Lasers—a flexible tool for PCB and device rework
Lasers—a flexible tool for
PCB and device rework
Bob Wettermann, CIT, BEST Inc., Rolling Meadows, Illinois, USA
component demarking/remarking
and sodium bicarbonate powder. Care must
While there are many
There are several reasons why demarking or
be taken so that the abrasive media does not
rework processes outlined by
remarking of components may take place
embed itself into soft conformal coatings,
both rework equipment vendors
including, but not limited to:
such as those that are silicon-based. Masking
and the IPC 7711/7721PCB
• Change of solder ball alloy type on
the surrounding areas with an ESD-safe
rework and repair documents,
an area array device
1
cover prevents nearby components or areas
there is a lack of repositories
• Protecting the intellectual property
of the PCB from becoming damaged. Dam-
of application notes for non-
of a PCB or device design
aging static charges can be generated as high-
mainstream laser-based PCB
• Marking of the date code or revision
velocity particles travel through the removal
rework processes.
level marking for a firmware or
tools’ delivery lines. Many micro-abrasion
Creative rework and
software change
systems have anti-static ionizers and ground-
• Marking the serial number for part
ing points contained within the unit.
repair solutions for PCBs
tracking purposes
Although mechanical grinding is the least
are required where there preferable method for the remarking of a
are challenges in salvaging
There are also several types of de-marking
component, it is the easiest procedure. A
populated PCBs. One such
methods for devices, including the mechani-
multitude of equipment rework stations con-
innovative approach involves
cal abrasion, re-labeling, chemical etching or
taining drills, grinders, rotating brushes, and
the use of lasers, which have
laser machining.
the like are commercially available, which
become commonplace in PCB
The micro-abrasive removal technique
2
the rework technician can use to grind off
uses high velocity particles to ‘etch away’
and stencil fabrication and
the markings. Care must be taken to control
part print markings. This method, which re-
are becoming more common
the depth and avoid undue stresses on
quires excellent dexterity, uses high-velocity
device leads. The lack of control in this pro-
so in the rework area.
abrasive particles accelerated and directed
cess means that only the most experienced
While novel laser rework
through a nozzle.
and skilled operators should perform this
processes cannot be described
Commonly used abrasive media include
technique. If the size of the markings is very
in an all encompassing ‘how ground walnut shells, glass or plastic beads,
small, the use of this technique might not be
to’ applications guide, examples
of their use as rework tools in
the PCB and electronic device
rework areas help to expand
the possibilities in users’ minds
of salvaging valuable PCBs.
Several examples, including
the demarking of a device,
the creation of traces on an
already-populated PCB,
polyimide flex selective mask
removal and PCB marking
will be described herein as
case studies on the use of
lasers for reworking PCBs.
Keywords: Laser, Rework,
Component Demarking, PCB
Marking, Laser-Etching, Flex
Circuits
This paper was originally presented
Figure 1. Laser marking of device after alloy conversion.
at SMTAI 2008.
20 – Global SMT & Packaging – November 2008
www.globalsmt.net
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