Patent Application
20090072823
Magnetic sensors have been in use for well over 2,000 years, primarily used to sense the Earth's magnetic field for direction finding or navigation. Today, magnetic sensors are still a primary means of navigation and many other uses have evolved. As a result, magnetic sensors may be found in medical, laboratory, and electronic instruments, weather buoys, virtual reality systems, and a variety of other systems.
Modern consumer and commercial electronic equipment design has generally involved the consolidation of numerous disparate functions into a single device and the evolution of devices of increasingly diminutive scale. Small devices and devices that incorporate numerous functions require their internal components to be as small as possible. The desire to incorporate wayfinding and navigation technology into such compact devices requires the requisite 2- and 3-dimensional sensors, for example magnetic sensors and/or tilt sensors, to be of minimum height in the Z-axis (i.e., out of the plane of the PCB). Mounting a vertical sensor along the Z-axis is a challenge for the semiconductor assembly industry, especially for applications that have space limitations. One solution to mount vertical (Z-axis) sensors for applications with limited space and cost sensitive, high volume, standard PCB processes is given in U.S. patent application Ser. No. 11/022,495 titled “Single package design for 3-axis magnetic sensor,” to Bohlinger et al., and herein incorporated by reference.
The present invention provides a 3-axis sensor with on-board sensor support chip on a single chip. In one aspect of the invention, a sensor package is provided comprising an X-axis sensor circuit component, a Y-axis sensor circuit component, or alternatively a combined X/Y-axis sensor circuit component, and a Z-axis sensor circuit component, each mounted to a top surface of a rigid substrate, or alternatively to a printed circuit board (PCB). The pads may be arranged in variety of designs, including a leadless chip carrier (LCC) design and a ball grid array (BGA) design. An application-specific integrated circuit (ASIC), or sensor support chip, is additionally mounted to the top surface of the rigid substrate. The sensor components and ASIC may be ball bonded or wire bonded to the substrate.
As can be appreciated, the invention offers a cost effective, miniature, signal-conditioned sensor by utilizing commercially available, low-cost assembly processes. The functionality of combined sensors and ASIC allows users to plug-and-play into their individual systems.
Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings:
Referring to
The ASIC 40 provides support functions to the sensors 20, 30. The ASIC 40 can contain one or more of the following functions: amplification for sensor signal(s), analog to digital converter, digital interface (commonly SPI or I2C), control logic, measurement interrupts, field interrupts, programmable gain, temperature compensation, linearization, microprocessing, and power management. As related to magneto-resistive sensors, the ASIC can contain bias current drivers (not shown) and set field drivers (not shown). The bias current drivers may be used for conducting a self-test and/or used in field operations to eliminate stray fields, as well as for driving the device 10 to a known bias state in a closed-loop configuration. The set/reset drivers may be used to maximize sensitivity from the sensors and/or to remove sensor bias.
The components 20, 30, 40 are bonded to the substrate 12 via, for example, wire bonding, ball bonding, or tape automated bonding (TAB). Each component 20, 30, 40 can be mounted to the substrate 12 using a standard silicon chip assembly process. The X-Y-axis sensor 20 has input/output (I/O) pads (not shown), that conductively connect to corresponding I/O pads 22 on the substrate 12 (
The Z-axis sensor 30 is configured and oriented to be sensitive to magnetic forces along the Z-axis. The Z-axis sensor 30 includes I/O pads 32 including solder bumps 36 arranged in an array along only one edge of the sensor 30. The pads 32 conductively communicate with corresponding solder-filled metal pads 38 (via the solder bumps 36) extending completely through the substrate 12. In this way, a standard re-flow process can be used to make the Z-axis sensor 30 connection along with the X-Y-axis sensor 20; the connections can be performed in the same step or in different steps. With the components 20, 30, 40 all securely mounted to the substrate 12, the package can be encapsulated according to standard practices.
While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, the wire bond pads and wires of the above-mentioned incorporated patent application can be incorporated into the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.
