JP2011243947A - Multilayer substrate and method of manufacturing same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of a multilayer substrate that uses a conventional film in which thermal expansion in thickness direction is high, with especially a long-term reliability at 150°C or lower being low, and the reliability is affected as becomes thinner or degree of multitude in layer grows.SOLUTION: An all-layer IVH structure resin multilayer wiring substrate is provided in which the thermal expansion coefficient of an adhesive layer in z-direction is made lower than the thermal expansion coefficient of a heat-resistant film 1 in z-direction at 125°C to 150°C, so that a long-term reliability in resistance can be assured at 150°C or lower while lead free reflow resistance is assured even if thickness is reduced or the number of layers is increased.

Description

  The present invention relates to a multilayer substrate in which a plurality of layers of wirings are electrically connected by inner via hole connection.

  In recent years, with the downsizing and high performance of electronic devices, multilayer wiring circuit boards capable of mounting semiconductor chips such as LSIs with high density not only for industrial use but also in the field of consumer equipment are being supplied at low cost. There has been a strong demand. In such a multilayer printed circuit board, it is important that a plurality of wiring patterns formed at a fine wiring pitch can be electrically connected with high connection reliability.

  In addition, in mobile devices represented by mobile phones, in particular, in addition to the trend of integration of functions, the trend of thinning of devices is remarkable in order to improve portability. High density and thinness is required.

  In response to such market demands, instead of the conventional multilayer wiring board, inner via hole connection for connecting any electrode of a multilayer wiring board using a film base material as an insulating layer with a conductive paste at an arbitrary wiring pattern position There is a method called an all-layer IVH structure resin multilayer wiring board.

  For example, Patent Document 1 describes that when an insulating film having a thickness of 10 μm or less is used, a wholly aromatic polyamide film is preferable in terms of properties such as mechanical strength and thermal expansion coefficient. An adhesive layer having a thickness of 20 microns or less and a thermal expansion coefficient of 150 ppm / ° C. or less is formed on a film (a thermal expansion coefficient in the thickness direction of 10 ppm / ° C. or less) to obtain an adhesive sheet. Have been proposed in which the coefficient of thermal expansion in the thickness direction is 100 ppm / ° C. or less.

  As such an application, it has been proposed to use an aramid film (Patent Document 1). This is because the thermal expansion coefficient of the aramid film itself is very low (for example, the thermal expansion coefficient of the aramid film “Mictron” manufactured by Toray Industries, Inc. is as extremely low as −3 to 5 ppm / ° C.).

  However, a material such as an aramid film having a very small coefficient of thermal expansion of −10 ppm to +10 ppm is a special and expensive material, and it has been difficult to use it for a multilayer substrate required by the market.

  Therefore, from the market, even if the thermal expansion coefficient is 10 ppm / ° C. or higher, 50 ppm / ° C. or higher, or even 100 ppm / ° C. or higher, a multilayer substrate using a cheaper heat-resistant film will be realized. Is required.

  However, the higher the thermal expansion coefficient of the heat-resistant film, the greater the thermal expansion coefficient in the xy direction of the heat-resistant film and the finer the wiring pattern when trying to produce a multilayer substrate having a fine pattern compatible with high-density mounting. Or, multilayering becomes difficult.

  Therefore, heat resistance films for multilayer substrates are required to reduce the thermal expansion coefficient particularly in the xy direction, but as a reaction, the thermal expansion coefficient in the thickness direction (z direction) of the heat resistance film increases. There is a problem that it ends up.

  As a result, a multilayer substrate using a heat-resistant film having a large thermal expansion coefficient for the insulating layer has a high glass transition point, for example, in a thermal shock test or a high temperature load test in which a temperature from 100 ° C. to 150 ° C. is applied for a long time (150 Even when a film base material is used, the thermal expansion in the z direction of the substrate itself is large, and there is a problem that it is difficult to ensure reliability. Reducing the thermal expansion coefficient in the z direction of the base material in response to these problems increases the thermal expansion coefficient in the xy direction. As a result, the lamination accuracy in multilayering decreases, making it difficult to make wiring finer and higher in density. I was trying.

JP 2008-277384 A

  However, when a film multilayer substrate is prepared using an aramid film, the thermal expansion coefficient of the aramid film itself is very low (for example, the thermal expansion coefficient of an aramid film “Mikutron” manufactured by Toray Industries, Inc. is −3 to 5 ppm / ° C. Therefore, there has been a problem that the thermal expansion coefficient of the entire multilayer wiring board depends on the thermal expansion coefficient of the adhesive layer.

  SUMMARY OF THE INVENTION The present invention solves the above-described problems, and an object thereof is to provide an all-layer IVH structure high-density thin multilayer wiring board structure using a film and electrically connecting wiring layers of a wiring board with high reliability. To do.

  In order to achieve the above object, the present invention provides a plurality of heat-resistant films, through-holes formed in the heat-resistant film, conductive paste filled in the through-holes, and electrically interlayers through the conductive paste. A multilayer substrate comprising a plurality of wiring layers to be connected and an adhesive layer for bonding the heat-resistant film and the wiring, wherein the total thickness of the adhesive layer is 0 of the total thickness of the heat-resistant film. It is useful to make a multilayer wiring board that is 7 times or more and 3.5 times or less.

  Furthermore, a plurality of heat-resistant films, a through-hole formed in the heat-resistant film, a conductive paste filled in the through-hole, a plurality of wiring layers electrically connected to each other through the conductive paste, A multilayer substrate comprising a heat-resistant film and an adhesive layer for bonding the wiring, wherein the thermal expansion coefficient of the heat-resistant film in the temperature range of 125 ° C. or higher and 150 ° C. or lower is expressed as α (Fz) or xy direction. When the thermal expansion coefficient is α (Fxy) and the z-direction thermal expansion coefficient of the adhesive layer is α (adz), the relationship of 3 × α (Fxy) <α (Fz) <10 × α (Fxy) and 10 ppm It is useful to make a multilayer substrate characterized by satisfying the relationship of / ° C. <α (adz) <α (Fz).

  As a result, it is possible to reduce the thermal expansion in the z direction of the substrate while maintaining the lamination accuracy in the multi-layering, and all the layers in which the wiring layers of the wiring substrate are electrically connected with high reliability while miniaturizing. An IVH structure high-density thin multilayer substrate is realized.

  In addition, connecting vias between layers with conductive paste filled in the through-holes increases the degree of freedom of via formation positions, and as a result, contributes to improved wiring density and lower via costs. it can.

  According to the multilayer substrate and the manufacturing method thereof of the present invention, it is possible to achieve both thinness and high density and high reliability, and it is possible to mount a plurality of electronic components at high density. Contributes to miniaturization and high performance of various electronic devices.

(A)-(f) Process sectional drawing which showed the manufacturing method of the wiring board in Embodiment 1 of this invention for every main process (A)-(d) Process sectional drawing which showed the manufacturing method of the wiring board in Embodiment 1 of this invention for every main process Cross-sectional view around the through hole in the multilayer substrate The figure which shows a mode that the conductive paste was filled into the through-hole Sectional drawing which shows a mode that a curved part is formed (A) Cross-sectional view of a double-sided wiring board in which the diameters of the holes on both sides of the heat-resistant film are substantially the same; (B) Cross-sectional view of a double-sided wiring board in which the same diameter is different and no curved portion is provided; Sectional view of a double-sided wiring board with a curved portion (A) SEM photograph of a portion where via portions in a multilayer wiring board are stacked in the thickness direction, (B) Schematic diagram of FIG. (A) SEM photograph of a portion where via portions in a multilayer wiring board are laminated in the thickness direction, (B) Schematic diagram of FIG. (A) SEM photograph of a portion where via portions in a multilayer wiring board are stacked in the thickness direction, (B) Schematic diagram of FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  A first embodiment of the present invention will be described with reference to FIGS. 1A to 1F and FIGS. 2A to 2D are cross-sectional views of main manufacturing steps of a multilayer wiring board according to the present invention. First, the insulating base 3 shown in FIG. 1A is obtained by forming the adhesive layer 2 on both surfaces of the heat-resistant film 1, and further, the protective film 4 is formed on the front and back surfaces thereof.

  As the heat resistant film 1, a flexible flexible wiring board material can be used, and a material having a high heat resistance and a small coefficient of thermal expansion in the xy direction is more preferable. Specifically, a polyimide film, an aramid film, and an LCP film are preferable in terms of heat resistance. Especially, as a polyimide film, “Kapton” (trademark of Toray DuPont), “Upilex” (Ube Industries, Ltd.) Trademarks), “Apical” (trademark of Kaneka Chemical Co., Ltd.), and “Aramika” (trademark of Asahi Kasei Co., Ltd.) are preferred as the aramid film. As a result, it is possible to form a multilayer wiring board having high heat resistance and high insulation reliability while ensuring the accuracy during lamination. With regard to the thickness, it is possible to use an extremely thin material of about 5 microns for a polyimide film and about 4 microns for an aramid film, and if these are used, an extremely thin multilayer wiring board can be formed. it can.

  As the adhesive layer 2, a thermosetting resin is used, and a material mainly composed of an epoxy resin or a polyimide resin can be used. As a material, it is better to add a plastic component or a filler in order to increase the adhesion and heat resistance with the cured wiring material and to reduce the thermal expansion coefficient in the thickness direction. As the plastic component, a silicone filler is particularly preferred for stress relaxation during heat shrinkage and high heat resistance. As for the filler, it is preferable to use an inorganic filler such as silica or alumina because it can further reduce thermal expansion and heat resistance. As a method for forming the adhesive layer 2, an adhesive varnish may be applied directly on the heat-resistant film 1, or an adhesive varnish may be applied on the protective film 4 and attached to the film for transfer. . The film surface is generally subjected to corona treatment or plasma treatment in order to improve the adhesion with the adhesive. Here, as an example, an epoxy adhesive was directly applied to both sides of a polyimide film having a thickness of 12.5 microns so as to have a thickness of 5 microns. In order to correct the warpage of the polyimide itself, substantially the same adhesive may be applied on the front and back sides of the polyimide so that the average thickness differs within a range of 1 micron or more and 8 microns or less. If it is 1 micron or less, the warp of the polyimide itself cannot be corrected, and if it is 8 microns or more, the thickness of the substrate becomes too thick. As a result, it is possible to improve productivity, reduce costs, and reduce adhesive management items.

  The protective film 4 formed on the front and back surfaces of the insulating base 3 is a film mainly composed of PET (polyethylene terephthalate) or PEN (polyethylene naphthalate), and is adhered to both sides of the insulating base 3 by lamination. It is a simple and highly productive manufacturing method. Lamination conditions are performed at a temperature at which the adhesive layer 2 is softened, and a method of laminating in a short time, such as laminating, is preferable so as not to advance curing of the thermosetting resin. Further, as described above, after the adhesive layer 2 is applied on the protective film 4, it can be laminated on the heat-resistant film 1 by lamination. Here, when a PEN or PET film was used as the protective film, it was excellent in tensile strength, so that even with a thickness of 12 microns, it could be stuck on the insulating base material 3 without wrinkling. In addition, since the PEN film can absorb a wavelength of 351 nm, there is an advantage that it is excellent in YAG laser processability of a third harmonic.

  Next, as shown in FIG.1 (b), the through-hole 5 which penetrates the protective film 4 and the insulating base material 3 is formed. The through-hole 5 can be formed by punching, drilling, or laser processing, but if a carbon dioxide laser or YAG laser is used, a small-diameter through-hole can be formed in a short period of time, realizing excellent productivity. it can. As an example, when a carbon dioxide laser is used, an insulating layer 3 having a total thickness of about 40 microns is formed by forming an adhesive layer on both sides of a polyimide film having a thickness of 12.5 microns, and then attaching a 9-micron PET film. On the other hand, a through hole having a diameter of 100 microns could be processed. In addition, when a third harmonic of a YAG laser was used, a 30 μm diameter through-hole could be processed in an electrically insulating substrate having a total thickness of about 40 microns.

  Subsequently, as shown in FIG. 1 (c), the conductive paste 6 is filled in the through holes 5. The conductive paste 6 is composed of metal conductive particles such as copper and silver and a resin component. It is more preferable to use a substantially spherical conductive particle because the paste viscosity can be kept low even when the conductive particle ratio in the conductive paste increases.

  At this time, the protective film 4 plays a role of protecting the conductive paste 6 from adhering to the surface of the insulating substrate 3 and a role of ensuring the filling amount of the conductive paste. Since the conductive paste can be filled by printing, it has an advantage of excellent productivity.

  Next, the state shown in FIG. 1D is obtained by peeling off the protective film 4. The conductive paste 6 has a filling amount secured by the protective film 4. That is, the conductive paste 6 protrudes from the surface of the insulating substrate 3 by the height of the thickness of the protective film 4 (numbers are not given to the protruding portions in FIG. 1D, but will be described later). Etc., a number is given as the protruding portion 20). Here, when the thickness of the protective film 4 is set to about 5 to 25% of the via diameter, the amount of the conductive paste taken to the protective film side when the protective film 4 is peeled off is more preferable. As an example, for an electrically insulating substrate having a total thickness of about 40 microns using the above-mentioned 12.5 micron polyimide film and a 12-micron protective film, the amount of protrusion is secured even at a through-hole diameter of 50 microns. I was able to.

  After the protective film 4 is peeled off, the wiring material 7 is laminated on both surfaces of the insulating base 3 as shown in FIG. 1E, and the adhesive layer 2 is cured by heat and pressure by hot press to insulate the wiring material 7. When the conductive paste 6 is compressed while being affixed to the substrate 3, the state shown in FIG. Here, although 9 micron electrolytic copper foil was used as the wiring material 7, when the multilayer wiring board is made thinner, electrolytic copper foil with a carrier having a thickness of 5 microns or rolled copper foil of 5 microns should be used. You can also.

  Moreover, about this electrically conductive paste 6, after filling, many resin exists between the electrically conductive particles in an electrically conductive paste, and sufficient electrical connection is not ensured. On the other hand, in the heating and pressing step, the conductive paste 6 is compressed, and the conductive particles in the conductive paste come into close contact with each other, so that electrical connection in the conductive paste can be ensured. The resin component in this conductive paste is indispensable in that it reduces the viscosity of the conductive paste during the filling process and stably fills the fine through-holes. It is important to ensure that the electrical connection is effectively discharged.

  Here, it is more preferable to use a thermosetting resin as the resin of the conductive paste, the viscosity of the conductive paste decreases during hot pressing, and the thermosetting resin is discharged out of the through-holes due to the compression of the conductive paste. The contact of the conductive particles in the paste can be made higher.

  In FIG. 1F, the thermal expansion coefficient in the z direction in the temperature range of 125 ° C. to 150 ° C. of the heat resistant film is α (Fz), the thermal expansion coefficient in the xy direction is α (Fxy), and the adhesive layer And the relationship of 3 × α (Fxy) <α (Fz) <10 × α (Fxy) and 10 ppm / ° C. <α (adz) <α (Fz) It is useful to make a multilayer substrate characterized by satisfying the above relationship. Thereby, the tolerance with respect to the long-term reliability test (thermal shock test, high temperature holding test, etc.) performed at 150 degrees C or less is improved dramatically. This is because α (adz) <α (Fz), that is, by making the thermal expansion coefficient of the adhesive layer in the z direction smaller than the thermal expansion coefficient of the heat resistant film in the z direction, the thermal expansion coefficient in the z direction as the substrate can be reduced. This is because the stress applied to the via in the z direction can be reduced. On the other hand, when α (adz) ≧ α (Fz), the stress applied to the via cannot be reduced, so it is difficult to ensure resistance to a long-term reliability test (thermal shock test, high temperature holding test, etc.). In addition, when the thermal expansion coefficient in the z direction of the adhesive layer is 10 ppm or less, the difference in thermal expansion coefficient between the adhesive layer in the z direction and the heat resistant film in the z direction is large, and stress is applied to the via so that internal destruction proceeds. It is difficult to ensure resistance to long-term reliability tests (thermal shock test, high temperature holding test, etc.). Therefore, 10 ppm / ° C. or more is preferable. At this time, by using a heat-resistant film satisfying the relationship of 3 × α (Fxy) <α (Fz) <10 × α (Fxy), it is possible to reduce the warp of the completed multilayer substrate and to obtain a multilayer substrate with high lamination accuracy. It can be secured at the same time. In the case of 3 × α (Fxy) ≧ α (Fz), the thermal expansion coefficient in the xy direction is increased, so that the stacking accuracy is lowered and it is difficult to have fine wiring. In the case of α (Fz) ≧ 10 × α (Fxy), the thermal expansion in the z direction is too large in the case of an organic material such as a heat-resistant film, so even if the thermal expansion coefficient of the adhesive layer is reduced, it is 150. It becomes difficult to ensure resistance to a long-term reliability test (thermal shock test, high temperature holding test, etc.) performed at a temperature of ℃ or less. Therefore, it is preferable to use a heat resistant film satisfying the relationship of 3 × α (Fxy) <α (Fz) <10 × α (Fxy). Further, the relationship of 3 × α (Fxy) <α (Fz) <10 × α (Fxy) and the relationship of 10 ppm / ° C. <α (adz) <α (Fz) should be satisfied at 125 ° C. or higher and 150 ° C. or lower. Is preferred. When satisfied only at a temperature lower than 125 ° C., it is difficult to ensure resistance to a long-term reliability test (thermal shock test, high temperature holding test, etc.) performed at 150 ° C. or lower. In addition, if satisfied at a temperature higher than 150 ° C., it is unavoidable that a very special adhesive or polyimide must be used and the cost becomes high. Therefore, the relationship of 3 × α (Fxy) <α (Fz) <10 × α (Fxy) and the relationship of 10 ppm / ° C <α (adz) <α (Fz) is satisfied at 125 ° C. or more and 150 ° C. or less. preferable.

  In the above example, the polyimide thickness is set to 12.5 microns, and the adhesive layer thickness is set to 5 microns on one side (total 10 microns). By making the adhesive layer thickness 0.7 times or more and 3.5 times or less in this way, the thermal expansion coefficient of the substrate itself can be reduced, and the spread of vias due to the flow of the adhesive during curing can be suppressed. Thus, a small diameter via can be formed. If it is less than 0.7 times, the thermal expansion coefficient in the z direction of the substrate itself cannot be reduced, and if it is more than 3.5 times, the spread of vias due to flow during curing of the adhesive cannot be suppressed. It is preferably 7 times or more and 3.5 times or less. This time, the thickness of the adhesive layer after heating and pressing was almost the same as the thickness of the adhesive layer 2 before curing, but this can be adjusted by adjusting the rheology during melting of the adhesive layer 2. Furthermore, by setting the glass transition temperature of the adhesive layer to 155 ° C. or more and 300 ° C. or less and the coefficient of thermal expansion of 155 ° C. or less to 10 ppm / ° C. or more and 150 ppm / ° C. or less, a long-term reliability test performed at 150 ° C. or less and 200 It is possible to easily and easily ensure the resistance to both lead-free reflow tests performed at a temperature of ℃ or higher. When the glass transition temperature is set to 155 ° C. or lower, the adhesive layer moves from the glass region to the rubber region when a temperature load of 150 ° C. is applied, and the thermal expansion coefficient increases, making it difficult to ensure reliability. On the other hand, when the glass transition point is set to 300 ° C. or higher, an epoxy adhesive has a very high curing density, so that the amount of curing shrinkage during heating and pressurization is large, and the substrate is likely to be warped or swelled. In addition, in the case of polyimide, a special solvent must be used at the time of coating, which is very disadvantageous in terms of cost. Therefore, it is preferable to set the glass transition temperature to 155 ° C. or higher and 300 ° C. or lower. The adhesive layer thickness is not limited to 5 microns, but can be adjusted according to the thickness of the polyimide and the diameter of the through hole.

  Next, when the wiring material 7 is patterned by etching to form the wiring 8, the state shown in FIG. 2A is obtained, and the double-sided wiring substrate 9 in which the wiring 8 protrudes from the insulating base 3 can be formed.

  Subsequently, as shown in FIG. 2 (b), after the electrical insulating base material 10 and the wiring material 7 are positioned and laminated on both sides of the double-sided wiring board 9, the materials are bonded by heating and pressing in a hot press process, and molding is performed. If it does, it will be in the state shown in FIG.2 (c). In addition, you may use resin press sheets, such as PE which supplement wiring embedding in the case of a hot press.

  Here, the electrically insulating base material 10 has the adhesive layer 2 formed on both surfaces of the heat-resistant film 1, the through holes 5 and the conductive paste 6 are provided, and the protective film 4 on the surface is removed. Basically, the same type of material can be used as the insulating base material 10 as the insulating base material 10, but the functions and functions required for the electrically insulating base material are different. It is also possible to do. In other words, since it is necessary to embed the wiring 8 for the electrically insulating substrate 10, specifically, the wiring 8 side may be set thicker than the opposite side so that the thickness of the adhesive on the front and back surfaces is different. Is possible. The application thickness of the adhesive can be adjusted by the pattern of the wiring 8.

  Subsequently, when the wiring material 7 on the outermost surface is patterned by etching or the like, the multilayer wiring board 11 shown in FIG. 2D is obtained. Here, a four-layer board is used as an example of the multilayer wiring board. However, the number of wiring layers is not limited to this, and the number of wiring layers can be increased by repeating the same process.

  [Table 1] and [Table 2] show the results of conducting a lead-free reflow test and a gas phase thermal shock test on the multilayer substrate having four wiring layers formed as described above.

  [Table 1] shows an example of a lead-free reflow test result (260 ° C. peak) (polyimide thickness: 12.5 μm). The ratio of the adhesive thickness to the polyimide thickness is 0.5, 0.7, It is a test result of lead-free reflow when 1.0, 3.5, and 4.0 are set.

  In [Table 1], Comparative Example 1 (no adhesive) is an example of a conventional product using liquid polyimide instead of a film. Comparative Example 2 uses a conventional adhesive that satisfies (α (adz) ≧ α (Fz)). The invention uses an adhesive (adhesive developed for the present application) that satisfies (α (adz) <α (Fz)). Here, the adhesive developed for the present application means that the epoxy resin and reaction initiator contained in the adhesive are devised, the glass transition point after curing is 150 ° C. or higher, and silica filler is added to heat in the z direction. The expansion coefficient is 10 ppm / ° C. or more and smaller than the thermal expansion coefficient in the z direction of polyimide.

  From the results of [Table 1], in the lead-free reflow test, Comparative Example 1 (without adhesive) was ○, but in Comparative Example 2, Δ was 0.5, and 0.7, 1.0, It was (triangle | delta) -x in 3.5 and 4.0. On the other hand, in the product of the invention, it was ◯ at a magnification of 0.5 to 3.5 and x at 4.0.

  [Table 2] shows an example of a gas-phase thermal shock test result (150 ° C.-65 ° C. for 30 minutes each) (polyimide thickness: 12.5 μm). It is a test result of a vapor phase thermal shock test when it is set to 0.5, 0.7, 1.0, 3.5, and 4.0.

  In [Table 2], Comparative Example 1 (without adhesive) is an example of a conventional product using liquid polyimide instead of a film. Comparative Example 2 uses a conventional adhesive that satisfies (α (adz) ≧ α (Fz)). The invention uses an adhesive (adhesive developed for the present application) that satisfies (α (adz) <α (Fz)). Here, the adhesive developed for the present application means that the epoxy resin and reaction initiator contained in the adhesive are devised, the glass transition point after curing is 150 ° C. or higher, and silica filler is added to heat in the z direction. The expansion coefficient is 10 ppm / ° C. or more and smaller than the thermal expansion coefficient in the z direction of polyimide.

  From the results of [Table 2], in the gas phase thermal shock test, Comparative Example 1 (without adhesive) was Δ to ×, but in Comparative Example 2, the magnification was 0.5, 0.7, 1.0. It was x in (triangle | delta) -x and magnification 3.5, 4.0. On the other hand, in the product according to the invention, Δ was 0.5 at a magnification, ○ was 0.7, 1.0, and 3.5, and X was 4.0.

  From the above [Table 1] and [Table 2], only when α (adz) <α (Fz) and the adhesive thickness is 0.7 to 3.5 times the polyimide thickness, The reliability to the phase thermal shock test could be secured at the same time.

  An example of the results of experiments on polyimide having a thickness different from that in Example 1 is shown using Example 2.

  By the same operation as in Example 1, a multilayer substrate having four wiring layers was prepared using polyimide of 25 microns and 7.5 microns, and the results of the lead-free reflow test and the vapor phase thermal shock test were obtained. It shows from [Table 3] to [Table 6].

  [Table 3] shows an example of a lead-free reflow test result (260 ° C. peak) (polyimide thickness: 25 μm), and the ratio of the adhesive thickness to the polyimide thickness is 0.5, 0.7, 1. It is a test result of lead-free reflow when it is set to 0, 3.5, and 4.0.

  In [Table 3], Comparative Example 1 (without an adhesive) is an example of a conventional product using liquid polyimide instead of a film. Comparative Example 2 uses a conventional adhesive that satisfies (α (adz) ≧ α (FIz)). The invention uses an adhesive (adhesive developed for the present application) that satisfies (α (adz) <α (Fz)). Here, the adhesive developed for the present application means that the epoxy resin and reaction initiator contained in the adhesive are devised, the glass transition point after curing is 150 ° C. or higher, and silica filler is added to heat in the z direction. The expansion coefficient is 10 ppm / ° C. or more and smaller than the thermal expansion coefficient in the z direction of polyimide.

  From the results of [Table 3], in the lead-free reflow test, Comparative Example 1 (without adhesive) was ◯, but in Comparative Example 2, Δ was 0.5 and magnifications were 0.7, 1.0, It was (triangle | delta) -x in 3.5 and 4.0. On the other hand, in the products according to the invention, the magnifications were 0.5, 0.7, 1.0, and 3.5, and ○ and 4.0 were x.

  [Table 4] shows an example of a gas-phase thermal shock test result (150 ° C.-65 ° C. for 30 minutes each) (polyimide thickness: 25 μm), and the ratio of the adhesive thickness to the polyimide thickness is 0.5. , 0.7, 1.0, 3.5, and 4.0, it is a test result of the vapor phase thermal shock test.

  In [Table 4], Comparative Example 1 (without an adhesive) is an example of a conventional product using liquid polyimide instead of a film. Comparative Example 2 uses a conventional adhesive that satisfies (α (adz) ≧ α (Fz)). The invention uses an adhesive (adhesive developed for the present application) that satisfies (α (adz) <α (Fz)). Here, the adhesive developed for the present application means that the epoxy resin and reaction initiator contained in the adhesive are devised, the glass transition point after curing is 150 ° C. or higher, and silica filler is added to heat in the z direction. The expansion coefficient is 10 ppm / ° C. or more and smaller than the thermal expansion coefficient in the z direction of polyimide.

  From the results of [Table 4], in the gas phase thermal shock test, Comparative Example 1 (without adhesive) was Δ to ×, but in Comparative Example 2, the magnification was 0.5, 0.7, 1.0. It was x in (triangle | delta) -x and magnification 3.5, 4.0. On the other hand, in the product according to the invention, Δ was 0.5 at a magnification, ○ was 0.7, 1.0, and 3.5, and X was 4.0.

  [Table 5] shows an example of a lead-free reflow test result (260 ° C. peak) (polyimide thickness: 7.5 μm), and the ratio of the adhesive thickness to the polyimide thickness is 0.5, 0.7, It is a test result of lead-free reflow when 1.0, 3.5, and 4.0 are set.

  In [Table 5], Comparative Example 1 (without adhesive) is an example of a conventional product using liquid polyimide instead of a film. Comparative Example 2 uses a conventional adhesive that satisfies (α (adz) ≧ α (Fz)). The invention uses an adhesive (adhesive developed for the present application) that satisfies (α (adz) <α (Fz)). Here, the adhesive developed for the present application means that the epoxy resin and reaction initiator contained in the adhesive are devised, the glass transition point after curing is 150 ° C. or higher, and silica filler is added to heat in the z direction. The expansion coefficient is 10 ppm / ° C. or more and smaller than the thermal expansion coefficient in the z direction of polyimide.

  From the results of [Table 5], in the lead-free reflow test, Comparative Example 1 (without adhesive) was ○, but in Comparative Example 2, Δ was 0.5, and 0.7, 1.0, It was (triangle | delta) -x in 3.5 and 4.0. On the other hand, in the products according to the invention, the magnifications were 0.5, 0.7, 1.0, and 3.5, and ○ and 4.0 were x.

  [Table 6] shows an example of a gas-phase thermal shock test result (150 ° C.-65 ° C. for 30 minutes each) (polyimide thickness: 7.5 μm). It is a test result of a vapor phase thermal shock test when it is set to 0.5, 0.7, 1.0, 3.5, and 4.0.

  In [Table 6], Comparative Example 1 (without adhesive) is an example of a conventional product using liquid polyimide instead of a film. Comparative Example 2 uses a conventional adhesive that satisfies (α (adz) ≧ α (Fz)). The invention uses an adhesive (adhesive developed for the present application) that satisfies (α (adz) <α (Fz)). Here, the adhesive developed for the present application means that the epoxy resin and reaction initiator contained in the adhesive are devised, the glass transition point after curing is 150 ° C. or higher, and silica filler is added to heat in the z direction. The expansion coefficient is 10 ppm / ° C. or more and smaller than the thermal expansion coefficient in the z direction of polyimide.

  From the results of [Table 6], in the gas phase thermal shock test, Comparative Example 1 (without adhesive) was Δ to ×, but in Comparative Example 2, the magnification was 0.5, 0.7, 1.0. It was x in (triangle | delta) -x and magnification 3.5, 4.0. On the other hand, in the product according to the invention, Δ was 0.5 at a magnification, ○ was 0.7, 1.0, and 3.5, and X was 4.0.

  From [Table 3] to [Table 6], α (adz) <α (Fz) and adhesive thickness even when the polyimide thickness is 25 μm and 7.5 μm, as in the case of using 12.5 μm. Only when the thickness is 0.7 times or more and 3.5 times or less of the polyimide thickness, the reliability to the lead-free reflow test and the vapor phase thermal shock test can be secured at the same time.

  In addition, it is thought that the same result is acquired even if the thickness of a polyimide is 5.0 micrometers or less.

  A multilayer substrate (2, 4, 6, 10 layers) in which the total number of wiring layers was changed by the same operation as in Example 1 and the results of conducting a lead-free reflow test and a gas phase thermal shock test were Table 7] and [Table 8].

  [Table 7] shows an example of the lead-free reflow test result (260 ° C. peak) (polyimide thickness: 12.5 μm adhesive thickness: 5 μm on both sides of the polyimide), and the total number of wiring layers is 2, 4 , 6 and 10 are test results of lead-free reflow when changed.

  In [Table 7], Comparative Example 1 (without adhesive) is an example of a conventional product using liquid polyimide instead of a film. Comparative Example 2 uses a conventional adhesive that satisfies (α (adz) ≧ α (Fz)). The invention uses an adhesive (adhesive developed for the present application) that satisfies (α (adz) <α (Fz)). Here, the adhesive developed for the present application means that the epoxy resin and reaction initiator contained in the adhesive are devised, the glass transition point after curing is 150 ° C. or higher, and silica filler is added to heat in the z direction. The expansion coefficient is 10 ppm / ° C. or more and smaller than the thermal expansion coefficient in the z direction of polyimide.

  From the results of [Table 7], in the lead-free reflow test, Comparative Example 1 (without adhesive) was ○ when the total number of wiring layers was 2, 4, 6, 10; When the total number of layers was 2, the case was ◯, the case of 4 was Δ to x, and the cases of 6 and 10 were x. On the other hand, when the total number of the wiring layers was 2, 4, 6, 10 in the invention, it was ◯.

  [Table 8] shows an example of a gas-phase thermal shock test result (150 ° C.-65 ° C. for 30 minutes each) (polyimide thickness: 12.5 μm, adhesive thickness: 5 μm on both sides of the polyimide) It is a test result of a gas phase thermal shock test when the total number of layers is changed to 2, 4, 6, and 10.

  In [Table 8], Comparative Example 1 (without adhesive) is an example of a conventional product using liquid polyimide instead of a film. Comparative Example 2 uses a conventional adhesive that satisfies (α (adz) ≧ α (Fz)). The invention uses an adhesive (adhesive developed for the present application) that satisfies (α (adz) <α (Fz)). Here, the adhesive developed for the present application means that the epoxy resin and reaction initiator contained in the adhesive are devised, the glass transition point after curing is 150 ° C. or higher, and silica filler is added to heat in the z direction. The expansion coefficient is 10 ppm / ° C. or more and smaller than the thermal expansion coefficient in the z direction of polyimide.

  From the results of [Table 8], in the gas phase thermal shock test, in Comparative Example 1 (without adhesive), the total number of wiring layers was [Delta] to X when 2, 6, and [Delta] to X when 4, 6, and 10. However, in Comparative Example 2, the total number of wiring layers was Δ˜x when 2, 4, and x when 6, 10. On the other hand, when the total number of the wiring layers was 2, 4, 6, 10 in the invention, it was ◯.

  As shown in [Table 7] and [Table 8], the effect of the present invention increases as the number of layers increases, and the reliability of the lead-free reflow test and the vapor-phase thermal shock test can be improved even with a 10-layer substrate. We were able to secure at the same time. In addition, if the adhesive thickness is 0.7 times or more and 3.5 times or less of the polyimide thickness, the same effect can be secured.

  Next, as Example 4, the results of experiments on the presence or absence of the compression effect of the conductive paste 6 are shown.

In Example 4, the compression effect of the conductive paste 6 in the multilayer substrate described in Examples 1 to 3 will be described with reference to FIGS.

In Example 4, when filling the through-hole 5 formed in the heat-resistant film 1 with the conductive paste 6, the through-hole 5 is curved by spreading a part of the heat-resistant film 1 surrounding the through-hole 5. A case where the diameter of the narrower one is expanded to reduce the interlayer connection resistance will be described.

  FIG. 3 is a cross-sectional view of the vicinity of the through hole in the multilayer substrate. FIG. 3 illustrates a state in which, for example, the conductive paste 6 is filled in a state in which the through hole 5 formed in the insulating base 3 composed of the heat-resistant film 1 and the adhesive layer 2 formed on both sides thereof is provided with a protruding portion. It corresponds to a sectional view.

  In FIG. 3, 12 is a conductive powder, such as a copper powder added to the conductive paste 6. Reference numeral 13 denotes a curved portion, which is a portion formed by expanding a part of the heat-resistant film 1 surrounding the through hole 5 (not shown). Reference numeral 14 denotes a side surface, which indicates an inner wall surface of the through hole 5 formed in the heat-resistant film 1. The surface roughness of the side surface 14 is determined based on the surface roughness of the surface of the heat-resistant film 1 (that is, the interface between the heat-resistant film 1 and the adhesive layer 2) (for example, Ra, where Ra is defined by JIS or the like). By increasing the length, the bending portion 13 can be easily formed as shown in FIG. This is because the side surface 14 is roughened (that is, the surface area per unit area is increased), whereby the through-hole 5 can be easily expanded (and the stress generated after the expansion can be reduced).

  Reference numeral 15 denotes a wiring center line, which corresponds to the center line of the wiring 8 constituting the multilayer substrate. Reference numeral 16 denotes a side surface auxiliary line, which is an auxiliary line indicating the angle of the side surface of the heat-resistant film 1 (for example, a trapezoid or a part of a cone). Reference numeral 17 denotes a bending portion auxiliary line, which is an auxiliary line indicating the inclination of the bending portion formed in the heat-resistant film 1 surrounding the through hole 5. δ represents an angle between the wiring center line 15 and the side surface auxiliary line 16. β indicates the angle between the side surface auxiliary line 16 and the curved portion auxiliary line 17. As shown in FIG. 3, it is desirable that “β <δ”. By making the angle δ larger than the angle β, as shown in FIG. 3, the narrower outlet of the through-hole 5 can be expanded more widely, and the connection resistance between the plurality of wirings 8 can be reduced.

  In FIG. 3, 18 is a surface contact part, The some copper powder 12 mutually deform | transforms, and shows the part which surface-contacts. In this way, the contact resistance between the copper powders 12 can be reduced by crushing the copper powders 12 until the copper powders 12 are deformed with each other. Moreover, the bending part 13 can be formed so that the copper powder 12 may crush until it mutually deform | transforms so that the through-hole 5 formed in the heat-resistant film 1 may be enclosed by applying a high pressure.

  Reference numeral 19 denotes a binder, which is a thermosetting resin or the like contained in the conductive paste 6.

  Next, using FIG. 4 and FIG. 5, a protruding portion 20 is provided in the conductive paste 6 filled in the through hole 5, and a curved portion 13 is formed around the through hole 5 using the protruding portion 20. Will be explained.

  FIG. 4 is a cross-sectional view showing a state where the through-hole 5 (not shown) is filled with the conductive paste 6 so as to provide a protruding portion.

  In FIG. 4, 20 is a protrusion part, and the protrusion part 20 is formed by peeling the protective film 4 as shown in above-mentioned FIG.1 (d). Note that the height (or the amount of protrusion) of the protruding portion 20 can be increased or decreased by adjusting the thickness of the protective film 4. 21 is an arrow.

  As shown by an arrow 21 in FIG. 4, a wiring material 7 made of copper foil or the like is laminated on the conductive paste 6 provided with the protrusions 20 or the adhesive layer 2. In addition, it is useful to pressurize and heat at the time of this lamination | stacking using a metal mold | die or a press apparatus.

  FIG. 4 is a cross-sectional view illustrating a process following FIG. As shown in FIG. 4, the conductive paste 6 in a state in which the protrusions 20 are provided in the through-holes 5 formed in the insulating base 3 made of the heat-resistant film 1 and the adhesive layer 2 formed on both surfaces thereof is used as a wiring material. Pressurize over 7. By doing so, the copper powders 12 are deformed with each other and brought into surface contact via the surface contact portion 18 (not shown) to obtain the state shown in FIG.

  FIG. 5 is a cross-sectional view showing that the curved portion 13 is positively formed during compression by making the diameter of the protruding portion 20 different on both surfaces of the heat-resistant film 1.

  In FIG. 5, the conductive paste 6 is formed so as to provide the protruding portions 20 a and 20 b on both surfaces of the heat resistant film 1. Thereafter, pressure is applied as shown by an arrow 21c through the wiring material 7 made of copper foil or the like. Here, when the diameter (or width) of the protruding portion 20a is an arrow 21a and the diameter (or width) of the protruding portion 20b is an arrow 21b, the relationship "arrow 21a> arrow 21b" is satisfied. Thus, a force for forming the curved portion 13 (not shown) as shown by the arrow 21d can be generated on the side surface 14 of the heat-resistant film 1. Then, the force shown by the arrow 21d is generated, and in this state, the wiring material 7 is brought into close contact with the conductive paste 6 and the adhesive layer 2 is heated and cured to fix the shape shown in FIG.

  Thus, by satisfying the relationship of “arrow 21a> arrow 21b”, the relationship of “β <δ” can be realized as shown in FIG. 3, and the narrower one of the through holes 5 (not shown) is narrower. The exit (or opening) can be greatly expanded, and the cross-sectional area of the via portion can be increased.

  An example of the results is shown in [Table 9]. [Table 9] is an example showing the relationship between via diameter and via resistance. In [Table 9], the via diameter indicates the relationship between the average diameter of the via (the average of the maximum diameter and the minimum diameter) and the resistance value at that time. In addition, the conventional example is a case where no protrusion is provided, and the embodiment is a case where a protrusion is provided.

  When no protrusion was provided, as shown in [Table 9], the contact between the copper powders 12 became point contact, and the resistance value was 5Ω or more (average via diameter 100 μm), 10Ω or more (average via diameter 75 μm). It was. Further, in the evaluation of reliability, xx indicates failure and ◯ indicates acceptance.

The resistance value includes the wiring resistance.
Reliability is calculated by calculating the rate of change from the initial stage after the circuit-formed multilayer substrate is processed in a high-temperature, high-humidity bath at 85 ° C and 85% for 24 hours and then passed through a 260 ° C peak reflow. . Reliability ○ means that the change in resistance value was less than ± 20%. Reliability XX has a resistance value change of 10 times or more.

  Next, the effect when the diameter of the projecting portion is made different between up and down will be described with reference to [Table 10].

  Further, it is desirable that the diameter (or the opening area) of the through holes 5 formed in the heat resistant film 1 is different on both surfaces of the heat resistant film 1. By making the diameter of the through hole 5 different on both surfaces of the heat-resistant film 1, the filling property of the conductive paste 6 into the through hole 5 is improved, and the narrow side of the through hole 5 (for example, the lower side in FIG. 1) is electrically conductive. By the force of the paste 6, it is possible to obtain an effect of spreading more widely, improving connection stability, and reducing via resistance.

  Furthermore, the thermal expansion coefficient in the xy direction of the heat resistant film 1 is desirably 80 ppm / ° C. or higher. When it is less than 80 ppm / ° C., after the conductive paste 6 filled so as to provide the protrusions 20 in the through-holes 5 of the heat-resistant film 1 is heated and integrated as shown in FIG. The tightening force may be low. Here, the tightening force means that when the binder 19 and the adhesive layer 2 of the conductive paste 6 are cured by heating and then cooled to room temperature (for example, 25 ° C.), the heat-resistant film 1 contracts in the xy direction, From the side surface 14, the conductive paste filled in the through hole 5 is tightened from the periphery. With this tightening force, the adhesion between the side surface 14 of the through-hole 5 formed in the heat-resistant film 1 and the conductive paste 6 filled in the through-hole 5 can be increased, and the side surface 14 of the through-hole 5 and the conductive paste 6 can be increased. Generation of delamination (or delamination or void) at the interface with the substrate is suppressed.

  In addition, as for the thermal expansion coefficient of the xy direction of the heat resistant film 1, 200 ppm / degrees C or less is desirable. When it exceeds 200 ppm / ° C., there is a possibility of affecting the matching accuracy between the patterns between layers when the multilayer wiring board 11 is laminated.

  As shown in FIG. 3 and the like described above, the heat-resistant film 1 exposed on the side surface of the through hole 5 formed in the heat-resistant film 1 has a side surface 14 formed by laser irradiation or the like.

  For example, as shown in FIG. 1B described above, a thin film having a thickness of 25 microns or less is used for the heat-resistant film 1, and the side surface 14 is formed on the heat-resistant film 1 exposed on the side surface of the through hole 5. Then, the conductive paste 6 containing conductive powder as a main component and including the binder 19 is pushed through the protruding portion 20. During the pressing, the adhesive layer 2 and the binder 19 are cured by heating, and then cooled to room temperature, so that the heat-resistant film 1 surrounds the periphery of the through-hole 5 formed in the heat-resistant film 1 surrounding the via portion. A curved portion is formed as shown by an arrow 21d (or protrudes to the outside of the heat-resistant film 1 or to the wiring 8 side). In addition, it is desirable that the curved portion has a ring shape that surrounds the periphery of the through hole 5 by 360 degrees. By making it into a ring shape, the pressure compression effect of the conductive paste 6 can be enhanced. By making the curved portion 13 into a ring shape, the effect of increasing the connection stability of the via portion and reducing the via resistance can be obtained.

  Next, it demonstrates still in detail using FIG. 6 (A)-(C). 6A is a cross-sectional view of the double-sided wiring board 9a when the diameters of the holes on both sides of the heat-resistant film 1 are substantially the same, and FIG. FIG. 6C is a cross-sectional view for explaining a double-sided wiring board 9b that is not provided with the bending portion 13, and FIG. It is sectional drawing of the double-sided wiring board 9c which provided the part 13. FIG.

  As shown in FIG. 6A, in a conventional multilayer wiring board 11 in which a plurality of thin heat-resistant films 1 having a thickness of 25 microns or less are laminated, a through-hole 5 (numbered) is formed in the heat-resistant film 1. Not provided) on both sides of the heat-resistant film 1, the diameters are substantially the same (for example, the difference in the diameters of the holes on both sides is 10% or less, further 5% or less), or the opening area is substantially the same (for example, the holes on both sides). In other words, the difference in the opening area is 10% or less, and further 5% or less. This is because, when the cross-sectional shape of the through-hole 5 formed in the heat-resistant film 1 is a trapezoid, the resistance value of the via portion increases due to the narrower opening portion of the through-hole 5 or the portion having a smaller opening area, or This is because the connection reliability of the via portion is affected.

  However, in the case of the structure of FIG. 6A, since the holes have no directionality, the filling property of the conductive paste 6 may be affected as the diameter becomes smaller.

  In FIG. 6B, the diameters of the through-holes 5 (not denoted by reference numerals) are holes on both sides of the first surface side (for example, the wiring 8a side) and the second surface side (for example, the wiring 8b side). At least one of the diameter or the opening area is different by 15% or more, further 20% or more.

  However, in the case of the structure of FIG. 6B, the large diameter (or opening area) side that contacts the wiring 8a side of the via portion that does not have the ring-shaped curved portion 13 is indicated by the arrow 21a and the small diameter that contacts the wiring 8b side ( Alternatively, when the side of the opening area is indicated by an arrow 21b, a difference of 15% or more, preferably 20% or more occurs between 21a and 21b. Therefore, the electrical resistance between the wirings 8a-8b is represented by an arrow 21b having a small diameter. It is greatly influenced by the diameter of the via part shown.

  As shown in FIG. 6 (C), the inventors addressed such a problem by applying a side surface 14 (numbered) to the heat-resistant film 1 surrounding the through hole 5 (not numbered) 360 degrees. This problem can be solved by providing a ring-shaped curved portion 13 centering on (not).

  That is, in FIG. 6C, the diameter (or opening area) of the through-hole 5 having the ring-shaped curved portion 13 in contact with the wiring 8c side is substantially the same as that of FIG. 6B as shown by the arrow 21c. is there. That is, 21a = 21c. On the other hand, in FIG. 6B, the smaller diameter (or the smaller opening area) is indicated by the arrow 21b, and in FIG. 6C, the smaller diameter (or the smaller opening area) is indicated by the arrow 21d. In this case, the relationship of [21d> 21b] is shown. This is a ring-shaped curved portion around the through-hole 5 (not numbered) of the heat-resistant film 1 in FIG. 6C. This is because 13 (number is not given) is provided.

  As shown in FIG. 6C, by providing a ring-shaped curved portion 13 (no number assigned) around the through-hole 5 (no number assigned) filled with the conductive paste 6 Since the diameter (or opening area or diameter) of the via on the small diameter side indicated by the arrow 21d can be made larger than the case indicated by the arrow 21b, it is useful for reducing the resistance and reliability of the via.

  As the heat resistant film 1, a commercially available polyimide film having heat resistance such as solder reflow is used. The thickness of the heat-resistant film 1 is preferably 25 microns or less, more preferably 18 microns or less. By setting the thickness of the heat-resistant film 1 to 25 microns or less, the ring-shaped curved portion 13 can be easily generated. The heat-resistant film 1 having a heat-resistant film 1 having a thickness of 30 microns or more, and further 50 microns or more has a high waist (for example, film rigidity). Therefore, even if the side surface 14 is formed, the ring-shaped curved portion 13 is hardly generated. There is a case.

  The thickness of the adhesive layer 2 is preferably 25 microns or less, more preferably 15 microns or less, 10 microns or less, and further preferably 7 microns or less. By setting the thickness of the adhesive layer 2 to 25 microns or less, the roughened surface provided on the side of the adhesive layer 2 of the wiring 8 (the roughened surface is not shown in FIGS. 1 and 2), the heat-resistant film 1 and The adhesive strength of can be increased. The thickness of the adhesive layer 2 is the smallest distance between the roughened surface provided on the adhesive layer 2 side of the wiring 8 and the heat resistant film (the distance between the convex portion of the rough surface of the roughened surface and the heat resistant film). ). If the thickness of the adhesive layer 2 exceeds 15 microns, the total thickness of the multilayer wiring board 11 may be affected.

  Note that in FIG. 3 described above, the difference in diameter of the through-hole 5 (not shown) is preferably 10% or more and 100% or less between both surfaces of the heat-resistant film 1. Alternatively, the larger diameter may be 110% or more and 200% or less compared to the smaller diameter.

  For example, as shown in FIG. 6C, the diameter of the large hole (arrow 21c) is 110% or more and 200% or less (that is, the difference in hole diameter is 10% or more with respect to the diameter of the small hole (arrow 21d)). 100% or less), the via resistance can be effectively reduced. In addition, when the diameter (arrow 21c) of a big hole is less than 110%, formation of the curved part 13 may become difficult. On the other hand, if it exceeds 200%, there is a possibility that fine patterning of the wiring 8 and the like will be affected.

  The shape of the curved portion 13 is preferably a ring shape surrounding the through hole 5. By making the ring shape, the shape of the conductive paste 6 constituting the via portion can be stabilized.

  7A and 7B are an SEM photograph of a portion where via portions are stacked in the thickness direction in a four-layer multilayer wiring board 11 prototyped by the inventors and a schematic diagram thereof, and the magnification is 500 times. It is.

  7A and 7B, reference numeral 22 denotes deformed powder, and the copper powder 12 (not shown) is electrically connected to each other through the surface contact portion 18 (not shown) in a deformed state. Yes. By using the copper powder 12 as the deformed powder 22, the via resistance is reduced, and the curved portion 13 is provided in a part of the heat-resistant film 1 constituting the via, so that the physical cross-sectional area of the via can be expanded.

  8A and 8B are an SEM photograph of a portion where via portions are stacked in the thickness direction in a four-layer multilayer wiring board 11 prototyped by the inventors, respectively, and a schematic diagram thereof. The magnification is 3000 times. It is.

  8 (A) and 8 (B), 22 is deformed powder, and copper powder 12 (not shown) is electrically connected to each other through the surface contact portion 18 (not shown) in a deformed state. Yes. By using the copper powder 12 as the deformed powder 22, the via resistance is reduced, and the curved portion 13 is provided in a part of the heat-resistant film 1 constituting the via, so that the physical cross-sectional area of the via can be expanded.

  FIGS. 9A and 9B are an SEM photograph and a schematic diagram of a portion where via portions are stacked in the thickness direction in a four-layer multilayer wiring board 11 prototyped by the inventors.

  9A and 9B, as the heat-resistant film 1, a commercially available polyimide film (thickness: 18 microns) was used. Further, the wiring material 7 (not given a number) made of copper foil constituting the wiring 8 is subjected to a roughening process for improving the adhesion with the adhesive layer 2.

  As shown in FIGS. 7A, 7B, 9A, and 9B, a curved portion 13 is provided in a part of the heat-resistant film 1, and the curved portion 13 is used to provide the heat-resistant film 1. It can be seen that the diameter of the smaller through-hole 5 can be increased.

  Further, as shown in FIGS. 7A, 7B, 9A, and 9B, when the curved portion 13 is formed in the via, the via portion is locally thickened so that the conductive paste 6 is coated. It can be seen that since the compressive force can be applied more effectively, the via resistance can be reduced and the ring-shaped curved portion 13 can be formed in the portion surrounding the through hole 5 of the heat-resistant film 1.

  Next, an example of an experimental result of optimization of the ring-shaped curved portion 13 will be described using [Table 10].

  [Table 10] shows the results of trial production of the invention products (samples (1) and (2)) and the conventional product (sample (3)). In [Table 10], the lower hole diameter refers to the smaller diameter of the through holes 5 formed in the heat-resistant film 1 (for example, the direction indicated by the arrow 21b in FIG. 5).

  Comprehensive judgment was made based on via resistance and usage of some products. In addition, “good” was evaluated as “good”, “decided” when it was unclear, and “NG” as “poor”.

  From [Table 10], as shown in FIG. 5 to FIG. 9A and FIG. 9B, a sample provided with a curved portion in the via portion, compared to a sample that did nothing (conventional sample (3)). (Inventive samples (1) and (2)), the lower hole diameter (for example, arrow 21b in FIG. 5) can be increased despite the small upper hole diameter (for example, arrow 21a in FIG. 5). It can be seen that the via resistance can be reduced.

  [Table 10] shows an example of the first embodiment. By using the multilayer wiring board 11 having the structure shown in FIG. Needless to say, resistance can be achieved.

  The present invention is composed of a thin-layer, light-weight, high-density wiring and highly reliable all-layer IVH structure multilayer wiring board and a manufacturing method thereof. The present invention makes it possible to achieve both long-term reliability of 150 ° C. or lower and resistance to a reflow test of 200 ° C. or higher, which has been difficult until now. As a result, even if it is used for a thin multilayer substrate having fine and high-density wiring, which is used for signal transmission for screen drawing of a mobile phone or a notebook computer, it is useful for manufacturing a highly reliable substrate.

DESCRIPTION OF SYMBOLS 1 Heat-resistant film 2 Adhesive layer 3 Insulating base material 4 Protective film 5 Through-hole 6 Conductive paste 7 Wiring material 8 Wiring 9 Double-sided wiring board 10 Electrically insulating base material 11 Multilayer wiring board 12 Copper powder 13 Curved part 14 Side surface 15 Wiring center line 16 Side auxiliary line 17 Bending part auxiliary line 18 Surface contact part 19 Binder 20 Protruding part 21 Arrow 22 Deformed powder

Claims (8)

A plurality of heat-resistant films, a through-hole formed in the heat-resistant film, a conductive paste mainly composed of conductive powder filled in the through-hole, and a plurality of layers electrically connected via the conductive paste A multilayer substrate comprising a wiring layer and an adhesive layer for bonding the heat-resistant film and the wiring,
The total thickness of the adhesive layer is 0.7 to 3.5 times the total thickness of the heat-resistant film,
The conductive paste has an aggregate formed by forming a surface contact portion in which the conductive powders are in surface contact with each other,
A multilayer substrate in which the thermal expansion coefficient in the z direction is larger than the thermal expansion coefficient in the xy direction of the heat resistant film. A plurality of heat-resistant films, a through-hole formed in the heat-resistant film, a conductive paste mainly composed of conductive powder filled in the through-hole, and a plurality of layers electrically connected via the conductive paste A multilayer substrate comprising a wiring layer and an adhesive layer for bonding the heat-resistant film and the wiring,
The total thickness of the adhesive layer is 0.7 to 3.5 times the total thickness of the heat-resistant film,
When the thermal expansion coefficient in the z direction in the temperature range of 125 ° C. or more and 150 ° C. or less of the heat resistant film is α (Fz) and the thermal expansion coefficient in the z direction of the adhesive layer is α (adz), 50 ppm / ° C. <α (Fz) <200 ppm / ° C.
10 ppm / ° C. <α (adz) <α (Fz)
Satisfies the multilayer board. A plurality of heat-resistant films, a through-hole formed in the heat-resistant film, a conductive paste mainly composed of conductive powder filled in the through-hole, and a plurality of layers electrically connected to each other via the conductive paste A multilayer substrate comprising a wiring and an adhesive layer for bonding the heat-resistant film and the wiring,
The thermal expansion coefficient in the z direction in the temperature range of 125 ° C. to 150 ° C. of the heat resistant film is α (Fz), the thermal expansion coefficient in the xy direction is α (Fxy), and the thermal expansion coefficient in the z direction of the adhesive layer is α. (Adz)
3 × α (Fxy) <α (Fz) <10 × α (Fxy)
10 ppm / ° C. <α (adz) <α (Fz)
Satisfied with
The conductive paste has an assembly that forms a surface contact portion when the conductive powders deform and contact each other to form a path that electrically connects the wirings. Multilayer board. The multilayer substrate according to any one of claims 1 to 3, wherein the heat-resistant film is polyimide having a thickness of 30 µm or less, and the thickness of the adhesive layer is 1 µm or more and 10 µm or less. At least a heat-resistant film having a thickness of 25 microns or less, wiring fixed to both surfaces of the heat-resistant film via an adhesive layer, holes formed in the heat-resistant film, and the holes filled in the wiring A multilayer wiring board having a conductive paste to be connected, the diameter of the hole being different from 10% to 100% on both surfaces of the heat-resistant film, and the average thickness of the adhesive layer being from 3 microns to 25 microns , Having a curved portion around the hole,
When the average center line of the wiring formed on the multilayer wiring board and the angle between the processed surface formed on the heat resistant film is β, the angle between the center line and the curved portion is α,
Multilayer substrate where α <β. The multilayer substrate according to claim 5, wherein the diameter of the hole formed in the heat-resistant film is different from 10% to 100% on both sides, and has a curved portion around the hole. An insulating base material process in which an adhesive layer is formed on both sides of the heat-resistant film to form an insulating base material;
A protective film process for forming a protective film on the insulating substrate;
A through hole step of forming a through hole in the insulating substrate;
A filling step of filling the through holes with a conductive paste;
A protrusion step of peeling the protective film and forming a protrusion made of the conductive paste,
An integration process in which a copper foil is disposed so as to cover the protruding portion and is heated under pressure, and the conductive paste, the copper foil, and the insulating base material are integrated.
After the integration step, patterning the copper foil to form a wiring, and
Have
In the integration step, the conductive powder contained in the conductive paste is filled with high density in the holes of the heat-resistant film until an aggregate is formed through a surface contact portion formed by surface contact with each other. A method for manufacturing a multilayer substrate. at least,
A protective process in which an adhesive layer is formed on both sides of the heat-resistant film and further protected with a protective film;
Forming a hole in the heat-resistant film having a diameter different from 10% to 100% on both sides;
A filling step of filling the holes with a conductive paste;
A protruding step of peeling the protective film and forming a protruding portion made of the conductive paste;
A compression bending step of compressing the protrusion with copper foil and providing a ring-shaped bending portion on the heat-resistant film around the hole;
A wiring forming step of patterning the copper foil to form a wiring;
The manufacturing method of the multilayer wiring board which has this.
In the temperature range of 125 ° C. or more and 150 ° C. or less of the heat-resistant film 1