JPS5855762A - Heating resistor for hot wire type flowmeter - Google Patents

Abstract

PURPOSE:To provide a titled resistor which withstands mechanical external forces such as oscillations sufficiently with less secular variation by joining and forming a metallized resistor on ceramic surfaces. CONSTITUTION:Metallic leads 5 are firmly joined to both ends of a ceramic pipe 1 or a ceramic plate 2 respectively by platinum paste or with plating layers formed beforehand of a metallic alloy. Since the ceramic material receives a metallizing treatment as a pretreatment for the purpose of bonding a resistor 10 firmly thereto, the ceramic material having a coefft. of expansion roughly equal to that of a metallizing material 8 and having good wettability with said material is selected. After the ceramic surfaces are cleaned, the ceramics are heated in a vacuum, and the metallizing material is metallized thereon by vapor deposition or the like to form film. Thereafter, the metallized material is joined to the resistor and is resistance-trimmed by a laser or the like, whereby a coating 15 of glass is applied on the surface of the resistor.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating resistor for a hot wire flowmeter suitable for detecting the intake air flow rate of an internal combustion engine, for example.

Conventionally, a heating resistor for a hot wire flowmeter has a structure in which a thin platinum wire is wound around an alumina pipe bobbin having leads at both ends.゛However, since there is no commercially available winding device for winding thin wires with a diameter of 50μ or less at equal pitches, the winding work had to be made in-house, and a device integrated with a terminal spot welding device was developed to match the production volume. I needed to go on.

In addition, since the windings were made of thin platinum wire, the inner diameter of the cap for positioning the windings was abnormally small, and even when made of super hard material, it was subject to severe wear and had to be replaced frequently.

On the other hand, platinum thin wire is made from a diameter of 6μ by drawing a die more than 60 times, so most of the cost is processing cost. For this reason, it was necessary to have a cost structure that was close to the material cost of 3cm in weight, so a method was devised to form a thick platinum film on the surface of the alumina pipe hobbin.

The thick film is formed by dipping the bobbin in a platinum thick film paste stirring solution containing a binder in advance, drying and firing, and trimming the deposited platinum thick film layer in a spiral shape with a laser to obtain the required resistance value. . When this sample was self-heated to 300C and a cycle test of 4 seconds ON and 14 seconds OFF was continued, the flow rate Q (Kg/H) was approximately 50,000 cycles.
) with respect to the output voltage V. It was found that the change in (V) was 15% or more in terms of ΔQ/Q. However, the permissible value for a flowmeter is 13% or less after a 100,000-mile durability test on a car.

The reason for this change is the difference in expansion coefficient between the platinum thick film and alumina joint (alumina 7.7 x 10
=, platinum 8.9 x 10-') weakens the bonding force and promotes internal distortion of the platinum particles, changing the resistance value. Further, although a thick platinum film is deposited to a thickness of 10 to 20 μm, a dense film is not obtained after firing, and the platinum layer is cracked, and the current flows through the bridge path from land to land. It is thought that such cracks change due to the expansion and contraction of platinum itself due to changes in temperature, and the movement of ions due to the flow of current is considered to be a cause of even more subtle changes over time.

Furthermore, when trimming a resistor using a laser, the energy of the laser that penetrates the thick-film resistor reaches the alumina surface, cuts into the alumina, and forms a groove in the bobbin.
The strength had deteriorated to the extent that it could not withstand vibration loads reaching G.

An object of the present invention is to provide a heating resistor for a hot-wire flowmeter that requires fewer processing steps, is inexpensive, has little change over time as a flow rate sensor element, and has sufficient resistance to external mechanical forces such as vibrations. .

The present invention will be explained in detail below. The bonding strength between the alumina pipe and the resistor formed on its surface is improved by the metallized layer, and the resistor is formed on the metallized layer to improve the adhesion between each bonding material and form a dense resistor film. obtain. The optimal conditions for metallization between the ceramic and the material to be bonded are such that the coefficients of thermal expansion are approximately similar to each other, and the metallizing material is larger by within about 10%, so that a constant compressive force is applied to the ceramic. desirable. The reason for this is that the compressive strength of ceramics is generally within about 10% of the tensile strength. Next, ceramics are not limited to alumina, and have good wettability with metallizing materials.

It is best to select and combine materials that are compatible with each other.

In this way, the diffusion of these materials at the joint is promoted and the joint strength is improved.

The metallizing material is a metal oxide or an inorganic material. The electrical resistance of the metallizing material is increased,
The resistor is deposited on this metallizing material to obtain a dense and stable resistive layer. In this case, the metallizing layer absorbs excess laser energy during trimming in which only the resistor layer is laser cut, and serves as a protective wall to prevent aromatic scratches from occurring on the ceramic. The resistor can be selected from a resistor that meets the optimum bonding conditions with the metallizing material, such as platinum, which has a relatively small temperature coefficient and expansion coefficient, and Ni, Cu, which has a relatively large coefficient of expansion. Platinum is chemically stable.

On the other hand, although it is required to work in a reducing atmosphere or an inert gas atmosphere to prevent the resistor from oxidizing, Ni and Cu are advantageous in that they are relatively inexpensive and have a large temperature coefficient.

The base ceramic materials include magnesia, holsterite, beryllia, steatite, and
Examples include alumina, zirconia, spinel, mullite, etc., and metallizing materials include FeNiCu alloy, Nb
+ Examples include Ti, Ta, Mo, and W. Bonding involves complex processes such as oxidation, wetting, adsorption, and diffusion of metals, so it is necessary to select and combine them in consideration of compatibility.

Focusing on high melting point metals as a metallizing treatment method. The metallizing composition is MO9MOO3゜w, wo.
, , MO-Mn, MO-Mn-T i.

MO8102, MOMOO2TlO21MO()z-M
n-T i, MO-sio2. w-Mno2-Tio2
-8in, W-Re-Mn02-Ti02, etc. To explain an example of the metallizing bonding mechanism, humidified forming gas M n+ during metallizing
H20-4M n O+ H2 This MnO contacts the glass phase in the alumina ceramic and melts into it. The glass phase becomes more fluid and enters the voids in the metallizing layer where sintering is progressing, bonding the alumina ceramic and the metallizing layer. At the same time, Mn
O reacts with AttOs to form Mn0-A40m, which becomes an intermediate layer. The surface of MO2Mn is slightly oxidized in the humidifying gas forming gas, and becomes well wetted with the glass phase, and the oxide on the MO9Mn surface melts into the glass phase that has entered and is completely bonded. Furthermore, Ni is deposited as a resistor by chemical plating or the like, and when cured, Ni interdiffuses with Mo and Mn into the remaining voids of the metallizing layer due to the heating temperature during curing, resulting in complete bonding. Metallizing can also be performed by vacuum processing methods such as vapor deposition, ion blasting, and sputtering. - To explain an example, before metallizing, the surface of the ceramic is polished with diamond powder, washed with water, and then air fired at 1000C to clean it.

Furthermore, it is then cleaned by plasma arc treatment. This ceramic material was heated in a vacuum of 5 x 10-"I'orr or less, and the ceramic substrate was heated in a resistance furnace for 5
Heat to 00-1000C. Add 10μ of MO on top of that.
Deposit about m. A resistor may be formed by plating 1IJi or the like on the metallized ceramics, or a metal resistor may be joined via a metal brazing material.

The next metallizing treatment method is thermal spraying. Thermal spraying methods include flame spraying, plasma spraying, explosion spraying, and line explosion spraying, but spraying melts metals, oxides, carbides, and silicides and forms a uniform film on the substrate. . There is also a method of using metal solder or oxide solder. In the method using metal solder, various types of metal solder are sandwiched between ceramics and metal, and heated in air, inert gas, reducing atmosphere, or vacuum to melt and bond the metal solder. Metal solders include (1) indium and indium alloys (2)
Aluminum (3) Pb-8n-Zn-8b alloy (4) T
There are i-Ni, Ti-cu, zr-Nj, and zr-Cu.

Here, to explain (4) in detail, Ni, (:u), which forms an alloy with a relatively low melting point with sTi, Zr, etc., is inserted between the ceramic and the metal, and it is heated once in vacuum or in an inert gas. Combine by heating operation.

In place of Ti and ZnO, these hydrogen compounds TiH,
ZrH or the like may also be used. When alumina and Ni are joined using Ti--Ni solder, the following process is considered to occur.

During heating during the bonding operation, Ti and Ni gather near the interface between the solder and alumina, and as shown in FIG. 1, Ti is selectively absorbed on the alumina side. FIG. 1 is an elemental analysis diagram obtained by XMA analysis of a state in which Nj was attached to alumina using a Tr-1 ruler.

This Ti diffuses into alumina and reacts. In particular, SiO2, which is contained in a small amount in alumina ceramics, reacts with Ti, reducing 5io2 and reducing T102,
T'0. T 1202 etc. are generated. Ti.

Si and these oxides diffuse and react with each other to form an intermediate layer at the interface, forming an airtight and mechanically stable bonded body. This is a method in which an oxide is used as a solder, and the solder is similarly inserted between ceramic and metal and heat-treated to join them.

When the atmosphere during bonding is high, the bonding is performed in an inert or reducing atmosphere or in a vacuum to prevent overoxidation of the sealing metal. Oxide solders are classified according to whether they are amorphous or crystalline after bonding, and Cao-A 120. -M g 0-B2O3 system, ca
o kt20B MgOS'02 series, etc. Bonding using these solders is ideal for metallizing plate-shaped ceramics. Note that FIG. 2 shows an elemental analysis diagram obtained by analyzing by XMA a state in which Nb is bonded to alumina via an oxide solder.

An embodiment of the present invention will be described below.

Ceramic pipe 1 as shown in FIG. 3(a), ceramic plate 2 as shown in FIG. 3(b), or ceramic plate 3 as shown in FIG.
As shown in Figure (C), metal leads 5 are firmly connected to both ends of the ceramic rod 3 through platinum paste or a plating layer or brazing material formed after metallizing a metal alloy or metal oxide into the ceramic in advance. . In this case, as shown in FIG. 4, the ceramic material is metallized as a preliminary treatment to firmly attach the resistor 10, so the ceramic material has a wettability similar to that of the metallized material 8 in terms of expansion coefficient. Selected based on quality. Here, alumina was used as the ceramic material. The expansion coefficient of alumina is 7.7 Xl0-' (1/ll
'). The metallizing material 8 is made by mixing MO-Mn with an organic binder to form a paint, which is applied to the surface of ceramics, and metallized at a temperature of 1000 to 1500 C in hydrogen gas, inert gas, or a mixture thereof. It is formed by M in the metallizing layer in the humidified forming gas during metallizing
A part of n becomes MnO. This MnO comes into contact with the glass phase in the alumina, melts into it, enters the voids in the metallizing layer, and joins the alumina and the metallizing layer. MnO reacts with At203 to form an intermediate layer MnO-
At,03 is formed. Further, the resistor is formed by plating Ni. Alternatively, it is formed by depositing a Cu raw film. Ni and Cu enter the empty and sparse portions of the metallizing layer that remain during the heat treatment after plating or the heating during Cu brazing, and interdiffuse with Mo and Mn to form a perfect bond. Ni is used as a resistor and has a temperature coefficient of 6700p9m/C, so high sensitivity can be obtained.

Here, the case where copper oxide method is used as metallization will be explained. Powders with a composition of C11094.2% and At2035.8% are mixed, heated in air for 1250 tons for 30 minutes, cooled, and pulverized. This is applied to the ceramic surface by spraying or dipping. - Then The coating material is heated to a melting point of 1190C or above, and then heated for about 10 minutes in a reducing atmosphere.
Copper is metallized by heating to 00C. In the metal soldering method, active metals Ti, Ni, or Cu are formed in advance on ceramics by vapor deposition, a sheet of Nib or Cu as a resistor is applied to this, and then the active metals Ti, Ni, or Cu are deposited on ceramics, and then a sheet of Nib or Cu as a resistor is applied to the ceramics.
Weld by heating with gas 1000-15001:'.

In the oxide soldering method, for example, Ca OA t20s-M
Oxide solders such as gO-based and CaO-Altos-MgO-8io-based are used as highly heat-resistant crystalline solders, but these solders are directly inserted between ceramics and metals and heat treated to bond them. . In the case of a sheet, such a method is relatively simple, but when metalizing the outer periphery of a cylinder or rod, a method is used in which a metallizing material is deposited in advance by vapor deposition or sputtering.

Examples of metallizing methods include cleaning the ceramic surface in advance as described above, heating it in a vacuum, depositing a metallizing film by vapor deposition, sputtering, ion plating, and thermal spraying.

After metalizing such ceramics, the resistor is bonded, the resistor is trimmed using a laser, etc., and the resistor surface is coated with glass to prevent deterioration over time.
Apply 5.

According to the embodiment described above, the following effects can be obtained.

(1) Since the resistor can be bonded to ceramics through the metallized layer, the bonding strength is improved, and the self-heating 300C,
It can withstand ON4w, 0FF4sec cooling and heating cycle tests, and provides a highly accurate flow rate sensor element with little change over time. Figure 5 shows experimental data proving this effect, and the metallized product that connects the white circles has extremely remarkable accuracy compared to the product that does not have metallization that connects the black circles.

The flow rate is 8~320Kg/H (1~320Kg/H).
40 m/s), the change over time is ±3%.
It can be summarized below.

(2) Inexpensive materials such as Cu and Ni can be used as resistor materials, resulting in cost reduction.

(3) As a resistor, it has a very large temperature coefficient6.
700 p9m/UN i Select material
The sensitivity as a flowmeter can be improved.

(4) It can be processed sufficiently using ready-made equipment, and productivity can be improved.

As is clear from the above description, (1) the heating resistor for a hot-wire flowmeter according to the present invention requires fewer processing steps, is inexpensive, has little change over time as a flow rate sensor element, and is susceptible to mechanical external forces such as vibrations. be able to withstand enough.

[Brief explanation of the drawing]

Figure 1 is an elemental analysis diagram analyzed by XMA with Ni applied to alumina using Ti-Ni solder, and Figure 2 is an XMA analysis of a state in which Nb is bonded to alumina via oxide solder. Elemental analysis diagram, Figure 3 (a), (b)
, (C) is a configuration diagram showing an embodiment of the present invention, and is a cross-sectional view of each flow sensor element, FIG. 4 is an enlarged cross-sectional view showing the state of film bonding of the flow sensor element, and FIG. It is a graph showing changes over time. 1... Ceramic pipe, 2... Ceramic plate, 3
...Ceramic rod, 5...Metal lead, 10...
Resistor, Arithmetic 1 (2)

Claims (1)

[Claims] 1. A resistor is formed on the outer peripheral surface of a ceramic with leads fixed to both ends, and a metallized resistor is bonded to the ceramic surface in the configuration of a heating resistor used as a sensor element of a flow meter. Features a heating resistor for hot wire flowmeters.