The pressure sensor is an assembly of a micromachined silicon part and pyrex™ glas. Four polysilicon Piezo Resistances have been implemented, on top of silicon, just above the sensor's membrane. The membrane is only a few micrometers thick and deflects depending on the pressure difference existing between its two sides.For differential sensors, the pyrex™ is drilled with a hole below the membrane (see picture left) so that pressure can be applied on both sides. For absolute sensors, the pyrex™ has no hole and vacuum is created in the cavity underneath the sensor when the pyrex™ is sealed with the silicon. This step is called "Anodic bonding".
Most Important Manufacturing steps
Electrical Wafer Sort (EWS)
SP4 process
Sensor design optimized for high output signal 1-12 bar sensors absolute and gauge 8 Mask levels Implanted Piezo Resistors Low offset drift Wafer are 100% electrically tested (see picture on the left)
Micromachining process
Anisotropic KOH etching of silicon for membrane forming Thickness control with eletrochemical etch-stop Anodic bonding of pyrex™ glas to silicon Double sided wafer alignment Reliable hermetic connection Wafer dicing on blue tape Two sides optical inspection
KOH etching
Die attach
Thick Film Hybrid Assembly
Screenprinting Die attach Pick & Place
Thick Film Hybrid Assembly (continued)
Wire bonding (gold and aluminium) Reflow soldering for SMD components Chip coating (globtop) Low stress humidity protection Flux free leadframe soldering Laser trimming of thick film resistors Laser marking
Wire bonding
Electrical trimming in pressure chamber
Test & Calibration
Automated sensor testing with temperature and pressure from -40°C to +125°C Passive and active laser trimming Electrical (on-chip) trimming High throughput pressure/temperature chamber Sensor characterization before mounting Pressure calibrators Printable version