Note: Descriptions are shown in the official language in which they were submitted.
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:1~ Back~round of the Inventio~
1$ ¦ ~O Field of the Invention. The invention relates
l9 Ito a.method and apparatus for assembling electronic devices, I
20 ¦and more particularly to a method and apparatus for
2~. 1assembling microminiature electronic apparatus involving
22 intagrated circuits or the like.
23 b. Prior Art. Previously, microminiature electronic
24 ~vices, such as calculators and watches, utilizing semiconductor
ntegrated circuits, were constructed by moun.ting circuit com-
~6 ponents on a printed circuit board, usually made of plas~ic
271 or ceramic material, and having conductive ipterconnections
28¦ ~etween components plated or printed o~ the circuit board.
291 Electronic co.-.,ponents were placed on the circuit board,.
301 aligned for correct positioning and then soldered or o.her-
31¦ wise affixed in place. This form of assembling is labor
321 int~nsive and for this reason much of the assembly work in
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mounting electronic components on circuit boards is done in
foreign countries where labor rates are less than in the United
States.
It is an object of the invention to devise a method
; and apparatus Eor improving the assembling of electronic devices,
especially microminiature devices involving integrated circuits
mounted on circuit boards or holders. Another ob;ect of the
invention is to provide an improved substrated for mounting
` components of microminiature electronic devices and to provide
for stronger, more rugged mounting of electronic components, and
which lends itself to automated assembly of electronic devices.
Yet another object of the invention is to provide for ease of
mounting of elec,ronic components on a circuit board, especially
for ease of placement of components in a very compact arrangement.
Summary of the Invention
In its broadest form, therefore, the present invention
provides in a circuit module having a conductive lead frame `
member partially encapsulated with a molding material, the lead
frame member having on its obverse side a first exposed surface
portion for providing an electrical and mechanical coupling to a
circuit means and on its reverse side a second exposed surface
portion disposed under the first exposed surface portion, wherein
th`e improvement comprises the lead frame member including at the
edge of its reverse side an integrally formed outwardly extend-
ing taper means for locking the lead frame member into the formed
molding material when the molding material hardens.
The present invention also provides the method of
assembling an electronic module comprising: forming a conduc-
tive lead frame member having an obverse and reverse surface
3~ to include an outwardly extending taper means at its reverse
surface; positioning the lead frame member in a mold; applying
pressure to the obverse and reverse surfaces of at least one
selected portion of the lead frame; and partially encapsulating
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the lead frame member with a mass of insulative molding material ~ -
- wherein the taper means at the reverse surface of the lead frame
- member locks into the molding material when the molding material `
hardens.
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The invention will be understood more clearly with
reference to the figures.
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Brief Description of the Drawings
Figure la is a top plan view, obverse side or face, of
substrates used in the method of the present invention, shown
in a web.
Figure lb is a side view of the substrates of Figure
la.
Figure 2a shows the obverse side of the substrates of
Figure la with insulative molding material applied thereto in
accord with the method of the present invention.
Figure 2b i~ a side cutaway view of the apparatus with
the cut taken along lines 2b-2b in Figure 2a.
Figure 3a shows the reverse side of the substrates of
Figure 2a, when the obverse side is turned top to bottom.
Figure 3b shows a side view of the apparatus of Figure
3a.
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Figure 4a shows the obverse side of a molded sub-
strate of Figures 2a and 3a which has been punched and die cut.
Figure 4b shows the reverse side of the substrate of
Figure 4a when the obverse side is turned top to bottom.
Figure 5 shows the reverse side of punched and die
; cut substrate of Figure 4b with components added.
Figure 6a shows the obverse side of the substrate of
Figure 5 with components added.
Figure 6b is a partial cutaway detailed view of the
substrate shown in Figure 6a taken along the line 6b in Figure
6a.
Figure 7 is a side view of an alternate embodiment
of the invention showing a pair of substrates in a single en-
capsulation.
Figure 8 is a detailed side sectional view showing a
preferred manner of anchoring substrates of the present inven-
tion in encapsulation material.
Figure 9a is a detailed plan view of a zig-zag con-
ductive path in the substrate of Figure 11.
Figure 9b is a side view taken along lines 9b-9b in
Figure 9a sh-owing a manner of providing elevational relief in
the zig-zag conductive path shown in Figure 9a.
Figure 10 is a partial side sectional view taken
along lines 10-10 in Figure 6a showing a battery contact
portion of the substrate of the present invention.
Figure 11 is a detailed view of ~he apparatus of
Figure 1.
D~scription of the Preferred Embodimen
While the present assembly method is illustrated by
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means of an example which is particularly apt for assembling
the electronic components of a digital watch, it will be
realized that the method of the present invention is applicable
to a wide class of electronic devices, such as calculators and
other devices and is not limited to electronic watches. In
carrying out the method of the present invention, it is
necessary to provide a substructure for assembling electronic `
circuits, without providing the underlying plastic or ceramic
substructure which has characterized the prior art. More
particularly, the method of the present invention is carried
out by directly utilizing a substructure which comprises a
unitary conductive substrate which is essentially planar and
has first regions for supporting electronic components and second
regions for making electrical connections. Portions of the
first and second regions are::held together by undesired third
regions, which will eventually be removed, but which provide
mechanical support between the first and second regions thereby
maintaining a unitary structure.
The substructure used for carrying out the method of
the present invention is illustrated in Figure la and in more
detail in Figure 11 which show~an elongated web of stamped or
etched substructures which comprise conductive metal substrates ~ !
approximately 0.006 inches in thickness. This thickness is
selected for ease of bending and formation by stamping or
etching, but is not critical. The material of the substrate
may be copper, aluminum or any metal having good conductivity,
or an intermediate conductor plated with a good conductivity
material. Since very thin interconnect members will be formed
within the substrate, the substrate material should be readily
bendable and one that lends itself to the formation of the
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interconnected by die stamping or chemical etching. It has
been found that copper is a preferred material. A chemical
etching process used for integrated circuit lead frame
etching may be employed for formation of the present substrate.
Figure la shows a plurality of substrates 11, 13, 15
in a web 17, having holes within the web l9a, l9b, l9c, l9d,
l9e for advancing the web. A plurality of substrates 11, 13, 15,
etc. may be simultaneously processed in accord with the teach-
ings of the present invention and thus the figures illustrate
a plurality of identical substrates for that purpose.
In the plan view of Figure la the substrate 11 is
indicated to have first desired regions, including 21, 22, 23,
which serve to support electronic components. The support
region is generally slightly larger than the portion of the
electronic components supported.
A group of second desired regions are wire-like
interconnections, including 31, 32, 33 between the first
desired regions. In some cases these interconnections would
correspond to the plating or printing of conductive paths on
printed circuit boards. In other cases the second regions would
correspond to hand-wired interconnections between components.
In still other instances, the second regions provide mechanical
support between various first regions within the substrate.
If mechanical support is provided between desired first regions
and electrical contact is not desired, the desired second
; region will usually be connected to an undesired third region
which will ultimately be removed. The desired second region
is usually continguous to an undesired third region and from
all appearances would appear to be in all respects identical
to a desired second region upon viewing the substrate at the
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outset.
The undesired temporary third regions are regions
which are to be removed from the substrate before breaking
electrical and mechanical contact between desired regions.
Electrical contact is broken because the two connected regions
are not intended to be at the same electrical potential.
Mechanical contact is broken primarily to break electrical
contact. However, the mechanical support which was provided
by the link afforded by the undesired third region is replaced
by another step in the method of the present invention sub-
sequent to the formation of the substrate herein described,
and described in more detail with reference to Figures 2a, 2b,
3a and 3b.
Holes are provided in desired portions of the sub-
strate, usually in selected portions of a first desired region
for ease of mounting of components. For example, the leads of
a resistor may be accomodated in specified holes within the
desired first regions. The electrical component, e.g. a
resistor, is inserted and soldered in place within the
appropriate holes when components are mounted, as described
below.
In Figure la a side view of the substrate is shown.
It is to be noted that the substrate is at the outset planar
in character. This allows the substrate to be manufactured
in continuous lengths and then cut for use or storage and
transportation.
The next step in the process, illustrated by products
of the process, in Figures 2a, 2b, 3a and 3b, consists of
adding a mass of insulative molding material, 27, 27', such as
silicone or epoxy, for encapsulating defined portions of the
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first and second regions to be held in place. The addition
of molding material is usually accomplished by means of a
mold consisting of two halves which come together with the
substrate sandwich in the middle. The molds, not shown,
have an internal cavity or core which is generally disc-
shaped and contains a plurality of pins therein, extending
from internal faces of the core.
There are generally two types of core pins including
a first very thin, blunt pin which applies more pressure to
selected segments of the first and second desired regions
than to non-selected segments thereby providing for differences
in elevation, i.e. elevational relief, between the selected
and non-selected segments. Holes 31', 32', 33' left by these
pins may be seen in Figure 3a. In the processing of substrates
for the present invention, it may be desirable to have certain
desired substrate portions higher or lower for the purpose of
allowing components to be mounted at desired elevations or to
allow interconnections to pass above or below components or
other interconnections. By applying more pressure to selected
segments of said first and second desired regions where
elevational relief is desired, a contemporaneous addition of
molding compound will freeze these elevational changes in
place. When the mold is removed, the pins are withdrawn with
; the mold and the desired segments remain in the position where
they were pushed by the pins and f~ozen in place by the molding
compound.
A second type of pin is a larger blunt pin which
comes into intimate contact with a desired portion which is
shielded from molding compound and kept free of molding
compound. Such a pin is intended to preserve the support
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characteristics of a desired region for the subsequent
mounting of a portion of an electronic component thereon.
For example, in assembling an electronic digital watch, a
support region 22 in Figure 2a would be provided for support-
ing an integrated circuit used for generating a reference
frequency. The position or pad for mounting the integrated
circuit or "watch chip" is one of the first desired regions
and should be kept free of molding compound using the large
blunt pins mentioned above. Accordingly, a pin corresponding
to a dimension slightly larger than the surface area of the
first desired portion for mounting the chip preserves a surface
thereof from contamination with molding compound by contact
with the surface during the injection of molding material into
the mold. The same treatment would be provided for support ~
region 21 which holds the watch display components, component
support portion 23 and battery tabs 24, 25.
In Figure 3a, molding compound is ~ept substantially
out of the component depressions 26' wherein a frequency
trimmer may be located, 29' wherein a crystal may be located,
28' wherein a resistor may be mounted, 30a' wherein a first
battery may be mounted, 3Ob' wherein a second battery may be
mounted, as well as another component region 34'. Each pin,
large or small, protrudes from an inside surface of the mold
in positions corresponding to the depressions shown in Figures
2a, 2b and 3a.
After the mold has been closed, molding material at
an appropriate temperature is injected into the mold until
the mold is filled. The molding material is allowed to harden
and then the mold is separated, in a conventional manner. The
resultant structure will have the appearance of the structure
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shown in Figures 2a and 3a. The substrate 11 can be seen to
include molding compound 27, 27' in Figures 2a, 2b, 3a and
3b, which is providing mechanical support for the desired
first and second regions. In other words, the desired first
regions which formerly relied upon some of the desired second
regions and the undesired third regions for mechanical support,
no longer rely on these regions for mechanical support but are
now held in place by the molding material.
; The side view of Figures 2b and 3b show the added
thickness of the substrate when encapsulated, in comparison to
Figure lb.
- As mentioned previously, the mold which was used for
application of the molding material is removed when the molding
material has hardened. Figure 4a generally shows the next step
in the process of the present invention, wherein undesired
third regions which formerly provided support are now removed.
The undesired third regions include superfluous web material
between the dashed lines 41, 43, which indicate punched cuts
which break metallic interconnections which were previously
provided for strength, but which are not desired from the
electrical standpoint. Another undesired third region is along -
~; the slit 44, on one side of the support region which holds the
"watch chip" of the present apparatus and the slit 45, along
one side of the support portion which holds the "driver chip"
for the watch display which is mounted on support portion 21.
In Figure 4b the lines 44', 45' correspond to the slits 44, 45
of Figure 4a. The superfluous undesired third regions are
those which are removed in the punching operation described
with respect to Figures 4a and 4b. After undesired third
regions are removed, molding flash is chemically etched.
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Figures 5 and 6a illustrate the next step of the
present method, the mounting of components on desired first
regions. In Figure 5 the components include batteries 51,
52, a frequency trimmer 53, a crystal os~illator 54, a first
resistor 55 and a circuit network 56.
In Figure 6a the components include time display
members 61, 62, 63, 64, a first integrated circuit 65 usually
referred to as a "watch chip" and a second integrated circuit
66, previously referred to as a "driver chip". Wire leads
are used to connect the various chips to the display elements
61, 62, 63, 64 and to other circuit elements, in a known
manner.
Contemporaneous to the mounting of components or at
the time the third undesired elements are cut away, a bending
tool may be used to form desired bends, such as for contact
of the electronic device by an external switch. In Figure 6a,
a switch tab 67 is shown which is bent in an upward direction
as indicated by the arrow in Figure 6b. It is seen that the
switch tab 67 is an extension of substrate 11.
It should be noted that~prior to the adding of molding
material, some electronic components may be mounted in a sub-
strate and molding compound poured over them. Generally it is
preferable to add the electronic components after the completion
of the molding operation for ease of repair of the components
in the event they fail. However, in some instances more rugged
construction may be achieved by inserting the components and
adding molding material over them.
In Figure 2b it should be noted that molding material
has been added to both sides of the substrate and not
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necessarily in corresponding regions. Thus, it is seen that
the insulative molding material encapsulates only defined
portions of said first and second desired regions.
While the step of adding molding material has been
described with reference to a single substrate, two or more
substrates could be used utilizing-the pins described herein
to provide for desired elevational relief and prevent short
circuits from occurring. This is illustrated in Figure 7.
In Figure 7, a pair of substrates 71, 72 is mounted
in a generally planar spaced relationship and corresponding
desired regions of each substrate are brought into conductive
contact and then molding compound is applied in the manner
previously set forth. In this manner, the compact geometry
of the substrate may be made even more compact laterally, at
a slight expense of increased thickness. The manner of bring-
ing the two s,ubstrates into contact is by maans of core pins
in the mold which are used to make changes in elevational relief
as previously described and more fully described below with
reference to Figure 9a and 9b.
An improved method of locking each substrate shown
in Figure 7 to the molding compound, as well as locking the
substrates of Figure la to the molding compound shown in
Figures 2a and 3a is indicated in Figure 8. Here it is seen
that the upper edge of the substrate 11 has an outwardly
extending taper 81 resembling a claw. Simllarly substrate 13
has an outwardly extending taper-at its edge, 82, with the
same claw-like shape. Claws 81, 82 serve as spikes into the
molding compound 83, once it hardens, thereby serving to lock
a substrate in place.
Figure 9a shows a zig-zag portion of a desired second
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region which is especially adapted for providing elevational
relief in the vertical plane, such as for making contact
between two parallel opposed substrates, such as illustrated
in Figure 7.
In Figure 9b a core pin 91, projecting from an
internal surface of a mold is shown projecting downwardly on
the central portion 93 of the U-shaped zig-zag member 90 of
Figure 9a. Pin 91 exerts a downward force indicated by the
arrow A in the figure pushing against central portion 93 and
forming bends at portions 92, 94 and again at regions 96, 97
shown in both Figures 9a and 9b. Once a bend is made, it
may be frozen in place by the hardening of molding material
over it. When molding material has hardened the core pin 91
is removed.
Figure 10 illustrates another bent region 101, a
portion of substrate 11 which has been bent upwardly by a tool
much like the switch 67, illustrated in Figure 6b. A battery,
not shown, occupies the cavity defined by wall 102 and pushed
down on the contact 101 for electrical connection therewith.
The bend region 101 has been bent by deforming it beyond its
elastic limit with a core pin and there is no need to hold
the bend in place with molding material.
Figure 11 is a more detailed view of the substrate of
the present invention, corresponding to one of the substrates
11, 13, 15 shown in Figure la. The substrate is a unitary
conductive member which is substantially planar before process-
ing as described above. The substrate illustrated in Figure 11
is adapted to have a perimeter 120 which will fit inside a watch
case. As previously mentioned, the substrate has first desired
regions 21a, 21b, 21c, 21d, 22, 23, . . . having dimensions
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slightly larger than the portion of electronic components to
be supported. For example, the region 22 accomodates a watch
chip module, while the region 23 accomodates a driver chip.
A first desired region need not support an entire component,
but merely a part of one. For example, a first desired region
may support one end of a resistor, while another first desired
region supports the other end.
A number of second desired regions 121, 122, 123, 124
. . . electrically connect some of the first regions. The
structure further includes undesired third regions which are
later removed and become void third regions. These regions
appear as integral parts of the first and second regions shown -~
in Figure 11, but are defined as third regions in as much as
they are the regions which must be cut away to achieve the
proper electrical potentials. For example, the vertical lines
131, 132 indicate third regions formed by punching through the
corresponding desired second regions 121, 123. The zig-zag
region 90, previously described with reference to Figure 9a,
is seen to be connected to the battery contact support 101'.
The exemplary substrate discussed with reference to
a substrate for assembling a watch circuit is approximately .005
inches thick and is made of copper alloy, such as berrylium
copper, although other materials, such as aluminum and steel
have also been previously used with success. The method and
apparatus of the present invention improves the assembly of
electronic devices, especially microminiature devices, because
less space is required for the mounting of components, a more
rugged construction is achieved and increased automation of
the assembly process is possible since indexing holes may be
provided within the substrate for mounting of electronic
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eomponents. Further, by eliminating the plastic and ceramie
circuit boards of the prior art, a more eompaet arrangement
in eleetronie device may be aehieved.
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