Structural Optimization Of Microdrills Of Printed Circuit Boards

Printed circuit boards(PCB)are widely used in the fields of mobile communication,digital electronics and screen display.The microholes can be used to realize the electrical connection between the inner and outer lines and the assembled positioning of the components.PCBs are anisotropic layered composite materials which are difficult to process.Many problems occurred during the process of drilling PCB using a weak rigid micro drill,such as large deviation of drilling,difficulty of chip removal,wear and break seriously of micro drill,poor hole position accuracy,higher hole wall roughness,bigger burrs and nail heads.The loss of micro drill restricts the profit margin and production efficiency of the PCB industry.It is urgent to improve the tool life of micro drills and the quality of microholes.Optimizing the micro drill structure to improve the performance of PCB products,as well as the reliability and service life of the terminal electronic products are needed.The influence of micro drill structure on the drilling performance and the micropore quality is revealed by studying the process of cutting HSPCB and FPC with different drilling tips based on the structure of PCB and the characteristics of microholes processing in view of the problems.A new micro drill structure with multi drilling angle is proposed.The mechanism of new micro drill torsional fracture,compression fracture and bending fracture are revealed.The dynamic characteristics of the new micro drill are analyzed.The simulation reveals the mechanism of micropore wall forming and the mechanism of thermal coupling in the process of drilling.The separation of micro drill with 3D printing was put forward.The main conclusions are as follows.In the microholes drilling performance and quality of PCB,the influence of point angle,the first angle and the second face angle on the chip morphology were small.There was no significant change in the micro drilling process of PCB.And the influence of the second face angle on the thrust force was small.The mass of the microhole and the tool wear were influenced by the drill tip.Thrust force increased with the increase of the point angle of micro drill.The first face angle had little effect on the thrust force.Drilling HSPCB with micro drill in point angle of 110°and 140°,and drilling FPC with 130° point angle micro drill,the tool wear of the micro drill was small.The micro drill with 20° first face angle was easy to crack.The point angle was the most important factor affecting the microhole quality,followed by the first face angle.The drill bit with small drill angle can be used to drill the HSPCB and the smaller hole diameter of the hole wall.For the FPC,the drilling angle of 130° should be adopted.Smaller first face angle gave rise to smaller roughness.Smaller tip angle made smaller burrs.The exit burrs produced by HSPCB were smaller than those of FPC.The drilling point angle had a great influence on the hole position accuracy of the micro drilling of the HSPCB.And the hole position accuracy increased with the increase of the point angle,which had little effect on the hole position precision of the FPC.The hole position accuracy decreased first and then increased with the increase of the first angle.The hole position accuracy of the FPC increased with the increase of the first face angle.In the parameterized design of micro drill structure,the 3D model of micro drill was established by using UG NX 3D modeling software,including drilling body forming,cutting drill point,opening spiral groove,cutting UC and structure forming,etc.The design plug-in of PCB micro drill can be obtained and the change of structure can be realized.On this basis,the structure design of multi point angle micro drill was proposed.Two pairs of blades were added to the drill tip to form the drill tip structure of three drill point angles,increasing the rake angle of the length of the cutting edge,increasing the effective cutting time of the cutting edge,and putting forward the anti wear ability of the blade surface.In view of the reliability of the micro drill structure,the finite element analysis method was used to analyze the hydrostatic analysis,transient dynamic analysis and the thermal coupling analysis of the drilling process.In the drilling process,micro drill was also subjected to three loads: torsion,compression and bending.Under the action of compression load,the stress of micro drill mainly concentrated on the transition part of the drill tip and the edge length and the drilling platform.Under the action of bending load,the stress in the local load concentrated rapidly and failed,and then the micro drill broke.The mode shapes of micro drill pairs appeared in pairs,and the natural frequencies of partial vibration of micro drill points vary little as a whole.In drilling process,the stress distribution was diffused from the contact part of the drill part to the workpiece part,and the temperature spread and transfered from the contact part to the periphery.Except for the hole wall passing away,most of the drilling temperature was discharged with chip.The stress concentration part of the workpiece was almost synchronous with the temperature concentrating part.In the aspect of new micro drill preparation,3D printing technology can be used to realize new complex structure micro drill manufacturing.On the basis of the above micro drill model,the model was first printed with resin 3D.The defects and forming quality of 3D were tested.Then the metal 3D micro drills were printed.And then the blunt blades were sharpened.Finally,the drilling experiment of the printed circuit board was carried out.Compared with the conventional structure bit,the new structure drill cut the chip with short chip but not strip chip.And the chip removal was easier.