Lead formation, assembly strip test, and singulation system

Details Lead formation, assembly strip test, and singulation system Lead formation, assembly strip test, and singulation system

2001-09-12

2004-04-13

Cuneo, Kamand (Department: 2829)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C324S755090

Reexamination Certificate

active

06720786

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to integrated circuits, and more particularly to methods and automated systems for efficiently testing integrated circuits.
BACKGROUND OF THE INVENTION
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.
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 bond pad
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
.
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.
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.
What is needed is an efficient and cost effective system and methods 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
The present invention is directed to a system 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.
Each assembly strip processed in accordance with the present invention includes multiple rows and columns (e.g., 5×12) 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.
In accordance with a disclosed embodiment of the present invention, a system for processing ICs mounted on assembly strips includes 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.
In accordance with an aspect of the present invention, a single drive apparatus is provided to manipulate both the lead length cut/form apparatus and the singulation apparatus, thereby reducing costs by eliminating separate drive mechanisms for these two operations. Note that the functional test apparatus, which is located between the lead length cut/form apparatus and the singulation apparatus, 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 apparatus to the functiona

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