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In this single chip sensor solution the reference pressure volume is trapped within the chip itself improving both the chip dimensions and overall reliability by eliminating the joint between the two chips. A single chip sensor solution is outlined with no need for the trapped reference volume between the support chip and the sensor membrane. In this paper the design of a novel LGA based MEMS Pressure sensor and barometer/altimeter design are demonstrated. The active part of the sensor is normally made up of two separate chips, the active membrane which flexes in response to external pressure the movement of which is translated into electrical signals by resistive or capacitive elements and a support chip with trapped between them a reference pressure volume. The current designs of pressure sensors rely on either a separate protective membrane, a Gel-Liquid to transmit the pressure to the active device or a Gel applied on top of the sensor. Pressure sensor designs by their nature require the active device to be in contact with the pressure to be measured, this requirement has until now restricted the possibility of applying large volume semiconductor package manufacturing techniques to pressure sensors and hence their large scale deployment in consumer applications. In this abstract we outline the critical design aspects for the design of high volume pressure sensor for MEMS applications. The design of such packages is outlined and the problems encountered in packaging multiple MEMS devices in this style of package structure discussed.
The individual assembly building blocks for the various device requirements are described in detail, in particular the development of novel assembly techniques for 90° chip mounting and interconnection is outlined.
These packages must take into account the particular devices constraints of each individual device within the same package. Increasing therefore more than one sensor is used within the same hand held device and instead of using separate device there is now a requirement for Multichip LGA based MEMS Packages.
In addition to these devices, digital compasses or magnetometeters and altimeters are now being introduced to include directional and height sensing functions. Recently following on from the success of accelerometer devices Gyroscopes devices are increasingly being adopted to add dynamic angular movement sensing putting two different sensors in different packages. One of the key factors in the adoption of the accelerometer devices was the development of LGA style packages which opened up these new market segments to MEMS devices by the use of a low cost, low stress flexibile platform, adaptable to different form factors and chip dimensions. The initial adoption of accelerometer devices has enabled human movement to become part of the man machine interface, simply tilting the device to change menu or navigate a web page. In consumer applications the size and cost of the package are becoming increasingly important especially in the applications for the user interface for Gaming and Mobile telephones. This packaging was already presented in the past year-, with a plastic cap with piping connections (one or two) The plastic cap is assembled on the HLGA by means of an epoxy adhesive screened around the pressure holes, which attached and seals the cap. Another pressure packaging is based on the integration of the HLGA (Holed HLGA packaging based on die capped and molded with a film assisted molding which leave the pressure port open). This packaging technology allows the reduction of the module dimension close to the die dimensions. ST developed the so-called RHLGA packaging (Reversed Hole LGA), which is made by a flip chip placed on an holed substrates, an epoxy dam connects the pressure die port with the hole, insulating it by the molding compound.
For ambient measurement the MEMS LGA module needs only onean hole, which connect the device pressure port with the external environment. From a customer point of view these two configurations means to have one or two pressure ports, which could require a piping interface if the measured pressure is not the ambient one. Cell phone, medical, white goods and other markets are looking for absolute pressure sensors as well as differential pressure sensors.