TECHNICAL FIELD

The present invention relates to a method for manufacturing a multilayer printed wiring board and a multilayer printed wiring board.

BACKGROUND

From the viewpoint of controlling the impedance of a transmission path, a printed wiring board having a microstrip line structure is known, in which an insulating resin layer embedded with a ground layer and an insulating resin layer embedded with a signal line are laminated via an adhesive layer (Patent Document 1).

PATENT DOCUMENT

[Patent Document 1] JP4943247B

However, in the manufacturing steps for a printed wiring board having a multilayer structure, when interlayer adhesion is performed by thermocompression bonding with an adhesive layer, the adhesive layer melts and the molten adhesive enters the gaps of a circuit of signal lines; therefore, the layer thickness changes from the initial state. Moreover, when pressure is applied under a high temperature in the thermocompression bonding step, the adhesive layer deforms, so that the thickness of the adhesive layer may deviate from the target design value or the thickness of the adhesive layer may vary. The change or variation in the thickness of the adhesive layer affects the distance between a signal line and an adjacent electrically conductive layer. The impedance changes depending on the distance between a signal line and an adjacent electrically conductive layer, and the change in the thickness of the adhesive layer and the uneven thickness hinder the manufacturing of a printed wiring board having impedance characteristics as initially designed.

SUMMARY

According to one or more embodiments of the present invention, a multilayer printed wiring board having impedance characteristics as initially designed in a method for manufacturing a multilayer printed wiring board including a thermocompression bonding step is manufactured.

(1) One or more embodiments of the present invention provide a method for manufacturing a multilayer printed wiring board. The method includes a step of preparing a first wiring board in which one or more signal lines are formed on a main surface of a first insulating substrate and a second wiring board in which an electrically conductive layer is formed on a main surface of a second insulating substrate. The second wiring board is to be laminated on the first wiring board. The method further includes a step of arranging a spacer at a position spaced apart from an outer edge of a circuit region by a predetermined distance along at least a part of the outer edge. The spacer has a predetermined thickness. The circuit region is formed with the one or more signal lines. The method further includes a step of forming an adhesive layer on the circuit region so that a space is provided between the adhesive layer and the spacer and a step of laminating the first wiring board and the second wiring board for thermocompression bonding. The predetermined distance is a distance that allows the space to be formed between the adhesive layer and the spacer after the step for thermocompression bonding.

(2) In the above invention, the predetermined thickness of the spacer can be calculated on the basis of a preliminarily set impedance of a transmission path including the one or more signal lines.

(3) In the above invention, the spacer may be arranged/set so as to surround the circuit region.

(4) In the above invention, the method may include a step of cutting a position between the spacer and the circuit region after the step for thermocompression bonding and a step of removing the spacer.

(5) In the above invention, the spacer may have a first adhesive layer that adheres to the first wiring board and/or a second adhesive layer that adheres to the second wiring board.

(6) In the above invention, the method may include cutting an outside of the spacer after the step for thermocompression bonding. The spacer is arranged/set so as to surround the circuit region along at least a part of the outer edge of the circuit region.

(7) One or more embodiments of the present invention provide a multilayer printed wiring board including a first wiring board in which one or more signal lines are formed on a main surface of a first insulating substrate, a spacer having a predetermined thickness and arranged/set along at least a part of an outer edge of a circuit region formed with the one or more signal lines, an adhesive layer covering at least the circuit region, a space formed between the spacer and the adhesive layer, and a second wiring board in which an electrically conductive layer is formed on a main surface of a second insulating substrate. The second wiring board is laminated via the adhesive layer on the first wiring board.

(8) In the above invention, the spacer may be formed along at least a part of the outer edge of the circuit region.

According to the method for manufacturing a multilayer printed wiring board of the present invention, a multilayer printed wiring board having the impedance as initially designed can be manufactured even through the thermocompression bonding step.

