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EWS
Laser Trimming:
The Competitive Edge
In Precision Linear Devices
By minimizing the need for test pads and creating more
space on the die for circuits, todays next-generation laser
trimming systems are helping semiconductor manufacturers
boost yields, functionality, and profitability in the
miniaturized world of precision linear devices.
by William Witt Bloomstein
T
oday, more than 70% of the worlds
analog semiconductor companies are
using laser-based trimming and link
blowing to enhance circuit performance,
boost yields, speed time-to-market, and
ensure higher profitability in thin film
semiconductor and silicon manufac-
turing. Significant advances in diode-
pumped solid state lasers, software tools,
reduced mechanical complexity, and
related systems technologies have ushered
in a new generation of laser-based trim-
ming systems that can offer high accuracy,
maintenance-free operation, and flexi-
bility in todays demanding production
environments.
As todays consumers demand products
that pack higher and higher levels of
functionality into smaller and smaller
designs, laser trimming and its unique
ability to eliminate test pads and create
more space on the die for circuits is
experiencing a rebirth. For a growing
number of manufacturers, using laser
systems to trim circuits, blow links, and
finetune performance is now viewed as
critical to their ability to carve a competi-
tive advantage or even compete in the
increasingly miniaturized world of
precision linear integrated circuits.
Microscope close-up showing L cut trims on thin film resistors.
T
ECH
N
EWS
Document1 12/7/01 3:00 PM Page 1 More popular than ever
I
t wasnt always like this. If youre like
many manufacturers, you may
remember the days when lasers were
associated more with maintenance, accu-
racy, and cost problems than anything
else. From both an engineering and relia-
bility standpoint, lasers in the early 1980s
were often costly and maintenance-inten-
sive, remembers Ron Erhardt, Test
Engineering Manager at Mountain View,
CA-based TelCom Semiconductor, Inc.,
one of the worlds fastest-growing preci-
sion analog semiconductor manufac-
turers. The older arc lamp lasers werent
as precise as they needed to be. But with
the advent of new diode-pumped laser
technology, everything has changed.
Today, TelCom uses several diode-
pumped laser systems to do laser link
blowing (fuse cutting) for a range of
analog and mixed signal ICs used in
power and thermal management, such as
notebooks, cell phones, and consumer
devices.
When we brought in the first diode-
pumped laser, there were a lot of fears
based on past experience, notes Erhardt.
We had to go through a lengthy cost
justification. But it was completely worth
it. The M310 from GSI Lumonics has
been vital to our success. More than 30%
of our products in design are now being
designed specifically for laser trim.
Allows more circuits and
devices on the die
There are many benefits associated with
using laser systems, but at the core is a
premise that drives virtually every manu-
facturers laser strategy today: by using
laser link blowing or trimming, real estate
dedicated to test pads can be now freed
up for higher device functionality and/or
die size reduction, lowering overall
process costs.
With laser trimming, were making
miniaturized parts that we couldnt other-
wise make, says Fred Mapplebeck, Trim
Technology Development Manager at
Norwood, MA-based Analog Devices, Inc.
A world leader in the manufacture of
precision integrated circuits used in
analog and digital signal processing,
Analog Devices currently deploys a large
number of laser systems around the
world, linked to test equipment (as an
integral part of the process) and to their
manufacturing network to collect data for
continuous quality control. Like TelCom,
Analog Devices has enjoyed significant
success with laser trimming systems such
as the M310 from GSI Lumonics.
Using laser trimming (as opposed to link
blowing), were tightening parameters to
specifications that we couldnt guarantee
through the traditional wafer manufac-
turing process, says Mapplebeck. To
pack so much functionality into such
small circuitry, the finishing touch
requires laser trimming.
The difference in lasers today is their
exceptional positioning accuracy,
continues Mapplebeck. In the old days,
we had to constantly finetune the lasers
position for every device type. Todays
lasers offer 4th generation technology
with galvanometer positioning systems
that are driven by high-performance
DACs. As DAC technology has improved,
so has laser accuracy.
The technical advantages of laser trim-
ming and laser link blowing are consider-
able. Resolution can be adjusted with a
greater granularity, more circuits can be
placed in a given amount of space, and
functionality can be boosted while dies
continue to shrink. Take the typical
analog circuit, explains TelComs Erhardt.
It requires 6-8 test pads if you blow fuses
electrically, each pad about 120 microns.
With laser link blowing, you can eliminate
5-7 of those test pads per circuit. If youre
working in 6/10ths micron geometry,
thats 25-30% of the die area which is now
available for added functionality.
The bottom line benefits
As manufacturers are quick to point out,
todays laser trimming and link blowing
strategies can create a number of strategic
advantages.
Laser trimming lets us ensure high yields
while providing strong product differenti-
ation in the marketplace, confirms
Mapplebeck from Analog Devices. The
benefits go directly to our market share
and profitability.
If you want to make your parts
smaller. Todays relentless drive for
miniaturization, particularly in
consumer electronics, is fueling the
demand for ever-smaller devices. Only
laser can handle small-package specs
like SOT 20 and SOT 23, which are
simply beyond the capabilities of elec-
trical link blowing.
If you want to make your parts more
accurate. More accurate parts require
more links. But manufacturers cant
afford to enlarge die sizes. Because it
eliminates the need for real estate-
hungry test pads, laser ensures higher
accuracy with smaller die sizes.
If you want to ship customer orders
faster. With laser, you can fab a single
mask with varying levels of device func-
tionality and then wait to customize
your wafers when the customer order
rolls in. For example, you can pre-
manufacture generic op-amps, and
then use laser link blowing to cut in
precise 5 volt or 15 volt functionality
depending on what the customer wants.
This combines JIT efficiencies with the
precision of semiconductor
manufacturing.
When are laser trimming
and link blowing the right
solutions for you?
Here are a few guidelines:
Myth
LASER IS TOO MAINTENANCE INTENSIVE.
Older conventional arc lamp lasers required constant recalibration and lamps that needed replacing
every 200 hours. But new lasers are virtually maintenance-free. The M310 Wafer Level Thin Film
Trim System from GSI Lumonics, for example, uses a galvanometer positioning system for fast trim-
ming and high reliability, eliminating the perpetual maintenance associated with moving-stage laser
trim systems. The systems wafer positioner (step-and-repeat table) sits on an air bearing so theres
no contact or friction, offering years of trouble-free operation.
Myth
LASER REQUIRES SPECIAL POWER SOURCE AND MANAGEMENT.
Older water-cooled lasers were temperamental and required excessive power. But today's laser
technology utilizes a solid-state diode laser source that eliminates the need for water cooling or a
special power source. With the M310's diode-pumped laser and power compensation sub-system,
customers can go a month or more between power adjustments for maximum system availability
and productivity.
Myth
LASER START-UP IS TOO DIFFICULT.
While older lasers were often hard to program, today's lasers are as easily programmed as any
electrical link blowing technology. New software tools make it easier than ever to develop a flexible,
scalable laser trimming strategy. The migration from other techniques, such as link blowing, is
usually painless. And there are other advantages. For example, the M310 from GSI Lumonics fea-
tures new CTRiMS software that ensures fast set-up of new devices for production trim in
as little as four hours, according to the manufacturer. CTRiMS offers integrated tools designed to
simplify debugging of new devices.
Myth
THE YIELDS ARE UNRELIABLE.
Earlier arc lamp lasers often didn't deliver acceptable levels of accuracy. Today's trim systems
consiste