JPS6237558B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention can be screen printed on a flexible printed wiring board, increasing the stability of the flexible printed wiring board, improving folding durability, having excellent voltage resistance, and being a highly reliable and inexpensive flexible product that can be followed in terms of flexibility. The present invention relates to a coverlay ink for printed wiring boards that can be used as printed wiring boards. In recent years, with the development of the electronic and electrical industry, there has been a demand for simplification, miniaturization, and high performance of communication and consumer equipment, and in particular, the use of flexible printed circuit boards made of plastic film, which is lightweight and can be mounted three-dimensionally. is attracting a lot of attention. however,
For three-dimensional mounting, a flexible board is required.
The need for folding has arisen, and as a result, problems such as shortness, folding durability, and voltage resistance have become a problem due to contact between wires or with other component conductors. Conventionally, two methods have been used for flexible printed wiring board cover layers. One method is to attach the same film as the wiring board or a different type of film to the flexible wiring board using an adhesive. Polyimide films are generally used for flexible wiring boards and coverlay films. This is because it has excellent mechanical properties, electrical properties, and chemical properties, and in particular, heat resistance and dimensional stability are superior to ordinary films. However, this method has the disadvantage that it is very difficult to align the wiring board and the coverlay film for bonding them together, regardless of the quality of the coverlay film. For example, if you want to lead a terminal on a wiring board, you must first make a small hole in a part of the coverlay film, and you must make sure that the small hole matches the terminal on the wiring board. The more holes there are, the more difficult the task becomes.
Very precise equipment is also required. In addition, the cost of the flexible printed wiring board itself increases due to the use of adhesives, and there are still problems with the adhesive itself. At present, no material with excellent heat resistance has been found. The second method is to prepare a coverlay ink and apply it to a flexible printed wiring board using a screen printing method. Since this method only requires making the screen board in advance, it improves work efficiency and mass productivity. However, conventional inks are insufficient as inks for screen printing, and protrusions, depressions, etc. are likely to occur on the coated surface, and the film thickness is often uneven and sparse. As a result, there were concerns about withstand voltage and other drawbacks, such as the possibility of shoots. It also had drawbacks of insufficient heat resistance, flexibility, and electrical properties. The present invention eliminates the conventional drawbacks and provides a cover layer for printed wiring boards that can be used for printed wiring boards and has excellent heat resistance, flexibility, electrical properties, especially insulation, adhesion, stability of printed wiring boards, and workability. The purpose is to obtain ink. The present invention consists of a silicone modified alkyd resin, 15 to 80 parts by weight of an inorganic filler with a specific gravity of 4.5 or less, and 30 to 60 parts by weight of an inorganic filler having a specific gravity of 4.5 or less per 100 parts by weight of the silicone modified alkyd resin.
Parts by weight, or silicone modified alkyd resin 100
An object of the present invention is to provide a coverlay ink for printed wiring boards (hereinafter referred to as "coverlay ink") which is prepared by adding 0.5 to 2.0 parts by weight of an antifoaming agent to the screen printing ink. Silicon-modified alkyd resins are obtained by reacting organopolysiloxanes or organoalkoxypolysiloxanes with alkyd resins. Silicon-modified alkyd resin has excellent flexibility, heat resistance, and electrical properties. The present inventor has discovered a coverlay ink for printed wiring boards that improves the stability of printed wiring boards and has excellent workability by adding an inorganic filler, a solvent, and an antifoaming agent to this silicone-modified alkyd resin. It is something that Inorganic fillers include talc powder, white carbon, barium sulfate, barium carbonate, lime carbonate, gypsum, white alumina, clay, silica, asbestin, magnesium carbonate, and precipitated magnesium carbonate. This is added in an amount of 15 to 80 parts by weight per 100 parts by weight of the silicon-modified alkyd resin. Within this range, the electrical properties, especially the insulation properties, will be significantly improved compared to the properties of the silicon-modified alkyd resin itself, and the insulation resistance after moisture resistance will be particularly good. Furthermore, the solder heat resistance and the surface hardness when applied and formed on a printed wiring board are also significantly improved. However, if the amount is outside this range and the amount is small, it will not be possible to obtain all of the above-mentioned required properties. For example, if the amount is less than 15 parts by weight, the stringiness of the resin itself is large and the effect of adding the inorganic filler is not apparent, making it unsuitable for use as a printing ink and causing bleeding and protrusions, resulting in an uneven thin film thickness. . Furthermore, the application method becomes difficult, resulting in poor work efficiency, and when this ink is applied to a printed wiring board and cured, the surface hardness becomes extremely poor. If the amount exceeds 80 parts by weight, the flexibility of the resin itself will decrease, the adhesion to printed wiring boards will be impaired, and the ink will not be sufficient as a printing ink, so it must have all the required properties. becomes difficult. In addition, these inorganic fillers should have a specific gravity of 4.5 or less. The reason why the specific gravity is limited to 4.5 or less is that the inorganic filler tends to sink to the bottom of the coating film, making it unsatisfactory. For example, when coated on a printed wiring board, the adhesion to the printed wiring board may be damaged and reduced, and the surface hardness of the coverlay body may be significantly reduced. Solvents and antifoaming agents are then added to provide the best screen printing ink. Solvent: 100 parts by weight of silicone modified alkyd resin
Add 30-60 parts by weight. If the amount is 30 parts by weight or less, which is outside this range, the viscosity of the ink itself will increase, resulting in uneven coating and some areas not being coated. Further, traces of the screen mesh remain on the coated surface, which tends to cause pinholes, and the high viscosity significantly impairs workability, which is undesirable. On the other hand, if the amount is 60 parts by weight or more, the ink will have a low viscosity and will tend to bleed, making it unsuitable for high-precision coverlay patterns. Furthermore, the thickness of the coated film tends to become thinner, and the reliability of the characteristics itself is not fully satisfied. The antifoaming agent is added in an amount of 0.5 to 2.0 parts by weight per 100 parts by weight of the silicone-modified alkyd resin. If the antifoaming agent is less than 0.5 parts by weight, a large amount of foam will be generated during printing. There is a state where the bubbles do not disappear as is, and a state where the bubbles disappear as time passes. However, due to the long time it takes to stand, the work efficiency is significantly reduced, and many pinholes are generated on the surface after baking and hardening. If the amount is more than 2.0 parts by weight, a new problem of repellency will occur in addition to the problem of foam, and a large amount of antifoaming agent will be added, which will impair the characteristics of the coverlay ink, which is not preferable. As the antifoaming agent, silicone antifoaming agents are particularly suitable. The coverlay ink thus obtained was applied and cured on a known polyimide flexible printed wiring board, and its properties were investigated, and the following results were obtained. First of all, it is flexible enough to withstand wrapping around a cylinder with a diameter of 2 mm, and is MIT based on JIS and P-8115.
Folding durability using a method using a folding durability tester, that is, the radius of curvature of the folded surface is 1 mm, and the bending angle is 135 on one side.
270° round trip at 1° speed 175 times/min, load
It shows folding resistance of 25 times or more under conditions of 100 g/mm and test piece dimensions of 15 mm x 110 mm or more, and can be fully used as a coverlay ink for flexible printed wiring boards. Even with soldering heat resistance caused by immersion in a 260℃ solder bath, it can withstand immersion for more than 60 seconds, and the coverlay body will not burn, blacken, decompose, become brittle, or undergo extreme deformation. It has sufficient heat resistance. In addition, the surface hardness of the coverlay body is superior to general coverlay inks, and exhibits a pencil hardness of H or less. The surface electrical insulation properties of the comb-shaped electrodes were 10 ¹⁴ Ω or more, and even after humidity resistance (standing at 40°C and 95% RH for 96 hours), the surface electrical insulation properties were excellent, showing 10 ¹² Ω or more. The present invention will be explained below with reference to Examples. Examples 1 to 6 Silicon-modified alkyd resin KR-204 (manufactured by Shin-Etsu Chemical Co., Ltd.) has a solid content of 50 Wt% and contains xylene as a solvent. Since xylene has a low boiling point, there is a possibility that it will scatter during ink mixing.
Therefore, replace the solvent with a solvent with a high boiling point beforehand. As a solvent, benzyl alcohol (boiling point
205,4 to 205,7°C) is preferred. Figure 1 shows how to replace the solvent. In the figure, 1 is a take-up roll, 2 is a kneading roll, 3 is a weir plate, 4 and 5 are pressure generating parts between the kneading rolls, 6 is a blade, and 7 is a roll rotation direction. The mixture is kneaded using the three-roll mill shown in FIG. 1 under the conditions shown in Table 1, and when most of the xylene solvent is scattered, benzyl alcohol is added. In this way, a silicone-modified alkyd resin in benzyl alcohol solvent is obtained. (In this case, it is best to aim for a resin solid content of about 80%.)

[Table] Furthermore, the resin solid content of the silicon-modified alkyd resin KR-204 obtained as described above was measured under the conditions shown in Table 2.

【table】

【table】

[Table] Next, silicone-modified alkyd resin KR-204, an inorganic filler, a solvent, and an antifoaming agent are blended according to the formulation example in Table 3. Using the three-roll machine shown in FIG. 1, the mixture is kneaded under the kneading conditions shown in Table 4 to obtain a coverlay ink for printed wiring boards. The coverlay ink thus obtained is applied onto a polyimide flexible printed wiring board that has been prepared in advance. The flexible printed wiring board is made of copper foil on one side, and the wiring pattern is prepared by a known method. However, the wiring pattern for measuring characteristics is as follows.

【table】

[Table] The wiring pattern for measuring the insulation resistance of coverlay ink is the black part shown in Figure 2. The wiring pattern for flexibility measurement is the black portion shown in FIG. The wiring pattern for measuring solder heat resistance is the blacked part shown in FIG. The coverlay ink was applied to the entire surface of the wiring patterns shown in Figures 2, 3, and 4 using a known screen printing method.
Bake and cure for 30 minutes in a hot air dryer at ℃. Table 5 shows the results of the characteristics of the printed wiring board with coverlay made in this way, such as flexibility, bending durability, heat resistance, electrical properties, surface hardness of the coverlay body, and adhesion between the wiring board and the coverlay body. Shown below.

【table】

[Table] The adhesion in this table was determined by the following test method. First, prepare the same sample as the sample for measuring solder heat resistance, and use a razor blade to form a total of 100 1 mm x 1 mm squares 9, 10 vertically 10 and 10 horizontally 11, as shown in Figure 5. Make incisions 12 using, for example, a knife. The depth of the cut is up to the surface of the underlying copper foil 14, as shown in FIG. Next, Sekisui Cellotape (manufactured by Sekisui Chemical Co., Ltd.) 16 is applied to the entire surface of the coverlay body 15 in which the notches have been made and pulled up in a 90 degree direction. 1mm at that time
Check if the ×1mm square peels off. If one or more pieces are peeled off, it is considered to be defective, and if no pieces are peeled off, it is considered to be good. Good workability means that no bubbles, blurring, smudges, or protrusions occur during printing, and the number of prints is 4 to 6 pages/
It means that it is a minute. Examples 7 to 12 Using white carbon as the inorganic filler, blending, manufacture of coverlay ink, manufacture of printed wiring board with coverlay, and evaluation of characteristics were carried out in the same manner as in Examples 1 to 6. Table 6 shows formulation examples, and Table 7 shows characteristic results.

【table】

[Table] Based on the above structure, the coverlay ink of the present invention is easy to work with, has excellent flexibility, electrical properties, soldering heat resistance, withstand voltage, and adhesion, and is suitable for screen printing on flexible printed wiring boards. This improves the stability of flexible printed wiring boards,
In addition, it is possible to obtain a highly reliable and inexpensive flexible wiring board that has improved bending durability, excellent voltage resistance, and can follow any flexibility.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a three-roll machine used during kneading in an embodiment of the present invention, Fig. 2 is a plan view of a wiring pattern for measuring insulation resistance in an embodiment of the present invention, and Fig. 3 is a cross-sectional view of a three-roll machine used during kneading in an embodiment of the present invention. A plan view of a wiring pattern for measuring flexibility in an embodiment of the invention,
FIG. 4 is a plan view of a wiring pattern for measuring solder heat resistance in an embodiment of the present invention, FIG. 5 is a plan view of a sample for measuring adhesion between a printed wiring board and a coverlay body in an embodiment of the present invention FIG. 6 shows a cross-sectional view of a sample for measuring adhesion between a printed wiring board and a coverlay body in an example of the present invention. 1: Taking roll, 2: Kneading roll, 3: Weir plate, 4, 5: Pressure generation part between taking rolls, 6: Blade, 7: Roll rotation direction, 8: Coverlay body with copper foil surface, 9: 1 mm x 1 mm square, 10,1
1: 10 pieces, 12: Razor blade notch, 13:
Polyimide film, 14: Copper foil, 15: Coverlay body, 16: Sekisui cello tape.

Claims (1)

[Claims] 1 Silicon modified alkyd resin, 15 to 80 parts by weight of an inorganic filler with a specific gravity of 4.5 or less per 100 parts by weight of silicon modified alkyd resin, 30 to 60 parts by weight of solvent, and 0.5 to 2.0 parts of antifoaming agent to 100 parts by weight of silicon modified alkyd resin. Coverlay ink for printed wiring boards consisting of heavy parts.