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Description  |
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TECHNICAL FIELD
The present invention relates to miniature capsules comprising surface
mounted and/or encapsulated optoelectric elements, such as photodetectors
(PD), light emitting diodes (LED) and/or laser diodes (LD), possibly
integrated with other electronic circuits, and methods for an accurate
positioning of an optocomponent on a support or substrate and for
production of such a mounted optocomponent.
BACKGROUND
Most of the optical components of today such as optical transmitters and
optical receivers for high velocity communication on optical fibers are
constructed, so that a permanent connection of an optical fiber is made to
an active surface of the optical component. In order to achieve such a
connection extremely accurate active adjustment of the fiber end is
required to find the correct position at the surface of the optical
component. It is also conventional, that the component is encapsulated
together with a piece of an optical fiber which is fixedly mounted, so
that a so called "pigtail" is obtained, i.e. so that a fixedly mounted
fiber piece extends permanently from the within capsule. The encapsulation
can be made hermetically with a metal material or by means of ceramics.
This method for connection by a "pigtail" results in the fact that the
finished encapsulated components will have a time consuming production,
will be very costly, will have a large volume and do not allow connectable
and detachable connections to an optical fiber.
STATE OF THE ART
The U.S. Pat. Nos. 5,123,066, 5,127,071, 5,113,466 and 5,170,453 describe
miniature capsules, designed so that connectable and detachable contacting
of optical fibers provided with connector means can be made directly to
encapsulated surface mounted photodetectors (PD), light emitting diodes
(LED) and/or laser diodes (LD).
In the patent U.S. Pat. No. 5,199,093 multi-part optical fiber connectors
are disclosed, where a passive integrated optical chip is disposed at the
coupling surface of a connector for optical coupling directly to ends of
optical fibers located inside another connector. The optical chip has its
own optical coupling surfaces located in the same level or plane as the
remaining portion of the coupling surface.
An optoelectronic assembly disclosed in the European patent application
EP-A1 0 535 473 comprises two components, transmitter and receiver
components, movably arranged in a housing. A alignment member is secured
to the housing producing an alignment of the components to an optical
connector when the connector is positioned within the alignment member.
The International patent application WO 94/28448, having a priority date
earlier than the present application but published after the filing of the
present application, discloses an optical interconnect for coupling the
ends of multiple optical fibers directly to the active surfaces of an
array of optoelectronic devices located on an optoelectronic board.
Guiding pins and tunnels/guide bores are provided for the alignment of a
multifiber connector to the optodevices.
In the International patent application WO 93/19847 an integrated circuit
module is disclosed which has microscopic self-alignment features. The
module comprises an integrated circuit chip and an interconnect member
having surfaces facing each other. One of the surfaces has shallow holes
and the other surface has protrusions which are shaped to fit into the
holes and prevent the surfaces from sliding on each other.
SUMMARY
It is an object of the invention to provide a capsule comprising
optoelectronic components, to which a connectable and detachable
connection of an optical fiber or a group of optical fibers provided with
suitable connector means can be accomplished, so that the fibers are
directly coupled to the capsule.
It is another object of the invention to provide a capsule comprising
optoelectronic components, to which a connection of a group of optical
fibers provided with suitable connector means can be accomplished, the
capsule being constructed to protect the optoelectronic components being
damaged or destroyed when a fiber connector is pushed against the capsule.
It is a further object of the invention to provide a capsule comprising
optical components, which can in a simple way be mounted on circuit boards
and has reasonable dimensions.
It is a further object of the invention to provide a capsule comprising
optical components, which allows a connection to optical fibers in an
accurate way and which has a low cost of production.
It is a further object of the invention to provide a method for accurately
mounting, in a simple way which can be easily automatized, an
optocomponent chip on a substrate or support.
The objects mentioned above are achieved by the invention, the
characteristics and features of which appear from the following
description and the appended claims.
A miniature capsule comprising surface mounted and/or encapsulated
optoelectric components, possibly integrated with other electronic
circuits, is designed so that a detachable connector means for optical
fibers can be placed against the capsule, whereby the end surfaces of the
optical fibers are coupled directly, with an accurate adjustment, to the
active surface of the components. The components can either be individual
or comprising a multitude of components, placed side by side in the shape
of an array. Preferably the capsule is designed with an interface for
multifiber connectors having guide pins (conventional types MT, MAC II).
The mounted optoelectric components are protected by covering them with a
transparent, rubber like material, which in addition acts as an
intermediate or transitional material having an adapted refractive index
for reduction of reflections at the interface between the end surfaces of
the fibers and the surface of the components.
An optical component capsule can have the shape of a substantially
rectangular block and comprises at least one optoelectronic component
having at least one optical exterior connection, i.e. for example a
suitable exterior surface, to a light wave guide and comprising electrical
connections at the surface of the capsule. The component is mounted on a
lateral surface or a top surface of the capsule, so that its optical
connection is located freely or accessible for coupling to some light wave
guide connector means. Guides are provided for receiving guide means of
the connector, such as guide pins, arranged in or at the capsule, having
axes which extend inwards through the plane of the same side surface of
the component. The guides can be of the type which is arranged at MT
connectors and then comprise bores having axes extending into the side
surface perpendicularly thereto.
The component is mounted in a recess in the surface of the capsule, so that
e.g. the optical connection surfaces of the components or at least the
surfaces thereof to which the fiber ends are to coupled, are located
approximately in the level of or somewhat inside or retracted in relation
to that portion of the surface where the recess is not arranged, for
protection of the components and for facilitating the coupling to an
exterior light wave-guide or exterior light wave-guides. The surface of
the capsule where the component is mounted, thus comprises a first portion
where the component is mounted and a second portion for contact with a
flat front surface of a connector and into and through which the bores for
the guide pins may extend and the first portion is retracted in relation
to the second portion, that is has a position more close to the body or
centre of the capsule, these surface portions being generally located
parallel to each other.
For connection to electrical terminals of the component electrical
conductors can be provided, which are also located on the retracted
surface of the capsule where the component is mounted. These conductors
can then continue from this surface to a bottom surface of the capsule
where it is to be placed on and attache to a substrate or support such as
a circuit board. At the bottom surface the conductors can be connected to
other electrical conductors, e.g. in the shape of printed pattern
conductive paths, on the substrate or support.
In the embodiment for connection to a MT connector the capsule has two
bores for guide pins and if the component only has one optical coupling
surface, the component is then advantageously mounted so that this optical
exterior coupling is located having its centre point on the connection
line between the bores for the guide pins, in particular between the axes
of the bores, and preferably even its optical exterior coupling area is
located having its centre point arranged centrally between the holes, i.e.
at the centre of the connection line.
In the case where the component has several optical coupling terminals or
coupling areas or comprises several components having each one at least
one exterior optical coupling terminal, the component/components are
preferably mounted so that the optical exterior coupling areas are located
having their centres evenly distributed and centred on the connection line
between the bores for the guide pins. In that case the component can e.g.
comprise several individual components which are mounted on or produced in
a plate-shaped carrier attached to the retracted side surface of the
capsule.
When mounting the component to a side or surface of the capsule generally a
very good accuracy is required in regard of the positioning of the
component so that its optical coupling surface/coupling surfaces are
located exactly correctly in relation to the guides for the guiding means
such as guide pins. For this alignment a modified Flip Chip method can be
used which simultaneously produces an alignment of the component in an
accurately predetermined position and the electrical connection of
component. This method can also be used generally for a simple mounting,
which is suited for automatization and provides a high accuracy, of small
components to a substrate or support.
Therefor, in a surface of the support or substrate first holes are produced
which extend inwards from the surface at least some distance into the
support. These holes can suitably be produced simultaneously with the
support and with the surface or the surface layer of the support such as
in moulding it. The support can be an electrically isolating block as
above having electrical conductors located therein and moulded therein,
for forming an optical capsule. At a side of a component plate bumps,
heaps or small contiguous amounts of a material, which is liquid when
heated and is in room temperature essentially solid or semi-solid, in
particular a tin solder material or a curable adhesive, in the shape of
small "isles" which can be in an electrical contact with electrical
conductors in or on the component plate. The isles are placed directly
correspondingly to the holes or generally having positions in relation to
each other which are adapted to the relative positions of the holes to
each other, so that when the plate is in a correct position above that
surface, where the holes are located, the axis of each hole extends
through the centre of a corresponding isle.
Then the plate is placed over the support having each one of its bumps at
least partly located above a corresponding hole and restrictedly free to
move along the surface, e.g. so that the surface of the support is
directed upwards and the plate rests on this surface, there being a not
too large friction in relation thereto. The bumps are then heated, so that
the material therein will be liquefied and then passes into the
corresponding hole. The surface tension forces in the material which is
now liquid will cause the plate to be displaced to a predetermined,
correct and intended position at the surface of the support. At last the
material in the bumps is allowed to solidify, in particular by allowing it
to cool. If the holes in the support have been made in and up to
electrical conductors inside the support, the material can when it is
liquid, if the conductors are not located too deeply in the holes, come in
contact with such a conductor and thereby accomplish an electrical
contact, when the material itself is electrically conductive.
Generally the holes have a very small diameter, typically of the magnitude
of order of 0.1 mm. They can be made as blind holes having a very small
depth, which can be of the same magnitude of order as the diameter, and
then advantageously an electrical conductor is located at the bottom of
such holes.
By this method an optical component capsule can be produced, comprising an
optoelectronic component plate having electrical connection terminals. In
the capsule there is then a support or substrate comprising an
electrically isolating material having electrical conductor paths. At a
surface of the isolating material holes are provided which extend in the
isolating material in and up to portions of electrical conductor paths
located below the surface. In the finished capsule the plate has
electrical connections at one side in the shape of protrusions of an
electrically isolating material which extend into the holes from the
surface of the isolating material and therein is in electrical contact
with portions of the electrical conductor paths. The support or substrate
can advantageously be a block of an electrically isolating material
comprising electrical conductor paths moulded therein of an electrically
conducting material, in particular of a metal such as copper.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail with reference to
non-limiting embodiments and with reference to the accompanying drawings
in which:
FIG. 1 is a perspective view of a circuit board including a capsule for
optoelectronic components and a fiber ribbon cable having connector means,
FIG. 2 is a perspective view of the capsule of FIG. 1 in a larger scale,
FIG. 3a is a view of the capsule and the connector means as seen from above
for coupling the connector means thereto,
FIG. 3b is a view similar to FIG. 3a but here the connector means are
placed against the capsule,
FIG. 4 is a sectional view of a capsule mounted on a support,
FIG. 5 is a sectional view of an alternative embodiment of a capsule
mounted on a support,
FIG. 6 is a side view, partly as seen in a section, of still another
alternative embodiment of a capsule mounted on a support,
FIG. 7 is a view of the front side of another embodiment of the capsule
with an associated optocomponent plate,
FIG. 8 is a sectional view of the capsule according to FIG. 7 without any
components,
FIG. 9 is a sectional view, in a larger scale, of the component plate
according to FIG. 7 as seen before mounting,
FIG. 10 is a larger scale, sectional fragmentary view of the capsule
according to FIG. 7 showing a part of the front portion of the capsule
including an attached component plate,
FIG. 11 is a perspective view similar to FIG. 1 of an alternative
embodiment of a capsule for optoelectronic components and a fiber ribbon
cable having connector means,
FIG. 12 is a side view of the front portion, the front-most part shown in a
sectional view, of still another alternative embodiment of a capsule
mounted on a support,
FIGS. 13a, 13b and 13c are schematic front views which illustrate various
ways of accurately positioning a component plate.
DETAILED DESCRIPTION
FIG. 1 is perspective view of a capsule i including optical components
mounted on a support or a substrate 3, which can be e.g. a pattern circuit
board, a multichip module or some other large electronic component. The
capsule is generally made of an electrically isolating, opaque material.
An optical multifiber cable of fiber ribbon cable 5, comprising e.g. four
optical fibers located at each other, side by side, is provided with a
connector means 7. The connector means 7 can be of MT-type and has guide
pins which for the coupling of the connector means 7 to the capsule 1 are
intended to accurately centre the connector means 7 in relation to the
capsule 1, by the fact that its guide pins 7 extend into accurately made
guide bores 11 in the front side of the capsule 1. The front side of the
connector is supposed to be essentially flat and the ends surfaces of the
optical fibers therein constitute are a part of this front surface and are
thus located in essentially the same plane as the rest of the front
surface. On the substrate or carrier 3 various electronic assistant or
auxiliary components, as is indicated by dotted lines 13, can be provided.
Electronic auxiliary components such as driver circuits and similar parts
can also be moulded into the capsule, see the description below.
FIG. 2 is a view of the capsule itself as illustrated in a larger scale. On
the front side or surface thereof, in addition to the guide holes 11,
surface mounted and/or encapsulated optoelectronic components 15 are
arranged. These components 15 can e.g. be PIN diodes, light emitting
diodes or light detecting elements and they may possibly be integrated
with some electronic circuits. In the case shown a group or "array" of PIN
diodes are illustrated. The components can be connected through bare
electrically conducting wires (26, see FIG. 4) (be "wire bonded") of a
suitable material to electrical conductor paths 17, which are also
arranged on the front side surface of the capsule 1 and extend from the
components 15 straight downwards to the bottom side of the capsule 1.
Centrally on the front side of the capsule 1 a shallow depression or recess
19 is provided, where the components 15 are placed, so that they are
located retracted in relation to the other portions of the front side. The
guide holes or bores 1 for the guide pins 9 of the connector means 7 are
however arranged in these other portions of the front side. Thereby, when
inserting the optical connector means 7 including its guide pins 9 into
the capsule 1 a controlled or predetermined, small distance can be
maintained between the exterior optical connector surfaces of the optical
components 15 and the corresponding coupling surfaces of the optical
connector means 5, in practice the end surfaces of the optical fibers
which are comprised in the fiber ribbon cable 5. The term "small distance"
is here to be taken as having the same magnitude of order as the thickness
of the components or diameter of the light waveguides or less. Thereby it
is avoided that the connecting surfaces are damaged by compression forces
when attaching the optical connector means 7. On the recessed portion 9 of
the front side of the capsule 1 also markings 21 are provided in the shape
of guide crosses, e.g. made as shallow and distinct grooves in the surface
of the capsule material, for facilitating a required accurate positioning
of the optical components 15 on the front side of the capsule, in
particular in relation to the position of the holes 11 for the guide pins.
The recessed portion also provides a protection of the conductors and
wires 26, 17 also located in the recess.
FIG. 3a is a view from above and schematically of the capsule 1 and the
optical connector means 7 before attachment of the connector means. It can
be seen here that the front coupling surfaces, which may be the active
surface, of the optical components 15 are located a little inside the
plane through the other portion of the front surface, as has been
mentioned above, for protecting the delicate components. In order to still
arrange a good optical coupling the optical components 15 are covered by
an elastic encapsulating material or layer 23, e.g. of silicon rubber,
having an adapted refractive index. Thereby a completely air-tight or
hermetic transition or continuation is obtained between the ends of the
optical fibers in the fiber ribbon cable 5 and the optical coupling
surfaces of the optical components 2, whereby light reflections are
reduced at these surfaces in the case where the refractive index of the
layer 23 is appropriately chosen. In FIG. 3b the same parts are
illustrated when they are brought against each other, the layer 23 which
has its refractive index adapted being somewhat compressed against the
flat front surface of the optical connector means 7, where the end
surfaces of the optical fibers in the fiber cable 5 are arranged.
FIG. 4 is a schematic view of the capsule 1 mounted on the support 3 as
seen in a cross section of the capsule 1. In this figure the bonding wires
26 are seen which connect electrically the components 15 to the fixedly
arranged conductor paths 17 on the front side of the capsule 1. It can be
further seen that the electrical conductors 17 on the front side of the
capsule 1 continue as electrical conductors 25 on the bottom side of the
capsule 1. These conductors 25 on the bottom side are then through tin
solder 27 or a similar material such as a conducting adhesive electrically
connected to conductive paths 29 on the top side of the support 3. These
conductive paths are in turn connected through soldered or bonded wires 31
to electrical terminals on a circuit plate 33 including integrated
electronic circuits such as suitable driver circuits, which are attached
to the top surface of the support 3.
FIG. 5 is a view similar to that of FIG. 4, illustrating a somewhat
different mounting of the optical components 15 is illustrated. Here they
are attached directly to an electronic integrated circuit located below
the components in the shape of a plate 35. The integrated circuit plate 35
is moulded into the capsule 1 itself on the front side thereof, so that
the top or front surface of the integrated circuit 35 is located in the
same plane as the other portion of the bottom surface in the recess 19. In
this case the bonding wires 26 connect electrical terminals on the
integrated circuit plate 15 to the electrical conductive paths 17 on the
front side of the capsule 1. Thereby no separate driver circuits are
needed since they may be arranged directly inside the capsule 1.
Another alternative embodiment is illustrated in the view of FIG. 6 which
is also similar to that of FIG. 4. An electronic integrated circuit plate
37 is here moulded into the capsule 1 and is connected in the same way as
a conventional encapsulated integrated circuit. Thus, also a lead frame 39
of an electrically conducting material is moulded into the capsule 1
having exterior electrical connector tongues or legs 41. These legs are as
above attached by means of tin solder or a similar material to conductive
paths 29 on the support 3. The electrical connection between the
integrated circuit 37 and the lead frame 39 is accomplished by means of
bonding wires 43. From the lead frame 39 suitable conducting portions
protrude through the front surface of the capsule 1, as is indicated at
45, where the electrically conducting wires 26 connect the optical
components 15 to precisely these conductors in the lead frame 39 and
therethrough to the integrated circuit.
Another possible mounting of the optical components 15 and the capsule 1 is
illustrated in the FIGS. 7-10. Here FIG. 7 is a view of the front side of
the capsule 1 without any mounted optical component 15. They exist as a
plate 47 shown in this Figure as located at a distance from the capsule
and comprising optical elements arranged thereon, which have optical
connector surfaces shown at 48. In FIG. 8 the capsule 1 is shown in a
sectional view along the broken line VIII in FIG. 7, where the portion
around the optical component 15 including a mounted optical component
plate 47 is illustrated in a larger scale in FIG. 10. The plate 47 of the
optical component 15 is constructed to comprise electrical connection
terminals on the rear side thereof and on these terminals, before mounting
the plate, very accurately placed small areas or isles 49 of a solder or
of a conducting adhesive are provided, as appears from the cross sectional
view of the component plate in FIG. 9.
On the front side of the capsule 1 blind holes 51 having a small diameter
are arranged, see FIG. 8, which are placed in correspondence to the isles
49 on the component plate 47, so that the relative locations of the centre
lines in the isles 49 coincide with the relative locations of the axes of
the circular holes 51. At the bottom of the rather short holes 51 portions
of electrical conductors 53 are arranged which are moulded into the
capsule 1 with the portions illustrated at a small distance from the
surface of the capsule in the recess 19 and they may for instance belong
to a lead frame, not shown. The holes 53 are located centrally in the
recess 19 and in an accurate position in relation to the bores 11 for
guide pins.
For mounting and connecting the component plate 47 it is placed first
rather accurately at its position, so that the isles 49 will be positioned
at least partly above the mouths of the holes 51. Then the front surface
of the capsule 1 where the recess 19 is located is suitably positioned so
that it is directed upwards. For a hole diameter of e.g. 0.1 mm and a
diameter of the isles 49 of approximately of the same size an alignment
laterally of the plate 47 comprising only about 0.1 mm is required which
is easily accomplished e.g. in an automatic pick-and-place-machine for
mounting electronic components or even manually. After that the plate
remains in a position located on the front surface of the capsule 1 which
is directed upwards and the plate is free to move-thereon laterally along
the surface. Then the component plate 47 and the front surface of the
capsule 1 inside the recess are heated so that also the portions of the
electrical conductors 53 at the bottom of the holes 51 will be
sufficiently hot. Then the material of the solder isles 49 is melted, if
it is a tin solder, and in any case the material will be liquid and fills
the holes 51 and will come in contact with the electrical conductors 53.
For suitable surface tension forces in the liquid material this process
will be occur completely automatically and in addition the surface
tensions forces will tend to pull the plate 47 laterally so that the isles
49 adjust themselves centrally above the respective hole 51, whereby an
automatic alignment of the plate 47 providing a very good accuracy is
obtained, simultaneously with the electrical connection. After that the
mounted assembly is allowed to cool. Thus, there must be sufficient
material included in each one of the isles 49 for completely filling one
of the holes 51 and in fact each one of the isles 49 must contain even
more material for securing sufficient surface tension forces for the
automatic alignment operation. The isles 49 will then generally have an
approximately semi-spherical shape of a diameter larger than the diameter
of the holes 51.
An alternative embodiment of the capsule is illustrated in FIG. 11. The
component plate 15 is here mounted on the bottom of a recess 55, the
recess 55 having sidewalls all around for protection of the component
plate 15 and its possible electrical connections. Thus the recess 55 has a
generally rectangular shape as viewed at the front, coupling surface of
the capsule 1, the sides or edges of the recess being located in parallel
to sides of the generally rectangular capsule 1. Thus in particular narrow
ribs 57 are located at the lower and top side of the recess, the front
surface of the ribs being located at the same level as the other
non-recessed portions of the capsule front surface.
The recess 55 having sidewalls all around can be produced when the capsule
is moulded but it can also be accomplished by attaching an apertured plate
59 to the flat front surface of a capsule block 1'. This flat surface can
then first be made by suitably grinding and polishing a moulded block,
where in the abrasive operation also ends of electrical conductors are
exposed, to which the components of the component plate 15 can be
electrically connected by wire-bonding, see also FIG. 6. Then the flat
plate 59 is attached permanently, by means of some suitable adhesive, in
an accurate position on the front surface, the guide holes for the guide
pins in the plate and in the capsule block being used for the positioning.
In FIG. 12 a view similar to that of FIG. 6 is shown, the component 15
being attached to the bottom surface of the recess 19 or 55 by means of
solder bumps 61 or bumps of an electrically conducting adhesive etc., some
of which are also connected to the exposed ends of conductors of a
leadframe moulded into the capsule 1.
Methods of accurate positioning the component plate 15 at the front side or
generally at an available or freely facing side of the capsule 1 are
illustrated in FIGS. 13a-13c for the case where a recess 55 having
sidewalls all around is used. In the first case, according to FIG. 13a,
cross-shaped marks 63 on the component plate or chip 15 are arranged which
are to be positioned at the interconnection line between the longitudinal
central axes of the guide bores 19 for the guide pins and precisely
symmetrical at or on that line, so that there is the same distance from
the marks 63 to its neighbouring guide hole 11. Therefor also marks in the
form of straight lines 65 made at the bottom of the recess are used.
According to the embodiment of FIG. 13b instead one corner of the
rectangular recess 55 is used for the positioning operation, the component
plate 15 being attached in the position where two connected edges thereof
are engaged with two adjoining sidewalls of the recess 55. In FIG. 13c the
positioning of the component plate 15 is made by guide heels/projections
or holes produced at the recess bottom surface in the moulding operation
and by corresponding guide holes or projections at the rear side of the
component carrier 15, the guide means being generally indicated at 67.
Also guide projections or platforms protruding from the bottom surface of
the recess for engaging no adjacent edges of the component chip 15 can be
used, this case being not shown.
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