RU2770908C1 - Method for producing thick-film resistors - Google Patents

Abstract

FIELD: electronic technology.SUBSTANCE: invention relates to electronic technology, namely to the production of permanent resistors, including as part of hybrid integrated circuits; it can be used in electronic, radio engineering and other related industries. Planar contacts are formed on insulating substrate by applying conductive paste by screen printing on the front surface of substrate, on which a resistive layer will be formed, followed by its burning, while preliminary annealing is carried out at a temperature of 700-790°C, a temperature change with an amplitude of ±5°C for 5-7 minutes, and then burning with ultrasonic exposure with a frequency of 60-70 kHz and an amplitude of 0.1-0.3 mcm at a temperature of 810-850°C.EFFECT: increase in the thermal coefficient of resistance by improving the uniformity of formed resistive layers; the proposed method provides an increase in the yield of suitable thick-film resistors while reducing the process time and ensures high compliance with the specified parameters.1 cl, 1 tbl, 1 ex

Description

The level of technology.

There is a known method for producing thick-film resistors [1], according to which the resistor is manufactured by traditional methods of thick-film technology, including successive screen printing on an insulating substrate of conductive and resistive layers, their drying and burning in an air atmosphere, and first the first resistive layer is applied, and then over of the resistive layer, the second conductor layer, while to form the conductor layers, a conductive paste is used, including a reducing agent (boron, aluminum, etc.), or a substance that decomposes upon burning to form such a reducing agent (nickel boride, etc.), and to form a resistive a layer of paste containing glass powder, or a glass-ceramic composition and an organic binder.

The disadvantage of the technology is the insufficiently high yield of suitable crystals and the relatively low thermal coefficient of resistance due to the inhomogeneous distribution of components in the body of the resistor, the complexity of the technology.

There is a known method of manufacturing precision chip resistors using hybrid technology, protected by a patent [2]. The difference of the proposed method is the formation of electrode contacts on the back side of the substrate, which complicates the technological process and reduces the yield of suitable components due to the inhomogeneity of the resistive layer.

The prototype was taken as a method for producing thick-film resistors [3], in which planar contacts are formed on an insulating ceramic substrate in the form of a plate by applying a conductive paste by screen printing on the front surface of the substrate. The resistive layer is formed by applying a high-temperature resistive paste by screen printing, followed by annealing under ultrasonic action on the molten paste, while annealing is carried out when exposed to ultrasound with a frequency of 85-100 kHz and an amplitude of 0.1-0.5 μm.

A significant disadvantage of this method is the lack of homogeneity of the resistive layers, which results in the need to adjust the values of the resistors with a large spread in their resistance, which reduces the yield and productivity of the process.

Technical task.

The technical result is to increase the uniformity of the resistive layers and the thermal coefficient of resistance, to increase the yield of usable resistors and the productivity of the process due to the preliminary annealing of the structure in a thermal field changing with a certain amplitude.

Decision.

To solve the stated technical problem, the following invention is attached.

A method for producing thick-film resistors, which includes applying a resistive paste to the surface of a dielectric substrate and annealing the layer under the action of ultrasound, characterized in that, in order to increase the productivity of the process and the uniformity of the resistive layer, preliminary annealing is carried out at a temperature of (700-790) ° C with a change in temperature with an amplitude ±5°C for 5-7 minutes, and then burning under ultrasonic exposure with a frequency of (60-70) KHz and an amplitude of (0.1-0.3) μm at a temperature of (810-850)°C.

The production of thick film resistors according to the proposed method is as follows:

As the basis of the manufactured resistors, an insulating substrate (for example, a ceramic plate) is used. First, planar contacts are formed on the insulating substrate by applying a conductive paste by screen printing on the front surface of the substrate (on which the resistive layer will be formed), followed by annealing. Then a resistive layer is formed by applying a high-temperature resistive paste by screen printing, followed by burning at a temperature of (700-790) ° C with a temperature change with an amplitude of ± 5 ° C for 5-7 minutes, and then at a temperature of (810-850) ° With ultrasonic exposure with a frequency of (60-70) KHz and an amplitude of 0.1-0.3 microns.

When exposed to a changing thermal field at temperatures below 700°C, the effectiveness of the effect does not provide a significant increase in the uniformity of the layers (the spread of resistor parameters reaches (50-60)%, at temperatures above 790°C, the effectiveness of the impact does not increase (the spread of the resistance of the resistors remains within (30 -35)%.The amplitude of the change in the firing temperature at this technological stage is experimentally determined to be ±5°С as the optimal value for the considered technological process.After this technological operation, the plates are moved in a conveyor furnace to the temperature range (810-850)°С, where are subjected to ultrasonic action with a frequency of (60-70) kHz and an amplitude of (0.1-0.3) μm At a firing temperature below 810 ° C, the inhomogeneity of the distribution of the metal phase remains in the layer of resistive paste, which leads to a spread in the parameters of the resistors within (30 -35)%.This requires the use of an additional resistor trimming operation. Above 850°C, the homogeneity of the layers practically does not change, but the energy consumption for heating and the cooling time of the resulting structures increases the cost of their production. Preliminary annealing in a changing thermal field makes it possible to reduce the frequency of ultrasonic exposure compared to the prototype patent, which has a positive effect on the economic performance of production. The optimal frequency ranges of ultrasonic exposure in the proposed method are determined experimentally. As a result of optimization, it was found that at a frequency of ultrasonic vibrations less than 60 kHz, the homogeneity of the layers does not increase sufficiently (within 40% of the resistance spread), at frequencies above 70 kHz, the uniformity remains at the level of 10%, which ensures high technological performance in terms of yield.

The choice of parameters for controlling ultrasonic actions is based on the theory described in [4]. The essence of the method is that heating transfers high-temperature technological systems into a metastable state, which can be controlled by relatively small influences and, for example, a phase transition can be carried out, bringing the system to the desired (required) state). External, relatively low-energy influences make it possible to control with less inertia, quickly and accurately achieving the desired result. By type, the energy of control actions may differ from the source of the base energy of the system. When applied to a complex heterogeneous system, such as a thick film, which includes oxides (glass), metal or alloy particles, an organic binder, the kinetic indicators of heating the composite are of fundamental importance. Different coefficients of thermal diffusivity of the system lead to different mobility of the elements of the system - metal particles heat up faster and become more mobile. Small control actions help the metal particles to form a sufficiently strong film in the volume of the composite (the benefit of such consolidation is dictated by thermodynamics - the energy of the consolidated system is less than the energy of the chaotic one). Changing thermal and ultrasonic fields contribute to the process of self-organization of the system, as a result of which particles of approximately the same size are bound, which subsequently ensures the possibility of current flow with minimal resistance and ensures a minimum of current noise of the device.

If necessary, the resistors are adjusted by removing part of the resistive layer with a focused laser beam. Further, an additional protective layer is formed by applying either a high-temperature protective paste by screen printing, followed by drying and burning and separation of the substrates into chips.

Example

An insulating substrate made of alumina ceramics was used as the basis of the resistor. The technological process for manufacturing resistors included the following sequence of operations:

1. Application of a layer of high-temperature conductive paste PP-8 on the front side of the substrate by screen printing

2. Drying in an IR oven at 150°C for 20 minutes to remove the organic binder

3. Burning in a conveyor oven at temperatures up to 840°C for 10 minutes to form contacts

4. Formation of the resistive layer by applying high temperature resistive paste

5. Drying of the applied layer in an infrared heating oven at a temperature of 150°C for 25 minutes

6. Preliminary annealing in a multizone furnace at a temperature of (700-790)°С with temperature fluctuations with an amplitude of ±5°С for 5-7 minutes

7. Burning in a multi-zone furnace at a temperature of (810-850) ° C for 5 minutes under ultrasonic exposure with a frequency of (60-70) KHz and an amplitude of (0.1-0.3) microns

8. Formation of a protective layer by applying a high-temperature protective paste (TU 011000387275) to the resistive layer

9. Drying of the applied protective layer in an IR oven at 150°C for 20 minutes

10. Burning of the protective layer in a multi-zone furnace at a maximum temperature of 600°C for 10 minutes

11. Adjustment of resistors with a focused laser beam (if necessary)

12. Resistance control of resistors was carried out according to GOST 21342.20-78 “Resistors. Resistance measurement method”. The temperature coefficient of resistance (TCR) was measured according to GOST 21842.15-78. "Resistors. Method for determining the temperature dependence of resistance.

The operating time was estimated + according to GOST 25359-82 “Electronic products. General requirements for reliability and test methods"

The reliability of the resistors is confirmed by tests. The failure rate in the maximum permissible operating modes (R=R _nom , T=85°C) is not more than 1-10 1/h during the operating time = 30,000 hours within the service life (T _he )=25 years.

The cost of production of resistors decreased by 40% compared to the base case due to short-term preliminary annealing in a changing thermal field (the total time of the technological process decreased by 25% and an increase in the yield from 72% to 98%.

Literature

1. RF patent No. 2086027 IPC H01C 17/06, publ. July 27, 1997

2. RF patent No. 2402088, IPC H01C 17/06, H01C 17/28, publ. October 20, 2010

3. RF patent No. 2755943, IPC H01C 17/00, publ. 09/23/2021

4. Kosushkin V.G. Control of crystal growth by low-energy influences (Monograph) From the scientific literature N.F. Bochkareva, 2004. 272 p.

Claims (1)

A method for producing thick-film resistors, which includes applying a resistive paste to the surface of a dielectric substrate and annealing the layer at a temperature when exposed to ultrasound, characterized in that, in order to increase the productivity of the process and the uniformity of the resistive layer, preliminary annealing is carried out at a temperature of 700-790 ° C with a change in temperature with an amplitude ±5°C for 5-7 minutes, and then burning under ultrasonic exposure with a frequency of 60-70 kHz and an amplitude of 0.1-0.3 μm at a temperature of 810-850°C.