Lasers—a flexible tool for PCB and device rework
Marking Attributes Laser Labeling
specialty requirements of a device or PCB
marking or the precision of the light source
Minimal downtime due to equipment malfunction, setup YES NA
that makes a laser a unique rework tool.
or part changeover requirements.
Capability to print alphanumeric text, barcodes, 2-D YES YES
references
codes and graphic logos anywhere on a PCB
1. IPC 1066-“Marking, Symbols and
Labels for Identification of Lead-Free
Invariant to PCB base material color No YES
and Other Reportable Materials in
Ability to accommodate multi-up PCBs without signifi- YES No Lead-Free Assemblies, components and
cant reduction in cycle time per panel Devices”
Minimal Inventory of stocked items to support process YES No
2. IPC 7721 2.3.6 “Coating Removal,
Micro Blasting Method”
Low cost operation per panel or board YES No
3. IPC 7721 6.1 “Jumper Wires”
Supports reworking of boards at subsequent processes YES Sometimes
4. Practical application of laser soldering in
electronics assembly, : Industrial Elec-
Table 1. Comparing the attributes of laser marking and labeling
tronics, 1997. ISIE ‘97., Beckett, P.M.
Fleming, A.R. Gilbert, J.M. Whitehead,
D.G. Proceedings of the IEEE Inter-
national Symposium on Electronics
Assembly, 7-11 Jul 1999
5. ANSI MS 10.8-1983 and MIL STD
1189A
Prior to owning his own businesses, Bob
Wettermann made his way through a variety of
career stops at companies ranging from a start-
up venture through mid-tier, all the way to a
Fortune 100 company. BEST Inc, his business,
provides test, rework and PCB repair services,
training services and PCB repair products.
Bob was awarded an electrical engineering
degree from the University of Illinois and also
holds an MBA from DePaul University. He
Figure 3. Opening a window in polyimide flex. holds patents in surface science, electrical con-
trols and electronics assembly products.
Currently Bob is a member of the SMTA and is
space reflectance ratio, which some HDI flex cutting, hole and via drilling, and
a CIT IPC instructor.
labels have a hard time reaching. selective polyimide removal are defined
The demand for PCBs to be more as spaces and traces in the less than 200
completely identified can be more readily µm ranges, and 250 µm or less for vias.
met by laser marking systems. Customers They are employed primarily in telecom,
are continually requesting that each board computer, IC manufacturing and medical
be viewed as unique in its function and device manufacturing. Certain classes of
marked as an end product. Laser marking CO2 lasers are tuned to be the most effi-
meets this demand as its ‘on-the-fly’ ma- cient (9.3 µm) to cut on polyimide for these
chining flexibility allows each board to be types of flex processing.
uniquely marked by feeding new data into In order to fix a design issue, a filter
the laser machining system. circuit consisting of several components
There are several advantages to utiliz- needed to be added to flex circuit. In order
ing laser marking as a step in the rework to make the component terminations, sev-
process. Densely populated PCBs with little eral areas of the 0.002” thick flex substrate
or no room for product information are needed to have ‘windows’ fabricated by
well suited to laser marking as they have an selective removal of the polyimide, which
ability to print very small, high aspect ratio could then expose the 5 mil wide underly-
markings. Laser marking provides a perma- ing copper trace, as shown in Figure 3.
nent mark on a wide variety of materials. conclusion
In addition, this technique allows for a very Lasers can be used to mark, create pads or
fast writing rate, which in turn allows for traces for jumpers. While there is a capital
greater rework throughput. cost associated with the procurement of
the laser, there are specific applications due
Flex circuit modification to the proximity of neighboring parts
5
, the
22 – Global SMT & Packaging – November 2008
www.globalsmt.net
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