JPS60162786A - Production of thin film resistor - Google Patents

Abstract

PURPOSE:To obtain an extremely thermally stable thin film resistor by forming a resistance film by a chemical plating method on an insulator then immersing the insulator into a surface treating bath contg. acyclic satd. carboxylic acid having >=1 carboxylic group and hypophosphite and further subjecting the same to a heating treatment in a gaseous N2 atmosphere. CONSTITUTION:An insulating substrate such as a ceramic substrate, plastic substrate or the like is immersed in a plating bath and a resistance film is formed by a chemical plating method. The insulating substrate is required to be preliminarily adhered with a catalytic metal such as Pd or the like. The compsn. of the resistance film is exemplified by Ni, Co, Ni-P, etc. The insulating substrate formed with the above-described resistance film is immersed into the surface treating bath contg. the above-described acyclic satd. carboxylic acid (e.g.; acetic acid) and hypophosphite (e.g.; NaHPO2) and adjusted to 6.0-8.0pH and >=85 deg.C temp. and is then subjected to a heating treatment at >=200 deg.C in a gaseous N2 atmosphere. The thin film resistor having improved thermal stability is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a thin film resistor that can be directly deposited on a circuit board, and more particularly to a processing method for improving the thermal stability of a thin film resistor. It is related to.

Conventionally, the common method for providing a resistor on a printed wiring board for electronic circuits is to mount a separately molded resistor component onto the printed wiring board by soldering. This poses a problem in that not only does the process become complicated, but it also cannot cope with miniaturization and weight reduction of electronic circuits, high-density packaging, and the like.

Therefore, in the past, a method such as screen printing was used, in which a resistor made of graphite powder mixed with silicon powder or talc powder was used as a resistor on an insulating substrate such as a printed wiring board, and this resistor was printed using a binder such as phenolic synthetic resin. So-called printed resistors, which are directly printed and molded using , are now being used. This printed resistor is formed as an extremely thin printed film on the board, so it is useful for high-density packaging. It also has the disadvantage that the silver paste used for this process tends to cause defects such as migration. □ Based on the above-mentioned background, there have been six methods, eight steps, two steps, and one method of forming a resistive film on an insulating substrate by chemical plating. The number of steps is reduced, and it is possible to achieve higher density packaging and reduce the occurrence of defects.

However, the resistance film obtained by the above chemical plating method has poor stability of resistance value against heat, for example, in the solder dipping process for mounting electronic components other than resistors.
Addition of a heat treatment process such as the 01 process causes a large change in the resistance value of the resistive film, which poses a serious problem in practice. The inventors investigated the change in resistance of thin film resistors subjected to normal hot water washing, and found that, for example, in the soldering process 70, the resistance was 1 to 2% after a solder dip was applied at 250°C for 5 seconds. was found to be 3-5%, and reached 5-IO% after aging at 125°C for 100 hours.

The inventors of the present invention have conducted intensive research to develop a method for improving the thermal stability of resistive films obtained by chemical plating, and have discovered that hypophosphite is a highly effective method for improving the thermal stability of resistive films obtained by chemical plating. It has the effect of strengthening the bond and preventing a decrease in resistance value due to thermal baking, and by using heat treatment in a nitrogen gas atmosphere, it is possible to strengthen the physical adhesion sound and further increase the effect. The present invention has been completely completed, and after completely forming a resistive film on an insulator by chemical plating, an acyclic saturated carboxylic acid having one or more carboxyl groups, a hypophosphite, and a total It is characterized by being immersed in a surface treatment bath with a table and adjusted to a pH of 6.0 to 8.0 and a temperature of 85°C or higher, and then subjected to heat treatment at a temperature of 200°C or higher in a nitrogen gas atmosphere. It is.

In the manufacturing method of the present invention, first, an insulating substrate such as a lamic substrate or a synthetic resin substrate is immersed in a plating bath, and a resistive film is formed by chemical plating.

Here, since the above chemical plating method is electroless plating,
It is necessary to perform a catalytic process, an accelerator process, etc. on the insulating substrate in advance, and attach a metal such as palladium to the surface of the insulating substrate to serve as a catalyst.

On the other hand, the composition of the plating bath may be any one commonly used for forming a resistive film, such as a chemical plating solution containing all nickel salts or cobalt salts and a reducing agent. can be mentioned. In this case, the composition of the resulting resistive film is Ni, Co
, Ni-P, Ni-B, Co-P, Co-
B, N1-Co-P, etc., or W in addition to the above composition.
, Cr, Fe, Mo.

Examples include those containing Sn, Cu, etc. Then, by adjusting the composition of the plating bath, the composition of the resulting resistive film can be changed as appropriate to completely control the specific resistance of the resistive film.

Furthermore, it is also effective to add a rhenium salt to the plating bath in order to increase the specific resistance of the resulting resistive film. Examples of this rhenium salt include potassium perrhenate and rhenium chloride, and the concentration in the plating bath is 0.
．． It is preferably from 0.001 mol/i to 0.008 mol/J. This means that the concentration of rhenium salt is 0.001 mol/
If it is less than i, a high resistance value cannot be obtained, and if it exceeds o, oos mol/ik, a resistive film cannot be formed.

Furthermore, if the plating bath is alkaline, nickel and cobalt are easily converted into hydroxides, so it is preferable to add citric acid, tartaric acid, or their sodium or potassium salts as complexing agents. Furthermore, organic acids such as acetic acid, glycolic acid, succinic acid, propionic acid, lactic acid, butyric acid, ethylenediaminetetraacetic acid, and their sodium salts and potassium salts may be used in combination.

Further, as the above-mentioned reducing agent, hypophosphorous acid and its salts are preferable, and almost any soluble hypophosphite can be used, but sodium salts are generally used.

In addition to the above basic components, stabilizers for the plating bath, additives for controlling the plating speed, etc. may be used, such as lead salts, thiourea, rhodan potassium, etc.
Sodium hyposulfite, boric acid, borate, fluoroborate,
Examples include things. When adjusting the composition by adding other metal salts in addition to the nickel salt and cobalt salt, for example, iron sulfate, chromium chloride, potassium molybdate, tin chloride, sodium tungstate, etc. are used.

Further, a PH adjuster is added to the plating bath to control the pH value to a predetermined value, and alkali hydroxide or aqueous ammonia is usually used as the PH adjuster.

After a resistive film is deposited on the insulating substrate in the above-mentioned plating bath, it is immersed in a surface treatment bath to perform a first thermal stabilization treatment.

- What is important in the above surface treatment bath is that it entirely contains hypophosphite, and the decomposition of this hypophosphite strengthens the bonds between the crystal grains that make up the resistance coating. , the surface of the resistive film is stabilized, and a decrease in the resistance value of the resistive film is prevented.

As the above-mentioned hypophosphite, a sodium salt is usually used, and the amount added is preferably 3 to 20 #/J. If the amount of sodium hypophosphite added is less than 32/J, no effect can be expected;
If j and f are exceeded, the resistance value will actually decrease.

In addition, if the above-mentioned hypophosphite is used alone, the pH value is too high (around PHIO) and the reducing power is too strong, which may actually lower the resistance value. It is necessary to use a mitigating agent to soften the reducing power of the salt.

As this mitigating agent, argon acids, inorganic acids, etc. can be considered, but if the above-mentioned inorganic acids are used, there is a risk that the resistance film previously formed by chemical plating may dissolve or peel off, and Dilution makes it unstable.

According to long-term tests conducted by the present inventors, it has been found that carboxylic acids are preferable as the above-mentioned relaxation agents, and in particular, acyclic saturated carboxylic acids having one or more carboxyl groups are most suitable. Further, among the above acyclic saturated carboxylic acids, those having an OH group, NH, group, etc. in the side chain, and the action of the carboxyl group of the above carboxylic acid is alleviated by the OH group, NH, group, etc. are preferable. That's what I found out.

The above-mentioned acyclic saturated carboxylic acid may be water-soluble, and specifically, a carboxyl group such as acetic acid, propionic acid, butyric acid, etc.
Acyclic saturated carboxylic acids having two or more carboxyl groups, such as oxalic acid, malonic acid, succinic acid, geltaric acid, adipic acid, and pimelic acid, glycolic acid, lactic acid, glyceric acid, and gourmanic acid. Acyclic saturated carboxylic acids having carboxyl groups such as acids and OH groups, carboxyl groups such as malic acid, tartaric acid, citric acid, etc.
? Acyclic saturated carboxylic acid having t2 or more and an OH group,
Examples include amino acids such as alanine, glycine, and glutamic acid, and complexing agents such as ethylenediaminetetraacetic acid. Among these, thermally stable malic acid was the most preferred.

Further, the concentration of the acyclic saturated carboxylic acid is 0°05 to 0.3 in terms of the equivalent of the carboxyl group of the carboxylic acid.
It is preferably within the range of gram equivalent/J.

Furthermore, in the above surface treatment bath, the influence of bath temperature and PH value is also large, and according to the experiments of the present inventors, the above bath temperature is 8.
It was revealed that it is preferable to adjust the temperature to 5°C or higher and the pH to 6.8 to 8.0. A sufficient effect cannot be obtained if the bath temperature is below 85°C. Further, when the PH value is less than 6.0, an increase in the resistance value is observed, and when the PH value exceeds 8.0, a decrease in the resistance value is observed.

It is desirable that the immersion time in the above surface treatment bath be 30 minutes or more. If the immersion time is 30 minutes or less, sufficient effects may not be obtained.

Next, the insulating substrate on which the resistive film has been formed is taken out from the surface treatment bath and heat-treated in a nitrogen gas atmosphere to give a second
Heat stabilization treatment is applied.

The heat treatment, which is the second thermal stabilization treatment, must be performed in an inert gas such as nitrogen gas, and if it is performed in the atmosphere, for example, the surface of the resistive film will be oxidized. In addition, the temperature condition is preferably within the range of 200 to 280°C. If the heating temperature is less than 200°C, the thermal stabilization effect will decrease, and if it exceeds 280°C, the above-mentioned resistance film will be formed. The crystal changes. Furthermore, the treatment time of the heat treatment is preferably 1 hour or more,
If the temperature is less than this, a sufficient effect cannot be obtained. By heating in this nitrogen gas atmosphere, the physical adhesion of the crystal grains constituting the resistive film is stabilized, and The resistive coating is further thermally stabilized.

In this way, the first thermal stabilization treatment and the second thermal stabilization treatment are performed on the resistive film to complete a thin film resistor.

The thin film resistor manufactured through the above steps is extremely thermally stable and highly reliable. For example, the amount of change in resistance value after one solder reflow process when mounting other circuit components is o, oi% or less, and the amount of change in resistance value after soldering dip for 5 seconds at 250°C is o,i ~ 0. 2%,
Furthermore, even after aging at 125° C. for 100 hours, the amount of change in resistance value was about 0.5 to inch.

By the way, we also investigated the effect of performing either the first heat stabilization treatment or the second heat stabilization treatment, but the resistance was low with only the heat treatment in the nitrogen gas atmosphere. It is difficult to maintain a stable value as the value decreases, and - immersion in the blade surface treatment bath alone has little effect. For example, after aging at 125° C. for 100 hours, the amount of change in resistance value is about 2 to 3 inches.

Hereinafter, specific examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples.

Example 1 An alumina ceramic substrate was prepared as an insulating substrate. This substrate was first brought into contact with trichloroethylene vapor, then immersed in a 20% NaOH aqueous solution for 5 minutes to degrease the substrate surface, and washed with water for 5 minutes.

Further, this substrate 't-15%HCjV was immersed in an aqueous solution for 1 minute, and then PdCJ2,5nCJ2. It was immersed in a catalyst solution containing HCJk for 5 minutes and washed with water for 3 minutes. Finally 3%
After immersing the HCJ in an aqueous solution for 5 minutes, the substrate was washed with water for 3 minutes to complete the pretreatment for the substrate.

Next, this substrate was immersed in a plating bath having the composition shown below to form a resistive film. Note that the temperature of the plating bath at this time was set at 85°C.

Plating bath composition Cobalt chloride 20t/no Potassium perrhenate L5f/11 Sodium citrate 1509/11 Sodium hypophosphite 50tt/J.

Ammonia water (CPH @ stabilizer) Amount to give pH 10.5 Subsequently, the insulating substrate on which the resistive film was formed was immersed for 60 minutes in a surface treatment bath having the following composition, and the first thermal stabilization treatment was performed.
Note that the temperature of the surface treatment bath was set at 90°C.

Surface treatment bath composition Malic acid 10 f/J.

Sodium hypophosphite 10f/J.

Ammonia water in an amount to give a pH of 7.4.Finally, a heat treatment was performed at 250° C. for 1 hour in a nitrogen gas atmosphere to produce a thin film resistor.

Example 2 A thin film resistor was manufactured in the same manner as in Example 1, except that the composition of the surface treatment bath in Example 1 was changed as follows.

Surface treatment bath composition Ethylenediaminetetraacetic acid 1t/- Sodium hypophosphite 5Of/J Sodium carbonate 2.5f/J Figure 1 shows the rate of change in resistance value of the thin film resistors manufactured in Example 1 and Example 2. Shown below. For comparison, the rate of change in resistance value of thin film resistors manufactured by changing the composition and treatment time of the surface treatment bath of Example 10 as shown in the following table is also shown.

From the table shown in FIG. 1, it can be seen that in the thin film resistor manufactured according to the present invention, the rate of change in resistance value is dramatically reduced, and the effect thereof is extremely large. −

[Brief explanation of the drawing]

FIG. 1 is a graph showing the rate of change in the resistance value of a thin film resistor ξJ manufactured by an embodiment of the present invention in comparison with that by other processing methods. Patent Applicant Sony Corporation Representative Patent Attorney Mimi Koike 1) Sakae Mura - No. 11 II

Claims (1)

[Claims] After forming a resistive film on the insulator by chemical plating,
Contains an acyclic saturated carboxylic acid having t1 or more carboxyl groups and a hypophosphite, and has a pH of 6.0 to 8.0. temperature 85
1. A method for manufacturing a thin film resistor, which comprises immersing the resist in a surface treatment bath adjusted to a temperature of 200° C. or higher, and further heat-treating the resist at a temperature of 200° C. or higher in a nitrogen gas atmosphere.