U.S. patent application number 09/839861 was filed with the patent office on 2001-08-16 for method of making a plastic pakage for an optical integrated circuit device.
Invention is credited to Glenn, Thomas P..
Application Number | 20010014486 09/839861 |
Document ID | / |
Family ID | 23264753 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010014486 |
Kind Code |
A1 |
Glenn, Thomas P. |
August 16, 2001 |
Method Of Making A Plastic Pakage For An Optical Integrated Circuit
Device
Abstract
A package for an integrated circuit device having an optical
cell is disclosed. A method of making the package also is
disclosed. The package includes a base of molded encapsulant
material. A metal leadframe is embedded in the plastic base at the
upper surface of the base. Encapsulant material covers the lower
and side surfaces of the die pad and the leads of the leadframe,
but does not cover the upper surfaces of the die pad and leads. The
side surfaces of the die pad and leads have locking features for
engaging the encapsulant material. An optical integrated circuit
device is attached to the exposed surface of the die pad. An
adhesive bead is applied around the optical device on the exposed
upper surface of the leads. An optically clear cover is placed on
and, in some embodiments, pressed into the still-viscous adhesive
bead. When hardened, the bead supports the cover above the optical
device. The side surfaces of the optically clear cover, or the
surface of the cover facing the optical device, are provided with
locking features that engage the adhesive bead and strengthen the
connection between the cover and the adhesive bead.
Inventors: |
Glenn, Thomas P.; (Gilbert,
AZ) |
Correspondence
Address: |
SKJERVEN MORRILL MACPHERSON LLP
25 METRO DRIVE
SUITE 700
SAN JOSE
CA
95110
US
|
Family ID: |
23264753 |
Appl. No.: |
09/839861 |
Filed: |
April 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09839861 |
Apr 20, 2001 |
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09324710 |
Jun 3, 1999 |
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Current U.S.
Class: |
438/64 ;
257/E23.193; 257/E31.117; 438/112; 438/118 |
Current CPC
Class: |
H01L 2924/00014
20130101; H01L 2924/00014 20130101; H01L 2924/00 20130101; H01L
2924/00 20130101; H01L 2924/00 20130101; H01L 2924/00 20130101;
H01L 2924/00 20130101; H01L 2224/45144 20130101; H01L 2924/14
20130101; H01L 2224/85447 20130101; H01L 2224/48655 20130101; H01L
2224/85444 20130101; H01L 31/0203 20130101; H01L 2224/85464
20130101; H01L 23/10 20130101; H01L 27/14618 20130101; H01L
2224/48091 20130101; H01L 2224/8592 20130101; H01L 2224/48247
20130101; H01L 2924/16195 20130101; H01L 2224/48647 20130101; H01L
2224/48639 20130101; H01L 24/48 20130101; H01L 2224/48091 20130101;
H01L 2224/85455 20130101; H01L 2924/18301 20130101; H01L 2224/48664
20130101; H01L 2924/01046 20130101; H01L 24/45 20130101; H01L
2224/48664 20130101; H01L 2924/0102 20130101; H01L 2924/01058
20130101; H01L 2224/48647 20130101; H01L 2924/1815 20130101; H01L
2224/48655 20130101; H01L 2924/16152 20130101; H01L 2924/01039
20130101; H01L 2924/01028 20130101; H01L 2924/01079 20130101; H01L
2224/48644 20130101; H01L 2224/45144 20130101; H01L 2924/01019
20130101; H01L 2224/48644 20130101; H01L 2224/85439 20130101; H01L
2224/48639 20130101 |
Class at
Publication: |
438/64 ; 438/112;
438/118 |
International
Class: |
H01L 021/00; H01L
021/44; H01L 021/48; H01L 021/50 |
Claims
1. A package for an integrated circuit device comprising: a base of
molded insulative material having a planar first surface; a die pad
in an embedded connection with said base at the first surface of
said base, wherein a first surface of the die pad is not covered by
the insulative material of the base; a plurality of leads, said
leads having a first portion in an embedded connection with said
base at the first surface of said base, and a second portion
extending from said base, wherein a first surface of the first
portion of each lead is not covered by the insulative material of
the base; an integrated circuit device having a first surface and
an opposite second surface, wherein the first surface of the
integrated circuit device includes a light sensitive portion, and
the second surface of the integrated circuit device is on the first
surface of the die pad; a bead of a first adhesive material, said
bead on the first surface of the base around the integrated circuit
device; and an optically clear package cover having a planar first
surface, wherein said first surface of the cover is connected to
the adhesive bead around the integrated circuit device and is
supported above the first surface of the integrated circuit device
by the bead.
2. The package of claim 1, wherein the die pad has a second surface
opposite the first surface of the die pad, and a side surface
between said first surface and said second surface, and the second
surface and side surface of the die pad are covered by the
insulative material of the base; the first portion of each of said
leads has a second surface opposite the first surface of the first
portion of the lead, and a side surface between the first surface
and the second surface, and the second surface and side surface of
the first portion of each lead are covered by the insulative
material of the base; and the side surface of the die pad and the
side surface of the first portion of the leads include a reentrant
portion in contact with said insulative material of the base.
3. The package of claim 2, wherein the side surface of the die pad
and of the first portion of the leads include asperities.
4. The package of claim 2, wherein the side surface of the die pad
and of the first portion of the leads include a central peak.
5. The package of claim 2, wherein the side surface of the die pad
and of the first portion of the leads include a central
depression.
6. The package of claim 1, wherein the die pad has a second surface
opposite the first surface of the die pad, and a side surface
between said first surface and said second surface, and the second
surface and side surface of the die pad are covered by the
insulative material of the base; the first portion of each of said
leads has a second surface opposite the first surface of the first
portion of the lead, and a side surface between the first surface
and the second surface, and the second surface and side surface of
the first portion of each lead are covered by the insulative
material of the base; and the side surface of the die pad includes
a means for enhancing the connection between the insulative base
and the die pad, and the side surface of the first portion of the
leads includes a means for enhancing the connection between the
insulative base and the first portion of the leads.
7. The package of claim 1, wherein said optically clear cover has a
planar second surface opposite said first surface, and a side
surface between said first surface and said second surface; and
wherein said adhesive bead contacts a peripheral portion of the
first surface of the cover and the side surface of the cover.
8. The package of claim 7, wherein said adhesive bead contacts a
peripheral portion of the second surface of the cover.
9. The package of claim 7, wherein the side surface of the cover
includes a means for enhancing the connection between the cover and
the adhesive bead.
10. The package of claim 7, wherein the side surface of the cover
includes a reentrant portion in contact with said bead.
11. The package of claim 7, wherein the side surface of the cover
includes a protruding arced portion, and the bead contacts said
arced portion.
12. The package of claim 7, wherein all or part of the side surface
of the cover in contact with said bead has a diagonal orientation
relative to the first surface of the cover.
13. The package of claim 7, wherein the side surface of the cover
has a first portion beginning at the first surface of the cover in
contact with the bead, and a second portion between said first
portion and the second surface of the cover, and said first portion
has a diagonal orientation relative to the second surface of the
cover, and the second portion is orthogonal.
14. The package of claim 7, wherein the side surface of the cover
includes an arc-shaped indentation.
15. The cover of claim 7, wherein the side surface of the cover has
a first orthogonal portion beginning at the first surface of the
cover, and a second orthogonal portion between said first portion
and the second surface of the cover, and the second orthogonal
portion is recessed from the first orthogonal portion.
16. The package of claim 1, wherein the first surface of the cover
includes a means for enhancing the connection between the bead and
the cover.
17. The package of claim 1, wherein the first surface of the cover
includes a groove in contact with said bead.
18. The package of claim 2, wherein said optically clear cover has
a planar second surface opposite said first surface, and a side
surface between said first surface and said second surface; said
adhesive bead contacts a peripheral portion of the first surface of
the cover and the side surface of the cover; and the side surface
of the cover includes a reentrant portion in contact with said
bead.
19. The package of claim 2, wherein said optically clear cover has
a planar second surface opposite said first surface and a side
surface between said first surface and said second surface; said
adhesive bead contacts a peripheral portion of the first surface of
the cover and the side surface of the cover; and the side surface
of the cover includes a means for enhancing the connection between
the cover and the adhesive bead.
20. The package of claim 2, wherein said optically clear cover has
a planar second surface opposite said first surface wherein the
first surface of the cover is in a connection with said bead around
the integrated circuit device; and the first surface of the cover
includes a means for enhancing the connection between the bead and
the cover.
21. The package of claim 20, wherein the package includes a
plurality of electrical conductors, with each conductor in a first
connection with a bonding pad on said integrated circuit device and
a second connection with a first portion of a lead, and the
adhesive bead covers said second connection, and a second adhesive
material covers said first connection.
22. The package of claim 1, wherein said integrated circuit device
has a side surface between the first surface and the second surface
of the integrated circuit device; and said adhesive bead contacts
the side surface of the integrated circuit device.
23. The package of claim 22, wherein the package includes a
plurality of electrical conductors, with each conductor in a first
connection with a bonding pad on said integrated circuit device and
a second connection with a first portion of a lead, and the
adhesive bead covers said second connection, and a second adhesive
material covers said first connection.
24. The package of claim 22, wherein said bead covers a peripheral
portion of the first surface of the integrated circuit device.
25. The package of claim 2, wherein said integrated circuit device
has a side surface between the first surface and the second surface
of the integrated circuit device; and said adhesive bead contacts
the side surface of the integrated circuit device.
26. The package of claim 10, wherein said integrated circuit device
has a side surface between the first surface and the second surface
of the integrated circuit device; and said adhesive bead contacts
the side surface of the integrated circuit device.
27. The package of claim 18, wherein said integrated circuit device
has a side surface between the first surface and the second surface
of the integrated circuit device; and said adhesive bead contacts
the side surface of the integrated circuit device.
28. The package of claim 2, wherein said adhesive bead covers a
peripheral portion of the first surface of the integrated circuit
device.
29. The package of claim 10, wherein said adhesive bead covers a
peripheral portion of the first surface of the integrated circuit
device.
30. The package of claim 18, wherein said adhesive bead covers a
peripheral portion of the first surface of the integrated circuit
device.
31. The package of claim 28, wherein said optical integrated
circuit device includes a plurality of bonding pads, and said
adhesive bead covers said bonding pads.
32. A package for an integrated circuit device comprising: a base
of molded insulative material having a planar first surface; a die
pad in an embedded connection with said base at the first surface
of said base, wherein a first surface of the die pad is not covered
by the insulative material of the base; a plurality of leads, said
leads having a first portion in an embedded connection with said
base at the first surface of said base, and a second portion
extending from said base, wherein a first surface of the first
portion of each lead is not covered by the insulative material of
the base; an integrated circuit device having a first surface and
an opposite second surface, wherein the first surface of the
integrated circuit device includes a light sensitive portion, and
the second surface of the integrated circuit device is on the first
surface of the die pad; an optically clear package cover in an
adhesive connection with the first surface of the base around the
integrated circuit device, said cover having a central cavity and
enclosing said integrated circuit device.
33. The package of claim 32, wherein said package cover has a
planar portion above said integrated circuit device.
34. The package of claim 32, wherein the package cover includes a
means for preventing scratches to a surface of the planar portion
of the cover.
35. The package of claim 32, wherein the die pad has a second
surface opposite the first surface of the die pad, and a side
surface between said first surface and said second surface, and the
second surface and side surface of the die pad are covered by the
insulative material of the base; the first portion of each of said
leads has a second surface opposite the first surface of the first
portion of the lead, and a side surface between the first surface
and the second surface, and the second surface and side surface of
the first portion of each lead are covered by the insulative
material of the base; and the side surface of the die pad and the
side surface of the first portion of the leads include a reentrant
portion in contact with said insulative material of the base.
36. The package of claim 35, wherein said package cover has a
planar portion above said integrated circuit device.
37. A method of making a package for an integrated circuit device
comprising: providing a metal leadframe, said leadframe including a
die pad and a plurality of leads, wherein said die pad and said
leads include a first surface, an opposite second surface, and a
side surface between the first surface and the second surface;
molding a base of an adhesive insulative material to the leadframe,
so that the second surface and side surface of the die pad and the
second surface and side surface of a first portion of the leads are
covered with the insulative material of the base, and the first
surfaces of the die pad and of the first portion of the leads are
exposed at a first surface of the base; providing an integrated
circuit device having a first surface that includes a light
sensitive portion, and an opposite second surface; placing the
second surface of the integrated circuit device on the first
surface of the die pad; electrically connecting the integrated
circuit device and the first portion of each of said leads;
applying a viscous adhesive bead on the first surface of the base
around said integrated circuit device, said bead extending to a
height above the first surface of the integrated circuit device;
providing an optically clear planar cover having a first surface;
placing said first surface of the cover on said adhesive bead
around said integrated circuit device, so that said cover transmits
light to said light sensitive portion and said integrated circuit
device is enclosed in a cavity formed by the first surface of said
base, said adhesive bead, and said first surface of said cover; and
hardening said adhesive bead, so that said adhesive bead supports
said optically clear cover above said integrated circuit
device.
38. The method of claim 37, wherein applying the adhesive bead
includes applying said adhesive bead substantially around said
integrated circuit device, leaving one or more discontinuities,
and, after said bead is hardened, applying additional adhesive
material to fill said one or more discontinuities.
39. The method of claim 37, wherein said optically clear cover
includes a second surface opposite said first surface, and a side
surface between the first surface and the second surface; and
further comprising pressing said optically clear cover into said
adhesive bead, so that said adhesive bead contacts a peripheral
portion of the first surface of the cover and the side surface of
the cover.
40. The package of claim 39, including pressing said cover into
said bead so that the adhesive bead contacts a peripheral portion
of the second surface of said optically clear cover.
41. The method of claim 37, further comprising providing the side
surface of the die pad and the side surface of the first portion of
the leads with a reentrant portion; and further comprising and
molding the base so as to cover the reentrant portion of both the
die pad and the first portion of the leads with the insulative
material of the base.
42. The method of claim 41, further comprising providing the side
surface of the die pad and the side surface of the first portion of
the leads with asperities; and further comprising molding the base
so as to cover the asperities of both the die pad and the first
portion of the leads with the insulative material of the base.
43. The method of 39, wherein providing the side surface of the die
pad and the side surface of the first portion of the leads with a
reentrant portion; and further comprising molding the base so as to
cover the reentrant portion of both the die pad and the first
portion of the leads with the insulative material of the base.
44. The method of claim 37, wherein the adhesive bead is applied a
lateral distance from the integrated circuit device.
45. The method of claim 41, wherein the adhesive bead is applied a
lateral distance from the integrated circuit device.
46. The method of claim 37, wherein the integrated circuit device
has a side surface between the first surface and the second surface
of the integrated circuit device; and further comprising applying
the bead of adhesive material so as to contact the side surface of
the integrated circuit device with the adhesive bead material.
47. The method of claim 46, further comprising applying the bead of
adhesive material so as to contact a peripheral portion of the
first surface of the integrated circuit device with the adhesive
bead.
48. The method of claim 41, wherein the integrated circuit device
has a side surface between the first surface and the second surface
of the integrated circuit device; and further comprising applying
the bead of adhesive material so as to contact the side surface of
the integrated circuit device with the adhesive bead material.
49. The method of claim 48, further comprising applying the bead of
adhesive material so as to contact a peripheral portion of the
first surface of the integrated circuit device with the adhesive
bead.
50. The method of claim 37, further comprising providing the side
surface of the optically clear cover with a reentrant portion, and
pressing the cover into the bead so as to cover said reentrant
portion with bead material.
51. The method of claim 41, further comprising providing the side
surface of the optically clear cover with a reentrant portion, and
pressing the cover into the bead so as to cover said reentrant
portion with bead material.
52. A method of making a package for an integrated circuit device
comprising: providing a metal leadframe, said leadframe including a
die pad and a plurality of leads, wherein said die pad and said
leads include a first surface, an opposite second surface, and a
side surface between the first surface and the second surface;
molding a base of an adhesive insulative material to the leadframe,
so that the second surface and side surface of the die pad and the
second surface and side surface of a first portion of the leads are
covered with the insulative material of the base, and the first
surfaces of the die pad and of the first portion of the leads are
exposed at a first surface of the base; providing an integrated
circuit device having a first surface that includes a light
sensitive portion, and an opposite second surface; placing the
second surface of the integrated circuit device on the first
surface of the die pad; electrically connecting the integrated
circuit device to the first portion of each of said leads;
providing an optically clear package cover having a planar first
portion; and adhering the package cover to the first surface of the
base so that the package cover encloses the integrated circuit
device and the first portion of the package cover is above the
light sensitive portion of the integrated circuit device.
53. The package of claim 52, further comprising: providing the side
surface of the die pad and the side surface of the first portion of
the leads with a reentrant portion; and further comprising and
molding the base so as to cover the reentrant portion of both the
die pad and the first portion of the leads with the insulative
material of the base.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed towards an improved
plastic package for an integrated circuit device, and a method of
making such a package.
BACKGROUND OF THE INVENTION
[0002] Integrated circuit device are conventionally enclosed in
plastic packages that provide protection from hostile environments
and enable electrical interconnection between the integrated
circuit device and printed circuit boards. FIG. 1 is a cross
sectional view of an inexpensive, conventional molded plastic
package 1 known as a plastic dual in line package ("p-dip"). The
elements of package 10 include an integrated circuit device 12,
adhesive material (not shown) to attach integrated circuit device
12 to die pad 17, bond wires 13 that electrically connect bonding
pads 14 on integrated circuit device 12 to individual leads 15 of
the leadframe, and an adhesive plastic encapsulant material which
covers the other components and forms package body 16.
[0003] In FIG. 1, molding compound (a.k.a., encapsulant material)
is molded above and below device 12, leads 15 and die pad 17 to
form package body 16. The peripheral sides 17 of package body 16
are sloped to facilitate release from the mold used to make the
package. Leads 15 extend from package body 16. There are a variety
of well-known alternative styles for the finishing the leads of
such a package, including PLCC and gull wing styles.
[0004] Further background information concerning conventional
plastic integrated circuit packages and leadframes is contained in
chapter 8 of the book Microelectronics Packaging Handbook (1989),
which was edited by R. Tummala and E. Rymaszewski, and is published
by Van Nostrand Reinhold, 115 Fifth Avenue, New York, N.Y.
[0005] The operation of certain types of optical integrated circuit
devices, such as erasable programmable read-only memory devices
("EPROM"), charge coupled devices ("CCD"), and camera-type devices
require that light be applied to a light-sensitive cell on a
surface of the device. For such devices, standard p-dip packages
cannot be used. FIG. 2 is an example of a conventional molded
package 20 for an optical integrated circuit device 23.
[0006] Package 20 includes some of the same features as package 10
of FIG. 1, so the same reference numbers will be used in FIG. 2.
Package 20 of FIG. 2 includes leads 15 and die pad 17, upon which
optical integrated circuit device 23 rests. Bond wires 13 extend
between individual bonding pads 14 on optical device 23 and an
individual lead 15. Encapsulant material is molded above and below
the leadframe to form package body 16.
[0007] Below leads 15, package 20 of FIG. 2 is the same as package
10 of FIG. 1. Above leads 15, however, package 20 is modified to
accommodate optical integrated circuit device 23. In particular, a
portion of molded package body 16, namely, support structure 21, is
formed on and above portions of leads 15. Support structure 21,
which is integral with package body 25 and formed of the same
material, surrounds optical device 23 and supports an optically
clear plastic or glass cover 27 above optical device 23. Cover 19
transmits light to a light sensitive cell 24 on optical device
23.
[0008] Package 20 of FIG. 2 has two significant drawbacks. First,
it is difficult to make. Second, it is expensive. Accordingly,
there is a need for an inexpensive, easy-to-make package for
optical integrated circuit devices.
SUMMARY OF THE INVENTION
[0009] The present invention includes improved packages for optical
integrated circuit devices, and methods of making such packages. In
one embodiment, a package within the present invention includes an
optical integrated circuit device on a die pad. Metal bonding pads
on the optical device are connected by bond wires to leads. The
lower half of the package, which supports the die pad and leads, is
molded insulative adhesive encapsulant material. The lower and side
surfaces of the die pad and leads are covered with encapsulant
material, so that the die pad and leads are in an embedded
connection with the molded package base. The upper surfaces of the
die pad and leads are not covered by the encapsulant material. The
side surfaces of the die pad and leads have reentrant portions and
asperities that lock the die pad and leads to the molded base. An
initially viscous and subsequently hardened insulative adhesive
bead surrounds the optical integrated circuit device. The bead
extends above the upper surface of the optical device and the bond
wires. An optically clear cover, which may be formed of
borosilicate glass or optically clear plastic, is adhesively
connected to and supported above the device by the bead. For
example, the bead is in a press-fitted interconnection with the
bead. The cover transmits light to a light-sensitive cell on the
upper surface of the optical device. The optically clear cover
includes locking features which enhance the connection of the cover
to the adhesive bead and thus to the package.
[0010] A method within the present invention for making such a
package includes a first step of providing a leadframe including a
die pad and radiating leads. The leadframe is conventional, except
that the normally orthogonal side surfaces of the die pad and leads
have been modified to include reentrant portion and asperities that
lock the leadframe to the plastic encapsulating material.
[0011] Step 2 places the leadframe in a conventional two-pocket
mold. The upper pocket of the mold is blanked out by a bar so that
encapsulant material does not enter the pocket. Insulative
encapsulant material is provided to the lower pocket of the mold.
Upon hardening, the encapsulant material forms the lower half of
the package. The lower and side surfaces of the die pad and leads
of the leadframe are covered by molded encapsulant material. The
upper surfaces of the die pad and leads are exposed. The reentrant
portions and asperities of the side surfaces of the die pad and
leads engage the encapsulate material, and prevent the die pad and
leads from being pulled from the molded package base.
[0012] Step 3 places and attaches an optical integrated circuit
device on the exposed upper surface of the die pad. Step 4
electrically connects individual metal bonding pads on the optical
device to individual leads of the leadframe. Step 5 applies a bead
of a viscous adhesive material, such as epoxy, around the optical
integrated circuit device. The bead covers and adheres to a portion
of the exposed upper surface of each of the radiating leads. The
location of the bead may vary. For example, the bead may be a
distance from the optical integrated circuit device, or
alternatively may contact the upper surface of the die pad and the
side surfaces of the optical device. In another alternative
embodiments, the bead covers the die pad, the side surfaces of the
optical device, and a peripheral portion of the upper surface of
the optical device.
[0013] Step 6 provides an optically clear planar cover. The side
surfaces of the cover include locking features, such as an
indentation or protrusion, that enhance the connection of the cover
to the bead. Alternately, the surface of the optically clear cover
that faces the bead includes locking features, such as a groove,
located where the bead meets the cover to enhance the connection
between the cover and the bead.
[0014] Step 7 squarely places the cover on the still-viscous bead
so that the cover is centered over the integrated circuit device,
and presses the cover into the bead. The bead material supports the
cover above the bond wires and optical device. Step 8 hardens the
bead. Step 9 is a debar and dejunk step, wherein the dam bar and
flash are removed. Step 10 trims and forms the leads. This step
removes the tie bar. The leads may be plated before Step 9, or
pre-plated leads may be used. The leads may be formed into a
variety of conventional styles, such as gull wing, through hole, or
PLCC styles.
[0015] The packages and methods of the present invention have
significant cost advantages over the prior art. These and other
advantages will become clear through the following detailed
discussion.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 is a cross-sectional side view of a conventional
molded p-dip package.
[0017] FIG. 2 is a cross-sectional side view of a conventional
molded p-dip package for an optical integrated circuit device.
[0018] FIG. 3 is a cross-sectional side view of a package for an
optical integrated circuit device.
[0019] FIG. 4 is a flow chart of a method of making a package for
an optical integrated circuit device.
[0020] FIG. 5 is a plan view of a leadframe.
[0021] FIG. 6 is a cross-sectional view of a die pad and lead of
the leadframe of FIG. 5 showing encapsulant locking features.
[0022] FIG. 7 is a cross-sectional view of a second embodiment of
the die pad and leads of the leadframe of FIG. 5.
[0023] FIG. 8 is a cross-sectional view of third embodiment of the
die pad and leads of the leadframe of FIG. 5.
[0024] FIG. 9 is a cross-sectional view of fourth embodiment of the
die pad and leads of the leadframe of FIG. 5.
[0025] FIG. 10 is a cross-sectional side view of an incomplete
package after encapsulant material is molded beneath and on the
side surfaces of the leadframe.
[0026] FIG. 11 is a cross-sectional side view of an incomplete
package after an adhesive bead is applied around the optical
integrated circuit device.
[0027] FIG. 12 is a cross-sectional side view of an alternative
package where the adhesive bead covers exposed portions of the die
pad and the side surfaces of the optical integrated circuit
device.
[0028] FIG. 12A is a cross-sectional side view of an alternative
package where the adhesive bead covers exposed portions of the die
pad, and the side surfaces and a peripheral portion of the upper
surface of the optical integrated circuit device.
[0029] FIG. 13 is a cross-sectional side view of a first
alternative optically clear cover for the package of FIG. 3 wherein
the side surfaces of the cover include an arced surface.
[0030] FIG. 14 is a cross-sectional side view of a second
alternative optically clear cover for the package of FIG. 3 wherein
the side surfaces of the cover have a diagonal orientation relative
to a planar first surface of the aperture cover.
[0031] FIG. 15 is a cross-sectional side view of a third
alternative optically clear cover for the package of FIG. 3 wherein
the side surfaces of the cover have a diagonal portion and an
orthogonal portion.
[0032] FIG. 16 is a cross-sectional side view of a fourth
alternative optically clear cover for the package of FIG. 3 wherein
the side surfaces of the cover include a rectangular lip and a
recessed orthogonal portion.
[0033] FIG. 17 is a cross-sectional side view of a fifth
alternative optically clear cover for the package of FIG. 3 wherein
the side surfaces of the cover include an arc-shaped
indentation.
[0034] FIG. 18 is a cross-sectional side view of an alternative
package where the optically clear cover is on the adhesive
bead.
[0035] FIG. 19 shows an alternative optically clear cover for the
package of FIG. 18 where a groove is cut into the cover where the
cover meets the adhesive bead.
[0036] FIG. 20 is a cross-sectional view of a fifth embodiment of
the die pad and leads of the leadframe of FIG. 5.
[0037] FIG. 21 is a cross-sectional view of an alternative package
having a molded cap above and around the optical device.
[0038] FIG. 22 is an alternative cap for the package of FIG. 21,
wherein the cap has an anti-scratch feature.
DETAILED DISCUSSION
[0039] FIG. 3 shows a package 30 in accordance with the present
invention. Package 3 includes a molded package base 31. Base 31 is
formed of a commercially available insulative molding compound,
such as SUMITOMO 6300H, a high stress compound from the Sumitomo
Company of Japan. Alternative compounds include NITTO MP-8000AN
plastic molding compound from the Nitto Company of Japan, or EME
7351 UT plastic molding compound from the Sumitomo Company.
[0040] Molded base 31 of FIG. 3 includes a substantially planar
upper first surface 32 (see FIG. 10 also), an opposite
substantially planar lower second surface 33, and tapered
peripheral side surfaces 34 between first surface 32 and second
surface 33.
[0041] Embedded in base 31 of FIG. 3 at first surface 32 is a
rectangular metal die pad 35. Die pad 35 has a planar or
substantially planar upper first surface 36, an opposite planar or
substantially planar lower second surface 37, and a side surfaces
38 between first surface 36 and second surface 37. The perimeter
shape of die pad 35 may vary. Second surface 37 and side surfaces
38 of die pad 35 are covered by the plastic molding material that
forms base 31. First surface 36 of die pad 25 is exposed, i.e., not
covered by the plastic molding material.
[0042] A plurality of metal leads 39 also are embedded in base 31
at first surface 32 of base 31. A first portion 40 (FIG. 10) of
each lead 39 is internal to package 30 and is in the same
horizontal plane as die pad 35. A second portion 41 (FIG. 10) of
each lead 39 extends beyond sides 38 of base 31 and ultimately is
bent into a through-hole configuration (FIG. 3). In alternative
embodiments, leads 39 may be formed into any conventional package
style, including PLCC and gull wing styles.
[0043] Each lead 39 of FIGS. 3 and 10 includes a planar or
substantially planar upper first surface 42, an opposite planar or
substantially planar second surface 43, and side surfaces 44
between first surface 42 and second surface 43. Second surfaces 43
and side surfaces 44 of first portions 40 of leads 39 are covered
by the plastic molding compound that forms base 31. First surfaces
42 of first portion 40 of leads 39 are exposed, i.e., not covered
by plastic molding compound.
[0044] Optical integrated circuit device 23 is centrally placed on
and attached to first surface 36 of die pad 35. Exemplary optical
integrated circuit devices are EPROMs, CCDs, and camera devices.
Optical device 23 has an upper first surface 45, an opposite lower
second surface 46, and orthogonal side surfaces 47 between first
surface 45 and second surface 46. Second surface 45 of optical
device 23 is on first surface 36 of die pad 35. Light sensitive
cell 24 is on first surface 45 of optical device 23. Each of a
plurality of metal bonding pads 14 at the perimeter of upper first
surface 45 of device 23 is connected by a gold bond wire 13 to a
first surface 42 of a first portion 40 of a lead 39.
[0045] Adjacent to and surrounding optical device 23 of FIG. 3 and
FIG. 11 is an adhesive bead 48. Bead 48 is completely around device
23 and is spaced apart from and does not contact optical device 23.
Adhesive beads for integrated circuit packages also are described
in U.S. patent application Ser. Nos. 08/844,536 (filed Apr. 18,
1997) and 09/050,666 filed (Mar. 30, 1998), which are incorporated
herein by reference in their entirety. An example material for bead
48 is HYSOL 4451 epoxy, which is available from the Dexter/Hysol
Corp. of City of Industry, Calif.
[0046] Adhesive bead 48 of FIG. 3 is applied in a viscous state
onto upper first surface 32 of base 31 around optical device 23. In
particular, bead 48 covers the exposed upper first surfaces 42 of
first portions 40 of leads 39. Bead 48 extends to a height above
first surface 32 of base 31 that is greater than the heights of
device 23 and bond wires 13.
[0047] An optically clear cover 49 forms the top of package 30 of
FIG. 3. Cover 49 has a planar first surface 50, an opposite planar
second surface 51, and orthogonal peripheral side surfaces 52
between first surface 50 and second surface 51. Cover 49 has a
rectangular perimeter in this embodiment, but the perimeter shape
and area of cover 49 may vary to match the perimeter shape of bead
48, which also may vary.
[0048] Second surface 51 of cover 49 is squarely and centrally
placed onto viscous bead 48, and then pressed into bead 48 so that
cover 49 is in a press-fitted interconnection with bead 48. The
material of bead 48 covers a peripheral portion of lower second
surface 51 of cover 49, side surfaces 52 of cover 49 around the
entire perimeter of cover 49, and a peripheral portion of upper
first surface 50 of cover 49. Bead 48 is then hardened.
[0049] Referring to FIG. 3, bead 48 supports cover 49 above upper
first surface 45 of device 23, bond wires 13, and upper first
surface 32 of base 31. For example, bead 48 may support cover 49 a
distance in the range of about 0.3 to 0.5 mm above upper first
surface 32 of base 31. Obviously, the dimensions of the elements of
package 3 of FIG. 3 vary depending on the application. For example,
larger optical devices 23 require larger packages.
[0050] Optical device 23 of FIG. 3 is located within a closed
cavity 53 that is created by and bounded by upper first surface 32
of base 31, bead 48 around optical device 23, and lower second
surface 51 of cover 49.
[0051] FIG. 4 is a flow chart showing one embodiment of a method
within the present invention for making a package like the example
shown in FIG. 3. Step 1 of FIG. 4 provides a thin metal leadframe
having encapsulant locking features on the side surfaces of the die
pad and leads of the leadframe.
[0052] FIG. 5 is a plan view of a leadframe 56 within the present
invention for making package 30 of FIG. 3. Snading is used in FIG.
5 to identify the metal of leadframe 56. The actual pattern of a
leadframe for making a package 30 within the present invention
varies with the application, so the pattern of leadframe 56 is
exemplary only. Alternatively, leadframes for multiple packages may
be formed from a single sheet of metal, and the multiple packages
can be formed in parallel.
[0053] Leadframe 56 is made of a conventional leadframe metal, such
as copper or copper alloys, plated copper or plated copper alloys,
Alloy 42 (42% nickel, 58% iron), or copper plated steel, depending
on the application. The surfaces of leads 39 to which bond wires
are attached may be plated with silver, gold, nickel palladium, or
copper, depending on the application.
[0054] Leadframe 56 of FIG. 5 includes a central die pad 35 and
radiating leads 39. A dam bar 57 and a tie bar 58 interconnect
leads 39. Staggered anchor ears 59 extend perpendicularly from the
lateral side surfaces 44 of first portion 40 of leads 39. In a
completed package, anchor ears 59 prevent leads 39 from being
pulled horizontally from package base 31. Alternatively, holes may
be formed in leads 39 instead of having anchor ears.
[0055] Leadframe 56 of FIG. 5 is identical to conventional
leadframes, except for side surfaces 38 of die pad 35 and side
surfaces 44 of leads 39. Whereas the side surfaces of the die pad
and leads of a conventional leadframe are orthogonal, side surfaces
28 and 32 of FIGS. 5-9 have locking features to ensure a secure
connection between die pad 35 and leads 39 and the plastic molding
compound that forms package base 31 of FIG. 3. As discussed above,
side surfaces 38 and 44 are covered by the plastic molding compound
which forms base 31 of FIG. 3.
[0056] FIGS. 6-9 and 20 provide alternative cross-sectional side
views of a die pad 35 and an exemplary lead 39 of leadframe 56 of
FIG. 5 and package 30 of FIG. 3. As shown, the die pad and leads of
FIGS. 6-9 and 20 have locking features that prevent the die pad and
leads from being pulled vertically from molded base 31 of FIG.
3.
[0057] In FIG. 6, side surfaces 38 of die pad 35 and side surfaces
44 of lead 39 have reentrant portions. In particular, the upper and
lower portions of side surfaces 38 and 44 are reentrant such that
there is a protruding central peak 60 between the reentrant
portions. Molding compound flows into the reentrant portions of
side surfaces 38 and 44. Accordingly, the reentrant portions of
side surfaces 38 of die pad 35 and side surfaces 44 of leads 39 of
FIG. 6 enhance the connection between the molding compound of base
31 of FIG. 3 and die pad 35 and leads 39.
[0058] In addition to having reentrant portions, side surfaces 38
of die pad 35 and side surfaces 44 of lead 39 of FIG. 6 have a
roughly-textured surface that includes numerous asperities. Molding
compound flows into the areas of the asperities. The asperities
also enhance the connection between the molding compound that forms
package base 31 of package 30 of FIG. 3 and die pad 35 and the
leads 39 of package 30.
[0059] FIG. 7 shows an alternative profile for side surfaces 38 of
die pad 35 and side surfaces 44 of leads 39 of leadframe 56 of FIG.
5 and package 30 of FIG. 3. In FIG. 7, side surfaces 38 and 44 each
have a reentrant central depression 61 and a roughly-textured
surface that includes numerous asperities. Molding compound flows
into central depression 61 and into the areas of the asperities.
The reentrant portion and asperities of side surfaces 38 and 44 of
FIG. 7 enhance the connection between the molding compound of
package base 31 of FIG. 3 and die pad 35 and the leads 39.
[0060] FIG. 8 shows an alternative profile for side surfaces 38 of
die pad 35 and side surfaces 44 of leads 39 of leadframe 56 of FIG.
5 and package 30 of FIG. 3. In the embodiment of FIG. 8, side
surfaces 38 and 44 include a protruding, rounded lip 62 adjacent to
lower second surfaces 37 and 43 of die pad 35 and lead 39,
respectively. Lip 62 has a roughly-textured surface which includes
numerous asperities. Side surfaces 38 and 44 also have a reentrant
orthogonal portion 63 between lip 62 and upper first surfaces 36
and 42 of die pad 35 and leads 39, respectively. Molding compound
flows around lip 62 and contacts orthogonal portion 63. Molding
compound material also flows into the asperities. Like the
embodiments of FIGS. 6 and 7, the reentrant portions and asperities
of side surfaces 38 of die pad 35 and side surfaces 44 of lead 39
of FIG. 8 enhance the connection between the molding compound of
molded base 31 of package 30 of FIG. 3 and die pad 35 and the leads
39 of package 30.
[0061] FIG. 9 shows an alternative profile for side surfaces 38 of
die pad 35 and side surfaces 44 of leads 39 of leadframe 56 of FIG.
5 and package 30 of FIG. 3. In this embodiment, side surfaces 38
and 44 each include a protruding rectangular lip 64 adjacent to
lower second surfaces 37 and 43 of die pad 35 and lead 39,
respectively. Side surfaces 38 and 44 also have a reentrant
orthogonal portion 65 between lip 64 and upper first surfaces 36
and 42 of die pad 35 and lead 39, respectively. Molding compound
flows around lip 64 and contacts orthogonal portion 65. Like the
embodiment of FIG. 8, the reentrant portions of side surfaces 38 of
die pad 35 and side surfaces 44 of lead 39 of FIG. 9 enhance the
connection between the molding compound of molded base 31 of FIG. 3
and die pad 35 and the leads 39 of package 30.
[0062] Leadframe 56 of FIG. 5 is formed from rolled strip metal
stock by wet chemical etching or mechanical stamping using
progressive devices. As is well known, chemical etching (also known
as chemical milling) is a process that uses photolithography and
metal-dissolving chemicals to etch a pattern into a metal strip.
The photoresist is exposed to ultraviolet light through a photo
mask having a desired pattern, and is subsequently developed and
cured. Metal dissolving chemicals are sprayed on or otherwise
applied to the masked strip, and exposed portions of the strip are
etched away, leaving the desired pattern. As is also well known,
progressive stamping uses sets of progressive devices to
mechanically remove metal from a metal strip. Each of a plurality
of stamping stations uses one of the devices to punch a distinct
small area of metal from the strip as the strip moves through the
stations. The combined work of the devices produces the desired
pattern of the leadframe.
[0063] A leadframe 56 (FIG. 5) having side surfaces 38 and 44 of
FIG. 6 can be formed by chemically etching the rolled strip metal
stock from both sides using a conventional liquid etchant. The etch
process is stopped early so that there is an underetching of all of
the side surfaces of the components of leadframe 56, including side
surfaces 38 of die pad 35 and side surfaces 44 of leads 39,
compared to the time it would take to form orthogonal side
surfaces. The size and shape of central peak 60 of FIG. 6 is
controlled by the amount of underetching. The wet etching also
creates the asperities.
[0064] A leadframe 56 (FIG. 5) having side surfaces 38 and 44 of
FIG. 7 can be formed by chemically etching the rolled strip metal
stock from one side using a conventional liquid etchant. The etch
process is continued beyond the time required to form orthogonal
side surfaces for the components of leadframe 56, i.e., there is an
overetching. The size and shape of central depression 61 of FIG. 7
is controlled by the amount of overetching. The etching also
creates the asperities.
[0065] A leadframe 56 (FIG. 5) having side surfaces 38 and 44 of
FIG. 8 can be formed in a two step process. The first step of such
a process involves forming a leadframe 56 by chemical etching or
progressive stamping so that the side surfaces of the components of
leadframe 56, including side surface 38 of die pad 35 and side
surface 44 of leads 39, have an orthogonal profile. The second step
involves coining the lower surface of the leadframe 56, i.e.,
applying a high pressure impact to the lower surface of the
leadframe 56. This coining step deforms the side surfaces of
leadframe 40 adjacent to the impacted surface so that the rounded,
asperity-marked protruding lips 62 of FIG. 8 are formed.
[0066] A leadframe 56 (FIG. 5) having side surfaces 38 and 44 of
FIG. 9 can be formed by progressive stamping. The side surfaces of
the components of leadframe 56, including side surfaces 38 of die
pad 35 and the side surfaces 44 of leads 39, can be provided with a
rectangular lip 64 and a reentrant orthogonal portion 65 by
including intermediate stamping steps which do not fully cut
through the rolled strip metal stock before finally cutting through
the rolled strip sheet. The intermediate stamping steps and the
final cutting steps combine to form the rectangular, protruding
lips 64 of side surfaces 38 and 44 of FIG. 9.
[0067] Step 2 of FIG. 4 places leadframe 56 in a mold having two
pockets for making conventional p-dip packages. In accordance with
the present invention, the upper pocket of the mold above leadframe
56 is blanked out by a pocket bar so that encapsulant material does
not enter the upper pocket and does not cover the upper surface of
leadframe 56. During the molding process, molding compound only
enters the lower pocket of the mold. A commercially available, high
stress molding compound by Sumitomo Company of Japan, SUMITOMO
6300H, is usable. Other standard encapsulant materials, such as
NITTO MP-8000AN molding compound from the Nitto Company of Japan,
and EME 7351 UT molding compound from the Sumitomo Company of Japan
also can be used.
[0068] FIG. 10 is a cross-sectional side view of an incomplete
package after Step 2 of FIG. 4. Step 2 forms package base 31, as
shown in FIGS. 3 and 10. Molding compound is molded beneath and on
the lower and side surfaces of the central portion of leadframe
56.
[0069] Referring to FIGS. 3, 6-9 and 20, Step 2 of FIG. 4 is
performed so that the molding compound covers lower second surface
37 and side surface 38 of die pad 35 and lower second surfaces 43
and side surfaces 44 of leads 39. Accordingly, the reentrant
portions and asperities (if any) shown in FIGS. 6-9 and 20 engage
the molding compound and lock die pad 35 and leads 39 to base 31
(FIGS. 3 and 10).
[0070] Step 2 concludes with a deflash step, wherein any excess
molding compound that inadvertently covers first surface 42 of
leads 39 or first surface 36 of die pad 35 is removed from first
surface 42 of leads 39 and first surface 36 of die pad 35. This may
be performed, for example, by directing a high pressure water
stream including polypropylene beads at the first surface 42 of
leads 39 and first surface 36 of die pad 35.
[0071] Referring to FIGS. 3, 5, and 10, Step 3 of FIG. 4 places
lower second surface 43 of optical integrated circuit device 23 on
the exposed upper first surface 36 of die pad 35 of leadframe 56,
and attaches second surface 43 of device 23 to first surface 36 of
die pad 35. Step 3 is performed with a conventional device attach
machine and adhesive.
[0072] Referring to FIG. 3, Step 4 of FIG. 4 electrically connects
each bonding pad 14 on optical device 23 to an upper first surface
42 of a first portion 40 of a lead 39. In the embodiment of FIG. 3,
conventional gold bond wires 13 are connected between pads 14 and
leads 39. Conventional bond wire attachment methods are used.
[0073] Referring to FIG. 10, Step 5 of FIG. 4 applies a bead of a
viscous adhesive material, such as epoxy, on the upper surfaces of
base 31 and leadframe 56 around optical device 23. FIG. 11 shows an
adhesive bead 48 on first surface 32 of base 31 and a portion of
first surfaces 42 of first portions 40 of leads 39 of leadframe
56.
[0074] Although not completely shown by FIG. 11, bead 48 surrounds
optical device 23. Bead 48 also covers and adheres to first surface
32 of base 31 and to a portion of the upper first surface 42 of a
first portion 40 of each lead 39. First surface 42 and bead 48 form
a cavity 53 around and above optical device 23. Cavity 53
ultimately is closed by the placement of cover 49 onto bead 48.
[0075] Example dimensions for bead 48 are about 0.5 mm to 0.8 mm in
width at base 31, and about 0.8 mm to 1.0 mm in height above base
31. Bead 48 must be sized so that, even in a viscous state, bead 48
will, at least temporarily, support cover 49 above bond wires 13,
optical device 23, and base 31. Upon hardening, bead 48 permanently
supports cover 49 above bond wires 13, optical device 23, and base
31 (FIG. 3).
[0076] FIG. 12 shows an alternative embodiment of a package within
the present invention. Package 66 of FIG. 12 is the same as package
30 of FIG. 3, and is made the same way, except with respect to the
location of the adhesive bead around optical device 23. Like bead
48 of FIG. 3, bead 67 of FIG. 12 covers portions of first surface
32 of base 31 and first surface 42 of radiating leads 39. In
addition, bead 67 covers an exposed peripheral portion of first
surface 36 of die pad 35 around device 23, a portion of side
surfaces 47 of optical device 23, and a lower portion of bond wires
13, including the connection between bond wires 13 and leads 39. In
FIG. 12, bead 67 does not contact first surface 45 of optical
device 23. To prevent corrosion, a dot 68 of the bead material or
some other adhesive material or epoxy covers the connection between
each bond wire 13 and bonding pad 14.
[0077] FIG. 12A shows another alternative embodiment of a package
within the present invention. Package 69 of FIG. 12A is identical
to package 30 of FIG. 3 and package 66 of FIG. 12, and is made the
same way, except as to the location of bead 70 around optical
device 23. Bead 70 of FIG. 12A covers portions of first surface 32
of base 31 and first surface 42 of leads 39, an exposed peripheral
portion of first surface 36 of die pad 35 around optical device 23,
the entirety of side surfaces 47 of optical device 23, bond wires
13, and a peripheral portion of upper first surface 45 of optical
device 23, including the connection between bonding pads 14 and
bond wires 13. Care is taken, however, that bead 70 does not
contact optical cell 24 of device 23.
[0078] Step 6 of FIG. 4 provides a thin optically clear cover
through which light may be transmitted. The size and perimeter
shape of the cover should be calculated to match the location and
perimeter shape of the adhesive bead around the optical device
(FIG. 11A). As shown in FIG. 3, cover 49 is sized so that the area
of cover 49 is equal to the area bounded by the mid-point of the
width of bead 48. Accordingly, cover 49 may be press-fitted into
bead 48 so that side surfaces 52 of cover 49 are covered by bead 48
(FIG. 3).
[0079] Example materials for cover 48 of FIG. 3 include glass, such
as borosilicate glass. An example thickness of a borosilicate glass
cover 48 is about 0.5 mm, but the thickness may vary with the
application. Alternatively, cover 48 can be made of any optically
clear material, such as polycarbonate, clear plastic or quartz.
[0080] Referring to FIG. 3, Step 7 of FIG. 4 places optically clear
cover 49 onto the still-viscous bead 48, so that a peripheral
portion of and all around second surface 51 of cover 49 contacts
the top of bead 48 all around cover 49 and optical device 23. Next,
cover 49 is pressed by gravity or the application of force into
bead 48, so that the entire height of side surfaces 52 and a
peripheral portion of and all around first surface 50 of cover 49
is covered by bead 48. In FIG. 3, cover 49 is in a press-fitted
interconnection with bead 48. Step 7 closes cavity 53.
[0081] Step 7 may be performed by hand, by a conventional pick and
place machine, or with the modified pick and place machine
described in U.S. patent application Ser. No. 08/844,536, which was
filed on Apr. 18, 1997 and is incorporated herein by reference.
[0082] In an alternative embodiment (not shown), cover 49 is
pressed a lesser distance into bead 48. In such an embodiment, all
or just the lower part of the height of side surfaces 52 is
press-fitted into bead 48, and bead 48 does not contact first
surface 50 of cover 49.
[0083] Step 8 of FIG. 4 hardens bead 48. Where bead 48 is an epoxy,
Step 8 is performed by heating package 30 and bead 48 at about 150
degrees Celsius for approximately one hour. Upon hardening, bead 48
supports cover 49 above optical device 23 and attaches cover 49 to
base 31 of package 30 of FIG. 3.
[0084] Step 9 is a debar and dejunk step. In Step 9, excess molding
compound that squirts out between the mold halves is removed. The
dam bar also is removed. Conventional methods using conventional
automated equipment are used.
[0085] Step 10 of FIG. 4 trims and forms leads 39 of package 30 of
FIG. 3 in a conventional manner. In this step, tie bar 58 is
removed and the leads are bent and cut into a selected
configuration. The leads may be plated before Step 10, if the leads
are not already plated. The leads may be formed into a variety of
conventional styles, such as gull wing, through hole, or PLCC
styles.
[0086] As shown in FIG. 3, side surfaces 52 of cover 49 are
orthogonal. Alternatively, the side surfaces of the optically clear
cover may include locking features that enhance the connection
between the optically clear package cover and adhesive bead 48
around optical device 23.
[0087] FIGS. 13-17 show alternative optically clear package covers
71, 75, 77, 81 and 85, respectively, for package 30 of FIG. 3. The
side surfaces of each cover in FIGS. 13-17 include a reentrant
portion(s) as a locking feature for enhancing the connection
between the optically clear cover and bead 48 and package 30 of
FIG. 3. To simplify the drawings, only the alternative covers and
bead 48 of package 30 are shown in FIGS. 13-17. The remainder of
package 30 of FIG. 3 is omitted.
[0088] FIG. 13 is a cross-sectional side view of a first
alternative optically clear cover 71 for package 30 of FIG. 3.
Cover 71 includes a side surface 72 between upper first surface 50
and lower second surface 51. Beginning at second surface 51, side
surface 72 of cover 71 includes a protruding arced portion 73.
Between arced portion 73 and first surface 50 is an orthogonal
portion 74. Bead 48 covers protruding portion 73 and applies
downward force on protruding portion 73, which locks cover 71 to
bead 48 and package 30. Bead 48 also contacts orthogonal portion
74. Side surface 72 may be formed by cutting cover 71 from a sheet
of glass or other optically clear material using a rounded saw
blade
[0089] FIG. 14 is a cross-sectional side view of a second
alternative optically clear cover 75 for package 30 of FIG. 3.
Cover 75 includes a side surface 76 between upper first surface 50
and lower second surface 51. Side surface 76 is flat and has a
diagonal orientation relative to first surface 50 and second
surface 51A. Side surface 76 slopes laterally inward from second
surface 51 toward first surface 50 of cover 75. Bead 48 covers all
or part of side surface 76 and applies downward force on side
surface 76, which locks cover 75 to bead 48 and package 30. Side
surface 76 may be formed by cutting cover 75 from a sheet of glass
or other optically clear material using a wedge-shaped saw
blade.
[0090] FIG. 15 is a cross-sectional side view of a third
alternative optically clear cover 77 for package 30 of FIG. 3.
Beginning adjacent to second surface 51, side surface 78 of cover
77 includes a protruding diagonal portion 79 that slopes laterally
inward from second surface 51 towards first surface 50. Beginning
at about a midpoint of side surface 78, between diagonal portion 79
and first surface 50, is an orthogonal portion 80. Bead 48 covers
diagonal portion 79 of side surface 78 and applies downward force
on side surface 78, which locks cover 77 to bead 48 and package 30.
Side surface 78 may be formed by cutting cover 77 from a sheet of
glass or other optically clear material using a saw blade having a
wedge-shaped tip and an orthogonal portion above the tip.
[0091] FIG. 16 is a cross-sectional side view of a fourth
alternative optically clear cover 81 for package 30 of FIG. 3.
Beginning adjacent to second surface 51, side surface 82 of cover
81 includes a protruding rectangular lip 83. Between lip 83 and
first surface 50 is an orthogonal portion 84. Bead 48 covers lip
83, contacts orthogonal portion 84, and applies downward force on
side surface 82, which locks cover 81 to bead 48 and package 30.
Side surface 82 may be formed using a step-cut saw blade.
[0092] FIG. 17 is a cross-sectional side view of a fifth
alternative optically clear cover 85 for package 30 of FIG. 3.
Cover 85 has a side surface 86. On side surface 86, near second
surface 51 of cover 85, is an 180 degree arc-shaped indentation 87.
The remainder of side surface 86 is orthogonal. Bead 48 flows into
indentation 87 and applies downward force on cover 85, which locks
cover 85 to bead 48 and package 30. Indentation 87 may be formed
with a rounded saw blade. Alternatively, such an indentation may
have other shapes, such as square or triangular.
[0093] Other shapes for the optically clear covers of the packages
of the present invention may be adapted from those disclosed in
U.S. patent application Ser. No. 09/118,197, which was filed on
Jul. 17, 1998 and is incorporated in full in the present
application by reference.
[0094] FIG. 18 shows an alternative package 88 within the present
invention. Package 88 is identical to package 30 of FIG. 3, and is
made the same way, except that the area of optically clear cover 89
is equal to or greater than the area within the outer perimeter of
adhesive bead 48. Accordingly, bead 48 contacts and adheres only to
lower second surface 51 of cover 89, and does not contact side
surfaces 52 or upper first surface 50 of cover 89. In such an
embodiment, second surface 51 of cover 89 is on and adhesively
connected to bead 48 around optical device 23, but is not pressed
into bead 48.
[0095] Optionally, an encapsulant locking feature, such as a groove
or equivalent, may be formed on or cut into second surface 51 where
cover 89 contacts bead 48. FIG. 19 shows an example groove 90 in a
cover 89. Groove 90 increases the surface area of cover 89 in
contact with bead 48, and thereby strengthens the connection
between cover 89 and bead 48 and package 30. Alternatively, groove
90 or an equivalent locking feature on second surface 51 may be
combined with one of the side surface locking features of FIGS.
13-17.
[0096] Similar to FIGS. 6-9, FIG. 20 shows a fifth alternative
profile of reentrant side surfaces 38 of die pad 35 and reentrant
side surfaces 44 of leadframe 56 of FIG. 5 and package 30 of FIG.
3. In this embodiment, side surfaces 38 and 44 each include an
approximately rectangular projection 91 as an encapsulant locking
feature. Projection 91 is between first surfaces 42 and 36 and
second surfaces 43 and 37 of die pad 35 and leads 39. Side surfaces
38 and 44 and projection 91 have asperities. Side surfaces 38 and
44, including projection 91, are formed by chemical etching from
both sides of die pad 35 and leads 39 using a mask.
[0097] FIG. 21 is a cross-sectional view of an alternative package
92 within the present invention for optical integrated circuit
device 23. Package 92 of FIG. 21 is similar to, but differs from
package 30 of FIG. 3 in that, instead of a planar cover 49 and bead
48, a shaped, molded cap 93 encloses optical device 23 above first
surface 32 of base 31. Cap 93 is a thin, hollow, approximately
cubic structure open at one side that forms a cavity 53 above and
around optical device 23. Cap 93 includes four thin, slightly
sloped, and approximately rectangular-in-area sidewalls 94 that are
joined to a thin, planar, approximately rectangular-in-area upper
side 95. (In the cross-sectional view of FIG. 21, only two
sidewalls 94 are shown). Cap 93 has an opening opposite to side 95
and adjacent to the foot-like extensions 96 of sidewalls 94. A
lower surface 97 of extensions 96 of sidewalls 94 of cap 93 is
adhesively joined by epoxy (not shown) to upper first surface 32 of
molded base 31 and upper first surface 42 of internal portion 40 of
leads 39, forming a tight seal around the perimeter of first
surface 32. Epoxy is applied onto first surface 32 of base 31
completely around optical device 23. Cap 93 is then placed onto
epoxy 99. Care is taken to ensure cap 93 is squarely placed on
upper first surface 32 so that planar upper side 95 of cap 93 is
parallel to upper first surface 45 and cell 24 of optical device
23. Cap 93 is injection molded, for example, and is formed of an
optically clear material, such as optically clear plastic or
polycarbonate. This package embodiment is used, for example, with
through hole lead configurations. Of course, other shapes for cap
93 are possible. The key feature is that cap 93 provides an
enclosure for device 23.
[0098] FIG. 22 shows an alternative, anti-scratch embodiment of a
cap for package 92. Cap 98 includes all of the features of cap 93,
plus a projection 99 that extends above and around the periphery of
upper side 95. Projection 101 prevents scratches on upper side 95
when cap 98 is inverted or something is placed on cap 98.
[0099] An alternative method for Step 5 of FIG. 4 is to apply
adhesive bead 48 of FIGS. 3 and 11 in two steps. A first step
applies the bead on upper surface 32 of base 31 substantially
around optical integrated circuit device 23, leaving a small gap or
dip in bead 48. After Step 8, the small gap or dip is filled with
additional bead material, closing cavity 53. Leaving such a gap or
dip in bead 48 allows gases within cavity 53 to escape while bead
48 hardens, and thus prevents cocking of cover 49. A bead material,
such as Hysol 4323, which sticks to itself, can be used. This
technique is described in U.S. patent application Ser. No.
08/844,536, which is incorporated by reference. Cap 93 of package
92 of FIG. 22 can be adhered to first surface 32 in the same two
step manner.
[0100] The embodiments described herein are merely examples of the
present invention. Artisans will appreciate that variations are
possible within the scope of the claims.
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