Patent Application
20150069537
The present invention relates generally to semiconductor packaging and, more particularly to a package-on-package type semiconductor pressure sensor.
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.
As shown in
One problem with the design of 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 assemble a pressure sensor device.
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 of assembling a semiconductor sensor device, and in another embodiment is the resulting semiconductor sensor device. A micro controller unit (MCU) die is mounted on a substrate or lead frame. An interposer is mounted on the MCU die. The MCU die and a first portion of the interposer are encapsulated in a molding compound, leaving a second portion of the interposer exposed. A pre-packaged pressure sensor then is mounted onto the exposed, second portion of the interposer. The interposer includes through metal vias or other wiring patterns that allow the interposer to provide electrical interconnection between the MCU die and the pre-packaged pressure sensor.
The sensor device 200 comprises a lead frame 202 having a die paddle 204 and multiple metal leads 206 separated by and embedded within an electrically insulating molding compound 208. The lead frame 202 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. The molding compound 208 may be an epoxy or other suitable material. The lead frame 202 and molding compound 208 together comprise a pre-molded lead frame that may be formed and obtained from a supplier as opposed to being formed at the sensor device assembly site.
The lead frame 202 functions as a substrate to which other elements of the sensor device 200 are mounted. More specifically, an MCU die 210 and an acceleration-sensing die (a.k.a. G-cell) 212 are mounted on and attached to the die paddle 204. Wire-bond pads on the MCU 210 are electrically connected to one or more of the leads 206 with bond wires 214, and one or more other wire-bond pads on the MCU 210 are electrically connected to one or more wire-bond pads on the G-cell 212 with bond wires 216. The G-cell 212, which is an optional component, is designed to sense gravity or acceleration in one, two, or three axes, depending on the particular implementation. The bond wires 214 and 216 are formed from a conductive material such as aluminium, silver, gold, or copper, and may be either coated or uncoated. Note that, in alternative designs, the MCU 210 and/or G-cell 212 can be electrically connected to the leads 206 using suitable flip-chip, solder-bump techniques instead of or in addition to wire bonding.
Conventional, electrically insulating die-attach adhesive (not shown) may be used to attach the MCU 210 and G-cell 212 to the die paddle 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.
An interposer 220 is mounted on a top surface of the MCU 210 with bump interconnections 218, and a pre-packaged pressure sensor 224 is mounted on a top surface of the interposer 220 with other bump interconnections 222. In one implementation, the interposer 220 comprises a single metal layer sandwiched between two insulating layers with one or more metal vias through the insulating layers. The metal vias and patterned metal features in the metal layer along with corresponding bump interconnections 218 and 222 provide electrical interconnections between the MCU 210 and the pre-packaged pressure sensor 224. In another embodiment, the interposer 220 may comprise a substrate formed of a non-conductive material (e.g., ceramic) with through metal vias.
The pre-packaged pressure sensor 224, which may itself be a BGA package, comprises a pressure-sensing die (i.e., P-cell) 226 mounted within a package housing 228. The P-cell 226 is designed to sense ambient atmospheric pressure. The pre-packaged pressure sensor 224 may take various forms, such as the P-cell 226 being electrically connected to leads (not explicitly shown in
The lead frame 202, MCU 210, G-cell 212, bond wires 214 and 216, and all but a portion of the top surface of the interposer 220 are encapsulated in a molding compound 238. The molding compound 238 may be a plastic, an epoxy, a silica-filled resin, a ceramic, a halide-free material, the like, or combinations thereof, is known in the art. As explained below in the context of
Thus, the pre-packaged pressure sensor 224 is electrically connected to the MCU by way of the bumps 222, interposer 220 and bumps 218. The MCU 210 functions as a controller for both the G-cell 212 and the P-cell 226 by, for example, controlling the operations of and processing signals generated by these two sensor dies. Note that, in some embodiments, the MCU 210 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, the G-cell 212 may be omitted. The MCU 210, G-cell 212, and P-cell 226 are well-known components of semiconductor sensor devices and thus detailed descriptions thereof are not necessary for a complete understanding of the invention.
The sensor device 200 can be manufactured with less cost than comparable sensor devices, like the conventional sensor device 100 of
One way of applying the molding compound is using a mold insert of a conventional injection-molding machine, as is known in the art. The molding material is typically applied as a liquid polymer, which is then heated to form a solid by curing in a UV or ambient atmosphere. The molding material can also be a solid that is heated to form a liquid for application and then cooled to form a solid mold. Subsequently, an oven is used to cure the molding material to complete the cross linking of the polymer. In alternative embodiments, other encapsulating processes may be used.
Note that, in this implementation, the lead frame molding compound 208 and the encapsulating molding compound 238 result from a single application of molding compound. In an alternative implementation, the lead frame is pre-molded prior to the step of
Although not explicitly depicted in the drawings, in real-world manufacturing, a two-dimensional array of different instances of sensor device 200 would be assembled on a multi-device lead frame that consists of a two-dimensional array of different instances of the lead frame structures of
As used herein, the term “mounted to” as in “a first die mounted to a die paddle” covers situations in which the first die is mounted directly to the lead frame with no other intervening dies or other structures (as in the mounting of MCU 210 to die paddle 204 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.
