Precision part tolerances are becoming increasingly tighter as designs become more complex. Laser cutting allows OEM’s to meet these demands and stay competitive when marketing their products. These processes are no longer fringe prototyping alone, but have become viable production options as well. Laser cutting services, such as A-laser, are able to meet the full complement of needs seen by our customers. Looking at our WIP today, the wide range of industries we touch is amazing. Laser micromachining of precision parts is growing each year and A-laser will stay at the forefront of these technologies.
precision parts contract manufacturing
March 8th, 2010laser micromachining precision microwashers
March 5th, 2010I haven’t referred to our microwasher capablities recently and just want a reminder out there that our laser cutting service maintains12 micron tolerances for these applications. Laser cutting microwashers provides a product that will fit just as the designers intended. As always, we are limited to very thin metal parts as well as non metal parts.
ITAR registering laser cutting services
March 3rd, 2010A-Laser is in the final stages of ITAR registration for our laser cutting services. This accomplishment will enhance our services and procedures, while allowing our customers to add to the business they can pursue. Our laser cutting processes are ideal for these applications due to the quality and consistency of our products. This is another step in our continuing effort to remain one of the most well respected and sought after laser cutting services in the United States.
Ultrafine structuring of flexible circuits
March 1st, 2010
Ultrafine str u c t u r i n g
of flexible
c i rc u i t s
The continuing trend
towards miniaturisation
requires the development
of new cost-effective and
environmentally friendly
materials and processes
for the electronics
industry. The gap between
chip production, now
producing sub-0.2 ?m
lines and spaces, and PCB
and packaging, must
inevitably shrink.
Dr. Dieter J. Meier,
LPKF Laser & Electronics AG, Germany
Fig. 1 – A possible
application for UV
lasers – laser
direct patterning
(LDP) of circuit
structures
Fig. 2 – LPD polymer film on
Si-wafer. A UV laser was used
to produce
³30 ?m features
2
M
ANUFACTURING
ablation possible at a rate of 0.13?m
/shot using a wavelength of 248nm
(KrF laser). The resultant structured
films can be used as alkaline as well as
acid resists and can be etched (subtractive)
or additively built-up (semiadditive).
Another way to laser structure thin
polymer films for lithographic applications
in electronics manufacture
an electrochemically synthesised
100nm thick polythiophene film that
can be ablated by a He-Cd laser at
325nm. Polythiophene has proved to
be chemically stable against all acids
and dilute alkalis, and it seems that it
may be used as a self-developed UV
resist. Using the process, it is possible
to produce 1.9-2.7?m grooves at a
pitch of 20?m.
Pd-doped polymer films laid onto
polyimide substrate may also be laser
patterned
by using an electroless metallising process
with copper as shown in fig. 3.
This produces
electroless metallisation process with
Cu, Ni and Au allows further processing
for the electronics industry.
Thin metal films laid down on a polymer
may also be patterned by a UV
laser. Here, the UV radiation penetrates
the metal film and cracks the chemical
bonds at the metal-polymer interface.
The resulting plasma plume lifts off the
metal layer in a mini explosion. Due to
the high photonic energy of the UV
laser it is assumed that this process
also includes thermal ablation
A UV laser was used to structure thin
Al/Zn-layers on polypropylene foils
with an XeCl-laser (wavelength
308nm)
150?m structures using a fluence
of 200mJ/cm
spaces.
[8] uses[9] and circuit tracks built up³20?m lines, and the[12] .[5], making it possible to produce2 and ³20 ?m lines and
Laser direct patterning
(LDP)
Fig. 4 shows the general idea for producing
flexible circuits in just three
steps. Given the foregoing results, it
should be possible to produce flexible
circuitry using LDP, and this article
looks at the results of research into this
potential use of laser technology
[ 1 1 ]
using a KrF UV laser source that “ima-
Fig. 3 – UV-patterned Pd-doped
polymer film
Fig. 4 – The production of
flexible circuits in a 3-step
LDP process
Additive build up
•
electroless Cu
•
electroless Ni
•
Film with layer Laser structuring
Mask
electroless Au
Fig. 5 – Laser ablation of flexible circuitry
through a chromium mask
Fig. 6 – Detail of a microcoil
patterned with optimised
power density Fig. 7 – 15 ?m (0.6 mil) ablated
tracks compared with human
hair
REPRINTED FROM PRINTED CIRCUIT EUROPE – 1
REPRINTED FROM PRINTED CIRCUIT EUROPE – 1
ST QUARTER 2001ST QUARTER 2001 3
M
ANUFACTURING
ges” the film through a chromium
mask (see fig. 5). This process uses an
adhesiveless flex polyimide substrate
on which is a 15nm Cr tiecoat and a
50nm Cu seed layer that has been processed
in a proprietary vacuum metallisation
process by an experienced
base materials manufacturer
[10].
Results and discussion
Optical evaluation of the first laser
ablated Cr/Cu metallisation indicated
the need for extensive tests to determi -
ne an optimum imaging power density,
that varies between 150-350mJ/cm
Figs. 6 and 7 show the results of
using the optimised technology
to produce circuits with 15
micron lines and spaces, and
table 1 shows some pro c e s s
parameters.
2.
After ablation
Although commercial quality
baths are used for the electroless
metallisation of the laser- s t ru c t u re d
substrates, special care is necessary
for the activation of the first ultra-thin
layers. Following the careful ultrasonic
removal of the laser debris, cleaning
agents should be used at low-concentrations
to avoid damaging the layers.
Electroless copper metallisation using
an appropriate bath then selectively
builds up at approx. 2?m/hour.
T
M
M
S
M
OTAL PROCESSING RANGE (INCHES) 8 X 8AX. LAYOUT DIMENSIONS (INCHES) 5,5 X 5,5IN. LINE AND SPACE WIDTH 15?m (0.6MIL)YSTEM RESOLUTION 2?m (0.08MIL)AX. THROUGHPUT 1.55 SQ. INCH/ SEC
M
W
AX. LASER POWER (W) 50AVELENGTH (nm) 248
T
ABLE 1 – PROCESS PARAMETERS FOR LDP PROCESS
2655.63nm
1327.81nm
0 nm
56 ?m
56 ?m 28 ?m
28 ?m
0 ?m
0 ?m
Fig. 8 – Additive build up with
electroless copper
(19 ?m line width)
R
EFERENCES
[1] C. Dunsky et al:. ”High Quality Microvia Formation with Imaged UV YAG Lasers”, Proceedings of the Techn.
Conference, San Diego 2000, S 15-5-1
[2] C. Vaucher: “Direct Imaging: will it fly or not?”, PCB-Fab, June 2000, 28ff
[3] R. Rhodes: “Laser Direct Imaging”, CircuiTree June 2000, 62ff
[4] E. Tadic: “Haaresbreite Feinststrukturen für zukünftige Produktgestaltungen”, SMT Ausgabe 1-2/2000, 12ff
[5] W. Ziegler et al.: “Ein Excimerlaser strukturiert metallbedampfte Folien”, F&M 101 (1993), 189ff
[6] R. Srinivasan et al.: “Self-developing photoetching of poly(ethylene terephthalate) films by far-ultraviolet
excimer laser radiation”, Appl. Phys. Lett. 41, 576,1982
[7] K. Suzuki et al.: “Polymer resist materials for excimer ablation lithography”, Applied Surface Science 127-129
(1998) 905-910
[8] T.K.S. Wong et al.: “Patterning of poly(3-alkylthiophene) thin films by direct-write ultraviolet laser
lithography”, Mat. Science and Eng. B55 (1998) 71-78
[9] J. Kickelhain: “Untersuchungen zur additiven Herstellung flexibler Feinstleiterstrukturen durch
Excimerlaserablation festhaftender, metallorganisch aktivierter Schichten auf Polyimidfilmen”, Dissertation,
Rostock 1999
[10] T. Bergstresser et al.: “The Effect of Moisture on Peel Strength of Adhesiveless Polyimide Laminates”,
Proceedings of the 5th Annual National Conference on Flexible Circuits, Denver, 1999
[11] D. J. Meier et al.: “Laser Structuring of Fine Lines”, Proceedings of the 5th Annual National Conference on
Flexible Circuits, Denver, 1999
[12] J. Koo et al. : “Removal of thin films from substrates by laser induced explosion”, US-Pat. 4,081,653
4
REPRINTED FROM PRINTED CIRCUIT EUROPE – 1ST QUARTER 2001
M
ANUFACTURING
Summary
Copper layers applied to polyimide
films by PVD processes to a maximum
thickness of 50nm can be ablated and
patterned with a UV laser machine. A
system has been developed that is suitable
for industrial use that allows the
production of
and spaces. Structures for flexible circuit
applications can be produced by
the additive build-up of functional
layers.
The advantages that this new technology
brings to the production of fine
line structures for HDI applications are
as follows:
³15?m (0.6mil) lines
•
etching
precision lines and spaces without
•
³15?m geometries
•
no photo imaging
•
fewer process steps => cost reduction
•
reduced chemicals and waste
•
desired
Now, as well as being used for microvia
drilling and laser direct imaging, the
UV laser can be used for laser patterning.
The author believes that this will
reduce the gap between thin film techniques
and PCB production.
tracks can be built up to 6?m as3
LPKF Laser and Electronics AG
Osteriede 7
30827 Garbsen – Germany
Tel.: +49 (0)5131 7095 0
Fax: +49 (0)5131 7095 90
E-mail: lpkf@lpkf.de
Website: www.lpkf.de
A
CKNOWLEDGEMENTS
The author would like to thank Mr. T.
Bergstresser (GOULD Electronics), Mr. A.
Boenke (LPKF Laser & Electronics AG),
Mr. C. Böker (Zeiss), Mr. L. Bruderreck
(Technolab Berlin), Mr. T. Kohlmeier
(Universität Hannover) and the company
Enthone-OMI.
Applications for the LDP
process
Figs. 9 to 12 illustrate some applications
for the LDP process.
Fig. 9 shows a detail of a microcoil
with 15 micron lines and spaces,
produced using LDP.
Fig. 10 shows a printer head application
with 12 micron lines and spaces.
Fig. 11 shows a flexible interposer.
This micropackaging (Chip Size
packaging) application has 15
micron lines and spaces.
Fig. 12 shows an LDP interposer.
This was completed as a CSP demonstrator
and has been tested successfully
according to the general reliability
test for electronic components.
Fig. 10 – Applications for the
LDP process.
High density interconnect
(12 ?m lines and spaces)
Fig. 11 – Applications for the
LDP process.
Flex interposer for CSPs
(15 ?m lines and spaces)
Fig. 9 – Microcoil
(15 ?m lines and spaces)
Fig. 12 – Laser-structured CSP
flexible interposer
application. This has been
tested successfully
Microvia forming using UV laser
February 26th, 2010?
Microvia forming using UV laser
By Bernd Lange, LPKF Laser & Electronics AG, Garbsen, Germany
The continuing trend of miniaturization in electronic packaging demands smaller and smaller structures in conductive materials such as copper, nickel and gold. Vias in PCB’s are becoming as small as 60?m and for packaging interposers and High Density Interconnect boards (HDI) the industry roadmaps predict microvias with 50?m to 30?m diameter for the near future.
An increasing number of reliable interconnections between the layers of HDI boards require smaller microvias and higher quality standards for the forming process of microvias.
For reliable interconnection the main requirements to microvias are:
• Clean vias without residue
• No delamination of copper and substrate
• Tapered sidewalls without undercut
• Big land diameter for robust interconnection to the inner layer
• No perforation of the inner layer
?
There are primarily four methods of microvia formation:
• Mechanically drilled vias
• Photo via formation / etching
• Plasma-etching
• Laser ablated vias
?
Mechanical drilling is well known to the PCB community and the machine providers try hard to control the drilling depth in order to qualify their machines for blind via formation. Nevertheless this method is limited by throughput and efficiency as well as by its accuracy especially when it comes to glass-fiber reinforced materials.
Photo via forming process is limited to photo imageable dielectrics. The expose and etch reliability, low copper adhesion and changing dielectric thickness together result in low yield. This method is usually not economical for small and mid size board houses.
Plasma etching is also limited to certain substrates and requires substantial capital investment, which makes it only attractive for very high volume production. The quality of the micro vias is a function of the exact process control.
It is not surprising that laser ablation with its flexibility and versatility quickly became the leading method for microvia forming. Two types of lasers are generally suitable to perform well in this field although they have very different characteristics and applications.
CO2 Laser
CO2 lasers are emitting infrared light with a wavelength between 9.3?m to 10.6?m.CO2 lasers are primarily used to drill bare substrates due to their inability to cut through copper. Recent developments of special absorption foils should also allow the ablation of very thin copper layers eventually.
CO2 lasers are available with a wide range of output power, providing the necessary margin for fast drill processing in circuit board substrates.
As vias are becoming smaller another shortcoming in the use of CO2 lasers emerges. The relatively long wavelength limits the minimal focus diameter in a given working field area. The formation of vias with diameters less than 75?m reaches the physical limits of this technology.
The practical use of CO2 lasers requires a long chain of process steps within very tight tolerances. The copper layer typically has to be opened by etching, which causes a number of additional alignment challenges. To address this the design usually needs to provide larger pads on the inner layer. Although CO2 lasers are perfectly capable to ablate organic substrates they can’t guarantee residue-free holes as the laser light reflects on the inner copper and thus reduces the energy absorption. This requires chemical desmear or plasma etching as another consecutive process step to clean the bottom of the via from eventual residue.
In an attempt to remove all residues completely with a CO2 laser it requires so much laser energy that this typically results in under cutting and delamination.
UV Laser
The other type of laser used for micro via formation is a solid-state laser emitting ultraviolet light. Looking at the absorption spectra of copper, epoxy, polyimide and glass it shows that ultraviolet light with a wavelength of 355nm will be absorbed from all those materials. In addition this light will be emitted with very short high-power pulses. Precisely focused to a small spot the extreme high power density creates very concentrated plasma that allows pinpoint ablation of the material.
This creates a number of significant advantages for the drilling of printed circuit boards.
1. Both copper and substrate can be drilled with the same laser using only one piece of equipment without the need of photochemical etching of the outer copper layer.
2. UV lasers are capable of removing the copper layer to expose the fiducials for proper alignment between drill pattern and artwork of the inner layers.
?
3. Microvias with superior quality, large and clean bottoms that are textured and won’t require desmearing.
4. The energy exposure in a very small spot for a very short time limits heat spread-out to the dill hole’s environment. This also reduces the danger of delamination of mushroom shaped holes.
5. UV lasers have a very small focus. This allows creating of microvias with diameters as small as 30?m with a high aspect ratio.
6. UV lasers allow production of “stacked vias” that connect three layers of the board with one another.
?
Other benefits of UV laser formation of microvias are:
1. The excellent alignment to the inner layer circuitry by using fiducials on the inner layer allows the use of smaller land pads.
2. The capability to form stacked vias, connecting three layers reduces the SBU steps.
?
New Challenges
Recently HDI circuits were used mostly in consumer handheld devices. RCC foils are perfectly capable of being laser drilled and meeting the performance requirements of such products.
The automotive and computer industry’s demands for HDI PCBs with extended temperature range and superior mechanical stability requires microvias formed in reinforced materials. Woven glass fibers bedded in epoxy provide the necessary material characteristics but they are also more difficult to drill with lasers because of their inhomogeneous absorption of laser light. The glass has a higher absorption threshold than the epoxy and it also has a relatively uneven distribution over the area.
New Possibilities
In the past most of the UV laser-drilling machines were limited by their laser output power and were very limited in their use with FR4 substrates. Resin coated copper (RCC) and similar non-reinforced materials were the materials of choice and numerous results of laser via formation in these materials were reported.
|
New laser sources especially developed under the requirements of the microvia formation process ensure excellent results in glass reinforced materials and accelerate the formation process. The following pictures show drilling results in FR4 with 1080 glass fiber. The micro via formation has been made with MicroLine Drill 600 of LPKF Laser & Electronics. Fig. 1: 700x magnification of a microvia in FR4. (Photo: LPKF) |
|
Fig. 2: Microvia in FR4 with 1 layer of 1080 glass reinforcement. (Photo: Fachhochschule Stralsund – University of Applied Sciences) |
|
Fig. 3: Flawless connection throughout the entire bottom of the via. (Photo: Fachhochschule Stralsund – University of Applied Sciences) |
laser micromachining optoelectronic components
February 24th, 2010A-laser produces a number of gasket and spacers for a wide range of industries, but some of the more intersting components come from the optoelectronics market. This market pushes our laser cutting service in terms of tool development for various materials as well as design. Our laser operators know their laser equipment inside and out in order to meet the requirements of the most demanding customers. We are committed to remaining a top level laser cutting service and look forward to the challenges any customer can throw our way.
exposing copper traces and pads using UV laser cutting
February 22nd, 2010A-laser has dialed in the process of skiving to copper in a manner that is quick enough to make it a useful production tool and with a level of cleanliness that other processes can’t match. UV skiving leaves virtually no carbon residue to cause shorts within circuits or contamination within a device. Laser cutting services have become an integral part of flexible circuit manufacturing processes and will continue to grow as companies gain a better understanding of the value added. A-laser has the right technology to support high tech companies in need of quality laser cutting services.
UV laser cutting applications
February 20th, 2010Ours is a tricky business at times. Laser cutting services cover a very wide spectrum. For instance, our UV lasers are better than just about any other piece of equipment when it comes to cutting 10 mil polyimide with a 1 mil tolerance. not many other companies can process such a thin material and achieve nearly the tolerances that can be met with our lasers. therefore, the most important item for us is the ability to identify these opportunities and make ourselves as easy as possible to find. UV lasers are a rarity and UV lasers that can reach 7-8 watts of power are just that much more unique. A-laser will remain a laser cutting service focused on niche market production and achieving the highest quality possible.
laser cutting blue steel using IR frequency lasers
February 17th, 2010Our laser cutting service customers have a range of needs and each material is selected for specific characteristics. Our laser operators are trained to recognize the variety of materials and adapt their laser settings to achieve the highest quality cuts possible.
laser cutting stents, catheters, and other tubes
February 15th, 2010A-laser is currently only used for 2-d applications, but I have inquiries about using our laser cutting services for tubbing applications. This is a market we are interested in, but have not yet made the leap. I would like to find out the ideal laser cutting system for these applications. We want to remain one of the highest quality laser cutting services available and will be very picky in the equipment we look to bring on. The world of laser cutting keeps growing in leaps and bounds and we want to be at the forefront of in house technology.