Inspection method of printed wiring board

A method of inspecting a printed wiring board includes preparing a printed wiring board having product and inspection regions such that the board has inner-layer lands in the regions, forming vias on the inner-layer lands in the regions, forming outer peripheral part(s) in the wiring board such that the outer peripheral part(s) expose outer peripheral portion(s) of the inner-layer land in the inspection region, determining a center coordinate of the inner-layer land in the inspection region based on a position of the outer peripheral part(s), determining a center coordinate of the via(s) in the inspection region based on a shape of the via(s) in the inspection region, determining a misalignment amount based on a distance between the center coordinate of the inner-layer land and the center coordinate of the via(s) in the inspection region, and determining alignment accuracy between the via and the inner-layer land based on the misalignment amount.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based upon and claims the benefit of priority to Japanese Patent Application No. 2020-174500, filed Oct. 16, 2020, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an inspection method of a printed wiring board for inspecting alignment accuracy of a via and an inner-layer land of the printed wiring board.

Description of Background Art

To guarantee quality of a printed wiring board, alignment accuracy between a via and an inner-layer land that have been manufactured in the printed wiring board is accurately inspected. As an inspection method for determining alignment accuracy between a via and an inner-layer land that have been manufactured, a misalignment amount of a via of a test coupon may be checked using X-rays (see, for example, Japanese Patent Application Laid-Open Publication No. 2008-181998). The entire contents of this publication are incorporated herein by reference.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method of inspecting a printed wiring board includes preparing a printed wiring board having a product region and a test coupon region such that the printed wiring board has an inner-layer land in the product region and an inner-layer land in the test coupon region, forming one or more vias on the inner-layer land in the product region and one or more vias on the inner-layer land in the test coupon region, forming one or more outer peripheral parts in the printed wiring board such that the one or more outer peripheral parts expose one or more outer peripheral portions of the inner-layer land in the test coupon region, determining a center coordinate of the inner-layer land in the test coupon region based on a position of the one or more outer peripheral parts, determining a center coordinate of the one or more vias formed on the inner-layer land in the test coupon region based on a shape of the one or more vias formed on the inner-layer land in the test coupon region, determining a misalignment amount based on a distance between the center coordinate of the inner-layer land in the test coupon region and the center coordinate of the one or more vias formed on the inner-layer land in the test coupon region, and determining alignment accuracy between the via and the inner-layer land based on the misalignment amount.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A printed wiring board that is an object of an inspection method according to an embodiment of the present invention is described with reference to the drawings.FIG.1illustrates an enlarged view of a portion of a printed wiring board10having a product region and a test coupon region of the embodiment. The printed wiring board10may be a substrate with a core having a lower layer formed by alternately laminating conductor layers and insulating layers on one side or both sides of a core substrate (not illustrated in the drawings), the conductor layers each having a predetermined circuit pattern. When the conductor layers are formed on both sides of the core substrate, conductor layers opposing each other via the core substrate may be connected to each other via through-hole conductors (not illustrated in the drawings). Or, the printed wiring board10may be a coreless substrate obtained by alternately laminating conductor layers and insulating layers on a support plate (not illustrated in the drawings) instead of a core substrate and then removing the support plate.

In the embodiment illustrated inFIG.1, the printed wiring board10has a product region1where a circuit is formed in a central portion of the printed wiring board10and a test coupon region2where misalignment or the like during manufacturing is inspected at an edge part of the printed wiring board10.

As illustrated inFIG.1, the printed wiring board10having the product region1and the test coupon region2includes: a lower layer11in which multiple conductor layers and multiple insulating layers are alternately provided; an inner-layer land (14-1) formed of a conductor layer and an inner-layer land (14-2) formed of a conductor layer that are respectively simultaneously formed in the product region1and the test coupon region2on the lower layer11; an insulating layer16that is formed on the inner-layer land (14-1) and the inner-layer land (14-2); and a via (18-1) and a via (18-2) that are respectively simultaneously formed in the product region1and the test coupon region2of the insulating layer16. InFIG.1, as will be described later, “20-1” and “20-3” are outer peripheral parts that are exposed by processing the inner-layer land (14-1) of the test coupon region2at the same time as processing the vias (18-1,18-2). The lower layer11may be a double-sided plate without lamination.

A feature of a method of inspecting a printed wiring board according to an embodiment of the present invention is that, in the example illustrated inFIG.1, a misalignment amount between the inner-layer land (14-2) and the via (18-2) of the test coupon region2is determined based on a center coordinate of the inner-layer land (14-2) and a center coordinate of the via (18-2) with respect to the inner-layer land (14-2), and alignment accuracy between the inner-layer land (14-2) and the via (18-2) is inspected based on the misalignment amount.

FIG.2is for describing a method of inspecting a printed wiring board according to an embodiment of the present invention. In the embodiment illustrated inFIG.2, the one circular via (18-2) is formed at a center of the quadrangular inner-layer land (14-2) in the test coupon region2. Then, a center coordinate of the inner-layer land (14-2) is OA, and a center coordinate of the via (18-2) with respect to the inner-layer land (14-2) is OB.

In the example illustrated inFIG.2, in the inspection method of a printed wiring board according to an embodiment of the present invention, first, in the test coupon region2, at the same time as processing the via (18-2), four outer peripheral parts ((20-1)-(20-4)) of the inner-layer land (14-2) are processed, and, together with the via (18-2), the outer peripheral parts ((20-1)-(20-4)) (here, one on each side) of the inner-layer land (14-2) are exposed. Next, based on positions of the exposed outer peripheral parts ((20-1)-(20-4)) of the inner-layer land (14-2), the center coordinate (OA) of the inner-layer land (14-2) is determined. Next, based on a shape of the processed via (18-2), the center coordinate (OB) of the via (18-2) with respect to the inner-layer land (14-2) is determined. Next, from the center coordinate (OA) of the inner-layer land (14-2) and the center coordinate (OB) of the via (18-2) with respect to the inner-layer land (14-2) that have been determined, a misalignment amount (OB-OA) between the via (18-2) and the inner-layer land (14-2) is determined. Then, based on the determined misalignment amount (OB-OA), alignment accuracy between the via (18-2) and the inner-layer land (14-2) is inspected. A design value of the center coordinate (OB) of the via (18-2) is the same as that of the center coordinate (OA) of the inner-layer land (14-2).

In the example illustrated inFIG.2, the inner-layer land (14-2) of the test coupon region2is formed at the same time as the inner-layer land (14-1) of the product region1, and the via (18-2) of the test coupon region2is formed at the same time as the via (18-1) of the product region1. Therefore, a misalignment amount between the inner-layer land (14-1) and the via (18-1) in the product region1is the same as the misalignment amount (OB-OA) between the inner-layer land (14-2) and the via (18-2) of the test coupon region2. As a result, for example, an inspection can be performed such as that, when the misalignment amount (OB-OA) in the printed wiring board10is within a predetermined range, it is determined as a normal product. Then, the inspection result can be applied to change a condition or the like for the next manufacturing process.

FIG.3is for describing a method of inspecting a printed wiring board according to another embodiment of the present invention. In the embodiment illustrated inFIG.3, four circular vias ((18-2-1)-(18-2-4)) are formed at four corners of the quadrangular inner-layer land (14-2) in the test coupon region2. Then, an intersection point between a line segment connecting a center (OB1) of the via (18-2-1) and a center (OB3) of the via (18-2-3), which are at opposing corners, and a line segment connecting a center (OB2) of the via (18-2-2) and a center (OB4) of the via (18-2-4), which are at opposing corners, is a center coordinate (OC) of the vias (18-2) with respect to the inner-layer land (14-2).

In the example illustrated inFIG.3, in the inspection method of a printed wiring board according to an embodiment of the present invention, first, in the test coupon region2, at the same time as processing the vias ((18-2-1)-(18-2-4)) at the four locations, four outer peripheral parts ((20-1)-(20-4)) of the inner-layer land (14-2) are processed, and, together with the vias ((18-2-1)-(18-2-4)), the outer peripheral parts ((20-1)-(20-4)) (here, one on each side) of the inner-layer land (14-2) are exposed. Next, based on positions of the exposed outer peripheral parts ((20-1)-(20-4)) of the inner-layer land (14-2), the center coordinate (OA) of the inner-layer land (14-2) is determined. Next, based on shapes of the processed vias ((18-2-1)-(18-2-4)), from the intersection point between the line segment connecting the center (OB1) of the via (18-2-1) and the center (OB3) of the via (18-2-3), which are at opposing corners, and the line segment connecting the center (OB2) of the via (18-2-2) and the center (OB4) of the via (18-2-4), which are at opposing corners, the center coordinate (OC) of the vias (18-2) with respect to the inner-layer land (14-2) is determined. Next, from the center coordinate (OA) of the inner-layer land (14-2) and the center coordinate (OC) of the vias (18-2) with respect to the inner-layer land (14-2) that have been determined, a misalignment amount (OC-OA) between the vias (18-2) and the inner-layer land (14-2) is determined. Then, based on the determined misalignment amount (OC-OA), alignment accuracy between the vias (18-2) and the inner-layer land (14-2) is inspected. A design value of the center coordinate (OC) determined from the vias ((18-2-1)-(18-2-4)) is the same as that of the center coordinate (OA) of the inner-layer land (14-2).

In the example illustrated inFIG.3, the inner-layer land (14-2) of the test coupon region2is formed at the same time as the inner-layer land (14-1) of the product region1, and the vias ((18-2-1)-(18-2-4)) of the test coupon region2are formed at the same time as the via (18-1) of the product region1. Therefore, the misalignment amount between the inner-layer land (14-1) and the via (18-1) in the product region1is the same as the misalignment amount (OC-OA) between the inner-layer land (14-2) and the vias (18-2) of the test coupon region2. As a result, for example, an inspection can be performed such as that, when the misalignment amount (OC-OA) in the printed wiring board10is within a predetermined range, it is determined as a normal product. Then, the inspection result can be applied to change a condition or the like for the next manufacturing process.

When a via in the test coupon region2has a deformed shape, when the misalignment amount (OB-OA) determined using the one via (18-2) illustrated inFIG.2and the misalignment amount (OC-OA) determined using the four vias ((18-2-1)-(18-2-4)) illustrated inFIG.3are compared, the misalignment amount (OC-OA) is smaller than the misalignment amount (OB-OA), and it is preferable to use the misalignment amount (OC-OA) determined using the four vias ((18-2-1)-(18-2-4)) for the inspection.

In the examples illustrated inFIGS.2and3, the inner-layer land (14-2) has a quadrangular shape. However, the inner-layer land (14-2) is not limited to having this shape, and may have other shapes such as a circular shape. Further, the inner-layer land (14-2) has four exposed parts, one on each side. However, the number of the exposed parts is not limited to this as long as the shape of the inner-layer land (14-2) can be determined from portions of the inner-layer land (14-2) that can be observed from the exposed parts. Further, with respect to the one inner-layer land (14-2), there is one via in the example ofFIG.2, and there are three vias in the example ofFIG.3. However, the number of the vias is not limited to these numbers as long as the center coordinate of the vias with respect to the inner-layer land can be determined.

An example of design of the test coupon region2is as follows. First, each via (18-2) has a diameter that is the same as that of the via (18-1) of the product region1, and at least one via (18-2) is provided for the inner-layer land (14-2). Further, the inner-layer land (14-2) preferably has a size of (300 μm)×(300 μm), and can have any shape. Further, openings of the outer peripheral parts ((20-1)-(20-4)) can be formed, for example, by irradiating laser with a via diameter of 60 μm at a pitch of 30 μm to 9 places of 3×3 in an overlapping manner.

In the example illustrated inFIG.2and in the example illustrated inFIG.3, in order to determine the center coordinate (OA) of the inner-layer land (14-2) based on the shapes of the exposed outer peripheral parts ((20-1)-(20-4)) of the inner-layer land (14-2), an image measuring device is measured. As an example of the image measuring device, a high-precision CNC image measuring device Hyper Quick Vision: Hyper QV606 manufactured by Mitutoyo can be used.

In an inspection method of a printed wiring board according to an embodiment of the present invention having the above-described structure, by quantifying the misalignment amount between the vias and the inner-layer land in the printed wiring board, the alignment accuracy between the vias and the inner-layer land can be accurately inspected.

In the inspection method described in Japanese Patent Application Laid-Open Publication No. 2008-181998, in a printed wiring board having a large thickness, the capability of recognizing a misalignment amount of a via based on a transmission image captured with X-ray is reduced. Therefore, alignment accuracy between a via and an inner-layer land cannot be inspected.

An inspection method of a printed wiring board according to an embodiment of the present invention includes: preparing a printed wiring board that has a product region and a test coupon region; processing a via on an inner-layer land in each of the product region and the test coupon region; exposing outer peripheral parts of the inner-layer land of the test coupon region by processing the outer peripheral parts at the same time as processing the via; determining a center coordinate (center coordinate (OA)) of the inner-layer land of the test coupon region based on positions of the exposed outer peripheral parts; determining a center coordinate (center coordinate (OB)) of the via processed in the test coupon region based on a shape of the via; determining a distance (misalignment amount) between the center coordinate (OA) and the center coordinate (OB); and confirming alignment accuracy between the via and the inner-layer land based on the misalignment amount.