Patent Publication Number: US-2022223488-A1

Title: Semiconductor packages including interface members for welding

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application No. 63/136,238, which was filed Jan. 12, 2021, is titled “Ultrasonic Welding For Integrated Circuits,” and is hereby incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Force sensors are useful to detect one or more forces experienced by a member of interest. In some instances, a force sensor may be useful to detect stress, torque, compression, strain, tension, etc. experienced by the member of interest (e.g., a shaft, strut, beam). To facilitate the detection of these forces, the force sensor (or some component thereof) is mounted to the member so forces experienced by the member may be transferred to the force sensor during operations. 
     SUMMARY 
     Some examples described herein include a semiconductor package. In some examples, the semiconductor package includes a semiconductor die, and a mold compound having a first side, a second side opposite the first side, and an axis extending between the first side and the second side, the mold compound covering the semiconductor die. In addition, the semiconductor package includes an interface member including a first portion and a second portion. The first portion is coupled to the second portion, the first portion is positioned along the first side, the second portion is positioned along the second side, and an engagement of a welding horn with the first portion is adapted to weld the second portion to a surface. 
     In some examples, the semiconductor package includes a semiconductor die that is configured to detect a force. In addition, the semiconductor package includes a mold compound having a first side, a second side opposite the first side, and an axis extending between the first side and the second side. The mold compound covers the semiconductor die. Further, the semiconductor package includes an interface member engaged along the second side of the mold compound and coupled to the semiconductor die. The interface layer includes a mounting pad that is exposed when viewed along the axis from the first side, and the mounting pad is adapted to engage with a horn of a welding device to secure the semiconductor package to a surface. 
     In some examples, the semiconductor package includes a semiconductor die that is configured to detect a force. In addition, the semiconductor package includes an interface member coupled to the semiconductor die. The interface layer includes a first portion that is to engage with a welding horn of a welding apparatus and a second portion that is to weld with a surface of a member of interest, the first portion and the second portion being positioned on opposing sides of the semiconductor die. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a force sensor coupled to a shaft with an ultrasonic welding apparatus according to some examples. 
         FIG. 2A  is a side cross-sectional view of a force sensor for mounting to a member of interest according to some examples. 
         FIG. 2B  is a side cross-sectional view of a force sensor mounted to a member of interest according to some examples. 
         FIG. 3A  is a bottom view of an interface member of a force sensor for mounting to a member of interest according to some examples. 
         FIG. 3B  is a bottom view of an interface member of a force sensor for mounting to a member of interest according to some examples. 
         FIG. 3C  is a bottom view of an interface member of a force sensor for mounting to a member of interest according to some examples. 
         FIG. 3D  is a bottom view of an interface member of a force sensor for mounting to a member of interest according to some examples. 
         FIG. 4  is a side cross-sectional view of a force sensor for mounting to a member of interest according to some examples. 
         FIG. 5  is a side cross-sectional view of a force sensor for mounting to a member of interest according to some examples. 
         FIG. 6  is a side cross-sectional view of a force sensor for mounting to a member of interest according to some examples. 
         FIG. 7  is a side cross-sectional view of a force sensor for mounting to a member of interest according to some examples. 
         FIG. 8  is a side cross-sectional view of a force sensor for mounting to a member of interest according to some examples. 
     
    
    
     DETAILED DESCRIPTION 
     A force sensor may be mounted to a member of interest for detecting (e.g., directly, indirectly) forces within the member. The force sensor is mounted to the member of interest, and forces experienced by the member may be transferred to the force sensor via the mounting. Some mounting devices or techniques may dampen or absorb forces that are transferred from the member of interest thereby causing the force sensor to be less effective at detecting these forces during operations. Thus, mounting the force sensor to the member of interest may have a meaningful effect on the quality of data that may be obtained by the force sensor during operations. 
     Welding techniques, such as ultrasonic welding, offer a quality connection between a force sensor and a member of interest that may allow forces to transfer efficiently and accurately from the member of interest to the force senor during operations. However, the vibrations resulting from ultrasonic welding may damage a force sensor. 
     Accordingly, examples described herein include force sensors that are subjectable to ultrasonic welding processes in order to secure the force sensor to a member of interest (e.g., a rotating shaft, structural beam). In some examples, the force sensors may include an interface layer that is adapted to melt and weld to a mounting surface on the member of interest and to direct vibrations of the welding process away from sensitive components of the force sensor (e.g., semiconductor die, wire bonds, die pad) during a welding operation. Thus, the force sensors described herein may be securely attached to a member of interest via ultrasonic welding without causing damage to the force sensor. 
     Referring now to  FIG. 1 , a force sensor  100  according to some examples is shown mounted to a shaft  102  that is rotatable about a central or longitudinal axis  104 . The shaft  102  may be a rotating shaft of a pump, compressor, drivetrain or other mechanical system. The force sensor  100  is mounted to a mounting surface  106  which may include a planar or facetted surface that is defined on the otherwise curved outer surface  108  of shaft  102 . 
     During operations, the force sensor  100  may detect, via the engagement with mounting surface  106 , the forces experienced by the shaft  102 . For instance, the shaft  102  may experience a torque about longitudinal axis  104 , axial stress (e.g., from tension or compression along longitudinal axis  104 ), bending stress, strain, etc. These various forces and stresses that may be experienced by the shaft  102  may be collectively and generally referred to herein as “forces.” The force sensor  100  may detect (e.g., directly or indirectly) any one or more of these forces during operations thereby allowing personnel to monitor the operating conditions of the shaft  102 . 
     In some examples, the force sensor  100  may be welded to the mounting surface  106  with an ultrasonic welding apparatus  110 . The ultrasonic welding apparatus  110  includes a transducer  112 , a converter  114 , a booster  116 , a sonotrode  118 , and a welding horn  120 . The transducer  112  and converter  114  are adapted to convert an electrical signal (e.g., a high frequency electrical signal) into vibrations. The vibrations are transferred to the booster  116  which may transform and boost the amplitude of vibrations that are subsequently transferred to the sonotrode  118 . The sonotrode  118  may be integrated with or coupled to the welding horn  120 . During operations, the sonotrode  118  and welding horn  120  may vibrate based on the output from booster  116 . A piston  122  may apply pressure to the ultrasonic welding apparatus  110  that presses the welding horn  120  into the force sensor  100 . With welding horn  120  pressed into engagement with force sensor  100 , the vibrations of welding horn  120  may cause the force sensor  100  (or a member or component thereof) to be welded to the mounting surface  106  of shaft  102 . Further details of the ultrasonic welding process and the structure of examples of force sensor  100  that facilitate the ultrasonic welding process are provided below. 
     Referring now to  FIGS. 2A and 2B , a force sensor  200  that may be the force sensor  100  of  FIG. 1  is shown according to some examples.  FIGS. 2A and 2B  show cross-sectional views of the force sensor  200  before and after, respectively, an ultrasonic welding operation.  FIGS. 2A-2D  may be collectively referred to herein as “ FIG. 2 .” 
     The force sensor  200  is a semiconductor package that includes a semiconductor die  202 . Accordingly, the force sensor  200  may be referred to herein as a “semiconductor package.” The semiconductor die  202  has a device side  204  and non-device side  206  opposite the device side  204 . An active circuit  208  (or more simply “circuit  208 ”) is formed on the device side  204 . The non-device side  206  of semiconductor die  202  is secured to a die pad  209  via a die attach layer (not shown) (e.g., solder paste, die attach adhesive, or similar semiconductor mounting technology). 
     A mold compound  210  (e.g., a polymer or resin material) may cover the semiconductor die  202  and die pad  209 . The mold compound  210  may protect the semiconductor die  202  and die pad  209  from the outside environment (e.g., specifically from dust, liquid, light, contaminants in the outside environment), and may prevent undesired contact with conductive surfaces or members during operations. As referred to herein, the term “mold compound” includes a covering for a semiconductor die that is formed through any suitable process, such as a cavity molding operation, glob encapsulation, dam-and-fill type encapsulation, ceramics, etc. The mold compound  210  may include a first side  212 , a second side  214  opposite first side  212 , and an outer perimeter  216  extending between the first side  212  and the second side  214  along an axis  218  that extends through (e.g., perpendicularly through) the sides  212 ,  214 . 
     The force sensor  200  also includes an interface member  220  that includes a first portion  222  and a second portion  224 . The first portion  222  is coupled to and positioned along the first side  212  of mold compound  210 , and the second portion  224  is coupled to and positioned along second side  214  of mold compound  210 . Thus, the first portion  222  and the second portion  224  are spaced from one another along axis  218  and are positioned on opposing sides of the semiconductor die  202 . The first portion  222  and the second portion  224  may be layers of material that are engaged with and may cover the first side  212  and second side  214 , respectively, of mold compound  210 . In some examples, the connection portions  226  may extend along the outer perimeter  216  between the first portion  222  and second portion  224 . 
     The interface member  220  also includes multiple connection portions  226  that are coupled to and span (or extend) between the first portion  222  and the second portion  224 . The connection portions  226  may extend axially between the first portion  222  and second portion  224  with respect to axis  218 . The connection portions  226  may be columns or pillars of material that are coupled to and extend between first portion  222  and second portion  224 , through the mold compound  210 . 
     In some examples, the interface member  220  (including the first portion  222 , second portion  224 , and connection portions  226 ) may be formed of a material that may be joined to another surface or member (e.g., mounting surface  234  described below) via an ultrasonic welding process. For instance, in some examples the interface member  220  may be formed of a metallic material such as copper, aluminum, steel, carbon, etc. In some examples, the interface member  220  (including first portion  222 , second portion  224 , and connection portions  226 ) may be formed as a monolithic body that is made up of one continuous piece of material. 
     Referring specifically to  FIG. 2B , during operations a welding horn  228  of an ultrasonic welding apparatus  230  (which may be similar to the ultrasonic welding apparatus  110  of  FIG. 1 ) may be pressed against the first portion  212  and vibrated as described above. The welding horn  228  may include multiple patterned projections or spikes  232  that engage with the first portion  222  to transfer vibrations thereto. During an ultrasonic welding process, the welding horn  228  is vibrated as it is pressed against the first portion  212  and the vibrations are transferred from the first portion  222 , through the connection portions  226  to the second portion  224 . The pressure and vibrations of the second portion  224  against the mounting surface  234  of a member of interest  236  (e.g., shaft  102  of  FIG. 1 ) cause the mounting surface  234  and second portion  224  to melt and weld to one another. 
     In addition, the pressure and contact between welding horn  228  and first portion  222  may cause distortion of the first portion  222  during the above-described ultrasonic welding process. In particular, the spikes  232  may dig into the first portion  222  and thereby form multiple recesses  223  in the first portion  222 . 
     Without being limited to this or any other theory, the interface member  220  may conduct the vibrations axially through force sensor  200  along axis  218  without causing damage to the mold compound  210 , semiconductor die  202 , or die pad  209 . Specifically, the interface member  220  is configured to route vibrations from welding horn  228  to pass through connection portions  226  to the second portion  224 . Thus, the vibrations may bypass the mold compound  210 , semiconductor die  202  and die pad  209  within force sensor  200 . In addition, the placement of the first portion  222  along first side  212  of mold compound  210  provides access to the welding horn  228  along axis  218  during welding the force sensor  200  to mounting surface  234 . 
     After force sensor  200  is welded to mounting surface  234 , forces experienced by the member  236  may be transferred to the circuit  208  via the welded connection between second portion  224  of interface member  220  and mounting surface  234 . The semiconductor die  202  may be configured to detect the transferred forces. In particular, the circuit  208  of semiconductor die  202  may detect the transferred forces via piezoresistive changes caused in the circuit  208  by the forces. The circuit  208  may also produce an output signal that includes (or is indicative of) the detected force(s). In some examples, the force sensor  200  may include additional components (e.g., semiconductor dies, passive components such as antennas, capacitors, resistors, etc.) that may process the output from the circuit  208  and/or communicate the output from the circuit  208  to other electronic devices (e.g., computers, semiconductor packages). 
     Referring now to  FIGS. 3A-3D , in some examples a second portion  302  of an interface member  304  of a force sensor  306  (e.g., second portion  224  of interface member  220  in  FIGS. 2A and 2B ) may include a patterned or textured surface (e.g., that may include a pattern of projections) for engagement with a mounting surface (e.g., mounting surface  234  in  FIGS. 2A and 2B ) of a member of interest (e.g., member  236  in  FIGS. 2A and 2B ).  FIGS. 3A-3B  may be collectively referred to herein as “ FIG. 3 .” The force sensor  306  may comprise a semiconductor package, and thus may be more generally referred to herein as a “semiconductor package.” 
     Referring specifically to  FIG. 3A , in some examples the patterned surface on second portion  302  includes multiple spaced projections  308  that are evenly spaced from one another along the second portion  302 . In some examples, the projections  308  may have a rectangular or square cross-section; however, any other suitable cross-sectional shape is contemplated for other examples (e.g., circle, oval, triangle). The second portion  302  may engage with a mounting surface via the projections  308 . Accordingly, during an ultrasonic welding operation, the projections  308  may be welded to the mounting surface of a member of interest in the manner described above. 
     Referring specifically to  FIGS. 3B and 3D , in some examples the pattern of projections on second portion  302  includes elongate projections  310  that extend between opposing sides  312  of an outer perimeter  314  of second portion  302 .  FIG. 3B  shows the elongate projections  310  extending between a first pair of opposing sides  312  along outer perimeter  314 , and  FIG. 3D  shows the elongate projections  310  extending between a second pair of opposing sides  312  of outer perimeter  314 . The second portion  302  may engage with a mounting surface via the elongate projections  310 . Accordingly, during an ultrasonic welding operation, the projections  310  may be welded to the mounting surface of a member of interest in the manner described above. 
     Referring specifically to  FIG. 3C , in some examples the pattern of projections on second portion  302  includes border projections  316  that extend along one or more (or all) of the sides  312  of outer perimeter  314 . In some examples, the border projections  316  may extend continuously about the entire outer perimeter  314  as shown in  FIG. 3C , or may extend about a portion (e.g., less than all) of the outer perimeter  314 . The second portion  302  may engage with a mounting surface via the elongate projections  316 . Accordingly, during an ultrasonic welding operation, the projections  316  may be welded to the mounting surface of a member of interest in the manner described above. 
     Referring now to  FIG. 4 , a force sensor  400  that may be the force sensor  100  of  FIG. 1  is shown according to some examples. The force sensor  400  is a semiconductor package that includes a semiconductor die  402 . Accordingly, the force sensor  400  may be referred to herein as a “semiconductor package.” The semiconductor die  402  has a device side  404  and non-device side  406  opposite the device side  404 . An active circuit  408  (or more simply “circuit  408 ”) is formed on the device side  404 . The non-device side  406  of semiconductor die  402  is secured to a die pad  409  via a solder paste (not shown). 
     A mold compound  410  (e.g., a polymer or resin material) may cover the semiconductor die  402  and die pad  409 . The mold compound  410  may protect the semiconductor die  402  and die pad  409  from the outside environment (e.g., specifically from dust, liquid, light, contaminants in the outside environment), and may prevent undesired contact with conductive surfaces or members during operations. The mold compound  410  may include a first side  412 , a second side  414  opposite first side  412 , and an outer perimeter  416  extending between the first side  412  and the second side  414  along an axis  418  that extends through (e.g., perpendicularly through) the sides  412 ,  414 . 
     The force sensor  400  also includes an interface member  420  that is coupled and positioned along the second side  414  of mold compound  410 . The interface member  420  may be an elongate member that extends beyond the outer perimeter  416  of mold compound  410  along one or more sides  422  of the outer perimeter  416 . In particular, in some examples the interface member  420  may extend beyond outer perimeter  416  along a pair of opposing sides  422  that are opposite (e.g., radially opposite) one another about axis  418 . The portions of interface member  420  that extend beyond outer perimeter  416  may form mounting pads  424  that may be exposed when viewed along axis  418  from the first side  412  of mold compound  410 . As was described above for interface member  220 , the interface member  420  may be formed of a material that may be joined to another member of surface via an ultrasonic welding process. For instance, the interface member  420  may be formed of a metallic material in some examples. In addition, the interface member  420  (including mounting pads  424 ) may be formed as a monolithic body that is made up of one continuous piece of material. Further, in some examples the mounting pads  424  may include a pattern of projections such as those shown in  FIGS. 3A-3D  and described above 
     During operations a welding horn  426  of an ultrasonic welding apparatus  428  (which may be similar to the ultrasonic welding apparatus  110  of  FIG. 1 ) may be pressed against the mounting pads  424  of interface member  420  and vibrated as described above. The welding horn  426  may include multiple engagement members  430  that are spaced from one another to define a receptacle  432 . The engagement members  430  include multiple patterned projections or spikes  434  that engage with the mounting pads  424  to transfer vibrations thereto. Specifically, the welding apparatus  428  may be lowered into engagement with force sensor  400  along axis  418  so mold compound  410  is received within receptacle  432  and engagement members  430  are engaged with mounting pads  424  to press the mounting pads  424  against a mounting surface  436  of a member of interest  438  (e.g., shaft  102  in  FIG. 1 ). In addition, the welding apparatus  428  is vibrated and the vibrations are transferred to the mounting pads  424 . The pressure and vibrations of the mounting pads  424  against the mounting surface  436  cause the mounting pads  424  and the mounting surface  436  to melt and weld to one another. During this process the interface member  420  conducts the vibrations from welding apparatus  428  away from the mold compound  410 , semiconductor die  402 , and die pad  409 . Accordingly, damage to these components is prevented. 
     In addition, as was described above for force sensor  200 , the engagement of the spikes  434  with mounting pads  424  during the ultrasonic welding process may cause distortion of the mounting pads  424 . In particular, the spikes  434  may dig into the mounting pads  424  and thereby form multiple recesses (e.g., recesses  223 ) therein. 
     The semiconductor die  402  may be configured to detect forces experienced by the member  438  of interest via the welded connection between the mounting pads  424  and the mounting surface  436 . Specifically, the circuit  408  of semiconductor die  402  may detect the forces via piezoresistive changes and may produce an output signal that includes (or is indicative of) the detected forces as described above. The force sensor  400  may include additional components for communicating and/or processing the output from circuit  408  during operations as described above. 
     Without being limited to this or any other theory, by exposing the mounting pads  424  beyond the outer perimeter  416  of mold compound  410 , the welding horn  426  may be lowered axially (e.g., along axis  418 ) toward first side  412  to contact the mounting pads  424  and perform an ultrasonic welding operation as described. In addition, vibrations experienced by the mounting pads  424  during the ultrasonic welding operation may be transferred through the mounting pads  424  and not the mold compound  410 , semiconductor die  402 , or die pad  409 . Thus, damages to these components of force sensor  400  is reduced during the ultrasonic welding operations described above. 
     Referring now to  FIG. 5 , a force sensor  500  that may be the force sensor  100  of  FIG. 1  is shown according to some examples. The force sensor  500  is a semiconductor package that includes a semiconductor die  502 . Accordingly, the force sensor  500  may be referred to herein as a “semiconductor package.” The semiconductor die  502  has a device side  504  and non-device side  506  opposite the device side  504 . An active circuit  508  (or more simply “circuit  508 ”) is formed on the device side  504 . The non-device side  506  of semiconductor die  502  is secured to a die pad  509  via a solder paste (not shown). 
     A mold compound  510  (e.g., a polymer or resin material) may cover the semiconductor die  502  and die pad  509 . The mold compound  510  may protect the semiconductor die  502  and die pad  509  from the outside environment (e.g., specifically from dust, liquid, light, contaminants in the outside environment), and may prevent undesired contact with conductive surfaces or members during operations. The mold compound  510  may include a first side  512 , a second side  514  opposite first side  512 , and an outer perimeter  516  extending between the first side  512  and the second side  514  along an axis  518  that extends through (e.g., perpendicularly through) the sides  512 ,  514 . 
     The force sensor  500  also includes an interface member  520  that is coupled to and positioned along the second side  514  of mold compound  510 . The interface member  520  may have multiple mounting pads  522  that are coupled to the die pad  509  and extend outward from the outer perimeter  516  of mold compound  510 . In some examples, the mounting pads  522  may be portions of a lead frame that also includes the die pad  509 . The mounting pads  522  extend beyond the outer perimeter  516  of mold compound  510  along one or more sides  524  of the outer perimeter  516 . In particular, in some examples the mounting pads  522  may extend beyond outer perimeter  516  along a pair of opposing sides  524  that are opposite (e.g., radially opposite) one another about axis  518 . Because the mounting pads  522  extend beyond the outer perimeter  516 , the mounting pads  522  may be exposed when viewed along axis  518  from the first side  512  of mold compound  510 . 
     In some examples, the mounting pads  522  may be integrally formed with the die pad  509 , so the mounting pads  522  and die pad  509  form a monolithic body that is made up of one continuous piece of material. For instance, the mounting pads  522  and die pad  509  may both be incorporated within a lead frame that is partially covered by mold compound  510  during manufacturing of the force sensor  500 . In some examples, the die pad  509  and interface member  520  (including mounting pads  522 ) may be formed of a metallic material (e.g., copper, aluminum, steel, carbon, etc.). In addition, in some examples the mounting pads  522  may include a pattern of projections such as those shown in  FIGS. 3A-3D  and described above. 
     During operations a welding horn  526  of an ultrasonic welding apparatus  528  (which may be similar to the ultrasonic welding apparatus  110  of  FIG. 1 ) may be pressed against the mounting pads  522  of interface member  520  and vibrated as described above. The welding horn  526  may include multiple engagement members  530  that are spaced from one another to define a receptacle  532 . The engagement members  530  include multiple patterned projections or spikes  534  that engage with the mounting pads  522  to transfer vibrations thereto. Specifically, the welding horn  526  may be lowered into engagement with force sensor  500  along axis  518  so mold compound  510  is received within receptacle  532  and engagement members  530  are engaged with mounting pads  522  to press the mounting pads  522  against a mounting surface  536  of a member  538  of interest (e.g., shaft  102  in  FIG. 1 ). In addition, the welding horn  526  is vibrated and the vibrations are transferred to the mounting pads  522 . The pressure and vibrations of the mounting pads  522  against the mounting surface  536  cause melting and welding of the mounting pads  522  and the mounting surface  536 . During this process the interface member  520  conducts the vibrations from welding horn  426  away from the mold compound  510 , semiconductor die  502 , and die pad  509 . Accordingly, damage to these components is prevented. 
     In addition, as was described above for force sensor  200 , the engagement of the spikes  534  with mounting pads  522  during the ultrasonic welding process may cause distortion of the mounting pads  522 . In particular, the spikes  534  may dig into the mounting pads  522  and thereby form multiple recesses (e.g., recesses  223 ) therein. 
     The semiconductor die  502  may be configured to detect forces experienced by the member  538  of interest via the welded connection between the mounting pads  522  and the mounting surface  536 . Specifically, the circuit  508  may detect the forces via piezoresistive changes and may produce an output signal that includes (or is indicative of) the detected forces as described above. The force sensor  500  may include additional components for communicating and/or processing the output from circuit  508  during operations as described above. 
     Without being limited to this or any other theory, by exposing the mounting pads  522  beyond the outer perimeter  516  of mold compound  510 , the welding horn  526  may be lowered axially (e.g., along axis  518 ) toward first side  512  to contact the mounting pads  522  and perform an ultrasonic welding operation as described. In addition, vibrations experienced by the mounting pads  522  during the ultrasonic welding operation may be transferred through the mounting pads  522  and not the mold compound  510 , semiconductor die  502 , or die pad  509 . Thus, damages to these components of force sensor  500  is reduced during the ultrasonic welding operations described above. 
     Referring now to  FIG. 6 , a force sensor  600  that may be the force sensor  100  of  FIG. 1  is shown according to some examples. The force sensor  600  is a semiconductor package that includes a semiconductor die  602 . Accordingly, the force sensor  600  may be referred to herein as a “semiconductor package.” The semiconductor die  602  has a device side  604  and non-device side  606  opposite the device side  604 . An active circuit  608  (or more simply “circuit  608 ”) is formed on the device side  604 . The non-device side  606  of semiconductor die  602  is secured to a die pad  609  via a solder paste (not shown). 
     A mold compound  610  (e.g., a polymer or resin material) may cover the semiconductor die  602  and die pad  609 . The mold compound  610  may protect the semiconductor die  602  and die pad  609  from the outside environment (e.g., specifically from dust, liquid, light, contaminants in the outside environment), and may prevent undesired contact with conductive surfaces or members during operations. The mold compound  610  may include a first side  612 , a second side  614  opposite first side  612 , and an outer perimeter  616  extending between the first side  612  and the second side  614  along an axis  618  that extends through (e.g., perpendicularly through) the sides  612 ,  614 . 
     The force sensor  600  also includes an interface member  620  that includes a first portion  622  and a second portion  624 . The first portion  622  is coupled to and positioned along the first side  612  of mold compound  610 , and the second portion  624  is coupled to and positioned along second side  614  of mold compound  610 . Thus, the first portion  622  and the second portion  624  are spaced from one another along axis  618  and are positioned on opposing sides of the semiconductor die  602 . The first portion  622  and the second portion  624  may be layers of material that are engaged with and may cover the first side  612  and second side  614 , respectively, of mold compound  610 . In some examples, the first portion  622  and the second portion  624  may cover a portion (e.g., less than all) of the first side  612  and the second side  614 , respectively. Specifically, as shown in  FIG. 6 , the first portion  622  and the second portion  624  may cover a portion of the first side  612  and second side  614 , respectively, that extends along the outer perimeter  616 . Thus, the first portion  622  and second portion  624  may extend along the outer perimeter  616  along the first side  612  and second side  614 , respectively, of mold compound  610 . In some examples, the second portion  624  may include a pattern of projections such as those shown in  FIGS. 3A-3D  and described above. 
     The interface member  620  also includes multiple connection portions  626  that are coupled to and span (or extend) between the first portion  622  and the second portion  624 . The connection portions  626  may extend axially between the first portion  622  and second portion  624  with respect to axis  618 . The connection portions  626  extend between the first portion  622  and the second portion  624  along the outer perimeter  616  of mold compound  610 . In some examples, the connection portions  626  may form a single, continuous body that extends along the outer perimeter  616  and that is coupled to the first portion  622  and the second portion  624 . 
     During operations a welding horn  628  of an ultrasonic welding apparatus  630  (which may be similar to the ultrasonic welding apparatus  110  of  FIG. 1 ) may be pressed against the first portion  612  and vibrated as described above. The welding horn  628  may include multiple engagement members  630  that are spaced from one another to align with the first portion  622 . The engagement members  630  include multiple patterned projections or spikes  634  that engage with the first portion  612  to transfer vibrations thereto. The engagement members  630  may include multiple patterned projections or spikes  634  that engage with the first portion  622  to transfer vibrations thereto. During an ultrasonic welding process, the welding horn  628  is vibrated as it is pressed against the first portion  612 , the vibrations are transferred from the first portion  622 , through the connection portions  626  to the second portion  624 . The pressure and vibrations of the second portion  624  against the mounting surface  636  of a member  638  of interest (e.g., shaft  102  of  FIG. 1 ) cause the mounting surface  634  and second portion  624  to melt and weld to one another. 
     In addition, the pressure and contact between welding horn  628  and first portion  622  may cause distortion of the first portion  622  during the above-described ultrasonic welding process. In particular, the spikes  634  may dig into the first portion  622  and thereby form multiple recesses (e.g., recesses  223 ) therein. 
     The semiconductor die  602  may be configured to detect forces experienced by the member  638  of interest via the welded connection between the second portion  624  and the mounting surface  636 . Specifically, the circuit  608  of semiconductor die  602  may detect the forces via piezoresistive changes and may produce an output signal that includes (or is indicative of) the detected forces as described above. The force sensor  600  may include additional components for communicating and/or processing the output from circuit  608  during operations as described above. 
     Without being limited to this or any other theory, the interface member  620  may conduct the vibrations axially through force sensor  600  without causing damage to the mold compound  610 , semiconductor die  602 , or die pad  609 . Specifically, the interface member  620  is configured to route vibrations from welding horn  628  through connection members  626  to the second portion  624 . Thus, the vibrations may bypass the mold compound  610 , semiconductor die  602  and die pad  609 . In addition, the placement of the first portion  622  along first side  612  of mold compound  610  provides access to the welding horn  628  along axis  618  during welding the force sensor  600  to mounting surface  636 . 
     Referring now to  FIG. 7 , a force sensor  700  that may be the force sensor  100  of  FIG. 1  is shown according to some examples. The force sensor  700  is a semiconductor package that includes a semiconductor die  702 . Accordingly, the force sensor  700  may be referred to herein as a “semiconductor package.” The semiconductor die  702  has a device side  704  and non-device side  706  opposite the device side  704 . An active circuit  708  (or more simply “circuit  708 ”) is formed on the device side  704 . The non-device side  706  of semiconductor die  702  is secured to a die pad  709  via a solder paste (not shown). 
     A mold compound  710  (e.g., a polymer or resin material) may cover the semiconductor die  702  and die pad  709 . The mold compound  710  may protect the semiconductor die  702  and die pad  709  from the outside environment (e.g., specifically from dust, liquid, light, contaminants in the outside environment), and may prevent undesired contact with conductive surfaces or members during operations. The mold compound  710  may include a first side  712 , a second side  714  opposite first side  712 , and an outer perimeter  716  extending between the first side  712  and the second side  714  along an axis  718  that extends through (e.g., perpendicularly through) the sides  712 ,  714 . 
     The force sensor  700  also includes an interface member  720  that is coupled to and positioned along the second side  714  of mold compound  710 . The interface member  720  may be a layer of material that is engaged with and that covers the second side  714  of mold compound  710 . In addition, the die pad  709  may be flush with the second side  714  of mold compound  710 . Accordingly, the interface member  720  may be engaged with and cover the die pad  709  along second side  714 . 
     During operations a welding horn  722  of an ultrasonic welding apparatus  724  (which may be similar to the ultrasonic welding apparatus  110  of  FIG. 1 ) may be pressed against the first side  712  of mold compound  710  and vibrated as described above. The welding horn  722  may include a receptacle  726  that is shaped and sized to receive the mold compound  710 . During an ultrasonic welding process, the welding horn  722  is vibrated as it is pressed against the first side  712 , the vibrations are transferred through the mold compound  710  to the interface member  720 . The pressure and vibrations of the interface member  720  against a mounting surface  728  of a member  730  of interest (e.g., shaft  102  of  FIG. 1 ) cause the interface member  720  and mounting surface  728  to melt and weld to one another. 
     The interface member  720  may be formed of any suitable material that may be joined to another member or surface via ultrasonic welding. For instance, in some examples interface member  720  may be formed of a metallic material. In addition, in some examples the interface member  720  may include a pattern of projections such as those shown in  FIGS. 3A-3D  and described above. 
     The semiconductor die  702  may be configured to detect forces experienced by the member  730  of interest via the welded connection between the interface member  720  and the mounting surface  728 . Specifically, the circuit  708  of semiconductor die  702  may detect the forces via piezoresistive changes and may produce an output signal that includes (or is indicative of) the detected forces as described above. The force sensor  700  may include additional components for communicating and/or processing the output from circuit  708  during operations as described above. 
     Referring now to  FIG. 8 , a force sensor  800  that may be the force sensor  100  of  FIG. 1  is shown according to some examples. The force sensor  800  is a semiconductor package that includes a semiconductor die  802 . Accordingly, the force sensor  800  may be referred to herein as a “semiconductor package.” The semiconductor die  802  has a device side  804  and non-device side  806  opposite the device side  804 . An active circuit  808  (or more simply “circuit  808 ”) is formed on the device side  804 . The non-device side  806  of semiconductor die  802  is secured to a die pad  809  via a solder paste (not shown). 
     The force sensor  800  also includes an interface member  810  that is coupled to and positioned along the die pad  809 . The interface member  810  may be a layer of material that is engaged with and that covers the die pad  809 . The interface member  810  may be positioned on an opposing side of die pad  809  from semiconductor die  802 . Accordingly, the die pad  809  may be positioned between the semiconductor die  802  and the interface member  810  along an axis  812  that extends through (e.g., perpendicularly through) the device side  804  and non-device side  806  of semiconductor die  802 . 
     During operations a welding horn  814  of an ultrasonic welding apparatus  816  (which may be similar to the ultrasonic welding apparatus  110  of  FIG. 1 ) may be pressed against the device side  804  of semiconductor die  802  and vibrated as described above. The welding horn  814  may include a receptacle  818  that is shaped and sized to receive the force sensor  800 . During an ultrasonic welding process, the welding horn  814  is vibrated as it is pressed against the device side  804 , the vibrations are transferred through the semiconductor die  802  and die pad  809  to the interface member  810 . The pressure and vibrations of the interface member  810  against a mounting surface  820  of a member  822  of interest (e.g., shaft  102  of  FIG. 1 ) causes the interface member  810  and mounting surface  820  to melt and weld to one another. 
     The interface member  810  may be formed of any suitable material that may be joined to another member or surface via ultrasonic welding. For instance, in some examples interface member  810  may be formed of a metallic material. In addition, in some examples the interface member  810  may include a pattern of projections such as those shown in  FIGS. 3A-3D  and described above. 
     The semiconductor die  802  may be configured to detect forces experienced by the member  822  of interest via the welded connection between the interface member  810  and the mounting surface  820 . Specifically, the circuit  808  of semiconductor die  802  may detect the forces via piezoresistive changes and may produce an output signal that includes (or is indicative of) the detected forces as described above. The force sensor  800  may include additional components for communicating and/or processing the output from circuit  808  during operations as described above. 
     The examples described herein include force sensors including interface members that may be welded to a member of interest (e.g., a rotating shaft, structural beam). In some examples, the force sensors may include a semiconductor die that is configured to detect a force that is experienced by the member of interest through the welded interface member. The interface layer is adapted to facilitate welding to the member of interest while avoiding damage to other portions of the force sensor (e.g., semiconductor die, wire bonds, die pad). Thus, the force sensors may be securely attached to a member of interest, and forces may be more efficiently and accurately transferred thereto. 
     While examples described herein have included semiconductor packages that function as force sensors (e.g., forces sensors  200 ,  306 ,  400 ,  500 ,  600 ,  700 ,  800 ), some examples described herein may include semiconductor packages that provide additional and/or different functionality (e.g., other than force sensing). For instance, the semiconductor packages according to examples herein may function as temperature sensors, magnetic sensors (e.g., Hall Effect sensors), or may provide a computational function (e.g., processing). Reference to force sensors is merely an example of the potential functions of the semiconductor packages described herein. Thus, generally speaking, examples described herein may include semiconductor packages having interface members as described herein that may be mounted to a suitable member or surface via an ultrasonic welding process. 
     In addition, some examples described herein have included a semiconductor die that includes a circuit on a side of the semiconductor die that is opposite the die pad and/or the interface member (or portion thereof) that engages with a mounting surface on a member of interest. However, in some examples, the circuit of the semiconductor die may be placed on a side of the semiconductor die that faces the die pad and/or the interface member (or portion thereof) that engages with a mounting surface on a member of interest. Thus, the specific arrangement and alignment of the circuit described above is merely an example arrangement and alignment of such circuits for examples contemplated herein. 
     In this description, the term “couple” may cover connections, communications or signal paths that enable a functional relationship consistent with this description. For example, if device A provides a signal to control device B to perform an action, then: (a) in a first example, device A is directly coupled to device B; or (b) in a second example, device A is indirectly coupled to device B through intervening component C if intervening component C does not substantially alter the functional relationship between device A and device B, so device B is controlled by device A via the control signal provided by device A. 
     A device that is “configured to” perform a task or function may be configured (e.g., programmed and/or hardwired) at a time of manufacturing by a manufacturer to perform the function and/or may be configurable (or reconfigurable) by a user after manufacturing to perform the function and/or other additional or alternative functions. The configuring may be through firmware and/or software programming of the device, through a construction and/or layout of hardware components and interconnections of the device, or a combination thereof. 
     A circuit or device that is described herein as including certain components may instead be adapted to be coupled to those components to form the described circuitry or device. For example, a structure described as including one or more semiconductor elements (such as transistors), one or more passive elements (such as resistors, capacitors, and/or inductors), and/or one or more sources (such as voltage and/or current sources) may instead include only the semiconductor elements within a single physical device (e.g., a semiconductor die and/or integrated circuit (IC) package) and may be adapted to be coupled to at least some of the passive elements and/or the sources to form the described structure either at a time of manufacture or after a time of manufacture by an end-user and/or a third-party. 
     While certain components may be described herein as being of a particular process technology, these components may be exchanged for components of other process technologies. 
     Unless otherwise stated, “about,” “approximately,” or “substantially” preceding a value means +/−10 percent of the stated value. Modifications are possible in the described examples, and other examples are possible within the scope of the claims.