Method for removing foreign matter from wiring board

Abstract

To provide a method for removing foreign matter by which foreign matter adhering to a substrate surface can be removed without damaging the wiring substrate. [Solution] The method for removing foreign matter from a wiring board according to the present invention includes preparing a wiring board on which thermoplastic resin-based foreign matter that has been heated during the manufacturing process of the wiring board is attached to the board surface, heating the foreign matter to a temperature at which the foreign matter can soften, and mechanically peeling and removing the foreign matter from the board surface using a peeling tool with a sharp tip that can engage with the foreign matter.

Description

[Technical Field]

[0001] The present invention relates to a method for removing foreign matter from a wiring board. [Background technology]

[0002] Conventionally, when manufacturing a wiring board, a conductor layer having a circuit pattern including electrode pads is formed on an insulating layer by electrolytic copper plating, and the conductor layer is covered with a solder resist layer. After that, openings are formed in the solder resist layer to expose the electrode pads, and the solder resist layer is heated to harden.

[0003] During the manufacturing process of this wiring board, minute foreign particles may adhere to the surface of the solder resist layer, which can impair the smoothness of the surface of the solder resist layer and cause problems with the connection to the electrode pads when electronic components are mounted on the wiring board via solder bumps formed on the electrode pads in a later process.

[0004] Patent Document 1 discloses a method for removing minute foreign matter adhering to the surface of an element substrate. In this method, a laser beam is emitted in a first direction parallel to the surface of the element substrate, and the laser beam is translated or rotated in a second direction parallel to the surface of the element substrate, thereby at least partially evaporating or decomposing the foreign matter on the surface of the element substrate and removing it. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-198309 Summary of the Invention [Problem to be solved by the invention]

[0006] In the technology disclosed in Patent Document 1, foreign matter is removed using a laser beam, which may cause dents to form on the substrate surface at the location where the foreign matter was removed due to the high heat of the laser beam, or may partially alter the substrate surface at the location where the foreign matter was removed. [Means for solving the problem]

[0007] The method for removing foreign matter from a wiring board according to the present invention comprises: preparing a wiring board having thermoplastic resin-based foreign matter attached to its surface due to heating during a manufacturing process of the wiring board; heating the foreign matter together with the wiring substrate to a temperature at which the foreign matter can be softened; removing the foreign matter from the surface of the substrate by mechanically peeling it off using a peeling tool having a sharp tip that can engage with the foreign matter; Includes: [Brief explanation of the drawings]

[0008] [Figure 1] 1A to 1C are explanatory views showing a step in an embodiment of a method for removing foreign matter from a wiring substrate according to the present invention. [Figure 2] 5A to 5C are explanatory views showing one step in the method for removing foreign matter from a wiring substrate according to the embodiment. [Figure 3] 5A to 5C are explanatory views showing one step in the method for removing foreign matter from a wiring substrate according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] <One embodiment of the method for removing foreign matter from a wiring board according to the present invention> Hereinafter, one embodiment of a method for removing foreign matter from a wiring board according to the present invention will be described with reference to the drawings. In the embodiment shown in Figures 1 to 3, the dimensions of each component, particularly the height dimension, are shown as dimensions different from the actual dimensions in order to better understand the features of the embodiment of the present invention. Furthermore, in order to better understand the features of the embodiment of the present invention, components that are normally present in a wiring board, such as insulating layers, conductor layers, and bumps, are not shown.

[0010] 1 to 3 are diagrams each showing a step in an embodiment of a method for removing foreign matter from a wiring board according to the present invention. Hereinafter, an embodiment of the method for removing foreign matter from a wiring board according to the present invention will be described in accordance with the steps shown in FIGS. 1 to 3.

[0011] First, as shown in FIG. 1, a wiring board 1 is prepared, which has a thermoplastic resin-based foreign substance 2 attached to the substrate surface 1a and heated together with the wiring board 1 during the manufacturing process of the wiring board 1. The wiring board 1 is also called a printed wiring board. Although not shown, the wiring board 1 has an insulating layer, which may be a resin insulating layer formed on a core substrate or the like. Next, a seed layer is formed on the insulating layer. The seed layer may be formed by chemical copper plating, for example.

[0012] Next, a plating resist layer is formed on the seed layer, and openings of a predetermined circuit pattern including electrode pad portions are formed in the plating resist layer by exposure and development, etc. Dry film resist (DFR) or the like can be used as the plating resist layer. The plating resist layer can be formed by laminating films or by applying a resin.

[0013] Next, electrolytic copper plating is applied to the seed layer exposed through the openings in the plating resist layer to form a conductor layer with the above-mentioned circuit pattern, including the electrode pads. These processes are performed once or multiple times to form a single-layer or multi-layer wiring board, and then the outermost conductor layer is covered with a solder resist layer. Like the plating resist layer, the solder resist layer can be formed by laminating a film or by applying a resin. Next, openings that expose the electrode pads are formed in the solder resist layer by etching or other methods, and the solder resist layer is heated and cured to produce the wiring board 1.

[0014] During this manufacturing process, the thermoplastic resin such as the dry film resist is heated, and minute foreign matter 2, which is a thermoplastic resin mixture, adheres to the substrate surface 1a on which the solder resist is formed, and the foreign matter 2 is also heated to about 200°C along with the solder resist.

[0015] Next, in this embodiment, as shown in FIG. 2 , a peeling tool 3 having a pointed tip, which is the right end in the figure, is prepared. The peeling tool 3 may be any long, slender tool, such as a needle or spatula, that is strong enough to peel off the foreign matter 2, and there are no particular restrictions on the material. Next, the wiring board 1 with the foreign matter 2 adhering to its surface is placed on a microscope or magnifying glass. The operator moves the field of view of the microscope or magnifying glass to search for the foreign matter 2, and then hooks the tip of the peeling tool 3 onto the found foreign matter 2 and applies a peeling force E to the base of the peeling tool 3. This peeling force E increases according to the principle of a lever, with the tip of the peeling tool 3 as a fulcrum, to become an acting force L, which is then applied directly to the foreign matter 2, peeling it off the substrate surface 1a of the wiring board 1.

[0016] When this peeling process is performed, the thermoplastic resin-based foreign matter 2 adhering to the substrate surface 1a has already been thermally decomposed (degraded) by the heat applied in the previous manufacturing process of the wiring board 1, and has become smaller in molecular weight, lowering its softening temperature. For this reason, the foreign matter 2 is likely to thermally expand when heated to approximately 90°C to 120°C, preferably approximately 100°C. It is presumed that the foreign matter 2 physically adhering to the substrate surface 1a succumbs to the stress generated by this thermal expansion and is easily peeled off when a physical trigger is applied using the peeling tool 3. This results in the manufacturing of a wiring board 1 in which the foreign matter 2 has been removed from the substrate surface 1a, as shown in Figure 3. [Explanation of symbols]

[0017] 1. Wiring board 1a Substrate surface 2 Foreign object 3 Peeling instruments E Peeling force L acting force

Claims

1. preparing a wiring board having thermoplastic resin-based foreign matter attached to its surface due to heating during a manufacturing process of the wiring board; heating the foreign matter to a temperature at which the foreign matter can be softened; removing the foreign matter from the surface of the substrate by mechanically peeling it off using a peeling tool having a sharp tip that can engage with the foreign matter; A method for removing foreign matter from a wiring board, comprising:

2. 2. The method for removing foreign matter from a wiring substrate according to claim 1, The temperature at which the foreign matter can be softened is 90°C to 120°C.

3. 2. The method for removing foreign matter from a wiring substrate according to claim 1, The surface of the substrate is mainly made of a thermoplastic resin.

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