AIR EMISSIONS FROM LASER DRILLING
OF PRINTED WIRING BOARD MATERIALS
Charles H, Darvin
U.S. Environmental Protection Agency
National Risk Management Research Laboratory
Research Triangle Park, NC
Carl J. Kershner, Ph.D.
Mound Laser and Photonics Center, Inc.
Miamisburg, OH
Abstract
The electronics packaging industry has traditionally relied upon mechanical drilling systems to prepare holes in printed wiring board
(PWB) material. Recently, however, a potentially new and innovative application for laser technology was developed for drilling P WB
holes. This application of lasers has the potential to significantly reduce the time and cost of producing PWBs. The process is also
predicted to reduce the volume of solid waste product generated during PWB manufacture. The continuing question presented on the
use of laser drilling is its potential for producing air pollution which may be generated from thermal decomposition at the laser drilling
site. Of particular interest for the study was the possible presence of phosgene (COCl2), dioxins, and hydrogen cyanide (HON) due to
the presence of N2 and Cl2 in the monomer and resin components of the PWB materials.
To address the question of potential air pollution generated during laser drilling of PWB material, a study was sponsored by the
Technology Institute for Manufacturing Electronics, the Mound Laser and Photonics Center, Inc., and EPA to characterize the gases
and particulate matter generated during the drilling process. The study identified the compounds and generated rates during drilling.
The typical compounds found in the emissions stream were trace amounts of C02, CO, HCN, and CH4.
This paper presents the results of this study and identifies the pollutants found during the drilling process.
Introduction
The electronics packaging industry has traditionally relied
upon mechanical carbide cutting tools to drill holes and
machine (rout) printed wiring board (PWB). materials. This
technique results in a large volume of process waste. Although
the process waste is typically not considered a hazardous waste,
its disposal does create a significant solid waste volume. Thus,
because of its non-hazardous nature, little interest has been
generated to reduce this volume. Pollution prevention and cost-
benefit analysis of the PWB manufacturing process have shown
that elimination of current entry and backup materials, and
tools (drill bits etc.) that essentially become part of the solid
waste stream, will result in significant benefit to the
environment as well as to the PWB industry. The traditional
mechanical method also limits feature size in circuit design that
results in limits to electronic packaging performance. Novel
mechanical technologies have been proposed which can
improve feature capabilities; however, these methods will not
reduce waste, nor will they prove beneficial when applied to
standard product designs. However, industry reports such as
the 1995, "National Technology Roadmap for Electronic
Interconnections: Cross-cutting Technologies," by the Institute
for Interconnecting and Packaging Electronic Circuits,
Northbrook, IL, have identified laser machining as a possible
alternative to conventional mechanical drilling.
Although laser drilling may represent apotential solution to the
solid waste problem for PWB manufacturing there are some
environmental questions with its application. Due to potential
high temperatures involved with the process, questions have
arisen about the possible formation of potentially hazardous
compounds. However, there is a lack of data that addresses the
gaseous and particulate matter byproduct emissions resulting
from laser drilling.
In 1996, the Environmental Protection Agency (EPA) entered
into a joint agreement with the Technology Institute for
Manufacturing Electronics to investigate the decomposition
products from tire application of laser technology to PWB

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manufacturing. Although the study represented only a small	one end, a side port for connecting to the vacuum pump, and an
part of a larger program to develop the use of laser systems for	aperture with an O-ring seal to the part being drilled.
PWB manufacturing, it was designed to address an important
issue concerning the technology's eventual application. This	Figure 1 - Laser Vacuum Drilling Apparatus
paper presents the findings and conclusions of an assessment of
the potential air pollution from laser machining and drilling of	Capture Cell: The capture cell used to trap and collect the laser
PWB materials.	drilling byproduct samples is shown in Figure 2. It was
constructed from a standard 3.81 cm diameter stainless steel
Literature searches pertaining to the environmental impact of	"T" with 6.99 cm diameter flanges. One end of the "T" was
traditional drilling and cutting operations have focused	closed with a 6.99 cm diameter flange containing a 2.54 cm
primarily upon solid waste byproducts generated during the	diameter sapphire window. The opposite end of the "T" was
manufacturing process. Airborne components have been	closed with a 1.90 cm thick double-sided flange positioned
analyzed only for particulate types and were based upon .	between the body of the "T" and another end-flange with a 2.54
quantities captured with conventional filter systems."	cm diameter sapphire window. A 0.64 cm diameter stainless
Unfortunately, the volatile portions of these airborne	steel tube, a bellows valve, and a metal gasket fitting assembly
'components have not been assessed. During traditional	welded to the double-sided flange.spacer served 'as an.
processing, the PWB materials will not experience elevated	evacuation and sampling port for tire cell. The bottom port of
temperatures which can cause their thermal decomposition into	the "T" was closed with a blank flange with an optical filter
hazardous compounds. While the epoxy may melt and flow, it	clamp post fastened to the center for holding the target to be
will not be pyrolyzed at normal processing temperatures.	drilled: The cell assembly was mounted on a three-axis
translation stage so that the laser beam could be directed to
A fortuitous consequence of the developmental research for the	within 25 [im of a designated target position. This all-metal
laser drilling process was that all the byproducts produced	gasketed capture cell assembly, after achieving the appropriate
during the process could be readily trapped and collected in the	. vacuum, was tested to have less than a 10"7 cm3 per sec leak
process enclosure. Emission evaluations were conducted while :	rate,
using a frequency-doubled neodymium doped yttrium-
aluminum-garnet (Nd:YAG) Q-switched pulsed laser, which,	Figure 2 - Vacuum Drilling By-product Capture Cell .....
during the project, was determined to be capable of producing
industry acceptable holes in thick composite FR-4 material. FR-	Gas Handling Manifold: The capture cell was connected to a
4 is a composite material of woven glass and epoxy resin in	multipurpose stainless steel gas handling and vacuum manifold
which laser drilling can involve both physical and	which was used for evacuation of the capture cell, volume
photochemical processes. Consequently, a wide range of	calibrations, infrared (IR) calibration sample preparations,
byproducts was considered possible at the start of this work. Of	evolution gas pressure measurements, and analytical sample
particular concern are possible byproducts with potential health	transfers. The vacuum manifold pump was capable of achieving
and environmental consequences, such as HCN, COCl,, and	pressures as low as 1.33 x 10" Pa. The manifold temperature
dioxins. This is due to the presence of N2 and Cl2 in the	and pressure were monitored using a thermocouple, and ion
monomer and resin components of FR-4.	and electronic manometer gauges. A 0 to 133 kPa electronic
manometer head in the main manifold section was used for
Vacuum Laser Drilling Apparatus: The gas evolution	pressure/volume/temperature (PVT) volume calibrations, IR
experiments were conducted using the second harmonic (532	sample preparation, and IR cell background gas charging. Zero •
nm) beam from a Nd:Y AG pulsed laser system. Similarlaser	to 1.33 Pa and 0 to 13.3 kPa.electronic manometer heads were
and drilling parameters developed in the laser selection and	attached directly at the capture cell port for monitoring the
process development phase, of the program were used for	sample gas pressure as it was produced, and for monitoring
generating the byproduct samples for analysis. A schematic of	quantitative sample transfers,
the laser drilling apparatus used in this preliminary
development phase of the study is shown in Figure 1. The	PVT Volume Calibrations: All volumes critical to the mass
apparatus consisted of an electro-optic (EO) Q-switched	balance and quantitative measurements in the study were
Nd:YAG laser, a harmonic generator module, a prism	calibrated via a standard PVT technique. A nominal 300 cm3
harmonic separator, beam steering and focusing optics, and a	reference volume was calibrated by determining the weight of
vacuum drilling nozzle. The vacuum drilling nozzle was	distilled water it would contain to within ±0,0 1 g. All other
constructed of stainless steel with an O-ring sealed window at	. .volumes were referenced to this standard via PVT
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measurements on the vacuum manifold, The measured volumes
are presented in Table 1.	•
Table 1 - Gas capture system component volumes
Component
Volume
(cm3)
s (cm5)
Standard Volume
304.36
0.01
Capture Cell
226. IB
0.12
Pressure Gauge
Manifold
37.91
0.06
4.8 in IR Cell
483.70
0.63
Sample Generation and Collection: Prior to each gas evolution
experiment, the gas capture cell was cleaned with acetone and
distilled water, dried at 100 cC for 24 hours, and stored in a
desiccator cabinet until ready for target mounting and
evacuation. The 38 mm high by 29 mm wide targets were cut
from 1.4 mm bare FR-4 or 1.5 mm (4 layer) copper clad FR-4.
A 6.35 mm laser alignment and indexing hole was drilled 12.7
mm from the top edge of each target. The targets were washed
with distilled water, dried at 100 °C for 24 hours, weighed to
±10 jxg resolution, and stored in a desiccator cabinet until
mounted in the capture cell.
Fourier Transform Infrared (FT-IR) Analyses: A Bomen Model
MB-155 Michelson Series FT-IR was used to analyze the
gaseous by-products captured from the laser drilling of the
PWB. The gas samples were analyzed on the MB-155 using a
4,8 m long-path Infared Analysis, Inc., ER absorption cell. To
: maintain quantitative reference to standard absoiption spectra,
the samples were prepared by expanding the collected
byproduct gas into the evacuated 4,8 mm IR cell and pressuring
to 1 kPa with ultra high pressure N2. The FT-IR spectra were
then obtained and referenced to a background spectrum taken
ofa lkPaN2 gas sample in tlie4.8mcell using identical FT-IR
settings.
FT-IR quantitative analyses were carried out using a calibration
data base of known concentrations either using the method of
Partial Least Squares or integrating the areas under the
respective absorption bands to calculate the unknown
concentrations. The standards data base was prepared for CO,
COj, and CH4 using Matheson certified gases! Due to the
difficulty in obtaining HCN gas commercially, its IR data base
was prepared on the vacuum line by reacting KCN and
concentrated H2SO, The gas was purified by bulb to bulb
distillation and transferred to the 4.8 m IR cell at a pressure
measured by an electronic manometer gauge.
Results
A summary of the byproduct mass balance data is presented in
Table 2 for 51 laser drilled holes in bare FR-4, and 10 laser
drilled holes in copper clad (4 layer) FR-4 board. The
particulate data were derived from the difference between the
total measured weight loss of the sample from drilling and the
measured weight of the collected gaseous products.
The absence of any other components of significant partial
pressure in the non-condensable byproduct gas was supported
by the mass spectroscopic analysis data. This showed that the
measured partial pressures of the identified compounds
accounted for more than 99% of the total sample pressure in
any specific analysis.
Table 2 - Byproduct analyses and mass balance summary
Gaseous Byproducts: A summary of the FT-IR and mass
spectroscopic analytical data of the non-condensable gaseous
byproducts were collected from laser drilling 61 holes in FR-4
and copper clad (4 layer) FR-4 PWB. The gaseous products
were calculated from the measured total volume of evolved gas,
the mole fractions from Table 3, and the formula weights of the
respective identified emission stream components. Good
agreement was achieved between the analytical techniques used
in the measurements for the major components. Moreover, the
low coefficient of variance (COV) for the major components
(CO and H2) and the acceptable COV of the minor components
(HCN, ,CH4, and C02) demonstrate a consistency of process for
the formation of non-condensable products from the drilling of
both bare FR-4 and copper clad FR-4 board material.
Table 3 - Non-condensable gaseous byproduct summary
. A typical FT-IR spectrum, showing the identified absorption
bands of the gaseous byproducts, is presented in Figure 3. As
can be seen from this spectrum, no other identifiable absorption
peaks are present. Species such as water vapor (IR absorption
bands at 1400-1900 and 3500-3800 cm"1) and phosgene (IR
absorption band at 1828 cm1) were not observed. The absence
of any other components of significant partial pressure in the
non-condensable byproduct gas was even more strongly
supported by the mass spectroscopic analysis data where the
measured partial pressures of the five identified components
accounted for more than 99% of the total sample pressure in
any specific analysis.
In an attempt to find additional components in the byproducts,
a continuous scan up to 150 Dalton was performed on one of
the mass spectrometer gas samples. All the expected peaks

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corresponding to the natural abundance of 13C, 15N, and 180
in the parent ions and their fragment ions and multiple
ionization components were detected. Some small peaks were
also found indicating the presence of small amounts of some
organic/inorganic compounds. However, these were at
concentrations too low for conclusive identification. From the
size and appearance of the peaks, it was concluded that none of
the unidentified species were present in concentrations greater
than 0.01 mole percent.
Figure 3 - FT-IR Spectrum of Laser Drilling Gaseous By-
products
Particulate Byproducts: The particulate byproducts resulting
from laser drilling were determined by difference. The gaseous
product weight was subtracted from the weight of the drilled
target weight loss.
Two different particulate types were observed in the solid
byproducts deposited inside the vacuum drilling chamber. One
was composed of shard-like solid debris of 10 -50 um
particulates, and the other consisted of a vapor deposited
coating made up of 0,2-0.5 jmi particulate agglomerates. There
were no significant differences found in the elemental
composition of these two particulate byproduct fractions. The
elemental analyses show both to be made up of Si, O, Ca, Na,
and Mg. The scanning electron microscope (SEM) and energy
dispersive X-ray (EDX) data for the solid byproducts from the
laser drilling of copper clad FR-4 were identical to those of the
bare FR-4, with the exception that copper was identified in the
particulate samples in addition to the glass constituents.
Approximately 22 wt,% of the material removed from the holes
during laser drilling was found in a gaseous fraction composed
of 58 mole % CO, 37 mole % H2,3 mole % HCN, 1 mole %
CH4, and a trace of C02and other organics. A major portion,
approximately 70 wt.%, of the solid byproducts from the laser
drilling were found by SEM analysis to be in the form of 10 -
50 (.im shard-like particulates. A small er portion, approximately
30 wt.%, were observed to be in the form of a vapor deposit of
0.2 - 0.5 um particulate agglomerates. Both solid fractions were
found by EDX elemental analyses to be made up of primarily
glass constituents, Si, O, Ca, Na, and Mg. Within the
experimental error of this study, the laser drilling byproducts
from copper clad (4 layer) and bare FR-4 PWB s were identical,
except for the presence of copper in the solid particulate
fraction from the copper clad boards.
Finally, this study represented only a small experiment to
identify any potentially toxic compounds that may result from
the laser drilling process. Potentially toxic levels of hazardous
compounds were not determined within the conditions of these
experiments.

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I
NRMRL-RTP-P-384 (Hcau tefwcomptetinx)
1. REPORT NO. 2.
EPA 600/A-99/010
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Air Emissions from Laser Drilling of Printed Wiring
Board Materials
6. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Charles H. Darvin (EPA) and Carl J, Kershner
(Mound)
Ullllllllllllllllllllllll ™
PB99-137424
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Mound,Laser and Photonics Center, Inc.
Miamisburg, Ohio 45343
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
CR824639
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Published paper; 5/95-7/97
14. SPONSORING AGENCY CODE
EPA/600/13
is.supplementary notes APPCD project officer is Charles H. Darvin, Mail Drop 61, 919/
541*-7633. Presented at IPC Printed Circuits Expo '99, Long Beach, CA, 3/14-18/99.
is.abstract paper gives results of a study to characterize gases generated during
laser drilling of printed wiring board (PWB) material and identifies the pollutants
and generation rates found during, the drilling process. Typically found in the emis-
sions stream were trace amounts of carbon dioxide, carbon monoxide, hydrocyanic
acid, and mathane. The electronics packaging industry has traditionally relied on
.mechanical drilling systems -to prepare holes in PWB material. Recently, however,
a potentially new and innovative application for laser technology was developed for ¦
drilling PWB holes. This application of lasers has the .potential to significantly re-
duce the time and cost of producing PWBs. The process is also predicted to reduce
the volume of solid waste product gene rated-during PWB'manufacture. The contin-
uing question presented on the'use of laser drilling is its potential for producing air
pollution which may be generated from -thermal decomposition at the laser drilling
site.
17. KEY WORDS AND DOCUMENT ANALYSIS
t. DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATl Ficld/Gioup
Pollution Pyrolysis
Printed Circuits
Lasers ¦ - -
Emission
Electronic Packaging
Wastes
Pollution Control
Stationary Sources
Printed Wiring Boards
Laser Drilling
Solid Waste
Thermal Decomposition
13 B 07D
09A
20E
14G
13 D
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
'• 4
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220*1 <9-73>

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