JP2827430B2 - Manufacturing method of multilayer printed wiring board - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a multilayer printed wiring board of a small electronic device such as a portable tape recorder and a video camera.

2. Description of the Related Art In recent years, as electronic devices have been downsized and have achieved high densities, thinning and high densification of printed wiring boards have been demanded, and multilayer printed wiring boards in which a number of circuit boards are stacked have been put to practical use.

Conventionally, these multilayer printed wiring boards have been heated while performing vertical alignment of a plurality of circuit boards, each having a wiring pattern formed on a copper-clad board by an etching method or the like, through an insulating material (prepreg) having an appropriate thickness. First, a multilayer board is manufactured by pressing and bonding and laminating, then the electrical connection of each layer is made by opening through holes penetrating from top to bottom, forming a conductor layer on this inner wall by plating etc. Short circuit was occurring.

In addition to this, as a short-circuiting method at an arbitrary position between the respective layers, in the case of a resin substrate such as
The structure shown in the figure is used. After forming a wiring pattern 82 on a substrate 81 as a first layer, a substrate 84 (or a prepreg with a hole) having a hole 83 formed at a required position as a second layer is aligned with the first layer and then joined, and then bonded. Plating the whole surface of the second layer, the bottom of the hole (on the first conductive layer)
Then, a conductor layer 85 is formed on the side surface of the hole. Thereafter, a wiring pattern is formed by leaving only a necessary portion of the plated portion of the second layer by an etching technique. Hereinafter, multilayering is performed in the same manner to produce a multilayer printed wiring board.

On the other hand, in the case of using a ceramic such as alumina as a substrate, as shown in FIG. 9, a wiring pattern 92 is formed on a ceramic green sheet 91 by resinate such as copper oxide.
To form On top of this, a bare hole is formed as a second layer at a short-circuit point with the first layer, screen printing is performed while sucking into the bare hole, a resinate is embedded, and normal screen printing is performed again to obtain a wiring pattern 93.
The green sheet 94 formed with is formed. In this way, the required number of green sheets, in which bare holes are filled with resinate, are accurately positioned and stacked. Finally, the laminated sheet is baked while applying pressure to reduce the resinate to form a metal conductor. For example, Nikkei New Material
See p85 article, November 20, 1989.

SUMMARY OF THE INVENTION However, in the first conventional method, in order to laminate printed wiring boards of respective layers, a prepreg obtained by impregnating glass cloth with an epoxy resin or the like in a semi-cured state is interposed between the respective layers. Was inevitably thick, which hindered the thinning of the printed wiring board.

Furthermore, it is impossible to form a through hole (bare hole) for short-circuiting the upper and lower layers at arbitrary positions, which complicates the circuit design, increases the number of stacked layers, and has the disadvantage of increasing the cost.

According to the second conventional method, a bare hole can be formed at an arbitrary position, but the process is very complicated and costly. Furthermore, plating is performed only on the periphery (inner wall) of the bare hole, and there is a high risk of disconnection.

In the third conventional method using ceramic green sheets, the process is considerably simplified and the connection state at the bare hole is good, but it has the disadvantage that the material cost is high and the weight of the substrate is heavy.

The present invention has been made in view of the above problems, and provides a method for manufacturing a lightweight multi-layer printed wiring board that has a simple process, is inexpensive, can form a bare hole at an arbitrary position, and has excellent electrical bonding properties.

Means for Solving the Problems The present invention is different from the electrical bonding method of the upper and lower layers by a bare hole, in which the upper and lower layers are directly connected by a wire, and the wire is formed on the first layer (lower layer). Bumps are formed by wire bonding in the upper and lower layers where connection is required.

Next, a thermosetting resin such as polyimide is applied thereon and thinned by a roll coating method, a spraying method, or a dipping method to a thickness smaller than the height of the bump to form an insulating layer. If the thermosetting resin is photo-curable, curing can be performed in a short time, and the process is more efficient.

Next, the head of the bump protruding on the insulating layer is cut with a cutter or the like to expose the metal surface. A second-layer wiring pattern is formed thereon, and the upper and lower layers are electrically connected. Hereinafter, the present invention provides a method of manufacturing a multilayer printed wiring board for performing multilayering in the same manner.

Since the insulating layer is formed by the casting method, the thickness can be reduced, and the thickness of the multilayer printed wiring board itself can be reduced. In addition, there is an advantage that the process is easy, the material cost is low, and the manufacturing cost can be greatly reduced. Further, the electrical connection between the upper and lower layers is large and stable as compared with the conventional through-hole type.

Embodiment A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a first embodiment of the present invention after a wiring pattern is formed, FIG. 2 is a schematic diagram of a bump forming process, FIG. 3 is a schematic diagram of a thermosetting resin coating process, and FIG. Is a schematic view of a process of cutting the protruding portion of the bump, and FIG.
The figure is a sectional view of the completed multilayer printed wiring board. Here, 11 is a polyimide film, 12 is a gold paste, 21 is a wire bonding device, 22 is a gold wire, 23 is a bump, 31 is a photocurable polyimide resin, 32 is a sprayer, 33 is an ultraviolet lamp, 41 is a bump, 42 is A polyimide insulating layer, 43 is a cutter, 51 is a polyimide insulating layer, 52 is a wiring pattern, 53 is a bump, and 54 is a chip component.

A gold paste 12 was applied on a polyimide film 11 (Kapton, manufactured by Du Pont-Toray Co., Ltd., film thickness: 25 μm) by a screen printing method to form a wiring pattern.

Next, a gold ball 22 having a wire diameter of 20 μm was applied to the tip of the gold ball by electric discharge using a wire bonding apparatus 21 at the junction (short circuit) with the upper layer (second layer) on the formed wiring pattern. This is joined to the required portion of the first layer wiring pattern by ultrasonic waves, and then the wire portion is immediately bent into a hairpin shape and cut to form a bump 23 having a tail on a head (stud). did. The size of the bump diameter was about 60 μm, and the height was about 50 μm. The bump shape is not limited to such a stud bump shape, but the presence of a stud has advantages that the adhesion to the base is excellent and the contact resistance is small.

Next, a photocurable polyimide resin 31 was sprayed on the
Spray in the yellow room, and coat the entire wiring pattern thinner than the bump height. Thereafter, ultraviolet rays are irradiated onto the resin by an ultraviolet lamp 33 to completely cure the polyimide resin, thereby forming an insulating layer (thickness: about 35 μm). However, in this state, the resin also exists on the bumps protruding on the polyimide resin, and the resin is in an insulating state. Therefore, the bumps 41 protruding from the polyimide insulating layer 42 are cut by the cutter 43 to expose the gold of the bumps.

Next, a wiring pattern was formed on the polyimide insulating layer 51 and the cut bumps 53 by screen printing a gold paste again. Thereafter, the same steps were repeated to form a multilayer, and chip components such as a resistor, a coil, a capacitor, and a semiconductor were mounted on the last surface portion to complete a multilayer printed wiring board.

At present, the use of gold paste as a wiring material is limited to digital circuits because of its high specific resistance, but the manufacturing process is easy and the manufacturing cost can be significantly reduced.

In the multilayer printed wiring board manufactured as described above, the thickness of the insulating layer was about 35 μm, the level difference (about 15 μm) of the wiring pattern made of gold paste could be suppressed, and a plurality of multilayers became possible. Furthermore, since the substrate is a polyimide film, the substrate has flexibility, and the substrate can be arranged at a curved place. Also, the manufacturing cost of the multilayer printed wiring board has been significantly reduced.

Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. FIG. 6 is a schematic view of a step of applying a thermosetting resin. 61 is a polyimide film, 62 is a nickel wiring pattern, 63 is a roll, 64 is a belt conveyor, 65 is a photocurable epoxy acrylate resin, 66 is an ultraviolet lamp, 67
Is a bump.

After treating the top of the polyimide film 61 with a stannous chloride solution to give sensitivity, a palladium chloride solution is applied,
This was thoroughly washed with water and then immersed in a caustic alkaline solution consisting of nickel sulfate and boric acid. About 15μ at 90 ° C for 1 hour
m. Next, a wiring pattern is printed thereon with resist ink, and immersed in an etching solution to dissolve unnecessary portions, thereby forming a wiring pattern. After that, the resist ink on the wiring pattern was removed, and bumps were formed at necessary positions on the pattern in the same manner as in the first embodiment.

Next, as shown in FIG. 6, a substrate having a nickel wiring pattern 62 and bumps 67 formed on a polyimide film 61 is placed on a belt conveyor 64 and passed under a roll 63 made of slightly soft rubber or the like. Apply curable epoxy acrylate resin 65 over the entire surface of the substrate, and then use an ultraviolet lamp
The resin was hardened through the base of 66. After that, the tip of the protruding bump is cut by a cutter, and the second layer wiring pattern is formed through the steps of plating, wiring pattern printing, etching, and resist removal again. Hereinafter, multilayering was performed in the same process.

Roll coating of the photocurable epoxy acrylate has the advantage of minimizing the amount of coating material used. However, the surface properties are considerably inferior to the spray method. On the other hand, by manufacturing the wiring material by plating, the manufacturing cost of the wiring pattern increases, but there is an advantage that the wiring resistance can be greatly reduced.

Hereinafter, a third embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a schematic view of a step of applying a thermosetting resin. 71 is an alumina substrate, 72 is a nickel wiring pattern, 73 is a bump, 74 is a protective film, 75 is a thermosetting phenol resin, and 76 is a hot blast stove.

A wiring pattern 72 was formed on an alumina substrate 71 by plating in the same manner as in the second embodiment. At this time, a protective film 74 is provided on the back side of the substrate. Next, after forming bumps 73 at necessary places in the same manner as in the first embodiment, the entire substrate was immersed in a thermosetting phenol resin 75, and the resin was cured in a hot air oven 76. The steps following the step of cutting the tip of the bump were performed in the same manner as in the first embodiment, a multilayer printed wiring board was manufactured, and finally the protective film was removed to complete the process.

Forming the protective film by the immersion method slightly increases the cost because the resin is also attached to the back surface of the substrate, but has the advantage that a dense protective film having excellent surface properties can be obtained.

When the multilayer printed wiring board of the above three embodiments and the conventional multilayer printed wiring board in which bare holes were formed in a glass / epoxy board were accelerated under the conditions of 85 ° C. and 85% RH, the change in resistance value was examined. In the example, almost no change in the resistance was observed even after 2000 hours, but the resistance was increased by about 1.6 times in the conventional product.

As described above, according to the present embodiment, since the upper and lower layers are electrically connected by the bumps, the number of steps can be significantly reduced and the cost can be reduced. Also, the connection resistance is small and the reliability is excellent. Further, since the insulating layer is formed by casting a thermosetting resin such as polyimide, the insulating layer can be made thin, and a lightweight and flexible multilayer printed wiring board can be obtained.

Effect of the Invention As described above, in the present invention, the electrical contact between the upper and lower layers is performed by forming bumps by wire bonding instead of using bare holes, so that the number of steps can be greatly reduced and cost can be reduced. Also, the connection resistance is reduced because the current flows through the entire bumps instead of being joined only by the inner wall portions as in the case of the bare hole. Excellent in reliability such as life. Furthermore, in order to form an insulating layer by casting of a thermosetting resin such as polyimide,
An insulating layer can be made thin, and a multilayer printed wiring board which is lighter and more flexible than a ceramic multilayer substrate can be obtained.

As described above, the present invention provides a method of manufacturing a lightweight and thin multilayer printed wiring board which can be manufactured at low cost with a small number of manufacturing steps, has low connection resistance, and is excellent in reliability.

[Brief description of the drawings]

FIG. 1 is a schematic view after forming a wiring pattern in this embodiment, FIG. 2 is a schematic view of a bump forming step in this embodiment, FIG. 3 is a schematic view of a thermosetting resin application step, and FIG. FIG. 5 is a cross-sectional view of a completed multilayer printed wiring board, FIG. 6 is a schematic view of a thermosetting resin coating process, and FIG. 7 is a thermosetting resin coating process. FIG. 8 is a schematic view of a conventional multilayer resin substrate made of glass, epoxy or the like, and FIG. 9 is a schematic view of a conventional ceramic multilayer substrate. 11: Polyimide film, 12: Gold paste, 21:
Wire bonding equipment, 22: Gold wire, 23: Bump, 31, 31 '... Photo-curable polyimide resin, 32: Sprayer, 33: UV lamp, 41: Bump, 42: Polyimide insulating layer, 43 ... cutter, 51 ... polyimide insulating layer, 52 ... wiring pattern, 53 ... bump, 54, 54 ', 54 "
…… Chip parts, 61 …… Polyimide film, 62 …… Nickel wiring pattern, 63 …… Roll, 64 …… Belt conveyor, 65 …… Photocurable epoxy acrylate resin, 66…
… UV lamp, 67… Bump, 71… Alumina substrate,
72: Nickel wiring pattern, 73: Bump, 74: Protective film, 75: Thermosetting phenol resin, 76: Hot air stove.

Claims (3)

(57) [Claims] 1. A step of forming a wiring pattern on a resin film or a ceramic plate and then forming a bump by wire bonding at a short-circuit portion with the upper wiring pattern, and roll coating a thermosetting resin layer on the wiring pattern. Forming a thinner than the bumps and curing the bumps sufficiently, and then cutting off the tips of the protruding bumps to expose the tips; and the cured thermosetting resin and the tips of the exposed bumps. Forming a second-layer wiring pattern thereon, and repeating the same steps as described above to perform multi-layering. 2. The method according to claim 1, wherein the thermosetting resin layer is formed by spraying instead of roll coating.
A method for producing the multilayer printed wiring board according to the above. 3. The method according to claim 1, wherein the thermosetting resin layer is formed by a dipping method instead of roll coating.
A method for producing the multilayer printed wiring board according to the above.