JPH04206686A - Manufacture of multilayer printed wiring board with small diameter via hole - Google Patents

Abstract

PURPOSE:To prevent an etching solution from soaking resultant from a deviated photo mask due to printing by burying a resin layer into a small hole and a through a hole, covering the land of each hole with tenting resist and then etching. CONSTITUTION:After a through hole and a small-sized via hole 3 are formed on a base material 7, liquid sensitivity resin is applied to the whole surface of the base material prior to a print process. During this process, resin soaks into the small hole and the small-sized via hole 3. After the resin is cured, only the cured resin on the surface of the base material 7 is eliminated where a resin layer 8 is formed. Then, a dry film is laminated on copper cladding 9 and developed, thereby forming tenting resist 1, which covers the lands of the through hole and the small-sized via hole 3. After it is etched with an etching solution 2, the resist 1 is separated and the resin layer 8 is also removed.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a high-density multilayer printed wiring board that makes extensive use of small-diameter via holes.

<Prior art> Conventionally, in this type of multilayer printed wiring board, a dual inline package type semiconductor integrated circuit device (hereinafter referred to as D
The through-hole grids required for mounting the DIP (IP) are arranged at intersections with a pitch of 2.54 mm in the vertical and horizontal directions, so when mounting components such as the DIP mentioned above at high density, there is a limit to the number of wiring lines that can be wired. , and the wiring density was low.

Therefore, in order to solve the above-mentioned drawbacks, we
8-2091. JP-A-58-2092゜ and JP-A-59
As disclosed in Japanese Patent No. 222,990, it has been proposed to increase wiring density by making extensive use of small-diameter via holes that do not fit into the through-hole lattice as described above.

In other words, this proposal improves wiring density by passing wiring lines that have small-diameter lands and via holes between grids, and thereby, for example, converting a 6-layer multilayer printed wiring board to a 4-layer multilayer printed wiring board. It has advantages such as being able to be formed as a plate, improving the degree of freedom in designing circuit wiring patterns, and reducing manufacturing costs.

<Problems to be Solved by the Invention> However, when forming the outer layer circuit of a multilayer printed wiring board with small-diameter via holes as described above by the tenting method, the following problems arise especially in the small-diameter via holes. .

In other words, the above-mentioned small-diameter via hole is a general term for a via hole that has a hole diameter of about 0.3 mm or less in terms of a normal drill diameter. It is necessary to form it to be less than mm.

Therefore, as shown in FIGS. 2(a) and 2(b), in forming the outer layer circuit by the tenting method, when taking into account the mask printing deviation caused by photolithography, In this case, the tent strength was not sufficient, and the etching liquid 2 seeped into the small diameter via hole 3, which caused the plating copper 4 of the small diameter via hole 3 to be etched, so-called copper erosion. Retention decreases.

Therefore, instead of the conventional tenting method as described above,
The subtract method, which uses solder plating as an etching resist, is used, but this method is more expensive than the tenting method, requires many post-processing steps such as fading and solder peeling, and requires wastewater treatment, etc. Pollution treatment equipment will also be required.

Moreover, due to the incomplete solder plating as described above, through-hole disconnection failures occur frequently.

By the way, the reason why the diameter of the land is formed to be φ0.5 mm or less as described above will be explained.

In other words, in the current tenting method, if the drill diameter is φ0.3 mm or less, the land diameter needs to be at least the drill diameter + 0.25 mm, and this is due to photomask baking misalignment in the tenting resist and Considering elongation, the tent strength is the limit value that can withstand the development and etching processes.

According to general design rules, the 2.54mm pinch is divided into 6 equal parts of 0.423mm as shown in Figure 3.
Three wiring lines 5 with a wiring width of 0.13 mm are formed on the pitch, and a land 6 is added to one of the three wiring lines. If the drill diameter is φOJ mm, the diameter is set to φ0.55 mm from the above limit value, so that the gap a between the land and the wiring line is 0.08 mm.
It will be 3 mm.

However, if the above-mentioned gap a is generally less than 0.1 mm, short circuits between lines due to residual development may occur during the photolithography process, or absolute resistance defects may occur during etching due to insufficient gap, resulting in an extremely low fractionation. .

Therefore, in order to make the gap a 0.1 mm or more, it was necessary to design the diameter of the land 6 to be φ0.5 mm or less. In addition, when the land diameter is designed to be φ0.5 mm,
The above gap a is 0. The length is 12 mm, ensuring the minimum necessary gap.

<Means for Solving the Problems> The present invention has been made in view of the above-mentioned vehicle condition, and its purpose is to provide a method for forming an outer layer circuit of a multilayer printed wiring board with small-diameter via holes by a tenting method. The purpose of the present invention is to prevent etching liquid from seeping into the tenting resist due to misalignment of photomask printing.To achieve the above object, the present invention provides a method for forming outer layer circuits of multilayer printed wiring boards having small diameter via holes and through holes. The present invention is characterized in that a resin layer is embedded in each of the holes, and then the land portion of each hole is covered with a tenting resist, etching is performed, and then the resist and resin layer are removed.

By the way, when using, for example, a photosensitive resin whose main component is an acrylic copolymer as the resin layer, and embedding this resin in each hole, first apply the resin in a liquid state to the surface of the wiring board using a roll coater. At the same time, the resin is applied using a curtain coater, a dip method, etc., and the resin is also buried in each hole. Thereafter, the resin is exposed to light and cured, and only the resin film applied to the surface is removed by mechanical polishing before the land portions are covered with the tenting resist.

Further, in order to remove the resin layer buried in each of the holes, etching is performed and then the tenting resist is peeled off and simultaneously removed.

Furthermore, instead of the above-mentioned resin, a cream-like release agent containing a silicone resin as a main component may be used, and in this case, the application is carried out by a roll coater method, thereby coating the surface of the wiring board and each of the above-mentioned holes. Apply resin inside to fill the hole.

In addition, since the liquid medicine is 300 to 400 poise at room temperature,
Since it is not sticky after application, it can be used for mechanical polishing as described above.

<Function> According to the present invention, even if a photomask printing misalignment occurs when forming a tenting resist to cover a small-diameter via hole, the resin layer embedded in the small-diameter via hole will not be stained by the etching solution. prevent crowding.

Moreover, since the resin layer supports the tenting resist, it prevents the tenting resist from being torn due to spray pressure during the development and etching steps.

<Example> Hereinafter, the manufacturing method according to the present invention will be explained in detail using FIG. 1.

In addition, in this example, by making extensive use of small-diameter via holes, a conventional six-layer multilayer printed wiring board was manufactured as a four-layer multilayer printed wiring board.
It forms the outer layer circuit, and the same members as in the past are given the same reference numerals.

In addition, the inner two layers among the above four layers are made of double-sided copper-clad epoxy base material MCL-67 (plate thickness 0.2 mm, copper foil 35 mm,
After forming a circuit on a substrate (manufactured by Hitachi Chemical Co., Ltd.) using the subtract method using tenting, the copper foil was treated with copper oxide to increase the bonding strength of the copper foil stack.

Furthermore, the two outer layers of the above four layers are made of a single-sided copper-clad epoxy base M with prepreg GEA-67N (product name of Hitachi Chemical Co., Ltd.) interposed on the upper and lower surfaces of the two inner layers as described above.
CL-E-67 was placed on each layer, and then heated and pressurized to form a layer. As a result, a four-layer multilayer printed wiring board (hereinafter referred to as base material) was obtained.

Next, in order to form an outer layer circuit on the base material obtained as above, the through-hole After forming small-diameter via holes, etc. on the base material, and before the baking process, a liquid photosensitive resin having the composition shown in Table 1 is coated on the surface of the base material using a roll coater.
Apply the entire surface according to the law.

At this time, the resin also enters the through hole and the small diameter λ ear hole. After the resin is air-dried, the entire surface is exposed to UV light at a dose of about 200 to 500 mJ/Cm2, and then heat is applied to about 120℃±5℃. harden.

After that, dry film PUT14BF for tenting
As a pretreatment for laminating T (product name of Hitachi Chemical Co., Ltd.), mechanical polishing is performed using a belt sander (#400) to remove only the cured resin film on the surface of the substrate cured as described above. As a result, as shown in FIG. 1, the resin layer 8 remains buried only in the small-diameter via hole 3 of the base material 7 and the through hole (not shown).

Next, a dry film is laminated onto the copper foil 9 on the surface of the base material 7 exposed by polishing as described above, and is baked and developed to form small-diameter via holes 4 and land portions of through holes (not shown), wiring lines, etc. After forming the tenting resist 1 covering the substrate, etching is performed by spouting the etching liquid 2 at a predetermined spray pressure, and then the tenting resist 1 described in "2" is peeled off with methylene chloride.

At this time, the resin in the through holes and small diameter via holes is also removed, thereby forming the outer layer circuit of the base H.

By the way, in the above examples, the liquid photosensitive resin is applied to the entire surface of the base material by a roll coater method, or instead of this, the cream mold release agent KJR9022 (Shin-Etsu Chemical Co., Ltd.) whose main component is silicone resin is used. Co., Ltd. product name) may be applied to the entire surface using a roll coater method. In this case, after the application is air-dried, the surface coating film is removed by mechanical polishing with a belt sander in the same manner as above, and then a dry film is applied. are laminated, baked, developed, and etched, and when the dry film is removed after etching, the resin in the through holes and small diameter via holes is removed using methylene chloride.

Therefore, according to the above-described embodiment, a resin layer is buried in the small-diameter via holes and through-holes, and then the land portions of the small-diameter via holes and through-holes, wiring lines, etc. are covered with tenting resist. Since etching is performed from scratch, the resin layer prevents the etching solution from penetrating and also supports the tenting resist. Even in small via holes with small land diameters, high-quality small via holes that do not corrode the copper can be created. You get a hole.

In particular, when a cream-like peeling agent whose main component is a silicone resin is used as the resin layer, mechanical polishing can be performed simply by applying the peeling agent and drying it in the air.

<Effects of the Invention> In the present invention, as described above, a resin layer is buried in small-diameter via holes and through holes, and then the land portion of each hole is covered with a tenting resist before etching. Since it prevents liquid from seeping in and supports the tenting resist, a high-quality small-diameter via hole without copper corrosion can be obtained even if the land diameter is small.

Therefore, in forming the outer layer circuits of multilayer printed wiring boards, which will become increasingly denser in the future, we have adopted the tenting subtract method, which is currently the most stable and effective in mass production, as a manufacturing process, and have also created high-quality, small-diameter via holes. A multilayer printed wiring board can be provided.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the main parts in the manufacturing method of the present invention,
FIG. 2 is a sectional view showing the main parts in a conventional manufacturing method, and FIG. 3 is an explanatory diagram illustrating wiring lines including via holes. 1...Tenting resist 3...Small diameter via hole 8...Resin layer 1st Figure 2 Figure 3

Claims (1)

[Claims] 1. In forming an outer layer circuit of a multilayer printed wiring board having small-diameter via holes and through holes, a resin layer is buried in each of the holes, and then the land portion of each hole is covered with a tenting resist and then etched. A method for manufacturing a multilayer printed wiring board with small-diameter via holes, characterized by removing the resist and resin layer.