FLOW RATE SENSOR

Abstract

Flow rate sensor (100) comprising: a ladder frame (4), a semiconductor chip (2) arranged on a surface of the lead frame (4) and in which a membrane (1) having a cavity portion (9) on the lead frame side is formed, a flow rate detection unit formed on the one surface having the membrane (1) of the semiconductor chip (2), and a resin (3) having a flow passage opening portion (8) exposing at least a part of the flow rate detection unit formed on the diaphragm (1) and covering the lead frame (4) and the semiconductor chip (2), wherein a lower side portion (13b) of the resin (3) covering another side arranged opposite to one side of the lead frame (4) has a thinned portion (7) which is thinner in an area facing an outer peripheral portion of the diaphragm (1) than in its outer region, and wherein the thinned portion (7) extends from a position facing the inside of the cavity portion (9) provided below the membrane (1) to a position facing the outside of the cavity portion (9), characterized in that an opening (6) is provided in an area of the thinned portion (7) which faces a central region of the membrane (1).

Description

Technical field

[0001] The present invention relates to a flow rate sensor. Technical background

[0002] A flow rate sensor is known in which a diaphragm is formed on a semiconductor chip using micromachining technology, and a flow rate detection unit is provided on the diaphragm. Such a flow rate sensor is used, for example, to measure the flow rate of air flowing into an internal combustion engine, for example, of a motor vehicle.

[0003] The above-mentioned flow rate sensor is formed on a lead frame by resin molding in a state where the semiconductor chip on which the flow rate detection unit is provided is mounted on the diaphragm, so that the flow rate detection unit is left exposed (see, for example, PTL 1). Citation listPatent literature

[0004] PTL 1: WO 2015 / 033589 A1 DE 11 2013 002 996 T5 discloses a flow rate sensor having the features in the preamble of present claims 1 and 2. Other conventional flow rate sensors are described in JP 2009-36639 A and JP 2017-203709 A. Summary of the inventionTechnical problem

[0005] PTL 1 does not disclose the deterioration of detection accuracy due to the deformation of the diaphragm during resin molding. Solution to the problem

[0006] A flow rate sensor according to the invention is defined by the features of the present independent claims 1 and 2. Beneficial effect

[0007] According to the invention, deterioration of detection accuracy due to deformation of the diaphragm during resin molding can be prevented. Brief description of the drawings

[0008] They show: Fig. 1 is a plan view of a flow rate sensor according to an embodiment of the invention when viewed from the top, Fig. 2 a plan view of the Fig. 1 flow rate sensor when viewed from the back, Fig. 3 a sectional view along a line III-III of the Fig. 1 shown flow rate sensor, Fig. 4 a sectional view along a line IV-IV of the Fig. 1 shown flow rate sensor, Fig. 5 is a sectional view of a process for sealing the flow rate sensor according to the invention with resin, Fig. 6 is a diagram showing a compression force acting in the X direction on a diaphragm of the flow rate sensor during resin molding, Fig. 7 is a diagram showing a compression force acting in the Y direction on the diaphragm of the flow rate sensor during resin molding, Fig. 8 is a diagram showing the bending deformation acting on the diaphragm of the flow rate sensor due to shrinkage during resin molding, Fig. 9 shows a flow rate sensor according to a first modification of the invention, being a plan view viewed from the back of the flow rate sensor, Fig. 10 shows a flow rate sensor according to a second modification of the invention, which is a plan view viewed from the back of the flow rate sensor, Fig. 11 shows a flow rate sensor according to a third modification of the invention, wherein Fig. 11(a) a Fig. 3 corresponding sectional view and Fig. 11(b) a Fig. 4 corresponding sectional view, Fig. 12 shows a flow rate sensor according to a fourth modification of the invention, which is a plan view viewed from the top of the flow rate sensor, and Fig. 13 shows a flow rate sensor according to a fifth modification of the invention, which is a plan view viewed from the top of the flow rate sensor. Description of embodiments

[0009] An embodiment of the invention will be described below with reference to the drawings. The following description and drawings serve to describe the invention by way of example, and omissions and simplifications are made therein where necessary for clarity. The invention may also be implemented in various other forms. Unless otherwise stated, the respective components of configurations may be single or multiple.

[0010] To facilitate understanding of the invention, the positions, sizes, shapes, ranges, or the like of the respective components of configurations illustrated in the drawings may not represent the actual positions, sizes, shapes, ranges, or the like. Therefore, the invention is not necessarily limited to the positions, sizes, shapes, ranges, or the like disclosed in the drawings.

[0011] Fig. 1 is a plan view of a flow rate sensor according to an embodiment of the invention when viewed from the top, Fig. 2 is a top view of the flow rate sensor of Fig. 1 when viewed from the back, Fig. 3 is a sectional view along a line III-III of the Fig. 1 shown flow rate sensor, and Fig. 4 is a sectional view along a line IV-IV of the Fig. 1 shown flow rate sensor.

[0012] In the following description, the figures show an X-direction, a Y-direction and a Z-direction.

[0013] As in Fig. 3, a flow rate sensor 100 includes a lead frame 4, a first semiconductor chip 2, a second semiconductor chip 5, a wire 11, and a resin 3.

[0014] The lead frame 4 is made of, for example, a metal such as copper. The lead frame 4 is arranged separately from a mounting portion (not shown) having a large area, on which the first semiconductor chip 2 and the second semiconductor chip 5 are mounted, and has a plurality of lead portions 4a (see Fig. 1 and Fig. 2) which are electrically connected to the mounting section by wires (not shown).

[0015] The first semiconductor chip 2 and the second semiconductor chip 5 are bonded to an upper surface in the Z direction (hereinafter referred to simply as the "upper surface") of the mounting portion of the lead frame 4 with an adhesive (not shown). As the adhesive, a resin containing a thermosetting resin such as an epoxy resin and a polyurethane resin, or a thermoplastic resin such as a polyimide resin, an acrylic resin, and a fluororesin as the main component can be used. Fine inorganic particles containing glass, carbon, mica, or the like as the main component can be mixed into the resin.

[0016] A diaphragm 1 is formed on the top surface of the first semiconductor chip 2. The diaphragm 1 is a portion thinner than a periphery, and a cavity portion 9 is provided below the diaphragm 1. The diaphragm 1 is formed by cutting out the first semiconductor chip 2 from the bottom surface and forming the rectangular trapezoidal cavity portion 9.

[0017] A flow rate detection unit (not shown) is formed on an upper surface of the first semiconductor chip 2. The flow rate detection unit includes, for example, a heat-generating resistor provided on an upper surface of the diaphragm 1 and a pair of measuring resistors arranged on both sides of this heat-generating resistor, as well as a heater control bridge and a temperature sensor bridge. The heat-generating resistor and the pair of measuring resistors are arranged along a direction in which a gas, such as air, flows, whose flow rate is to be detected. Specifically, the heat-generating resistor and the pair of measuring resistors are arranged such that the measuring resistor on the upstream side, where a gas to be measured flows, is cooled by the gas, and the measuring resistor on the downstream side is heated by heat from the heat-generating resistor.The second semiconductor chip 5 includes a CPU, an input circuit, an output circuit, a memory, and the like, and a control circuit for measuring the flow rate.

[0018] As the gas flows, the measuring resistor upstream of the heat-generating resistor is cooled, and the temperature of the measuring resistor downstream of the heat-generating resistor rises due to the gas being raised by the heat-generating resistor. The flow rate of the gas is obtained based on a potential difference generated by the temperature difference between the pair of measuring resistors. Details of such a flow rate detection unit are set forth in WO 2015 / 033589, as described in PTL 1.

[0019] However, the flow rate detecting unit is not limited to implementing the above method, and it may be implemented by another method.

[0020] The first semiconductor chip 2 and the second semiconductor chip 5 are each bonded to the lead frame 4 by a wire made of gold or the like.

[0021] As in Fig. As shown in Figure 3, the resin 3 covers the lead frame 4, the first semiconductor chip 2, the second semiconductor chip 5, and the wire 11, except for an area of an outer peripheral portion of the diaphragm 1 and an area on the underside of the lead frame 4 facing the diaphragm 1. As the material of the resin 3, a thermosetting resin such as an epoxy resin or a phenolic resin, or a thermoplastic resin such as polycarbonate, polyethylene terephthalate, polyphenylene sulfide, or polybutylene terephthalate can be used. Further, fine metal particles such as gold, silver, copper, and tin, or fine inorganic particles containing quartz, glass, carbon, mica, talc, and the like as main components can be mixed into the resin. The resin 3 can be made conductive, and the linear expansion coefficient of the resin 3 can be adjusted.

[0022] As in the Fig. 3 and Fig. 4, a top-side resin portion 13a above the lead frame 4 in the Z direction includes a raised portion 12 covering the first semiconductor chip 2, a base portion 14 covering the second semiconductor chip 5, and a lower rear portion 15 having a surface 15a flush with the upper surface 2a of the first semiconductor chip 2. The raised portion 12 of the top-side resin portion 13a is provided with an opening portion 8 exposing the diaphragm 1 and an outer peripheral portion near the diaphragm 1. As shown in Fig. As shown in Figure 1, the opening portion 8 is provided over the entire length of the flow rate sensor 100 in the Y direction, and the lower rear portion 15 is provided in the opening portion 8. The raised portion 12 includes a first raised portion 12a covering an area extending on one side of the first semiconductor chip 2, and a second raised portion 12b provided in the X direction separately from the first raised portion, with the opening portion 8 sandwiched therebetween, and covering an area on the other side opposite to the one side of the first semiconductor chip 2. That is, a pair of raised portions 12 formed on the top-side resin portion 13a are formed on both sides in the X direction, with the opening portion 8 sandwiched therebetween. In the opening portion 8 of the resin 3, as shown in Fig. 4, the surface 15a of the lower rear portion 15 of the resin 3 is in contact with the upper surface 2a of the first semiconductor chip 2. Therefore, as indicated by an arrow in Fig. 1, the gas such as air whose flow rate is to be measured is passed through the upper portion 8 provided between the raised portions 12 of the upper-side resin portion 13a so as to flow in the Y direction.

[0023] In a lower-side resin portion 13b in the Z direction below the lead frame 4, a rectangular opening 6 and a groove 16, which is a recess surrounding the opening 6, are formed in a region facing the diaphragm 1, with the lead frame 4 sandwiched therebetween. The lead frame 4 is exposed from the opening 6. As shown in Fig. 2, the opening 6 and the groove 16 have a rectangular shape in a plan view. In the lower-side resin portion 13b, a thinned portion 7 is formed between a side surface 16a of the groove 16 and a side surface 6a of the opening 6. The side surface of the opening 6, which is an inner side surface of the thinned portion 7, is located inside the cavity portion 9 provided below the diaphragm 1, and the side surface 16a of the groove 16, which is an outer side surface of the thinned portion 7, is located outside the cavity portion 9 provided below the diaphragm 1. In other words, with reference to Fig. 3, the protrusion of each of the side surface 6a of the opening 6 on the plus side in the X direction and the side surface 6a on the minus side in the X direction on the semiconductor chip 2 side is located in a region where the cavity portion 9 extends. The protrusion of each of the side surface 16a of the groove 16 on the plus side in the X direction and the side surface 16a on the minus side in the X direction on the semiconductor chip 2 side is located outside the region where the cavity portion 9 extends.

[0024] A region outside the side surface 16a of the groove 16 of the lower-side resin portion 13b, that is, a region of the lower-side resin portion 13b around the groove 16, is thicker than the thinned portion 7. The thicker portion has a uniform thickness overall, and its bottom surface is flat. The thinned portion 7 is formed only in the outer peripheral portion near the area facing the diaphragm 1. Therefore, as described later, bending deformation can be effectively applied to the diaphragm 1.

[0025] Fig. 5 is a sectional view showing a resin sealing process for the flow rate sensor according to the invention, illustrating a state in which the flow rate sensor is installed in a mold and molding is performed.

[0026] A process for forming the flow rate sensor 100 is outlined below.

[0027] The first semiconductor chip 2, which has the diaphragm 1, and the second semiconductor chip 5 are attached to the attachment portion of the lead frame 4, which has the lead portion 4a, by an adhesive. Although not shown, the lead frame 4 at this point has a ridge connecting the attachment portion and the lead portion 4a on the outer periphery of the lead frame 4. The first semiconductor chip 2 and the lead frame 4, and the second semiconductor chip 5 and the lead frame 4, are bonded by the wires 11, respectively. Further, each lead portion 4a and the attachment portion of the lead frame 4 are bonded by a wire (not shown). Then, in this state, the flow rate sensor 100 is installed and molded in a mold 10. The mold 10 consists of an upper and a lower mold, in Fig. 5, however, the upper and lower forms are shown as one element without separation.

[0028] The diaphragm 1 and the outer peripheral portion near it are exposed from the resin 3. Therefore, a neighboring area of the upper surface of the diaphragm 1 is clamped by a clamping portion 10a. However, because the diaphragm 1 has a thin-film structure, a cavity 10b is provided in a part of the clamping portion 10a facing the diaphragm 1 so that the mold 10 does not directly contact the diaphragm 1. In this way, the clamping portion 10a can only contact the first semiconductor chip 2 near the outer peripheral portion of the diaphragm 1 and not contact the diaphragm 1. This can prevent deformation of the diaphragm 1 due to the pressing force of the clamping portion 10a. The clamping portion 10a can be formed separately from the mold 10 and attached to the mold 10 so as to be movable in the Z direction. A region where the clamping portion 10a is provided is the opening portion 8 of the resin 3.

[0029] Although not shown, a low-rigidity film may be sandwiched between the clamping portion 10a and the first semiconductor chip 2 to prevent damage to the first semiconductor chip 2. By disposing the low-rigidity film between the clamping portion 10a and the first semiconductor chip 2, the pressing force of the clamping portion 10a against the first semiconductor chip 2 is reduced, and the deformation of the diaphragm 1 is further reduced. In addition, the penetration of the resin 3 into the side of the diaphragm 1 can be more effectively prevented.

[0030] A portion of the lead frame 4 facing the cavity portion provided below the diaphragm 1 is supported by a support portion 10c provided in the mold 10. The support portion 10c has a shape in which the opening 6, the thinned portion 7, and the groove 16 are formed in the resin 3. That is, the support portion 10c has a shape in which an opening forming portion 21 for forming the opening 6 protrudes above a groove forming portion 22 forming the groove 16. The height of the opening forming portion 21 in the Z direction should match the thickness of the thinned portion 7.

[0031] After the respective elements as in Fig. 5, a resin material 3a is poured into the mold 10 and a cavity is filled with the resin material 3a. Subsequently, the resin material 3a is cooled and allowed to harden. When a sealed semiconductor chip intermediate product is then removed from the mold 10 and the land is cut off, the Fig. 1 to 4 enclosed in the resin 3.

[0032] In a cooling process in which the resin material 3a is brought into the cured state when poured into the mold 10, a shrinkage force acts on the first semiconductor chip 2 due to the shrinkage of the resin material 3a and the lead frame 4. That is, a compressive force acts on the outer peripheral surface of the first semiconductor chip 2 during resin molding. Fig. 6 is a diagram showing a compressive force acting on the diaphragm of the flow rate sensor in the X direction during resin molding, and Fig. Figure 7 is a diagram showing a compressive force acting on the diaphragm of the flow rate sensor in the Y direction during resin molding.

[0033] The metal lead frame 4 and the resin 3 have larger linear expansion coefficients than the first semiconductor chip 2 made of a semiconductor material such as silicon. Therefore, during the cooling process, a load due to shrinkage of the lead frame 4 and the resin 3 acts on the first semiconductor chip 2. In particular, the diaphragm 1 is easily warped by the compressive force because of its thin thickness. If the diaphragm 1 is deformed by warping or the like, the accuracy of detecting the gas flow rate is reduced.

[0034] According to the present embodiment, the groove 16, as shown in the Fig. 6 and Fig. 7, is formed on the outer periphery of the opening 6, and the thinned portion 7 is formed on the resin 3 in a region opposite to the outer periphery portion in the vicinity of the diaphragm 1.

[0035] When the linear expansion coefficient of the lead frame 4 is larger than the linear expansion coefficient of the resin 3, due to the formation of the thinned portion 7, a side of the lead frame 4 constrained by the resin 3 and opposite to the thinned portion 7 tends to shrink.

[0036] Fig. Figure 8 is a diagram showing the bending deformation acting on the diaphragm of the flow rate sensor due to shrinkage during resin molding.

[0037] When the side of the lead frame 4 opposite the thinned section 7 shrinks, as shown in Fig. As shown in Fig. 8, the bending deformation caused by the upper surface 2a of the first semiconductor chip 2 becoming convex is applied to the first semiconductor chip 2 in a direction that cancels the concave deformation caused by the deformation of the diaphragm 1 in a direction toward the cavity portion 9. Therefore, the shrinkage force acting on the diaphragm 1 is reduced, and the warpage of the diaphragm 1 is prevented. When the linear expansion coefficient of the resin 3 is smaller than the linear expansion coefficient of the lead frame 4, the deformation of the diaphragm 1 is substantially prevented.

[0038] In a related-art flow rate sensor, the thinned portion 7 is not formed on the bottom resin portion 13b, and the outer surface of the opening 6 is uniformly thicker than the thinned portion 7. In other words, the opening 6 is formed rectangularly concave from the bottom surface of the bottom resin portion 13b. When the thickness of the resin 3 is thick, its rigidity increases, so that the shrinkage of the bottom surface of the lead frame 4 is smaller than in the embodiment having the thinned portion. Therefore, bending deformation in which the top surface 2a of the first semiconductor chip 2 is convex is unlikely to occur. Therefore, compared with the flow rate sensor according to the embodiment, concave deformation toward the cavity portion 9 is likely to occur on the diaphragm 1.

[0039] With reference to Fig. 6, a region of the thinned portion 7 of the resin 3 on the underside of the diaphragm 1 in the X direction is described. The positional relationship of the respective parts is described below as a perspective view of the flow rate sensor viewed from above.

[0040] The thinned portion 7 of the resin 3 on the underside of the diaphragm 1 is formed in a region facing the outer peripheral portion of the diaphragm 1 within the cavity portion 9 and an outer peripheral portion near the outside of the cavity portion 9. According to this configuration, the tensile force due to the bending deformation, with the top surface of the first semiconductor chip 2 having the diaphragm 1 convex on an XZ plane, is likely to act on the entire surface of the diaphragm 1. Therefore, as shown in Fig. 6, it is desirable that the dimension L RXof the thinned section 7 of the resin 3 in the X direction on the underside of the membrane 1 is larger than the dimension L DX of the membrane 1 in the X direction.

[0041] With reference to Fig. 7, the area of the thinned portion 7 of the resin 3 on the underside of the diaphragm 1 in the Y direction is described. The thinned portion 7 of the resin 3 on the underside of the diaphragm 1 is formed in an area opposite to the outer peripheral portion of the diaphragm 1 within the cavity portion 9 and the outer peripheral portion near the outside of the cavity portion 9. According to this configuration, the tensile force due to bending deformation, with the top surface of the first semiconductor chip 2 having the diaphragm 1 convex on a YZ surface, is likely to act on the entire surface of the diaphragm 1. Therefore, it is desirable that the dimension L RYof the thinned section 7 of the molding resin in the Y direction on the underside of the membrane 1 is larger than the dimension L DY of membrane 1 in Y-direction.

[0042] Fig. 6 is with Fig. 7 compared.

[0043] As in Fig. 6, in the X-direction, an upper region on one side of the first semiconductor chip 2 and an upper region on the other side opposite to one side are covered by the raised portion 12. On the other hand, as shown in Fig. As shown in Fig. 7, the surface 15a of the lower rear portion 15 of the resin 3 in the Y direction coincides with the upper surface 2a of the first semiconductor chip 2, and the first semiconductor chip 2 is not covered with the resin 3. Therefore, the force acting on the first semiconductor chip 2 in the X direction due to the shrinkage force of the resin 3 is larger than that acting in the Y direction. Therefore, in order to reduce the load acting on the first semiconductor chip 2, it is necessary to make the bending deformation at which the upper surface 2a of the first semiconductor chip 2 is convex larger on the XZ surface than on the YZ surface.

[0044] In other words, it is necessary to make the bending on the XZ plane, at which the top surface 2a of the first semiconductor chip 2 becomes convex, easier than the bending on the YZ plane.

[0045] For this purpose, the length of the thinned portion 7 in the Y direction must be increased more than in the X direction. It is assumed that setting the length of the thinned portion 7 in the X direction to be approximately equal to the length in the Y direction will only reduce the rigidity of the resin 3 and not achieve any advantage. Therefore, it is desirable that the length L RY of the thinned section 7 of the resin 3 in the Y direction is greater than the length L RX in the X direction. In other words, it is desirable that the thinned portion 7 may have a shape in which the length in a direction along the opening portion 8 of the resin 3, that is, in a direction in which the gas flows, is greater than the length in a direction orthogonal to the direction along the opening portion 8.

[0046] According to the present embodiment, the thinned portion 7 is shown as having a rectangular shape as described above, however, as long as the thinned portion 7 of the resin 3 has a shape in which the length L RY in the Y direction is greater than the length L RX in the X direction, an elongated polygonal shape with five or more vertices or sides, or an elliptical shape.

[0047] According to the present embodiment, the following effects can be achieved.

[0048] (1) In the flow rate sensor 100 having the resin 3 covering the lead frame 4 and the first semiconductor chip 2, with at least a part of the flow rate detection unit formed on one surface of the diaphragm 1 exposed from the opening portion, the bottom resin portion 13b of the resin 3 covering the other side of the lead frame 4 has, on the opposite side in the area facing the outer peripheral portion of the diaphragm 1, the thinned portion 7 that is thinner than its surroundings. With such a configuration, the side of the lead frame 4 constrained by the resin 3, which faces the thinned portion 7, tends to shrink, and bending deformation in the direction in which the deformation acting on the diaphragm 1 due to the shrinkage of the resin 3 is reduced, acts on the diaphragm 1.Therefore, the deformation of the diaphragm 1 and the resulting deterioration of the detection accuracy can be prevented.

[0049] (2) The thinned portion 7 extends from a position facing the inside of the cavity portion 9 provided below the diaphragm 1 to a position facing the outside of the cavity portion 9. That is, the thinned portion 7 is formed in a region facing the outer peripheral portion near the diaphragm 1. Therefore, the bending deformation can be effectively applied to the diaphragm 1.

[0050] (3) The top-side resin portion 13a covering one side of the lead frame 4 includes the first raised portion 12a covering a side edge of the first semiconductor chip 2 and the second raised portion 12b provided separately from the first raised portion 12a, with the opening portion 8 sandwiched therebetween and covering a region on the opposite side to the region of the first semiconductor chip 2, wherein the thinned portion 7 has a shape in which the length along the opening portion 8 in the fluid flow direction is greater than the length in the direction orthogonal to the direction along the opening portion 8.Therefore, the depth of the gas flow guiding opening portion 8 is increased, so that in the flow rate sensor 100 in which the raised portion 12 is provided on the resin 3, the bending deformation can be effectively applied to the diaphragm 1 while ensuring the rigidity of the resin 3. (First modification)

[0051] Fig. 9 shows a flow rate sensor according to the first modification of the invention, which is a plan view viewed from the back of the flow rate sensor.

[0052] In the flow rate sensor 100 shown in the first modification, the thinned portion 7 has a cross shape in a plan view. As the area of the thinned portion 7 increases, the rigidity of the resin 3 and the strength of the flow rate sensor 100 decrease. Therefore, it is necessary to reduce the area of the thinned portion 7 and effectively prevent the deformation of the diaphragm 1. As shown in Fig. 9, when the thinned portion 7 is cross-shaped in plan view, the proportion (area) of an area occupied by the thinned portion 7 in the resin 3 can be made smaller than in the case shown in Fig. 2 shown rectangular shape.

[0053] The Fig. The cross shape shown in Fig. 9 has a vertical portion extending in the Y direction, which is the direction along the opening portion 8, and a horizontal portion extending in the X direction, which is the direction perpendicular to the Y direction, and the intersection point between the vertical portion and the horizontal portion is located at a position opposite to the central region of the diaphragm 1. Further, the length of the vertical portion of the thinned portion 7 is greater than the length of the horizontal portion. Therefore, as described above, in a structure including the pair of raised portions 12a, 12b extending in the Y direction, which is the direction along the opening portion 8, the bending deformation in which the top surface 2a of the first semiconductor chip 2 is convex is larger in the XZ plane than in the YZ plane.

[0054] Other configurations of the first modification are similar to those according to the above embodiment.

[0055] Therefore, the flow rate sensor 100 according to the first modification also has the same effects (1) to (3) as those according to the above embodiment.

[0056] In the flow rate sensor 100 according to the first modification, since the area of the thinned portion 7 can be made smaller than in the above embodiment, the deformation of the diaphragm 1 can be prevented while ensuring the rigidity of the resin 3. (Second modification)

[0057] Fig. 10 shows a flow rate sensor according to the second modification of the invention, which is a plan view viewed from the back of the flow rate sensor.

[0058] The thinned section 7 of the Fig. 10 has a shape which is obtained by deforming the Fig. 9, wherein a cross-shaped stepped portion 31 is formed around the intersection of the vertical and horizontal portions. The stepped portion 31 faces the outer peripheral portion near the cavity portion 9 of the diaphragm 1.

[0059] Other configurations of the second modification are similar to those of the first modification.

[0060] Therefore, the flow rate sensor 100 of the second modification also has the same effects as those of the first modification. (Third modification)

[0061] The Fig. 11(a) and Fig. 11(b) show a flow rate sensor according to the third modification of the invention, wherein Fig. 11(a) a Fig. 3 corresponding sectional view and Fig. 11(b) a Fig. 4 is the corresponding sectional view.

[0062] The flow rate sensor 100 of the third modification differs from the above embodiment in that the side surface 6a of the Fig. 3 and the side surface 16a of the thinned section 7 shown in Fig. 4 are formed as inclined surfaces 6b and 16b, respectively, which extend outwards in the thickness direction of the thinned portion 7.

[0063] By arranging the side surface of the thinned portion 7 and the side surface of the groove as the inclined surfaces 6b, 16b, air entrapment voids during resin molding can be prevented and the releasability when removing the flow rate sensor from the mold 10 can be improved.

[0064] Other configurations of the third modification are similar to those according to the above embodiment, and corresponding elements are designated by the same reference numerals, and their description is omitted.

[0065] The flow rate sensor 100 according to the third modification also has the same effects (1) to (3) as those according to the above embodiment. (Fourth modification)

[0066] Fig. 12 shows a flow rate sensor according to the fourth modification of the invention, which is a plan view viewed from the top of the flow rate sensor.

[0067] The flow rate sensor 100 of the fourth modification differs from the above embodiment in that the two raised portions 12a, 12b formed on the upper-side resin portion 13a are connected at two end portions in the Y direction by connecting portions 12c. In this way, the raised portions 12a, 12b can be formed continuously as a whole.

[0068] It should be noted that one of the two connecting portions 12c may not be formed, so that an open arrangement is formed.

[0069] Other configurations of the fourth modification are similar to those according to the above embodiment.

[0070] Therefore, the flow rate sensor 100 according to the fourth modification also has the same effects (1) to (3) as those according to the above embodiment. (Fifth Modification)

[0071] Fig.13 shows a flow rate sensor according to the fifth modification of the invention, which is a plan view viewed from the top of the flow rate sensor.

[0072] The flow rate sensor 100 of the fifth modification differs from the above embodiment in that the two raised portions 12a, 12b formed on the upper-side resin portion 13a have such a length that they do not reach both end portions in the Y direction.

[0073] At both end portions in the Y direction where the raised portions 12a, 12b are not formed, the opening portion 8 is formed by a step portion between the base portion 14 and the lower rear portion 15.

[0074] As described above, the raised portions 12a, 12b may not have a configuration in which the length extends over the entire Y direction.

[0075] Other configurations of the fifth modification are similar to those according to the above embodiment.

[0076] Therefore, the flow rate sensor 100 according to the fifth modification also has the same effects (1) to (3) as those according to the above embodiment.

[0077] According to the above embodiment, the flow rate sensor 100 is an example of the configuration including the first semiconductor chip 2 and the second semiconductor chip 5. However, a flow rate sensor including a semiconductor chip can be obtained by providing a control circuit of the flow rate detection unit on the first semiconductor chip 2.

[0078] According to the above embodiment and each modification, the resin 3 of the flow rate sensor 100 is exemplified as being provided with the raised portion 12. However, a flat structure may be formed in which the raised portion 12 is not formed and the entire portion has the thickness of the base portion 14. Even in this case, however, it is preferable that the surface 15a of the lower rear portion 15 be flush with the upper surface 2a of the diaphragm 1 so that the gas can flow smoothly in the opening portion 8, which forms the flow passage of the gas.

[0079] A through hole extending in the thickness direction (Z direction) may be formed in a portion of the lead frame 4 opposite to the cavity portion 9, and the inside of the cavity portion 9 may always be open to the outside so that no pressure difference occurs between the area inside and outside the cavity portion 9.

[0080] The above embodiment and the above modifications can be combined with each other.

[0081] Although various embodiments and modifications have been described above, the invention is not limited to the contents of the embodiments and modifications. List of reference symbols 1 membrane 2 first semiconductor chip (semiconductor chip) 3 resin 4 ladder frames 5 second semiconductor chip 6 Opening 6a side surface 6b inclined surface 7 thinned section 8 Opening section (flow passage opening section) 9 Cavity section 12 elevated section 12a first elevated section 12b second elevated section 13a upper resin section 13b underside resin section 16b inclined surface 31 step section 100 flow rate sensor L DY Dimension of membrane 1 in Y direction L DX Dimension of membrane 1 in X-direction L RX Dimension of the thinned section 7 in X-direction L RY Dimension of the thinned section 7 in Y direction

Claims

[1] Flow rate sensor (100) comprising: a ladder frame (4), a semiconductor chip (2) arranged on a surface of the lead frame (4) and in which a membrane (1) having a cavity portion (9) on the lead frame side is formed, a flow rate detection unit formed on the one surface having the membrane (1) of the semiconductor chip (2), and a resin (3) having a flow passage opening portion (8) exposing at least a part of the flow rate detection unit formed on the diaphragm (1) and covering the lead frame (4) and the semiconductor chip (2), wherein a lower side portion (13b) of the resin (3) covering another side arranged opposite to one side of the lead frame (4) has a thinned portion (7) which is thinner in an area facing an outer peripheral portion of the diaphragm (1) than in its outer region, and wherein the thinned portion (7) extends from a position facing the inside of the cavity portion (9) provided below the membrane (1) to a position facing the outside of the cavity portion (9), characterized by that an opening (6) is provided in an area of the thinned portion (7) which faces a central region of the membrane (1). [2] Flow rate sensor (100) comprising: a ladder frame (4), a semiconductor chip (2) arranged on a surface of the lead frame (4) and in which a membrane (1) having a cavity portion (9) on the lead frame side is formed, a flow rate detection unit formed on the one surface having the membrane (1) of the semiconductor chip (2), and a resin (3) having a flow passage opening portion (8) exposing at least a part of the flow rate detection unit formed on the diaphragm (1) and covering the lead frame (4) and the semiconductor chip (2), wherein a lower side portion (13b) of the resin (3) covering another side arranged opposite to one side of the lead frame (4) has a thinned portion (7) which is thinner in an area facing an outer peripheral portion of the diaphragm (1) than in its outer region, characterized bythat a top-side portion (13a) of the resin (3) covering the one side of the lead frame (4) has a first raised portion (12a) covering a region on one side of the semiconductor chip (2), and a second raised portion (12b) provided separately from the first raised portion (12a), the flow passage opening portion (8) being sandwiched therebetween and covering a region on the side opposite to the region on the one side of the semiconductor chip (2), and the thinned portion (7) has a shape in which the length (L RY ) along the flow passage opening portion (8) extending in a direction in which a fluid to be detected flows is greater than the length (L RX ) in a direction orthogonal to the direction extending along the flow passage opening portion (8). [3] The flow rate sensor (100) according to claim 2, wherein the thinned portion (7) has a polygonal shape having four or more vertices or sides or an elliptical shape in a plan view. [4] The flow rate sensor (100) according to claim 2, wherein the thinned portion (7) has a cross shape including a vertical portion extending in the direction along the flow passage opening portion (8) and a horizontal portion extending in the direction orthogonal to the direction along the flow passage opening portion (8). [5] The flow rate sensor (100) according to claim 4, wherein the thinned portion (7) is provided with a shape having a step portion (31) connecting the vertical portion and the horizontal portion at an intersection point between the vertical portion and the horizontal portion. [6] The flow rate sensor (100) according to claim 1 or 2, wherein the inner side surface and the outer side surface of the thinned portion (7) are inclined and extend outward in the thickness direction of the resin (3). [7] The flow rate sensor (100) according to any one of claims 1 to 6, wherein the linear expansion coefficient of the resin (3) is smaller than the linear expansion coefficient of the lead frame (4).

Images