WO2002093258A1

WO2002093258A1 - Method for producing stamping tools

Info

Publication number: WO2002093258A1
Application number: PCT/CH2002/000250
Authority: WO
Inventors: Philippe Steiert; Walter Schmidt
Original assignee: Elmicron Ag
Priority date: 2001-05-14
Filing date: 2002-05-08
Publication date: 2002-11-21

Abstract

The invention relates to a method for producing hot-stamping tools. Said method is essentially characterised in that a primary mould is used, comprising grooves for the strip conductors and mechanically produced recesses for the holes and microholes. The tool is produced from said primary mould by means of galvanic moulding.

Description

METHOD FOR THE PRODUCTION OF EMBOSSING TOOLS

The invention relates to the field of the production of printed circuit boards and analog connecting substrates. Specifically, the invention includes a method for producing tools for an embossing process, in particular a hot embossing process, according to the definition of the independent claims.

Modern circuit boards and analog connection substrates, such as high-density interconnects (HDI), multi-chip modules (MCM) and also so-called interposers - substrates such as chip-scale packages (CSP) or ball grid arrays (BGA) are characterized by an ever higher packing density, which at the same time requires the use of microholes and ever finer conductor structures. At the same time, the pressure towards lower costs and also towards environmentally neutral processes and materials is constantly increasing.

Conventional methods for producing the microholes are based either on laser drilling, plasma processes or photochemical processes. The processes for producing the conductor structures use practically 100% photochemical processes, combined with subtractive etching of the metal layers to be structured. These processes have a number of technical disadvantages and also in terms of costs, and they are also not without problems in terms of the environment, so that new, better processes are sought. Such a new method is described in the application PCT / CHO 1/00004, in which the process of hot stamping is used for structuring and at the same time for producing the microholes. This process not only allows the very economical production of such substrates, but is also suitable for producing the finest conductor structures with a high yield in a very environmentally friendly manner.

The manufacture of the embossing tool, on the other hand, is not trivial, since it must contain the fine structures and other properties, such as the service life and flatness, also play an important role.

Such tools are usually produced using the so-called LIGA technology, which requires parallel X-rays to expose the photoresists used. These can practically only be provided by synchrotron systems, which understandably increases the costs for tool manufacture massively.

For this reason, the low-cost LIGA technology (LC-LIGA) was developed, which uses parallel UV light for exposure. This can massively reduce costs. Figures la to lg show the essential steps for producing such a tool. The method described is known per se and is also used in a modified form for the production of precisely shaped micro parts, such as gears, etc.

The starting point is usually a doped silicon wafer or a glass plate 1 coated with an electrically highly conductive metal 3 (FIG. 1 a). This is coated with a special photoresist 5, the thickness of which is precisely defined (FIG. 1b). Then the photoresist 5 is exposed through a corresponding mask 7 by means of parallel UV light 9 (FIG. 1c) and then developed (FIG. 1d). By using a special resist and the parallel UV light source, it is possible to ensure that even the finest structures are imaged very precisely, the structures produced having very precise, rectangular cross sections.

So that metal can be deposited homogeneously not only on the exposed areas of the conductive base layer, but also on larger areas of the resist 5, the surface must be covered beforehand with a thin, conductive layer 11 made of copper or another metal (Fig. Le). This layer can either be produced chemically or by vapor deposition or sputtering. A metal, usually hard nickel, is then electrodeposited on this structure, the original 3 and the vapor-deposited metal layer 11 serving as the base and thus as the cathode.

The depressions created in the resist are filled bubble-free (Fig. Lf). The deposition lasts until a homogeneous, continuous metal layer 13 is formed, which can then be removed from the carrier (FIG. 1g). It should be noted that all the structures produced have exactly the same height, since the resist is of the same thickness in all areas.

In many applications, however, structures are required that are of different heights, ie many embossed structures must have areas of different depths. The production of such multi-layer tools is even more difficult because two photo steps are necessary. FIGS. 2a-2f schematically show the essential steps for producing an embossing tool with two structures of different heights. The production process is identical to FIG. 1 until the first structured resist layer 5 is produced (FIGS. 2a and 2b). After the development of the first layer of photoresist 5, a second layer 5 'is applied and this is exposed and developed analogously to the first. After application of the electrically conductive metal layer 11 (FIG. 2d), hard nickel is again deposited (FIG. 2e) and thus a two-stage tool 13 ′ (FIG. 2f) is produced.

It is clear that this manufacturing process is quite complex. In addition, it often proves to be a disadvantage that it is not possible to produce conical but rather cylindrical or cuboid shapes.

It is therefore an object of the invention to provide a method for producing embossing dies which not only enables the tools to be produced much more economically, but also opens up the possibility of producing different, for example conical, structures from rectangular structures.

This object is achieved by the invention as defined in the independent claims.

The method according to the invention for producing hot stamping tools is essentially characterized in that a master mold is produced which has grooves for the conductor tracks and mechanically provided depressions for the holes and microholes. The tool is produced from this original form by means of galvanic molding. A major advantage of the method is that any hole shape and size can be shaped using suitable plunge-cut tools. The production of tools with combinations of different elevations with different sizes / shapes is also easily possible. This massively improves the flexibility and economy of the manufacturing process.

In the following, exemplary embodiments of the invention are described in somewhat more detail on the basis of schematic drawings. Show in the drawings

- Figures la to lg a method according to the prior art

- Figures 2a to 2f another method according to the prior art

FIGS. 3a to 3f a first exemplary embodiment of the method according to the invention (method A)

FIGS. 4a to 4e a second exemplary embodiment of the method according to the invention (method B)

- Figures 5a to 5h, a third embodiment of the inventive method (method C)

FIGS. 6a to 6e a further exemplary embodiment of the method according to the invention (method D) FIGS. 7a to 7e another exemplary embodiment of the method according to the invention (method E),

Figure 8 shows the original form produced according to the method E as an intermediate product in a partially sectioned view and

FIG. 9 shows a piercing tool as can be used for method E.

A first exemplary embodiment of the method according to the invention (method A) enables the production of embossing tools with theoretically any number of height levels. According to this example, a metallic preliminary product formed as sheet metal is assumed. For example, a copper sheet with a thickness of 0.3 to approx. 2 mm is used as the starting material (FIG. 3a). In a first step, indentations 21.1, 21.2 are made in the preliminary product 21, with simple piercing using a suitable tool 23, 25 taking place at precisely defined locations (FIG. 3b).

The piercing tool 23, 25 can have any desired, for example conical, angular shapes. For example, it can be conical or pyramid-shaped. Chisel-shaped tools are also possible. The depth of the impressions can be limited by the tool itself. The machine that generates these impressions can also be designed so that the depth can be set with the help of control software.

3b shows two impressions of different depths. Of course, you can create any number of different depths if necessary. These impressions are more or less punctiform, that is, they represent local, punctiform depressions that are used in the embossing tool, for example, to produce microholes or screenings. The impressions are between 5 and 100 μm deep. Experience has shown that the metal is compressed with such small impressions and not or hardly noticeably displaced, so that there are no crater edges.

A photoresist 27 is then applied analogously to the known method described above, this is exposed through a mask and then developed. FIG. 3c shows the archetype 30 that is created as a result. The mask naturally has to be registered against the already existing impressions (that is, the photoresist layer must not cover it after development and removal), but this is not a problem.

In order to achieve a homogeneous metal deposition, it is also recommended in this method to coat the entire surface with a conductive metal layer 29 (FIG. 3d) onto which the hard nickel layer 31 is then applied galvanically (FIG. 3e). The galvanic deposition of material is preferably carried out until an essentially smooth and flat surface (rear surface) 31.1 has been created. After the separation and cleaning, the embossing tool 31 is ready to be used (FIG. 3f).

With regard to the galvanic filling of structures which may also be pronounced and the achievement of a smooth surface 31.1 even for thin layers, reference is made here, inter alia, to patent application PCT / CH01 / 00004. This reference also applies to all the methods described below and in particular also to variants where part of the tool is made of copper. - ö -

The advantages of the process are obvious:

Use of a very inexpensive carrier material (copper sheet)

The copper sheet has a thermal expansion of 19 ppm / ° K which corresponds exactly to the value of nickel. As a result, there are no tensions between the two metals, as is common with the combination of Si or glass with nickel. This leads to an improvement in the flatness of the tools.

All that is required is a photochemical process, although multi-stage tools can be manufactured. There is therefore no need for a second exposure mask.

- The deepest structures are to be made conical in this process, which makes it easy to remove the embossing mold. In addition, the deposition of hard nickel is much easier to do without the installation of cavities.

A second embodiment of the method according to the invention (method B) is shown in FIGS. 4a to 4e. This differs from the method essentially in that the electrodeposited metal layer is made in two layers. The archetype 30 of FIG. 4a corresponds here to the archetype of FIG. 3c. After coating with a conductive metal 29 (FIG. 4b), a metal 41 with high hardness (hard nickel) is deposited in a first deposition. Although this material has the advantage that it guarantees a long service life of the embossing tool, on the other hand it is relatively poorly planarized during electroplating and rear surfaces are created which are relatively uneven. In such a case, the galvanically deposited metal part on the back would have to be planarized by grinding or lapping in order to ensure that the embossing tool lies flat on the stamp.

If a softer nickel layer 43 or a copper layer is subsequently applied after a layer thickness of approximately 100-300 μm hard nickel, the deposition can be influenced by certain additives in such a way that very flat rear surfaces 43.1 are created.

If copper is used as the second metal, this also has the advantage that the vertical thermal conductivity of the metal composite can be increased significantly. This is particularly advantageous because during hot stamping, the heat has to be transferred to the material to be stamped via the heated press stamps via the tool. In the case of thick tools made of nickel, this would represent a relatively high thermal resistance and accordingly a temperature jump, i.e. the temperature of the press punches would have to be chosen higher, which would have a negative effect on the service life of the heating rods.

The method C according to FIGS. 5a to 5h allows the production of a multi-stage embossing tool with only one photochemical process and also eliminates the conductive layer, which is usually generated by a vapor deposition process.

The starting point is a copper sheet 51 analogous to the previous method (FIG. 5a). This is coated with a thin layer of a photoresist 53 (FIG. 5b), which is exposed and developed through a mask in accordance with conventional methods (FIG. 5c). Usually the generated image contains only that Conductor structures, while the punctiform structures for the microholes are not yet included.

In a conventional etching process, the copper is now etched in accordance with the resist structure. Due to the isotropic nature of this wet-chemical process, there is an undercut, so that rounded, conical grooves 51.1 are formed (FIG. 5d). The resist is stripped (FIG. 5e) and then the punctiform depressions 51.2, 51.3 can, as already described above, be produced mechanically, different depths again being possible (FIG. 5f).

In this case, a conductive layer is no longer required, but nickel 55 can be deposited directly (FIG. 5g).

This method can also be combined with method B, ie the tool can also have two or more metal layers.

The advantages are:

Use of conventional methods for the photochemical structuring of the resist. For example, no parallel UV light required and conventional resists can also be used.

Elimination of the evaporated conductive layer. The structured copper sheet can be viewed as a master die, from which practically any number of embossing tools can be molded. If a stamping tool has a defect, a new tool can be produced quickly and inexpensively. This is in contrast to archetypes, which still have insulating (resist) material on their surface, which structure may not be retained when the tool is detached, and which would in any case have to be newly coated with conductor material.

- The etched, conical recesses also produce correspondingly shaped recesses in the material to be embossed. This makes it much easier to detach the embossing tool.

Method D described below with reference to FIGS. 6a to 6e differs from method C in that a plastic film 61 is used as the starting material instead of a copper plate (FIG. 6a). This makes it possible to produce the depressions 61.1 for the conductor tracks directly by means of laser ablation (FIG. 6b). The essentially punctiform depressions 61.2, 61.3 for the holes / microholes can be made mechanically, for example, as in the methods described above. Alternatively, they can also be generated using laser ablation. Since the plastic film is in most cases electrically non-conductive, it must be covered with a conductive layer 63 prior to electroplating (FIG. 6c). However, electrically conductive plastics can also be used, which makes the application of the conductive layer unnecessary.

After electroplating, the tool 65 (FIG. 6d) can be removed directly (FIG. 6e). This method can also be combined with method B. - 1Z -

In principle, a copper base would also be possible in this case if correspondingly short-wave UV lasers are available. The removal rate is considerably lower than that of plastic, but then no additional conductive layer is required and the copper plate can also be used as a master for further deductions.

Although the generation of the embossed structures by means of sequentially working laser ablation is very time-consuming, this method only requires software data and is therefore very flexible and very appropriate for small series and prototypes.

Method E (FIGS. 7a to 7e) differs from method D in that the depressions are generated mechanically both for the microholes and for the conductor tracks.

A metal sheet 71 or also a plastic film made of a plastically deformable plastic, which depending on the plastic that is subsequently hardenable after the deformation process, can be used as the starting material.

While the recesses 71.1 for the microholes are produced by simply pressing in a correspondingly shaped tool, conductor tracks are one-dimensionally extended structures which can also run in different directions.

The method must therefore be modified in such a way that the tool 73 for pressing the conductor structures 71.2 into copper or plastic is shaped like a chisel. The cutting edge of the Meisseis is in the direction of the ladder to align and the impressions can then be carried out overlapping, which in total leads to grooves.

FIG. 8 shows the spatial representation of two impressions for microholes 71.1 and three grooves 71.2, which were produced by a chisel-shaped press-in tool according to FIG. 9. By turning this insertion tool accordingly, grooves can be formed in any direction.

In principle, the chisel-shaped indentation tool can have almost any cross section. The width of the insertion tool in cross section may not only taper in the direction pointing away from the material to be machined - in the coordinate system shown in the figure in the x direction. In addition, the cross section in the direction of the conductor path - in the z direction - must of course be essentially constant except for any tapering at the edge.

Furthermore, it is also possible to produce the smallest grooves by machining processes, which in turn can then be molded using hard nickel.

Claims

PATENT CLAIMS

1. A method for producing an embossing tool for embossing conductor track structures and holes and / or microholes in a substrate by pressing holes in a preliminary product with an indenting tool, introducing extensive depressions for conductor tracks into the preliminary product and then galvanically embossing the stamping tool is molded.

A method according to claim 1, characterized in that the preliminary product is metallic.

3. The method according to claim 1, characterized in that the preliminary product is a plastic film or a plastic plate.

4. The method according to any one of the preceding claims, characterized in that, in order to provide the expanded depressions, the preliminary product is covered with a photoresist layer of defined thickness after the holes or microholes have been pressed in, which layer is subsequently structured in such a way that recesses at the locations arise where holes or

There are microholes, as well as at those points where the extended recesses for the conductor tracks are to be created, and that the original shape thus created is provided with a thin conductor layer before molding. - 10 -

A method according to claim 2, characterized in that the substantially unstructured metallic preliminary product for providing the extensive depressions is covered with a photoresist layer, that this photoresist layer is then structured so that there are recesses at the locations where the depressions for the conductor tracks are to be created so that the recesses are then etched, whereupon the photoresist material is removed and the recesses for the holes / microholes are mechanically made.

6. The method according to claim 3, characterized in that the extended depressions for the conductor tracks are made by laser ablation.

Method according to one of claims 1 to 4, characterized in that the extended depressions for the conductor tracks are also made mechanically with a chisel-shaped insertion tool.

8. A method for producing an embossing tool for embossing conductor track structures and holes and / or microholes in a substrate, by introducing essentially punctiform depressions for the holes and / or microholes into extensive depressions for the conductor tracks by a preliminary product made of a polymer material and then the preliminary product is provided with a thin conductive layer and the embossing tool is electroplated, the essentially punctiform depressions and extensive depressions being preferably made mechanically or with laser ablation.

9. The method according to any one of the preceding claims, wherein in the galvanic molding of the tool, a first layer of a hard metal is electrodeposited in a first step and a second layer of a less hard metal is deposited in a second step, the tool at least includes these two layers.

10. The method according to any one of the preceding claims, characterized in that the galvanic deposition is carried out until a substantially flat and smooth rear surface is formed.