JP2893260B2 - Method of firing resistance paste - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sintering a resistance paste, and more particularly to a method for sintering a resistance paste applied to an organic substrate that cannot withstand high-temperature sintering such as a glass epoxy substrate. The present invention relates to a method for baking a resistance paste suitable for mass production, in which a predetermined resistance value is obtained, a rate of change by solder immersion falls within a standard, and no discoloration of a substrate occurs, and baking can be performed in a short time.

2. Description of the Related Art Conventionally, in place of a fixed resistor, a resistive paste applied to a substrate by printing or the like is used, and the substrate is heated and baked at a predetermined temperature for a predetermined time to have a stable resistance value on a circuit. It has been used as a fixed resistor.

In this case, if the substrate is a ceramic substrate, there is no possibility that the substrate will be discolored even if the substrate is baked at a high temperature for a long time. It is possible to perform firing so as to sufficiently fall within the standard.

However, in the case of an organic substrate, such as a glass epoxy substrate, which cannot withstand high temperatures, it is not easy to fire the resistance paste so as to obtain a sheet resistance value and a change rate of solder immersion which are sufficiently within the standard. That is, conventionally, after applying the resistive paste to the substrate, it has been considered only that the resistive paste is baked for a predetermined time at a constant temperature according to the type of the resistive paste. I never did.

For this reason, if the firing time is too short, the sheet resistance within the standard cannot be obtained sufficiently, the rate of change due to solder immersion becomes large, and it becomes impractical. If fired for a long time, the substrate will be discolored this time, which will impair the commercial value of the substrate. In any case, it is extremely difficult to practically form a resistor circuit on an organic substrate using a resistor paste. .

Object The present invention has been made in order to eliminate the above-mentioned disadvantages of the prior art, and an object of the present invention is to apply a high-purity purified carbon or graphite fine powder applied to an organic substrate having low heat resistance. Using a conductive paste as a binder, a thermosetting resin is used as a binder, and a low-volatility, high-boiling solvent is used for viscosity adjustment.The resist paste is first heated to a temperature of 100 ° C or higher and 200 ° C or lower using far infrared rays for 60 seconds. For 90 to 90 seconds, and then heat and bake with a temperature profile near the soldering temperature for about 1/18 of the predetermined time or for 5 to 10 seconds, so that the area resistance value and the solder immersion within the standard are satisfied. It is an object of the present invention to provide a method for firing a resistor paste having a satisfactory property such that a sufficient change rate can be obtained and the discoloration of the substrate does not matter at all even for an organic substrate such as a glass epoxy substrate. Another object of the present invention is to improve the production efficiency by effectively utilizing a far-infrared heating furnace so that a printed resistor can be formed on a substrate in a short time. Yet another object is to facilitate setting a temperature profile for firing the resistive paste. Another purpose is
By using far-infrared rays, the resistance paste is hardened uniformly from the inside to the outside of the resistance paste to achieve a uniform printing resistance and a stable internal structure. Is to be able to raise the temperature, energy saving is achieved, and economical firing can be performed. Still another object is to use a far-infrared heating furnace to enable the use of a conveyor heating furnace for baking resistance paste, to facilitate systemization, and to provide a baking method of resistance paste suitable for mass production. is there.

Structure In short, the method of baking the resistance paste of the present invention (claim 1), volatilization using a fine powder of high-purity purified carbon or graphite applied to an organic substrate having low heat resistance as a conductive material and a thermosetting resin as a binder. Resistive paste using a low boiling high-solvent for viscosity adjustment, first heated at a temperature of 100 ° C. or more and 200 ° C. or less for 60 seconds to 90 seconds using far-infrared rays, and then said near the soldering temperature It is characterized in that it is heated and baked with a temperature profile such that it is heated for about 1/18 of the heating time.

Further, the firing method of the resistor paste of the present invention (claim 2) is as follows.
A resistor that uses high-purity purified carbon or graphite fine powder applied to an organic substrate with low heat resistance as a conductive material, uses a thermosetting resin as a binder, and uses a slowly volatile high-boiling solvent for viscosity adjustment. The paste is first heated at a temperature of 180 ° C. or more and 200 ° C. or less for 60 seconds to 90
For 2 seconds, then at a temperature between 235 ° C and 265 ° C
It is characterized in that it is heated and baked with a temperature profile such as heating for 10 seconds to 10 seconds.

Hereinafter, the present invention will be described based on embodiments shown in the drawings. First, the resistance paste used in the present invention will be described. In the material composition of the resistance paste, fine powder such as high-purity purified carbon or graphite is used as a conductive material, and a thermosetting material such as epoxy, phenol, melamine, or acrylic is used as a binder. Resin is used. Furthermore, a high-boiling solvent having low volatility is used for adjusting the viscosity of the resistance paste.

In the production of a resistance paste, a number of properties are required for each component. For example, the properties of the functional powder include fine and uniform particles, high purity and high quality, little variation in resistance value, and good compatibility between the powder and the compounded resin.

Next, the properties of the polymer are that it has good compatibility with powder, that it does not form a film even when it is left at room temperature, that its resistance value does not fluctuate even when it is left at room temperature, that it does not cure at room temperature and that it is quickly cured by heating. To be cured, the cured film is less likely to change in volume due to temperature and humidity, has some flexibility, excellent adhesion to the substrate, heat resistance,
It is excellent in moisture resistance and excellent in interlayer adhesion with an undercoat or overcoat agent.

Secondly, the solvent properties are that it has excellent stability for continuous printing (does not clog the plate or attack the emulsion film), has a low evaporation rate at room temperature and does not adsorb moisture,
Viscosity does not change rapidly at around room temperature ± 10 ° C, and steam at room temperature or during heating has no irritating odor or toxicity.

As a resistance paste that satisfies these conditions, for example, a resistance paste TU-1K (“TU-1K” manufactured by Asahi Chemical Laboratory Co., Ltd.)
-1K "is a trademark of Asahi Chemical Laboratory Co., Ltd.) The rate of change in resistance after soldering is a very slight rate of change of about 0.5% at two points of soldering temperature 240 ° C. and 260 ° C. It has excellent reliability in practical use. This TU-1K
Resistance paste does not show a sharp endothermic or exothermic reaction up to the soldering temperature, even for the differential thermal analysis curve,
It is assumed that the volume change of the resistor for that purpose is extremely small.

In addition, the resistance paste TU-1K manufactured by Asahi Chemical Laboratory Co., Ltd. and the resistance paste provided in a series related thereto assuming that heating and firing are performed by a conventional box type dryer (forced hot air circulation method). Are as shown in Table 1. Among the resistance pastes, the resistance paste of the TU-OO-5 series is for a ceramic substrate, and the resistance paste of the TU-OO-8 series is for a glass epoxy substrate. The standard value of the change rate of solder immersion for both series is ± 5.
%.

The present inventors have conducted intensive research to find a temperature profile that passes all three items, such as the sheet resistance, the rate of change in solder immersion, and the degree of discoloration of the substrate, when such resistance pastes are used and heated and baked. Was.

As a result, according to the temperature profile as shown in FIG. 1, it was found that all these conditions were satisfied and satisfactory results were obtained.

FIG. 1 shows the change in the substrate surface temperature T with respect to the heating time t, that is, the temperature profile, with the vertical axis representing the substrate surface temperature T (° C.) and the horizontal axis representing the substrate heating time t (seconds). Things.

In this temperature profile, the substrate surface temperature T
Rises rapidly from time 0 seconds to after 30 seconds and temporarily reaches a steady state, and is maintained at a constant temperature T1 for time tA.
This temperature T1 is not less than 100 ° C. and not more than 200 ° C.

After this time tA, the surface temperature of the substrate starts to rise, and when the time t exceeds 120 seconds, the temperature T rises rapidly, and only near the soldering temperature for a time tB of about 1/18 of the time tA. Temperature T2.

In this way, the substrate is heated and fired at a temperature of 200 ° C or less for a long time at first, and then the substrate is heated and fired at a temperature profile such that the surface temperature of the substrate is raised to near the soldering temperature and heated and fired at a high temperature. It became clear that all three conditions could be satisfied. In particular, regarding the rate of change of solder immersion, once the resistance paste is heated to the soldering temperature, the empirical factor that was exposed to high temperatures when the completed resistance paste later came into contact with the molten solder as a resistor was Presence is presumed to be the cause of decreasing the rate of change due to solder immersion.

When an optimum temperature profile was obtained from such temperature profiles, the best results could be obtained by the following combinations of temperature and time.

Temperature T1 = 180 ° C to 200 ° C Temperature T2 = 235 ° C to 265 ° C Time tA = 60 seconds to 90 seconds Time tB = 5 seconds to 10 seconds An example of this temperature and time combination is shown in FIG. According to the profile, temperature T1 is 193 ° C, time tA
Is 90 seconds, temperature T2 is 264 ° C, and time tB is 5 seconds. Substrate firing is completed in only 180 seconds in total, and all of the above conditions are satisfied. It has been found that it can be realized on a substrate.

In practice, a heating furnace for firing the resistance paste is:
The reflow soldering device using far infrared rays can be used as it is, which is very convenient.

Effect The present invention is applied to an organic substrate having a low heat resistance as described above, using a fine powder of high-purity purified carbon or graphite as a conductive material, using a thermosetting resin as a binder, and a high-boiling solvent having a low volatility. The resistance paste used for viscosity adjustment is first 100 ° C or more 200 ° C using far infrared rays
Heat at the following temperature for 60 seconds to 90 seconds, and then near the soldering temperature for about 1/18 of the heating time or 5 seconds to
Heating and sintering with a temperature profile such as heating for 10 seconds ensures that the sheet resistance value within the standard and the rate of change by solder immersion are sufficiently obtained, and that even if the substrate is an organic substrate such as a glass epoxy substrate, the discoloration of the substrate is completely suppressed. There is an effect that it is possible to provide a method for sintering a resistive paste having good characteristics so as not to cause a problem. In addition, since the far-infrared heating furnace can be used effectively, the printed resistor can be formed on the substrate in a short time, and there is an effect that the productivity can be improved. Further, there is an effect that the temperature profile for firing the resistance paste can be easily set. In addition, the use of far-infrared rays allows the resistance paste to be cured from the inside to the outside, so that the resistance paste can be solidified uniformly, and the internal structure can achieve stable printing resistance, and can be heated at a temperature higher than the ambient temperature. It is possible to increase the temperature of the object, that is, the resistance paste, and it is possible to achieve an effect of saving energy and performing economical firing. Further, the use of the far-infrared heating furnace makes it possible to use a conveyor heating furnace for sintering the resistance paste, thereby facilitating the systemization and providing a method of sintering the resistance paste suitable for mass production.

Example 1 When each of the resistor pastes in Table 2 was fired according to the temperature profile shown in FIG. 2, it was possible to obtain resistors having very good characteristics as shown in the table.

That is, the resistance value was well within the standard, and the rate of change in solder immersion was -4.7% at maximum in TU-100K-5, and the others were lower than that. In addition, the discoloration of the substrate is visually observed, ◎ indicates that the color has not changed, ○ indicates that the color has changed slightly, and x indicates that the color has changed to such an extent that it cannot be used.The result is ◎, and the color change is recognized. Did not.

Example 2 By varying the times T1, tA, T2, and tB in the temperature profile shown in FIG. 2, the resistance paste TU-10K-5 was baked, and the area resistance value and the rate of change in the solder immersion were within the standard, respectively. In the case, it was indicated by 、, and in the case of out of specification, it was indicated by ×, and the discoloration of the substrate was indicated in the same manner as in Example 1.

As a result, only the four temperature profiles indicated by shading in Table 3 satisfied all the conditions and passed.

Comparative Example 1 When the four types of resistance pastes shown in Table 4 were baked with the temperature profile shown in FIG. 3, the results shown in the same table were obtained. The rate of change was out of specification and there was no discoloration, but it was rejected.

Comparative Example 2 When the four types of resistance pastes shown in Table 5 were baked with the temperature profile shown in FIG. 4, the results shown in the same table were obtained. There was no, but it was rejected.

Comparative Example 3 When the four types of resistance pastes shown in Table 6 were baked with the temperature profile shown in FIG. 5, the results shown in the table were obtained. However, both the resistance value and the rate of change in solder immersion were within the specifications. , Discoloration was recognized, and it was rejected.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an example of a temperature profile for firing a resistor paste according to an embodiment of the present invention, FIG. 2 is a similar diagram according to Embodiment 1 of the present invention, and FIG. 3 to 5 are similar diagrams according to the comparative example.

Claims (2)

(57) [Claims] 1. A high-purity purified carbon or graphite fine powder applied to an organic substrate having low heat resistance, a thermosetting resin as a binder, and a volatile, high-boiling solvent for viscosity adjustment. The resistance paste used as above is first heated at a temperature of 100 ° C. or more and 200 ° C. or less for 60 seconds to 90 seconds using far-infrared rays, and then heated around the soldering temperature for about 1/18 of the heating time. And baking with a temperature profile as described above. 2. A high-purity purified carbon or graphite fine powder applied to an organic substrate having low heat resistance, a thermosetting resin as a binder, and a low-volatile, high-boiling solvent for viscosity adjustment. The resistance paste used as above is first heated at a temperature of 180 ° C. or more and 200 ° C. or less for 60 seconds to 90 seconds using far infrared rays, and then heated at a temperature of 235 ° C. or more and 265 ° C. or less for 5 seconds to 10 seconds. A method for baking a resistance paste, wherein the baking is performed by heating under such a temperature profile.