JP3049944B2 - Assembly method of oil-filled semiconductor pressure sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oil-filled semiconductor pressure sensor for detecting fluid pressure such as oil pressure or pressure of corrosive gas.

[0002]

2. Description of the Related Art As pressure sensors, semiconductor pressure sensors having a pressure-sensitive chip formed by diffusing strain gauge resistors in a diaphragm portion of a silicon wafer have recently been used in various fields. When such a pressure sensor is applied to pressure detection of an oil pressure, a corrosive gas, or the like, in a pressure sensor of a surface pressurization type, the pressure-sensitive chip may be contaminated or corroded to cause deterioration in characteristics. Therefore, as a semiconductor pressure sensor for such applications, a seal diaphragm separates the pressure-sensitive chip from the side to be measured, and seals the inside with oil such as silicone oil, using oil as a pressure-conducting medium. An oil-filled semiconductor pressure sensor that detects a pressure applied to a diaphragm by transmitting the pressure to a pressure-sensitive chip is used.

FIG. 5 shows an assembly structure of a conventional oil-filled semiconductor pressure sensor. In FIG. 5, reference numeral 1 denotes a semiconductor pressure-sensitive chip (chip size is about several mm); The pedestal 3 is a Kovar stem on which a pressure-sensitive chip assembly is mounted, 4 is a lead terminal mounted on the stem 3, 5 is a bonding wire internally wired between the pressure-sensitive chip 1 and the lead terminal 4, 6 is Pressure sensitive chip 1
, A cylindrical metal case welded and joined to the stem 3 around the metal case 7, a metal seal diaphragm 7 closing the open end surface of the metal case 6, a metal cap 8 covering the pressurized surface side of the seal diaphragm 7, 9a is a pressure guiding hole opened in the cap 8, 9 is a silicone oil filled in a space surrounded by the stem 3, the metal case 6, and the sealing diaphragm 7, 1
Reference numeral 0 denotes a printed wiring board of an external circuit connected to the lead terminal 4.

Here, the metal sealing diaphragm 7 is formed by pressing concentric concave and convex surfaces on a very thin stainless steel plate having a thickness of about 20 to 40 μm.
At the time of assembly, the outer peripheral edge of the diaphragm is sandwiched between the flange surfaces of the metal case 6 and the metal cap 8 and overlapped and set on a rotary welding jig. In this state, a roller is locally formed above and below the flange. An electric current is applied to the welded portion from the welding power source 12 through the roller type electrode 11 while applying the welding electrode 11 and rotating the welding jig, so that seam welding is performed between the seal diaphragm 7 and the entire circumference of the flange. A pipe for injecting silicone oil is connected to the stem 3 in advance. After the seal diaphragm is welded and joined, the space in the case is evacuated to seal the silicone oil 9, and then the pipe is sealed off. ing.

In the pressure sensor having such a structure, the pressure to be measured is applied to the seal diaphragm 7 through the pressure guiding hole 8a formed in the cap 8, and further propagates through the medium of the silicone oil 9 to act on the pressure-sensitive chip 2, thereby causing the pressure-sensitive tip 2. It is detected electrically as a change in resistance.

[0006]

As described above, in the assembling method of assembling the pressure sensor, the metal seal diaphragm 7 is superimposed on the flange portions of the metal case 6 and the metal cap 8 in the assembling step to perform seam welding. It takes about 1 minute of work time for each pressure sensor to weld the entire circumference of, so that it is not suitable for mass production. In view of this, the inventors have attempted to use a projection resistance welding method as a welding method instead of the seam resistance welding method with the aim of improving mass productivity.

In this projection resistance welding method, a projection having a height of about 100 μm is formed in a ring shape over the entire circumference by adjusting the radius from the center to each flange surface of the metal case 6 and the metal cap 8 in advance. A welding electrode is applied to the entire periphery of the flange in a tentatively assembled state in which the outer peripheral edge of the metal seal diaphragm 7 is sandwiched between the protrusions, and current is intensively applied to the protrusion while applying a pressing force to weld the seal diaphragm. In this projection resistance welding method, the welding time for one pressure sensor is only about 5 seconds, and it has been confirmed that a much higher throughput can be obtained as compared with the conventional seam welding method. .

However, when the projection welding is performed, if there is any slight relative misalignment between the components in a state where the metal case, the metal sealing diaphragm, and the metal cap are superimposed one on top of the other, the metal case may be displaced. The projection and the projection of the metal cap do not overlap vertically, and when a pressing force is applied, the thin seal diaphragm is deformed and its outer peripheral portion is warped. At this point, the outer peripheral edge of the seal diaphragm comes into direct contact with the metal case and the metal cap. In addition, when projection welding is performed by passing a current from the welding electrode in this state, a part of the welding current flows around the contact portion other than the protrusion and flows, and as a result, the penetration of the protrusion becomes insufficient, Defects occur in welding such that a highly airtight joint between the seal diaphragm and the metal case cannot be secured.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to solve the above-mentioned problems and to prevent the occurrence of defects at the time of projection welding between a metal case and a metal sealing diaphragm to prevent airtightness. It is an object of the present invention to provide a method of assembling an oil-filled semiconductor pressure sensor capable of ensuring a high welded state.

[0010]

In order to achieve the above object, in the assembling method of the present invention, a projection is formed over the entire circumference of the metal case and the metal cap so as to be aligned with each other on the flange surface. The metal case, the metal seal diaphragm, and the metal cap were overlapped by sandwiching the peripheral edge of the metal seal diaphragm between the protrusions, and electrical insulation was applied to the remaining surface area of the overlapped surface excluding the protrusions. In this state, projection welding is performed by applying a pressing force from the outside.

Further, there is an embodiment as described below as means for electrically insulating a superposed surface in the above method. (1) An insulation coating is formed on the metal seal diaphragm in advance in a peripheral region outside the projection welding portion, and projection welding is performed. (2) Projection welding is performed by sandwiching the insulating sheet in the outer peripheral region from the protrusion between the metal case and the flange surface of the metal cap and the metal seal diaphragm.

(3) An insulation coating is formed on the metal case and the flange surface of the metal cap in a region other than the projections in advance, and projection welding is performed.

[0013]

According to the above-described assembling method, a pressing force is applied from the outside due to a center shift or the like in a state where the metal sealing diaphragm is sandwiched between the projections formed on the flange surface of the metal case and the metal cap. Even when the seal diaphragm is deformed and the outer peripheral edge of the diaphragm is warped due to the deformation, the metal surface between the metal seal diaphragm, the metal case, and the metal cap is interposed between the metal seal diaphragm, the metal case, and the metal cap at a portion other than the protrusion due to the insulation. Never touch each other directly. Therefore, at the time of projection welding, all of the current flows through the projection, and the current is prevented from sneaking to other locations. As a result, the entire peripheral area of the protrusion is uniformly welded to the metal seal diaphragm, and a highly airtight welded joint between the components is ensured.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings of each embodiment, the same members corresponding to FIG. 5 are denoted by the same reference numerals. Embodiment 1 FIGS. 1 and 2 show an embodiment corresponding to claims 1 and 2 of the present invention. In the drawings, first, a metal case 6 which is welded to a metal sealing diaphragm 7 is joined.
The flange surface of the metal cap 8 is adjusted to a radius position from the center in advance and has a height of 100 μ over the entire circumference of the flange.
Ring protrusions 6a and 8b of about m are formed so as to bulge out so as to face each other. Further, as shown in FIG. 2, the metal seal diaphragm 7 is provided on the upper and lower surfaces on the outer peripheral side from the welded joint (the portion in contact with the protrusions 6a and 8b).
For example, a polyimide resin is coated to a thickness of about 20 to 30 μm to form an electrical insulating film 13.

In the pressure sensor assembling step, a metal case 6 is welded to the stem 3 on which the pressure-sensitive chip 1 is mounted, and then a metal sealing diaphragm 7 and a metal cap 8 are superimposed on the metal case 6 in this order. As a result, the seal diaphragm is sandwiched between the protrusions 6a and 8b to temporarily assemble. In this temporary assembly process, the insulating film 13 is used as a positioning guide to assemble the assembly by determining the overlapping position so that the projections 6a and 8b of the metal case 6 and the metal cap 8 are in contact with the inner peripheral side thereof, thereby assembling the components. Correct positioning is uniquely performed. Next, while maintaining the tentatively assembled state, the welding electrodes 14 and 15 are set above and below the pressure sensor as shown in the figure, and the welding power source 12 supplies power to the electrodes 14 and 15 from above while applying a pressing force from above and below to perform projection. Perform welding. After welding, a silicone oil (not shown) is sealed in the space in the case as in the related art to complete a pressure sensor product.

As described above, the metal sealing diaphragm 7
By forming the insulating film 13 on the outer peripheral edge of the seal diaphragm in advance, even if the seal diaphragm itself warps when a pressing force is applied in the projection welding process, the seal diaphragm 7 is formed at a position other than the protrusions 6a and 8b. The metal background does not touch the flanges of the metal case 6 and the metal cap 8. Thereby, at the time of welding, the projections 6a,
Since the current is prevented from unreasonably wrapping around a portion other than the portion 8b, and all the current flows concentratedly on the protrusions 8a and 8b,
A highly airtight welded joint state with the metal seal diaphragm 7 is obtained.

Embodiment 2 FIG. 3 shows an embodiment according to claim 3 of the present invention. In this example,
In addition to the component parts of the pressure sensor, a ring-shaped insulating sheet 16 having a split structure made of, for example, a fluorine resin having a thickness of about 50 μm is prepared as shown in FIG. Then, when performing projection welding in a tentatively assembled state in which the metal sealing diaphragm 7 is sandwiched between the metal case 6 and the projections 6a and 8b of the metal cap 8, the insulating sheet 16 as shown in FIG. The outer peripheral side is inserted and sandwiched in a gap remaining between the upper and lower surfaces of the metal seal diaphragm 7 and the flange surfaces of the metal case 6 and the metal cap 8,
In this state, the welding electrode is energized to perform projection welding. By interposing the insulating sheet 16 in the remaining gap at the welding location in this manner, unnecessary warpage and deformation due to pressurization of the metal sealing diaphragm 7 can be prevented, and the welding current can be reduced by the protrusion 6a as in the first embodiment. , 8b, and can reliably perform projection welding in a stable state while avoiding sneaking around.

It is to be noted that the insulating sheet 16 can be withdrawn from the welded portion after the projection welding and used repeatedly. Embodiment 3 FIG. 4 shows an embodiment corresponding to claim 4 of the present invention. In this embodiment, the protrusions 6a,
For example, a polyimide resin is coated on the surface area excluding 8b to a thickness of about 50 μm to form an insulating film 17, and then a pressure sensor is temporarily assembled and the metal case 6, the metal cap 8, the metal seal diaphragm 7 and Projection welding between In this method,
As in the first and second embodiments, even if the peripheral edge of the metal sealing diaphragm 7 warps due to the pressing force, the protrusions 6a, 8
There is no danger that the diaphragm will directly touch the metal surface of the metal case 6 and the metal cap 8 at a location other than b. Therefore, unnecessary sneak of the welding current is avoided to prevent the protrusions 6a, 8
Projection welding between b and the metallic seal diaphragm 7 can ensure a highly airtight joint.

[0019]

As described above, according to the assembling method of the present invention, the projection welding method is employed as a method for welding and joining the metal seal diaphragm to the metal case in the pressure sensor assembling step. Compared with the conventional seam welding method, the welding time per one pressure sensor is greatly reduced, and the productivity of the pressure sensor is improved. In addition, in a state where the metal sealing diaphragm is sandwiched between the projections formed on the metal case and the metal cap and the projection welding is performed, the remaining surface of the overlap except for the projection which is a regular welding point is electrically insulated. Therefore, even if the thin seal diaphragm warps or deforms due to external pressure, there is no danger that the metal background of each part will come into direct contact with the parts other than the projections. In addition to high mass productivity, high quality with no welding defects, such as preventing undesired wraparound and avoiding the occurrence of welding defects due to this, ensuring a highly airtight welding joint state required for filling of insulating oil Can be manufactured.

[Brief description of the drawings]

FIG. 1 is a welding process diagram of a metal seal diaphragm corresponding to a first embodiment of the present invention.

2A and 2B are partial views showing a metal seal diaphragm in FIG. 1, wherein FIG. 2A is a cross-sectional view and FIG.

3A and 3B are diagrams illustrating an embodiment corresponding to the second embodiment of the present invention, in which FIG. 3A is a cross-sectional view illustrating a tentatively assembled state at the time of welding and joining;
(B) is a plan view of the insulating sheet in FIG.

FIG. 4 is a configuration sectional view of an embodiment corresponding to a third embodiment of the present invention;

FIG. 5 is an explanatory view of a configuration of a conventional oil-filled semiconductor pressure sensor and a welding process of a metal sealing diaphragm.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pressure-sensitive chip 3 Stem 6 Metal case 6a Projection 7 Metal seal diaphragm 8 Metal cap 8b Projection 9 Silicone oil 13 Insulating coating 14 Welding electrode 15 Welding electrode 16 Insulating sheet 17 Insulating coating

Claims (4)

(57) [Claims] 1. A pressure-sensitive chip mounted on a stem, a metal case surrounding an outer periphery of the pressure-sensitive chip and connected to the stem, a metal seal diaphragm covering an open surface of the metal case, and the seal diaphragm. A method of assembling an oil-filled semiconductor pressure sensor in which an insulating oil is sealed in a case, comprising an assembly with a metal cap with a pressure guiding hole that covers the pressure side of By aligning each other to form a projection over the entire circumference,
A state in which a metal case, a metal seal diaphragm, and a metal cap are overlapped by sandwiching a peripheral edge of a metal seal diaphragm between the protrusions, and electrical insulation is applied to a remaining surface area of the overlapped surface excluding the protrusions. And a projection welding by applying a pressing force from the outside to the oil-filled semiconductor pressure sensor. 2. An oil-filled semiconductor according to claim 1, wherein an insulating film is formed in advance on an outer peripheral region of the metal sealing diaphragm from a projection welding point, and the projection welding is performed. How to assemble a pressure sensor. 3. The assembly method according to claim 1, wherein the projection welding is performed by sandwiching an insulating sheet in an outer peripheral region from a projection between the metal case and the flange surface of the metal cap and the metal sealing diaphragm. To assemble an oil-filled semiconductor pressure sensor. 4. An oil-filled mold according to claim 1, wherein an insulating coating is formed in advance on the flange surface of the metal case and the metal cap in a region other than the projections, and projection welding is performed. How to assemble a semiconductor pressure sensor.