Study Of Micro-hole Drilling Process And Quality On Flexible Printed Circuit Board

Millipore (less than1mm aperture) is an important part of flexible printed circuit board. The quality of micro holes may directly affect the reliability and life quality of subsequent hole wall copper plating and electronic product. Thus, the drilling process is an important link of flexible printed circuit board manufacturing processes. Nowadays, flexible plates of micro holes are mainly manufactured by mechanical drilling. As the demand for the market of technology in FPCB products is getting higher and higher, the FPCB layer will be increasing and the line width and line spacing will be narrower with the smaller aperture. Higher and stricter requirements about the quality of the micro hole machining will be needed actually. However, it has not yet in-depth research and there are a lot of problems in the process of production at the moment for flexible sheet micro holes mechanical drilling. Therefore, it is necessary for the study of FPCB micro hole drilling processing in-depth.In this paper, for the urgent needs of high technology about flexible plates, methods of theoretical analysis and lots of experiment will be put forward, emphatically from the flexible plate into the drill micro-hole drilling process skid deflection, chip removal condition, chip morphology, cutting force, cutting temperature, the micro drill wear and quality of drilling micro holes on the flexible plate micro hole drilling process system. The results are as follows:The root cause of drill tip deflection skid when the moment of micro-drill drilling into the FPCB is lateral unbalanced force. Use the drilling accessories such as cover plate can be improved the drill tip deflection and skid phenomenon in the process of drilling, but the collocation of different drilling accessories for drilling in the drilling deflection skid have different effects.Feed speed morphology has a great influence on cuttings. Under the condition of the same spindle speed, the length and thickness of the cuttings will increase with the increasing feed speed. Feed rate, the greater the size of drilling cuttings, bit of chip removal ability will decrease, with the chips attaching the bit easily. With the feed speed getting higher, the cuttings, generated by the upper and lower drill bit, may have difference The difference can be found by the surface of adhesive adhesion in the position of the copper scrap from non-metallic materials.Micro drill in the drilling process, micro-drill interleaved drilling copper foil and polyimide (PI) film, adhesive and the change of the drilling force produced by the corresponding change alternately. The drilling force may decrease when drilling copper foil and adhesive, PI film respectively. Drilling axial force may decrease with the increasing of spindle speed, and the corresponding will get obviously with the increase of feed speed. Drill diameter to the drilling axial force is a significant parameter, and with the influence of the drill bit diameter, the greater the drilling axial force may get larger.Cutting temperature is accumulated during drilling. Drilling temperature has a great relationship with the speed of inway and outway. When the retract rate and feed rate is low, it is not easy to accumulate heat. When drilling the blade and feed speed get larger, the time interval between adjacent holes will be shorter, and the heat will be gradually accumulated with the increasing temperature. When drilling with low temperature air cooling can largely decrease the temperature of drilling.It mainly has two forms of wear during micro drilling, the chisel edge wear and the flank wear. With the increasing of spindle speed and feed speed, the wear and tear will gradually get fierce. With the increasing of holes number, the wear and tear of bits will deteriorate. The combination of cover plates will increase the complexity of during drilling, which may affect the wear of bits.Holes position accuracy increases with the increases of spindle speed and the retract speed, decreases with the increase of feed rate, along with the rapid increase the diameter of the drill bit. Micro distributed bit drilling increasing number can lead to lower precision. That increasing entry board thickness accuracy of holes location is reduced, cover plate reasonable use way can effectively improve the accuracy of hole location. Flexible plate laminated layers of different drilling can also affect holes position accuracy, hole position accuracy will reduce along with the increase in laminated layer.Micro holes inward and outward appearance were the major influenced by factors of drill diameter, hole number and the cover plate usage. Bit diameter will affect the number of micro holes, exit burr and inlet roundness error. Along with the rising of the drill bit diameter, exit burr quantity increases, the error of the pore aperture smaller. Drilling can affect the number of the width of the ring of microcellular plastic deformation at the entrance, hole number, the more plastic deformation ring size is larger. Cover plate of micro holes entrance burr is more significant, the influence of cold punching plate is applied to make hole cover plate when the entrance of the quality is best, followed by coating aluminium; Than ordinary aluminum plate without using plate inlet are of good quality. Pressure foot morphology on micro holes exports the most outstanding, the influence of between middle pressure is too small, if drilling process causes a micro holes exit burr is too large. Plate hardness is also a main factor affecting the exit burr, burr size exports will decreases with the increase of plate surface hardness.In terms of quality of micro holes wall, micro hole drilling process of lateral force and axial force and the temperature are the root causes that causing hole drilling nail head and exit burr of the PI. PI inside the nail head thickness and exit burr height will slightly decrease with the spindle speed increasing, and lead to a trend of increase with the feed speed and the number of drilling increasing. In the process of micro hole drilling, the upper aperture of hole is larger than the bellowing.and other defects etc.