Laser Micromachining Definition

Laser micromachining is defined as laser cutting, drilling, etching, stripping, skiving materials such as plastics, glass, ceramic and thin metals with dimensions from 1 micron to 1mm (0.040"). Maximum machining thickness is 1mm. When laser drilling holes, the entrance diameter is larger than the exit diameter. The typical half angle side wall taper is 3 to 5 degrees, material dependent.

Methods of Laser Micromachining

Laser micromachining is performed by two different methods.

A.) Mask Projection:

Excimer lasers utilize the mask projection technique that is akin to laser lithography, the same leading edge technology that manufactures next generation microcomputer chips. The excimer laser illuminates a mask (that is not in contact with the part) that contains a pattern such as a circle, rectangle or any complex shape. This pattern is imaged by downstream optics to produce an identical yet significantly smaller pattern.

Most often, the mask is fabricated inexpensively by chemically etching stainless steel masks whose pattern is typically 150 microns (0.006") or greater. Since the mask projection technique optically reduces or "demagnifies" the mask pattern by an integral amount (typically 5 to 30 times), simple low cost methods can be used to fabricate the mask. In some specific applications, with dimensional requirements less than 5 microns, glass mask (metal deposited on quartz) are used.

Mask Projection has a number of advantages:

" Complex pattern: Any complex pattern such as an "8" or "S" can be produced flawlessly without any stitching or scalloping issues (caused by overlapping a circular laser spot) because the entire pattern is machined at one time.

" Edge quality: When laser micromachining blind channels, the excimer laser can image a long thin rectangular image with perfectly straight line edges. When drilling holes, perfectly circular holes with "ink jet-type" precision is achieved.

" Throughput: A large process area can be laser micromachined at one time, maximizing process throughput and lowering costs.

" The business case for using excimer lasers in a mask projection method usually comes down to process throughput. Having UV laser sources up to 100W in average power, as opposed to 2.5W to 10W with DPSS, allows excimer lasers to be a cost-effective manufacturing solution.

" This is especially the case at 193nm laser wavelength that is not currently attainable by DPSS lasers at reasonable average powers (ie; 30W). The 193nm laser wavelength is used for laser micromachining specific materials such as pebax, nylon, glass and bioabsorbable materials.

To automate the mask projection technique, programmable mask changers are deployed where multiple mask pattern are mounted on a high speed linear mask stage, permitting different mask patterns to be shuttled in on-the-fly. Co-ordinated opposing motor schemes throughout advantages.

Alternatively, a contact mask approach can be used where the mask is in direct contact with the part, eliminating part registration issues associated with stitching patterns together.

B.) Direct-Write:

More information to come.

Direct Write has a number of advantages:

" Maskless: There is no mask pattern. Just point and shoot the laser beam.

" Ease of programming: The drawing is converted by a CAD/CAM program to the machine code, used to drive the motion controller of the laser system.

In the direct-write method (a), the laser beam passes through beam-shaped apertures and focusing lenses to produce a spot on the workpiece. In the mask-projection method (b), an image of the desired pattern is first produced on metal or glass.