Research On PCB In-situ Drilling Temperature Measurement Technology Based On Thin Film Thermocouple

With the rapid development of computer,mobile devices,communication facilities and other industries,printed circuit boards are widely used in industrial production and daily life.The manufacturing process of PCB is complex,and the hole processing is an important step related to the quality of PCB.The diameter of drill bit used for hole processing is smaller between 0.1 mm and 1mm and the spindle speed of drilling equipment is higher,In addition,the complex structure of the PCB layer results in a large amount of cutting heat in the drilling area due to thermo-mechanical coupling.The traditional temperature measurement methods have some shortcomings,such as long sensing time and large environmental impact,and can not achieve real-time and accurate measurement.In this paper,the thin film thermocouple is directly deposited on the surface of PCB.Combined with the high-speed acquisition of temperature signals,real-time and accurate in-situ temperature measurement during drilling process is realized.Specific research contents are as follows:According to the cross-section structure of PCB,the finite element model of micro-drill and PCB is established by the method of alternating layered material modeling.The drilling process is simulated,and the temperature distribution cloud and temperature change curve are obtained.The results show that:The temperature field mainly distributes in the cylindrical area with the drill axis as the axis.With the drill penetration,the temperature of the junction at the hole wall increases gradually.The temperature at the bottom hole wall is the highest when drilling through the circuit board,so the best temperature measurement method for thin film thermocouple sputtering on the surface of PCB is determined.SiO2 insulating film,NiCr/NiSi thermocouple film and SiO2 protective film were prepared on the surface of PCB by DC pulsed magnetron sputtering.It is found that the SiO2 insulating film prepared by step deposition method has uniform thickness and excellent insulation performance,and its insulation resistance reaches 3.65×107?.The surface of NiCr/NiSi thin film Thermoelectrode is compact and uniform without obvious defects.The static characteristics of the thin film thermocouple sensor are studied by using the self-developed static automatic calibration system.The results show that the Seebeck coefficient of the thin film thermocouple sensor is 37.4?V/?,the non-linear error and the repeatability error are 0.65%and 1.13%respectively.It means that the sensor has high sensitivity,good linearity and temperature measurement stability.The dynamic response time of the thin film thermocouple sensor is 95?s,which is close to the theoretical value of 39.35?s.The in-situ drilling temperature of PCB is measured in real time through drilling experiment.The results show that the maximum temperature of four,twelve and twenty layers are 49.33?,53.92? and 63.94? respectively.The experimental results show that the thin film thermocouple sensor responds quickly and senses temperature quickly.It can realize in-situ temperature measurement in PCB drilling process and provide a new technical means and method for in-situ drilling temperature measurement.