Laser Sources

Laser Wavelengths

Machining dimensions are proportional to approximately twice the laser wavelength. The shorter the laser wavelength, the smaller the feature size is realizable.

Resonetics has the largest number of excimer lasers in the United States for contract manufacturing. With + 50 excimer lasers operating in the ultra-violet wavelength (193nm, 248nm, 308nm) with average power approaching 100 Watts, these lasers are ideal for processing of plastics, glass, ceramics and thin metals with tolerances approaching 1 micron.

By operating in the ultra-violet region, the excimer laser ablate or vaporize the material, minimizing debris or heat affected zone. This photo chemical ablation process works by the laser breaking the molecular bonds within the material and ablated material is ejected upward and away from the material surface at supersonic speed.

 

Laser Wavelengths (Continued)

Resonetics utilizes short pulsed CO2 lasers operating at 10.6 micron wavelength. The CO2 (Carbon Dioxide) lasers operate at average power of 150W with repetition rates of 10khz. The CO2 laser has the highest processing speed, two orders of magnitude faster than excimer lasers and one order of magnitude faster than DPSS lasers.

Of course, there are consequences to this processing speed. They include thermal effects such as potential melting or cracking, limited machining dimensions (0.003") and tolerances (0.0015") and not suitable for blind hole drilling or precise selective material removal.

Excimer Lasers

An excimer laser is gas powered laser, automatically filled with a specific gas mix and run for a period of time before the existing gas fill is evacuated and replenished with new gas. The excimer laser achieves the highest average power (up to 100 Watts) in the ultraviolet spectrum, with laser wavelengths ranging from 157nm, 193nm, 248nm, 308nm and 351nm.

Excimer lasers became industrial workhorses when the semiconductor industry gravitated from UV lamp sources to excimer lasers to produce next generation computer chips. Today's lithographic tools, scanner and steppers, deploy excimer lasers. In the case of laser micromachining applications, excimer lasers are utilized as lithographic tools in the range of 1 micron features (or higher).

DPSS (Diode-pumped Solid State Lasers)

Diode-pumped solid-state lasers are solid-state lasers that are pumped by a series of diode bars. There has been significant development over the years, propelled by the microelectronics industry (micro vias in cell phones and other hand-held portable devices) to reach the ultraviolet spectrum at 355nm and 266nm. The fundamental laser wavelength is 1.06 microns and non-linear crystals are used to double (532nm), triple (355nm) and quadruple (266nm) the laser wavelength with the penalty of lower average power and higher pulse to pulse variation.

Femtosecond Lasers

Femtosecond or ultrafast lasers are solid state lasers that produce a temporal pulse in the femtosecond regime (10-15 sec). The laser consists of an oscillator, regenerative amplifier, amplifier pump laser and stretcher/compressor unit. In some ways, this technology is viewed as the "holy grail" because the extremely short pulse duration removes material as a multiphoton ablation process, ideal for any material type with little or no heat affected zone. The technology is becoming more industrialized, packaged in a single unit, with average power of a few watts and repetition rates up to 5 khz.

Femtosecond Laser White Paper

CO2 Lasers (Carbon Dioxide)

CO2 lasers are gas powered lasers with a sealed laser tube (no gas filling required) that have been the mainstay of laser machining for decades. These lasers operate in the infrared spectrum (9.4 microns or 10.6 microns) with average powers in the kilowatts with high repetition rates. In the field of laser micromachining, the applications are limited because the smallest achievable spot size is 50-75 microns diameter. Still, the laser is applicable for certain "through hole" applications where high throughput and low operating costs are required.

The excimer laser has a typical pulse duration of 20 nsec. The temporal pulse is so short that there isn't time to generate heat, minimizing any thermal effects such as melting. This is especially the case as the wavelength gets shorter, such as at 193nm.

The laser source operates at a repetition rate up to 200hz with an etch rate of approx. 0.1 to 0.5 microns per pulse. The laser can drill through or blind holes. By counting the number of pulses, the depth of machining can be accurately controlled. As an example, the laser is ideal for selective removal of a top coating or layer without damaging the underlying layer.

The excimer laser removes material precisely, like peeling an onion layer-bylayer. By using short wavelength such as excimer lasers, machining dimension as small as 1 micron is realizable.

Resonetics operates Diode-pumped solid state lasers (DPSS) which are relatively low power laser sources (10W or less) operating at high repetition rates (50 khz), suited for direct write applications such as laser cutting of plastics and thin metal foils or laser drilling of non-repeatable hole patterns in polymers and ceramics. These lasers operate in the fundamental wavelength (1.06 microns) but can be doubled (532nm), tripled (355nm) or quadrupled (266nm) to handle a variety of materials and machining patterns.

CO2 lasers are the industrial workhorse of laser machining utilizing a spot size of .003" or .004'. Machining tolerances approach one-half the laser spot size. CO2 laser machining is a thermal process, liquefying the material to allow coaxial gas to push the machined material out the back

side. Unlike a UV laser (excimer or DPSS at 355nm or 266nm), the CO2 laser vibrates the molecular bonds of the material, generating heat that is used to liquefy the material.