Nano to pico
to femto: Pulse widths
for optimal laser
CHOICE OF PULSE WIDTH HAS HIGH IMPACT
ON QUALITY, THROUGHPUT, AND COST
RAJESH PATEL, JIM BOVATSEK, AND HERMAN CHUI
The goal of any machining process is to achieve the desired high-qual- ity results in the shortest time pos- sible and in the most economical way. Laser machining, compared to conventional mechanical machining techniques such as cutting, milling,
and drilling, can achieve localized, high-quality, and precise
machining. With the right choice of laser, one can also achieve
a high-yield, high-throughput, and economical process.
One industry where lasers are heavily used is in manufacturing mobile devices. The demand to make smaller, faster,
lighter, and lower-cost mobile devices has required laser
micromachining processes that can meet this challenge.
Other industries, such as medical device manufacturing,
clean energy, automotive, and aerospace, have also adopted
laser machining to varying degrees.
While several laser parameters
affect the machining results, the
choice of pulse width is one of the
important factors that affect the
precision, throughput, quality, and
economics of the process. Pulsed lasers with pulse widths in
the nanosecond-to-femtosecond range are commonly used
for precision micromachining of various materials. This article
describes the tradeoff among throughput, quality, and cost for
commonly used nanosecond, picosecond, and femtosecond
lasers for micromachining.
Nanosecond pulse widths
It is well established that, for the same average power, nanosecond lasers result in a higher rate of material removal and,
therefore, higher throughput vs. picosecond and femtosecond
lasers because of the fact that the majority of material removal
takes place by melting. The material is heated by the laser pulse
from room temperature to its melting temperature, and is eventually removed by evaporation and molten material expulsion.
The precision and quality of machining, however, suffers
since the molten material removed usually clings to the edges of
FIGURE 1. An 80µm-diameter
through-via hole drilled in copper-polyamide-copper FPCB film with
an average burr height of 2µm
around its edge.