JPH0577161B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a carbon paste for high resistance. This type of material is used, for example, as a resistive material in printed wiring boards. [Prior Art] Carbon paste used as a resistor is required to have good heat resistance, with little variation in resistance value due to thermal changes (especially solder bath temperature) after printing and firing. This is because when the heat resistance is good, fluctuations in resistance value due to heat can be suppressed. However, the thermal properties of printed antibodies using conventional carbon paste cannot be said to be sufficiently good. In particular, resistors formed from high-resistance pastes with a low carbon component ratio have the problem of large fluctuations in resistance due to thermal characteristics such as heating due to solder dips during board manufacturing and thermal aging. be. Recently, attempts have been made to construct printed resistor boards in which resistors are further stacked on the wiring pattern surface in order to increase component mounting density. An example of a structure in which a resistor is formed on a pattern surface is shown in FIGS. 3A and 3B. In such a structure in which a resistor is formed on a wiring pattern surface, this surface is directly dipped with solder, so naturally the problem of resistance value fluctuation due to heat is likely to occur. For example, in the structure shown in FIG. 3A (referred to as structure A), the printed low antibody 4 is formed on the side of the substrate material 1 on which the copper wiring pattern 2 is formed. In this structure A,
An undercoat 3 is formed on a portion where a printed resistor 4 is to be formed, a printed resistor 4 is formed on the undercoat 3 with carbon paste, and a silver electrode is formed across the printed resistor 4 and the copper pattern 2. A top coat 7 is applied to cover the printed resistor 4, the silver electrode 6, and a part of the pattern 2. When solder dipping is performed on this structure A, the heat of the solder enters the solder bath on the resistor side and is almost directly applied to the printed resistor 4. Therefore, even if the top coat 7 is applied, the resistance value will fluctuate due to heat. drift) is more likely to occur. In the structure shown in FIG. 3B (referred to as structure B), the printed resistor 4 is formed on the wiring pattern 2 side as in structure A, although the order of forming the electrodes and the resistor is different. In this structure B, since the connecting portion between the silver electrode 6' and the printed resistor 4 can be made small as a whole, the influence of diffusion from the interface can be reduced. On the other hand, however, since the printed resistor 4 has a long structure, it may shrink significantly when heat is applied, which may cause drift. The first graph shows the resistance value drift when solder dip and thermal aging tests were performed on printed resistor boards (structures A and B) using conventional carbon paste.
Shown in the table. Tests were conducted for resistances of 1, 10, 30, and 50 kΩ/□. Solder dip temperature is 245-260℃
I tested it three times. The top coat 7 is made of enethiol-based or epoxy-modified urethane-based UV.
Cured ink was used. The results were almost the same in both cases.

[Purpose of the invention]

The present invention has been developed in view of the above circumstances, and is an advantageous high resistor that has good thermal characteristics, has small resistance value fluctuations, can be used as a resistor over a wide range, is not limited in applicability, and can be used with an appropriate viscosity. The purpose is to provide carbon paste for [Structure of the Invention] The carbon paste of the present invention includes the addition of 13 to 20 wt% of aminosilane coupling agent coating talc, which is a highly heat-resistant insulating filler, to a paste containing fine carbon particles and a polymer resin; It is characterized in that the viscosity is adjusted using a solvent. Aminosilane coupling agent coating talc content, which is a high heat-resistant insulating filler, is 13~
The fact that the content of 20 wt% has a critical effect is proven in detail in the examples described later. In carrying out the present invention, cross-linked polystyrene beads, benzoguanamine resin, etc. may be optionally used as a highly heat-resistant insulating filler in combination with the aminosilane coupling agent coating talc, as long as the effects of the present invention are not impaired. [Function of the Invention] The present invention improves thermal properties by adding coating talc, an aminosilane coupling agent, which is an insulating filler with good heat resistance, to a carbon paste composition. When a high-resistance paste is made with the mixing ratio of this filler within the range of the present invention, it is possible to make resistance fluctuations due to solder dip, thermal aging, etc. extremely small, for example within ±5%. Therefore, a good resistor with less thermal drift in resistance value can be obtained. In other words, in order to increase the resistance of carbon paste, the amount of carbon must be reduced, resulting in an increase in binder resin. However, as the amount of resin increases, the influence of resin behavior increases, and the resistance value of carbon paste decreases. Characteristics become unstable. It is known to reduce the amount of carbon and mix in an insulating filler, but this does not necessarily stabilize the resistance value characteristics, and on the contrary, it is not possible to obtain the appropriate viscosity due to problems such as filler settling, which ultimately suppresses resistance value fluctuations. However, in the present invention, the amount of carbon is reduced and an aminosilane coupling agent coating talc with good dispersibility and heat resistance is added, thereby eliminating the need to increase the overall amount of resin and improving the resistance value characteristics. It was possible to obtain a stable high-resistance carbon paste. Conventionally, it was difficult to use high-resistance carbon pastes, so many low-resistance ones had to be used, and as a result, they could not be applied to small areas, but in the case of the carbon paste of the present invention, has high resistance (e.g. sheet resistance value 50~
Since it is highly reliable even with a high resistance of 100 kΩ/□, it can be used and can therefore be applied to places with a small area. For similar reasons, higher density and smaller size are possible. Furthermore, since the carbon paste of the present invention has had its viscosity adjusted with a solvent, it can be used at an appropriate viscosity. Furthermore, in the present invention, since the aminosilane coupling agent coating talc, which is an insulating filler with a light specific gravity, is used, there is no problem of sedimentation in the paste, and the carbon paste is stable and of high quality. As mentioned above, there is a conventional example of adding alumina to carbon paste in order to obtain a high-resistance resistor (Japanese Patent Application Laid-open No. 81902/1983), but alumina has a large specific gravity and insufficient dispersibility. However, the present invention does not have the problem of sedimentation and is easy to use at an appropriate viscosity. It has the advantage of being [Embodiments of the Invention] Examples of the present invention will be described below. It should be noted that, as a matter of course, the following examples illustrate the present invention, but the present invention is not limited thereto. In this example, a paste containing carbon as the main conductive material and a polymer resin was used.
Using a commercially available phenolic carbon paste (sheet resistance value, 20 kΩ/□, e.g. Asahi Kaken TU series, etc.), add 5 to 20 parts of the insulating filler shown in Table 2 below (total of 100 parts),
Add so that the resistance value after firing is 60 ± 5 kΩ / □, stir for 30 to 60 minutes with a rice cracker, adjust the viscosity with butyl cellosolve as a solvent, and blend various insulating fillers. A carbon paste of the same type was obtained. Using various carbon pastes obtained as described above, resistor pairs were printed and formed on wiring boards to prepare samples for evaluation. The manufacturing process for forming this sample will be described later, but the structure of each sample was the same as in FIGS. 3A and 3B, and was manufactured by forming resistor pairs on the wiring pattern surface. For the top coat, enethiol-based and epoxy-modified urethane acrylate-based UV curing inks were used. The evaluation method was to measure resistance value fluctuations using the following test. Solder dip: 245-260℃, 5 seconds 3 times Heat aging: 85℃, 500 hours

【table】

[Table] In the above table, ◯ indicates good and × indicates poor. (In the table, - indicates no measurement or measurement impossible). From this test result, it can be seen that all of the samples of the present invention are good. Comparative samples had large resistance fluctuations after solder dipping (Samples 1, 5, and 6), large resistance fluctuations during thermal aging (Samples 3 and 5), or poor dispersion (Samples 1, 5, and 6). 2, 4), sedimentation occurred in the paste (Samples 1, 2, 4), but all the samples of the present invention were good. In this way, by adding a highly heat-resistant insulating filler to the carbon paste, the absolute amount of polymer resin in the carbon paste, which is susceptible to thermal effects (shrinkage), is reduced, improving heat resistance and making it possible to reduce solder depth. , resistance value fluctuations due to thermal aging can be reduced (for example, ±5% or less). By creating this blended carbon paste, a wide range of sheet resistance values (for example, from less than 10kΩ/□ to 50kΩ/□) can be used with confidence, making it possible to replace most chip resistors with printed resistors. Summer. It is easy to design, has a degree of freedom, and is advantageous in terms of service. Next, the addition amount of aminosilane coupling agent coating talc, which is a filler, is 13 to 13% of the total amount.
The effect of 20wt% on resistance value drift will be described in more detail. Figure 1 shows the horizontal axis; vertical axis versus filler content (wt%); resistor sheet resistance when aminosilane coupling agent coating talc is used as an insulating heat-resistant filler with other components held constant. It shows the relationship of (kΩ/□). Generally, as the content of insulating filler in a conductive paste increases, the sheet resistance value of a resistor formed from the paste increases. However, from FIG. 1, it can be seen that the rate of increase in sheet resistance value is not simply constant as the filler content (or addition amount) increases. When the filler content is 10wt% or less, almost no increase in sheet resistance is observed;
When the filler content exceeded 13 wt%, the sheet resistance value began to increase, and when the filler content exceeded 13 wt%, the sheet resistance value showed a stable linear increase (in the range of ). On the other hand, FIG. 2 shows the variation in the sheet resistance value of the resistance pair (Drift, %)showed that. When the filler content is 17 to 20 wt% or less (the range of and in FIG. 2), the value of Drift% is small and stable. When it gets close to 25wt%, the Drift value,
And the range of fluctuation increases rapidly, making it unusable. As a result of the above, from a filler content of 13wt%, which shows a stable linear increase in sheet resistance,
It can be seen that the effects of the present invention are brought about within the range of filler content up to 2 wt% where the value of Drift% is small and a stable state is maintained. Further, when no filler is contained (no additives) and the sheet resistance value is 20 kΩ/□, there is no large drift, but the fluctuation is somewhat larger than when the filler is added at 5 to 17 or 20 wt%. Sheet resistance value without filler is 50kΩ/□
If the resistance value exceeds a certain level, the value of Drift cannot be sufficiently suppressed, not only when there is no filler, but also when filler is added to the extent that the resistance value does not change. As the filler content increases, the sheet resistance itself changes and becomes too large, making it difficult to obtain a predetermined value. Therefore, considering both the trends in Figures 1 and 2, (1) If a relatively low sheet resistance value is required, filler should be added to a small amount of 10 wt% or less of the total ( range) The sheet resistance value is the same value as without additives, and only the reduction of Drift% is attempted (2) Resistance pair with relatively high sheet resistance value (20kΩ/
□ or above), the composition is such that the sheet resistance without filler is lower than the desired sheet resistance, for example, about 1/2, and the filler content is added to this. It has now become possible to adjust the addition at ~20 wt% to obtain the desired sheet resistance value and also to reduce the Drift value. The technique (2) above corresponds to the present invention. In addition, similar results were obtained when fillers were used in combination with aminosilane coupling agent coating talc, cross-linked polystyrene beads, and benzoguanamine resin spherical fine powder. When crosslinked polystyrene beads are used together as a filler, for example, specifically Fine Pearl (registered trademark, Sumitomo Chemical Industries, Ltd.) can be used. This is a transparent spherical material that mainly consists of cross-linked polystyrene beads and also contains resin beads such as polystyrene and MMA. Further, when a benzoguanamine resin spherical fine powder is used in combination as a filler, for example, specifically, Epostor (registered trademark, Nippon Shokubai Kagaku Kogyo Co., Ltd.) can be used. This is a benzoguanamine formaldehyde condensate and is a white spherical powder having the chemical structure shown below.

[Chemical formula] Also, Epostor S (same as above) can be used as a similar material, and since its particle surface is hydrophobic, it is compatible with various organic solvents and oils and fats. Next, an example of a substrate structure to which the present invention can be applied will be described. The samples used in the above examples also have the same structure. What is shown in FIG. 4 is an example of the above-mentioned structure A. To explain this in the order of manufacturing steps, first, as shown by reference numeral a in FIG.
form. Here, paper-phenol (XPC-FR) was used as the material. However, the material 1 may be paper-epoxy, glass-epoxy, etc., and any suitable substrate material can be used. Further, it may be a single-sided or double-sided board, or a multilayer board, and can be implemented in various forms. The pattern 2 is made of copper or other material that can be patterned. Pattern formation can be performed by etching. After the above pattern formation, as shown by symbol b,
Print undercoat 3. In this example, epoxy resin CR-20G (Asahi Kaken) was used as the material and was cured at 150° C. for 10 to 30 minutes to obtain undercoat 3. Other appropriate materials such as phenol-based materials can be used. This undercoat 3 is
This is applied to pattern 2 to be isolated, and the film thickness here is 10 to 20 μm. Next, as shown by symbol c, carbon paste was printed on this undercoat 3 to form a printed resistor 4. The carbon paste of the present invention can be used as the carbon paste for the printed resistor 4. Next, silver electrodes 6 were printed as indicated by d. In this example, the material is epoxy paste silver paste LS-
500 (Asahi Kaken) and was cured at 150°C for 20 to 40 minutes to obtain a silver electrode 6'. The film thickness was 10 to 20μ.
Other thermosetting resin-based conductive pastes can be used as the material. Next, a top coat 7 was printed as indicated by symbol e. In this example, the top coat 7 was formed by printing using one example of a photocurable composition. Its composition is as follows. Base: 40 parts of epoxy-modified urethane acrylate, especially

〔Effect of the invention〕

As mentioned above, the carbon paste for high resistance of the present invention has good thermal properties and small resistance fluctuations, so it can be used as a wide range of resistances, has no restrictions on applicability, and has the advantage of being able to be used at an appropriate viscosity. It is something.

[Brief explanation of drawings]

1 and 2 are graphs showing the effect of filler in one embodiment of the present invention. 3 to 5 are diagrams showing structural examples of printed resistor substrates, to which the present invention can be applied. 4...Printed resistor.

Claims (1)

[Claims] 1. Adding 13 to 20 wt% of aminosilane coupling agent coating talc, which is a highly heat-resistant insulating filler, to the conductive paste containing carbon fine particles and polymer resin, and adjusting the viscosity with a solvent. Carbon paste for high resistance.