Note: Descriptions are shown in the official language in which they were submitted.
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MICRO-REPLICATION IN METAL
FIELD OF INVENTION
The present invention relates to a method of micro-
replication in metal, a device for producing micro-
replications in metal and to a medal micro-replicated element
produced in accordance with the invention. Micro-replicating
methods and devices are preferably intended for use in
producing with great precision and at low costs reproduceable
building optocomponents, contact devices or other precision
elements adapted for aligning optical chips with waveguides
or fibres. An optocomponent building element that has an
aligning facility can be readily mounted on a circuit board
while connected to a waveguide or to a fibre and to a laser
or a photodiode.
DESCRIPTION OF THE PRIOR ART
A common method of aligning optical chips with waveguides or
fibres in optocomponents is to etch a desired microstructure
in silicon in the form of a V-groove into which a waveguide
or fibre can be fitted. With techniques used at present,
optical chips are often solder-mounted on a ceramic or
silicon carrier. This method quickly presents problems with
respect to the dissipation of heat generated in the mounted
component. This problem is particularly pronounced in the
case of mounted semiconductor lasers of small dimensions,
with which the heat generating' region is concentrated to
narrow bands of circa 2 ~m that extend transversely through
the chip close to its surface.
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SUMMARY OF THE INVENTION
With the intention of preventing damage to the chip as a
result of its becoming hot, or with the intention of at least
limiting the affects of such heating, a chip that carries a
waveguide or fibre connection has been soldered either to a
metal carrier or to a metal lead frame, wherewith the thermal
resistance will be much lower than when the chip is solder-
mounted on a ceramic or silicon carrier. The invention
enables a microstructure to be produced with great precision
with respect to the alignment of a waveguide or a fibre in a
metal surface with the aid of an embossing/stamping tool at
low cost.
The embossing process may be carried out on a metal carrier
or directly on a metal lead frame intended for plastic
encapsulation. An embossing process can be automated
relatively easily, since the material to be embossed can be
worked in the form of short strips or in the form of long
strips wound onto reels. An assembly in which optical chips
are soldered onto metal carriers provided with embossed
waveguide or fibre receiving grooves will result in improved
heat dissipation and therewith greatly increase the useful
life of the finished component with enhanced mean fault time
(MFT) .
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a metal element provided with a
microstructure in accordance with the invention.
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Figures 2A and B show respectively an inventive embossing
tool from beneath and in section.
Figures 3A and B are detailed illustrations of the active
part of the inventive embossing tool, seen from one side and
from above.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Practical trials have shown that it is possible to emboss
microstructures- in copper with repeated high measurement
precision and with only slight wear on the embossing tool
used. Microstructures embossed in metal carriers enable
optical components to be aligned and mounted directly on a
copper lead frame or a lead frame made of some other alloy,
for later inclusion as a building element in a plastic
capsule, for instance.
The embossing technique provider two obvious advantages over
known techniques in which lasers are mounted on a carrier
which is then mounted on a lead frame. Firstly, the costs
entailed by purchasing and producing such carriers are
eliminated. Secondly, advantages are also afforded with
respect to dissipation of the heat that is generated in the
active regions of the lasers. However, there is the added
cost of the embossing process. and of the tool required
herefor. The precision tools to be used to emboss micro
replications may be manufactur~ad by grinding or otherwise
working the tool material directly, or in the following
manner, for instance:
- Applying a photoresist to a silicon disc.
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- Fitting a photomask having a suitable groove pattern over
the silicon disc.
- Exposing the photoresist in those openings present in the
photomask.
- Washing away exposed resist or, alternatively, unexposed
resist.
- Etching the desired structure in the disc.
- Washing away photoresist residues.
This results in a plurality of mutually identical three-
dimensional silicon structures in the case of two-dimensional
photomasks. The aforesaid technique is known to the art, but
is mentioned here to provide a better overall picture of the
procedure used to produce an embossing tool with desired
precision. This procedure can be continued in accordance with
either one of the two alternative methods described below.
1. A patterned silicon disc is coated with a layer of
material that possesses sufficient hardness.
2. The disc is plated with nickel or some other suitable
material.
3. The plating is planarised.
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4. The silicon is etched so as to separated the plated and
planarised moulding therefrom. The hardness of the plated
surface can be enhanced by sputtering or further plating the
surface with an appropriate metal.
5. The moulding is sawn in two, so as to separate the
mutually identical structures.
6. A structure is placed in a holder in an embossing tool,
said holder being adapted to thE: structure.
7. The various parts of the embossing tool are assembled to
provide a finished embossing tool.
Alternative B
1-4. According to Alternative A.
5. The non-planarised side is coated with a layer which
makes later separation possible.
6. The disc is plated with nickel or some other metal.
7. The plating is planarised.
8. The two planarised mouldings are separated from one
another.
9. The moulding is sawn in two so as to separate the
mutually identical structures.
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10. The moulding is placed in a holder and subjected to
spark processing in an electro discharge machine (EDM).
11. Spark processing is effected directly in the material in
which microstructures shall be embossed in the metal/lead
frame.
12. The various parts of the embossing tool are assembled to
provide a finished embossing tool.
Figure 1 illustrates an example of an embossed microstructure
in a metal element 1 that has a recessed or sunken surface 2
which includes a V-groove 3 for aligning an optofibre or a
waveguide. To facilitate mounting of a chip, the metal
surface may also be provided with a chip mounting surface 4
that includes chip positioning markings in the form of
grooves 5. The embossed metal surface enables a chip to be
aligned with a waveguide or a fibre with a great degree of
accuracy.
As evident from Figures 2A and B, the embossing tool 6 may
have the form of a stamp with which a protective holder 8 is
arranged around the active part 7 of the tool. The active
tool part will suitably have a configuration with which
grooves, such as V-grooves, can be embossed in a metal
surface. The protective holder will be sprung, e.g. with an
Adiprene plate 9, so as to be able to expose the active tool
part in the actual embossing process.
Figures 3A and B show that the active part 7 may be
configured with an embossing surface, which in this case is
comprised of a flat surface 10 and a ridged area 11 such as
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to form a planar surface, or alternatively a recessed
surface, and a V-groove when embossing a metal surface. In
order to enable an optofibre to be fitted in the V-groove,
the active tool part may have a width of 1.20 mm for
instance, and the width of the ridge may be 0.16 mm and its
length 3.20 mm, and the angle a may be 45°.
With this micro replication in metal, a carrier in the form
of lead frames and in strip form for instance, may be
provided automatically in a manufacturing process with V-
grooves and connected to a chip such as lasers or
photodiodes. Waveguides or fibres can then be aligned
automatically with the aid of t:he embossed grooves so as to
obtain correct alignment of the waveguide or the fibre with
the carrier mounted laser or photodiode. The inventive
embossing technique enables micro replication to be achieved
in the automatic manufacturing process to a high degree of
reliability and with great precision at low costs.
It will be understood that the invention is not restricted to
the aforedescribed and illustrated exemplifying embodiment
thereof, and that modifications can be made within the scope
of the following Claims.
