Patent Application
20150014793
The present invention relates generally to semiconductor sensor devices, and more particularly to semiconductor pressure sensors.
Semiconductor sensor devices such as pressure sensors are well known. Such devices use semiconductor pressure sensing dies. These dies are susceptible to mechanical damage during packaging and environmental damage when in use, and thus they must be carefully packaged. Further, pressure sensing dies, such as piezo resistive transducers (PRTs) and parameterized layout cells (P-cells), do not allow full encapsulation because that would impede their functionality.
The device 100 includes a pressure sensing die (P-cell) 106, acceleration sensing die (G-cell) 108, and micro-control unit (MCU) 110, which are mounted to a lead frame flag 112, electrically connected to package leads 118 with bond wires (not shown), and covered with a pressure sensitive gel 114, which enables the pressure of the ambient atmosphere to reach the pressure sensitive active region on the top side of the P-cell 106 while protecting each of the dies 106, 108, 110 and the bond wires from mechanical damage during packaging and environmental damage (e.g., contamination and/or corrosion) when in use. The entire die/substrate assembly is encased in molding compound 102 and covered with a lid 104, which has a vent hole 116 that exposes the gel-covered P-cell 106 to ambient atmospheric pressure outside the sensor device.
One problem with the design of sensor device 100 is the high manufacturing cost due to the pre-molded package base, the metal lid, and the large volume of pressure sensitive gel. Accordingly, it would be advantageous to have a more-economical way to assemble semiconductor sensor devices.
Embodiments of the present disclosure are illustrated by way of example and are not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the thicknesses of layers and regions may be exaggerated for clarity.
Detailed illustrative embodiments of the present disclosure are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present disclosure. Embodiments of the present disclosure may be embodied in many alternative forms and should not be construed as limited to only the embodiments set forth herein. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the disclosure.
As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It further will be understood that the terms “comprises,” “comprising,” “has,” “having,” “includes,” and/or “including” specify the presence of stated features, steps, or components, but do not preclude the presence or addition of one or more other features, steps, or components. It also should be noted that, in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
In one embodiment, the present invention provides a method for assembling a semiconductor sensor device, and another embodiment is the resulting semiconductor sensor device. One or more dies including a pressure sensing die are mounted to at least a first die attach pad of a lead frame. The lead frame also has an outer frame with a plurality of attached leads. The first die attach pad is connected to the outer frame by a plurality of tie bars. The lead frame defines a first lateral plane, and the first die attach pad defines a second lateral plane vertically offset from the first lateral plane. The pressure sensing die is mounted to the first die attach pad, which has an opening that provides access to an active region of the die. The one or more dies are electrically connected to corresponding leads of the lead frame with bond wires. The wire bonded dies, the first die attach pad, and the corresponding leads are encapsulated in a molding compound, while preserving access to the active region of the pressure sensing die via the opening in the first die attach pad. Pressure sensitive gel is applied through the opening in the first die attach pad to cover the active region of the pressure sensing die. The sensor device is separated from one or more other adjacent devices, where the multiple leads are detached from the outer frame of the lead frame.
Another embodiment of the present invention is a semiconductor sensor device comprising a first die attach pad having an opening, one or more dies including a pressure sensing die mounted to the first die attach pad, a plurality of leads, bond wires electrically connecting the dies to corresponding ones of the leads, a plurality of tie bars connected to the first die attach pad, pressure sensitive gel covering an active region of the pressure sensing die, and molding compound that encapsulates the first die attach pad, the one or more dies, the leads, the bond wires, and the tie bars. The plurality of leads lie in a first lateral plane, and the first die attach pad lies in a second lateral plane that is vertically offset from the first lateral plane. The opening in the first die attach pad provides access to the active region of the pressure sensing die. There is a hole in the molding compound corresponding to the opening in the first die attach pad, which exposes the gel-covered active region of the pressure sensing die to ambient atmospheric pressure outside of the molding compound.
The sensor device 200 includes a first, pressure sensing die 202 and a second die 204, which may be an application specific integrated circuit (ASIC). The pressure sensing die (a.k.a. P-cell) 202 is designed to sense ambient atmospheric pressure. The ASIC die 204 is designed to control the operation of and process signals generated by the P-cell 202, and may be a microcontroller or micro-control unit (MCU), as is know in the art. The ASIC die 204 is synonymously referred to herein as MCU 204. Note that, in some embodiments, the ASIC die 204 may implement both the functionality of an MCU and that of one or more other sensors, such as an acceleration sensing G-cell.
Mounted above (in
Mounted above the die attach pad 206 and gel 210 is a lid 212 also having a hole 214 adjacent to the hole in the die attach pad 206 and to the P-cell 202 active region. The lid 212 is formed of a durable and stiff material, such as stainless steel, copper, plated metal, or a polymer, so that the P-cell 202 is protected. Depending on the implementation, the lid 212 may have any suitable shape, such as round, square, or rectangular. The hole 214 in the lid 212 enables ambient atmospheric pressure immediately outside the sensor device 200 to reach the gel 210 and the hole 208 in the die attach pad 206, enabling ambient air pressure to reach the active region of the P-cell 202 via the gel 210.
In an analogous manner, mounted above the MCU 204 is a metal die attach pad 216, which includes neither a hole nor a pressure sensitive gel.
The P-cell 202 and MCU 204 are electrically connected to each other and to metal package leads 218 with bond wires 220. In particular, the bond wires 220 are wire bonded between bond pads of the P-cell 202 and corresponding bond pads on the MCU 204 using a suitable, known wire bonding process and suitable, known wire bonding equipment to provide the electrical interconnection between the P-cell 202 and MCU 204. Similarly, the P-cell 202 and MCU 204 are both electrically connected to corresponding package leads 218 by wire bonding between other bond pads on the P-cell 202 and MCU 204 and corresponding package leads 218. The bond wires 220 are formed from a conductive material such as aluminium, gold, or copper, and may be either coated or uncoated. Note that the package leads 218 are vertically offset from the die attach pads 206 and 216.
The entire assembly is encapsulated with a suitable molding compound 222. The molding compound 222 may be a plastic, an epoxy, a silica-filled resin, a ceramic, a halide-free material, the like, or combinations thereof, as is known in the art.
The sensor device 200 is less costly to assemble than comparable sensor devices, like those that are assembled using a pre-molded lead frame, such as the conventional sensor device 100 of
The lead frame 300 has a die attach pad 206 including a hole 208, a die attach pad 216, and a plurality of package leads 218, which all are interconnected by an outer frame 302. The die attach pads 206 and 216 are connected to the outer frame 302 by tie bars 304 having down-set structures 306. As shown in
After encapsulation, the molding tape 702 and mold pin 704 are removed, a lid 212 is installed, and pressure sensitive gel 210 of
Although not depicted in the drawings, in real-world manufacturing, a two-dimensional array of the sensor devices 200 is assembled in a multi-device lead frame that includes of a two-dimensional array of the lead frames 300 of
In the assembly technique illustrated in
According to other assembly techniques, epoxy is used to connect the dies to the die attach pads instead of DAF tape.
As used herein, the term “mounted to” as in “a first die mounted to a die attach pad” covers situations in which the first die is mounted directly to the die attach pad with no other intervening dies (as in the mounting of P-cell 202 to die attach pad 206 in
MCUs, P-cells, and G-cells are well-known components of semiconductor devices and thus detailed descriptions thereof are not necessary for a complete understanding of the disclosure.
Although
Although
Although the disclosure has been described in the context of embodiments having a pressure sensing P-cell die and a separate MCU die, those skilled in the art will understand that the invention can also be implemented in an embodiment in which the pressure sensing functionality and the MCU functionality are implemented in a single, multi-function die. Such an embodiment may be manufactured using a lead frame having only a single die attach pad with a suitable hole to expose the active pressure sensing region of the multi-function die.
By now it should be appreciated that there has been provided an improved packaged semiconductor sensor device and a method of forming the packaged semiconductor sensor device. Circuit details are not disclosed because knowledge thereof is not required for a complete understanding of the invention.
Although the invention has been described using relative terms such as “front,” “back,” “top,” “bottom,” “over,” “above,” “under” and the like in the description and in the claims, such terms are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the disclosure described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.
Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. Further, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles.
Although the disclosure is described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. Any benefits, advantages, or solutions to problems that are described herein with regard to specific embodiments are not intended to be construed as a critical, required, or essential feature or element of any or all the claims.
It should be understood that the steps of the exemplary methods set forth herein are not necessarily required to be performed in the order described, and the order of the steps of such methods should be understood to be merely exemplary. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments of the invention.
Although the elements in the following method claims, if any, are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.
Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”
The embodiments covered by the claims in this application are limited to embodiments that (1) are enabled by this specification and (2) correspond to statutory subject matter. Non enabled embodiments and embodiments that correspond to non statutory subject matter are explicitly disclaimed even if they fall within the scope of the claims.
