JPH02304901A - Fixed film resistor - Google Patents

Abstract

PURPOSE:To make the center of a resistor film hard to thermally deteriorate by using polymer varnish as a first coating layer in external contact with the resistor film, using specific inorganic varnish as a second coating layer, and using insulating varnish as a third coating layer. CONSTITUTION:Polymer varnish such as phenolic resin or polyimide resin is used as a first coating layer 7 in external contact with a resistor film, inorganic varnish with thermal conductivity not less than 5X10<-3>cal/cm.sec. deg.C is used as a second coating layer 8, and insulating varnish such as epoxy resin in used as a third coating layer 9. That is, inorganic varnish with 10 times or more as high thermal conductivity as that of phenolic resin or epoxy resin is used as an encapsulant material. Thereby the surface temperature of the center of a resistor decreases make the resistor film hard to thermally deteriorate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to fixed film resistors used in various ITT child devices.

C. Conventional technology] Fixed film resistors are generally formed as follows.

That is, as shown in FIG. 1, a resistor having a resistive film 2 on the surface of a circular porcelain base 1 is connected to a cap-shaped terminal 3 by a method such as press fitting, and the resistive film 2 is trimmed into a spiral shape 4.

Further, this entire body is covered with an exterior 5 made of an insulating material such as epoxy resin or phenol resin.

[Problems to be solved by the present invention] Phenol resins and epoxy resins used as the exterior of conventional fixed film resistors have low thermal conductivity (0.2X
10-10-1X10'''3) Therefore, when current is passed through the resistor, the self-heating generated from the resistive film causes heat generation in Figure 2 (A
) and (B), the surface temperature at the center of the resistor becomes extremely high.

Therefore, thermal deterioration in the center of the spirally trimmed resistive film becomes severe.

[Means Adopted by the Present Invention] The present invention uses an inorganic paint having a thermal conductivity 10 times or more higher than that of phenol resin or epoxy resin as an exterior material.

However, when inorganic paints are directly coated on a resistive film, the resistance value changes greatly in environmental tests such as thermal shock and high temperature load life.

Furthermore, since inorganic paints have a higher water absorption rate than phenolic resins or epoxy resins, they impair the moisture resistance of resistors.

Therefore, the present invention has a three-layer exterior structure as shown in FIG. 3, the first layer 7 circumscribing the resistive film is coated with a polymer paint such as phenol resin or polyimide resin, and the second layer B has a thermal conductivity. An inorganic paint having a temperature of 5×10-”cal/cm@sec*°C or higher is coated, and the third layer 9 is coated with an insulating paint such as an epoxy resin.

[Example] The porcelain substrate 1 in FIG. 3 has a thermal conductivity of 10
Using alumina-based porcelain having a temperature of 1 O-'' cat/cmΦsec·°C, a resistor formed by depositing a nichrome-based resistance film 2 on its surface is trimmed into a spiral shape 4 using a laser trimming device.

Using the above resistance element, the 1N, 2nd and 3rd layers of the exterior
Each layer was coated with the paint shown in Table 1.

Sample Nu 1 is a conventional packaging, and samples Na 2 and N13 are packagings according to the invention.

FIG. 4 shows the surface temperature of each sample when a current was passed so that the power applied to each sample was IW.

Table 1 [Effects of the present invention] As shown in Fig. 4, the resistor according to the present invention has a lower surface temperature in the center of the resistor than the conventional resistor, so thermal deterioration of the resistive film is reduced compared to the conventional resistor. . Therefore, the change in resistance value became smaller.

For example, a resistor whose resistance value before trimming was 100 Ω was trimmed to a completed resistance value of 100 Ω, and the resistor element was coated with Nal+Na2 and N113 shown in Table 1.

When a load of rated power IW was applied to each sample for 1000 hours in an environment with an ambient temperature of 70°C and the change in resistance value before and after that was measured, the change in resistance value for sample Na1 was ÷0.45%, and the change in resistance value for sample Na2 was ÷0.45%. And the resistance value change of sample N113 was +0.
The values were extremely small at 18% and +0.2%.

[Brief explanation of the drawing]

FIGS. 1(A) and 1(B) are a structural diagram and a sectional view of a fixed film resistor. Figures 2 (A) and (B) are the surface temperatures when a current is passed through the fixed film resistor. Figure 3 is a cross-sectional view of the fixed film resistor according to the present invention. ) is the surface temperature of the conventional fixed film resistor and the fixed film resistor according to the present invention when the rated current is applied.Throughout FIGS. 1: E!i device base 2: Resistance film 3: Cap-type terminal 4 Drimming groove 5: Exterior 6: Lead wire 7: 1st layer in the exterior 8: 211th layer in the exterior! 9: In the exterior 3M Figure 1 Cl5) Figure 2 (A) CB)

Claims (1)

[Claims] As a protective exterior for a resistor having a resistance film on the surface of a cylindrical porcelain substrate, the first layer circumscribing the resistance film is coated with a polymer paint such as phenol resin or polyimide resin, and the second layer has a thermal conductivity of 5×10. ＾-3＾cal/cm・sec・℃
A fixed film resistor characterized in that it is coated with the above inorganic paint and the third layer is coated with an insulating paint such as epoxy resin.