Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Making plural separate devices
Reexamination Certificate
2002-02-27
2004-05-04
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Making plural separate devices
Reexamination Certificate
active
06730545
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of IC chip manufacturing. More particularly, embodiments of the present invention relate to a method of back-end manufacturing IC packaged chips using an integrated automated back-end IC manufacturing assembly.
BACKGROUND ART
Conventional back-end IC manufacturing facilities, at contract assembly houses as well as several original equipment manufactures (OEMs), have a moderate to low level of automation and equipment integration. These lines typically require several manual steps and depend upon operator intervention for many, if not nearly all, operation, maintenance, lot management and inspection steps. Since this is typically a batch type process, there maybe a high level of work-in-progress (WIP) inventory, as well as relatively high cycle times. This type of factory management may not be suitable for manufacturing where flexibility is key, and daily operation may require several changeovers in die, package and leadframe types.
Presently, the back-end manufacturing process for ICs (i.e. from manufactured wafer to tested and packaged die) is labor intense. In order to manufacture an IC chip, in the back-end, from the initial step of wafer reception to the packaging and shipping of the finished chip, there are many personnel and specialized pieces of equipment involved. Further, the process of back-end manufacturing an IC chip is a relatively long one. The complete process typically takes anywhere from four to six weeks to obtain a final packaged chip, and generally takes on the order of 1.5 to 2 weeks when using special “rush” or “hot lot” procedures.
Due to the length of the back-end manufacturing process and the required manpower, IC (IC) chips are generally manufactured in batches. That is, the process of back-end manufacturing a single IC is done on a large scale with individual large batches running through discrete process steps. This large scale is utilized to, add a standard of efficiency to an otherwise complex process. For instance, a wafer that is received from an outside vendor is cut into strips. Each strip may contain approximately 200 die, and there may be 50 strips in a batch. Therefore, a typical batch of ICs, formed through a single back-end IC manufacturing process, may contain 10,000 or more IC chips.
An embodiment of a conventional batch-oriented back-end IC manufacturing process is illustrated in FIG.
1
. This embodiment illustrates the length of a conventional back-end IC manufacturing process. Batches of chips move from one stage of the process to the next. In block diagram
100
, the back-end manufacturing line includes front-of-line portion
100
A, end-of-line portion
100
B, test
128
, and finish portion
100
C. The back-end IC manufacturing process begins with die attach station (D/A)
110
. Although a die preparation process is required, this is typically done outside front-of-line portion
100
A. Furthermore, the die preparation process may take place in a different location than the rest of the back-end IC manufacturing process.
Front-of-line portion
100
A includes die attach station (D/A)
110
, cure station
112
, plasma treatment station
114
, wire bond station (W/B)
116
, and another plasma station
118
typically a plasma cleaning station). The back-end IC manufacturing process includes many aspects which require human material handling stations (HM)
150
. HM
150
steps are represented in
FIG. 1
with arrows. These HM
150
steps include transferring the batch from one step of the process to the next, as well as between specific manual visual inspection stations (MVI)
105
.
In the front-of-line portion
100
A, the cure station
112
may carry out a curing process in a machine designed to heat a batch of strips to a temperature of about 150 degrees Celsius, for a period of one hour, in order to cure the glue used in the die attach step. This cure station
112
is followed by a plasma station
114
cleaning step utilizing oxygen (O
2
) or Argon (Ar). The next step is wire bond station (W/B)
116
followed by MVI
105
. Another plasma station
118
cleaning step is done following wire bond station (W/B)
116
and another MVI
105
. The plasma station
118
cleaning step is similar to plasma station
114
cleaning step, and each plasma step may last anywhere from 30 minutes to one hour.
With reference still to
FIG. 1
, back-end manufacturing line
100
continues with an end-of-line portion
100
B where need for human interaction also exists. End-of-line portion
100
B begins with mold station
120
. HM
150
is utilized to move the batch through each MVI
105
. The next step in end-of-line portion
100
B is post mold cure station (PMC)
122
. PMC
122
is a curing step which requires a temperature of 175-degree Celsius and a timeframe of approximately 5 hours. After PMC
122
, the strip undergoes solder ball attach station (SBA)
124
. Following SBA
124
, MVI
105
takes place to ensure proper attachment of the ball to each strip in the batch. The batch is then processed through saw station
126
. Saw station
126
separates the batch into individual IC chips. The final step in end-of-line portion
100
B is MVI
105
of the completed saw station
126
step. Throughout the back-end manufacturing process, MVI
105
normally includes additional quality control and assurance measures.
Following the completion of end-of-line portion
100
B, back-end manufacturing line
100
continues with test portion
128
. In test portion
128
, as illustrated in the previous portions, the need for human interaction includes human handling during both the testing, and inspecting phases.
With reference still to
FIG. 1
, back-end manufacturing line
100
further illustrates the final portion of the back-end IC manufacturing process. The final portion is illustrated as finish portion
100
C. Finish portion
100
C includes mark station
130
, dry bake station
132
, and tape and reel station (T/R)
134
. Most significantly, dry bake station
132
is a 24-hour dry bake step performed prior to T/R
134
. Dry bake station
132
is required by modern back-end IC manufacturing processes in order to meet the stringent moisture sensitivity level (MSL) 3 IC chip packaging requirements. Specifically, MSL 3 is a moisture level benchmark that meets demanding requirements placed on back-end IC manufacturers.
Therefore, in a typical back-end IC manufacturing line, a production cycle may span a period of four to six weeks. Moreover, the processing cycle may be done at the batch level which results in approximately 10,000 or more IC chips per stage. This batch level process results in a large inventory of on band IC chips. In an effort to control production overruns, a manufacturer will normally use a build-to-forecast model based on contract back-end IC manufacturing techniques.
Disadvantages of the batch level process include the large minimum order size and the long timeframe for the manufacture of a specific type of IC. For example, if a customer requests an uncommon or highly demanded type of IC, e.g., one that is not in inventory, they would typically place a special order. In this case, a small order may not be economically worthwhile. Specifically, the batch level process is generally cost prohibitive unless the customer orders a specified minimum amount of product. Further, it generally takes a minimum of four to six weeks to process a special order. Moreover, this minimum time conventionally includes time to reset and/or maintain machinery, and/or instruct inspectors on expected differences in the back-end IC manufacturing process.
Another disadvantage of the conventional batch process is the multitude of procedures using human interaction with the batch in transporting the batch from stage to stage, or during certain stages, such as visual inspection (HM). These procedures include MVI, quality assurance (QA), and handling throughout the entire back-end IC manufacturing process. Specifically, MVI typically involves a pause in the back-end IC manufacturing process so that an operator can manual
Chang Bo Soon
Rodgers Thurman J.
Cypress Semiconductor Corporation
Niebling John F.
Stevenson Andre′ C.
Wagner , Murabito & Hao LLP
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