U.S. patent application number 10/638181 was filed with the patent office on 2005-02-17 for method of forming a leadframe for a semiconductor package.
This patent application is currently assigned to Semiconductor Components Industries, LLC. Invention is credited to Quah, Guan Keng, Truhitte, Darrell D..
Application Number | 20050037544 10/638181 |
Document ID | / |
Family ID | 34104628 |
Filed Date | 2005-02-17 |
United States Patent
Application |
20050037544 |
Kind Code |
A1 |
Quah, Guan Keng ; et
al. |
February 17, 2005 |
METHOD OF FORMING A LEADFRAME FOR A SEMICONDUCTOR PACKAGE
Abstract
A method of forming a leadframe (10) provides blocking fulcrums
(21,23) adjacent to the leads (12,13,14, and 15). During the
process of encapsulating the leadframe (10), the blocking fulcrums
(21,23) restrict encapsulating material from exiting the mold
cavity and from attaching to the leads (12,13,14, and 15).
Inventors: |
Quah, Guan Keng; (Gilbert,
AZ) ; Truhitte, Darrell D.; (Phoenix, AZ) |
Correspondence
Address: |
James J. Stipanuk
Semiconductor Components Industries, L.L.C.
Patent Administration Dept - MD/A700
P.O. Box 62890
Phoenix
AZ
85082-2890
US
|
Assignee: |
Semiconductor Components
Industries, LLC
|
Family ID: |
34104628 |
Appl. No.: |
10/638181 |
Filed: |
August 11, 2003 |
Current U.S.
Class: |
438/123 ;
257/E21.504; 257/E23.046 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H01L 21/4842 20130101; H01L 23/49548 20130101; H01L 2924/0002
20130101; H01L 2924/00 20130101; H01L 21/565 20130101 |
Class at
Publication: |
438/123 |
International
Class: |
H01B 013/00 |
Claims
1. A method of forming a leadframe for a semiconductor device
comprising: forming a leadframe strip having a main panel and a
plurality of cavity sections; forming a plurality of leads
extending from the main panel a first distance into a cavity
section of the plurality of cavity sections; forming three sides of
each of the plurality of leads detached from the main panel and
forming a proximal end of each of the plurality of leads attached
to the main panel; and forming a blocking fulcrum extending from
the main panel adjacent to a side of a lead of the plurality of
leads and detached from the side of the lead of the plurality of
leads and including terminating the blocking fulcrum no greater
than a second distance from the cavity section.
2. The method of claim 1 wherein forming the blocking fulcrum
extending from the main panel includes forming the blocking fulcrum
to extend less than the first distance into the cavity section.
3. The method of claim 1 wherein forming three sides of each of the
plurality of leads detached from the main panel includes cutting at
least one side of at least one lead of the plurality of leads away
from the blocking fulcrum.
4. The method of claim 3 further including realigning the blocking
fulcrum and the least one lead of the plurality of leads subsequent
to cutting the at least one side of at least one lead of the
plurality of leads away from the blocking fulcrum.
5. The method of claim 1 further including forming a relief feature
extending laterally across a portion of a width of the blocking
fulcrum near the proximal end of the blocking fulcrum.
6. The method of claim 5 further including forming the relief
feature having a shape that is one of a V shape or a U shape.
7. The method of claim 1 further including forming a relief port
through the main panel near the proximal end of the blocking
fulcrum including forming the relief port having a shape that is
one of a circle, a square, a rectangle, or a triangle.
8. The method of claim 7 further including forming a relief opening
through the main panel near the proximal end of the side of the
lead of the plurality of leads.
9. The method of claim 1 wherein forming the blocking fulcrum
extending from the main panel adjacent to the side of the lead of
the plurality of leads and detached from the side of the lead of
the plurality of leads and including terminating the blocking
fulcrum no greater than the second distance from the cavity section
includes forming the second distance no greater than 50
microns.
10. A method of forming a semiconductor package from a leadframe
comprising: providing the leadframe having leads and having a
blocking fulcrum extending from a main panel of the leadframe
toward a cavity section of the leadframe; encapsulating the cavity
section of the leadframe to form a body; and moving the blocking
fulcrum away from a plane of the leads and away from the body.
11. The method of claim 10 further including plating the leads of
the semiconductor package.
12. The method of claim 10 further including singulating the body
and the leads from the main panel and the blocking fulcrum.
13. The method of claim 10 wherein moving the blocking fulcrum away
from the plane of the leads includes bending the blocking
fulcrum.
14. A leadframe for a semiconductor package comprising: a leadframe
strip having a main panel and a plurality of cavity sections; a
plurality of leads having a proximal end attached to the main panel
and having sides extending from the main panel a first distance
into a cavity section of the plurality of cavity sections, the
sides detached from the main panel; and a blocking fulcrum
extending from the main panel toward the cavity section, the
blocking fulcrum detached from the sides and terminating no greater
than a second distance from the cavity section.
15. The leadframe of claim 14 wherein the blocking fulcrum
extending from the main panel toward the cavity section includes
the blocking fulcrum being spaced from the sides.
16. The leadframe of claim 15 wherein the blocking fulcrum being
spaced from the sides includes the blocking fulcrum spaced no more
than about 25 microns from the sides.
17. The leadframe of claim 14 further including a relief opening
through the main panel where the sides intersect the main
panel.
18. The leadframe of claim 14 further including an indentation
extending across a portion of the blocking fulcrum where the
blocking fulcrum intersects the main panel.
19. The leadframe of claim 14 wherein the blocking fulcrum
extending from the main panel toward the cavity section includes
the blocking fulcrum extending adjacent to at least one side of the
sides.
20. The leadframe of claim 14 wherein the second distance is no
greater than approximately fifty microns.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates, in general, to packaging, and
more particularly, to methods of forming leadframes and
semiconductor packages.
[0002] In the past, various methods were utilized to manufacture
both semiconductor packages and the leadframes utilized in
manufacturing the semiconductor packages. One leadframe
manufacturing method produced a leadframe having a dam-bar that
extended laterally between the leads and that was connected to each
lead of the leadframe. When the leadframe was molded into a
package, the dam-bar was intended to prevent the molding compound
from reaching the package leads. The dam-bar had to be positioned
sufficiently far from the package body to leave room to excise the
dam-bar without damaging the package body. The large space between
the package body and the dam-bar allowed the mold material to
escape and fill the space. The material also attached to the side
of the leads.
[0003] Another method produced a leadframe that did not have a
dam-bar. The molding equipment or mold that was utilized to produce
the semiconductor package had channels or recesses into which the
leads were placed. During the molding operation, mold material
often traveled through the channels and attached to the sides of
the leads. This mold material often is referred to as flash or
flashing.
[0004] The flashing that resulted from these processes had to be
removed from the leads after the molding operations were complete.
In some cases, the flashing was along the entire length of the lead
and could be up to 0.15 millimeters thick. Flash removal procedures
included using a high-pressure jet of water or of particles or a
chemical jet to remove the flashing. The pressure often was in the
range of about two hundred fifty to four hundred twenty five
Kilo-grams/square centi-meter (250-425 KGm/cm.sup.2).
[0005] As the size of semiconductor packages and leads for the
packages continued to decrease, the leads and the packages became
more delicate and more easily damaged. The smaller lead and package
sizes made it more difficult to prevent the mold material from
escaping the mold cavities, thus, made it more difficult to keep
the mold material from adhering to the leads. In some cases the
flashing was longer than the finished lead length and could be
thicker than the lead width. This made flashing removal very
difficult. Additionally, the smaller lead and package size made it
more difficult to remove the flashing without damaging the leads
and the packages.
[0006] Accordingly, it is desirable to have a leadframe having
small leads, that reduces the amount of mold material escaping from
the mold cavity and along the leads, that reduces the amount of
mold material or flashing adhering to the leads, and that minimizes
lead damage during flashing removal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 illustrates an enlarged plan view of a portion of an
embodiment of a leadframe in accordance with the present
invention;
[0008] FIG. 2 illustrates an enlarged plan view of an embodiment of
a portion of the leadframe of FIG. 1 in accordance with the present
invention;
[0009] FIG. 3 illustrates a greatly enlarged cross-sectional view
of an embodiment of a portion of the leadframe of FIG. 2 in
accordance with the present invention;
[0010] FIG. 4 illustrates a greatly enlarged plan view of an
embodiment of another portion of the leadframe of FIG. 2 in
accordance with the present invention;
[0011] FIG. 5 illustrates a greatly enlarged isometric view of a
portion of the leadframe of FIG. 2 at a stage of manufacturing the
leadframe in accordance with the present invention;
[0012] FIG. 6 illustrates a greatly enlarged isometric view of the
portion of the leadframe of FIG. 5 at a subsequent stage of
manufacturing the leadframe in accordance with the present
invention;
[0013] FIG. 7 illustrates an enlarged plan view of a second
embodiment of a portion of the leadframe of FIG. 1 in accordance
with the present invention;
[0014] FIG. 8 illustrates an enlarged plan view of a third
embodiment of a portion of the leadframe of FIG. 1 in accordance
with the present invention;
[0015] FIG. 9 illustrates an enlarged isometric view of the
leadframe of FIG. 1 at a stage of manufacturing a semiconductor
package in accordance with the present invention;
[0016] FIG. 10 illustrates an enlarged elevation view of a portion
of the semiconductor package of FIG. 9 at a manufacturing stage in
accordance with the present invention; and
[0017] FIG. 11 illustrates an enlarged plan view of a fourth
embodiment of a portion of the leadframe of FIG. 1 in accordance
with the present invention.
[0018] For simplicity and clarity of illustration, elements in the
figures are not necessarily to scale, and the same reference
numbers in different figures denote the same elements.
Additionally, descriptions and details of well known steps and
elements are omitted for simplicity of the description.
DETAILED DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 illustrates an enlarged plan view of a portion of an
embodiment of a leadframe strip or leadframe 10. Leadframe 10
typically is produced as a strip that has a plurality of package
sites 20 at which semiconductor packages are to be formed.
Leadframe 10 includes a main panel section or main panel 11 that
supports all the other elements of leadframe 10 during the
manufacturing process. As is well known in the art, main panel 11
typically is a long thin sheet of metal from which the other
elements of leadframe 10 are produced.
[0020] FIG. 2 illustrates a further enlarged plan view of leadframe
10 of FIG. 1 illustrating an embodiment of a portion of one package
site 25 of the plurality of package sites 20 shown in FIG. 1. This
explanation has references to both FIG. 1 and FIG. 2. Site 25, and
typically each site 20, includes a cavity section 40 which is
intended to be encapsulated during the process of forming a
semiconductor package from leadframe 10. Cavity section 40 is
illustrated in general by a dashed box. Site 25, thus sites 20 and
leadframe 10, includes a plurality of leads that includes leads 12,
13, 14, and 15 that extend from panel 11 into cavity section 40.
Leads 12, 13, 14, and 15 may be referred to hereinafter as the
plurality of leads or as leads 12-15. For clarity of the
description and drawings, four leads are illustrated, however,
those skilled in the art realize various numbers of leads may
extend into cavity section 40. A proximal end of each lead 12, 13,
14, and 15 is attached to panel 11, and the sides extend from panel
11 a first distance into cavity section 40. Generally, the sides
extend perpendicularly to a near side of section 40. A distal end
of each lead 12, 13, 14, and 15 is within cavity section 40. The
distal end of lead 15 has a die attach area or flag 17 that is
formed for attaching a semiconductor die thereto. A distal end 18
of leads 12, 13, and 14 have a bonding area that will be utilized
for attaching bonding wires to the semiconductor die that will be
attached to flag 17. Such flags and bonding areas are well known to
those skilled in the art.
[0021] Site 25, and typically each site 20, of leadframe 10 are
also formed to include a plurality of blocking fulcrums that assist
in blocking encapsulation material from flowing along the plurality
of leads and from attaching to the plurality of leads. The
plurality of blocking fulcrums include blocking fulcrums 21 and 22.
In general, one of fulcrums 21 or 22 is formed adjacent each side
of each lead 12, 13, 14, or 15. Other embodiments may have more
than one fulcrum between leads or may have fewer. Although fulcrums
21 and 22 are illustrated with different widths, the width of each
blocking fulcrum generally is determined from a number of
parameters including the number of leads, lead spacing, and the
width of the leads. A proximal end of fulcrums 21 and 22 is
attached to panel 11. Fulcrums 21 and 22 have sides 31 that extend
from the proximal end toward section 40 and terminate at a distal
end 32. Preferably, a distance 30 separates ends 32 from the edge
of cavity section 40. However, in some cases, ends 32 may extend a
small distance or second distance into section 40. In such a case,
ends 32 terminate a shorter distance into section 40 than do the
ends of leads 12-15, thus, the first distance of ends 18 is larger
than the second distance of ends 32. Distance 30 can be up to about
fifty (50) microns and preferably is no greater than about ten (10)
microns. For the case where ends 32 extend the second distance into
section 40, the second distance generally is no greater than about
fifty (50) microns. Sides 31 typically are adjacent to one of leads
12-15 and separated from the adjacent lead by a small spacing 35
(see FIG. 4).
[0022] As will be seen subsequently, during the process of
encapsulating sites 20 of leadframe 10 fulcrums 21 and 22
substantially prevent the flow of encapsulating compound from
escaping and attaching to leads 12-15. After the encapsulation
process, fulcrums 21 and 22 will be moved away from the plane of
leads 12-15 and leadframe 10. In order to facilitate the movement,
leadframe 10 may be formed to include optional relief features 36
that assist in controlling any bending or other movement that
occurs at the proximal end of fulcrums 21 and 22. Features 36 are
illustrated by dashed lines. Typically, features 36 are
indentations that are made in the surface of panel 11. As will be
seen hereinafter, during the process of forming a semiconductor
package from leadframe 10, features 36 provide a location for
fulcrums 21 and 22 to move or to bend. This minimizes the
deformation of panel 11 and improves the planarity of leads 12-15
as well as the planarity of panel 11. Features 36 are located at
the point that is most desirable for fulcrums 21 and 23 to bend or
otherwise move. Typically, features 36 are located laterally across
fulcrums 21 and 23 at the proximal end of the respective fulcrum.
Features 36 have a length that is sufficient to control the
movement as desired. In the preferred embodiment, features 36
extend approximately across the width of fulcrums 21 and 22,
however, in other embodiments features 36 may only extend a portion
of the width of fulcrums 21 and 22.
[0023] FIG. 3 illustrates a greatly enlarged cross-sectional view
of feature 36 of leadframe 10 along section line 2-2 of FIG. 2.
Features 36 can have various depths and shapes, for example a V
shape, a U shape, or other shape, that assists controlling the
location along panel 11 where bending or other movement of fulcrums
21 and 22 occurs. In the preferred embodiment, features 36 are V
shaped. In order to facilitate the controlled movement, the depth
of features 36 typically is less than about one-half the thickness
of panel 11 and preferably is no greater than about one-fourth. The
width of feature 36 at the surface of panel 11 is usually no
greater than about four times the depth and preferably is no
greater than about two times the depth. Features 36 may be formed
on either surface of panel 11 or may be formed on both surfaces as
illustrated by the dashed lines in FIG. 3. Features 36 provide some
control over the bending or other movement of fulcrums 21 and 22,
thus, improve the manufacturing process. However, features 36 are
optional and could be omitted in some embodiments.
[0024] FIG. 4 illustrates a greatly enlarged plan view of spacing
35 of leadframe 10. Spacing 35 is formed sufficiently small to
substantially prevent the encapsulating compound of the
encapsulating material from traveling along the portion of leads
12-15 that is external to section 40. Those skilled in the art
realize that some of the resin used in the encapsulating material
may escape but that such is not considered the encapsulating
compound part of the encapsulating material. Spacing 35 typically
is less than about twenty five (25) microns and preferably is
substantially zero.
[0025] Referring back to FIG. 1 and FIG. 2, various well-known
techniques can be utilized to form leadframe 10. For example, the
openings within cavity section 40 can be stamped from a piece of
sheet metal using techniques that are well known in the art. This
stamping operation could also cut fulcrums 21 and 22 to terminate
at end 32 and could form optional features 36. Thereafter, a
shearing operation can be employed to cut fulcrums 21 and 22 along
sides 31 in order to separate fulcrums 21 and 22 from leads 12-15
and from panel 11. Thus, three sides of each of leads 12-15 become
detached from panel 11. In some cases, the shearing operation may
bend or displace portions of fulcrums 21 and 22 or portions of
leads 12-15 (See FIG. 5). In such cases a realignment operation can
be utilized to bend fulcrums 21 and 22 or leads 12-15 back close to
alignment such as close to aligning to the plane of panel 11 (See
FIG. 6). For example, a light coining or light spanking may be
employed to implement the realignment operation. Improving the
alignment minimizes space 35 and assists in substantially
preventing encapsulating compound from reaching leads 12-15.
Alternatively, the stamping operation could also sever fulcrums 21
and 22 from leads 12-15. Those skilled in the art realize that
leadframe 10 could also be etched. Additionally, a laser or water
jet could be used to form leads 12-15, fulcrums 21 and 22, and
features 36.
[0026] FIG. 5 illustrates a greatly enlarged isometric view of a
portion of leadframe 10 of FIG. 1 at a stage of manufacturing
leadframe 10. At the stage illustrated in FIG. 5, fulcrums 21 and
23 were sheared from leads 12-15. In some cases, leads 12-15 or
fulcrums 21 and 23 may potentially be slightly misaligned or
misshaped. For clarity of the drawing such potential misshape is
shown in an exaggerated form.
[0027] FIG. 6 illustrates a greatly enlarged isometric view of the
portion of leadframe 10 of FIG. 5 at a subsequent stage of
manufacturing after the realignment operation.
[0028] FIG. 7 illustrates an enlarged plan view of a second
embodiment of a portion of leadframe 10 of FIG. 1 illustrating an
embodiment of a portion of a package site 38 that is an alternate
embodiment of site 25 shown in FIG. 2. This explanation has
references to FIG. 1 and FIG. 2. Site 38 includes an optional
relief port 34 that provides some control over the bending or other
movement of fulcrums 21 and 22, thus, improves the process of
manufacturing packages using leadframe 10. Port 34 assists in
controlling any moving that occurs at the proximal end of fulcrums
21 and 22. Ports 34 are opening through panel 11 that are formed at
the proximal end or near the proximal end of fulcrums 21 and 23.
Any number or all of fulcrums 21 and 23 may have ports 34. Ports 34
can have various shapes including a square, a rectangle, a circle,
a triangle, or other shape that assists in controlling the
movement. In the preferred embodiment, ports 34 are rectangles.
Ports 34 typically have a length that is less than about eighty
percent (80%) of the width of the respective fulcrum 21 or 23. The
width of ports 34 generally is large enough to assist the movement
and small enough to ensure that the molds can close and seal.
[0029] FIG. 8 illustrates an enlarged plan view of a third
embodiment of a portion of leadframe 10 of FIG. 1 illustrating an
embodiment of a portion of a package site 50 that is an alternate
embodiment of site 25 shown in FIG. 2. This explanation has
references to FIG. 1, FIG. 2, and FIG. 3. Site 50 includes an
optional relief opening 33. Relief openings 33 are holes that are
formed through leadframe 10 at the proximal end of fulcrums 21 and
22 where sides 31 would intersect panel 11. Thus, openings 33 are
positioned at the proximal end of the sides of leads 12-15.
Typically, openings 33 have a width that is less than about
one-half the width of the adjacent lead 12-15, and preferably is
less than about one-fourth the width of the adjacent lead. Openings
33 can have various shapes such as a rectangle, a square, a circle,
a triangle etc. In the preferred embodiment, openings 33 are
circles. Relief openings 33 can be stamped out of panel 11 when the
inner portion of section 40 is stamped out. Openings 33 provide
some control over the movement of fulcrums 21 and 22, thus, improve
the manufacturing process. Additionally, during any shearing
operation used to form leads 12-15, openings 33 assist in ensuring
that the sides of leads 12-15 and fulcrums 21 and 23 have uniform
lengths. Openings 33 are optional and could be omitted in some
embodiments.
[0030] FIG. 9 illustrates an enlarged isometric view of leadframe
10 after several steps in the process of manufacturing a
semiconductor package from leadframe 10. As is well know in the
art, a semiconductor die typically is attached to flag 17 and wire
bonded to leads 12, 13, and 14. Subsequently, leadframe 10 is
placed into a mold and cavity section 40 is encapsulated. During
the encapsulation process, the molds clamp down on leads 12=15 and
on fulcrums 21 and 22. When the molds are closed on leadframe 10, a
molding cavity within the molds typically corresponds to the shape
and location of cavity section 40. A chase or runner from the mold
may extend across one of fulcrums 21 or 22 into the mold cavity
that overlies cavity section 40. During the molding operation,
encapsulation material is forced into the mold cavity to
encapsulate cavity section 40. During this encapsulation step,
fulcrums 21 and 22 block the encapsulation material and restrict it
from escaping the mold cavity. Thus, it is important that distance
30 be very small to prevent the encapsulating compound from
escaping and touching leads 12-15. Also, the small size of spacing
35 substantially prevents the encapsulating compound from moving
along the sides of leads 12-15, thus, preventing the encapsulating
compound from attaching to leads 12-15. Because spacing 35 is very
small, very little and preferably no, encapsulating compound
attaches to leads 12-15. Even with the small size of spacing 35,
some amount of encapsulation material may escape from the cavity
and attach to the leads. Typically, the amount of encapsulating
compound attached to leads 12, 13, 14, and 15 is less than about
one-third of the amount left by prior art methods. The small size
of spacing 35 also restricts the thickness of the encapsulating
material that attaches to the sides of leads 12-15 to less than
about fifty (50) microns. After the encapsulation operation, the
molds are opened leaving a package body 45 encapsulating cavity
section 40 and surrounding the distal ends of leads 12-15. In the
preferred embodiment, body 45 is separated from fulcrums 21 and 22
by distance 30 (see FIG. 1).
[0031] Subsequent to the molding operation, fulcrums 21 and 22 are
moved so that leads 12-15 can be plated. The movement carries sides
31 pass the sides of leads 12-15. Fulcrums 21 and 22 may be moved
above or below panel 11, or may be moved both above and below.
Distance 30 and spacing 35 are formed to be a size that facilitates
such movement without damaging leads 12-15 or body 45. Fulcrums 21
and 22 generally are moved a distance that is sufficient to ensure
they do not interfere with subsequent plating operations. For
example, if the plating material is plated to a thickness of about
ten (10) microns, fulcrums 21 and 22 should be moved at least ten
(10) microns. In some cases fulcrums 21 and 22 may be moved up to
ninety degrees (90.degree.) or up to about one hundred eighty
degrees (180.degree.) to assist in plating the leads and in
singulating the package from panel 11.
[0032] During the movement of fulcrums 21 and 23, any or all of
optional features 36, ports 34, and openings 33 can assist in
controlling the movement of fulcrums 21 and 22 to occur at the
proximal end so that the majority of fulcrums 21 and 22 remain
straight and move without damaging leads 12-15. In some cases, such
as distance 30 being too large, moving fulcrums 21 and 23 may also
assist in removing some of the encapsulation material or flashing
that may be attached to leads 12-15.
[0033] After fulcrums 21 and 22 are moved, leadframe 10 is plated.
Plating of the leads is well known in the art. Subsequently, the
encapsulated package is singulated from panel 11 by cutting leads
12, 13, 14, and 15 to extend a desired length from body 45. This
singulation operation typically leaves fulcrums 21 and 22 attached
to panel 11. All surfaces of leads 12, 13, 14, and 15 are plated
and no bare sections remain. It should also be noted, that some
small portions of the encapsulation material may remain on the
leads, however, this portion is very small and very thin, thus, any
subsequent de-flashing operations can be done much more easily than
prior de-flashing operations thereby preventing damage to the
leads. For example, a lower pressure water jet may be used at a
pressure that is about four or five time less than the pressure of
prior high pressure water jet operations. If required, this
de-flashing step typically is performed prior to plating. The lower
pressure reduces damage to the package and to leads 12, 13, 14, and
15 thereby improving reliability and lowering the manufacturing
costs.
[0034] Typically, leads 12, 13, 14, and 15 are less than about 0.2
milli-meters wide and less than about 0.1 milli-meters thick.
However fulcrums 21 and 22 and spacing 35 can be used to improve
leadframes, and packages using the leadframes, having leads that
are thicker or wider or thinner or narrower.
[0035] Although body 45 is shown with leads 12-15 near the bottom
of one side of body 45, those skilled in the art realize that leads
12-15 could be formed on all sides of body 45 and at various
locations along the surface of each side.
[0036] FIG. 10 illustrates an enlarged elevation view of a portion
of the semiconductor package of FIG. 9 at a point during the
manufacturing stage discussed in the description of FIG. 9. After
the encapsulation operation, encapsulation material in the form of
a mold gate 46 may be attached to body 45 and may be on one of
fulcrums 21 or 22. Typically, a notch is formed in gate 46 near to
the connection to body 45. This notch provides a weak spot that
assists breaking gate 46 close to body 45. If such mold gate 46 is
formed on one of fulcrums 21 and 22, the movement of fulcrums 21
and 22 may break mold gate 46 away from body 45 and away from the
semiconductor package. Using fulcrums 21 and 22 to remove the mold
gate reduces the amount of mechanical trimming that is
required.
[0037] FIG. 11 illustrates an enlarged plan view of a fourth
embodiment of a portion of leadframe 10 of FIG. 1 illustrating an
embodiment of a portion of a package site 55 that is another
alternate embodiment of site 25 shown in FIG. 2. This explanation
has references to FIG. 1, FIG. 2, and FIG. 3. Site 55 includes a
plurality of blocking fulcrums including blocking fulcrums 56 and
57, that function similarly to fulcrums 21. However, fulcrums 56
and 57 are formed to have a length that positions ends 32 further
within cavity section 40 than fulcrums 21. The length of fulcrums
56 and 57 allow fulcrums 56 and 57 to extend under the package body
that will be formed over cavity section 40. When fulcrums 56 and 57
are excised, a stand-off will be formed on the bottom of the
package body. In some embodiments ends 32 of fulcrums 56 could be
less than one hundred microns from touching each other.
Additionally, fulcrums 56 and 57 have a side 58 that extends past
the end of cavity section 40. When the leadframe that has site 55
is used to form a semiconductor package, fulcrums 56 and 57 will be
moved down from the plane of the bottom surface of panel 11. After
the movement, each fulcrum 56 and 57 may leave a recess in the
bottom surface of the package body where fulcrums 56 and 57 were
previously located. Fulcrums 57 are shown to have different lengths
than fulcrums 56 to illustrate two different combinations of
lengths and positions of ends 32.
[0038] In view of all of the above, it is evident that a novel
device and method is disclosed. Forming a blocking fulcrum adjacent
to the sides of the leads facilitates using the blocking fulcrum to
restrict mold material from reaching the leads. Making the spacing
between the leads and the blocking fulcrums very small
substantially prevents encapsulating compound from traveling along
the sides of the leads and substantially prevents flashing on the
leads. Although described with a transfer molding operation, the
leadframe and method is also applicable to injection molding.
* * * * *