequent alkaline bath, the resist coating is removed, the so-called resist stripping, and the base layer is exposed. However, the subsequent etching of this base layer also leads to a partial underwashing of the conductor track structure, because the further etching resist previously applied to the reinforcement layer does not protect the contact area with the adjacent coating. The conductor track structure is finally exposed by removing the further etching resist by stripping the galvanically applied tin layer using sodium hydroxide solution, ammonium chloride and nitric acid.

DE 889 10884 T2 already discloses a method for the selective plating of a metal substrate, for example an electrical contact, by selectively removing a polymeric plating coating on the metal substrate by means of a laser. Here, a laser length is chosen that is strongly absorbed by the metal substrate. The metal substrate is heated, thereby causing ablative removal of the coating over the selective areas of the substrate and plating the exposed areas of the substrate.

From US 7 140 103 B2 a method for producing a printed circuit board with high density is known in which a copper foil-clad board is plated on the surface by electroless copper plating. After the entire surface has been coated by electrolytic copper plating, etching is carried out until thin sections of copper foil are removed and the base material in these sections is exposed, whereby a pattern is formed. Preferably, parts of the plating resist layer are dissolved and removed by irradiation with a UV laser beam. DE 198 11 578 A1 discloses a multi-day printed circuit board in which at least two electrically insulating support layers are arranged one above the other. From US 4501 638 A a method for producing a plated-through hole is known in which a hole is produced in an insulating layer between two metal layers by etching and then the upper layer is pressed onto the lower layer.

From DE 198 52832 A1 a method for producing a metal-plastic laminate is known in which a metal film is formed into a depression by embossing or deep-drawing and then a plastic film is laminated onto the formed metal film. The plated-through hole is made possible by bulging the metal foil in the area of a recess in the plastic foil.

The invention is based on the object of creating a way of simplifying the production of conductor track structures with plated-through holes. In particular, the undesired flushing should be avoided when removing the base layer.

This object is achieved according to the invention with a method according to the features of claim 1. The further embodiment of the invention can be found in the claims.

According to the invention, a method is provided in which, by means of electromagnetic radiation, in particular from a laser, a line-shaped recess is introduced into the, in particular, etch-resistant resist coating including the base layer underneath, the carrier substrate not being removed or only being removed to a very small depth and through the ring-shaped closed, linear recess, several areas to be removed are enclosed and thermally and electrically isolated from the adjacent conductor track structures, the recess being introduced along a respective circumference of the areas, and then the areas to be removed are heated until the adhesion of the base layer to the carrier substrate is significantly reduced and the base layer together with the etch-resistant and / or, in the case of electroplated coatings, resistant resist coating from the carrier substrate under the influence of gravity or an external force kung is removed over a large area.

According to the invention, this eliminates the process step of the etching process for removing the etch-resistant coating and, in the prior art, initially for this purpose Reinforcement layer to be applied further etching resist. Rather, an astonishingly simple way in a two-stage process is first created a linear or groove-shaped recess, which is at the same time closed in a ring around the enclosed area, for the thermal separation of the base layer from the conductor track structure built up by the reinforcement layer. Thereafter, thermal energy is introduced into the area of the base layer enclosed by the recess with the etch-resistant coating on it, which leads to rapid heating of the base layer in the enclosed area due to the thermally insulating effect of the recess and also of the carrier substrate. The energy input is continued until the base layer has reached a temperature at which the adhesive forces to the carrier substrate are reduced in such a way that the entire area can easily be separated from the carrier substrate by the action of gravity or by additional external force, for example . It has been shown that radiant heat is advantageous for the thermal energy input. The desired heating does not have to be limited to the area to be stepped off, because the low material thickness of the base layer results in a much faster temperature rise than in the conductor track structures created by the reinforcement layer. In contrast, the thermal energy is particularly preferably introduced by electromagnetic radiation directed, in particular restricted thereto, towards the areas to be removed.

In the case of the rubout method known from the prior art, there has been the restriction that the pitch must be very large for thick conductor tracks, since large material thicknesses require a high level of heat input for detachment, combined with the disadvantage that high temperatures for detachment of adjacent conductor tracks being able to lead. In contrast, according to the invention, the thin copper layer of the base layer, through which only a reduced heat input is required, allows thick conductor tracks with a low pitch to be created. Since the laser process (isolation and ruboui) is carried out according to the invention on the protected starting copper layer, the process is not influenced by the copper-plated layer. In addition, short process times, as previously only known on very thin copper layers (5 μm or 9 μm), will also be possible on galvanically reinforced circuit boards.

According to the invention, it is not necessary for the linear recesses to be introduced exactly, parallel to the course of the conductor track structure. Rather, the areas to be removed can be carried out in terms of a simplified removal process For example, continuous or convex recesses are included, so that the distance to the conductor track structure can vary in the course of the recesses.

In that, according to a particularly preferred embodiment of the invention, a plurality of openings connecting the outer sides are first made in the carrier substrate, which in each case has at least in sections an electrically conductive base layer on opposite outer sides, and then a resist coating is applied to the outer sides, spanning or covering the respective opening, which is then partially removed according to the conductor track structures to be produced including the sections including the openings on at least one outside, in particular on both outside sides, the opposite outer sides are connected in an electrically conductive manner through the openings with the electrical reinforcement layer as a plated-through hole. On the other hand, it is particularly advantageous if the electrical reinforcement layer is separated from the adjoining etch-resistant coating by making the recess, that is to say the recess is made along the contact surface between the reinforcement layer and the coating. As a result, the coating can be removed again at least almost without leaving any residue, which proves to be advantageous in particular when the electrical conductor track structure is later contacted with electronic components.

The area enclosed by the recess could be removed as a whole in order to enable a quick removal process. On the other hand, it is particularly advantageous if the area to be removed is first subdivided into several sub-areas that are thermally insulated from one another by making further linear recesses. It has been shown that in this way the removal process of the base layer can be accelerated by first creating partial areas and heating them, for example by means of laser radiation, quickly and precisely limited to the respective partial area to be removed. As a result, strip-shaped partial areas in particular can be removed significantly better, with, according to a particularly preferred variant, the area to be removed being subdivided into partial areas of largely the same size.

The respective surface of the area or partial area to be removed can be heated by means of suitable radiation, in particular laser radiation, through the resist coating directly in the base layer. In another, likewise particularly advantageous variant, the resist coating is applied after the recess has been made at least partially removed and then the base layer is flatly removed by heating and reducing the adhesive forces. Since the resist coating is removed mechanically or through the introduction of thermal energy, for example by vaporization, the resist coating can be removed with almost no residue. The base layer is then removed over the entire surface. These combined process steps further reduce the removal time.

The selection of a suitable electromagnetic radiation for making the recess can preferably be made as a function of the respective material properties. According to a particularly practical embodiment of the method, laser radiation is used as electromagnetic radiation for this purpose, with the radiation or its parameters being able to be varied if necessary in the case of a two-stage removal of the coating and the base layer.

The same radiation source can advantageously also be used in order to heat the areas to be ablated by means of laser radiation and to correspondingly reduce the adhesion of the base layer to the carrier substrate.

As a result, the base layer can be heated to the required temperature in a very short time within the area enclosed by the recesses for thermal insulation and can be removed flatly with little effort.

For this purpose, mechanical forces or gravity can be used as a support. A particularly practical embodiment is also achieved in that the heated surface is separated from the substrate by means of a targeted supply of compressed air. The heated base layer in the area is detached as a whole from the carrier substrate by means of a targeted jet of compressed air.

This effect can be further supported by the fact that the heated surface is separated from the substrate by suction, so that the detached parts are reliably removed and disposed of, so that in particular their unwanted reattachment can be excluded.

In this way, the base layer and / or the coating of the area to be removed or the partial areas as a whole can be detached from the carrier substrate, in particular over a large area Foil, For example, a polymer film is applied so that the previously introduced openings are spanned by the coating and the coating material does not penetrate into the openings. This significantly simplifies the exposure and application of the reinforcement layer in these areas.

Before the etch-resistant coating is applied, an activator is particularly preferably applied to the inner wall surface of the opening in order to improve the material structure of the reinforcement layer. In particular, the base layer can have a material thickness between 5 μm and 9 μm and the reinforcement layer can have a material thickness between 15 μm and 50 μm.

The invention allows various embodiments. To further clarify its basic principle, one of them is shown in the drawing and is described below. This shows in a flowchart with reference to FIGS. 1 to 3 the individual steps a to j when carrying out the method according to the invention, which is explained in more detail below with reference to the representations.

A double-sided printed circuit board made of a carrier substrate 1, for example made of FR4, and a 5 μm to 9 μm thick copper-clad base layer 2 on both sides serves as the starting material for carrying out the method.

In a first method step, a through-hole is made in the carrier substrate 1 and the two outer base layers 2 as an opening 3 as the basis for the subsequent through-hole plating (FIG. 1b).

For this purpose, an activator 4 for an improved galvanic layer structure is first applied to the inner wall surfaces of the openings 3 (FIG. 1c) and then an etch-resistant polymeric resist coating 5 spanning the openings 3 is applied to the respective base layer 2 as Gaivanoresist (FIG. 1d}). .

The layout of the conductor track structure to be produced is then transferred to the previously laminated resist coating 5, for example by exposure and wet washing, or by direct removal by means of laser radiation to be able to copper. For this purpose, an electrical reinforcement layer 8 corresponding to the conductor track structure is applied to the section freed from the etch-resistant resist coating 5 on the base layer 2, which at the same time electrically conductively connects the opposite base layers in the area of the openings 3 as a through-hole 7 (FIG. 2f).

Due to the galvanic construction of the conductor track structure, up to 25 μm of copper is built up in order to reliably produce the through-hole contact 7. The final thickness of the conductor track results from the sum of the base layer 2 and the galvanically built-up copper of the reinforcement layer 6.

Immediately adjacent to the reinforcement layer 6 of the conductor track structure, a linear recess 9 is made in the resist coating 5 and the underlying base layer 2 by means of laser radiation 8, the carrier substrate 1 not being removed (FIG. 2g).

Since the areas 10 to be removed are enclosed by the annularly closed, linear recess 9 and thermally insulated from the adjacent reinforcement layer 8 of the conductor track structures, they can then be heated in a targeted manner by a heat source 12 until the adhesion of the base layer 2 to the carrier substrate 1 is significantly reduced ( 2h), in order to finally remove the base layer 2 together with the etch-resistant coating 5 from the carrier substrate 1 by the pressure difference p of a suction 11 (FIG. 3i) and thus produce the desired conductor track structures on the non-conductive carrier substrate 1 (FIG. 3j).

REFERENCE LIST

1 carrier substrate

2 base layer.

3 breakthrough

4 activator

5 resist coating

6 reinforcement layer

7 through-hole plating

8 laser radiation

9 recess

10 area

11 suction

12 heat source

Δ _P pressure difference

Claims

PATENT CLAIMS

1. A method for the production of conductor track structures arranged in different planes on a non-conductive carrier substrate (1), each of which has at least in sections an electrically conductive base layer (2) on at least one outer side, an etch-resistant resist coating (5) being applied, then according to the generating conductor track structures on at least one outer side, in particular on both outer sides, the resist coating (5) is partially removed and an electrical reinforcing layer (6) of the conductor track structure is applied to the areas freed from the etch-resistant coating (5) on the base layer (2), thereby characterized in that at least one linear recess (9) is introduced into the resist coating (5) including the underlying base layer (2) by means of electromagnetic radiation, the carrier substrate {1} not being removed or only to a very small depth and being removed by the lens cover A plurality of areas (10) to be removed are enclosed and thermally insulated from the adjacent conductor track structures, the recess (9) being introduced along a respective circumference of the areas (10), and then the areas (10) to be removed are heated, until the adhesion of the base layer (2) on the carrier substrate (1) is significantly reduced in order to remove the base layer (2) together with the resist coating (5) from the carrier substrate (1) in the area (10) to be removed,

2. The method according to claim 1, characterized in that the carrier substrate (1) in each case at least in sections an electrically conductive base layer (2) on opposite outer sides, wherein a plurality of openings connecting the outer sides are first made in the carrier substrate (1) and then on the A resist coating (5) is applied to the outer sides, spanning the respective opening (3), which is then partially removed on at least one outer side, in particular on both outer sides, in accordance with the conductor track structures to be produced, including the sections opening up the openings (3), so that the electrical reinforcement layer (6) of the conductor track structure in the area of the openings (3) connects the opposite outer sides as a through-hole connection in an electrically conductive manner.

3. The method according to claim 1 or 2, characterized in that the reinforcement layer (6) is separated from the adjacent etch-resistant coating (5) by introducing the recess (9).

4. The method according to at least one of the preceding claims, characterized in that the area to be removed (10) is first divided into several mutually thermally insulated sub-areas by introducing further lens-shaped recesses (9).

5. The method according to at least one of the preceding claims, characterized in that the resist coating (5) is at least partially removed after the recess (9) has been made and then the base layer (2) is removed over the entire surface.

6. The method according to at least one of the preceding claims, characterized in that a laser radiation (8) is used as electromagnetic radiation.

7. The method according to at least one of the preceding claims, characterized in that the areas to be removed are heated by means of a laser beam (8).

8. The method according to at least one of the preceding claims, characterized in that regardless of the thickness of the electrical reinforcement layer (6) when introducing the recess (9), the process parameters, in particular the process parameters of the laser radiation (8) for the material of the base layer (2) can be set.

9. The method according to at least one of the preceding claims, characterized in that the heated base layer (2) in the region (10) is separated from the carrier substrate (1) by means of a targeted supply of compressed air.

10. The method according to at least one of the preceding claims, characterized in that the heated base layer (2) in the region (10) is separated from the carrier substrate (1) by suction.

11. The method according to at least one of the preceding claims, characterized in that the base layer (2) and / or the resist coating (5) of the area (10) to be removed or the partial areas as a whole are detached from the carrier substrate (1).

12. The method according to at least one of the preceding claims, characterized in that the resist coating (5) is applied to the base layer (2) as a dry resist, in particular by laminating a film (polymer film).