Patent Application
20150054099
The present invention relates generally to semiconductor sensor devices and, more particularly to a method of assembling a semiconductor pressure sensor device.
Semiconductor sensor devices, such as pressure sensors, are well known. Such devices use semiconductor pressure sensor 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 sensor dies, such as piezo resistive transducers (PRTs) and parameterized layout cells (P-cells), do not allow full encapsulation because that would impede their functionality.
As shown in
One problem with the sensor device 100 is the high manufacturing cost due to the use of a pre-molded lead frame, the metal lid 104, and the large volume of pressure-sensitive gel 114. Accordingly, it would be advantageous to have a more economical way to package dies in 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.
One embodiment of the disclosure is a method for manufacturing a semiconductor sensor device, and another embodiment is the resulting semiconductor sensor device. At least two dies, comprising (i) a pressure sensor die having a pressure-sensitive active region and (ii) at least one other die, are die-bonded to a lead frame. The at least two dies are wire-bonded to corresponding leads of the lead frame using bond wires. A mold pin is placed over the pressure sensor die and its bond wires. Mold compound is applied to encapsulate the at least one other die and its bond wires. The mold pin is removed leaving a recess in the mold compound surrounding the pressure sensor die and its bond wires. Pressure-sensitive gel is applied in the recess to cover the active region of the pressure sensor die and its bond wires.
Another embodiment of the disclosure is a semiconductor sensor device comprising (i) a pre-molded lead frame, (ii) two or more dies including a pressure sensor die and at least one other die mounted to the lead frame, (iii) bond wires electrically interconnecting the two or more dies and the lead frame, (iv) mold compound encapsulating the at least one other die and its associated bond wires, and (v) pressure-sensitive gel covering an active region of the pressure sensor die and its associated bond wires. At least one lead of the lead frame is wire bonded to both (i) the pressure sensor die and (ii) the at least one other die, and the pressure sensor die is located in a cavity of a flag of the lead frame.
Sensor device 200 includes a pressure sensor die 202 and an ASIC die 204 mounted to (e.g., physically attached and electrically coupled to) a pre-molded lead frame 206, and an acceleration-sensing die 208 mounted to ASIC die 204. Pressure sensor die (aka P-cell) 202 is designed to sense ambient atmospheric pressure, while acceleration-sensing die (aka G-cell) 208 is designed to sense gravity or acceleration in one, two, or all three axes, depending on the particular implementation. ASIC die 204 functions as the master control unit (MCU) for P-cell 202 and G-cell 208 by, for example, controlling the operations of and processing signals generated by those two sensor dies. ASIC die 204 is synonymously referred to herein as MCU 204. Note that, in some embodiments, 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, in which latter case, G-cell 208 may be omitted.
Pre-molded lead frame 206 comprises electrically conductive leads 210 embedded in an electrically insulating mold compound 212. Lead 210 may be formed of copper, an alloy of copper, a copper plated iron/nickel alloy, plated aluminum, or the like. Often, copper leads are pre-plated first with a nickel base layer, then a palladium mid layer, and finally with a very thin, gold upper layer. Mold compound 212 may be an epoxy or other suitable material.
Conventional, electrically insulating die-attach adhesive 224 may be used to attach (i) P-cell 202 and MCU 204 to lead frame 206 and (ii) G-cell 208 to MCU 204. Those skilled in the art will understand that suitable alternative means, such as die-attach tape, may be used to attach some or all of these dies. P-cell 202, MCU 204, and G-cell 208 are well known components of semiconductor sensor devices and thus detailed descriptions thereof are not necessary for a complete understanding of the disclosure.
The electrical interconnection between P-cell 202 and MCU 204 is provided via one or more shared lead(s) 210A of lead frame 206 by respective, associated bond wires 214 wire-bonded between (i) bond pads on P-cell 202 and MCU 204 and (ii) lead(s) 210A using a suitable, known wire-bonding process and suitable, known wire-bonding equipment. Similarly, the electrical interconnection between MCU 204 and G-cell 208 is provided by wire-bonding between other bond pads on MCU 204 and bond pads on G-cell 208. Furthermore, the electrical interconnection between MCU 204 and the outside world is provided via one or more lead(s) 210B of lead frame 206 by bond wires 214 wire-bonded between still other pads on MCU 204 and lead(s) 210B. Bond wires 214 are formed from a conductive material such as aluminium, gold, or copper, and may be either coated or uncoated. Note that, in alternative designs, G-cell 208 can be electrically connected to MCU 204 using suitable flip-chip, solder-bump techniques instead of or in addition to wire-bonding.
MCU 204, G-cell 208, and their associated bond wires 214 are encapsulated within a suitable mold compound 216. The mold compound 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.
A pressure-sensitive gel material 218, such as a silicon-based gel, is deposited over P-cell 214 and its associated bond wires 214, filling most of the recess formed in mold compound 216 around P-cell 214. Note that, in alternative implementations, less of gel material 218 may be applied within the recess as long as the pressure-sensitive active region (typically on the top side) of P-cell 214 and its associated bond wires are covered by the gel. Pressure-sensitive gel material 218 enables the pressure of the ambient atmosphere to reach the active region of P-cell 202, while protecting P-cell 202 and its associated bond wires 214 from (i) mechanical damage during packaging and (ii) environmental damage (e.g., contamination and/or corrosion) when in use. Examples of suitable pressure-sensitive gel material 218 are available from Dow Corning Corporation of Midland, Mich. The gel material may be dispensed with a nozzle of a conventional dispensing machine, as is known in the art.
A lid 220 having an opening or vent hole 222 is mounted over the gel-covered P-cell 202 fitting snugly into a seat formed within mold compound 216, thereby providing a protective cover for the P-cell. Vent hole 222 allows the ambient atmospheric pressure immediately outside sensor device 200 to reach (i) the pressure-sensitive gel material 218 and therethrough (ii) the active region of P-cell 202. Although shown centered in
Lid 220 is formed of a durable and stiff material, such as stainless steel, plated metal, or polymer, so that P-cell 202 is protected. Lid 220 is sized and shaped depending on the size and shape of P-cell 202 mounted to the lead frame under the lid. Accordingly, depending on the implementation, the lid may have any suitable shape, such as round, square, or rectangular.
Sensor device 200 can be manufactured with less cost than comparable sensor devices, like those based on the conventional design of sensor device 100 of
In particular,
In the implementation shown in
Referring again to
The shapes of the leads 210 of the lead frame 206, specifically lead(s) 210A, enable the indirect electrical interconnection of the P-cell 202 and MCU 204 by wire bonding both dies 202, 204 to one or more shared lead(s) 210A. This lead sharing, in turn, allows the mold pin 502 to be placed over the P-cell 202 in a way that does not impinge on either the bond wires 214 connecting the P-cell 202 to shared lead(s) 210A or the bond wires 214 connecting the MCU 204 to the same shared lead(s) 210A. In this way, the bond wires associated with the MCU 204 can be encapsulated by the mold compound 216, while the bond wires associated with the P-cell 202 are covered with the gel material 218. These features enable the sensor device 200 to be manufactured with only a single die-bonding cycle and only a single wire-bonding cycle.
Although not depicted in the drawings, in practice, a plurality of sensor devices are formed simultaneously by using a lead frame sheet that has a two-dimensional array of the lead frames, and then the die bonding and wire bonding steps are performed on all of the lead frames in the array. Similarly, all of the separate devices are encapsulated with the molding compound at the same time too. After assembly, e.g., using the process depicted in
As used herein, the term “mounted to” as in “a first die mounted to a lead frame” covers situations in which the first die is mounted directly to the lead frame with no other intervening dies (as in the mounting of P-cell 202 to lead frame 206 in
Although
Although
By now it should be appreciated that there has been provided an improved packaged semiconductor sensor device and a method of forming the improved 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.
