Micro-hole Processing Technology of Circuit Board Composite（3）
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Update time : 2017-07-24 11:06:10
3 vibration drilling
Vibration drilling is a branch of vibration cutting, is based on the cutting theory and vibration theory based on the new drilling method. Ordinary drilling is a continuous cutting process, and vibration drilling is a pulse intermittent cutting process, in the drilling process through the vibration device to drill between the workpiece and produce a controlled relative movement. In the process of vibration drilling, when the main cutting edge and the workpiece is not separated (no separate vibration drilling), the cutting speed and direction parameters such as cyclical changes; when the main cutting edge and the workpiece when the cut off (separate vibration drilling ), The cutting process becomes a pulsed intermittent cutting.
When the vibration parameters (vibration frequency and amplitude), feed and spindle speed are suitable, the drilling accuracy, dimensional accuracy and roundness can be improved, the surface roughness is reduced, the burr is reduced, and the tool life is prolonged. The axial force variation of GFRP composites is similar to that of ordinary drilling, but the axial force is smaller than that of ordinary drilling. The axial force is affected by the feed rate, vibration frequency and amplitude. Wang et al. Showed that when the amplitude was 6μm, the vibration frequency was 300Hz and the feed rate was 250mm / min, the axial force could reach 1.5N minimum. GFRP material in the glass fiber criss-cross, its strength and hardness is very large, not easy to cut off, and its surrounding matrix is softer, easy to force the drill to the knife, changing the direction of the drill forward, forming a large drill deviation. Vibration drilling with a rigid effect, in the drill, the drill bit by the role of bending deformation is small, into the drilling positioning error is also much smaller than the ordinary drilling.
For multi-layer composites, step-variable multi-variable parametric vibration drilling is a more optimized process, which can solve the contradiction between the quality and efficiency of fiber composite drilling. It takes full account of the structure, performance and specific process of the multi-layer composite material. It maintains the optimal machining state in the drilling process. When drilling, the optimum drilling parameters of the uppermost material are used. The drilling parameters are divided into multiple sections, and the vibration parameters and cutting parameters are mutated and stepwise in terms of the performance of the laminates. The vibration cutting parameters can be optimized and processed. The effect is better than the corresponding conditions of ordinary drilling. Zhao Hongwei et al. Used the electronically controlled micro-hole vibrating drilling machine to carry out micro-hole drilling test on multi-layer composite materials. The drilling error of the drift of the stepwise three-parameter vibration drilling, the hole expansion ΔD, and the exit burr height H are significantly lower than those of the normal drilling. Rumkumar and so on compared with the GFRP composite vibration drilling and drilling the axial force, torque and tool wear, found that the number of drilling in the drilling of more than 30 will appear when the axial force, the sharp increase in torque, and vibration drill The number of drilling holes can be more than 60, and vibration drilling than ordinary drilling axial force, torque and tool wear values are small.
4 laser drilling
Circuit board composite materials in the processing of less than 0.2mm diameter holes, the use of mechanical drilling, tool wear to speed up, easy to break, the cost increases, and the laser beam can be reduced to the micron diameter spot, is the ideal tool for processing micropores. Laser drilling as a contactless drilling technology, is the laser beam focused into a very small spot, the energy of the light melting or gasification material to form micropores, with drilling speed, high efficiency, no tool loss, processing surface High quality, especially suitable for composite microporous drilling. Especially in the hard, crisp, soft and other materials on a large number of high-density group hole processing.
The use of laser drilling composite materials prone to complex physical and chemical changes, the removal of the material there are two main mechanisms: ① thermal processing mechanism, laser heating materials, so that material melting, gasification; ② photochemical mechanism, laser energy directly for To overcome the chemical bonds between the material molecules, so that the material is broken down into small gaseous molecules or atoms. The key to drilling fiber reinforced composites is to select the appropriate laser source, depending on the properties of the material being processed, such as absorption, melting and gasification temperatures, thermal conductivity, etc. for specific wavelengths. Commonly used laser sources are CO2 laser, KrF excimer laser and Nd: YAG laser.
4.1CO2 laser processing
CO2 laser wavelength range of 9.3 ~ 10.6μm, belonging to the infrared laser, the removal of materials for the thermal processing mechanism. CO2 laser drilling resin-based fiber reinforced composite materials, the laser power and processing time on the processing quality of the larger, set the appropriate laser power and processing time can significantly improve the processing quality. Aoyama et al. Used a CO2 continuous laser with a wavelength of 10.6 μm and a maximum output power of 25OW to drill the micropores with a diameter of 0.3 mm on the glass / epoxy composite and found that when the laser power was 35 W and the processing time was OAS ,auxiliary
When the gas is air, the pore walls of the epoxy resin are almost free
Heat damage; and when the laser power is 75W, the processing time is 0.1s, the auxiliary gas is nitrogen, the hole wall surface appears black material. This is due to the laser energy continuous irradiation of the resin, so that the temperature of the resin too late to cool, accumulated to a certain extent, the resin will be heat damage. Hirogaki et al. Used CO2 pulsed laser drilling glass / epoxy and aramid fiber / epoxy composites with a wavelength of 10.6 μm and a maximum output of 100 W. It was found that if the irradiation time was less than 5 ms, the epoxy resin hardly appeared Heat damage. This is because reducing the irradiation time of the laser pulse can reduce the energy absorbed by the material, and the time interval between the pulses causes the material to be cooled, so that the thermal damage of the resin is further reduced.
4.2KrF excimer laser processing
KrF excimer laser commonly used wavelength of 248nm, belonging to ultraviolet laser, excision material for the photochemical mechanism. High-energy ultraviolet photon can make the material directly split into atoms, to achieve the purpose of removal of materials. KrF excimer laser can significantly reduce laser processing heat damage. Zheng et al. Used KrF laser drilling glass / epoxy composites with a wavelength of 248nm, a pulse width of 20ns and an energy density of 400nd / cm2. Not only did the black material appear on the wall, but also the depth of the hole was accurately controlled. The secondary pulse drilling depth is 0.12 μm.
However, the KrF excimer laser drilling hole may exhibit taper, which is due to the diffraction effect of the beam at the edge of the machined shape, resulting in a decrease in the density and etch rate of the energy; another reason may be the use of uncorrected prisms Of the spherical deviation caused. With the increase of energy density, the taper gradually decreases, even the negative taper. This may be due to the fact that the beam energy density is greater than the critical energy generated by the diffraction at the boundary and the defocusing effect causes the beam diameter to become larger.
4.3Nd: YAG laser processing
Nd: YAG laser commonly used wavelengths of 1.06μm and 355nm, belonging to the infrared laser and ultraviolet laser, respectively, the two wavelengths corresponding to the thermal processing mechanism and photochemical mechanism. Nd: YAG laser drilling, laser power and pulse frequency have a significant impact on heat damage. Yang et al. Used a Nd: YAG laser with a wavelength of 355nm and an average power of 12W to drill a 1.6mm thick fiberglass / epoxy composite. It was found that the higher the power and the higher the processing temperature at a given pulse frequency, Accelerating the coking of epoxy resin and the melting of glass fibers, and the equivalent width of heat damage increases with increasing laser power. At a given laser power, the equivalent width of the thermal damage increases at a pulse frequency of 7 kHz, which increases with increasing frequency at less than 7 kHz, and decreases by more than 7 kHz when the width of the heat is reduced. This is because the higher the frequency, the shorter the time interval between the laser pulses, the shorter the cooling time of the machining surface, and the longer the pulse frequency when the frequency exceeds 7 kHz, the longer the pulse duration and the peak power of the laser pulse The smaller the temperature of the machined surface, the less the equivalent width of the thermal damage. With the wavelength of 355nm, power 0.3W, pulse frequency 1KHz Nd: YAG laser drilling, hole wall surface almost no heat damage.
Due to the type of composite fiber and the direction of each layer of fiber, the accuracy of the hole in the Nd: YAG laser drilling process is reduced, and the interface between the layers is discontinuous and the fiber is expanded. Rodden et al. Drilled a 2 mm thick carbon fiber / epoxy composite panel with Nd: YAG laser with a pulse width of 0.1 ms and found that the shape of the hole changed from an ellipse to an ellipse at the interface between the layers The former is due to the thermal conductivity of carbon fiber is much larger than the thermal conductivity of epoxy resin, the heat first along the direction of carbon fiber conduction, leading to the hole along the direction of carbon fiber was stretched; the latter because of each layer of carbon fiber direction Different, resulting in inter-layer hole discontinuity. When the carbon fiber / PEEK composites with a wavelength of 1.06μm and the maximum average output energy of 135W and the pulse duration of 0.5 ~ 5ms were drilled by Nd: YAG pulsed laser, it was found that the carbon fibers around the hole appeared at the end Of the radial expansion of up to 50%. Due to the intense thermal expansion of the fiber, the local filling structure is irreversibly changed, and the rapid pressurization of the micropores in the fiber structure reinforces this effect.
Vibration drilling is a branch of vibration cutting, is based on the cutting theory and vibration theory based on the new drilling method. Ordinary drilling is a continuous cutting process, and vibration drilling is a pulse intermittent cutting process, in the drilling process through the vibration device to drill between the workpiece and produce a controlled relative movement. In the process of vibration drilling, when the main cutting edge and the workpiece is not separated (no separate vibration drilling), the cutting speed and direction parameters such as cyclical changes; when the main cutting edge and the workpiece when the cut off (separate vibration drilling ), The cutting process becomes a pulsed intermittent cutting.
When the vibration parameters (vibration frequency and amplitude), feed and spindle speed are suitable, the drilling accuracy, dimensional accuracy and roundness can be improved, the surface roughness is reduced, the burr is reduced, and the tool life is prolonged. The axial force variation of GFRP composites is similar to that of ordinary drilling, but the axial force is smaller than that of ordinary drilling. The axial force is affected by the feed rate, vibration frequency and amplitude. Wang et al. Showed that when the amplitude was 6μm, the vibration frequency was 300Hz and the feed rate was 250mm / min, the axial force could reach 1.5N minimum. GFRP material in the glass fiber criss-cross, its strength and hardness is very large, not easy to cut off, and its surrounding matrix is softer, easy to force the drill to the knife, changing the direction of the drill forward, forming a large drill deviation. Vibration drilling with a rigid effect, in the drill, the drill bit by the role of bending deformation is small, into the drilling positioning error is also much smaller than the ordinary drilling.
For multi-layer composites, step-variable multi-variable parametric vibration drilling is a more optimized process, which can solve the contradiction between the quality and efficiency of fiber composite drilling. It takes full account of the structure, performance and specific process of the multi-layer composite material. It maintains the optimal machining state in the drilling process. When drilling, the optimum drilling parameters of the uppermost material are used. The drilling parameters are divided into multiple sections, and the vibration parameters and cutting parameters are mutated and stepwise in terms of the performance of the laminates. The vibration cutting parameters can be optimized and processed. The effect is better than the corresponding conditions of ordinary drilling. Zhao Hongwei et al. Used the electronically controlled micro-hole vibrating drilling machine to carry out micro-hole drilling test on multi-layer composite materials. The drilling error of the drift of the stepwise three-parameter vibration drilling, the hole expansion ΔD, and the exit burr height H are significantly lower than those of the normal drilling. Rumkumar and so on compared with the GFRP composite vibration drilling and drilling the axial force, torque and tool wear, found that the number of drilling in the drilling of more than 30 will appear when the axial force, the sharp increase in torque, and vibration drill The number of drilling holes can be more than 60, and vibration drilling than ordinary drilling axial force, torque and tool wear values are small.
4 laser drilling
Circuit board composite materials in the processing of less than 0.2mm diameter holes, the use of mechanical drilling, tool wear to speed up, easy to break, the cost increases, and the laser beam can be reduced to the micron diameter spot, is the ideal tool for processing micropores. Laser drilling as a contactless drilling technology, is the laser beam focused into a very small spot, the energy of the light melting or gasification material to form micropores, with drilling speed, high efficiency, no tool loss, processing surface High quality, especially suitable for composite microporous drilling. Especially in the hard, crisp, soft and other materials on a large number of high-density group hole processing.
The use of laser drilling composite materials prone to complex physical and chemical changes, the removal of the material there are two main mechanisms: ① thermal processing mechanism, laser heating materials, so that material melting, gasification; ② photochemical mechanism, laser energy directly for To overcome the chemical bonds between the material molecules, so that the material is broken down into small gaseous molecules or atoms. The key to drilling fiber reinforced composites is to select the appropriate laser source, depending on the properties of the material being processed, such as absorption, melting and gasification temperatures, thermal conductivity, etc. for specific wavelengths. Commonly used laser sources are CO2 laser, KrF excimer laser and Nd: YAG laser.
4.1CO2 laser processing
CO2 laser wavelength range of 9.3 ~ 10.6μm, belonging to the infrared laser, the removal of materials for the thermal processing mechanism. CO2 laser drilling resin-based fiber reinforced composite materials, the laser power and processing time on the processing quality of the larger, set the appropriate laser power and processing time can significantly improve the processing quality. Aoyama et al. Used a CO2 continuous laser with a wavelength of 10.6 μm and a maximum output power of 25OW to drill the micropores with a diameter of 0.3 mm on the glass / epoxy composite and found that when the laser power was 35 W and the processing time was OAS ,auxiliary
When the gas is air, the pore walls of the epoxy resin are almost free
Heat damage; and when the laser power is 75W, the processing time is 0.1s, the auxiliary gas is nitrogen, the hole wall surface appears black material. This is due to the laser energy continuous irradiation of the resin, so that the temperature of the resin too late to cool, accumulated to a certain extent, the resin will be heat damage. Hirogaki et al. Used CO2 pulsed laser drilling glass / epoxy and aramid fiber / epoxy composites with a wavelength of 10.6 μm and a maximum output of 100 W. It was found that if the irradiation time was less than 5 ms, the epoxy resin hardly appeared Heat damage. This is because reducing the irradiation time of the laser pulse can reduce the energy absorbed by the material, and the time interval between the pulses causes the material to be cooled, so that the thermal damage of the resin is further reduced.
4.2KrF excimer laser processing
KrF excimer laser commonly used wavelength of 248nm, belonging to ultraviolet laser, excision material for the photochemical mechanism. High-energy ultraviolet photon can make the material directly split into atoms, to achieve the purpose of removal of materials. KrF excimer laser can significantly reduce laser processing heat damage. Zheng et al. Used KrF laser drilling glass / epoxy composites with a wavelength of 248nm, a pulse width of 20ns and an energy density of 400nd / cm2. Not only did the black material appear on the wall, but also the depth of the hole was accurately controlled. The secondary pulse drilling depth is 0.12 μm.
However, the KrF excimer laser drilling hole may exhibit taper, which is due to the diffraction effect of the beam at the edge of the machined shape, resulting in a decrease in the density and etch rate of the energy; another reason may be the use of uncorrected prisms Of the spherical deviation caused. With the increase of energy density, the taper gradually decreases, even the negative taper. This may be due to the fact that the beam energy density is greater than the critical energy generated by the diffraction at the boundary and the defocusing effect causes the beam diameter to become larger.
4.3Nd: YAG laser processing
Nd: YAG laser commonly used wavelengths of 1.06μm and 355nm, belonging to the infrared laser and ultraviolet laser, respectively, the two wavelengths corresponding to the thermal processing mechanism and photochemical mechanism. Nd: YAG laser drilling, laser power and pulse frequency have a significant impact on heat damage. Yang et al. Used a Nd: YAG laser with a wavelength of 355nm and an average power of 12W to drill a 1.6mm thick fiberglass / epoxy composite. It was found that the higher the power and the higher the processing temperature at a given pulse frequency, Accelerating the coking of epoxy resin and the melting of glass fibers, and the equivalent width of heat damage increases with increasing laser power. At a given laser power, the equivalent width of the thermal damage increases at a pulse frequency of 7 kHz, which increases with increasing frequency at less than 7 kHz, and decreases by more than 7 kHz when the width of the heat is reduced. This is because the higher the frequency, the shorter the time interval between the laser pulses, the shorter the cooling time of the machining surface, and the longer the pulse frequency when the frequency exceeds 7 kHz, the longer the pulse duration and the peak power of the laser pulse The smaller the temperature of the machined surface, the less the equivalent width of the thermal damage. With the wavelength of 355nm, power 0.3W, pulse frequency 1KHz Nd: YAG laser drilling, hole wall surface almost no heat damage.
Due to the type of composite fiber and the direction of each layer of fiber, the accuracy of the hole in the Nd: YAG laser drilling process is reduced, and the interface between the layers is discontinuous and the fiber is expanded. Rodden et al. Drilled a 2 mm thick carbon fiber / epoxy composite panel with Nd: YAG laser with a pulse width of 0.1 ms and found that the shape of the hole changed from an ellipse to an ellipse at the interface between the layers The former is due to the thermal conductivity of carbon fiber is much larger than the thermal conductivity of epoxy resin, the heat first along the direction of carbon fiber conduction, leading to the hole along the direction of carbon fiber was stretched; the latter because of each layer of carbon fiber direction Different, resulting in inter-layer hole discontinuity. When the carbon fiber / PEEK composites with a wavelength of 1.06μm and the maximum average output energy of 135W and the pulse duration of 0.5 ~ 5ms were drilled by Nd: YAG pulsed laser, it was found that the carbon fibers around the hole appeared at the end Of the radial expansion of up to 50%. Due to the intense thermal expansion of the fiber, the local filling structure is irreversibly changed, and the rapid pressurization of the micropores in the fiber structure reinforces this effect.