JPS58162098A - Method of producing multilayer printed board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a multilayer printed board in which a plurality of unit boards having through holes are laminated.

In order to miniaturize electronic devices, higher density and multilayer printed boards are required, and various multilayer printed boards have been proposed. Generally speaking, the current manufacturing method for multilayer printed boards uses graded through holes made of copper-clad laminates. This is a multilayer printed board obtained by drilling holes between the outer layer (surface) and the inner layer, then plating through holes, and then etching the outer layer into a circuit pattern. Although this is advantageous in terms of through-ball connection reliability, a significant drawback is that when highly multi-layered,
The diameter of the through ball increases due to hole machinability, which goes against the trend of increasing the density of the pattern.

An alternative method is a build-up method in which a circuit is formed by plating without using a copper-clad laminate. This is a multilayer printed board in which insulating layers and circuits are repeatedly formed layer by layer.This has the divine purpose of being able to form small through balls anywhere you want, but the drawback is that it requires a very large number of manufacturing steps. be.

A multilayer printed board that can solve the above two drawbacks of multilayer printed boards at once is a multilayer printed board in which a plurality of printed boards on which small through balls are formed are laminated as unit boards. When unit boards are stacked on top of each other, an adhesive conductive paste is formed on the circuits that are in contact with the circuits of other unit boards, which is melted by the heating during pressure molding described later and electrically connects the opposing circuits. This is a product in which multiple unit substrates are bonded and integrated by heat and pressure molding, and there is no change in manufacturability even if the number of layers is increased to a high degree, and high-density patterns can be obtained at the unit substrate stage. This has the great advantage of not damaging what was created. However, this multilayer printed board had a major drawback in that the reliability of the circuit connections between the unit boards was poor.

The present invention uses a printed board for board-to-board connection that has electrically connected micro pins made of easily melted metal on both sides,
This is placed between the unit boards, and the unit boards are stacked so that the micro pins are inserted into the through holes of the unit boards, and the unit boards are connected by heating and pressurizing them to melt the micro pins and integrate them. The purpose is to provide a multilayer printed board with excellent connection reliability between boards.

The present invention will be explained in detail below using the drawings.

FIGS. 1(a) to 1('e) are explanatory diagrams of the main manufacturing steps of the multilayer printed board of the present invention, showing the cross-sectional structure of the main parts in each step. Each process will be explained in accordance with the order of the drawings.

(a): 4. A high-density printed board 1 is manufactured and prepared using a known technique as a starting board. 2 is an insulating base material, 5 is a circuit pattern, and 4 is a through hole. Although the figure shows a double-sided printed board, a multilayer printed board having a circuit on the inner layer can also be used as the starting board.

(b) Second, in order to maintain insulation between the surface circuits of the starting substrate, an insulating coating 5 is formed on areas other than the through holes 4 to form a unit substrate 1'.

The insulating coating 5 can be formed by screen printing a thick insulating paste, but for high-density patterns, the through holes 4 can be formed by laminating a photocurable solder film and then exposing and developing it. A method of removing the film is preferred.

(C): Next, micro pins 6゜6' made of easily melted metal.
A printed board 7 for inter-board connection having on both sides is manufactured and prepared by the manufacturing method described later. Here micro pins 6 and 6'
are electrically connected via conductive paste 8 in the hole of printed board 7. The micro pins 6 and 6' are characterized in that their diameters are smaller than the diameters of the through holes 4 of the unit substrate 1'.

(d): A plurality of unit substrates 1' having insulating coatings 5 formed on their surfaces are stacked together via printed boards 7 for inter-board connection. At this time, the micro pins 6, 6' located on both sides of the printed board 7 for connection between boards are placed in the through holes 4 of the unit board 1'.
is inserted.

(e) = Heating and pressurizing to a temperature equal to or higher than the melting temperature of the micropin. When the micro pins are melted and then cooled to room temperature, the unit substrate 1' and the printed board 7 for connecting between boards are integrated, and the multilayer printed board of the present invention having excellent connection reliability between boards is obtained. At this time, the insulating coating 5 acts as an adhesive between the plates.

Note that 9 in the figure is the molten metal produced by melting the micro pin, but this molten metal 9 may not completely fill the through hole 4, and voids may remain when the through hole 4 is cooled to room temperature. be. This may reduce the connection reliability, so before stacking the unit board 1' and the board-to-board connection printed board 7, as shown in FIG. A more reliable multilayer printed board can be obtained by embedding micropins into the micropins and integrating them with the conductive paste when the micropins are melted. The above conductive paste (thick film conductive paste) includes not only solder paste but also copper in an organic binder.

A material in which metal powder such as silver is dispersed can be used.

Next, a method for manufacturing the board-to-board connection printed board 7, which is the gist of the present invention, will be explained.

FIGS. 6(A) to 6(J) are explanatory diagrams of the main manufacturing steps of the printed board for connection between boards of the present invention, showing the cross-sectional structure of the main parts in each step. Each process will be explained in accordance with the order of the drawings.

(A) - First, a copper-clad flexible board 12 consisting of two copper foils 10 on the front and back sides and an insulating board 11 is prepared.

The thickness of the copper-clad flexible board 12 is preferably 0.1 to Q.2 mm in view of the relationship between hole machinability and strength.

(13) Holes 13 are made in the copper-clad flexible board 12 by machining using nitrile, punching, etc., or by laser processing.

(C); The conductive paste 14 is held in the hole 13 by burying the conductive paste (thick film conductive paste) 14 in the hole 15 and performing heat treatment.

The conductive paste 14 is printed on holes 1 by screen printing method etc.
6, and as the material, not only solder paste but also an organic binder in which metal powder is dispersed can be used. The heat treatment may vary depending on the material, but if it is performed at 150 to 180°C for 10 to 1000 seconds, the conductive paste 14 will be firmly held within the holes 16.

(D): Next, apply dry film photoresist 1 on both sides.
5 is laminated using a hot roll laminator.

(E): Ultraviolet rays 18 are irradiated through a photomask 17 in which a black circle 16 larger than the diameter of the hole 16 is formed only in the position corresponding to the hole 13, and the photoresist 19 in the area outside the black circle 16 is hardened. to make it solvent insoluble.

(F) - Next, a dry film photoresist 15' is laminated thereon again.

(G) In the same way as in Step 1 (E), ultraviolet rays are irradiated through a photomask to harden the photoresist 19' except for the areas corresponding to the holes 13, making it solvent-insoluble (II): Next, development with a solvent is carried out. A round window 20 is formed in a portion corresponding to the hole 13, and a conductive paste 14 and a copper foil 10 are formed.
The surface 21 of is exposed. The reason why two layers of photoresist 19 and 19' are formed is to make the depth smaller than the diameter of the round window 20, and the number can be increased to six or more layers depending on the required height of the micropin. With a single layer of resist, it is not possible to make the depth deeper than the diameter of the round window 20 due to resolution problems.

(I) Next, by performing solder plating, the solder-plated pillars 22 are formed inside the round window 20 and on the surface 21.
form.

(・I): After peeling off the photoresists 19 and 19',
By etching and removing the portions of the copper foil 10 other than the plating pillars 22 using a ferric chloride aqueous solution, a printed circuit board 7 for connection between micro-pins 6 and 6' (-1) can be obtained.

Examples will be described below, but the present invention is not limited thereto)]
It's not a bastard.

[Example 1]: The lattice pitch i is determined by the subtractive method.
, 25mm and through hole diameter [], 22. A high-density printed board with 2 mm diameter was prepared, and the circuit pattern other than the null hole portion was covered with a photocurable solder mask (75 μm thick) to form a unit board (total thickness 0.4 mm).

A printed board for connection between boards was produced as follows.

0.15mm thick copper clad] flexible/pull board (copper foil 188
Drill a hole of Q, 1+r3 mφ in the (℃ thickness), and use solder paste (manufactured by Tamura) in the hole by screen printing.

88-3222) was embedded and heat treated at 165° C. for 10 seconds. Next, a 100 μm thick dry film photoresist (manufactured by Hitachi Chemical Co., Ltd., SR・-1) was applied.
O00) was laminated at 80°C using a hot roll laminator. After aligning a photomask with a black circle of 0.15 mm in diameter and irradiating it with ultraviolet rays, the same dry film photoresist as above was laminated again, and after aligning the photomask and irradiating it with ultraviolet rays, trichloroethane was used as a solvent. The photoresist has a diameter of 0.
．． 15. A round window with a depth of 0.2 mm was formed to expose the copper foil of the flexible board and the surface of the solder (conductive paste) in the hole. Then it was soaked in a phenolsulfonic acid bath (
Electroplating was carried out at 25°C and 2A for 90 minutes, and a solder-plated pillar (
A height of 0.2 mm) was formed.

In order to avoid electric field concentration during plating, the substrate was rotated to form plating columns of uniform height. After removing the resist with methylene chloride, a ferric chloride aqueous solution was sprayed to etch the copper foil in areas other than the plating pillars to obtain a printed board with micro pins. The diameter of the micro pin is 015. The height was 0.2 mm.

The nine printed boards for board-to-board connection obtained through the above process and the ten unit boards were stacked alternately.

By doing this using a guide bin, it was possible to easily insert the micropin into the through hole V of the unit board. The above 19 sheets stacked at 30kg/cm2, 180℃
After heating and press molding for 3 minutes, the product was cooled with water to room temperature under pressure. The micro pins are melted by the heat and pressure described above and integrated with the copper of the through-hole circuit, and the photocurable solder mask (film) as an insulating coating is cured by thermal crosslinking, and at the same time it is bonded to the unit board and the bullet plate for connection between the boards. was firmly attached.

In order to evaluate the connection reliability of the 20-layer multilayer board thus obtained, a thermal shock test (-65°C) was conducted.

30 minutes → 125°C, 30 minutes) As a result, no problems such as wire breakage occurred even after 100 cycles [Example 2]
; Solder paste (manufactured by Tamura, 88-3) was applied by screen printing into the through holes of the unit board of Example 1.
2.22) was embedded. The amount of filling was set to about 1/2 of the internal volume of the through hole to prevent the micro pin from protruding when inserted. This unit board 10
The sheets were stacked alternately with nine printed boards for inter-board connection, and integrated by heating and pressure molding under the same conditions as in Example 1 to obtain a 20-layer multilayer board. This multilayer board can provide stable inter-board connections up to more than 500 cycles of thermal shock testing.
The reliability was further improved compared to the multilayer board of Example 1.

[Example 6]: An organic conductive paste (manufactured by Epoch Co., Ltd., Epotenoku WE-12) was embedded into the through holes of the unit substrate of Example 1 by screen printing to an extent of about 1/2 of the internal volume of the through holes. . After stacking 10 unit boards alternately with 9 printed boards for board-to-board connection in the same manner as in Example 1, heat and pressure molding was carried out under the conditions of a pressure of 60 kg/f:m2, 170°C, and 60 minutes. This was integrated to obtain a 20-layer multilayer board. In this multilayer board, a stable connection between the boards was obtained up to 25'0 cycles of the thermal shock test.

[Example 4]: Lattice pinoch 1 by subtractive method
．． A high-density 4-layer board with a through-hole diameter of 25 mm and a through-hole diameter of Q, 'l mmφ was fabricated, and the circuits and C-turns other than the through-hole portion were covered with a photocurable solder mask (75 μm thick), and a unit board (total thickness of 0 .6mm).

Solder paste (made by Tamura,
5S-3222) was embedded in an amount equivalent to approximately 2/mouth of the internal volume of the through hole. After 10 unit boards embedded with paste were stacked alternately with 9 printed boards for interboard connection of Example 1, they were heated and pressed under the same conditions as in Example 1 to obtain a 40-layer multilayer board. This multilayer board showed stable inter-board connection reliability over 500 cycles of thermal shock testing.

As explained above, the multilayer printed board of the present invention uses a printed board for board-to-board connection that has electrically connected micro pins made of high-melting metal on both sides, and arranges this on a unit board to form a through-hole in the unit board. The unit boards are stacked so that the micro pins are inserted into the circuit board, and the micro pins are melted and integrated by applying heat and pressure.This ensures long-term reliability without compromising the high density of the circuit pattern on the unit board. It has the advantage of being superior in terms of gender.

Electronic devices with high-density packaging of LSIs require a multilayer printed board with 20 or more layers, but the multilayer printed board of the present invention has excellent reliability and economic efficiency, so it will be useful in making electronic devices more economical. demonstrate. Furthermore, since the number of layers is unlimited in principle, electronic devices such as computers and computers can be miniaturized to an extreme extent.

[Brief explanation of the drawing]

Figures 1 (a) to (e) are explanatory diagrams of the manufacturing process of the multilayer printed board of the present invention, Figure 2 is a cross-sectional view of the through holes of the unit board filled with conductive paste, and Figures 6 (A) to (J ) is an explanatory diagram of the manufacturing process of the printed board for board-to-board connection of the present invention. 1...High-density printed board 1'...Unit board 2...
・Insulating base material 6...Circuit pattern 4...Through hole 5...°Insulating coating 6.6...
・Micro pin 7... Printed board for connection between boards 8.8'... Conductive paste 9... Molten metal 10.
・Copper foil 11... Insulating board 12... Copper-clad flexible board 16... Missing 14... Conductive paste 15
．． 15'...Dry film photoresist 16...
Black circle 17...Photomask 18...Ultraviolet light 19.19':...Photoresist (light curing resist) 2
0...Round window 21...Surface of copper foil and conductive paste 22...Plated pillar Patent applicant Nippon Telegraph and Telephone Corporation Patent attorney Junnosuke Nakamura 1-1 Figure 4 '1-2 Figure '4 p3) 'IF3 diagram

Claims (2)

[Claims] (1) A method for manufacturing a multilayer printed board including the following steps. ■ A first step of preparing a plurality of unit substrates having through holes; ■ Having micro pins made of easily meltable metal on both sides and having a diameter smaller than the diameter of the through hole of the unit substrate; A second step of preparing a printed board for board-to-board connection that is electrically connected, ○ Arranging the board-to-board connection printed board between the unit boards, and forming a board-to-board connection board in the through hole of the unit board. The sixth step is to stack the printed boards so that the micro pins are inserted, heat and pressure treatment is performed at a temperature higher than the melting point of the metal of the micro pins to melt the micro pins and connect the boards. Fourth step. (2) The through-holes of the unit board prepared in the first step are filled with conductive paste in advance, and the unit board is laminated with a printed board for board-to-board connection in the sixth step. 2. The method of manufacturing a multilayer printed board according to claim 1, wherein the micro pins of the printed board for board-to-board connection and the conductive paste are present in the holes. (b) The multilayer printed board according to claim 1, characterized in that the printed board for inter-board connection prepared in the second step is made by the following steps: manufacturing method. ■ A process of drilling holes at predetermined positions on a copper-clad flexible board and filling the holes with conductive paste; ■ Laminating dry film-like photoresist multiple times on both sides of the copper-clad flexible board that has gone through the above process, and applying each photoresist. A process of exposing the surface of the conductive paste and copper foil by exposing and developing a hole in the copper-clad flexible board to open a round window with a diameter larger than the diameter of the hole and a depth deeper than the diameter of the hole, ○ Solder plating is performed on the exposed surface to form micro pins, which are plated columns with a thickness larger than the diameter of the round window, and then the dry film-like photorect is removed with a solvent; A process to remove copper foil from the surface of a flexible board other than micro pins by etching.