U.S. patent application number 09/876582 was filed with the patent office on 2001-10-18 for ultra mold for encapsulating very thin packages.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Lajza, John J. JR., Ramsey, Charles R., Smith, Robert M..
Application Number | 20010030382 09/876582 |
Document ID | / |
Family ID | 23051163 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010030382 |
Kind Code |
A1 |
Lajza, John J. JR. ; et
al. |
October 18, 2001 |
Ultra mold for encapsulating very thin packages
Abstract
A method of encapsulating a workpiece, particularly a
microelectronic device, to achieve a very thin encapsulating layer
and reduce the finished device size. The method includes
positioning the workpiece in the mold cavity of a mold capable of
reducing its volume while the mold compound is in a liquid state
from a first volume, where mold compound may be easily added
without creating voids, to a second smaller volume which defines
the finished workpiece size. The second volume is below the size
which would permit the void-free encapsulation of the workpiece in
a conventional thermosetting plastic transfer molding machine. The
mold may be opened in two stages to prevent damage to thin molded
microelectronic devices by opening the perimeter of the mold first
while the molded device is still being supported by large molding
surfaces. The invention also includes the mold used in the
method.
Inventors: |
Lajza, John J. JR.; (Essex
Junction, VT) ; Ramsey, Charles R.; (Essex Junction,
VT) ; Smith, Robert M.; (Jericho, VT) |
Correspondence
Address: |
DELIO & PETERSON
121 WHITNEY AVENUE
NEW HAVEN
CT
06510
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
23051163 |
Appl. No.: |
09/876582 |
Filed: |
June 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09876582 |
Jun 7, 2001 |
|
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09275169 |
Mar 24, 1999 |
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Current U.S.
Class: |
264/272.13 ;
257/E21.504; 264/275; 264/279; 264/294; 425/116; 425/128;
425/129.1 |
Current CPC
Class: |
B29C 33/20 20130101;
H01L 2924/0002 20130101; H01L 21/565 20130101; B29C 43/18 20130101;
B29C 45/561 20130101; B29C 43/34 20130101; B29C 37/005 20130101;
H01L 2924/00 20130101; B29L 2031/3061 20130101; B29C 43/36
20130101; B29C 2043/3444 20130101; B29C 45/14 20130101; H01L
2924/0002 20130101; B29C 2043/5883 20130101 |
Class at
Publication: |
264/272.13 ;
264/294; 264/275; 264/279; 425/116; 425/128; 425/129.1 |
International
Class: |
B29C 043/18; B29C
045/14 |
Claims
Thus, having described the invention, what is claimed is:
1. A method of encapsulating a workpiece comprising the steps of:
providing a mold cavity in a mold, the mold cavity having a first
volume; positioning the workpiece in the mold cavity; adding mold
compound to the mold cavity to encapsulate the workpiece; reducing
the volume of the mold cavity to a second volume less than the
first volume; and curing the mold compound.
2. The method of encapsulating a workpiece according to claim 1
wherein the step of providing a mold cavity having a first volume
comprises providing a mold cavity having a first volume of a size
sufficiently large to permit laminar flow of the mold compound
around substantially all sides of the workpiece during the step of
adding mold compound to the mold cavity.
3. The method of encapsulating a workpiece according to claim 2
wherein the step of reducing the volume of the mold cavity to a
second volume comprises reducing the volume of the mold cavity to a
second volume having a size less than a size necessary to permit
laminar flow of the mold compound around substantially all sides of
the microelectronic device.
4. The method of encapsulating a workpiece according to claim 1
wherein the step of adding mold compound to the mold cavity,
comprises adding liquid mold compound having properties which allow
the mold compound to enter the mold cavity and substantially
entirely surround the workpiece in laminar flow.
5. The method of encapsulating a workpiece according to claim 1
wherein the step of adding mold compound to the mold cavity,
comprises adding a volume of mold compound greater than the second
volume of the mold cavity, and wherein the step of reducing the
volume of the mold cavity to the second volume includes squeezing
out an excess of mold compound from the mold cavity.
6. The method of encapsulating a workpiece according to claim 1
wherein: the mold cavity includes a pair of opposed mold surfaces
on opposite sides of the workpiece; and the step of reducing the
volume of the mold cavity to a second volume comprises reducing the
distance between the opposed mold surfaces of the mold cavity.
7. The method of encapsulating a workpiece according to claim 6
wherein the step of reducing the volume of the mold cavity to a
second volume comprises reducing the distance from the opposed mold
surfaces of the mold cavity to the workpiece to less than about 250
micrometers.
8. The method of encapsulating a workpiece according to claim 6
wherein the pair of opposed mold surfaces in the mold cavity are
located at defined distances from the workpiece to equalize flow
fronts of the mold compound on opposite sides of the workpiece
during the step of adding mold compound to the mold cavity.
9. The method of encapsulating a workpiece according to claim 6
wherein: the pair of opposed mold surfaces are surfaces on a pair
of opposed cavity plates and the cavity plates include at least one
inclined ramp surface bearing against a corresponding inclined ramp
surface on at least one of two opposed drive plates; and the step
of reducing the volume of the mold cavity comprises providing
relative motion between the mold and the opposed drive plates.
10. The method of encapsulating a workpiece according to claim 6
wherein: the mold is held between a pair of opposed drive plates,
each drive plate having an inclined ramp surface, the inclined ramp
surfaces on the opposed drive plates defining a tapered clamp
cavity; and the step of reducing the volume of the mold cavity
comprises moving the mold into the tapered clamp cavity, by moving
the drive plates or the mold, to reduce the distance between the
opposed mold surfaces of the mold cavity.
11. The method of encapsulating a workpiece according to claim 10
further including the step of opening the mold in two stages, the
first stage including opening a perimeter of the mold, and the
second stage comprising opening the cavity plates.
12. The method of encapsulating a workpiece according to claim 11
wherein during the first stage of opening the perimeter of the mold
the drive plates are simultaneously moved apart and driven to
reposition the cavity plates deeper in the tapered clamp cavity,
said movement apart and repositioning canceling outward motion of
the cavity plates so that the cavity plates are not separated
during the first stage.
13. The method of encapsulating a workpiece according to claim 6
wherein: the mold surfaces are formed on a pair of opposed cavity
plates; and the step of reducing the volume of the mold cavity
comprises driving the opposed cavity plates towards each other with
linear drivers.
14. The method of encapsulating a workpiece according to claim 13
wherein the linear drivers are screw thread drivers or hydraulic
drivers.
15. The method of encapsulating a workpiece according to claim 1
wherein: the mold cavity includes an inlet and a vent; and the step
of adding mold compound to the mold cavity comprises adding mold
compound through the inlet, the first volume of the mold cavity
being shaped, and the inlet and vent being positioned relative to
the workpiece in the mold cavity, to substantially fill the mold
cavity with mold compound before the mold compound reaches the
vent.
16. The method of encapsulating a workpiece according to claim 1
wherein the step of adding mold compound to the mold cavity
comprises: providing a measured amount of a non-liquid mold
compound; heating the mold compound to liquefy the mold compound;
and pressurizing the mold compound to inject it through the inlet
into the mold cavity.
17. The method of encapsulating a workpiece according to claim 1
wherein the mold compound is a thermosetting plastic.
18. The method of encapsulating a workpiece according to claim 1
wherein the mold compound includes a filler.
19. The method of encapsulating a workpiece according to claim 18
wherein the filler is silica.
20. The method of encapsulating a workpiece according to claim 1
further including the step of opening the mold in two stages, the
first stage including opening a perimeter of the mold, and the
second stage comprising opening the remainder of the mold.
21. The method of encapsulating a workpiece according to claim 1
wherein the workpiece is an electronic workpiece.
22. The method of encapsulating a workpiece according to claim 21
wherein the workpiece is a microelectronic device.
23. A mold for encapsulating a workpiece comprising: a mold cavity
having a volume defined by a plurality of mold surfaces, a first
one of the mold surfaces being movable to reduce the volume of the
mold cavity from a first volume to a smaller second volume, the
mold cavity being openable to receive the workpiece; and an inlet
communicating with the mold cavity for adding mold compound to the
mold cavity to encapsulate the workpiece; the mold surfaces being
sufficiently far from the workpiece in the first volume to allow
mold compound to be added to the mold cavity without forming
voids.
24. The mold for encapsulating a workpiece according to claim 23
wherein: the mold cavity is shaped to receive a substantially
planar workpiece; the first mold surface is substantially planar;
and the plurality of mold surfaces includes a second mold surface
opposite the first mold surface, the second mold surface being
movable with the first mold surface to reduce the volume of the
mold cavity to the second volume.
25. The mold for encapsulating a workpiece according to claim 24
wherein the first and second mold surfaces move in opposition to
each other from first positions to second positions, the first
positions being sufficiently far from the workpiece that mold
compound may be added to the mold cavity through the inlet without
forming voids, and the second positions being sufficiently close to
the workpiece that mold compound added to the mold cavity through
the inlet would form voids.
26. The mold for encapsulating a workpiece according to claim 23
wherein the plurality of mold surfaces includes opposed clamp
plates, the clamp plates being openable to receive the workpiece
and clampable with sufficient force to hold the mold cavity closed
as mold compound is added to the mold cavity.
27. The mold for encapsulating a workpiece according to claim 26
wherein the clamp plates define a perimeter for the mold
cavity.
28. The mold for encapsulating a workpiece according to claim 23
wherein the mold cavity is shaped to receive an electronic
workpiece.
29. The mold for encapsulating a workpiece according to claim 28
wherein the mold cavity is shaped to receive a microelectronic
device.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the encapsulation of thin
workpieces, particularly electronic and microelectronic devices, to
achieve a very thin, but void-free seal around the workpiece.
[0003] 2. Description of Related Art
[0004] Microelectronic devices must be protected against moisture
as well as assembly process and other environmental contaminants.
This is commonly done by encapsulating the device in a mold
compound, such as a thermosetting plastic, applied by a transfer
molding process.
[0005] In a typical transfer molding machine used in the
microelectronics industry, a thin electronic workpiece mounted on a
lead frame is clamped between two halves of a split mold. The mold
defines a mold cavity around the device with sufficient clearance
to allow mold compound to be injected and flow around the device to
encapsulate it. During the molding process mold compound is
injected into an inlet and air inside the mold escapes from a
vent.
[0006] The mold compound is initially provided in a non-liquid
pellet form containing a desired quantity of the compound. The
pellet is heated under pressure in a chamber until it is liquefied.
A plunger then drives the liquefied mold compound into the mold
cavity. The mold compound is allowed to cure and the mold is
opened, releasing the encapsulated microelectronic device.
[0007] Because smaller microelectronic devices are highly
desirable, device manufacturers would like to reduce the thickness
of the encapsulating layer of mold compound which encases each
device. Thinner encapsulating layers also aid in improving device
performance or reliability with regard to heat dissipation,
resistance to coating damage under thermal stress and other
parameters. However, as the distance between the inner mold
surfaces and the electronic workpiece is decreased, it becomes more
difficult to obtain a high quality void-free encapsulant around the
entire device.
[0008] To obtain a void-free seal, the liquefied mold compound must
enter the mold inlet and entirely fill the space in the mold cavity
before the mold compound flow front arrives at the mold vent. If
the mold compound reaches the vent before the mold is completely
filled, an air bubble is trapped in the mold, creating a void.
[0009] To completely fill the mold cavity, the mold compound must
flow between the upper mold surface and the upper surface of the
device, between the lower mold surface and the lower surface of the
device, and into the space surrounding the outer perimeter of the
device. However, as the distance between the upper and lower mold
surfaces and the device is reduced, so as to make the encapsulating
coating thinner, it becomes more difficult for the mold compound to
penetrate these regions.
[0010] If this distance is reduced too far, the mold compound will
flow around the outer perimeter of the device before the mold
compound flow front has displaced the air in the space above and
below the device. The result is a void in the encapsulation
material as an air bubble is pinched off in the center of the
device.
[0011] As a result, transfer molding of semiconductor devices with
conventional equipment has required that the distance from the
inner mold surfaces to the device be at least about 200-250
micrometers. This ensures that there will be laminar flow of the
molding compound into the mold and around the device. The exact
minimum distance limit is, of course, a function of the specific
mold compound used, the fillers it contains and process parameters,
such as temperature, but, in general, reducing the distance from
the inner mold surfaces to the device to less than some minimum
distance results in unacceptable manufacturing losses due to the
formation of voids.
[0012] Provided that sufficient clearance between the inner mold
surfaces and the device is maintained, however, the flow of the
mold compound during injection remains laminar, and the flow fronts
above and below the device remain relatively balanced, so as to
prevent the formation of voids. On the other hand, it is known that
acceptable sealing of the device and protection against
environmental contamination can be achieved with an encapsulation
thickness that is well below this thickness limit.
SUMMARY OF THE INVENTION
[0013] Bearing in mind the problems and deficiencies of the prior
art, it is therefore an object of the present invention to provide
a method of encapsulating an electronic workpiece with an outer
coating of mold compound which is thinner than the thickness limit
heretofore achievable with conventional transfer molding.
[0014] A further object of the invention is to provide a method of
encapsulating an electronic workpiece with a coating of mold
compound that is void-free.
[0015] It is yet another object of the present invention to provide
a method of encapsulating an electronic workpiece by varying the
mold dimensions while the mold compound is in a liquid state.
[0016] Yet another object of the present invention to provide a
mold for encapsulating an electronic workpiece that can vary in
volume from a first volume where mold compound can be injected
easily and completely surround the device with a relatively thick
coating to a second reduced volume in which only a thin
encapsulating coating remains.
[0017] Still other objects and advantages of the invention will in
part be obvious and will in part be apparent from the
specification.
[0018] The above and other objects and advantages, which will be
apparent to one of skill in the art, are achieved in the present
invention which is directed to a method of encapsulating an
electronic workpiece and to a mold for use in the method. In the
most basic form of the method of this invention, a mold cavity
having a first volume has an electronic workpiece positioned
therein. Mold compound is added to the mold cavity to encapsulate
the microelectronic device, and the volume of the mold cavity is
then reduced to a second volume less than the first volume. The
mold compound is then cured and the device removed.
[0019] In the preferred method of the invention, the mold has a
first volume with a size sufficiently large to permit laminar flow
of the mold compound around substantially all sides of the
electronic workpiece during the step of adding mold compound to the
mold cavity. The second volume has a size less than the size
necessary to permit such laminar flow. This allows the mold to
produce very thin coatings of a thickness less than would otherwise
be possible by conventional transfer molding techniques.
[0020] In the most highly preferred method of the invention, the
mold cavity is adapted to receive a substantially planar electronic
workpiece and includes a pair of opposed mold surfaces on opposite
sides of the device. The volume of the mold cavity is reduced to
the second volume by reducing the distance between the pair of
opposed mold surfaces of the mold cavity.
[0021] The volume is reduced in one aspect of the method of this
invention by providing a tapered clamp cavity defined between two
opposed clamp plates having inclined ramp surfaces. The mold is
held between the opposed clamp plates and is moved deeper into the
tapered clamp cavity to reduce the distance between opposed mold
surfaces of the mold cavity.
[0022] The mold compound used in connection with this method is
typically a thermosetting plastic. In accordance with the method,
the mold compound includes a filler. The filler is typically
silica, but other fillers can be used to enhance thermal,
electrical or mechanical properties of the mold compound.
[0023] The invention is particularly suitable for encapsulating
microelectronic devices, but is also suitable for encapsulating
other thin electronic workpieces, including printed circuits,
various types of electronic components, microcircuits and the
like.
[0024] The invention also includes the mold used in connection with
the method described above. The mold includes a mold cavity having
a volume defined by a plurality of mold surfaces, a first one of
the mold surfaces being movable to reduce the volume of the mold
cavity from a first volume to a smaller second volume. The mold
cavity is openable to receive a microelectronic device, and an
inlet communicates with the mold cavity for adding mold compound.
The mold surfaces are sufficiently far from the electronic
workpiece when the mold is in the first volume configuration to
allow mold compound to be added to the mold cavity without forming
voids.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The features of the invention believed to be novel and the
elements characteristic of the invention are set forth with
particularity in the appended claims. The figures are for
illustration purposes only and are not drawn to scale. The
invention itself, however, both as to organization and method of
operation, may best be understood by reference to the detailed
description which follows taken in conjunction with the
accompanying drawings in which:
[0026] FIG. 1 is a side view, in cross-section, of a mold
containing a microelectronic device and lead frame to be
encapsulated in accordance with the method of this invention. The
mold is shown in its large, first volume, configuration and is
clamped and ready to be filled with mold compound.
[0027] FIG. 2 is a side view, in cross-section, of the mold in FIG.
1, still in the first volume configuration, showing the mold at an
intermediate time during the transfer molding operation. Mold
compound is shown being transferred from an inlet at the left into
the mold and balanced flow fronts above and below the device are
depicted.
[0028] FIG. 3 is a side view, in cross-section, of the mold in FIG.
1, still in the first volume configuration, showing the mold
completely filled, prior to reducing the volume of the mold to the
second volume.
[0029] FIG. 4 is a side view, in cross-section, of the mold in FIG.
1, showing the mold in the reduced, second volume
configuration.
[0030] FIG. 5 is a side view, in cross-section, of the mold in FIG.
1, showing the mold being opened to release the device.
[0031] FIG. 6 is a side view, in cross-section, of an alternative
embodiment of the mold of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0032] In describing the preferred embodiment of the present
invention, reference will be made herein to FIGS. 1-6 of the
drawings in which like numerals refer to like features of the
invention. Features of the invention are not necessarily shown to
scale in the drawings.
[0033] FIG. 1 illustrates a preferred embodiment of a mold used in
connection with the method of encapsulating an electronic workpiece
described herein. The mold 10 includes a mold cavity 12 having an
inlet 14 and a vent 16. The inner surfaces at the perimeter of the
mold cavity are formed by upper clamp plate 18a, 18b and lower
clamp plate 20a, 20b.
[0034] The clamp plate 18a, 18b defines a generally rectangular
perimeter for the upper portion of the mold cavity. Upper movable
cavity plate 22 sits within the rectangular opening in the upper
clamp plate 18a, 18b, and it will be understood that in the cross
sectional view of FIG. 1, the right side 18a and the left side 18b
are the right and left portions of a single clamp plate appearing
in cross section. The lower clamp plate 20a, 20b is similar, having
a generally rectangular opening sealed by the lower movable cavity
plate 24.
[0035] The upper and lower movable cavity plates 22, 24 define the
upper and lower surfaces of the mold cavity 12 respectively. The
mold 10, including the upper and lower movable cavity plates 22,
24, is mounted between upper and lower drive plates 26, 28. The
upper and lower drive plates 26, 28 contact the upper and lower
movable cavity plates 22, 24, and prevent them from moving outward
during the molding operation as mold compound is introduced into
the mold.
[0036] The upper and lower clamp plates can be separated to receive
a microelectronic device 30 mounted on a lead frame 32. The clamp
plates 18, 20 are clamped together in a conventional way with an
external clamping mechanism that provides a vertical clamping force
sufficient to hold the lead frame and to allow a mold compound,
preferably a thermosetting resin, to be added to the mold cavity
12.
[0037] Inlet 14 is connected to a chamber in the transfer molding
machine (not shown) which heats a pellet of thermosetting resin to
liquefy it. The liquefied resin is injected under pressure into the
mold shown in FIG. 1 through the inlet 14.
[0038] FIG. 2 shows the mold compound 34 flowing into the mold
cavity 12 with two relatively uniform and equalized flow fronts 36,
38 on opposite sides of the microelectronic device 30. It will be
noted in FIG. 2 that the flow fronts are curved and that the resin
34 in the boundary layer regions close to the device 30 and close
to the upper and lower inner surfaces of the mold cavity 40, 42 lag
behind the portion of the flow front which is at the maximum
distance from these surfaces.
[0039] This curvature of the mold compound flow front is caused by
the friction between the moving mold compound and the inner
surfaces of the mold. The movable cavity plates 22, 24 are set such
that void-free filling of the mold cavity can be reliably completed
for each molding operation.
[0040] The movable cavity plates 22, 24 move relative to the
microelectronic device 30 so as to increase or decrease the
distance between their inner surfaces 40, 42 and the device 30. The
distance is set to permit a laminar flow of the mold compound
between the inner surfaces 40, 42 and the outer surfaces of the
lead frame and microelectronic device 30. This insures that the
mold compound 34 will substantially completely fill the interior of
the mold cavity before the mold compound arrives at the vent 16 at
the opposite end of the mold cavity.
[0041] For a conventional mold compound, this distance will be
greater than 200 micrometers, preferably greater than 250
micrometers. As the mold compound 34 is added, the clamp plates 18,
20 are prevented from separating by conventional clamping means
(not shown) and the movable cavity plates 22, 24 are prevented from
opening further by the drive plates 26, 28.
[0042] FIG. 3 shows the mold cavity 12 completely filled with the
mold compound 34. At this stage of the molding operation, the mold
compound is still in its liquid form. FIGS. 1, 2 and 3 all show the
mold 10 with the mold cavity 12 in its largest volume position
which is the first volume configuration used for filling the mold.
This first volume configuration permits the mold compound 34 to
easily flow into all areas of the mold, particular the region
directly above and below the center of the electronic workpiece
30.
[0043] FIG. 4 shows the mold in the reduced or second volume
configuration. In this configuration, the upper and lower movable
cavity plates 22, 24, have been driven towards the device 30 by the
relative motion between the upper and lower drive plates 26, 28 and
the mold.
[0044] The upper drive plate 26 includes an inclined ramp surface
46. The lower drive plate 28 also includes an inclined ramp surface
48, which faces the ramp surface 46. The upper and lower movable
cavity plates have matching angled surfaces 50, 52 which slide on
the ramp surfaces 46, 48.
[0045] As the drive plates move to the right and the clamp plates
move to relative to the drive plates in the direction shown by
arrow 54, the movable cavity plates are compressed toward each
other by the action of the ramp surfaces 46, 48. This reduces the
distance from the inner surfaces 40, 42 to the device 30 and
decreases the volume of the mold cavity. As the volume of the mold
cavity is reduced, mold compound is squeezed out of the mold
cavity. The excess mold material is preferably squeezed back into
the mold inlet 14, however the mold may also be provided with
alternative outlets for the excess material, or the vent 16 may be
used.
[0046] With the mold in the first volume configuration of FIGS.
1-3, the mold cavity is filled easily and completely as the mold
compound enters the mold and spreads in laminar flow. After the
mold is filled, the volume is reduced to the second volume
configuration of FIG. 4. This second volume configuration is below
the volume which allows such laminar flow.
[0047] The control over the volume of the mold allows different
mold compounds to be used. Specifically, fillers may be added to
the mold compound having desirable properties, but which might
otherwise increase viscosity or not be capable of use in a
conventional transfer molding machine.
[0048] Alternatively, additives that are presently in use solely to
improve the thermosetting resin molding properties, but which
otherwise have little value in the cured mold compound, may be
eliminated due to the ease with which the mold of this invention
may be filled.
[0049] FIG. 5 shows the mold as it is being opened to remove the
molded device 30. At this point in the removal process, the clamp
plates have been have been separated by moving the upper clamp
plate 18a, 18b vertically up and the lower clamp plate 20a, 20b
vertically down. This separation can be seen best at the vent 16
and the mold inlet 14 where clamp plates 18b, 20b have moved away
from the mold compound 34.
[0050] The upper and lower drive plates 26, 28, have also been
moved vertically away from each other, and they have been moved by
the same distance that the upper and lower clamp plates were moved.
However, this motion of the drive plates away from the device 30
does not cause the cavity plates 22, 24 to open. The separation of
the drive plates is exactly cancelled out by actively moving the
drive plates horizontally to the right (in FIG. 5) so that the
cavity plates 22, 24 are now deeper in the tapered cavity formed
between the ramp surfaces 46, 48.
[0051] Moving the drive plates vertically apart with the clamp
plates is typically done by mounting the upper and lower drive
plates to the same external clamping mechanism as the upper and
lower clamp plates. The drive plates are mounted to the external
vertical clamping mechanism so that they can be moved horizontally,
and a horizontal drive mechanism is provided to accomplish this
motion, as needed to move the ramp surfaces 46, 48 relative to the
clamp plates in the directions described above.
[0052] The net result of the simultaneous vertical outward motion
of the drive plates with the horizontal motion is to keep the
molded device clamped between the inner surfaces of the mold cavity
40, 42 until the entire perimeter of that device has been separated
from the perimeter molding surfaces on the clamp plates.
[0053] This technique provides a significant advantage for the thin
molded devices of the present invention as compared to prior
removal techniques. With the technique described here, the molded
device 30 is fully supported by the movable cavity plates 22, 24
during the critical stage when the mold is first opened. It is not
uncommon for the molding compound to stick to the mold surface
slightly as the mold is opened. By opening the perimeter first, the
device is partially freed and the risk of damaging the molded
device is significantly reduced.
[0054] After the perimeter is opened to the stage seen in FIG. 5,
the remainder of the mold is opened by separating movable cavity
plates 22, 24 to remove the molded device.
[0055] FIG. 6 shows an alternative mold design in accordance with
the present invention. In this embodiment, the cavity plates 22, 24
are opened and closed by vertical drivers 56, 58 operating drive
rods 60, 62. The vertical drivers and drive rods may be any type of
linear driver. Threaded rods driven by screw drivers and motors may
be used, as may hydraulic piston/cylinder drivers or appropriately
designed pneumatic piston/cylinder actuators.
[0056] Regardless of whether the design in FIGS. 1-5 or the design
in FIG. 6 is used, the cavity plates 22, 24 need to be strongly
supported. During the molding process, the cavity plates need to
provide sufficient clamping force to resist the outward pressure
from the injected molding compound. After the molding compound is
injected, the cavity plate drivers need to provide sufficient
closing force to close the mold and eject excess molding
compound.
[0057] In both designs, the preferred method of opening the mold is
to open the perimeter first, then open the cavity plates. The
construction of the mold with the separate motion for the cavity
plates permits this method of opening the mold in all cases.
[0058] While the present invention has been particularly described,
in conjunction with a specific preferred embodiment, it is evident
that many alternatives, modifications and variations will be
apparent to those skilled in the art in light of the foregoing
description. It is therefore contemplated that the appended claims
will embrace any such alternatives, modifications and variations as
falling within the true scope and spirit of the present
invention.
* * * * *