JP3989820B2 - Multilayer wiring board and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flat-type multilayer wiring board having a rigid wiring circuit portion and a flexible wiring circuit portion, and a method for manufacturing the same.
[0002]
[Prior art]
For example, with respect to wiring boards that form electrical circuits, such as medical equipment such as CT scanners and catheters, and PC peripherals such as MT heads and PC cards, etc. In addition to lightening, flexibility is required. In response to such demands, the rigid configuration is shown in FIG. 7 in a perspective view, and in FIG. 8 in an enlarged sectional view along the line AA in FIG. A hybrid wiring board in which the wiring circuit units 101 and 102 and the flexible wiring circuit unit 120 are integrally combined has been developed. (For example, refer to Patent Document 1).
[0003]
7 and 8, reference numerals 101 and 102 denote rigid wiring circuit portions having a total thickness of about 100 μm. For example, polyimide resin films 103 and 104 and glass epoxy resin sheets 105, 106, 107, 108, 109, and 110 are used. , 111, 112, 113, 114, 115, 116 constitute an interlayer insulator, and necessary wiring patterns 130 are formed in multiple layers between each film layer and on the outer surface. On the other hand, the flexible wiring circuit section 120 is formed by extending a polyimide resin film 103 (104) constituting one layer of an interlayer insulator layer of the rigid wiring circuit sections 101 and 102, and wiring patterns on both surfaces using this as an interlayer insulator. 131 is formed.
[0004]
The rigid wiring circuit units 101 and 102 are configured to mount required electronic components on the outer surface thereof, while the flexible wiring circuit unit 120 is provided between the rigid wiring circuit units 101 and 102. While contributing to the connection, the positions and directions of the rigid wiring circuit portions 101 and 102 can be bent so as to be arbitrarily set.
[0005]
In the configuration of the wiring board, the polyimide resin films 103 and 104 and the glass epoxy resin sheets 105..., 111... Constituting the interlayer insulator of the rigid wiring circuit portions 101 and 102 or the polyimide resin films 103. 104 and the glass epoxy resin sheets 105... 111 are joined to each other through a thermosetting adhesive layer. The interlayer connection includes a through hole type and a via type, and these interlayer connection conductors 140 are formed by embedding a conductor or forming a plating film on the inner wall surface of the through hole. In FIG. 7 , reference numeral 151 denotes an electronic component mounting land, and 152 denotes a connection terminal portion.
[0006]
This type of mixed wiring board is manufactured as follows. First, a copper foil-bonded sheet is prepared by bonding a copper foil having a thickness of about 12 to 18 μm to the main surface of the polyimide resin film 103 (104) having a thickness of about 100 to 200 μm via an adhesive layer. Next, a predetermined region of the copper foil-bonded sheet is subjected to perforation processing to provide a through hole for interlayer connection, and then the inner wall surface of the through hole is formed into a plated conductor or filled with a conductive composition to form an interlayer connection conductor. 140 is formed. Thereafter, the copper foils on both sides are subjected to a photo-etching process to form a wiring pattern 130 to obtain a flexible wiring film in which the wiring patterns 130 on both sides are connected.
[0007]
On the other hand, a plurality of copper foil-bonded sheets prepared by bonding a copper foil having a thickness of about 12 to 18 μm to one main surface of a semi-cured glass-epoxy resin sheet having a thickness of about 100 μm via an adhesive layer is prepared. . Here, the semi-cured glass-epoxy resin-based sheet forms an interlayer insulator of the rigid wiring circuit portions 101 and 102. Therefore, the structure corresponding to the flexible region of the wiring film is cut away. Next, after drilling a predetermined region of these copper foil-bonded sheets and providing a through hole for interlayer connection, the inner wall surface of the through hole is made into a plated conductor or filled with a conductive composition to connect the interlayer. A conductor 140 is formed. Thereafter, the copper foil is subjected to a photo-etching process to obtain a rigid wiring circuit part wiring sheet having an interlayer connection conductor 140 connected to the wiring pattern.
[0008]
The prepared wiring film having flexibility, a rigid wiring circuit wiring sheet, and if necessary, a cover sheet are aligned and laminated. At this time, a thermosetting adhesive layer is interposed on a region surface where the rigid wiring circuit portion wiring sheets contact each other. Further, a dummy member having a good releasability is fitted and arranged on the exposed surface of the flexible wiring film, in other words, the notch portion of the rigid wiring circuit portion wiring sheet to flatten the surface.
[0009]
Then, the pressurizing and heating processes are performed on the stacked arrangement body to join and integrate the rigid wiring circuit part wiring sheets and the flexible wiring film and the rigid wiring circuit part wiring sheet. Thus, a wiring board in which the multilayer rigid wiring circuit portions 101 and 102 are integrated via the flexible wiring circuit portion 120 is manufactured. In addition, joining and integration with a rigid wiring circuit unit wiring sheet can be performed in multiple stages for each rigid wiring circuit unit wiring sheet, or can be created by a so-called build-up method. it can.
[0010]
Further, as means for simplifying the configuration of the rigid wiring circuit portions 101 and 102, an uncured thermosetting resin layer having a thickness of about 250 to 300 μm is formed on the surface on which the wiring pattern 130 is formed, and a predetermined region surface is electrically conductive. Protruding conductors are provided using a composition or conductive metal as a raw material, and a copper foil having a thickness of about 15 μm is positioned and laminated. Thereafter, the laminated body is heated and pressurized to be joined and integrated to produce a circuit board in which a copper foil is electrically connected by a protruding conductor through which an uncured thermosetting resin layer is inserted. The copper foil of the copper foil-clad circuit board is etched to form a wiring pattern. This method is attracting attention as a means suitable for productivity and high-density wiring patterning because the interlayer connection conductor can be easily and finely formed.
[0011]
[Patent Document 1]
JP-A-8-23149 (FIG. 1, pages 7-8)
[0012]
[Problems to be solved by the invention]
However, since the wiring board having the rigid wiring circuit portions 101 and 102 and the flexible wiring circuit portion exhibits a certain degree of flexibility, it contributes to shortening the size and thickness of electronic devices to be used, such as digital cameras and mobile phones. However, on the other hand, the following problems are recognized. That is, in the main part configuration shown in FIG. 7, the rigid wiring circuit units 101 and 102 are thicker than the flexible wiring circuit unit 120 that integrates them, which is inconvenient in handling operation and uses space. Efficiency is also reduced, and sometimes downsizing is impeded. Further, due to the flexibility required for the flexible wiring circuit portion 120, the thickness of the polyimide resin (thermosetting resin) layer 103 is also limited, and the wiring pattern for connection between the rigid wiring circuit portions 101 and 102 is also limited. Is done. In other words, there is a limit on the thickness due to the flexibility of the polyimide resin film that forms the interlayer insulator, and there is a restriction on the wiring density due to the electrical characteristics of the polyimide resin film itself, so it cannot be said that the function and performance as a wiring board are sufficient. .
On the other hand, in the manufacturing method, in addition to the notch processing of the interlayer insulator film of the rigid wiring circuit portions 101 and 102, alignment, dummy member fitting arrangement, uniform pressurization, heating difficulty, etc. There is also a problem that the process becomes complicated. That is, it cannot be said that it is sufficient as a means for mass-manufacturing a highly reliable wiring board with uniform specifications and high yield at all times.
[0013]
The present invention has been made in view of the above circumstances, and provides a rigid wiring circuit unit and a wiring board having a flexible wiring circuit unit that are highly reliable and more compact, and a method for manufacturing the same. With the goal.
[0014]
[Means for Solving the Problems]
The present invention relates to a thermoplastic resin-based flexible insulator layer and a thermosetting resin-based rigid insulator layer that is fused and formed on the side of the flexible insulator layer so as to extend integrally therewith. multiple sheets of insulating sheet having bets is the form a laminated structure are laminated by aligning the mutual each flexible insulator layer, an interlayer wiring patterns are connected by an interlayer connection conductor, the flexible insulator of the multilayer structure Provided is a multilayer wiring board in which a layer and a surface of the rigid insulator layer are formed on the same surface.
[0016]
Furthermore, the present invention provides a first flexible insulating layer made of thermoplastic resin and an uncured or semi-cured first thermosetting resin layer which can be fused together in the same side of the layer. Producing a first insulating sheet formed by joining together,
Sandwiching the first insulating sheet, a copper foil provided with a protruding interlayer connection conductor on one main surface side, a step of laminating a copper foil on the other main surface side to form a laminate, and
The laminated body is heated and pressed in the laminating direction to melt and cure the thermosetting resin layer to form a rigid insulator layer, which is integrated with the first flexible insulator layer, and the copper foils on both sides are Creating a double-sided copper foil bonded plate electrically connected with a protruding interlayer connection conductor through which the first insulating sheet is inserted;
A step of forming a core substrate by performing a photo-etching process on the copper foils on both sides to form a wiring pattern;
A second flexible insulator layer of thermoplastic resin and an uncured or semi-cured second thermosetting resin layer are bonded to the surface of the wiring pattern so that both layers can be fused together. A step of laminating a second insulating sheet formed by joining together and a copper foil provided with a protruding interlayer connection conductor on one main surface side of the second insulating sheet;
A multilayer wiring element in which the laminated body is integrated by heating and pressing in the laminating direction, and the protruding interlayer connection conductor having the second insulating sheet inserted thereinto is electrically connected to the wiring pattern of the core substrate opposed to the multilayer wiring element. Producing a plate;
The copper foil of the multilayer wiring board is subjected to a photo-etching process to form a wiring pattern,
A method for producing a multilayer wiring board is provided.
[0017]
When the uncured or semi-cured thermosetting resin layer is fluid when heated, it prevents resin flow at the boundary between the flexible insulator layer and the uncured or semi-cured thermosetting resin layer. It is preferable that a weir is provided.
[0018]
Moreover, it is preferable that the flexible insulator layer is formed of a liquid crystal polymer.
[0019]
According to the present invention, as an insulator of a wiring board, a flexible region is an insulating layer made of a thermoplastic resin, and a region requiring a rigid rigidity necessary for circuit arrangement is made of a thermosetting resin, selectively and fitted. Insulating resin sheets that are integrally configured on the same surface in combination are used. With the adoption of such a configuration, the thickness is made uniform throughout the flexible wiring circuit part and the rigid wiring circuit part, and while achieving short, small and thin, high density wiring or high functionality and high performance. A wiring board for mounting that can be bent reliably is provided.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the invention will be described with reference to FIGS. 1 to 5.
[0021]
FIG. 1 is an enlarged cross-sectional view showing a main part of the wiring board according to the first embodiment. In FIG. 1, a wiring board 10 is obtained by impregnating a glass cloth with a flexible insulating layer 11 of a thermoplastic resin layer made of a liquid crystal polymer film having a thickness of 25 to 100 μm, for example, a Vectran film having a melting point of 280 to 350 ° C., and an epoxy resin. An insulator sheet 13 composed of a rigid insulator layer 12 is provided. The flexible insulator layer 11 and the rigid insulator layer 12 are disposed adjacent to each other in the same plane so as to form the same surface, and the opposite sides are abutted and the boundary 20 is joined by fusion to be integrated. It is extended to. Wiring patterns 14 and 15 are integrally disposed on both main surfaces of the insulating sheet 13. The wiring patterns 14 and 15 are electrically connected by an interlayer connection conductor 16 having an insulating sheet 13 inserted in the thickness direction.
[0022]
Here, each wiring pattern 14 and 15 is electrically connected by inserting a protruding connection conductor 16 protruding from the surface of the wiring pattern 15 into the rigid insulator layer 12. That is, a protruding connection conductor 16 such as a conductive bump printed in a substantially conical shape or a pyramid shape, or a metal protrusion selectively grown on the insulating layer 12 is inserted from the tip side. In this configuration, the wiring pattern 14 is electrically connected to the opposing wiring pattern 14. The wiring patterns 14 and 15 are generally formed by photo-etching a conductive layer such as copper foil, but are selected by screen printing of a conductive paste or patterning by printing a plating resist. It may be formed by means such as typical plating.
[0023]
The flexible insulator layer 11 forms a flexible wiring circuit portion 17 together with the wiring patterns 14 and 15, and the rigid insulator layer 12 forms a rigid wiring circuit portion 18 together with the wiring patterns 14 and 15 formed on the surface. .
[0024]
The feature of this embodiment is that the flexible insulator layer 11 and the rigid insulator layer 12 form an insulator sheet 13 having a common surface. As a result, the wirings 14 and 15 can be formed into an integrated pattern at the same time, and the manufacturing process can be reduced as will be described later, thereby contributing to cost reduction. Moreover, since the wiring board including the flexible insulator layer can be made thin, it is advantageous for making the device compact.
[0025]
FIG. 2 is an enlarged cross-sectional view showing a main part of the wiring board according to the second embodiment. The wiring board of this embodiment has a multi-layered configuration with respect to the first embodiment. 1 denote the same parts. That is, the insulating sheet having the structure shown in FIG. 1 is laminated on the two layers 13 and 13a, and the flexible insulating layers 11 and 11a of each sheet are aligned so that the flexibility is not impaired. Is formed. Since each interlayer insulator sheet has a thin structure, it is thin even if it has multiple layers, and the flexible portion has sufficient flexibility so that it has bending resistance.
[0026]
In the wiring board according to each of the above embodiments, a liquid crystal polymer is suitable as a thermoplastic resin for forming the flexible insulating layer 11 of the flexible wiring circuit portion 17. For example, Kisdar (trade name, manufactured by Dartco), Vectra (product) (Manufactured by Clanese), a multiaxially oriented thermoplastic polymer. Vectran A type (melting point 285 ° C.), Vectran C type (melting point 325 ° C.), BIAC film (melting point 325 ° C.) and the like are commercially available. This type of liquid crystal polymer generally has almost no hygroscopicity, has a dielectric constant of about 3.0 (1 MHz), and has excellent high frequency characteristics, and thus exhibits high-speed signal transmission stability. In addition to the liquid crystal polymer, various materials such as polyetherimide can be used as the thermoplastic resin.
[0027]
In addition, the thermosetting resin system that forms the insulator 12 of the rigid wiring circuit section 18 may be one or more of epoxy resin, bismaleimide triazine resin, polyimide resin, phenol resin, silicone resin, and the like. A mixed system, and a combination of these resins and a filler such as an insulating inorganic material, a reinforcing material such as a glass cloth, a mat, or a nonwoven fabric can be used.
[0028]
Furthermore, the interlayer connection conductor 16 is composed of a conductive metal such as gold, silver, copper, or solder, or a mixed system of this conductive metal powder and a binder resin. Here, examples of the binder resin include polycarbonate resin, polysulfone resin, polyester resin, phenoxy resin, phenol resin, and polyimide resin.
[0029]
Next, the manufacturing method of the wiring board which concerns on embodiment of this invention is demonstrated.
[0030]
First, an insulating sheet 13 is prepared as shown in FIG. 3 in which the main part configuration is shown in plan and in FIG. That is, for example, a flexible insulating layer 11 made of a liquid crystal polymer-based thermoplastic resin and an uncured or semi-cured material that is mechanically butt-contacted with the side of the interlayer insulating layer 11 so as to form the same surface side by side in this layer An insulating sheet 13 made of a thermosetting resin layer 12 is prepared in advance. Here, the insulating sheet 12 is formed by punching a semi-cured thermosetting resin-based sheet, for example, a glass-epoxy prepreg sheet, opening a predetermined area (notch), and then opening the notch (notch) area. 11 pieces of insulating layers of liquid crystal polymer that have been punched in advance are fitted. In two steps (step cure) in the subsequent process, by heating and pressurizing, the epoxy resin having a lower melting point than the liquid crystal polymer melts and fuses to the side of the insulator layer 11 to cure, and the thermosetting resin layer Becomes a rigid insulator layer 12. Thus, the insulating layers 11 and 12 are integrated and become a composite insulating sheet having the same flat surface. Note that the insulating sheet 13 shown in FIG.
[0031]
Next, as shown in FIG. 4, a copper foil 31 having a thickness of 12 to 18 μm provided with a protruding (conical) interlayer connection conductor 16 on one main surface side of the insulating sheet 13, A simple copper foil 32 is laminated on the other main surface side to form a laminate. After that, when a backing plate is disposed on both the copper foils 31 and 32 of the laminate and heated and pressurized at a heating temperature of about 180 ° C. and a resin pressure of about 4 to 6 MPa, the thermosetting resin layer 12 is melted. Next, when heated and pressurized at a heating temperature of about 300 ° C. and a resin pressure of about 4 to 6 MPa, it is fused to the flexible insulating layer 11 to form a rigid insulating layer, and at the same time, the protruding interlayer connection of the copper foil 31 The conductor 16 penetrates the insulating sheet 30 and is electrically connected to the copper foil 32 to produce a double-sided copper foil-attached plate.
[0032]
Next, the copper foils 31 and 32 on both sides were subjected to a photo-etching process to form a wiring pattern, whereby the flexible wiring circuit portion 17 and the rigid wiring circuit portion 18 were integrated as shown in FIG. A wiring sheet can be obtained. As shown in FIG. 3, the wiring board having the configuration shown in FIG. 1 can be obtained by separating the sheet into wiring board units by cutting lines 34.
[0033]
In the method for manufacturing a wiring board according to this embodiment, the protruding (conical) interlayer connection conductor 16 on the copper foil 31 is provided by the following means, for example. That is, on one main surface side of the copper foil 31, for example, a conductive mask is printed by positioning and arranging a metal mask having holes of a diameter of 0.1 to 0.3 mm in a predetermined portion of a stainless steel sheet. After the conductive paste is dried, printing is repeated a plurality of times by the method of printing again at the same position using the same metal mask, thereby forming a chevron bump.
[0034]
In the method for manufacturing a wiring board, at least one of the semi-cured thermosetting resin-based insulating layer 12 region and the liquid crystal polymer insulating layer 11 region of the insulating sheet 13 is easily formed during heating and pressure molding. If there is a risk of flowing, use a non-flow type thermosetting resin, or as shown in FIGS. 5 and 6, the surface of the copper foil 31 provided with the protruding interlayer connection conductor 16 or opposite to the surface. It is preferable that a protrusion 33 (prevention weir) for preventing resin outflow is provided on the surface of the copper foil 32 so as to correspond to the boundary 20 between the thermoplastic resin layer 11 and the semi-cured thermosetting resin layer 12. For example, when the thermosetting resin is cured, the thermosetting resin melts, flows out to the thermoplastic resin layer side having a higher melting point, and overflows over the boundary layer 20. For this reason, the weir is formed by arranging the connection conductors 33 on the boundary as shown in FIG.
[0035]
In the above manufacturing method, the interlayer insulating material used, that is, the liquid crystal polymer and the thermosetting resin-based sheet or film are mainly composed of the above-exemplified resins. Further, the wiring pattern forming means, the material, and the like are also in the same manner as described above.
[0036]
Furthermore, the multilayer wiring board of the embodiment shown in FIG. 2 can be easily manufactured by combining the wiring board structures of the above-described embodiments. The insulator sheet 13 of the above embodiment and the wiring patterns 14 and 15 on both sides are prepared as the core substrate 10, and a buildup wiring layer 13 a which is another insulator sheet is laminated and integrated thereon.
[0037]
That is, as the build-up wiring layer, for example, an uncured or mechanically butt-contacted side of the insulator layer 11a so as to form the same surface side by side with the flexible insulator layer 11a of a liquid crystal polymer thermoplastic resin. A copper foil 35 having a thickness of 12 to 18 μm provided with an insulating sheet 13a composed of a semi-cured thermosetting resin layer 12a and a protruding (conical) interlayer connection conductor 16a is prepared.
[0038]
Next, the insulating sheet 13a and the copper foil 35 are laminated so that the connecting conductor of the copper foil faces the core substrate side and the insulating sheet 13a is sandwiched between the core substrate 10 and the copper foil 35.
[0039]
When this laminate is heated and pressed in two steps from the lamination direction, the thermosetting resin layer melts and thermosets, and then the thermoplastic resin melts and the copper foil connecting conductor 16a is inserted through the sheet and the core substrate. Are electrically connected to the wiring pattern and integrated with the core substrate as a build-up wiring layer.
[0040]
In this example of the manufacturing method, there is a flexible wiring circuit part that can be bent and a rigid wiring circuit part that is suitable for mounting electronic components, and there is no possibility of causing peeling or damage even after repeated bending. A wiring board exhibiting high electrical characteristics can be manufactured with high yield.
[0041]
The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. For example, the number of built-in wiring patterns may be a three-layered form or a multilayered form of five or more layers, and a combination of a liquid crystal polymer and a thermoplastic resin can be appropriately selected depending on the application.
[0042]
【The invention's effect】
According to the present invention, it is possible to provide a highly reliable wiring board that has a flexible wiring circuit part that can be bent and a rigid wiring circuit part that is suitable for mounting electronic components, and that is compact and has excellent specifications. That is, not only the configuration is simplified, but also a wiring board that is thin and has a highly reliable function and suitable for the circuit configuration of small electronic devices is provided.
[0043]
Furthermore, according to the manufacturing method of the present invention, not only the configuration is simplified, but also a mass production with a high yield, a thin, highly reliable function, and suitable for a circuit configuration of a small electronic device. A wiring board can be easily provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a main configuration of an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing the main configuration of another embodiment of the present invention.
FIG. 3 is a plan view showing the main configuration of a multi-sided insulating sheet of the manufacturing method according to one embodiment of the present invention.
FIG. 4 is a cross-sectional view illustrating a manufacturing method according to one embodiment of the present invention.
FIG. 5 is a cross-sectional view illustrating a manufacturing method according to another embodiment of the present invention.
FIG. 6 is a plan view showing a main configuration of a multi-sided insulating sheet of a manufacturing method according to another embodiment of the present invention.
FIG. 7 is a perspective view showing a main configuration of a wiring board having a conventional flexible wiring circuit portion and a rigid wiring circuit portion.
8 is an enlarged cross-sectional view taken along line AA in FIG.
[Explanation of symbols]
10: Wiring board 11: Flexible insulator layer 12: Rigid insulator layer 13: Insulator sheet 14, 15: Wiring pattern 16: Interlayer connection conductor 17: Flexible wiring circuit portion 18: Rigid wiring circuit portion 20: Boundary

Claims (4)

Insulation having a thermoplastic resin-based flexible insulating layer and a thermosetting resin-based rigid insulating layer fused and formed on the side of the flexible insulating layer to form the same surface and extend integrally multiple sheets of sheet forms a laminated structure are laminated by aligning the mutual wherein each flexible insulator layer, an interlayer wiring patterns are connected by an interlayer connection conductor, the said flexible insulator layer of said laminated structure rigid A multilayer wiring board, wherein the surface of the insulator layer is formed on the same surface . The first flexible insulating layer of thermoplastic resin and the uncured or semi-cured first thermosetting resin layer are formed by bonding the sides of the layers in the same plane so that both layers can be fused. Producing the first insulating sheet,
  Sandwiching the first insulating sheet, a copper foil provided with a protruding interlayer connection conductor on one main surface side, a step of laminating a copper foil on the other main surface side to form a laminate, and
  The laminated body is heated and pressed in the laminating direction to melt and cure the thermosetting resin layer to form a rigid insulator layer, which is integrated with the first flexible insulator layer, and the copper foils on both sides are A step of creating a double-sided copper foil bonded plate electrically connected by a protruding interlayer connection conductor through which the first insulating sheet is inserted;
  A step of forming a core substrate by performing a photo-etching process on the copper foils on both sides to form a wiring pattern;
  A second flexible insulator layer made of thermoplastic resin and an uncured or semi-cured second thermosetting resin layer are bonded to the surface of the wiring pattern so that both the layers can be fused. A step of laminating a second insulating sheet formed by joining together and a copper foil provided with a protruding interlayer connection conductor on one main surface side of the second insulating sheet;
  A multilayer wiring element in which the laminated body is integrated by heating and pressing in the laminating direction, and a protruding interlayer connection conductor having a second insulating sheet inserted thereinto is electrically connected to the wiring pattern of the core substrate opposed to the multilayer wiring element. Producing a plate;
  The copper foil of the multilayer wiring board is subjected to a photo-etching process to form a wiring pattern,
A method for producing a multilayer wiring board, comprising: 3. The method for producing a multilayer wiring board according to claim 2, wherein a weir for preventing resin flow is provided at a boundary between the flexible insulator layer and the uncured or semi-cured thermosetting resin layer. The method for producing a multilayer wiring board according to claim 2 or 3, wherein the flexible insulator layer is formed of a liquid crystal polymer.

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