Patent Application
20120139067
The present invention relates generally to pressure sensor packaging, and more particularly to a method of assembling quad flat no-lead (QFN) pressure sensor packages.
Portable electronic devices are starting to integrate sensors into handheld and desktop electronics with requirements of low power and a small form factor. Key markets are in the cellular, mobile electronics and desktop arenas. For example, pressure sensors are being used in small form factors to measure barometric pressure as a means to analyze surroundings. This is occurring in portable devices for weather measurement or in control systems for electronics dependent on operating pressures. Pressure sensors may be packaged with a microcontroller to attain compensated pressure values using the raw data provided by the pressure sensor.
Pressure sensors and pressure sensor packages come in a variety of sizes and configurations. The pressure sensor die typically has a thin differential pressure-sensing membrane that is susceptible to mechanical damage during handling and packaging. For this reason, the sensor die typically is mounted in a pre-molded package and then sealed in the package using a separate cover/lid.
One way of packaging the pressure sensor die is mounting the die to a premolded lead frame and encapsulating the package with a mold compound. However, dies such as piezo resistive transducer (PRT), parameterized layout cell (Pcell) and Gyro do not allow full encapsulation because that would impede their functionality. As a result, the premolded lead frame requires a metal lid or cap be placed over the die to protect it from the outside environment. However, premolded lead frames are relatively expensive, which increases the overall cost of the packaged device.
Accordingly, it would be advantageous to be able to efficiently package pressure sensor dies in which the risk of environmental damage to the pressure sensor die is substantially reduced or eliminated while reducing the overall packaging costs.
The present invention is illustrated by way of example and is 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 invention are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. The present invention may be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. 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 invention. 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,” “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 packaging a pressure sensor die. The method includes providing a plurality of lead frames. Each of the plurality of lead frames includes a die pad and a plurality of lead fingers. A tape is attached to a first side of the plurality of lead frames and a non-conductive material is deposited on a second side of the lead frames. The non-conductive material is cured and the tape is removed to attach pressure sensor dies to respective die pads of the lead frames with a die attach adhesive. The die attach adhesive is then cured and bond pads of the respective pressure sensor dies are electrically connected to the lead fingers of the lead frames with wires using a wire bonding process. A gel is dispensed onto a top surface of each of the pressure sensor dies. The gel is cured and a lid is attached to each of the lead frames with a lid attach adhesive such that the lids cover the pressure sensor dies. The lid attach adhesive is cured and the plurality of lead frames are singulated to form individual pressure sensor packages.
In another embodiment, the present invention is a packaged pressure sensor die formed in accordance with the above-described method.
Referring now to
A pressure sensor die 18 is attached and electrically coupled to the lead frame 12. In this exemplary embodiment of the invention, the pressure sensor die 18 includes a piezo resistive transducer (PRT) die. The pressure sensor die 18 may be attached to the lead frame 12 using a die attach adhesive. The pressure sensor die 18 and the lead frame 12 are well known components of pressure sensors and thus detailed descriptions thereof are not necessary for a complete understanding of the present invention.
In this embodiment of the invention, the pressure sensor die 18 is electrically coupled to the lead fingers 18 of the lead frame 12 with bond wires 20. The bond wires 20 are bonded to pads on an active surface 22 of the pressure sensor die 18 and to the lead fingers 16 of the lead frame 12, using a well known wire bonding process and known wire bonding equipment.
Another way of electrically connecting the pressure sensor die 18 to the lead fingers 16 of the lead frame 12 is to connect bond pads of the pressure sensor die 18 to the lead fingers 16 with flip-chip bumps (not shown) attached to an underside of the pressure sensor die 18. The flip-chip bumps may include solder bumps, gold balls, molded studs, or combinations thereof, as is known in the art.
The pressure sensor die package 10 includes a non-conductive material 24 such as a non-conductive adhesive or a solder mask disposed within gaps 26 and 28 between the die pad 14 and the lead fingers 16. A gel 30 such as a silicon-based gel is disposed on a top surface of the pressure sensor die 18 to cover the bond pads and the electrical connections (wire bonds) of the pressure sensor die 18 as well as the die 18 itself.
The packaged pressure sensor die 10 includes a lid 32 that covers the pressure sensor die 18, the die pad 14, the gaps 26, 28, and the bond wires 20. The lid 32 may include a molded, footed metal lid, as is known in the art. In this exemplary embodiment of the invention, the lid 32 is attached to the lead frame 12 with a lid attach adhesive 34 such as a non-conductive epoxy. However, other attachment mechanisms may be used. The lid 32 includes a vent hole 36 on a top surface thereof. It should be noted that the non-conductive material 24 and the lid attach adhesive 34 substantially preventingress of moisture into the pressure sensor die 18 by interlocking the lead frame 12 and the metal lid 32 at the sides and bottom of the packaged pressure sensor die 10. The example configuration of the packaged pressure sensor die 10 of
Referring now to
Although the individual elements of the packages 10 and 40 may be well known, the method of assembly of such elements in the conventional packages is cumbersome and as previously discussed requires premolded lead frames. However, the inventors have discovered a novel method of forming the packaged pressure sensor die 10 that will be described with reference to
The deposited non-conductive material 24 is subsequently cured in a conventional oven followed by removal of the tape 50 from the lead frames 12, as shown in
The present invention, as described above, allows for packaging a pressure sensor die without requiring premolded lead frames to package the die. A simple deposition technique such as screen printing is employed to apply a layer of a non-conductive material to interlock the leads and lead frames. The pressure sensor dies are attached to the respective lead frames with a die attach adhesive, electrically coupled to the lead fingers, and a gel is disposed on the pressure sensor dies to cover the bond pads of the pressure sensor dies. Subsequently, the lid is attached to the package using a footed lid that can be attached to the lead fingers, instead of having to use a lid that is attached to a mold wall. Thus, a mold wall also is not required.
Thus, the present invention provides a method of packaging a pressure sensor die such as QFN packages with a lower package profile that does not require a premolded lead frame for facilitating lid attachment thereby reducing manufacturing costs for such packages. The pressure sensor die packaged using the process described above is protected from air moisture as the lead frame and the metal lid are interlocked at the sides and bottom of the package.
By now it should be appreciated that there has been provided an improved packaged pressure sensor die and a method of forming the packaged pressure sensor die. 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,” “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 invention 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 invention 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201010601547.9 | Dec 2010 | CN | national |
