The UV Laser Based Printed Circuit Board (PCB) Drilling Machine

The trend in the Printed Circuit Boards (PCB) design towards the smaller features at very high densities is quite essential in order to support the fast-growing market for the high-tech customer products. This requires new laser processing capabilities with the use of the PCB drilling machines.

The PCB drill machines are a new generation of drilling, which makes the use of the high power picoseconds laser to allow high quality and higher throughput production of blind holes in the PC-Boards.

How the machine works

The PCB drill machine uses a short lapse pulse with the high power density to quickly feed energy into the work piece causing the material to melt and vaporize. The greater the pulse energy, the more the material it is melted and vaporized. Vaporization will cause the material volume in the drilled hole to increase suddenly creating a high pressure. This will cause the vapor pressure to expel the molten material from the hole.

Percussion Drilling with UV Lasers

The PCB drill machine has to make through holes (vias), and blind holes have to be drilled into the Printed Circuit Board (PCB) which acts as the interconnections between the layered systems. Both the holes should have straight walls. Percussion drilling with the use of UV laser is a method of choice for most of the PCBs drilling. They reach very high drilling rates of several thousand holes per second and can drill diameters as small as 75μm. The use of UV lasers makes it possible to drill smaller diameters. However, these lasers are limited to only a few tens of watts of the average power thus limiting the drilling rate.

Steps Involved in the Industrial UV Laser PCB Drilling

1. Absorption

The PCB drilling machine has UV wavelength of frequency converted lasers which is absorbed in the copper as well as the composite material and the plastics used for the PCB to allow much smaller diameter due to the shorter wavelength.

The modern picoseconds lasers allow the processing of a vast range of materials even with the fundamental wavelength of 1330nm. Using a peak power of more than 40MW and an intensity of several GW/cm2, the multiphoton absorption occurs. The nonlinear absorption allows the laser to process even highly transparent materials with very low optical penetration depth.

2. Depth Control

The creation of blind holes is easily achieved by controlling the number of pulses. Ramping on the pulse energy is therefore not required. The modern laser drilling machines are built in an external modulator that is used to control and adjust the pulse energy from pulse to pulse allowing pulse picking of single pulses in very precise control of the drilling process.

3. Shaping the Holes

A Gaussian intensity distribution can lead to increased damage to the copper layers in the center part of the hole and a larger taper angle of the sidewalls. The sidewalls can be affected when trying to fill the hole with copper. A top-hat beam shaper DOE is used to shape the intensity profile in a way that the angle of the hole is improved and the radius is reduced to achieve the desired shape.

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