Wiring board

[0020] based on figure 1 as well as figure 2 A wiring board according to an embodiment will be described. figure 1 The illustrated wiring board A includes an insulating substrate 10 in which a plurality of insulating layers 13 having via holes 14 are laminated on the upper and lower surfaces of an insulating plate 11 having through holes 12 .

[0021] The insulating plate 11 is a member that becomes the core substrate of the wiring substrate A. As shown in FIG. The insulating plate 11 is formed of, for example, an electrical insulating material obtained by impregnating a thermosetting resin such as epoxy resin and bismaleimide triazine resin into a glass fabric woven into glass fiber bundles vertically and horizontally. owned. The thickness of the insulating plate 11 is about 0.3 to 1.5 mm. The diameter of the through hole 12 is about 0.1 to 0.3 mm.

[0022] Each insulating layer 13 laminated on the upper and lower surfaces of the insulating plate 11 is a reinforcing insulating layer. The insulating layer 13 is formed of an insulating material obtained by dispersing an inorganic insulating filler such as silicon oxide powder in a thermosetting resin such as epoxy resin at about 30 to 70 mass %. The thickness of each insulating layer 13 is about 20 to 60 μm. A plurality of via holes 14 having a diameter of about 30 to 100 μm are formed from the upper surface to the lower surface of each insulating layer 13 .

[0023] On the surface and inside of the insulating substrate 10, a plurality of conductors 15a and 15b are arranged. The conductor 15a is a conductor for differential signals. The conductor 15b is a conductor for grounding or power supply. The conductors 15a and 15b are formed of copper, for example. The conductors 15a and 15b have a thickness of about 5 to 50 μm.

[0024] Through-conductors 16 a and 16 b are attached to the through-hole 12 . The through conductors 16a are through conductors for differential signals. The through-conductor 16b is a through-conductor for grounding or power supply. The through conductors 16a and 16b are formed of copper, for example. The thickness of the through conductors 16a and 16b is about 5 to 25 μm. The inside of the through-hole 12 to which the through-conductors 16a and 16b are attached is filled with resin.

[0025] The via hole 14 is filled with via hole conductors 17a and 17b. The via-hole conductor 17a is a via-hole conductor for differential signals. The via-hole conductor 17b is a via-hole conductor for grounding or power supply. The via-hole conductors 17a and 17b are formed of copper, for example.

[0026] A plurality of semiconductor element connection pads 18 a and 18 b are formed in the center portion of the upper surface of the insulating substrate 10 . The semiconductor element connection pads 18a and 18b are formed by part of the conductors 15a and 15b. These semiconductor element connection pads 18a and 18b are formed in a two-dimensional arrangement. The semiconductor element connection pad 18a is a semiconductor element connection pad for differential signals. The semiconductor element connection pad 18b is a semiconductor element connection pad for grounding or power supply. The semiconductor element connection pads 18a and 18b are electrically connected to electrodes of the semiconductor element S via solder.

[0027] External connection pads 19 a and 19 b are formed on the lower surface of the insulating substrate 10 . External connection pads 19a, 19b are formed by part of conductors 15a, 15b. These external connection pads 19a and 19b are formed in a two-dimensional arrangement. The external connection pads 19a are external connection pads for differential signals. The external connection pad 19b is an external connection pad for ground or power supply. The external connection pads 19a and 19b are connected to the wiring conductors of the external circuit board via solder.

[0028] Furthermore, the solder resist layer 20 is attached to the surface of the insulating layer 13 of the outermost layer and the conductors 15a and 15b. The solder resist layer 20 on the upper surface side has openings exposing the centers of the semiconductor element connection pads 18a and 18b. The solder resist layer 20 on the lower surface side has openings exposing the central portions of the external connection pads 19a and 19b. The solder resist layer 20 is formed of, for example, a thermosetting resin such as an acrylic-modified epoxy resin containing a filler such as silica. The thickness of the solder resist layer 20 is about 10 to 50 μm.

[0029] figure 1The illustrated wiring board A includes a transmission path for differential signals, and a transmission path for grounding or power supply. The transmission path for differential signals connects semiconductor element connection pads 18a for differential signals and external connection pads 19a to each other via conductors 15a, through conductors 16a, and via conductors 17a. On the transmission path for differential signals, a pair of transmission paths for differential signals are arranged adjacent to each other. The through-conductor 16a and the via-hole conductor 17a are connected to the center of the external connection pad 19a for differential signals. The transmission path for grounding or power supply connects the semiconductor element connection pad 18b and the external connection pad 19b to each other via the conductor 15b, the through conductor 16b, and the via conductor 17b.

[0030] like figure 2 As shown, in wiring board A, diameter d1 and arrangement pitch P1 of external connection pads 19a for differential signals are smaller than diameter d2 and arrangement pitch P2 of external connection pads 19b for grounding or power supply. Furthermore, the arrangement pitch P3 of the through conductors 16a connected to the external connection pads 19a for differential signals is equal to or less than the arrangement pitch P1 of the external connection pads 19a for differential signals.

[0031] The diameter d1 of the external connection pads 19a for differential signals is preferably smaller than the diameter d2 of the external connection pads 19b for grounding or power supply by about 100 to 300 μm. The arrangement pitch P1 of the external connection pads 19a for differential signals is preferably smaller than the arrangement pitch P2 of the external connection pads 19b for grounding or power supply by about 0.35 to 0.8 mm. Furthermore, the difference between the arrangement pitch P3 of the through conductors 16a connected to the external connection pads 19a for differential signals and the arrangement pitch P1 of the external connection pads 19a for differential signals is about 0 to 0.25 mm.

[0032] Specifically, the diameter d1 is about 300 to 500 μm, preferably about 400 μm. The arrangement pitches P1 and P3 are about 0.45 to 0.7 mm, preferably about 0.55 mm. The diameter d2 is about 400 to 800 μm, preferably about 640 μm. The arrangement pitch P2 is about 0.8 to 1.5 mm, preferably about 1 mm.

[0033] As described above, in the present invention, the diameter d1 and arrangement pitch P1 of the external connection pads 19a for differential signals are formed to be smaller than the diameter d2 and arrangement pitch P2 of the external connection pads 19b for ground or power. Thereby, the electrostatic capacitance between the adjacent external connection pads 19a for differential signals can be reduced, and the value of the impedance can be increased to be close to 100Ω. Furthermore, the arrangement pitch P3 of the through conductors 16a connected to the external connection pads 19a for differential signals is equal to or less than the arrangement pitch P1 of the external connection pads 19a for differential signals. Thereby, the electrostatic capacitance between the adjacent through-conductors 16a for differential signals can be increased, and the value of the impedance can be reduced to be close to 100Ω.

[0034] In addition, the external connection pads 19a for differential signals, the through conductors 16a connected to the external connection pads 19a for differential signals, the conductors 15a for differential signals, the via conductors 17a, and the semiconductor element connection pads 18a resonates, reducing reflections between them.

[0035] Thereby, by suppressing the impedance mismatch between the external connection pads 19a for differential signals and the through conductors 16a, and reducing the reflection of the signal, it is possible to provide a wiring board capable of efficiently transmitting high-frequency signals. The ratio of the number of the external connection pads 19a for differential signals to the external connection pads 19 is about 1 to 20%. Thereby, even if the diameter d1 of the external connection pad 19a for differential signals is reduced, the influence on the connection reliability between the wiring board and the external circuit board is small.

[0036] The present invention is not limited to the above-described one embodiment, and various modifications can be made without departing from the gist of the present invention. For example, in the wiring board A according to the above-described embodiment, the arrangement pitch P3 and the arrangement pitch P1 are substantially the same pitch. However, the arrangement pitch P3 is not particularly limited as long as it is equal to or less than the arrangement pitch P1.

[0037] In the wiring board A according to the above-described embodiment, the insulating substrate 10 is formed of the insulating plate 11 and the insulating layers 13 each of which is laminated two layers on the upper and lower surfaces of the insulating plate. However, the number of layers of insulating layers laminated on the upper and lower surfaces of the insulating plate is not limited, and the number of layers may be different on the upper and lower surfaces of the insulating plate.

[0038] In the wiring board A according to the above-described embodiment, the through conductors 16 a and 16 b are attached to the wall surface of the through hole 12 , and the inside of the through hole 12 is filled with resin. However, through-holes may be filled with through-conductors.