WO2002092326A1

WO2002092326A1 - Extrusion die

Info

Publication number: WO2002092326A1
Application number: PCT/CH2002/000251
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 extrusion die (1, 3) comprises a pressure plate (5, 7) and an electrically-conducting stamping die (11, 13, 41, 43) mounted thereon. The pressure plate (5, 7) comprises cooling means (9), whereas the stamping die (11, 13, 41, 43) may be directly heated, for example by electrical conduction.

Description

PRESS TEMPLE

The invention relates to the field of embossing structures on dielectric substrates, in particular in printed circuit board and connecting substrate technology. It relates in particular to stamps, a method and an embossing tool according to the preambles 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 methods for manufacturing 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.

For hot embossing of substrates, embossing tools are required which are designed as matrices and which usually contain fine structures which are to be taught to the starting product. Such are present as, for example, molded, metallic, relatively thin plates which have the structures in the form of suitable elevations. For the formation and manufacture of such embossing tools, reference is made to the Swiss patent application by the same applicant, which has the same application date as the present application. The content of this patent application is included here insofar as it relates to the design and manufacture of embossing tools. Such embossing tools are mounted on heatable and coolable embossing stamps, with two-sided embossing the two tools for the two sides having to be aligned exactly with one another. It is important that the tools fit snugly on the press rams so that the heat transfer from the ram to the tool is not inhomogeneous.

Fig. 1 shows schematically a sectional view through such an arrangement. One recognizes the two press punches 1, 3 with the press plates 5, 7, which each have a precisely controllable heating and also a cooling. The heating and cooling are indicated by round channel openings 9. In principle, such an arrangement is already known for conventional stamping tools. The press punches 1, 3 also each have an embossing tool 11, 13. The assembly of the tools 11, 13 - shown schematically here are new embossing tools - can be carried out on the stamp by a material connection, such as by soldering or gluing, these methods making disassembly very difficult. In addition, the tool can be form-fitting by using screws. Clamps etc. are attached (not shown in Fig. 1). However, this means that the embossing tools are relatively thick, since otherwise their mechanical strength is insufficient. For new, thinner embossing tools, the small thickness of the tools would make it impossible to attach mechanical fastening elements.

The figure also shows guide means 15 through which the mutual alignment of the embossing tools should be as good as possible.

A disadvantage of the arrangement shown in FIG. 1 is the relatively long distance that the heat has to travel from the heater to the embossing tool. This is associated with a relatively large thermal mass, which has to be heated up and cooled down again. This causes long cycle times, which can be up to an hour. The inertia of warming up and cooling is increased if the tools are attached with thermally insulating adhesives or if the mechanical connection is not perfectly positive.

In addition, in such an arrangement according to the prior art, the tool is relatively thick (for example 4-8 mm thick), so that it has the necessary mechanical stability, which also ensures a flat surface that lies against the press die and thus the form-fitting connection , As a result, the production of the embossing tools takes a relatively long time, for example a plating process of several days has to be accepted. In addition, the demands placed on the flatness of the rigid embossing tool are extremely high, since the depressions to be made are only a few μm to a few dozen μm deep. Bumps of, for example, 10 μm over a distance of 10 cm can make a stamping tool unusable, for example.

Another problem is the exact alignment of the two embossing tools with each other. Typically, registration is determined by trial embossing, which is assessed by a special microscope attached to the hot stamping machine. The position of an embossing tool is corrected on the basis of the evaluation of this sample embossing. This procedure is complex and often requires several trial runs.

This invention is therefore based on the object of providing a stamp which overcomes the disadvantages of existing arrangements and which, in particular, permits faster and yet controlled heating and cooling of the tools and thus also allows the process cycles to be shortened considerably. The embossing tools should be relatively economical to manufacture. They should also preferably facilitate the mutual alignment of the embossing tools.

The object is achieved by the invention as defined in the patent claims.

According to a first aspect of the invention, the press ram arrangement is essentially characterized in that embossing tools are arranged on a press ram with cooling means. The embossing tools themselves are provided with a heater. This can consist, for example, of at least two power connections through which a voltage can be applied across the metallic embossing tool, thereby generating Joule heat.

According to another important aspect, the embossing tools are designed as relatively thin metal foils which are backed with a soft press cushion. This aspect is based on the idea of achieving the best possible thermal and mechanical contact between the stamp and the stamping tool, in that the latter is designed to be relatively flexible and in that minor unevenness in the film can be compensated for by the press cushion.

An important idea on which the invention is based is the use of thin embossing tools which are only between 50 and 300 μm thick. Such tools can be manufactured using a method as described in the aforementioned Swiss patent application by the same applicant. The small thickness compared to conventional tools (4-8 mm thickness) shortens the plating process from several days to a few hours, which not only saves costs, but also shortens the lead time for prototype orders.

With embossing on both sides and with rigid, ie thick, tools, the flatness of the tools is of the greatest importance. Since stresses are always built into the deposited material when hard nickel is plated, it is very difficult to produce very flat tools. It is therefore extremely advantageous to make the tools thin and at the same time to back them up with a relatively soft press cushion, which allows the tools to adapt themselves to the different pressure distributions. This press cushion, which is made from a temperature-resistant plastic, such as Teflon, or silicone on the other hand, must not be too thick, otherwise the heat transfer will be reduced too much.

The fixation of the tool by vacuum is another possibility that does not require any integral connection and thus also enables the tool to be changed easily. Registration with the other tool for the back can still be done using registration bolts or a method described below.

In order to shorten the cycle time even further, a concept was developed which, as a basic idea, provides for direct heating of the embossing tool through the passage of electricity. The relatively thin, metallic embossing tools, which essentially consist of nickel, for example, are electrically connected to a control device that regulates the current according to the measured values of a temperature sensor, and are heated to a temperature to be set by a controlled current passage.

To do this, the embossing tool must be electrically insulated from the press plate, which can be accomplished using the Teflon or silicone press cushion mentioned above.

The advantages of this arrangement are clear:

The thermal mass of the nickel foil is very small, which allows quick heating and cooling times. The press plate can only be used for cooling. The temperature distribution is more homogeneous.

Energy can be saved.

Due to the low temperature (e.g. room temperature) of the press plates, other active elements can be integrated into them. According to a first example, piezo elements are arranged inside a press plate. These can be controlled individually, which leads to the piezo elements expanding and being able to deform the press plate locally. At the same time, these elements can be used to measure the local compressive stresses, which leads to a self-regulating, active system. If one element measures a lower compressive stress compared to the other elements, one must assume that the pressure in the embossing material is applied unevenly. The element can then be extended by applying a voltage, which is equivalent to an increase in the local pressure. If all elements are coupled via a corresponding control, a very even pressure distribution can be achieved.

According to a special embodiment, a press plate is divided into individual elements by slots. Other arrangements of the active piezo elements that lead to bending, twisting or warping of the press plates are also possible.

At the same time, the piezo elements can also be used to introduce additional energy in the form of ultrasonic energy into the embossed material. This can further shorten the embossing time and improve quality. After the actual hot stamping and cooling of the stamped product, it is separated from the tool. In the case of very fine and deep structures, this can lead to problems in that parts of the plastic stick to these structures. On the one hand, this creates breakouts in the embossed structure, on the other hand, the remnants remain in the tool, which is also undesirable. The use of ultrasound during the separation facilitates this delicate process and the yield, as well as the tool life, is increased.

According to a further aspect of the invention, the embossing tool is designed in such a way that the exact alignment of the two embossing tools is very easy for one another and to a certain extent takes place automatically. This brings great relief in

Comparison with the procedure described above according to the prior art.

On one embossing tool, special grid arrangements of cone, pyramid or cutting tip are provided in several places, which find their corresponding inverse structures on the other embossing tool.

If you place the two tools on top of each other, these structures snap into each other and the registration is complete. This sandwich of two embossing tools that are precisely aligned with each other can now be pushed between the press punches. If the press is closed slightly and the holding vacuum switched on, the two halves are sucked onto the press rams and held there in a stable position.

The embossed goods must be excluded from the registration grids, otherwise embossing will also occur at these points, which is naturally not desirable. The registration grids are produced with the embossing tools and are therefore optimally adjusted to the embossing pattern. These conical grids can also only be produced with the help of one in the simultaneously filed Swiss patent application by the same applicant, since the conventional method only allows rectangular structures.

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

- Figure 1 is a sectional view of a stamping arrangement according to the prior art, but with a new type only indicated schematically

embossing tool

FIG. 2 shows a sectional view of a press punch arrangement according to the invention,

FIG. 3 shows a sectional view of half of a further press punch arrangement,

- Figure 4a is a sectional view of two spaced embossing tools, each with a grid arrangement of pyramidal tips and and

4b shows the sectional view of FIG. 4a, the embossing tools resting on one another and the tips engaging in one another. 2 shows a press ram arrangement with two press rams 1, 3 and press plates 5, 7, each of which has at least coolant. The coolants are indicated by round channel openings 9. A coolant, for example, can circulate in such channel openings. However, the coolants can equally well have any other form. The tools 11, 13 are designed, for example, as novel tools, the manufacture of which is disclosed in the simultaneously filed patent application by the same applicant. They have a thickness of 30 μm to 1 mm, for example between 50 and 300 μm. They are made of an electrically conductive material, for example nickel, a nickel alloy or a combination of layers of a nickel alloy with layers of a copper alloy or of some other conductor material or another combination of conductor materials. Between the tools 11, 13 and the press plates 5, 7 there is also a thin layer 15, 17 of electrically insulating material as a press cushion, for example in the form of a Teflon film, a silicone film or a layer of another heat-resistant plastic. Also shown are power supply means 21, by means of which a voltage can be applied across the tools between connections 23, 25.

In operation, the press plates 5, 7 of the press rams are, for example, continuously and continuously cooled and kept at a predetermined temperature, for example approximately at room temperature, at the cooling water temperature or at the evaporation temperature of a coolant used at the pressure prevailing in the cooling system. If the embossing tools now have to be heated to a temperature used for a process step in the hot embossing process, a voltage is applied across the tools until they are heated to the desired temperature by the resulting Joule heat. The electrically generated heat output is then reduced, so that the temperature is kept constant and only the heat flowing to the embossing plates 5, 7 is compensated. A temperature sensor or several temperature sensors can be attached to the tools 11, 13. During the entire process, the temperature of the embossing tools is higher than that of the press plates 5, 7; the latter is at most slightly higher than the temperature of the coolant or the temperature that the press plates have when no heating is switched on.

Because the embossing tools 11, 13 are relatively thin, their electrical resistance is high compared to the electrical resistance of existing embossing tools. Depending on the material, heating is made possible or facilitated by the flow of current, since feed lines which are not centimeter thick are required for the required current strength and the electrical contacts do not heat up excessively as a result.

When the tools are to be cooled, the power through the stamping tools is simply switched off. The heat stored in the tools then flows away in a short time, since the tools are thin and have a low heat capacity. As a result, the temperature of the tools quickly adjusts to that of the press plates 5, 7.

As an alternative to the above procedure, the cooling of the press plates can also be switched off during the phase during which the embossing tools 11, 13 must be warm.

The embodiment of FIG. 3 differs from that of FIG. 2 in that 7 piezo elements 31 are arranged in the interior of the press plate. The piezo elements 31 can be controlled individually, for example, which is indicated in the figure by the individual voltage supply means 33. The press plates are then made of a material and dimensioned accordingly that at least its surface facing the tool is easily mechanically deformable.

The coolants are preferably introduced into or attached to the press plate in the vicinity of the surface facing the tool.

In FIGS. 4a and 4b, the press plates have been omitted for reasons of clarity. FIG. 4a shows two embossing tools 41, 43, each with two areas with a raster structure 41.1, 41.2, 43.1, 43.2 of pyramid-shaped tips. The grid structures opposite each other are complementary. As a result of the structure tapering towards the outside, guide means are formed. When the tools for the embossing process lie on top of one another, the complementary structures interlock and bring about a very efficient and easily accomplished lateral alignment of the tools.

Claims

Press stamp (1, 3) of an embossing device for embossing structures in dielectric substrates, comprising a press plate (5, 7) and an electrically conductive embossing tool (11, 13, 41, 43) attached thereto, the press plate (5, 7) coolant (9), characterized in that the embossing tool (11, 13, 41, 43) can be heated directly.

2. Press stamp according to claim 1, characterized in that between the

Press plate (5, 7) and the press plate (5, 7) an electrically insulating layer (15, 17) is arranged and that means (21, 23, 25) are present to the

Heat the embossing tool (11, 13, 41, 43) by the flow of electrical current.

3. Press stamp according to claim 1 or 2, characterized by at least one piezo element (31) for locally deforming the press plate (5, 7), for measuring the local compressive stresses or for introducing energy in the form of

Ultrasound in the embossed material.

Press stamp according to claim 3, characterized in that the piezo element is arranged inside the press plate (5, 7) and is therefore at least partially surrounded by it. Press stamp according to one of the preceding claims, characterized in that the embossing tools can be fixed to the press plate with a vacuum.

6. Press stamp of an embossing device for embossing structures in dielectric substrates, in particular according to one of claims 1 to 5, having an

Press plate (5, 7) and an embossing tool (11, 13, 41, 43) attached thereto, the press plate (5, 7) having coolant (9), characterized in that the thickness of the embossing tool is between 30 μm and 1 mm, is preferably between 50 .mu.m and 300 .mu.m, and that between the press plate (5, 7) and the embossing tool (11, 13, 41, 43) acts as a press pad and is heat-resistant up to temperatures of at least approx. 400 ° C., electrically insulating Layer (15, 17) is attached.

7. A method for heating an embossing tool (11, 13, 41, 43) of a stamping arrangement with a press plate (5, 7) to which the embossing tool is attached to a specific temperature, characterized in that the press plate (5, 7) cooled and the embossing tool is heated directly.

8. press stamp with a press plate (5, 7) and an embossing tool (41, 43) attached thereto, preferably according to one of claims 1 to 6, characterized in that the embossing tool has a grid structure (41.1,

41.3, 43.1, 43.3) for engaging in a complementary raster structure of a further embossing tool, the raster structure having guide means for laterally positioning the embossing tool (41, 43) relative to the further embossing tool.

9. embossing tool (41, 43) for a press stamp, preferably according to one of claims 1 to 6 or 8, characterized by an at least in one area arranged raster structure (41.1, 41.3, 43.1, 43.3) for engaging in a complementary raster structure of another embossing tool , wherein the raster structure includes guide means for laterally positioning the embossing tool (41, 43) relative to the further embossing tool.