JP2015169597A - Pressure sensor and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor equipped with a configuration with which it is possible to prevent the crack or breakdown of a semiconductor element.SOLUTION: A semiconductor element 30 is secured to a metal stem 20 via a junction glass 40. The junction glass 40 is such that the thickness of the junction glass 40 from a diaphragm 23 of the metal stem 20 to the other face 32 of the semiconductor element 30 is larger than the thickness from one face 31 to the other face 32 of the semiconductor element 30. Furthermore, the junction glass 40 has a fillet part 41 enclosing the entire circumference of the semiconductor element 30 and joined to a side face 33 of the semiconductor element 30 over the entire circumference. A thermal stress due to cooling/heating cycles is thereby suppressed from being applied to the side face 33 of the semiconductor element 30, making it possible to prevent the side face 33 of the semiconductor element 30 from becoming the starting point of crack or breakdown. Therefore, the crack or breakdown of the semiconductor element 30 can be prevented.

Description

  The present invention relates to a pressure sensor in which a semiconductor element is fixed to a diaphragm of a metal stem and a manufacturing method thereof.

  Conventionally, a configuration of a pressure sensor including a stem having a diaphragm distorted by application of pressure and a semiconductor element fixed on the diaphragm has been proposed in, for example, Patent Document 1. The semiconductor element is a sensor chip configured to output a sensor signal corresponding to the distortion of the diaphragm. The semiconductor element is fixed to the stem via a metal film formed on the diaphragm.

JP 2008-64526 A

  However, in the above conventional technique, when the pressure sensor is used in an environment subjected to a thermal cycle, the side surface portion of the semiconductor element receives a thermal stress based on the expansion and contraction of the stem. The thermal stress that the semiconductor element receives from the stem becomes more prominent as the difference between the thermal expansion coefficient of the stem and the thermal expansion coefficient of the semiconductor element increases. For this reason, there exists a problem that a crack and destruction will arise in a semiconductor element from the side part of a semiconductor element.

  In view of the above, it is a first object of the present invention to provide a pressure sensor having a configuration capable of preventing cracking and destruction of a semiconductor element. A second object is to provide a method for manufacturing the pressure sensor.

  In order to achieve the above object, the invention according to claim 1 includes a metal stem (20) having a diaphragm (23) which is distorted when pressure is applied. Moreover, the plate-shaped thing which has one surface (31), the other surface (32) on the opposite side to this one surface (31), and the side surface (33) adjacent to one surface (31) and the other surface (32) The semiconductor element (30) for outputting a sensor signal corresponding to the distortion of the diaphragm (23) is provided. Furthermore, it is provided between the other surface (32) of the semiconductor element (30) and the diaphragm (23), and includes a bonding glass (40) for fixing the semiconductor element (30) to the diaphragm (23).

  The semiconductor element (30) has a smaller thermal expansion coefficient than the metal stem (20). Further, the bonding glass (40) has a thickness of the bonding glass (40) from the diaphragm (23) to the other surface (32) of the semiconductor element (30) from the one surface (31) to the other surface (30). 32), and a fillet portion (41) that surrounds the entire periphery of the semiconductor element (30) and is joined to the side surface (33) of the semiconductor element (30) over the entire periphery. ).

  According to this, since the side surface (33) of the semiconductor element (30) is covered with the fillet portion (41) around the entire periphery of the semiconductor element (30), the thermal stress due to the thermal cycle is applied to the semiconductor element (30). ) Is difficult to apply to the side surface (33). Therefore, even if the pressure sensor is exposed to a cooling cycle, the side surface (33) of the semiconductor element (30) can be prevented from starting to crack or break. Therefore, the crack and destruction of the semiconductor element (30) can be prevented.

  In the invention of claim 5, a glass material (42) is prepared, and the glass material (42) is heat-treated at a glass softening temperature or higher and a glass decomposition temperature or lower to form a bonded glass (40) to form a semiconductor element 30) is bonded to the metal stem (20), and the periphery of the semiconductor element (30) is entirely surrounded by the glass material (42), and the entire periphery is bonded to the side surface (33) of the semiconductor element (30). Forming a fillet portion (41).

  According to this, when forming bonding glass (40), the side surface (33) of a semiconductor element (30) can be covered with a fillet part (41) over the perimeter of a semiconductor element (30). For this reason, it is possible to obtain a structure in which the thermal stress due to the thermal cycle is difficult to be applied to the side surface (33) of the semiconductor element (30). Therefore, it is possible to obtain a structure capable of preventing cracking and destruction of the semiconductor element (30) in the cooling / heating cycle.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is sectional drawing which showed the whole structure of the pressure sensor which concerns on one Embodiment of this invention. It is A arrow directional view of FIG. FIG. 3 is a sectional view taken along line III-III in FIG. 2. It is sectional drawing of the workpiece | work in the manufacturing process of a pressure sensor. It is the figure which showed the relationship between the thickness of a semiconductor element, and the thickness of a fillet part. It is the figure which showed the presence or absence of the crack and destruction of a semiconductor element and joining glass in a cooling cycle when changing the thickness of a fillet part with respect to the thickness of a semiconductor element. It is the figure which showed the cross section of the fillet part in case a / b is 1. In other embodiment, it is the figure which showed an example of the cross-sectional shape of a fillet part. In other embodiment, it is the figure which showed an example of the cross-sectional shape of a fillet part. In other embodiment, it is the figure which showed an example of the cross-sectional shape of a fillet part.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The pressure sensor according to the present embodiment is attached to a fuel pipe in a fuel injection system such as a common rail of an automobile and detects a high pressure of a gas or a gas-liquid mixture as a pressure medium in the fuel pipe. is there. For example, the pressure sensor is configured to detect a high pressure of 200 MPa to 300 MPa.

  As shown in FIG. 1, the pressure sensor 1 includes a housing 10, a metal stem 20, a semiconductor element 30, a bonding glass 40, and a connector case 50.

  The housing 10 is a hollow case in which a metal material such as stainless steel is processed by cutting or the like, and a male screw portion 11 that can be screwed to a fuel pipe that is a measurement object is formed on an outer peripheral surface of one end side of the housing 10. Has been. On one end side of the housing 10, a through hole 13 communicating with an opening 12 formed on the other end side of the housing 10 is formed. The opening 12 of the housing 10 is configured by being surrounded by a peripheral wall 14.

  The metal stem 20 is a hollow cylindrical metal member provided with a pressure introduction hole 21 into which a pressure medium is introduced. As the metal stem 20, for example, a material made of SUS430 or SUS630, or a material made of SUS and having a high chromium content is used. The thermal expansion coefficient of the metal stem 20 is, for example, 11 ppm to 14 ppm.

  The metal stem 20 has a diaphragm 23 that is provided at a hollow cylindrical one end 22 so as to close one of the pressure introduction holes 21 and is distorted by the pressure of the pressure medium introduced into the pressure introduction hole 21. That is, the diaphragm 23 is a thin pressure receiving means that can be deformed by applying pressure.

  Further, the metal stem 20 has a stepped portion 24 having a larger outer diameter than the cylindrical portion in which the pressure introducing hole 21 is provided on the one end portion 22 side. The planar shape of the stepped portion 24 when the metal stem 20 side is viewed from the connector case 50 side is, for example, circular. A cylindrical portion in which the step portion 24 of the metal stem 20 contacts the bottom surface of the opening 12 of the housing 10 in an annular shape and the pressure introducing hole 21 is formed is attached to the through hole 13 of the housing 10. The metal stem 20 is attached to the housing 10 by, for example, screwing. As a result, the pressure medium is introduced into the diaphragm 23 through the pressure introduction hole 21.

  The semiconductor element 30 is pressure detecting means that is bonded to the diaphragm 23 via the bonding glass 40 and outputs a sensor signal corresponding to the distortion of the diaphragm 23. The semiconductor element 30 has a plate shape formed from a semiconductor substrate such as a silicon substrate. The semiconductor element 30 has a smaller thermal expansion coefficient than the metal stem 20. The difference in thermal expansion coefficient between the semiconductor element 30 and the metal stem 20 is, for example, 13 ppm.

  The semiconductor element 30 has one surface 31, another surface 32 opposite to the one surface 31, and one surface 31 and a side surface 33 adjacent to the other surface 32. In the present embodiment, the one surface 31 and the other surface 32 of the semiconductor element 30 are rectangular.

  A plurality of gauge resistors are formed on the semiconductor substrate so as to constitute a Wheatstone bridge circuit. Thus, when pressure is applied to the semiconductor substrate, the resistance value of each gauge resistor changes due to the piezoresistance effect. Therefore, the Wheatstone bridge circuit outputs a sensor signal corresponding to the pressure based on a change in the resistance value of each gauge resistor. Note that an amplification circuit (not shown) that performs amplification processing or the like on the sensor signal is also formed on the semiconductor substrate.

  A circuit board 60 that generates an output signal corresponding to the sensor signal from the semiconductor element 30 is disposed on the step portion 24 of the metal stem 20. The semiconductor element 30 is electrically connected to the circuit board 60 via bonding wires 70. The circuit board 60 includes an IC chip having a signal conversion function or the like, and the sensor signal of the semiconductor element 30 is input to the IC chip or the like and converted into an output signal.

  The bonding glass 40 is provided on the opposite side of the diaphragm 23 of the one end portion 22 of the metal stem 20 from the pressure introducing hole 21. The bonding glass 40 is a bonding means for attaching the semiconductor element 30 to the metal stem 20.

  In addition, the bonding glass 40 is such that the thickness of the bonding glass 40 from the diaphragm 23 of the metal stem 20 to the other surface 32 of the semiconductor element 30 is larger than the thickness from one surface 31 to the other surface 32 of the semiconductor element 30. For example, the thickness of the semiconductor element 30 is 100 μm, and the thickness of the portion sandwiched between the diaphragm 23 and the semiconductor element 30 in the bonding glass 40 is 250 μm.

  As described above, since the difference in thermal expansion coefficient between the metal stem 20 and the semiconductor element 30 is large, the semiconductor element 30 and the bonding glass 40 are subjected to thermal stress accompanying the shrinkage of the metal stem 20. Therefore, the bonding glass 40 is formed to be thicker than the semiconductor element 30 in order to obtain a bonding strength with respect to a temperature rise / fall in the firing process of the bonding glass 40 and a thermal stress received from a cooling cycle in the usage environment of the pressure sensor 1.

  The connector case 50 forms a connector for outputting an output signal to the outside. The connector case 50 is formed of, for example, a resin material, and a pin-like terminal 51 is integrally formed by insert molding or the like. Both ends of the terminal 51 are insert-molded in resin so as to be exposed from the connector case 50.

  The connector case 50 is fixed by caulking so that the end of the peripheral wall 14 of the housing 10 holds the connector case 50 in a state where the one end 52 is fitted to the other end of the housing 10 via the O-ring 80. . One end side of the terminal 51 is electrically connected to the terminal of the circuit board 60 through the terminal 90. As a result, the connector case 50 is integrated with the housing 10 to form a package, and the semiconductor element 30, the circuit board 60, the electrical connection portion and the like inside the package are protected from moisture and mechanical external force. On the other hand, the other end side of the terminal 51 is exposed in an opening 53 provided on the other end side of the connector case 50. The above is the overall configuration of the pressure sensor 1 according to the present embodiment.

  Next, specific configurations of the metal stem 20, the semiconductor element 30, and the bonding glass 40 in the configuration of the pressure sensor 1 will be described. As shown in FIG. 2, the maximum length of the diaphragm 23 in the surface direction of the one surface 31 of the semiconductor element 30 is smaller than the maximum length of the one surface 31 of the semiconductor element 30.

  In the present embodiment, the planar shape of the diaphragm 23 is circular, and the one surface 31 of the semiconductor element 30 is square. Therefore, the length of the diameter of the diaphragm 23 is smaller than the length of the diagonal line of the one surface 31 of the semiconductor element 30. Thereby, in the thickness direction of the semiconductor element 30, the region where the gauge resistance is formed in the semiconductor element 30 and the diaphragm 23 can be overlapped.

  In addition, the bonding glass 40 has a fillet portion 41 that extends around the entire periphery of the semiconductor element 30 and is bonded to the side surface 33 of the semiconductor element 30 over the entire periphery. In other words, the entire outer peripheral portion of the semiconductor element 30 is covered with the fillet portion 41 having a predetermined height. The fillet portion 41 is a part of the bonding glass 40 and is a portion located around the semiconductor element 30.

  Here, the maximum length of the one surface 31 of the semiconductor element 30 is smaller than the maximum length of the bonding glass 40 in the surface direction of the one surface 31 of the semiconductor element 30. In the present embodiment, the planar shape of the bonding glass 40 is circular, and the one surface 31 of the semiconductor element 30 is square. Therefore, the length of the diagonal line of the one surface 31 of the semiconductor element 30 is smaller than the length of the diameter of the bonding glass 40. Accordingly, not only the side surface 33 of the semiconductor element 30 but also the corner portion 34 that is a connection portion of the two side surfaces 33 is covered with the fillet portion 41.

  As shown in FIG. 3, the fillet portion 41 has the thickest portion in contact with the side surface 33 of the semiconductor element 30, and the thickness decreases toward the outside centering on the semiconductor element 30. That is, the fillet portion 41 is formed in a slope shape. 2 and 3, the inner side of the metal stem 20 than the circuit board 60 is shown.

  Then, the manufacturing method of the pressure sensor 1 which concerns on this embodiment is demonstrated. First, the connector case 50 in which the housing 10, the circuit board 60, the terminal 90, the O-ring 80, and the terminal 51 are insert-molded is prepared.

  Moreover, the workpiece | work 100 shown by FIG. 4 is comprised. Specifically, a solid glass material 42 in which granular glass is formed is prepared. The glass material 42 is a tablet glass in which a low melting point glass is formed in a tablet shape. Further, the semiconductor element 30 is prepared by a predetermined semiconductor process. Further, a metal stem 20 is prepared.

  Then, a paste (not shown) is placed on the metal stem 20, and a glass material 42 is placed on the metal stem 20 so as to cover the paste. Further, paste is disposed on the glass material 42, and the semiconductor element 30 is disposed on the glass material 42 so as to cover the paste. The glue is used for positioning the glass material 42 and the semiconductor element 30. The glue spreads thinly and enters the gap created by the glass particles being pressed. Thus, the workpiece 100 is completed.

  Thereafter, the workpiece 100 is mounted on a firing jig (not shown) and placed in a reflow furnace (not shown). And the glass material 42 is heat-processed more than glass softening temperature and below glass decomposition temperature because the workpiece | work 100 moves and passes through the reflow furnace controlled by predetermined temperature. Specifically, heat treatment is performed at 500 ° C. or lower (for example, 430 ° C.). By heat-treating the glass material 42 at 500 ° C. or less, the semiconductor element 30 formed by the semiconductor substrate can be prevented from melting.

  When the glass material 42 is thus heat-treated, the bonded glass 40 can be formed from the glass material 42. At this time, the glass material 42 melts and the semiconductor element 30 sinks into the glass material 42. Thereby, the fillet part 41 joined to the side surface 33 of the semiconductor element 30 is formed all around the periphery of the semiconductor element 30 with a part of the glass material 42. That is, the fillet portion 41 is formed at the same time when the semiconductor element 30 is joined to the metal stem 20. In other words, the fillet portion 41 is formed as a part of the bonding glass 40. Further, the semiconductor element 30 is bonded to the metal stem 20 via the bonding glass 40. The paste is burned away by the heat treatment of the glass material 42.

  Note that the glass material 42 may be heated in a state where a weight is placed on the semiconductor element 30 in order to make the semiconductor element 30 easily sink into the melted glass material 42.

  Thereafter, the metal stem 20 is attached to the through hole 13 of the housing 10, and the circuit board 60 is disposed on the step portion 24 of the metal stem 20, and the semiconductor element 30 and the circuit board 60 are wire-bonded to electrically connect both. Connect to. Thereafter, the pressure sensor 1 is completed by caulking and fixing the connector case 50 to the housing 10 via the O-ring 80.

  In the pressure sensor 1 manufactured as described above, the inventors relate the relationship between the thickness of the fillet portion 41 formed to be bonded to the side surface 33 of the semiconductor element 30 and the crack / breakage of the bonding glass 40 and the semiconductor element 30. Examined.

  First, as shown in FIG. 5, the inventors defined the thickness of the fillet portion 41 from the other surface 32 of the semiconductor element 30 to the bonding position on the side surface 33 in the fillet portion 41 as a. Further, the thickness of the semiconductor element 30 from the other surface 32 to the one surface 31 of the semiconductor element 30 was defined as b. Then, the pressure sensor 1 was subjected to 200 cycles of a cooling cycle with a temperature difference between 250 ° C. and −40 ° C., and the presence / absence of crack / breakage of the bonding glass 40 and the semiconductor element 30 was examined by changing the value of a / b. . In addition, 20 samples were manufactured for every value of a / b, and the thermal cycle test was done.

  Further, as shown in FIG. 6, in this embodiment, the thickness b of the semiconductor element 30 is fixed to 100 μm, and the thickness a of the fillet portion 41 is changed from 100 μm to 0 μm. As a result, when a / b was 0, that is, when the fillet portion 41 was not formed, the semiconductor element 30 was peeled off from the bonding glass 40 and was broken. Further, when a / b was 0.05, a crack occurred in the semiconductor element 30 and a part of the semiconductor element 30 was peeled from the bonding glass 40. Further, when a / b was 0.1, the semiconductor element 30 was cracked.

  On the other hand, no crack or breakage occurred in the semiconductor element 30 and the bonding glass 40 when a / b was 1.0 to 0.2. That is, no cracks or fractures occurred in all 20 samples. Therefore, the fillet portion 41 is bonded to the side surface 33 of the semiconductor element 30 so as to satisfy the condition of 0.2 ≦ a / b ≦ 1, thereby preventing the semiconductor element 30 from being cracked or broken. Can do. When a / b is 1, as shown in FIG. 7, the fillet portion 41 has a shape that covers the entire side surface 33 of the semiconductor element 30.

  As described above, the pressure sensor 1 of the present embodiment is characterized in that the fillet portion 41 joined to the side surface 33 of the semiconductor element 30 is provided over the entire circumference of the semiconductor element 30. Thereby, since the side surface 33 of the semiconductor element 30 is covered with the fillet portion 41 around the entire periphery of the semiconductor element 30, the side surface 33 and the corner portion 34 of the semiconductor element 30 do not become a starting point of cracking or breaking. Can be. Therefore, cracks and destruction of the semiconductor element 30 can be prevented.

(Other embodiments)
The configuration of the pressure sensor 1 shown in each of the above embodiments is an example, and is not limited to the configuration shown above, and may be another configuration that can realize the present invention. For example, the one surface 31 of the semiconductor element 30 is not limited to a square shape (square), and may be a rectangle. Further, it may be circular or elliptical. When the one surface 31 is circular, the maximum length of the one surface 31 of the semiconductor element 30 corresponds to the diameter of the circle. When the one surface 31 is elliptical, the maximum length of the one surface 31 of the semiconductor element 30 is on the major axis of the ellipse. Equivalent to.

  The same applies to the planar shape of the diaphragm 23. When the planar shape of the diaphragm 23 is a quadrangle, the maximum length of the diaphragm 23 corresponds to a diagonal length, and when the diaphragm 23 is an ellipse, the maximum length of the diaphragm 23 corresponds to a major axis. Further, the planar shape of the bonding glass 40 is not limited to a circle or an ellipse, and may be a quadrangular shape in accordance with the planar shape of the one surface 31 of the semiconductor element 30.

  In the above embodiment, the solidified tablet glass is used as the glass material 42, but paste glass may be used. In this case, first, paste glass is applied to the metal stem 20 with a dispenser device or the like, and then the bonding glass 40 is formed by a predetermined heat treatment. Thereafter, the semiconductor element 30 is mounted on the bonding glass 40, and a paste glass is applied to the outer periphery of the semiconductor element 30 in accordance with the shape and size of the semiconductor element 30 with a dispenser device or the like, and heat treatment is performed to form the fillet portion 41. can do.

  The fillet portion 41 is not limited to the shape shown in the above embodiment. For example, as shown in FIG. 8, the fillet portion 41 may have a gentle step shape instead of a linear slope. Further, as shown in FIG. 9, the fillet portion 41 may have a gentle step shape while covering the entire side surface 33 of the semiconductor element 30. Furthermore, as shown in FIG. 10, the fillet portion 41 may have a shape that rises so that a part of the fillet portion 41 is located on the side 31 of the semiconductor element 30 with respect to the side surface 33 of the semiconductor element 30. In consideration of wire bonding to the semiconductor element 30, it is preferable that the fillet portion 41 has a height that does not exceed the one surface 31 of the semiconductor element 30.

20 Metal Stem 23 Diaphragm 30 Semiconductor Element 31 One Side 32 Other Side 33 Side 40 Joint Glass 41 Fillet

Claims (6)

A metal stem (20) having a diaphragm (23) which is distorted when pressure is applied;
A plate-like one having one surface (31), the other surface (32) opposite to the one surface (31), and the side surface (33) adjacent to the one surface (31) and the other surface (32) A semiconductor element (30) for outputting a sensor signal corresponding to the distortion of the diaphragm (23);
A bonding glass (40) disposed between the other surface (32) of the semiconductor element (30) and the diaphragm (23) and fixing the semiconductor element (30) to the diaphragm (23);
With
The semiconductor element (30) has a smaller coefficient of thermal expansion than the metal stem (20),
In the bonding glass (40), the thickness of the bonding glass (40) from the diaphragm (23) to the other surface (32) of the semiconductor element (30) is different from the one surface (31) of the semiconductor element (30). The thickness is larger than the thickness up to the surface (32), and the entire periphery of the semiconductor element (30) is joined to the side surface (33) of the semiconductor element (30) over the entire circumference. A pressure sensor having a fillet portion (41). The thickness of the fillet part (41) from the other surface (32) of the semiconductor element (30) to the bonding position on the side surface (33) of the fillet part (41) is defined as a, and the semiconductor element (30 ) When the thickness of the semiconductor element (30) from the other surface (32) to the one surface (31) is defined as b,
The said fillet part (41) is joined to the side surface (33) of the said semiconductor element (30) so that the conditions of 0.2 <= a / b <= 1 may be satisfy | filled. Pressure sensor.   The maximum length of one surface (31) of the semiconductor element (30) is smaller than the maximum length of the bonding glass (40) in the surface direction of the one surface (31) of the semiconductor element (30). The pressure sensor according to claim 1 or 2.   The maximum length of the diaphragm (23) in the surface direction of the one surface (31) of the semiconductor element (30) is smaller than the maximum length of the one surface (31) of the semiconductor element (30). The pressure sensor according to any one of claims 1 to 3. A metal stem (20) having a diaphragm (23) which is distorted when pressure is applied;
A plate-like one having one surface (31), the other surface (32) opposite to the one surface (31), and the side surface (33) adjacent to the one surface (31) and the other surface (32) A semiconductor element (30) having a smaller coefficient of thermal expansion than the metal stem (20) and outputting a sensor signal corresponding to the distortion of the diaphragm (23);
The semiconductor element (30) is disposed between the other surface (32) and the diaphragm (23), and the thickness from the diaphragm (23) to the other surface (32) of the semiconductor element (30) is the semiconductor element. (30) a bonding glass (40) that is larger than the thickness from one surface (31) to the other surface (32), and fixes the semiconductor element (30) to the diaphragm (23);
A method of manufacturing a pressure sensor comprising:
A glass material (42) is prepared, and the glass material (42) is heat-treated at a glass softening temperature or higher and a glass decomposition temperature or lower to form the bonding glass (40), and the semiconductor element (30) is connected to the metal stem. (20), and the glass material (42) was used to cover the entire periphery of the semiconductor element (30) and to the side surface (33) of the semiconductor element (30) over the entire periphery. A method for manufacturing a pressure sensor, comprising a step of forming a fillet portion (41).   In the step of forming the fillet portion (41), the glass material (42) is made of low-melting glass, and the glass material (42) is heat-treated at 500 ° C or lower. 5. A method for manufacturing a pressure sensor according to 5.

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