Method Of Bonding A Piezoelectric Ultrasonic Transducer

Abstract

A method of bonding an electrode of a piezoelectric ultrasonic transducer to an electrically conductive layer of a support substrate, in order to support the piezoelectric ultrasonic transducer and establish an electrical connection between the electrode and the electrically conductive layer. The method includes: roughening the surface of one or both of the electrode and the electrically conductive layer; applying an adhesive to one or both of the electrode and the electrically conductive layer; assembling the electrode and the electrically conductive layer; and curing the adhesive. An assembly, an ultrasonic flow meter, and surface mount technology assembly is also disclosed.

Claims

1. A method of bonding an electrode of a piezoelectric ultrasonic transducer to an electrically conductive layer of a support substrate to support the piezoelectric ultrasonic transducer and establish an electrical connection between the electrode and the electrically conductive layer; the method comprising: applying the electrically conductive layer to the support substrate, roughening the surface of one or both of the electrode and the electrically conductive layer; applying an adhesive to one or both of the electrode and the electrically conductive layer; assembling the electrode and the electrically conductive layer; and curing the adhesive.

2. The method according to claim 1, wherein said surface(s) of one or both of the electrode and the electrically conductive layer is/are substantially flat.

3. The method according to claim 1, wherein the adhesive is an electrically non-conductive adhesive.

4. The method according to claim 1, wherein the adhesive contains less than 10% by volume of electrically conductive particles.

5. The method according to claim 1, wherein the adhesive is curable at ambient temperatures between 10 C. and 80 C.

6. The method according to claim 1, wherein said roughening increases the roughness of the surface the electrode or the electrically conductive layer.

7. The method according to claim 1, wherein said roughening of said electrode is performed as post-processing on said electrode of said piezoelectric ultrasonic transducer.

8. The method according to claim 1, wherein the roughening of the electrically conductive layer is performed by applying the electrically conductive layer to a roughened surface of the support substrate.

9. The method according to claim 1, wherein the roughening of one or both of the electrode and the electrically conductive layer is performed by sand blasting or rasping or sanding with an abrasive.

10. The method according to claim 1, wherein the roughening of one or both of the electrode and the electrically conductive layer is performed by laser ablation.

11. The method according to claim 1, wherein the roughening of one or both of the electrode and the electrically conductive layer is performed by electrical discharge machining.

12. The method according to claim 1, wherein the roughening comprises forming elevated surface structures on a surface.

13. The method according to claim 1, wherein said method comprises providing an ultrasonic transducer housing for an ultrasonic flow meter, the ultrasonic transducer housing being formed by electrically non-conductive material and said support substrate forming one or more support surfaces for one or more piezoelectric ultrasonic transducers and the one or more support surfaces being at least partly covered by one or more of said electrically conductive layers; performing said assembling, subsequently to said roughening and applying an adhesive, by placing each of said one or more piezoelectric ultrasonic transducers on said one or more support surfaces so that a first electrode of each of the one or more piezoelectric ultrasonic transducers is placed as said electrode on said electrically conductive layer.

14. An ultrasonic flow meter comprising: two piezoelectric ultrasonic transducers each comprising a first and a second electrode; an ultrasonic flow meter housing, at least a part of which forms a support substrate for supporting said two piezoelectric ultrasonic transducers on an electrically conductive layer of the support substrate; an adhesive applied between said electrically conductive layer and said first electrode; wherein one or both of said electrically conductive layer and said first electrode of each piezoelectric ultrasonic transducer has a roughened surface.

15. The method according to claim 1, wherein said roughening the electrically conductive layer is performed during or before manufacture of the electrically conductive layer.

16. The method according to claim 1, wherein said electrode is a first electrode and said piezoelectric ultrasonic transducer further comprises a second electrode.

17. The method according to claim 16, wherein said first and second electrodes are located on opposite sides of said piezoelectric ultrasonic transducer, wherein said piezoelectric ultrasonic transducer comprises a first and a second surface, the first and second being opposite and substantially flat, the first and second surfaces being connected via one or more sides, wherein said first electrode extends over a part of or all of the first surface, and wherein said first electrode does not extend onto said second surface.

18. The method according to claim 1, wherein the support substrate is formed by a non-conductive material.

19. The method according to claim 1, wherein the support substrate forms part of an ultrasonic transducer housing.

20. An assembly of a support substrate and a piezoelectric ultrasonic transducer, the assembly comprising: the support substrate having an electrically conductive layer; the piezoelectric ultrasonic transducer having an electrode; and an adhesive applied between said electrically conductive layer and said electrode; wherein one or both of said electrically conductive layer and said electrode has a roughened surface.

21. The assembly according to claim 20, wherein said assembly forms part of an ultrasonic flow meter, the support substrate forming one or more support surfaces for one or more piezoelectric ultrasonic transducers; said electrode comprising a first electrode of said piezoelectric ultrasonic transducers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0150] The invention will in the following be described with reference to the drawings where

[0151] FIGS. 1A-C illustrate a method of bonding a piezoelectric ultrasonic transducer UT to an electrically conductive layer ECL of a support substrate SS according to an embodiment of the invention,

[0152] FIG. 2 illustrates a piezoelectric ultrasonic transducer UTbonded to an electrically conductive layer ECL of a support substrate SS according to an embodiment of the invention,

[0153] FIG. 3 illustrates a piezoelectric ultrasonic transducer UTbonded to an electrically conductive layer ECL of a support substrate SS according to an embodiment of the invention,

[0154] FIG. 4 illustrates an electronic component EC bonded to an electrically conductive layer ECL of a support substrate SS according to an embodiment of the invention,

[0155] FIG. 5 illustrates an electronic component EC bonded to an electrically conductive layer ECL of a support substrate SS according to an embodiment of the invention,

[0156] FIG. 6 illustrates an ultrasonic flow meter UM in an exploded perspective view according to an embodiment of the invention,

[0157] FIGS. 7A-B illustrate an ultrasonic flow meter UM in a cross-sectional side view and an exploded view of the fixation of one of the ultrasonic transducers according to an embodiment of the invention,

[0158] FIGS. 8A-C illustrate surfaces of an electrode ELEC or an electrically conductive layer ECL according to different embodiments of the invention,

[0159] FIGS. 9A-B illustrate surfaces of an electrode ELEC or an electrically conductive layer ECL according to different embodiments of the invention,

[0160] FIGS. 10A-B illustrate a surface of an electrode ELEC or an electrically conductive layer ECL according to an embodiment of the invention,

[0161] FIGS. 11A-B illustrate a surface of an electrode ELEC or an electrically conductive layer ECL according to an embodiment of the invention, and

[0162] FIG. 12 illustrates a piezoelectric ultrasonic transducer UT according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0163] FIGS. 1A-C illustrate a method of bonding a piezoelectric ultrasonic transducer to an electrically conductive layer ECL of a support substrate SS according to an embodiment of the invention.

[0164] First, the piezoelectric ultrasonic transducer UT is provided, as illustrated in FIG. 1. The piezoelectric ultrasonic transducer UT comprises a electrode shown as the lower electrode as a first electrode ELEC1, and further comprises a second electrode ELEC2 shown as the upper electrode The first and second electrodes ELEC1, ELEC2 are positioned on opposite sides of the ultrasonic transducer UT. As illustrated on FIG. 1A, the electrodes ELEC1, ELEC2 are substantially flat and smooth, i.e. without any surface roughness or structures. The piezoelectric ultrasonic transducer UT may for example comprise a piezoelectric disk. This is described in relation to other embodiments, as described below.

[0165] The support substrate SS comprises an electrically conductive layer ECL, as also illustrated on FIG. 1A. The support substrate SS and the electrically conductive layer ECL may be substantially flat, as illustrated on FIG. 1A.

[0166] The electrically conductive layer ECL is in FIG. 1A shown as a layer applied to the support substrate SS, but in other embodiments the support substrate SS may be conductive so as to form the electrically conductive layer ECL.

[0167] Then, the first electrode ELEC1 shown in FIG. 1A as the bottom electrode ELEC1 is roughened to obtain an electrode ELEC1 having a roughened surface as shown in FIG. 1B. The roughening creates or induces surface structures STR in the first electrode ELEC1, as illustrated in FIG. 1B. The surface structures STR may comprise peaks, and/or surface structures other than peaks, e.g. ridges, depending on the specific method of roughening. Alternatively, or in combination therewith, the electrically conductive layer ECL may be roughened. This is illustrated in FIGS. 2 and 3, respectively.

[0168] An adhesive ADH is applied to the electrically conductive layer ECL. In certain alternative embodiments, the adhesive ADH is applied to the first electrode ELEC1 instead of or in combination with being applied to the electrically conductive layer ECL.

[0169] Finally, the first electrode ELEC1 and the electrically conductive layer ECL are assembled and the adhesive ADH is cured to obtain a bonded piezoelectric ultrasonic transducer UT on the electrically conductive layer ECL of the support substrate SS. The piezoelectric ultrasonic transducer UT is illustrated in FIG. 10.

[0170] As shown in FIG. 10, electrical connection is established between the first electrode ELEC1 and the electrically conductive layer ECL due to a number of surface structures STR made by the roughening.

[0171] Also, as illustrated in FIG. 10, the piezoelectric ultrasonic transducer UT is supported on the electrically conductive layer ECL of the support substrate SS.

[0172] As can be seen on FIG. 10, a certain amount of excess adhesive ADH has been pushed out from the space between the ultrasonic transducer UT and the electrically conductive layer ECL. In order for the excess adhesive ADH not to make unintended electrical contact, the adhesive ADH may preferably be electrically non-conductive. This may be especially advantageous when the amount of excess adhesive ADH is larger than shown in FIG. 10.

[0173] Now, referring to FIG. 2, a further embodiment of the invention is illustrated. As shown in FIG. 2, the electrically conductive layer ECL, not the electrode ELEC1, has been roughened to create peaks or other types of surface structures STR establishing electrical connection between the first electrode ELEC1 and the electrically conductive layer ECL.

[0174] Now, referring to FIG. 3, a further embodiment of the invention is illustrated. As shown in FIG. 3, both the electrically conductive layer ECL and the first electrode ELEC1 have been roughened to create surface structures STR establishing electrical connection between the first electrode ELEC1 and the electrically conductive layer ECL. In this context it should be understood that the roughening of the electrically conductive layer ECL and the roughening of the first electrode ELEC1 may be performed by the same technique, or by different techniques, depending on the specific situation and circumstances.

[0175] The method of bonding embodiments illustrated on FIGS. 2 and 3 may be performed in accordance with the embodiment illustrated on FIGS. 1A-C. Only, as an alternative or in addition to roughening the first electrode ELEC1, the electrically conductive layer ECL is roughened.

[0176] For example, similar to the embodiment of FIGS. 1A-C, an adhesive ADH may be applied to the electrically conductive layer ECL and/or to the first electrode ELEC1.

[0177] Furthermore, the principle illustrated for a piezoelectric ultrasonic transducer UT on FIGS. 1A-C, FIGS. 2 and/or 3 may in some embodiments apply for other types of electronic components EC.

[0178] The support substrate SS and the electrically conductive layer ECL thereon illustrated on FIGS. 1A-C and FIGS. 2 and 3 may be substantially flat and smooth, i.e. without any curvature or surface structure, before the roughening.

[0179] Now referring to FIGS. 4 and 5, further embodiments of the invention is illustrated. On both FIGS. 4 and 5, the electronic component EC comprises two electrodes ELEC, illustrated to the right and left, respectively. In both FIGS. 4 and 5 the electrodes ELEC are bonded an electrically conductive layer ECL of the support substrate SS.

[0180] For both embodiments, the electrically conductive layer ECL for the left electrode ELEC and the electrically conductive layer ECL for the right electrode ELEC are separated, as illustrated, and electrically insulated from each other to avoid short circuiting. The electrical insulation e.g. may be facilitated by the support substrate SS being electrically insulating or by the two electrically conductive layers ECL being attached to separate support substrates SS.

[0181] Now, referring to FIG. 6 an ultrasonic flow meter UM is shown according to an embodiment of the invention. The ultrasonic flow meter UM is shown in an exploded view.

[0182] The ultrasonic flow meter UM comprises a housing HOU, a flow conduit FC, a flow tube FT, two ultrasonic transducers UT. The ultrasonic flow meter UM may comprise further components, such as e.g. a display for displaying consumption data and/or other relevant data, such as information relating to the operation status. The electronic circuit CIR may comprise an antenna and electronic components allowing the ultrasonic flow meter UM to transmit and/or receive data, for example to transmit consumption data to an external receiver.

[0183] The housing HOU may be assembled on the flow conduit FC in different ways, e.g. by means of locking pins (not shown) or other suitable methods. The flow tube FT may be inserted into the flow conduit where it may be fixated.

[0184] The flow tube FT may comprise ultrasonic reflector (not shown) for reflecting an ultrasound signal transmitted by one of the two ultrasonic transducers UT onto the other ultrasonic transducer UT and vice versa, i.e. whereby the ultrasonic reflectors establishes a path for the ultrasound signal from one of the two ultrasonic transducers UT to the other ultrasonic transducer UT, and vice versa.

[0185] In some embodiments the ultrasonic flow meter UM may not comprise a flow tube FT. In such embodiments, the ultrasonic reflectors (not shown) should be provided in other ways, or the flow conduit FC or another insert therein should function as an ultrasonic reflector, i.e. reflecting the ultrasound signal.

[0186] The ultrasonic transducers UT are bonded to an electrically conductive layer (not shown) on part of the inside of the housing HOU. One way this can be performed is illustrated on FIGS. 7A-B.

[0187] Now referring to FIGS. 7A-B, an ultrasonic flow meter UM according to an embodiment of the invention is illustrated. The ultrasonic flow meter UM may be similar to the ultrasonic flow meter UM described in relation with FIG. 6.

[0188] As illustrated in FIG. 7A, the ultrasonic flow meter UM comprises ultrasonic reflectors UR for establishing a path for the ultrasound from one ultrasonic transducer UT to the other via the ultrasonic reflectors UR (the path is shown as the dashed line. In FIG. 7A, the ultrasonic flow meter UM comprises three ultrasonic reflectors UR. In alternative embodiments, the ultrasonic flow meter UM may comprise only a single ultrasonic reflector UR, two ultrasonic reflectors UR, or even three or more ultrasonic reflectors UR, such as four or five ultrasonic reflectors UR.

[0189] Also illustrated is that the ultrasonic flow meter UM comprises a battery BAT for powering the ultrasonic flow meter UM including its components, such as the electronic circuit CIR and the ultrasonic transducers UT. Other power sources may be used as an alternative to or in combination with batteries, such other power sources comprising e.g. solar cells, power grid, etc.

[0190] The electronic circuit CIR is a control circuit adapted to control the ultrasonic flow meter UM, including the transmission and reception of ultrasound signal by the ultrasonic transducers UT, and the display DIS and any communication to external receivers.

[0191] The ultrasonic flow meter UM further comprises a display DIS for displaying consumption data and/or other relevant data, such as information relating to the operation status.

[0192] The ultrasonic flow meter UM may be of the transit time type flow meter measuring the difference between the transit time of the ultrasound from one ultrasonic transducer to the other ultrasonic transducer and vice versa.

[0193] The electrodes of the ultrasonic transducer UT are separately connected to the electronic circuit CIR.

[0194] On FIG. 7B the fixation of one of the ultrasonic transducers UT is illustrated in more detail. The electronic transducer UT comprises a first and electrode ELEC1 facing downwards and a second electrode ELEC2 facing upwards. As seen, the surface of the first electrode ELEC1 is shown as with a roughened surface. Thus, the first electrode ELEC1 of the ultrasonic transducer UT may be bonded to the electrically conductive layer ECL of the support substrate SS in a similar way to the illustrated embodiments of FIGS. 1A-C or any of the alternative embodiments illustrated on FIGS. 2-3.

[0195] The first electrode ELEC1 shown as the bottom electrode on FIG. 7B is connected to the electronic circuit CIR via the electrically conductive layer ECL and via an electrical connector CON. The second electrode ELEC2 shown as the upper electrode in FIG. 7B is connected to the electronic circuit CIR via a further electronic connected CON, which may comprise a spring connector. As shown in FIG. 7A, bottom electrodes (not shown) of the two ultrasonic transducers UT shown in FIG. 7A are connected to the electronic circuit CIR via a common electrically conductive layer ECL and a common electrical connector CON. In certain alternative embodiments separate electrically conductive layers ECL and electrical connectors CON may be utilized.

[0196] It should be noted, though, that not all dimensions, if any, shown in FIGS. 1-7 are drawn to scale, but that some dimensions are enlarge or decreased for illustrative purposes. For example the thickness of the electrically conductive layer ECL, the thickness of the adhesive ADH, the thickness of the electrodes ELEC1, ELEC2, and the size of the structures STR are for most embodiments enlarged relative to actual dimensions.

[0197] Referring to FIGS. 8A-C, illustrations of cross-sectional side view profiles of surfaces of an electrode ELEC or an electrically conductive layer ECL with surface structures STR created by roughening is shown according to different embodiments of the invention.

[0198] FIG. 8A shows a number of surface structures STR extending from the surface of the electrode ELEC or electrically conductive layer ECL. In some embodiments, the surface structures STR may for example be line-formed structures, e.g. similar to what is illustrated on FIG. 9A. In other embodiments, the surface structures STR may be peaks having cone-like or frustrated cone-like shapes, e.g. similar to those illustrated on FIG. 9B.

[0199] FIG. 8B shows a number of surface structures STR extending from the surface of the electrode ELEC or electrically conductive layer ECL. In some embodiments the surface structures STR may form lines, whereas in other embodiments the surface structures STR have statistically similar cross-sections in all direction. The latter may for example be made using the technique electronic discharge machining, EDM.

[0200] FIG. 8C shows a number of surface structures STR extending from the surface of the electrode ELEC or electrically conductive layer ECL. In some embodiments the surface structures STR may form lines, whereas in other embodiments the surface structures STR have statistically similar cross-sections in all direction.

[0201] Now referring to FIG. 9A, an illustration of a surface of an electrode ELEC with surface structures STR created by roughening is shown in a perspective view according to an embodiment of the invention. The surface structures STR on FIG. 9A are formed as lines on the surface of the electrode ELEC, i.e. as linear or near-linear formed elevations on the surface of the electrode ELEC. It should be emphasized that FIG. 9A is for illustrative purposes only and that the dimensions therefore not necessarily are realistic. For example, in some embodiments the ratio between the average dimension of the surface structure (e.g. the average height) and the average spacing between the surface structures may be different compared to what is shown on FIG. 9A.

[0202] Referring to FIG. 9B, an illustration of a surface of an electrode ELEC with surface structures STR created by roughening is shown in a perspective view according to an embodiment of the invention. The surface structures STR on FIG. 9B are formed as cones on the surface of the electrode ELEC, i.e. as point-formed cone-shaped elevations on the surface of the electrode ELEC. It should be emphasized that FIG. 9B is for illustrative purposes only and that the dimensions therefore not necessarily are realistic. For example, in some embodiments the ratio between the average dimension of the surface structure (e.g. the average height) and the average spacing between the surface structures may be different compared to what is shown on FIG. 9B.

[0203] Turning to FIGS. 10A and 10B a further example of surface structures STR established by means of roughening a surface of an electrode ELEC or an electrically conductive layer ECL is shown according to an embodiment of the invention. FIG. 10A shows a cross-sectional side view of a surface of an electrode ELEC or an electrically conductive layer ECL, whereas FIG. 10B shows a perspective view of the same.

[0204] The surface structures STR shown in FIGS. 10A and 10B may be an example of surface structures which may be made by means of laser machining, such as machining by continuous or pulsed lasers. Especially the use of pulsed lasers with pulse lengths in the nanosecond range or longer may be applicable.

[0205] On FIGS. 11A and 11B another example of surface structures STR established by means of roughening a surface of an electrode ELEC or an electrically conductive layer ECL is shown according to an embodiment of the invention. FIG. 11A shows a cross-sectional side view of a surface of an electrode ELEC or an electrically conductive layer ECL, whereas FIG. 11B shows a perspective view of the same.

[0206] The surface structures STR shown in FIGS. 11A and 11B may for example be an example of surface structures which may be made by means of abrasion by sandpaper or by a pointed or sharp object, such as a diamond-tipped object.

[0207] Now, referring to FIG. 12, a piezoelectric ultrasonic transducer UT according to an embodiment of the invention is illustrated.

[0208] The piezoelectric ultrasonic transducer UT comprises a piezoelectric disk having a first and a second surface SUR1, SUR2, the first and second surfaces SUR1, SUR2 being opposite and substantially flat. The surfaces SUR1, SUR2 are connected by a single curved side SID, whereby the two surfaces SUR1, SUR2 and the side SID together forms the outer surface of the piezoelectric disk.

[0209] A first electrode ELEC1 has been applied to a part of the first surface SUR1, thus leaving a narrow band of the first surfaces SUR1 exposed and uncovered by the first electrode ELEC1. In some embodiments the first electrode may cover all of the first surfaces SUR1.

[0210] Similarly, second electrode ELEC2 has been applied to a part of the second surface SUR2. The second electrode ELEC2 may cover part of or all of the second surfaces SUR2, similar to what is described for the first electrode ELEC1.

[0211] It is noted that the first electrode ELEC1 and the second ELEC2 of the ultrasonic transducer UT illustrated in FIG. 12 are substantially similar, and that the ultrasonic transducer UT therefore may be used with the first electrode bonded to the electrically conductive layer ECL as illustrated on previous figures, or with the second electrode ELEC2 bonded to the electrically conductive layer ELC.

LIST OF FIGURE REFERENCES

[0212] ELEC. Electrode [0213] ELEC1. First electrode [0214] ELEC2. Second electrode [0215] EC. Electronic component [0216] ECL. Electrically conductive layer [0217] SS. Support substrate [0218] CON. Electrical connector [0219] ADH. Adhesive [0220] UM. Ultrasonic flow meter [0221] UT. Piezoelectric ultrasonic transducer [0222] HOU. Housing [0223] CIR. Electronic circuit [0224] FT. Flow tube [0225] DIS. Display [0226] BAT. Battery [0227] FC. Flow conduit [0228] UR. Ultrasonic reflector [0229] STR. Surface structure [0230] SUR. Surface [0231] SURi. i'th surface [0232] SID. Side