Research On Key Technologies Of Design And Manufacturing Process Of High Temperature Pressure Core For Leadless Packagin

Pressure sensors play a very important role in fields such as aerospace,meteorological exploration,and industrial control.Temperature resistance of pressure sensors is a necessity in the realms of nuclear power,metallurgy,chemical engineering,engine monitoring,and other fields.Thus,high temperature pressure sensors are a major area of research at present.Currently,the packaging forms of silicon piezoresistive pressure sensors on the market at home and abroad are mostly oil filled isolation structures with leads.Oil filled isolation is designed to isolate the pressure medium from the pressure sensitive chip and protect the pressure sensitive chip.In this paper,a silicon pressure sensor with no exposed lead packaging structure is proposed to overcome the drawbacks of existing technologies,such as large volume and low high-temperature resistance,which renders it unsuitable for small-volume and high-temperature resistant scenarios.The primary research conducted is.(1)An investigation was conducted into the operational principle of a piezoresistive SOI high temperature pressure sensor,including the piezoresistive effect,the Wheatstone measuring bridge’s formula calculation,the link between strain and the deformation of an elastic membrane with pressure,and the piezoresistive pressure sensor’s working principle.The pressure sensitive film and strain resistance were analyzed,and the resistance bar parameters and distribution of the photolithography pattern at different ranges were calculated.The mechanical simulation analysis of the chip was conducted,and the maximum stress of the chip was less than the compressive limit.The structural simulation was conducted under a small pressure of 3 times the overload.The final calculation result showed that the maximum stress was less than the compressive limit of the material.(2)The parallel method of theory and simulation is adopted for the leadless packaged pressure sensor,and the key technologies are studied.Multilayer electrode technology(three-layer material: Cr-Au – Pt)improves the corrosion resistance of pressure sensors by using wet etching on Ti N as a substrate to form a completely new metal electrode layer.It is analyzed that the key to the firmness and stability of the anodic bonding technology between the chip and the socket depends on the number of Si-O bonds.At the same time,the change of the bonding force of the bonding surface at high temperature is also analyzed.The connection method between the sensitive chip electrode and the outer lead is to use insulating glass paste sintering to form a low impedance electrical connection,which can significantly reduce the contact resistance between the sensor electrode and the core,reduce measurement errors,and meet the design requirements.(3)According to the above design ideas,the processing process is optimized.Select a SOI substrate made of oxygen injection isolation technology(SIMOX),and then conduct high concentration B diffusion on the upper layer of monocrystalline silicon.Use plasma dry etching or wet etching to etch the resistance strip.Use LPCVD to deposit a Si3N4 protective film on both sides,photolithography on the back side,and anisotropic etching of the silicon cup;Finally,the front side is photolithographed with lead holes and multi-layer metallization is performed.The key processes such as chip electrode sintering and the assembly of sensor chips were analyzed.The key process parts mainly include: sintering of outer leads and chip electrodes,and membrane resistance corrosion doping concentration technology.The sintering process of the outer lead and chip electrode uses silver glass paste sintered at high temperature,and then cooled by slow annealing to ensure the interconnection of the sensitive chip electrode and the outer lead.The ion doping concentration is determined by examining the relationship between the average resistivity and the surface impurity concentration,as well as the calculation results,in light of the fact that varying doping concentrations during the etching of sensitive chips not only influence the piezoresistive coefficient,but also the intensity of the variation of the piezoresistive coefficient with temperature and the resistance value of the force sensitive resistor.According to the design requirements of the packaging structure,the packaging structure of the high-temperature pressure sensor was designed and the sensor packaging was completed.(4)The pressuretest,conducted after the sensor had been packaged,revealed that the sensor had a good linearity in both normal and 350℃ high temperature conditions,with a nonlinearity of 0.01(which is below the desired 0.2).The sensor’s operating temperature was determined to be at least 350℃,allowing it to function in high-temperature and harsh conditions.To verify this,a high temperature test was conducted,and the full scale output of the sensor at 350℃ was 108.45 m V,which was not less than 90 m V,and a non-linear value of0.08(which was less than 0.2).