Low Cost integrated Package for Tyre Pressure Monitoring Systems A.J. van der Wiel Melexis Outline • • • • • • • • • Tyre Pressure Monitoring Systems System Requirements The Sensor The ASIC Why MCM Integration The Package Melexis’ Package Integration Process Measured Characteristics Outlook 1 TPMS • Stand-alone system • Tyre Environment • Large temperature range • High acceleration forces • Wireless data transfer • Calibrated system • 10 year operational • System components • • • • • • • Pressure sensor Temperature sensor Roll sensor Read-out electronics RF and/or LF transmitter Battery Passive components System Requirements • Functionality • • • • • 3% Accuracy -40 °C to 125 °C 0 – 1500 g centrifugal forces High moisture and solvent environment inside the tyre 10 year operational on 1 battery • Programming • Calibration • Timing constants • Identification 2 The Sensor • Silicon chip ~1.0 x 1.0 x 0.5 mm2 • Integrated Strain Gauges as Wheatstone bridge • All silicon for excellent drift behaviour The Asic • • • • 0.6u cmos process Double poly - double metal ROM - RAM - EEPROM Flash memory for software development and limited production • On chip active/passive LF interface (receive) • Power supply range: 1.8 to 5 V • Temperature measurement 3 Why MCM Integration • Minimising number of components • Cost saving • Smaller product • Better reliability • Sensor calibration before system assembly • Sensor characteristics stored in ASIC • No temperature ramping after final assembly The Package: Requirements • Low Cost - High Volume production • SOIC compatible • • • • MCM package Expose sensor to pressure Minimal stress at sensor Low g sensitivity 4 The Package: Assembly Process • • • • • • • • Die attach dispense on lead frame Pick and place die on lead frame Bake Wire bond Protective Gel dispense Bake Mould Singulation The package X-ray graps FluoroGel protection • Resist solvents and high temperature range • No offset change after gel removal • Thin gel layer assures small g sensitivity 5 Characteristics Parameter Unit MLX90268 On the market Sensitivity mV/V/Bar 3 3 Offset mV/V ±5 ± 10 Linearity %FS 0.2 0.2 Hysteresis % FS 0.1 0.1 k 42 5 TC Sensitivity %FS/°C -0.2 -0.2 TC Offset %FS/°C ± 0.03 ± 0.04 Acceleration error mBar/g < 0.05 ? kV 2 2 Bridge Resistance ESD Conclusions • MCM with sensor and ASIC reduces: • Number of components final product • Size of final product • Test and calibration of final product • Packaging is the key to System Integration • Realisation of a MCM with sensor and ASIC • TPMS requirements met by adding a gel dispense to standard SOIC packaging 6 Questions and comments please! 7