JPS6155551B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention can be screen printed on a flexible printed wiring board, increases the stability of the flexible printed wiring board, improves folding durability, has excellent voltage resistance, and is highly reliable and inexpensive that can be followed in terms of flexibility. The present invention relates to a coverlay ink for printed broken line boards that can be used to make flexible 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,
In order to mount the board three-dimensionally, it is necessary to fold the flexible printed circuit board, and as a result, problems such as short bending durability or withstand voltage have become a problem due to contact between lines or other component conductors. A solution to this problem is to coverlay the flexible printed wiring board, and two methods are used for this coverlay. 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. In this case, polyimide films are generally used for flexible wiring boards and coverlay films. It has excellent mechanical properties,
This is because it has electrical and chemical properties, particularly heat resistance and dimensional stability, which are more remarkable than ordinary films. However, this method has the disadvantage that it is very difficult to align the wiring board and coverlay film for bonding, regardless of the quality of the coverlay film.For example, when you want to lead the terminals of a wiring board, cover the A small hole must be made in a part of the film, and the hole must be aligned with the terminal on the wiring board. As the number of small holes increases, the work becomes more difficult and requires extremely precise equipment. In addition, the cost of the flexible printed wiring board itself increases due to the use of adhesives, etc.
There are still problems with the adhesive itself, and currently no adhesive has been found that adheres well to both coverlay films such as polyimide films and printed wiring surfaces, and has excellent electrical properties and heat resistance. Another 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 a screen plate in advance, it improves work efficiency and mass production. 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 voltage resistance, and there were also drawbacks to the occurrence of shoots. Also heat resistant,
It also had disadvantages of insufficient flexibility and electrical properties. The present invention improves the conventional drawbacks, and is used for printed wiring boards that have excellent heat resistance, flexibility, electrical properties,
It is an object of the present invention to provide a coverlay ink for printed wiring boards which is particularly excellent in insulation, adhesion, stability of printed wiring boards, and workability. The present invention uses a resin composition containing 2 to 30 parts by weight of an amino resin and 5 to 30 parts by weight of an acrylic ester to 100 parts by weight of an unsaturated polyester resin, and a resin composition having a specific gravity of 4.5 or less to 100 parts by weight of the above resin composition. An object of the present invention is to provide a coverlay ink for printed wiring boards (hereinafter referred to as coverlay ink) which is made into a screen printing ink by adding 5 to 20 parts by weight of an inorganic filler and 0.5 to 2.0 parts by weight of an antifoaming agent. Note that this composition may also contain an organic peroxide that serves as a curing catalyst. The unsaturated polyester resin here includes, for example, unsaturated polybasic acids such as maleic anhydride and fumaric acid, saturated acids such as phthalic anhydride, terephthalic acid, isophthalic acid, and adipic acid, and ethylene glycol and propylene glycol. unsaturated alkyds synthesized from glycols, such as those dissolved in vinyl monomers such as styrene, and unsaturated alkyds synthesized from glycols such as After the coalescence is formed, an organic amine compound and dioxane are added to make it easy to cause a chelate reaction, and then a hydroxide of a polyvalent ionized metal such as aluminum hydroxide or iron hydroxide is chemically reacted by a chelate reaction. It is made by adding vinyl monomers such as styrene to the sticky polymer obtained by bonding. 2 to 30% amino resin added to unsaturated polyester resin
When it is mixed in parts by weight, the curability becomes good and the electrical properties can be improved (initial and after moisture resistance, the insulation resistance increases). If the amount is outside this range and the amount is small, the insulation properties will be low and curing will be slow, making it impossible to achieve all the required properties. If the amount is large, it becomes hard and brittle and has reduced flexibility, making it difficult to provide all the required properties. Examples of the amino resin include methylated melamine resin, benzoguanamine resin, and butylated melamine resin. Further, when 5 to 30 parts by weight of acrylic ester is mixed, flexibility is improved and it is also suitable for adjusting the viscosity of the resin composition. If the amount is small outside this range, it will be difficult to obtain sufficient flexibility.
If the amount is large, the initial insulation resistance will decrease and it will not be possible to provide all the required characteristics. Examples of acrylic esters include 2-ethylhexyl acrylate, methyl methacrylate, lauryl tridecyl acrylate, tetrahydrofurfuryl acrylate, and glycidyl methacrylate. The present invention provides a cover for a printed wiring board that improves the stability of the printed wiring board and has excellent workability by adding an inorganic filler and an antifoaming agent to the resin composition (hereinafter referred to as the resin composition). This is the discovery of rain ink. Inorganic fillers include talcum powder, white carbon, barium sulfate, barium carbonate, lime carbonate, gypsum, white alumina, clay, silica, magnesium carbonate, and precipitated magnesium carbonate. Add this to 5 to 100 parts by weight of the resin composition.
Add 20 parts by weight. Within this range, the resin composition will have significantly improved electrical properties, especially insulation properties, and particularly good insulation resistance after moisture resistance. 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 5 parts by weight, the leakage ability of the resin composition itself is large and the effect of adding the inorganic filler is not manifested, so it is not suitable for use as a printing ink and tends to bleed and protrude, resulting in an uneven thin film. It becomes thick. 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 significantly worse. If it exceeds 20 parts by weight, the flexibility of the resin composition itself will decrease, and the adhesion to printed wiring boards will be impaired, and it will not be sufficient as a printing ink, so it may not have all the required properties. It becomes difficult to In addition, these inorganic fillers should have a specific gravity of 4.5 or less. specific gravity
The reason for using 4.5 or less is that the inorganic filler sinks to the bottom of the coating film, making it impossible to satisfy the desired characteristics. For example, when coated onto a printed wiring board, the adhesion to the printed wiring board may be damaged and reduced, and the surface hardening of the cover layer may be significantly reduced. Next, antifoaming agents are added to make the best screen printing ink. The antifoaming agent is added in an amount of 0.5 to 2.0 parts by weight per 100 parts by weight of the resin composition. If the antifoaming agent is less than 0.5 part 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, the flexibility is able to withstand wrapping around a cylinder with a diameter of 2 mm, and the bending durability was measured using a method using an MIT folding durability tester in accordance with JIS and P-8115, that is, the radius of curvature of the folded surface was 1 mm, and the bending angle was 1 mm. is 135° on one side
One round trip of 270°, speed 175 times/min, load 100
g/mm, and the bending resistance was 25 times or more under conditions of test piece dimensions of 15 mm x 110 mm or more, and it 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, exhibiting a pencil hardness of 3H or higher. 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 was 10 ¹² Ω or more, which is excellent. The present invention will be explained below with reference to Examples. Examples 1 to 7 Table 1 shows formulation examples. The unsaturated polyester is a commercially available product manufactured by Aikoku Sangyo Co., Ltd.
It is CPP0600. The amino resin used is a methylated melamine resin, which is manufactured by Sanwa Chemical Co., Ltd. and has the trade name Nikaratsuku MW-30. The acrylic ester used is 2-ethylhexyl acrylate, which is a trade name 2EHA manufactured by Osaka Organic Chemical Industry Co., Ltd. Talc powder is used as the inorganic filler, and a silicone antifoaming agent, trade name Paintad S, commercially available from Dow Corning, is used as the antifoaming agent. The resin compositions are blended and mixed in advance according to the blending examples in Table 1. Next, an inorganic filler and an antifoaming agent are added. The kneading method is carried out using a three-roll mill as shown in FIG.
In the figure, 1 is a take-up roll, 2 is a kneading roll,
3 is a weir plate, 4 and 5 are inter-roll pressure generating parts, 6 is a blade, and 7 is a roll rotation direction. The mixture was kneaded using the three-roll machine shown in FIG. 1 under the kneading conditions shown in Table 2 to obtain a coverlay ink for printed wiring boards.

【table】

[Table] The coverlay ink thus obtained is applied onto a polyimide flexible printed wiring board 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. The wiring pattern for measuring the insulation resistance of the coverlay ink is the black portion B shown in FIG. The wiring pattern for flexibility measurement is the black portion shown in FIG. The wiring pattern for measuring solder heat resistance is the black portion B 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 for 30 minutes in a hot air dryer at 180℃ to harden. 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, were evaluated in the third table.
Shown in the table. The adhesion in this table was determined by the following test method. First, prepare a sample equivalent to the sample for measuring solder heat resistance, and as shown in Figure 5, use a razor blade to solidify 10 squares 9 of 1 mm x 1 mm, 10 in the vertical direction and 10 in the horizontal direction, 11 in total. 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.

[Table] 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. In addition, good workability refers to a state in which no bubbles, blurring, smearing, or protrusions occur during printing, and the number of printed sheets is 4.
~6 sheets/min. Examples 8 to 14 Using white carbon as the inorganic filler, blending, production of coverlay ink, production of printed wiring board with coverlay, and evaluation of characteristics were carried out in the same manner as in Examples 1 to 7. Table 4 shows formulation examples, and Table 5 shows characteristic results.

【table】

[Table] As can be seen from the above description, the coverlay ink of the present invention has good workability, excellent flexibility, electrical properties, soldering heat resistance, withstand voltage, and adhesion.
A highly reliable flexible printed wiring board that increases the stability of the flexible printed wiring board by screen printing on the flexible printed wiring board, improves folding durability, has excellent voltage resistance, and can follow any flexibility. This is something that can be obtained.

[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... Tori roll, 2... Kneading roll, 3...
Weir plate, 4, 5... Pressure generating part between rolls, 6...
Blade, 7... Roll rotation direction, 8... Coverlay body with copper foil surface, 9... 1 mm x 1 mm square,
10, 11...10 pieces, 12...Razor blade incision, 13...Polyimide film, 14...Copper foil, 15...Coverlay body, 16...Sexy cello tape.

Claims (1)

[Claims] 1 2 to 30 parts by weight of amino resin, 5 parts by weight of acrylic ester per 100 parts by weight of unsaturated polyester resin
~30 parts by weight of the resin composition and 100 parts by weight of the above resin composition
Inorganic filler with a specific gravity of 4.5 or less based on parts by weight 5~
A coverlay ink for printed wiring boards containing 20 parts by weight and 0.5 to 2.0 parts by weight of an antifoaming agent.