Pressure sensor chips are die, IC chips or sensing elements devices that sense changes in pressure. They can be used as stand alone devices or can be embedded in ceramic or plastic-based packages such as surface mount or through-hole chips. Some devices produce an analog current or analog voltage that is proportional to the input signal. Others produce a digital parallel output signal, a pulse width modulation (PWM) output voltage, or a logic output based on threshold input values. Pressure sensor chips with serial interfaces allow communication with embedded microcontrollers and other digital systems. Common pressure measurements include absolute, gauge, differential, and vacuum pressure. Typically, pressure sensor chips are designed for medical, automotive, industrial, consumer product, and military applications. Sensors are manufactured as signal conditioning chips, stand-alone transducers, or integrated transducers that include both signal conditioning and the sensor on the same die.
Performance specifications for pressure sensor chips include pressure range, supply voltage, impedance, impedance temperature coefficient, bandwidth, and accuracy. Typically, pressure range values are expressed in pounds per square inch (psi). The supply voltage or excitation is the input voltage required to operate pressure sensor chips. Impedance, the total opposition to the flow of current, is measured at the sensor input. The impedance temperature coefficient is typically expressed in parts per million (ppm) and measures changes in input impedance per degree of temperature change. Bandwidth is the frequency range over which devices meet specifications for accuracy, the maximum difference that exists between the actual value and the indicated output value. Accuracy can be expressed as a percentage of full scale or in absolute terms.
Integrated Circuit (IC) Package Types
There are several integrated circuit (IC) package types for pressure sensor chips. SC-170, one of the smallest available IC packages, is used in handheld devices such as cellular phones and personal digital assistants (PDAs). SOT23 is a rectangular, surface mounted, small outline transistor (SOT) package with three or more gull wing leads and a very small footprint. SOT123, another small outline transistor (SOT) package, is flanged, ceramic, and surface mounted with two mounting holes and four leads. Other IC package types include SO-8 and SO-16, both of which are small outline (SO) packages and TO-8, a transistor outline (TO) package. Bare die and quarter size outline package (QSOP) devices are also available.
Pressure sensor chips are packaged in tape reels, trays or rails, shipping tubes or stick magazines, and in bulk packs. Tape reel assemblies include a carrier tape with embossed cavities for storing individual components. A cover tape seals the carrier tape in place and the composite tape is wound on a reel that can be loaded into industry-standard, pick-and-place board assembly equipment. Pressure sensor chips with leads on four sides are often packed in trays or rails that are made of carbon-powder or fiber materials and molded into rectangular outlines that contain matrices of uniformly spaced pockets. Shipping tubes or stick magazines are containers made of rigid polyvinylchloride (PVC) and extruded in industry-standard sizes. Bulk packs are used to distribute components as individual parts.