Polymers

-polyimide, and polyimide/adhesive layers in flexible circuit or wirestripping applications

-epoxy and epoxy/adhesive layers in PWB construction

-parylene, as a conformal coating on implantable medical devices

-various tubing materials used for catheter tubing

-as a coating material for pharmaceutical tablets, where drilling a precision hole leads to controlled release of medication

Metals

- copper as used as the conductor for PWBs and flex circuits

- thin metal films (e.g. gold, nickel or ITO) on polymer or glass substrates for precision flex circuitry or flat panel display applications

▲[top]

Ceramics and glass

-a wide variety of ceramics (alumina, zirconia, piezoelectrics, as well as nitrides) can be machined by several laser types, from simple cutting with a YAG laser, or precision machining with UV sources (excimer or YAG harmonics) for hybrid circuits and ink jet printer nozzles

- glass can be machined (e.g. precision holes or controlled-depth trenches) or marked with lasers. The choice of laser would depend on the desired effect and surface quality.

- ceramic capacitors can also be marked with the UV output from excimer or harmonics of YAG lasers

Thin films

- ITO and other thin (metal) films (typically on glass or on polyester, polyimide, PET or other polymer substrate) can easily be patterned with lasers for e.g. flat panel display applications

Benefits of Laser Processing

Precision. The ability to exactly define the size and shape of the laser beam, and position it with high tolerance, leads to an exacting precision often not available with conventional processes.

Controllability. Each pulse of a laser removes a fixed depth of material, with this depth controlled by the energy density of the beam on the material. By exposing the target to a prescribed number of pulses, control of depth can be exercised to the sub-micron level. Repeatability. The interaction of the laser beam with the target material is a highly reproducible process, providing highly repetitive results, part after part.

Cleanliness. The material removed by the laser interaction is typically vapourized, leaving little process debris on the part. Quite often post-process cleaning is unnecessary, while for some materials a standard industry cleaning step is adequate (e.g. via drilling in flex or PWB panels requires a standard chemical desmear to enhance subsequent plating).

▲[top]

Technology

The beam from an excimer or TEA- CO₂ laser is typically rectangular in shape, with a 'top hat' intensity profile. Such beams are best utilized in parallel processing of many features simultaneously through the technique of mask imaging. The features to be produced are first generated in a metal mask, which is then placed in the beam. A lens is used to produce a demagnified image of the mask pattern, allowing very small features to be generated in the target material. Since the image is demagnified, the light intensity is increased to values well above the ablation threshold, providing very clean sidewalls in standard polymer materials. Arrays of holes can be generated by stepping and repeating this pattern. Slots can be generated by focusing the beam to a line, and translating the part underneath the beam at an appropriate speed.

Beam homogenizers have been designed to improve the utilization of these top hat beam profiles by folding in the weak edges of the beam. More sophisticated optics (holographic optical elements) are also available for the optimum beam utilization in high volume repetitive patterning applications.

Since both the excimer and TEA- CO₂ lasers are most efficiently used in a mask imaging mode, the material is moved underneath a fixed beam location with XY motion stages. However, in this situation, processing of random patterns of small holes or slots is typically inefficient with regard to both beam utilization and time to move from feature to feature. Another limiting factor is the repetition rate of these lasers, in the range of 100-500 Hz.

Fortunately, alternative, complementary laser sources have become available. RF-excited CO₂ lasers produce low energy, high repetition rate pulses in a Gaussian profile beam. Such devices have also been made to operate in the 9µm band, providing good absorption in key materials such as polyimide. Rather than area processing, the beam is used in focused spot mode, so that the limited pulse energy can exceed the energy density of the ablation threshold. The high repetition rate then allows high drilling or cutting rates.

▲[top]

Developments in diode-pumped solid state lasers have generated similar low energy, high repetition rate sources in the UV region. While the average powers are significantly lower than excimer lasers, the excellent Gaussian beam quality (allowing very small focal spot sizes) and high repetition rates enables very efficient processing of many materials. The shorter wavelengths available from the UV lasers (excimer and DPSS) allow for smaller features than can be generated by the longer wavelength CO₂ lasers.

As mentioned above, large top-hat beams are most efficiently used to process large areas of material on a pulse-by-pulse basis. The more holes that can be imaged onto the area defined by the optimum energy density, the higher the effective drilling rate. An XY table set is used for the step-and-repeat positioning of the material under the imaged beam location. Depending on the application and usage that the machine will experience, the XY tables will use either a lead screw drive, or linear motors. If high accuracy or repeatability is required, then precision glass scale linear encoders can be used with the tables. 

Smaller beams from higher repetition rate TEA-CO₂ lasers as well as the RF- CO₂ and UV-DPSS lasers can be used in a variety of ways. Very fast beam repositioning can be accomplished over reasonable field sizes by programmable galvanometer-based mirrors and telecentric lenses. If very large panels need to be processed, the galvo beam delivery is used in combination with XY tables. This latter configuration is that used by the popular line of DrillStar® PWB drilling machines manufactured by GSI Lumonics.

Sophisticated motion control is interfaced to the operator through a PC running a Windows® environment.  Operator access is limited to the basic commands required to load and run a pre-set job.  Administrator access is password protected and allows creation of job files as well as service and calibration settings.  Alignment to fiducial marks on the panel is achieved through an integrated vision system.  Panels can be loaded manually, or an optional autoloader can be provided.  Systems are designed to be robust in high volume manufacturing.