Interconnection substrate

Abstract

An interconnection substrate includes: a substrate having a first surface and a second surface opposite the first surface; and a transmission line including two parallel through-hole interconnections that are exposed to the first and second surfaces and are formed inside the substrate. Also, at least one of the two through-hole interconnections includes a narrow portion having a smaller diameter than a diameter of the through-hole interconnection in the first surface and a diameter of the through-hole interconnection in the second surface.

Claims

1. An interconnection substrate, comprising: a substrate having a first surface and a second surface opposite the first surface; a thermal relaxation resin provided on the first surface; and a transmission line including two parallel surface wirings formed on the thermal relaxation resin and two parallel through-hole interconnections, the two parallel through-hole interconnections being exposed to the first and second surfaces and being formed inside the substrate, and one of the two parallel through-hole interconnections being electrically connected to one of the two surface wirings and an other of the two parallel through-hole interconnections being electrically connected to an other of the two surface wirings, wherein at least one of the two through-hole interconnections includes a narrow portion having a smaller diameter than a diameter of the through-hole interconnection in the first surface and a diameter of the through-hole interconnection in the second surface, and the two surface wirings are connected to respective through-hole interconnections through a pitch adjusting portion configured to adjust each wiring pitch.

2. The interconnection substrate according to claim 1, wherein each of the two through-hole interconnections has the narrow portion, and the narrow portions of the two through-hole interconnections are disposed at the same distance from the first surface.

3. The interconnection substrate according to claim 2, wherein in the narrow portion, a portion having a smallest diameter is provided at a center of the substrate in a thickness direction of the substrate.

4. The interconnection substrate according to claim 2, wherein shapes of the two through-hole interconnections on a cross-section parallel to the first surface are the same throughout an entire thickness of the substrate.

5. The interconnection substrate according to claim 1, wherein the substrate is an monolithic structure.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A is a transparent perspective view showing an example of the configuration of an interconnection substrate of the present invention.

(2) FIG. 1B is a transparent perspective view showing a modification of the interconnection substrate according to an embodiment of the present invention.

(3) FIG. 2 is an enlarged transparent perspective view of portions of through-hole interconnections in the interconnection substrate shown in FIG. 1.

(4) FIG. 3 is an enlarged plan view of portions of through-hole interconnections in the interconnection substrate shown in FIG. 1.

(5) FIG. 4A is a diagram for explaining the principle of the present invention, and is a cross-sectional view showing an example of the through-hole interconnections of the interconnection substrate according to the present invention.

(6) FIG. 4B is a cross-sectional view showing a modification of the through-hole interconnections of the interconnection substrate according to the present invention.

(7) FIG. 4C is a cross-sectional view showing a modification of the through-hole interconnections of the interconnection substrate according to the present invention.

(8) FIG. 5A is an enlarged plan view of portions of through-hole interconnections in an interconnection substrate including straight-shaped through-hole interconnections.

(9) FIG. 5B is a transparent perspective view showing the interconnection substrate including straight-shaped through-hole interconnections.

(10) FIG. 6 is a diagram showing an electromagnetic field simulation result of the frequency characteristics of the reflection coefficient in the interconnection substrate shown in FIG. 5.

(11) FIG. 7 is a diagram showing an electromagnetic field simulation result of the frequency characteristics of the reflection coefficient in the interconnection substrate shown in FIG. 1.

(12) FIG. 8 is a cross-sectional view showing another example of the through-hole interconnections.

(13) FIG. 9 is a cross-sectional view showing another example of the through-hole interconnections.

(14) FIG. 10 is a cross-sectional view showing another example of the through-hole interconnections.

(15) FIG. 11A is a cross-sectional view showing an example of the conventional interposer substrate.

(16) FIG. 11B is a transparent perspective view showing an example of the conventional interposer substrate.

(17) FIG. 12 is a transparent perspective view showing an example of through-hole interconnections based on the conventional differential transmission method.

(18) FIG. 13 is a cross-sectional view showing the conventional differential through-hole interconnections.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(19) Hereinafter, an interconnection substrate according to an embodiment of the present invention will be described with reference to the figures.

(20) FIG. 1A is a transparent perspective view showing a configuration example of an interconnection substrate 1 according to an embodiment of the present invention.

(21) The interconnection substrate 1 according to the embodiment of the present invention includes a transmission line 12 and two through-hole interconnections 16A and 16B on one surface 10a (first surface) of a substrate 10. The transmission line 12 is configured to include two surface wirings 11A and 11B disposed in parallel, and the two through-hole interconnections 16A and 16B are formed by filling or depositing conductors in through holes 14A and 14B formed in the substrate 10 and are electrically connected to the two surface wirings 11A and 11B, respectively.

(22) Although a case where the transmission line 12 is used as a differential transmission line will be referred to in the explanation of the embodiment of the present invention, the transmission line 12 of the present invention is not limited to the differential transmission line. In addition, when the transmission line 12 is used as a differential transmission line, a ground wiring (not shown) may be appropriately provided on the interconnection substrate 1.

(23) The substrate 10 is formed of a material having small dielectric loss in a high-frequency region. Examples of the material of the substrate 10 are fluorine-based resin materials, for example, quartz, borosilicate glass, high insulating silicon, fine ceramics, liquid crystal polymers, Teflon (registered trademark), etc. Fluorine-based materials, such as quartz, liquid crystal polymers, and Teflon, are preferably used as the materials of the substrate 10 since the dielectric constant is especially small. The thickness of the substrate 10 is preferably set so that the interconnection substrate 1 has a predetermined thickness or more and the transportability of a wafer is satisfied. For example, the thickness of the substrate 10 is set to 0.1 to 2.0 mm. In addition, the substrate 10 of the present invention is preferably an monolithic structure.

(24) The transmission line 12 is configured to include the two parallel surface wirings 11A and 11B (surface wirings). The two surface wirings 11A and 11B have positive and negative polarities, respectively, and form a transmission line in pairs.

(25) The surface wirings 11A and 11B are formed of a conductor having low resistance. For example, the surface wirings 11A and 11B are formed by electrolytic plating of Cu. The film thickness, the wiring width, and the distance of the surface wirings 11A (+) and 11B (−) can be designed to have desired characteristic impedance.

(26) As shown in FIG. 1B, in order to reduce the thermal stress on the substrate 10 that occurs when forming the surface wirings, a thermal relaxation resin 17 may be provided on the one surface 10a of the substrate 10, and the surface wirings 11A and 11B may be formed on the thermal relaxation resin 17. As a material of the thermal relaxation resin 17, it is preferable to use polyimide resin or silicon resin having high heat resistance. In FIG. 1B the thermal relaxation resin 17 is also provided on the other surface (second surface) 10b of the substrate 10. However, the thermal relaxation resin 17 may be provided on only one of the surfaces 10a and 10b.

(27) Electrode pads 13A and 13B are electrically connected to the surface wirings 11A and 11B, respectively. The electrode pads 13A and 13B are formed on one surface 10a of the substrate 10, and at least parts of the electrode pads 13A and 13B are provided so as to be exposed to the hole from one opening of the through holes 14A and 14B.

(28) As materials of the electrode pads 13A and 13B, for example, materials having excellent electrical conductivity, such as aluminum (Al), copper (Cu), aluminum silicon (Al—Si) alloy, or aluminum silicon copper (Al—Si—Cu) alloy, are preferably used.

(29) FIG. 2 is an enlarged transparent perspective view of portions of the through-hole interconnections 16A and 16B in the interconnection substrate 1 according to the embodiment of the present invention. FIG. 3 is an enlarged plan view of portions of the through-hole interconnections 16A and 16B in the interconnection substrate 1 according to the embodiment of the present invention.

(30) The through-hole interconnections 16A and 16B are disposed so as to penetrate the substrate 10 from the other surface 10b side to the one surface 10a side of the substrate 10, and the through-hole interconnections 16A and 16B are configured to include through holes 14A and 14B, through which parts of the electrode pads 13A and 13B are exposed, and conductors that are filled or deposited within the through holes 14A and 14B. The through-hole interconnections 16A and 16B are electrically connected to the two surface wirings 11A and 11B, which form the transmission line 12, through the electrode pads 13A and 13B, respectively.

(31) As shown in FIG. 2, in the interconnection substrate 1 according to the embodiment of the present invention, at least one of the two through holes 14A and 14B has narrow portions 15A and 15B in which the distance between the two through holes 14A and 14B is locally increased. That is, at least one of the two through-hole interconnections 16A and 16B formed by filling or depositing conductors within the two through holes 14A and 14B has narrow portions 15A and 15B in which the separation distance between the two through-hole interconnections 16A and 16B is locally increased.

(32) As an example, FIG. 2 shows a case where both of the two through holes 14A and 14B have the narrow portions 15A and 15B. The narrow portions 15A and 15B of the two through holes 14A and 14B are disposed at the same distance from one surface of the substrate 10. Here, the narrow portions 15A and 15B are located at the center of the substrate 10 in the thickness direction. In the example shown in FIG. 2, in the shapes of the two through holes 14A and 14B, the diameters of the through holes at the same distance from one surface of the substrate 10 are the same. That is, the cross-sectional shapes of the two through holes 14A and 14B that are parallel to one surface of the substrate 10 are the same throughout the entire thickness of the substrate. If the two through holes 14A and 14B have the same cross-sectional shape, the phases of high-frequency signals flowing through both the through-hole interconnections are less likely to shift in time, which is preferable. Specifically, assuming that a direction perpendicular to the signal transmission direction from one end of a through hole is an X axis and the above end of the through hole is the origin of the signal phase, a signal phase difference between a through hole of positive polarity and a through hole of negative polarity at X=0 is 0. On the other hand, when the narrow portions 15A and 15B are disposed at different distances from one surface of the substrate 10, the length of the signal path is different between the through hole on the positive polarity side and the through hole on the negative polarity side. For this reason, the phase difference is not 0. This causes a phase difference and thus causes waveform distortion of a skew.

(33) In the two through-hole interconnections 16A and 16B, at least one of the two through holes 14A and 14B has the narrow portions 15A and 15B. Therefore, it is possible to achieve the same effect that the distance between the conventional straight-shaped through holes is increased. That is, in the conventional straight-shaped through-hole interconnections, assuming that the distance between the through holes to satisfy the predetermined impedance conditions is X and the distance between through-hole interconnections including narrow portions is Y, the relationship of Y<X is necessarily satisfied.

(34) The basic principle of the present invention is that, when the distance between the through-hole interconnections 16A and 16B including the narrow portions 15A and 15B according to the embodiment of the present invention is the same as the distance between the conventional straight-shaped through-hole interconnections, the relationship of C.sub.0>C.sub.1 is satisfied assuming that the capacitive component for the former case is C.sub.0 (F) and the capacitive component for the latter case is C.sub.1 (F). By narrowing the distance between the through holes 14A and 14B including the narrow portions 15A and 15B, a capacitive component corresponding to the deficit is increased. As a result, it is possible to narrow the distance between the through holes 14A and 14B.

(35) As a result, in the present invention, it is possible to narrow the distance between the two through-hole interconnections 16A and 16B, and thus, to provide the interconnection substrate 1 with which high-density mounting can be realized.

(36) In the related art (FIGS. 11A to 13), on the surface of the substrate 100, V-shaped pitch adjusting portions 111Ap (111A) and 111Bp (111B) for adjusting the pitches between the two parallel transmission lines 111A and 111B (112) and the two parallel through-hole interconnections 110A and 110B are formed between the two parallel transmission lines 111A and 111B (112) and the two parallel through-hole interconnections 110A and 110B. In the V-shaped pitch adjusting portion, the distance between wirings is not constant. Therefore, impedance mismatch occurs and a signal waveform is distorted. For this reason, there has been a problem in that the transmission characteristics are degraded.

(37) However, according to the present invention (FIGS. 1 to 3), since it is possible to reduce the distance between the through-hole interconnections 16A and 16B as described above, it is not necessary to greatly change the distance between wirings in the V-shaped pitch adjusting portions 11Ap (11A) and 11Bp (11B). That is, the distance between wirings in the pitch adjusting portions 11Ap (11A) and 11Bp (11B) can be made close to the distance between the surface wirings 11A and 11B. As a result, since impedance mismatch is less likely to occur in the pitch adjusting portions 11Ap (11A) and 11Bp (11B), degradation of the transmission characteristics can be suppressed.

(38) FIG. 4A is a diagram for explaining the principle of the present invention, and is a cross-sectional view showing parts of the through-hole interconnections 16A and 16B in the interconnection substrate 1. Assuming that the diameter of each of top and bottom surface portions of the through holes 14A and 14B of the through-hole interconnections 16A and 16B is D, the through holes 14A and 14B of the through-hole interconnections 16A and 16B have portions (narrow portions 15A and 15B) whose diameters inside the through holes 14A and 14B are reduced by ΔD. That is, the diameter of each of the narrow portions 15A and 15B is (D−ΔD).

(39) Here, the apparent inductance L.sub.0 per unit length of the through-hole interconnections 16A and 16B can be expressed by the diameter D [mm] and the height H [mm] of the through-hole interconnections 16A and 16B as in Math. 5.

(40) $\begin{array}{cc}{L}_0=0.2H\left(2.303\log \frac{4H}{D}-0.75\right)\left[nH\right]& \left[\mathrm{Math}.5\right]\end{array}$

(41) The unit length referred to herein is defined as the thickness of the substrate 10. In addition, the apparent capacitance C.sub.0 per unit length between the through-hole interconnections 16A and 16B is expressed by Math. 6 assuming that the apparent facing area is S′ and the dielectric constant of the dielectric is ∈.

(42) $\begin{array}{cc}{C}_0=\mathrm{.Math.}\frac{S^{\prime }}{X}& \left[\mathrm{Math}.6\right]\end{array}$

(43) However, according to the embodiment of the present invention, without changing the diameters of the top and bottom surfaces of the through-hole interconnections 16A and 16B, it is possible to increase the apparent inductance per unit length of the through-hole interconnections 16A and 16B and to reduce the apparent capacitance per unit length between the through-hole interconnections 16A and 16B by introducing the narrow portions 15A and 15B inside the through-hole interconnections 16A and 16B. That is, assuming that the apparent differential impedance is Z.sub.0diff, the actual inductance L.sub.1 is greater than L.sub.0, and the actual capacitance C.sub.1 per unit length is smaller than C.sub.0 for Math. 7.

(44) $\begin{array}{cc}{Z}_{0\mathrm{diff}}=\sqrt{\frac{L_0}{C_0}}=100\Omega & \left[\mathrm{Math}.7\right]\end{array}$

(45) Therefore, assuming that the actual differential impedance is Z.sub.diff−dash, Math. 8 is greater than 100 Ω.

(46) $\begin{array}{cc}{Z}_{\mathrm{diff}-\mathrm{dash}}=\sqrt{\frac{L_1}{C_1}}& \left[\mathrm{Math}.8\right]\end{array}$

(47) In order to set the differential impedance Z.sub.diff−dash to 100 Ω, it is necessary to reduce Z.sub.diff−dash somehow. When realizing this by increasing the capacitance C.sub.1, this is realized by shortening the distance between the through-hole interconnections 16A and 16B by δX, as will be described later.

(48) That is, by applying the present invention using the above-described mechanism, it is possible to shorten the distance between the through-hole interconnections 16A and 16B by δX, in other words, to miniaturize the footprint by δX, which could not be realized in the related art.

(49) Specifically, for example, when the through-hole interconnections 16A and 16B including the narrow portions 15A and 15B are provided on the glass substrate 10, it is possible to shorten the distance up to Y=X−δX=300 μm in the present embodiment while X=350 μm in the related art. Therefore, an effect that the footprint can be reduced by δX=50 μm is obtained.

(50) However, it is not difficult to imagine obtaining greater δX than in the embodiment described above by making the narrow portions 15A and 15B steeper, for example.

(51) In addition, the narrow portions 15A and 15B are not limited to the shape in which the diameter of the through-hole interconnections linearly decreases toward the center of the substrate in the thickness direction as shown in FIG. 4A. For example, each narrow portion may be curved as shown in FIG. 4B. In addition, as shown in FIG. 4C, each narrow portion may be formed to have a predetermined length in the thickness direction of the substrate at a fixed diameter. In the present invention, the narrow portion refers to a region including a portion having a smaller diameter than that of through-hole interconnections in the bottom surface portion 10b and the top surface portion 10a of the substrate among the through-hole interconnections.

(52) From the point of view of the ease of control of inductance and capacitance, it is preferable to form the narrow portions so that the diameter of the through-hole interconnections decreases continuously toward the center of the substrate in the thickness direction (or toward any other location other than the center of the substrate in the thickness direction).

(53) The effect of the present embodiment is obtained by an increase in the apparent inductance per unit length using the narrow portions 15A and 15B of the through-hole interconnections 16A and 1613 and a reduction in the apparent capacitance per unit length between the through holes 14A and 14B based on the introduction of the narrow portions 15A and 15B of the through-hole interconnections 16A and 16B.

(54) FIG. 6 shows an electromagnetic field simulation result of the frequency characteristics of the reflection coefficient for an interconnection substrate 100 including conventional straight-shaped through-hole interconnections 110A and 110B (see FIGS. 5A and 5B). “HFSS” and three-dimensional electromagnetic field analysis software by ANSYS, Inc. were used for the electromagnetic field analysis.

(55) The impedance of a port is set to 100 Ω. A transmission line (differential transmission line) connecting a through-hole interconnection and a port to each other is designed to have differential impedance=100 Ω. The simulation was performed under the conditions in which the distance between the through-hole interconnections 110A and 110B was 300 and 357.5 μm. Since the reflection loss S.sub.ddll in the case of the 357.5 μm distance is smaller than that in the case of the 300 μm distance (that is, reflection in the case of the 357.5 μm distance is smaller than that in the case of the 300 μm distance), it can be considered that the differential impedance in the case of through-hole interconnections of 357.5 μm is close to 100 Ω. The reflection loss is less than approximately −25 dB.

(56) On the other hand, FIG. 7 shows a simulation result for the interconnection substrate 1 (see FIG. 1) including the through-hole interconnections 16A and 16B including the narrow portions 15A and 15B according to the embodiment of the present invention.

(57) The distance between the through-hole interconnections 16A and 16B was 300 μm. The reflection loss was less than approximately −25 dB. Therefore, the effect in the case of the distance 357.5 μm using the straight shape can be realized with the distance 300 μm in the through-hole interconnections 16A and 16B including the narrow portions 15A and 15B according to the embodiment of the present invention.

(58) That is, by using the through-hole interconnections according to the embodiment of the present invention, the distance between the through-hole interconnections 16A and 16B can be reduced by 57.5 μm compared with the distance between the conventional through-hole interconnections. In addition, even if the through holes 14A and 14B of the through-hole interconnections 16A and 16B are filled with metal or only the inner walls are coated, the effects of the present invention are effective.

(59) As shown in FIG. 3, in the interconnection substrate 1 of the present embodiment, the two surface wirings 11A and 11B that form the transmission line 12 are not parallel near portions connected to the through-hole interconnections 16A and 16B. In the example shown in FIG. 2, a case is shown in which the distance between the two surface wirings 11A and 11B is large near portions connected to the through-hole interconnections 16A and 16B.

(60) In the conventional interconnection substrate, there has been a problem in that the determined pitch between differential wirings is not fixed up to the differential through-hole interconnections and this causes impedance mismatch to influence the waveform. On the other hand, in the interconnection substrate 1 of the present embodiment, the through-hole interconnections 16A and 16B include the narrow portions 15A and 15B. Therefore, since it is possible to reduce the difference between the pitch between the two surface wirings 11A and 11B that form the transmission line 12 and the distance between the through holes 14A and 14B, it is possible to reduce the influence on the waveform due to impedance discontinuities.

(61) In the above explanation, an example of the case where portions having smallest diameters of the narrow portions 15A and 15B are provided at the center of the substrate 10 in the thickness direction has been given. However, the present invention is not limited to this. For example, as shown in FIG. 8, portions having smallest diameters of the narrow portions 15A and 15B may be provided anywhere other than the center in the thickness direction of the substrate 10.

(62) When portions having smallest diameters of the narrow portions are provided at the center of the substrate in the thickness direction, it is possible to maximize the capacitance between conductors. On the other hand, when portions having smallest diameters of the narrow portions are provided in a region other than the center in the thickness direction of the substrate 10, it is possible to adjust the capacitance by shifting the thickness-direction positions of the portions having smallest diameters of the narrow portions without changing the separation distance.

(63) In addition, the case where both of the two through holes 14A and 1413 have the narrow portions 15A and 15B has been described as an example. However, the present invention is not limited to this. For example, as shown in FIG. 9, only one (through hole 14A) of two through holes may have the narrow portion 15A.

(64) When both the two through holes 14A and 14B have the narrow portions 15A and 15B the narrow portions 15A and 15B of the two through holes 14A and 14B may be disposed at different distances from one surface of the substrate 10 as shown in FIG. 10, for example.

(65) Such a method of forming the through holes 14A and 14B including the narrow portions 15A and 15B is not particularly limited. For example, a resist (protective film) is placed on the substrate 10 except for a portion where the through holes 14A and 14B are formed, and sandblasting is performed from both sides of the substrate 10. Finally, by peeling off the resist, the through holes 14A and 14B can be formed.

(66) Specifically, by disposing a resist on both the one surface 10a and the other surface 10b of the substrate 10 except for a portion where the through holes 14A and 14B are formed and performing sandblasting on the substrate 10 through the resist, through holes including the narrow portions 15A and 15B having smaller diameters than that of the through-hole interconnections in one surface 10a of the substrate 10 and that of the through-hole interconnections in the other surface 10b of the substrate 10 can be formed inside the substrate.

(67) While the interconnection substrate of the present invention has been described, the present invention is not limited to this, and various modifications can be made without departing from the scope of the invention.

(68) The present invention can be widely applied to interconnection substrates including transmission lines.