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 drilling 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 75m. 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.

4. Drilling rate

The drilling rate is strongly dependent on the material. It needs to

be in the range of a few thousand holes per second to fit the

production. Increasing the average power of the laser from 50W to 100W

more than doubles the drilling rate of the thru holes.

The High-Speed PCB Drilling Machine.

Below is a short description of the typical machine features that are

commonly available on the market.

- Large plastic base for easy positioning of the PCB

- Variable rpm that is infinitely adjustable

- Quick spring chuck without drill locking key making it suitable for

drilling shank size

- Adjustable drilling stroke - where the upper and lower

drilling stroke can be defined as the optimal up and down movement of

the strokes

- Adjustable control lever that can be set at the desired level.

- Dust exhaust connection socket for chip removal - it can be connected

to a vacuum cleaner or a central air exhaust system.

- Drill spot illumination to offer a better view of the work surface

area.

The PCB drilling systems with picoseconds lasers are available in

the market. This new generation of industry ready picoseconds lasers

have an average power of 100W and more will make them a capable tool

for mass production. Further miniaturization with diameters down to 10

m is possible by adapting to the focusing optics and beam shapers.

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