JPH02288295A - Manufacturing method of printed wiring board - Google Patents

Abstract

PURPOSE:To make the material of a resin inductive layer solventless, as a printing method for a circuit board provided with a step, so as to prevent generation of bubbles thereby preventing the withstand voltage from decreasing by forming a resin conductives layer out of thermosetting material so that it may cover the upper surface and the side face of the resin inductive layer extensively and that the ends may reach the surface of a resin insulating plate. CONSTITUTION:The hardening of a resin conductive layer is done by thermosetting, and the thermosetting temperature is in the range not exceeding Tg of a resin insulating plate and lower than Tg by 20 deg.C or less and the hardening of a resin inductive layer is done by thermosetting before hardening of the resin conductive layer, and the hardening temperature is lower than Tg of the resin insulating plate by 20 deg.C or more, and further, a second resin insulating layer is provided at the upper layer of the resin conductive layer, and the hardening is done by thermosetting. The conductive resin layer is surely printed astride the face of the resin insulating plate 1 so that the circuit-board conductor pattern 2 and the resin inductive layer may not be exposed. As a printing method for the resin inductive layer 3, stencil printing is more advantageous than screen printing since it does not engulf bubbles. As material of the resin inductive layer 3, epoxy resin is made a basis.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a printed wiring board to be housed in electronic equipment.

(Prior art) Conventionally, parts of a circuit board that require electromagnetic shielding are covered with metal foil, or the circuit board is housed in a metal case, and a filter is installed to prevent frequencies other than normal signals. (
conducts noise (noise) to the outside.

Alternatively, there is a technology that prevents leakage in the form of radiation.

In addition, a metal layer or a layer containing metal powder is pasted as a shield layer on an insulating film or printed insulating resin, printed,
It has also been proposed to perform the process by laminating or vapor depositing.

Furthermore, the following new proposals have also been made.

This is a method in which an insulating resin dielectric layer is formed on a specific part of the printed conductor on one or both sides of the circuit board by means such as screen printing, and a resin conductive layer is formed on top of that, resulting in a structural As shown in FIG. 2, a circuit-like conductive pattern 2 is formed on a resin insulating plate or an insulating sheet 1, a resin dielectric layer 3 is provided thereon, and a resin conductive layer 4 is formed on it. It is formed.

(Problem to be Solved by the Invention) In this proposal, regular intervals are provided horizontally from end A to B of the resin dielectric layer 3, and the resin conductive layer 4 is connected to the resin dielectric layer 3.
It is set back from the end face. The reason for providing the above-mentioned regular intervals is to first form the conductive pattern 2 (formed by selective etching as a typical example) and the resin conductive layer 4 (as a typical example,
This is to prevent mutual short-circuiting by maintaining a long creepage distance of the copper paste (formed by screen mesh printing and heat curing). This is also to compensate for the poor printing accuracy of the resin conductive layer 4.

Printing accuracy is affected not only by the printing machine and printing plate, but also by the characteristics of the material being printed and management technology. What is important for unnecessary radiation prevention technology is the degree of radiation prevention and its persistence. The problem is the magnitude of electrolytic corrosion. In the conventional example shown in FIG. 2, since there are portions 8 and 9 of the circuit conductor pattern 2 and the resin dielectric Jf#3 exposed to the atmosphere, the degree of prevention of unnecessary radiation is not satisfactory.

Furthermore, as the resin dielectric layer, a commercially available solder resist (melamine, phenol, acid anhydride-cured epoxy resin, imidasol-cured epoxy resin, etc.) is used by heating and curing the resin insulating board 1 without thermally destroying it. Solder resists generate bubbles during printing and curing, and also contain impurities such as chlorine (CI) and sodium (Na).
Zinc (Zn), Aerosil silicon dioxide, antimony (
Since it does not contain migration inhibitors such as sb), the withstand voltage of the resin dielectric layer 3 is unstable, and discoloration, insulation resistance deterioration, short circuits, etc. due to migration occur within a relatively short period of time, making it unnecessary. Not only the radiation attenuation effect was reduced, but also the conductive pattern 2 lost its function.

The purpose of the present invention is to eliminate the conventional drawbacks, to avoid exposing the resin dielectric layer sandwiched between the conductor pattern and the resin conductive layer, and to eliminate the material of the resin dielectric layer as a printing method for circuit boards with steps. An object of the present invention is to provide an excellent method for manufacturing a printed wiring board that prevents generation of bubbles due to solventization and prevents a decrease in withstand voltage.

(Means for Solving the Problems) The method for manufacturing a printed wiring board of the present invention includes forming circuit-like conductor patterns as parallel conductive layers on both sides of a resin insulating board by a printing method, and has a structure in which a resin insulating plate is sandwiched, and a pinhole-free resin dielectric layer with a thickness of 15/71I or more is printed continuously on the surface and side surfaces of the circuit conductor pattern by a screen method or a stencil method. form and cover the top, bottom, left and right,
Finally, a resin conductive layer is placed opposite the parallel conductive layer across the resin dielectric layer, and the end of the resin conductive layer is extended to the insulating surface of the resin insulating plate without the circuit conductor pattern,
It covers the resin dielectric layer. In addition, the resin conductive layer is cured by heat curing, and the curing temperature is equal to that of the resin insulating board.
rg and within 20°C lower than Tg, and the resin dielectric layer is cured by thermosetting before the resin conductive layer, and the curing temperature is 20°C lower than Tg of the resin insulating board.
℃ or lower, and a second resin insulating layer is provided on the upper layer of the resin conductive layer, and the curing is performed by thermosetting, and the curing temperature exceeds the thermosetting temperature of the resin conductive layer, Further, the resin conductive layer and the second resin insulating layer are thermally cured at the same time at a temperature not exceeding 'rg of the resin conductive layer, and the second resin insulating layer is printed on the resin conductive layer or the second resin insulating layer. Printing extends beyond the scope of application of volatile, halogen-free leveling of the solder coat. In addition, in order to completely remove the solvent and uncured components in the resin conductive layer during simultaneous thermal curing, the resin conductive layer is preheated to 70°C or higher with less than 1 g of resin in the resin conductive layer. In addition, the resin conductive layer is thermally cured in an inert atmosphere, preferably in a semi-inert atmosphere having a nitrogen partial pressure of 60 to 90, and the conductive resin is cured by heating. Later, in order to prevent oil adhesion, air oxidation, thermal oxidation, etc. to the circuit conductor pattern that is in contact with the outside air, soldering must be done with rosin, synthetic rosin, or with a halide content of 0.001% by weight or less. The flux resin is converted into a flux resin liquid using a solvent, and is fixed by heating at a temperature of 70°C or less.Furthermore, after thermosetting, the flux resin liquid is applied to the resin conductive layer, and solder reflow coating is performed. Furthermore, the thermosetting resin conductive layer is printed with a resin insulating layer selectively or on the entire surface and sides so as not to come into contact with the outside air, and then thermosetted.

(Function) According to the present invention, the resin dielectric layer sandwiched between the four-electric pattern and the resin conductive layer acts as a medium for unnecessary radiation and performs wavelength shortening and re-radiation, so the resin dielectric layer should not be exposed. , covered with a resin conductive layer. Next, as a printing method for circuit boards with uneven surfaces, we changed the material of the resin dielectric layer to a solvent-free material and replaced the mesh screen with a stencil, so both of them contained air bubbles (air bubbles).

This prevents the generation of water vapor, solvents in resin, volatile matter) and prevents a drop in withstand voltage. Furthermore, by limiting the material and curing agent of the printed resin dielectric layer, its residual content, and the amount of ionic impurities, insulation resistance deterioration due to electrolytic corrosion and migration will not occur at all.

(Example) An embodiment of the present invention will be described based on FIG.

FIG. 1 is a sectional view of a printed wiring board manufactured by the method of the present invention. In this figure, the same parts as the conventional one shown in FIG. 2 are given the same reference numerals.

In FIG. 1, 1 is a resin insulating plate, on both surfaces of which circuit-like conductive patterns 2 and 2' are formed.
. It is formed so as to reach the insulating surface of the resin insulating plate 1 where there is no circuit-like conductor pattern, and further covered with resin layers 5 and 5'.

First, as shown in FIG. 1, the conductive resin layer is printed across the surface of the resin insulating board 1 so as not to expose the circuit conductor pattern 2 and the resin dielectric layer 3. As for the printing method.

Stencil printing is more advantageous than screen printing because it does not introduce air bubbles. The material of the resin dielectric layer 3 is based on epoxy resin, and Cg.

Ionic impurities such as Na are 5ppm (121℃ extracted water)
The following are desirable. As the curing agent, a solvent-free one which suppresses migration and contains 5 ppm or less of ionic impurities of an aromatic amine adduct compound containing fine metal particles is used in an amount of 5 to 90% by weight, preferably 20 to 50% by weight. The curing temperature is preferably 85 to 220°C, preferably 105 to 150°C. The standard printing thickness is about 15 μm in one printing, but it can be varied from 5 to 50.4+m depending on the mask, and it is also possible to increase the JIX thickness by printing multiple times. The experimental withstand voltage is 40℃90%
85℃ or 130℃ after 240H humidification with RI-I
250-2000V and DC500-2500V were obtained.

Below, the results obtained when various manufacturing conditions were changed will be described.

■As shown in Figure 1, conductive patterns 2, 2 made of copper foil with a thickness of 35 μm are placed on both sides of a resin insulation board 1 with a thickness of 1.
The six-resin insulating plate 1 on which ' is formed is a glass cloth substrate impregnated with an aromatic amine adduct curing type epoxy resin. After printing the resin dielectric layer 3°3' twice so as to completely cover the conductive patterns 2 and 2', it was placed in an atmospheric furnace at 150°C together with the resin insulating plate 1 and heated for about 50 minutes. and heat cure.

The thickness of the heat-cured resin dielectric layers 3, 3' is 30 μm (thickness + sjM is printed twice). Next, add copper powder, 50 parts of aromatic amine adduct, and 50 parts of epoxy resin.
The resin dielectric layers 3, 3' are entirely covered with a resin conductive layer 4, 4' consisting of a resin of ’. Table 1 of the appendix shows a comparison of the shielding effect, that is, the degree of attenuation of radiation, between the printed wiring board manufactured according to the present invention and the conventional printed wiring board.

■If the resin insulating plate 1 has a Tg of 115°C, the resin conductive layer 4
, 4', ■: When a photocuring (quinone distribution as a photopolymerization initiator in acrylic resin) type is used.

[Phase], [Stock]: Thermosetting temperature 135°C, 150°C (epoxy resin.

Acid anhydride curing agent) and ◎ heat curing temperature of 130°C (aromatic amine curing agent) are used.

A comparison of the degree of attenuation in the cases of ■, ■, [Stock], and ◎ is shown in Appendix Table 2.

Differences in the degree of attenuation can also be caused by differences in the resin used for the resin conductive layer.

■ Set the curing temperature of the resin dielectric layer 3 to 4!1 Tg of the resin insulating board 1.
The curing temperature was 115°C and 130°C.

When set at 145℃, A: Withstand voltage when resin dielectric layer is melamine, formalin, or lacquer (40'C 90% RH, after 240H) B: Withstand voltage when epoxy, imidazole is used C: Epoxy, aroma A comparison of A (conventional example), B (conventional example), and C (invention) in terms of withstand voltage for group amine ducts is shown in Appendix Table 3.

■When forming a second resin insulating layer with a thickness of 15 Ijm as a protective coat after forming the resin conductive layer at a curing temperature of 130°C, the curing temperature is set as follows to form the lower resin conductive layer. Check the resistance value. If the second resin insulating layer is heated and cured above the curing temperature of the resin conductive layer, it will have an adverse effect on the lower resin conductive layer 4, so it is best not to exceed the curing temperature above 10°C. In general, the case of the present invention is the most stable. The results are shown in Appendix Table 4.

(2) The resin conductive layer 4 and the second resin conductive layer 5 were simultaneously thermally cured at a temperature not exceeding T g of the resin conductive layer 4 of 145°C. By the method of the present invention, for the first time, it was possible to carry out the process without changing the resistance value of the resin conductive layer. The results are shown in Appendix Table 5.

■After heating the resin conductive layer 4, apply solder coating.

The resistance value of the resin conductive layer 4 is stabilized. The solder coat is a type of glue flow soldering, and the a-button is 60/40
This is done by solder dipping and leveling.

Although it is necessary to use flux at this time, the change in resistance value may increase due to the influence of the flux used.
Commercially available halides that cause rusting on conductor surfaces should be removed from 0.1 to 0.
．． There is a big difference between the rosin oil-based volatile flux used in the present invention and the rosin oil-based volatile flux added in an amount of 3% by weight. That is, Table 6 of the appendix shows the resistance change after humidification (40° C., 90% RH, 240 hours) when only flux was applied and the sample was passed through a flow temperature of 220° C. without soldering.

As a result of comparing the change in conductor resistance due to moisture absorption when a resin conductive paste is coated with solder and when flux remains inside, it is found that when rosin oil flux is used as in the present invention, there is a change in conductor resistance and the need for cleaning and removal. At the point where there is no
It has great practical value.

(2) When thermosetting the resin conductive layer and the second resin insulating layer at the same time, vaporized components in the resin conductive layer immediately before thermosetting are removed to reduce the influence on the resin of the second resin insulating layer. When gas is released from the resin in the vaporized components, heating beyond the Tg or curing temperature of the resin will affect the conductive properties of the resin conductive layer.

For the resin conductive layer, the curing temperature was 130°C and the Tg was 80°C.
C. and 145.degree. C., and the curing temperature of the second resin insulating layer is 120.degree. At this time, the simultaneous heat curing conditions were set to 130
℃, the degree of preheating temperature and its conditions are shown in Table 7 of the appendix.

In formulation C of the present invention, if the conductive resin layer is preheated to a temperature lower than the Tg of the resin and at least 70°C,
After simultaneous heating at 30° C., there is no blistering of the second resin insulating layer.

(2) When the resin conductive layer 4 is formed at a curing temperature of 130° C., the portions exposed to air will be oxidized and the color tone will be impaired. Not only that, but the contact resistance value and soldering properties are impaired. The curing time is set to, for example, 30 to 120 minutes.

The properties of discoloration and soldering in air are shown in Appendix Table 8.

If it is less than 95%, the oxide must be removed by pickling and solvent washing, followed by water washing and drying. The present invention makes this step unnecessary. When the degree of oxidation increases, it causes problems such as deterioration of appearance and finish of solder coat, and also causes problems due to increase in contact resistance value and furthermore, conductor resistance value.

(2) If the portion of the resin conductive layer 4 that is not covered by the second insulating resin layer is left in the air, discoloration and deterioration of solderability will occur over time. Therefore, a coating that does not interfere with soldering is desired. When a commercially available rosin type flux is used, oxidation is promoted instead.

This is because commercially available fluxes contain 0.1 to 0.3% by weight of halide as an activator. Rosin that does not contain any halides has a Tg of 70°C or less,
It is unsuitable for use in the present invention. For example, 85℃85
When an electric field is applied in %RH, electrolytic corrosion occurs, and discoloration or soldering causes poor quality. However, in order to protect the resin conductive layer 4, a synthetic rosin with a Tg of 135° C. or higher, containing no halide, or o, ooi
Synthetic rosin or rosin oil with a Tg of 105°C or higher (after volatilizing the solvent) from 105°C to 180% by weight
It is best to use a vaporizer (one that evaporates away) at ℃. This state is shown in Appendix Table 9.

[Phase] If solder paste flow soldering is performed on the resin conductive layer 4 which has been thermally cured in an inert atmosphere at 130°C as shown in (1) above, the result will be complete even if flux cleaning after reflow soldering is omitted. or other malfunctions.

■The resin conductive layer 4 thermoset under the conditions shown in ■ above is applied to the first layer.
As shown in Figure (b), it is simultaneously formed on the surfaces of the resin insulating layers 6, 6' and the wall surface 8 of the hole 7, and is cured to form a through hole in the hole 7, or on the end surface of the resin insulating plate 1. If necessary, it is made of the same material as the resin dielectric layer 3, and is formed separately and simultaneously with the resin dielectric layer 3.

This method allows printing of a resin conductive layer on the end surfaces of the plate and the wall surfaces of the holes without any additional steps.

(Effects of the Invention) According to the present invention, the resin dielectric layer sandwiched between the conductor pattern layer and the resin conductive layer acts as a medium for unnecessary radiation, shortens the wavelength, and causes re-radiation, so the resin dielectric layer is not exposed. Next, as a printing method for circuit boards with steps, the material for the resin dielectric layer was made solvent-free, and the mesh screen was replaced with a stencil to prevent air bubbles from forming. Deterioration of insulation resistance due to electrolytic corrosion and migration can be prevented by limiting the material of the resin insulation layer, the curing agent, its residual content, and the amount of ionic impurities, and its practical effects are extremely significant.

Table 1 Table 2 Table 9 85℃85%RH100V DC applied teno corrosion occurred

[Brief explanation of the drawing]

FIGS. 1A and 1B are sectional views of a printed wiring board according to an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional printed wiring board. 1...Resin insulating plate, 2,2''...Circuit-like conductor pattern, 3,3'...Resin dielectric layer, 4,4'
... Resin conductive layer, 5... Second resin conductive layer, 6.
6'... Resin insulating layer, 7... Hole, 8... Wall surface. Patent applicant: Matsushita Electric Industrial Co., Ltd. Table 5 No'-) L7 (Table 8)

Claims (11)

[Claims] (1) A circuit-like conductor pattern is formed on both sides of a resin insulating plate using a thermosetting material, and a resin dielectric layer made of a thermosetting material is formed to completely cover the upper surface and side surfaces of the conductor pattern. Next, a resin conductive layer is formed using a thermosetting material so that the upper surface and side surfaces of the resin dielectric layer are completely covered and the ends thereof reach the surface of the resin insulating plate, and if necessary, A method for producing a printed wiring board, which further comprises covering the printed wiring board with a resin layer. (2) The printed wiring according to claim (1), wherein the resin conductive layer is cured by thermosetting, and the curing temperature is within a range of not exceeding the Tg (glass transition temperature) of the resin insulating board but less than 20°C lower than the Tg. Method of manufacturing the board. (3) The printed wiring board according to claim (1), wherein the resin dielectric layer is cured by thermosetting before the resin conductive layer is cured, and the curing temperature is 20° C. or more lower than the Tg of the resin insulating board. manufacturing method. (4) providing a second resin insulating layer on the resin conductive layer;
The method for manufacturing a printed wiring board according to claim 1, wherein the curing is carried out by thermosetting, and the curing temperature exceeds the thermosetting temperature of the resin conductive layer. (5) The method for manufacturing a printed wiring board according to claim 1, wherein the resin conductive layer and the second resin insulating layer are thermally cured simultaneously at a temperature not exceeding Tg of the resin conductive layer. (6) A claim in which the printing of the second resin insulating layer is extended beyond the range in which volatile, halogen-free leveling of the resin conductive layer or its solder coating is applied.
5) The method for manufacturing the printed wiring board described above. (7) When performing simultaneous thermal curing, in order to completely remove the solvent and uncured components in the resin conductive layer, preheating is performed at a temperature below the Tg of the resin and the resin in the conductive layer and above 70°C. The method for manufacturing a printed wiring board according to claim 5, wherein the method is performed on a resin conductive layer. (8) The method for manufacturing a printed wiring board according to claim (4), wherein the thermosetting of the resin conductive layer is carried out in an inert atmosphere, preferably in a semi-inert gas reservoir having a nitrogen partial pressure of 60 to 90. . (9) In order to prevent oil adhesion, air oxidation, thermal oxidation, etc. to the circuit conductor pattern that is exposed to the outside air after the conductive pattern is hardened and formed by heating the conductive resin, solderable rosin, synthetic rosin, or 0.001% by weight
3. The method of manufacturing a printed wiring board according to claim 2, wherein a flux resin having a regulated halide content is prepared as a flux resin liquid using a solvent, and is heated and fixed at a temperature of 70° C. or lower. (10) The method for manufacturing a printed wiring board according to claim (9), wherein after thermosetting, the flux resin liquid is provided on the resin conductive layer and solder reflow coating is performed. (11) The method for producing a printed wiring board according to claim (1), wherein the thermosetting resin conductive layer is printed selectively or on the entire surface and side surfaces of the thermosetting resin conductive layer so as not to come into contact with the outside air, and then thermosetting.