Patent Application
20140210019
The present invention relates generally to MEMS packages and more specifically to packages for integrated MEM sensors.
There is a need to provide low cost packages for MEM sensors that need access to the ambient environment. Examples of such sensors are pressure sensors, chemical sensors, sound sensors and the like. As the devices become smaller in size the packages for the sensors must become correspondingly smaller. What is needed is a package for MEM sensors that address the above-identified issue.
The package should be simple, easily implemented, cost effective and adaptable to existing environments. The present invention addresses such a need.
An integrated MEMS sensor package is disclosed. The package comprises a sensor chip with a top surface and a bottom surface. In some embodiments, the top surface comprises an opening. The bottom surface is attached to a substrate with electrical inter-connects. A lid cover with an opening is attached to the top surface; the opening allows for a path for the ambient environment to the MEMS.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
The present invention relates generally to MEMS and more specifically to integrated MEMS sensors. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein.
An integrated MEMS sensor package is disclosed that has significant advantages over conventional sensor packages. An integrated MEMS sensor package in accordance with an embodiment enables a reduction in all three package dimensions, thereby lowering cost. For example, the package size is 4 mm×4 mm×1.0 mm using existing multi-layer substrate with a metal lid. By providing a package in accordance with the present invention, the same die can fit in a 3 mm×3 mm×0.8 mm.
Utilizing a package in accordance with the present invention may also reduce product development time to a high volume market with rapid package prototype. An alternative to achieve a smaller package size is to use film assisted molding which has long lead time for prototype because a custom mold is required. A package in accordance with the described embodiments may also provide stress isolation between a MEMS die and a substrate by an attachment mechanism. To describe the features of the package in more detail, refer now to the following description in conjunction with the accompanying figures.
The CMOS die 106 is bonded to the MEMS die 105 through wafer bonding. In one embodiment, MEMS die 105 is bonded to CMOS die through wafer bonding techniques that use vertical fabrication processes as described in U.S. Pat. No. 7,104,129 “Vertically Integrated MEMS Structure with Electronics in a Hermetically Sealed Cavity”, which is incorporated herein by reference. MEMS die 105 may include gyroscope, accelerometer, magnetometer, microphone, and pressure sensor. In some embodiments, the MEMS die 105 includes an opening 107 and provides for example as a path for the ambient for a pressure sensor or acoustic signal for a microphone. In an embodiment, an integrated MEMS package 100 is hermetically sealed at wafer level via eutectic bonding. In an embodiment, to minimize the die size, bond wires 116 are connected to wire bond pads 118a on one side of the die. In another embodiment, the bond wires may be connected to bond pads placed on more than one side of the die. Bond pad 118a may be placed on the substrate closer to the CMOS die; bond pad 118b may be placed on the substrate away from the CMOS die and connected through connectors 114. Bond pad 118b provides a larger pitch for connecting to a PCB substrate. CMOS die 106 is then bonded to the substrate 102, using a low stress adhesive material 112, such as Room Temperature Vulcanizing (RTV) silicone elastomer which is commonly used for a pressure sensor. Substrate 102 may be a multi-layer substrate such as Land Grid Array (LGA).
Bond wire 116, wire bond pads 118a and bond pads 118b provide the electrical connections from the die 106 to the substrate 112. In an embodiment, bond wire 116 is protected with a glop-top material such as RTV silicone which has very small stress on the pressure sensor. Adhesive material 112 such as RTV silicone is selectively placed on the top surface of MEMS 120 using a standard, automatic dispenser and a lid 110 (shaped as a crown) is bonded to the MEMS 120 surface.
The process of attaching lid 100 can be an individual die or in an array. In an embodiment, the RTV silicone bond line is typically 25 μm, multiple layers of RTV silicone bond line can be applied if a thicker bond line is required to meet the device performance. The sidewalls 108 of the lid 110 have a vertical gap 109 above substrate 102. In an embodiment, the vertical gap 109 provides access to the ambient environment for pressure sensor and microphone. In a different embodiment, the vertical gap may be filled with adhesive material such that the lid is not rigidly attached to the substrate. n an embodiment, lid 110 can have an opening 104. Opening 104 can be formed close to the opening 107 of the MEMS die 105 to allow access to ambient. In an embodiment, lid 110 can be made of metal such as plated stainless steel or plastic (e.g. liquid crystal polymer). The top surface of the lid 110 can also be used for product marking 122.
In another embodiment as shown in
In another embodiment, one or more extensions may be provided from the lid to the substrate. The extensions may be made from a conductive material to provide an electrical path to ground the lid.
In this embodiment, stack 550 includes a MEMS/CMOS die 504 coupled to the substrate 506 via adhesive material 112. Die 504 is coupled to the CMOS/MEMS die 502. Stack 550 can include any combination of MEMS and CMOS dies. 502 can be either a CMOS or MEMS. Similarly, 504 can be either MEMS or CMOS. In an embodiment. 502 and 504 can be coupled with adhesive material if 502 and 504 are CMOS. In another embodiment, 502 and 504 may be coupled with wafer bonding when 502 and 504 are MEMS and CMOS. In stack 540, CMOS die 512 is coupled to the substrate 506 via adhesive material 112. The CMOS die 512 is also bonded by wafer bonding to MEMS die 514. In an embodiment MEMS die 514 may include an opening 508 for a MEMS device requiring exposure to ambient. Bond wires 526 connects bond pad 525 to bond pad 524 on substrate 506. Bond wire 532 connects bond pad 530 to bond pad 528 on substrate 506. Bond wire 536 may connect bond pad 534 to bond pad 528 on substrate 506. Package 500 may include a lid 545 with or without opening 546 for providing an access path to ambient. The lid 545 may be attached to MEMS die 514 and die 502 by adhesive material 112. In some embodiments, lid 545 may include a sidewall similar to lid 110.
The sensor chips can be any of the integrated MEMS sensors described in the specification before attaching to the substrate. The test strip comprises of a multilayer Printed Circuit Board (PCB) with electrical signal routed from the device under test to the ZIF connectors.
Method of Testing
The sensor chips are placed on test strip in rows and columns and attached to the test substrate by an adhesive material. The substrate carrier can be a multilayer Printed Circuit Board. The adhesive material is cured before wire bonding the sensor chip to the test substrate. A lid is attached to the sensor chip using the adhesive material. In some embodiments, adhesive material is also placed so as to cover the wire bonds. The test substrate is cured before connecting to the ZIF connectors. The test substrate is placed on a testing platform for parallel testing of the sensor chips. After testing, the test strip is singulated to provide individual packages for example as in
Integrated MEM sensors packages in accordance with at least some of the above-identified embodiments provide advantages in cost and product height that meet the next generation mobile consumer device component requirements. First, an edge of the lid is not bonded to the multi-layer substrate. The sidewalls of the lid have a small gap above the substrate. Second, the lid is bonded directly to the surface of the MEMS die. These features reduce the package in all three dimensions as compared to the existing open-cavity package variety.
For example, a 2.7 mm×2.4 mm×0.42 mm die can fit in a 3 mm×3 mm×0.8 mm package size. In a conventional open-cavity package, this same die would require a package size of 4 mm×4 mm×1.0 mm. A 3×3 package is only 56% the area of a 4×4 package; hence, the package cost can be reduced by approximately half. As mobile devices (smartphone and tablet) continue to reduce in thickness, the components must also scale accordingly. A package in accordance with some embodiments can reduce product height by >20% and enables new products to continue to meet the mobile, consumer market requirements.
Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.
