U.S. patent application number 09/953698 was filed with the patent office on 2003-01-30 for lead formation, assembly strip test and singulation method.
This patent application is currently assigned to Integrated Device Technology, Inc.. Invention is credited to Choe, Peng Cheong, Song, Kong Lam.
Application Number | 20030022405 09/953698 |
Document ID | / |
Family ID | 19749517 |
Filed Date | 2003-01-30 |
United States Patent
Application |
20030022405 |
Kind Code |
A1 |
Song, Kong Lam ; et
al. |
January 30, 2003 |
LEAD FORMATION, ASSEMBLY STRIP TEST AND SINGULATION METHOD
Abstract
A method for testing integrated circuits (ICs) mounted on an
assembly strip after lead formation and before separation from the
assembly strip. The ICs are arranged in rows and columns on each
assembly strip such that the sides of each IC are connected to
leads extending from the assembly strip, and the ends of each IC
are held by the assembly strip. The strips are loaded into the
system and passed to a first station at which leads are cut and
formed while the ends of each IC remain connected to the assembly
strip. The assembly strips are then passed to a test apparatus that
transmits test signals to the ICs through the formed leads. The IC
devices are then separated from the assembly strip using a
singulation apparatus, and the separated ICs are stored in tubes
for delivery. Visual inspection is also performed at various
stages.
Inventors: |
Song, Kong Lam; (Penang,
MY) ; Choe, Peng Cheong; (Penang, MY) |
Correspondence
Address: |
BEVER, HOFFMAN & HARMS, LLP
2099 GATEWAY PLACE
SUITE 320
SAN JOSE
CA
95110
US
|
Assignee: |
Integrated Device Technology,
Inc.
|
Family ID: |
19749517 |
Appl. No.: |
09/953698 |
Filed: |
September 12, 2001 |
Current U.S.
Class: |
438/15 ;
257/E23.031; 438/14 |
Current CPC
Class: |
H01L 2924/14 20130101;
H01L 23/495 20130101; G01R 1/0433 20130101; H01L 2224/48247
20130101; H01L 24/97 20130101; H01L 2224/48091 20130101; G01R
31/2831 20130101; H01L 2224/48091 20130101; H01L 2924/00014
20130101; H01L 2924/14 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
438/15 ;
438/14 |
International
Class: |
H01L 021/66; G01R
031/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 25, 2001 |
MY |
P I20013529 |
Claims
1. An assembly strip test method for testing integrated circuits
mounted on a matrix-type lead frame defining a plane, the method
comprising: cutting and forming leads of the integrated circuits
such that the leads are bent out of the plane defined by lead
frame, wherein the integrated circuits remain connected to the lead
frame after the leads are formed; performing functional testing on
the integrated circuits by transmitting test signals onto the
formed leads of the integrated circuits; and separating the tested
integrated circuits from the lead frame.
2. The method according to claim 1, further comprising: moving the
lead frame on a conveyor from a first apparatus for cutting and
forming the leads to a second apparatus for function testing the
integrated circuits; and moving the lead frame on the conveyor from
the second apparatus to a third apparatus for separating the
integrated circuits from the lead frame.
3. The method according to claim 1, further comprising
automatically inspecting the leads of the integrated circuits after
performing functional testing and before separating the integrated
circuits from the lead frame.
4. The method according to claim 1, wherein cutting and forming the
leads comprises cutting the leads using a first mechanism,
preforming the leads using a second mechanism, and then forming the
leads into a final form using a third mechanism.
5. The method according to claim 4, wherein cutting the leads
comprises supporting a package body of the integrated circuit and
positioning the leads of the integrated circuit between a
stationary die and a movable punch, and then moving the movable
punch toward the stationary die, and wherein the stationary die
includes a first edge, and the movable punch includes a second edge
positioned over the first edge such that the first and second edges
cut the leads when the movable punch is moved toward the stationary
die.
6. The method according to claim 4, wherein preforming the leads
comprises supporting a package body of the integrated circuit and
positioning the leads of the integrated circuit between a
stationary anvil and a movable structure including a preform punch
and a second anvil slidably mounted on the preform punch, and
moving the movable structure toward the stationary anvil, wherein
the first anvil includes a first shoulder for supporting the leads,
and the second anvil includes a second shoulder positioned such
that portions of the leads located adjacent to a package of the
integrated circuit are held between the first and second shoulders
when the second anvil is moved toward the first anvil, and wherein
the first anvil includes a first chamfered surface, and the preform
punch includes a second chamfered surface arranged such that the
leads are bent between the first and second chamfered surfaces when
the preform punch is moved toward the first anvil.
7. The method according to claim 4, wherein the forming the leads
into the final form comprises supporting a package body of the
integrated circuit and positioning the leads of the integrated
circuit between a stationary anvil and a movable structure
including a second anvil and a lead forming portion rotatably
connected to the second anvil, and moving the movable structure
toward the stationary anvil, wherein the first anvil includes a
rail for supporting the leads, and the second anvil includes a
shoulder positioned such that portions of the leads located
adjacent to a package of the integrated circuit are pinched between
the rail and the shoulder when the second anvil is moved toward the
first anvil, and wherein the lead forming portion includes a cam
form pad arranged such that the leads are formed between the cam
form pad and the rail when the lead forming portion is rotated
relative to the second anvil.
8. The method according to claim 1, further comprising
automatically moving the matrix-type lead frame from a first
apparatus for cutting and forming the leads of the integrated
circuits to a second apparatus for performing functional testing
using a conveyor.
9. The method according to claim 8, wherein functional testing the
integrated circuits comprises: moving the matrix-type lead frame
such that one or more integrated circuits are positioned between a
stationary anvil and a movable probe assembly; moving the movable
probe assembly toward the stationary anvil, wherein the probe
assembly includes a probe array having a plurality of probes
arranged such that the probes contact the leads when the probe
assembly is moved toward the anvil by the ball-screw drive; and
transmitting test signals to the probes.
10. The method according to claim 9, wherein moving the movable
probe assembly comprises contacting a base portion of each lead
located adjacent to a package of the integrated circuit using a
first set of probes when the probe assembly is moved a first
distance toward the anvil, and contacting a foot of each lead using
a second set of probes when the probe assembly is moved a second
distance toward the anvil.
11. The method according to claim 1, further comprising
automatically moving the matrix-type lead frame from a first
apparatus for functional testing the integrated circuits to a
second apparatus for separating the tested integrated circuits from
the lead frame using a conveyor.
12. The method according to claim 11, wherein separating the
integrated circuits comprises positioning one or more integrated
circuits between a stationary anvil and a movable structure
including a stripper and a punch, and then moving the movable
structure toward the stationary anvil such that the stripper
pinches a leadframe of the assembly strip against the stationary
anvil, and the punch pushes the integrated circuit such that the
integrated circuit is separated from the leadframe when the
stripper and punch are moved toward the anvil.
13. A method for testing integrated circuits formed on an assembly
strip, the assembly strip including a leadframe defining a plane
and a plurality of integrated circuits mounted on the lead frame,
each integrated circuit being electrically connected to a plurality
of leads extending between the integrated circuit and the
leadframe, the method comprising: cutting and forming the leads of
each integrated circuit such that the leads are bent away of the
plane defined by the assembly strip; and functional testing the
integrated circuits using a plurality of probes that are arranged
to contact the cut and formed leads.
14. The method according to claim 13, further comprising
automatically moving the lead frame from a first apparatus for
cutting and forming the leads of the integrated circuits to a
second apparatus for performing functional testing using a
conveyor.
15. The method according to claim 13, wherein cutting and forming
the leads comprises cutting the leads using a first mechanism,
preforming the leads using a second mechanism, and then forming the
leads into a final form using a third mechanism.
16. The method according to claim 15, further comprising driving
the first, second, and third mechanisms using a single drive
apparatus.
17. The method according to claim 13, further comprising
automatically moving the matrix-type lead frame from a first
apparatus for functional testing the integrated circuits to a
second apparatus for separating the tested integrated circuits from
the lead frame using a conveyor.
18. A method for testing integrated circuits formed on an assembly
strip, the assembly strip including a lead frame defining a plane
and a plurality of integrated circuits connected to the lead frame,
each integrated circuit including a package body housing an
integrated circuit chip that is electrically coupled to a plurality
of leads extending from the package body, the method comprising:
forming the leads such that portions of the leads are bent out of
the plane defined by the lead frame; and functional testing the
integrated circuits by moving the lead frame such that one or more
integrated circuits are positioned between a stationary anvil and a
movable probe assembly, moving the movable probe assembly toward
the stationary anvil, and transmitting test signals to the probe
assembly, wherein the probe assembly includes a probe array having
a plurality of probes arranged such that the probes contact the
leads when the probe assembly is moved toward the anvil.
19. The method according to claim 18, wherein moving the movable
probe assembly comprises contacting a base portion of each lead
located adjacent to a package of the integrated circuit using a
first set of probes when the probe assembly is moved a first
distance toward the anvil, and contacting a foot of each lead using
a second set of probes when the probe assembly is moved a second
distance toward the anvil.
20. The method according to claim 18, further comprising
automatically moving the lead frame from a first apparatus for
cutting and forming the leads of the integrated circuits to a
second apparatus for performing functional testing using a
conveyor.
Description
FIELD OF THE INVENTION
[0001] This invention relates to integrated circuits, and more
particularly to methods and automated systems for efficiently
testing integrated circuits.
BACKGROUND OF THE INVENTION
[0002] Molded IC devices are often assembled (packaged) on
matrix-type lead frame structures in which the IC devices are
arranged in multiple rows and columns, and then tested while
connected to the matrix-type lead frame (i.e., before being
singulated (separated) into individual IC devices). As utilized
herein, the term "assembly strip" is used to describe the integral
structure formed by such a matrix-type lead frame structure with IC
devices packaged thereon. Assembly strips facilitate low-cost
automated production by allowing several IC devices to be tested
simultaneously (i.e., in parallel), thereby reducing manufacturing
time and costs.
[0003] FIGS. 1(A) through 1(C) are perspective views showing a
conventional process of assembling IC devices using a lead frame
100, which is simplified for descriptive purposes. Referring to
FIG. 1(A), lead frame 100 is etched or stamped from a thin sheet
metal strip, and includes side rails 110, cross rails 120, and
multiple die attach regions 130. Each die attach region 130
includes a die attach platform 132 connected to side rails 110 by
tie bars 135, and patterns of narrow leads 140 that radiate inward
from side rails 110 and cross rails 120 toward die attach platform
132. Note that leads 140 do not contact die attach platform 132.
During a first stage of the bonding process that is shown in FIG.
1(A), an IC die 150 is mounted onto each die attach platform 132
using, for example, an epoxy resin. A pattern of die bond pads 152
are provided on an upper surface of IC die 150 that are
electrically connected to the integrated circuit formed thereon. As
shown in FIG. 1(B), after IC die 150 is secured to die attach
platform 132, each die attach platform 152 is electrically
connected to a corresponding lead 140 by a fine-diameter gold bond
wire 160 using well-established wire bond techniques. Subsequently,
as indicated in FIG. 1(C), die attach platform 132, the inner ends
of leads 140, die 150, and bond wires 160 are covered with a
thermoset plastic casing 170 during a transfer molding operation.
Note that a portion of each lead 140 is exposed along the sides of
casing 170. The integral structure including lead frame 100 and the
fully packaged IC device is referred to below as assembly strip
105.
[0004] FIGS. 2(A) through 2(C) show a conventional process for
functional testing, lead formation, and singulation (i.e.,
separation of individual IC devices 200 from assembly strip 105),
which is performed after the assembly process shown in FIGS. 1(A)
through 1(C). First, as shown in FIG. 2(A), the conventional
process includes cutting leads 140 such that they are separated
from side rails 110 and cross rails 120 of lead frame 100. Note
that IC devices 200 remain connected to assembly strip 105 by tie
bars 135, and that leads 140 remain flattened (i.e., in plane with
side rails 110 and cross rails 120 of lead frame 100). As shown in
FIG. 2(B), functional testing is then performed during which test
signals are transmitted from a tester 210 to IC devices 200 via
probes 215, which are pressed against leads 140 by a suitable
mechanism. Note that functional testing is performed while leads
140 are flat (i.e., in the plane defined by lead frame 100).
Finally, as indicated in FIG. 2(C), lead forming and singulation is
performed to produce individual IC devices 200 having fully formed
leads 140. After singulation, lead frame 100 is discarded.
[0005] A problem with the conventional testing and singulation
process shown in FIGS. 2(A) through 2(C) is that three separate
systems are required to perform each of lead cutting (FIG. 2(A)),
functional testing (FIG. 2(B)), and singulation (FIG. 2(C)),
thereby increasing the total production cost per IC device 200.
Further, transferring assembly strips 105 between these separate
systems inevitably leads to accidents that damage IC devices 200,
further increasing production costs.
[0006] What is needed is an efficient and cost effective system and
method for performing functional testing, lead formation, and
singulation of IC devices that avoids the cost and handling issues
associated with the conventional methods described above.
SUMMARY OF THE INVENTION
[0007] The present invention is directed to a method for processing
and testing ICs mounted on an assembly strip in which both
functional and visual lead inspection are performed after cutting
and forming the leads, and prior to singulation (i.e., prior to
separation of the individual ICs from the assembly strip).
Accordingly, the present invention facilitates functional testing,
lead formation, and singulation using a single, relatively
inexpensive system, thereby reducing overall production costs when
compared to conventional methods for performing these procedures.
Further, because the assembly strips remain attached to a single
system throughout functional testing, lead formation, and
singulation, the present invention also minimizes handling by
eliminating transfer between independent systems, thereby reducing
the costs associated with damage caused during such transfers.
[0008] Each assembly strip processed in accordance with the present
invention includes multiple rows and columns (e.g., 5.times.12) of
ICs that are mounted on a matrix-type lead frame. In one
embodiment, the lead frame includes IC mounting regions made up of
a die attach platform that is connected at opposite ends to the
lead frame, and parallel leads extending from opposing sides of the
die attach platform to lead tie bars of the lead frame. An IC is
mounted on each die attach platform and connected (e.g., using wire
bonding techniques) to the leads located adjacent to the die attach
platform. Subsequently, packaging material (e.g., thermoset
plastic) is formed over the IC, bonding wires and die attach
platform.
[0009] In accordance with a disclosed embodiment of the present
invention, a method for processing ICs mounted on assembly strips
utilizes a lead length cut/form apparatus, a functional test
apparatus, and a singulation apparatus. After the IC dies are
mounted on the assembly strip, they are loaded into magazines and
systematically moved by an onloader to a conveyor, which moves the
assembly strips to the lead length cut/form apparatus. The lead
length cut/form apparatus cuts the leads connected to the package
of each IC, preforms (i.e., bends) the leads, and forms the leads
into a desired final form without separating the ICs from the
assembly strip. The assembly strips are then passed to the
functional test module in which probes (e.g., pogo pins) are
pressed against the fully formed leads and functional tests are
transmitted to the ICs from a tester. Visual inspection of the
leads is then performed to identify defective leads, e.g., damaged
leads, bent leads, or missing leads. After functional and visual
testing, the assembly strips are passed to a singulation apparatus
that separates the ICs from the assembly strip frame, and to an
offloader that loads the separated ICs into storage tubes. An
optional second visual inspection may be performed after
singulation and prior to loading to detect package defects that may
have occurred during the testing and singulation operations, or
during preceding processes.
[0010] In accordance with an aspect of the present invention, the
lead cut/form process and singulation process are performed using a
single drive apparatus, thereby reducing costs by eliminating the
need for separate drive mechanisms for these two operations. Note
that the functional testing process, which is performed between the
lead length cut/form and singulation processes, is provided with a
separate ball-screw drive that facilitates testing of the ICs. A
conveyor is utilized to automatically pass each assembly strip from
the lead length cut/form process to the functional test process,
and from the functional test process to the singulation process,
thereby minimizing IC damage caused by transporting the assembly
strips between separate systems.
[0011] In accordance with another aspect of the present invention,
functional testing is performed using a stationary anvil and a
probe assembly that is moved toward and away from the anvil by the
ball-screw drive. The anvil includes a trough and a pair of rails
that hold the IC devices during testing. The probe assembly
includes probes (e.g., pogo pins) that are pressed against the
leads of the IC devices, which are supported by the rails to
prevent damage. The probes are arranged to include a first set
positioned to contact a portion of the leads located on top of the
rails when the probe assembly is initially moved toward the anvil,
and a second set positioned to contact the feet of the leads when
the probe assembly is moved further toward the anvil. Accordingly,
the functional testing module facilitates functional testing while
preventing damage to the leads, thereby reducing the number of
systems needed to perform the testing and singulation process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] These and other features, aspects and advantages of the
present invention will become better understood with regard to the
following description, appended claims, and accompanying drawings,
where:
[0013] FIGS. 1(A), 1(B), and 1(C) are perspective views showing a
conventional IC device assembly process;
[0014] FIG. 2(A), 2(B), and 2(C) are perspective views showing a
conventional process for functional testing, lead formation, and
singulation of IC devices using an assembly strip;
[0015] FIG. 3 is a block diagram showing a system for IC device
lead formation, functional test, and singulation according to an
embodiment of the present invention;
[0016] FIG. 3A is a simplified side view depicting a portion of the
system shown in FIG. 3;
[0017] FIG. 4 is partial plan view showing an exemplary assembly
strip utilized in accordance with an embodiment of the present
invention;
[0018] FIGS. 5(A) and 5(B) are plan and side section views showing
an IC device mounted on the assembly strip of FIG. 4;
[0019] FIGS. 6(A), 6(B), and 6(C) are simplified cross-sectional
side views showing portions of a lead length cut/form apparatus of
the system shown in FIG. 3;
[0020] FIGS. 7(A), 7(B) and 7(C) are end views showing the assembly
strip of FIG. 4 showing the lead length cut/form process;
[0021] FIG. 8 is a plan view showing an exemplary IC device after
lead formation is completed; and
[0022] FIGS. 9(A) and 9(B) are side and partial front views,
respectively, showing a functional test apparatus utilized in the
system of FIG. 3.
DETAILED DESCRIPTION OF THE DRAWINGS
[0023] FIG. 3 is a block diagram showing a system 300 for
processing and testing integrated circuits (ICs) that are mounted
on assembly strips 305. System 300 generally includes a conveyor
mechanism (workholder) 301, a drive apparatus 310, a lead length
cut/form apparatus 320, a functional test apparatus 330, and a
singulation apparatus 350.
[0024] Conveyor 301 transports assembly strips 305 to lead length
cut/form apparatus 320, from lead length cut/form apparatus 320 to
functional test apparatus 330, and from functional test apparatus
330 to singulation apparatus 350. Note that conveyor 301 may be
separated into segments that feed into each of the apparatus, or
may be formed using a continuous belt. A system controller (not
shown) controls the speed and position of conveyor 301.
[0025] FIG. 3A is a simplified side view depicting selected
functional aspects of system 300. As indicated in FIG. 3A, conveyor
301 is mounted on a base 309 that supports each of lead length
cut/form apparatus 320, functional test apparatus 330, and
singulation apparatus 350, and feeds assembly frames through system
300 (e.g., in a horizontal direction indicated by the X arrow).
Drive apparatus 310 is mounted over base 309, and includes a motor
315 for turning a cam mechanism (depicted as including a shaft 313
and cam wheels 314) that is utilized to operate both functional
test apparatus 330 and singulation apparatus 350. In particular,
lead length cut/form apparatus 320 includes a stationary (first)
portion 320A rigidly mounted on base 309, and a movable (second)
portion 320B that is reciprocated toward and away from stationary
portion 320A (i.e., in the vertical direction indicated by arrow Y)
through contact with the cam mechanism of drive apparatus 310 when
the cam mechanism is turned by motor 315. Similarly, singulation
apparatus 350 includes a stationary (first) portion 350A mounted on
base 309, and a movable (second) portion 350B contacting the cam
mechanism of drive apparatus 310 such that movable portion 350B is
reciprocated toward and away from stationary portion 350A when the
cam mechanism is turned. Functional test apparatus 330, which is
located between lead length cut/form apparatus 320 and singulation
apparatus 350, includes a stationary (first) portion 330A mounted
on base 309, and a movable (second) portion 330B mounted over
stationary portion 330A. Note that movable portion 330B is
reciprocated toward and away from stationary portion 330A by a
separate drive 330C to facilitate IC testing procedures.
[0026] FIGS. 4, 5(A) and 5(B) show assembly strip 305 in additional
detail.
[0027] FIG. 4 is a partial view showing opposing ends of exemplary
assembly strip 305. Assembly strip 305 includes a matrix-type lead
frame 400 including side rails 410 and cross rails 420, and
includes several rows of IC mounting regions 430 located between
cross rails 420, each mounting region 430 including one IC device
440 mounted thereon. In one embodiment, each row includes five (5)
mounting regions 430, and assembly strip 305 includes twelve (12)
columns.
[0028] FIGS. 5(A) and 5(B) are plan and cross-sectional side views,
respectively, showing one mounting region 430 in additional detail.
Referring to FIG. 5(B), each IC device 440 includes a die 500
mounted on a die attach platform 432, with die 500 being is
electrically connected to leads 435 by bond wires 510. A
thermoplastic IC package 520 is formed over die 500, bond wires
510, and ends of leads 435 using techniques described above with
reference to FIGS. 1(A) through 1(C). Referring to FIG. 5(A), each
IC device 440 is mounted and packaged such that ends 522 of each IC
package 520 are secured to connection structures 422 of cross rails
420 by tie bars (not shown). Similarly, leads 435 extend between
sides 524 of each IC package 522 and lead tie bars 415 of assembly
strip 305. Note that when assembly strip 305 is formed (i.e., by
stamping or etching a metal sheet according to known methods),
leads 435 are integrally connected to lead tie bars 415.
[0029] Referring back to FIG. 3, in one embodiment assembly strips
305 are introduced into system 300 using a loading apparatus
(ONLOADER) 302. In one embodiment, onloader 302 includes a first
magazine (MAG) 303-1 and a second magazine 303-2 that respectively
store multiple assembly strips 305, and a pick-and-place mechanism
306 for moving assembly strips 305 from magazines 303-1 and 303-2
onto conveyor 301 using known techniques. From onloader 302,
conveyor 301 transfers assembly strips 305 to cut/form apparatus
320, functional test apparatus 330, and singulation apparatus 350,
respectively, for processing in the order described below.
[0030] Referring to center-left region of FIG. 3, according to an
embodiment of the present invention, lead length cut/form apparatus
320 includes a lead length cut mechanism 322, a lead preform
mechanism 324, and a lead form mechanism 326. Lead length cut
mechanism 322, lead preform mechanism 324, and lead form mechanism
326 include movable portions that are reciprocated by drive
apparatus 310, and are successively arranged along the path of
conveyor 301 such that leads 435 (see FIG. 5(A)) of each assembly
strip 305 are successively cut, preformed, and formed in the manner
described below.
[0031] FIGS. 6(A), 6(B), and 6(C) are simplified cross-sectional
side views showing representative portions of lead length cut
mechanism 322, lead preform mechanism 324, and lead form mechanism
326, respectively, in additional detail. In one embodiment, each
mechanism is formed as a separate unit mounted on base 309. Those
of ordinary skill in the art will recognize that two or more of
these mechanisms may be combined to perform the cutting,
preforming, and forming processes using less than three separate
mechanisms. Further, additional mechanisms may be added to
facilitate a more gradual lead forming process.
[0032] Referring to FIG. 6(A), lead length cut mechanism 322
includes an anvil 610, a lead length cut die 615, and a lead length
cut punch 620. Anvil 610 is mounted on base 309 and supports
package 520 of IC device 440 during the lead length cutting
process. Lead length cut die 615 is also mounted on base 309, and
includes upper edges 617 that support leads 435, and serve as one
part of the lead cutting mechanism. Lead length cut punch 620 is
movably mounted over anvil 610, and is connected to the cam
mechanism of drive apparatus 310 such that it reciprocates in
vertical direction (indicated by the two-headed arrow Y). Lead
length cut punch 620 includes lower edges 622 that serve as the
second part of the lead cutting mechanism. During the lead length
cutting process, the assembly strip is moved such that IC device
440 is located between anvil 620 and lead length cutting punch 620
(i.e., the assembly strip is moved perpendicular to the page), and
then punch 620 is moved downward (toward die 615) to sever the end
of each lead 435. Punch 620 is then moved upward, and the assembly
strip is moved to position another IC device for the lead length
cutting process.
[0033] FIG. 6(B) shows lead preform mechanism 324, which includes a
lower (first) anvil 630, a lead preform punch 640, and an upper
(second) anvil 645. Lower anvil 630 is mounted on base 309 and
supports package 520 of IC device 440 during the lead preforming
process. Lower anvil 630 also includes shoulders 632 that support a
portion of leads 435 located adjacent to package 520, and chamfered
surfaces 634 that have, for example, a 45 downward slope relative
to the plane defined by the assembly strip. Lead preform punch 640
is movably mounted over anvil 610, and is connected to the cam
mechanism of drive apparatus 310 such that it reciprocates in
vertical direction. Lead preform punch 640 includes lower chamfered
surfaces 644 that have the same slope as chamfered surfaces 632
formed on lower anvil 630, and are positioned directly over
chamfered surfaces 632. Upper anvil 645 is slidably mounted on
preform punch 640, and includes shoulders 647 that cooperates with
shoulders 632 of lower anvil 630 to support the portion of leads
435 located near package 520 during the preform process. During the
lead preform process, the assembly strip is moved such that IC
device 440 is located between lower anvil 630 and lead length
cutting punch 640 (i.e., perpendicular to the page), and then punch
640 is moved downward (toward lower anvil 630). First, shoulders
647 of upper anvil 645 contact the portions of leads 435 located
adjacent to package 520 (i.e., these lead portions are pinched
between shoulders 632 and shoulders 647). Next, preform punch 640
moves downward to bend leads 435 at a 45 angle between chamfered
surface 634 and chamfered surface 644. Punch 640 is then moved
upward, and the assembly strip is moved to position another IC
device for the lead preform process.
[0034] FIG. 6(C) shows lead forming mechanism 326, which includes a
lower (first) anvil 650, an upper (second) anvil 660, and a cam
portion 670. Lower anvil 650 is mounted on base 309 and includes a
trough that receives and supports package 520 of IC device 440
during the lead forming process. Lower anvil 650 also includes a
pair of rails 652 that supports a portion of leads 435 located
adjacent to package 520. Upper anvil 660 is movably mounted over
anvil 610, and is connected to the cam mechanism of drive apparatus
310 such that it reciprocates in vertical direction, and includes
shoulders 662 that cooperates with rails 652 to hold portions of
leads 435 located near package 520 during the lead forming process.
Cam portion 670 is rotatably connected to upper anvil 660, and
includes a cam form pad 672 that contacts and bends the free ends
of leads 435 during the lead forming process to form feet at the
free ends. During the lead forming process, the assembly strip is
moved such that IC device 440 is located between lower anvil 650
and upper anvil 660, and then upper anvil 660 is moved downward.
First, shoulders 662 of upper anvil 660 contact the portions of
leads 435 located adjacent to package 520 (i.e., these lead
portions are pinched between shoulders 662 and rails 652). Next,
cam portion 670 rotates inward such that cam form pads 672 press
leads 435 against rails 652, thereby bending leads 435 between cam
form pads 672 and rails 652 to form feet. Upper anvil 660 and cam
portion 670 are then moved upward, and the assembly strip is moved
to position another IC device for the lead forming process.
[0035] FIGS. 7(A), 7(B) and 7(C) are end views showing assembly
strip 305 as it is processed by lead length cut/form apparatus 320
(shown in FIG. 3). Note that each of lead length cut mechanism 322,
lead preform mechanism 324, and lead form mechanism 326, which are
described above with reference to FIGS. 6(A) through 6(C), include
multiple processing sites for cutting, preforming, or forming the
leads of one or more rows of IC devices simultaneously.
Specifically, as shown in FIG. 7(A), leads 435 of one row of IC
devices 440 are cut by lead length cut mechanism 322 (FIG. 6(A)) at
a point adjacent to lead tie bars 415 (i.e., such that each lead
435 becomes a cantilever structure with a fixed end supported by IC
package 520). Next, as shown in FIG. 7(B), leads 435 are bent
downward relative to package 520 (i.e., out of plane PI defined by
assembly strip 305) by lead preform mechanism 324 (FIG. 6(B)) at an
angle of approximately 45. Finally, as shown in FIG. 7(C), the free
ends of leads 435 are bent by lead form mechanism 326 (FIG. 6(C))
to form feet 437 that define a second plane P2 located below plane
P1. Because all three procedures shown in FIGS. 7(A) through 7(C)
(i.e., lead cut, lead preform, and lead form) are performed by
apparatus 320 before functional testing, total manufacturing costs
are reduced because separate lead cutting and lead forming
apparatus are not required. That is, total cost is reduced because
each of lead length cut mechanism 322, lead preform mechanism 324,
and lead form mechanism 326 are driven by a single mechanism (i.e.,
drive apparatus 310), instead of two or more drive mechanisms that
are required using conventional methods. Further, because lead
length cut mechanism 322, lead preform mechanism 324, and lead form
mechanism 326 are linked by conveyor 301 such that assembly strips
305 are automatically transferred between these mechanisms, damage
to leads 435 that can occur during transportation between two
separate systems is also avoided, further reducing total production
costs.
[0036] FIG. 8 is an enlarged plan view showing IC 440 after the
cut/form procedure performed by apparatus 320 is completed. Note
that leads 435 are separated from lead tie bars 415, but ends 522
of IC device 440 remains connected to connection structures 422 of
assembly strip 305. Accordingly, IC devices 440 remain fixedly
connected to assembly strip 305 throughout the lead cutting and
forming process, thereby facilitating automated testing (described
below).
[0037] Returning to FIG. 3, after lead formation, assembly strips
305 are then passed via conveyor 301 to functional test apparatus
330. Functional test apparatus 330 includes a separate ball-screw
drive 332, a test module 334, and tester (e.g., a computer or
workstation) 336.
[0038] FIGS. 9(A) and 9(B) are side and partial front views showing
functional test apparatus 330 in additional detail.
[0039] Referring to FIG. 9(A), functional test apparatus 330
includes an anvil 910 that is mounted on base 309. Mounted over
anvil 910 is a probe assembly 920, which includes a lower plate 924
that supports a probe array 930. Mounted above lower plate 924 is a
non-conductive intermediate plate 926 and a non-conductive top
plate 928. Sandwiched between intermediate plate 926 and top plate
928 is a printed circuit board (PCB) 940 including a socket 945
from which a cable 948 extends between PCB 940 and tester 336.
Probe array 930 extends from a lower surface of lower plate 924,
and includes probes (e.g., dual spring pogo pins) 935 having one
end extending toward anvil 910, and a second end pressed against
corresponding contact pads (not shown) formed on a lower surface of
PCB 940.
[0040] Referring to FIG. 9(B), anvil 917 includes several troughs
915 and pairs of rails 917, each pair of rails 917 being located
along the outside edges of an associated trough 915. Troughs 915
are shaped to receive and support the lower package body of IC
devices 440, and rails 917 are shaped to support a portion of leads
435 located adjacent to the package body during functional testing,
which is described below. Note that the bent portion of leads 435
(i.e., including feet 437) extend over rails 917 such that feet 437
are positioned over lands 919.
[0041] During operation, conveyor 301 (shown in FIG. 3) pushes
assembly strip 305 in the X direction such that a group of IC
devices 440 are positioned on anvil 917 with leads 435 located
under probes 935. The ball-screw drive 332 moves probe assembly 920
downward towards anvil 910 such that the ends of probes 935 contact
leads 435. Once the probe assembly is fully lowered, the system
controller sends a "start test" signal to the tester 336 to
initiate the functional test. As indicated in FIG. 9(B), in one
embodiment, probes 935 include a first set 935A which contacts an
upper portion of leads 435 (i.e., adjacent the package body), and a
second set 935B that subsequently contacts feet 437. Because first
probe set 935 contacts leads 435 adjacent to the package body, IC
devices 440 are securely held in position before second probe set
935B contacts feet 437. Note that first probe set 935A serves both
to hold IC devices 440 during testing, and to provide enhanced
electrical connection between the tester (not shown) and IC devices
440. Accordingly, functional test apparatus 330 facilitates testing
IC devices 440 after leads 435 are fully formed, and with minimal
risk of damaging or bending leads 435. Test signals are then
transmitted to and from tester 336 via cable 948, socket 945, PCB
940, and probes 935 to leads 435. As discussed above, leads 435 are
connected, for example, by bond wires to the IC die packaged
therein, thereby facilitating functional testing of the IC die. An
optional marking system (not shown) may be used to mark IC devices
440 that fail functional testing. Upon completing functional
testing of the group of IC devices 440, tester 336 sends an "end of
test" signal to the system controller. Ball-screw drive 332 then
raises probe assembly 920, and the conveyor pushes assembly strip
305 to position a new group of IC devices 440 under probes 935.
This functional testing process is then repeated until all IC
devices 440 on assembly strip 305 are tested.
[0042] Note that functional test apparatus 330 is described above
as testing groups of ten IC devices 440 (i.e., in a so-called "2 UP
X 5" arrangement). Accordingly, multiple IC devices 440 are tested
simultaneously, thereby minimizing overall production costs. Of
course, other arrangements may be utilized to test a different
number or pattern of IC devices.
[0043] Returning to FIG. 3, upon leaving functional test apparatus
330, assembly strips 305 pass through an optional lead vision
inspection station 340 including a first vision system 342 that
checks the leads of each IC device 440 using known techniques. In
particular, vision system 342 checks for damaged leads, bent leads,
missing leads, or short leads.
[0044] After lead vision inspection, assembly strips 305 are passed
to singulation apparatus 350. In one embodiment, singulation
apparatus 350 utilizes standard equipment that includes an anvil
and a singulation die mounted on the system base, and a stripper
and a punch movably mounted over the anvil and connected to the cam
mechanism of drive apparatus 310 (see FIG. 3A). Similar to
structures described above, the anvil includes a package support,
and the singulation die supports the rails of the assembly strip.
After positioning the assembly strip, the stripper is moved
downward against the rails, and the punch then pushes the package
downward. Referring to FIG. 8, this downward force breaks the tie
bars (not shown) connecting ends 522 of each IC device 440 to
connecting structures 422 of assembly strip 305, thereby separating
IC device 440 from assembly strip 305. Referring to FIG. 3,
separated lead frames are passed into a scrape lead frame (L/F)
chute 352, and the separated IC devices 440 are passed to a buffer
station 360.
[0045] Buffer station 360 includes a second vision system 362 that
performs an automated inspection of each IC device 440 using known
techniques. In particular, vision system 362 checks each IC device
440 for package surface damage, voids, and device markings. Buffer
station 360 then segregates the IC devices for manipulation by an
offloading mechanism 370. In particular, buffer station 360 routes
the "good" IC devices to a chute feeding into a first set of
storage tubes 380. Alternatively, buffer station 360 routes "bad"
IC devices (i.e., rejects from functional test, vision system 342,
or vision system 362) to a chute feeding into a second set of
storage tubes 390.
[0046] Although the present invention has been described with
respect to certain specific embodiments, it will be clear to those
skilled in the art that the inventive features of the present
invention are applicable to other embodiments as well, all of which
are intended to fall within the scope of the present invention.
* * * * *