Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means
Reexamination Certificate
2003-05-06
2004-08-10
Osele, Mark A. (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With microwave gas energizing means
C156S583200, C029S426300, C029S426600, C438S464000
Reexamination Certificate
active
06773543
ABSTRACT:
The present invention relates generally to the delivery of bare die for placement onto printed circuit boards during the assembly process and more specifically, a method and apparatus for concurrently removing, inverting and transporting flip-chips from a semiconductor wafer to an automated pick-and-place machine for subsequent placement onto a circuit board substrate. More particularly, the invention relates to the accelerated throughput of the direct bare die feeding process which performs the function of removing known to be good die from a sawed wafer disposed on a adhesive coated film, inverting, so as the active surface is downward, and subsequently conveying to a distal pick-up location that is accessible to the assembly machine.
BACKGROUND OF THE INVENTION
The present invention is an improvement of the throughput characteristics of a die extracting and delivery system associated with automated pick and place equipment, particularly those systems requiring the extraction, flipping and placement of numerous die or components at high speeds. It can be appreciated that methods for removing and delivering bare die from a wafer have been in use for many years. The present invention includes, among other aspects and features, a novel method for tandem handling of a multitude of die employing a linear array of vacuum nozzles for buffering, transferring and transporting the die.
Typically, the method for delivering bare die in the production of printed circuit boards (PCB), is to use a conventional tape and reel feeder whereby the bare die are “prepackaged” by first removing them from the wafer and predisposing them within a linear strip having pockets equidistantly embossed therewithin and covered by a thin film or cover tape. Alternative means would include placing the die into a matrix tray which has been portioned for each die. The primary concern with traditional methods for delivering bare die is the costs and reliability associated with placing the die into the embossed tape and then having to remove the flip-chip and discard the cover and pocket tape as waste during the assembly process. The preferred method to this double handling would eliminate the pre-packaging of the die by extracting the die directly from the wafer, placing it onto a conveyance means and presenting the die directly to a placement machine. An example of such a direct die feeder is shown in U.S. Pat. No. 6,173,750 issued to Davis et al, as well as U.S. Pat. No. 5,671,530 issued to Combs et al. These patents disclose an apparatus that removes die from a vertically oriented wafer and presents the die for subsequent placement onto a PCB. Because the referenced Davis patent is intended to replace the traditional tape feeders mentioned above, it is designed to interface to the placement machine as if it were a standard tape and reel feeder.
The present invention is considered a further improvement to a direct die from wafer feeder used with automated pick-and-place equipment, particularly those systems requiring the manipulation and placement of numerous die at high speeds. The present invention includes, among other aspects and features, a novel means for holding, turning over, and parallel queuing of die or flip-chips using a multitude of vacuum ports and a rotatable picking member.
There are numerous methods of attaching a die to the substrate of a PCB. The most common method is to bond wires to the upward facing circuit of a die that has been previously placed and affixed to the substrate. Electrical connections are thereby facilitated with the “bonding” of wires to pads on the exposed surface of the die to corresponding contacts on the substrate. In an alternative method, solder bumps are placed on the die circuit and then the die is turned over or “flipped” so as the solder bumps are aligned with corresponding pads on the substrate. The mechanical and electrical connections are accomplished by melting the solder bumps within an oven. The process is well known in the art as a controlled-collapse chip connection, or simply the C-4 process. It is a common practice in the industry to refer to a flip-chip as a bumped bare die or chip, the term “flip” is appended to chip in as much as the bare die must be turned over during the delivery process so as the circuit side of the flip-chip contacts the PCB. In this specification the term “die” is used prior to turning the chip over, at which time the term flip-chip will generally be used.
The Davis U.S. Pat. No. 6,173,750 has an inherent maximum throughput governed by the concatenated steps of; (1) extracting, (2) flipping and (3) depositing onto the shuttle one die at a time. Furthermore, in the prior art, transference of the die from the wafer occurs only when the die shuttle is in the re-fill or loading position, hence when the shuttle is in the distal export location and waiting for the placement machine, the die extraction activity must remain in a wait state. Therefore, the inability to multiplex the “die picking from the wafer process” with the “die delivery to the placement machine process” significantly limits throughput. Accordingly the motivation for the present invention relies on the requirement to concurrently perform these operations, thusly providing flip-chips at a rate that is synchronous with the cycle time of the placement machine.
The present bare die feeder apparatus may not be as suitable for accelerated throughput requirements associated with circuit boards having a relatively high flip-chip component population, such as is the case with cell phones and similar miro-electronic devices. The metric for capacity is generally considered to be the total components which can be placed in a unit of time. Therefore the feeder cycle time is a function of the total number of feeders on the machine divided into the rated capacity of the placement machine. In the case of a multi-head placement machine the placement rate may often exceed the die feeder delivering throughput capabilities and accordingly the assembly process is required to enter a wait cycle that compromises productivity and thereby increases the overhead.
In these respects, the method for rapid bare die removal from a wafer according to the present invention is considered to be an improvement over the conventional concepts and designs of the prior art, and in so doing provides for an apparatus primarily developed for the purpose of the accelerated delivery of die as they are co-processed and queued for subsequent placement.
The present invention is directed towards a dual stage approach whereby flip-chips are removed from a wafer concurrently with the flip-chips being presented for placement. As described herein, one embodiment of the present invention is directed toward buffering the flipped-chips while the shuttle is being unloaded by the placement machine
SUMMARY OF THE INVENTION
In view of the foregoing limitations inherent in the known types of methods for delivering bare die now presented in the prior art, the present invention provides a new method for concurrent bare die removal from a wafer containing a plurality of flip-chips wherein a multiplexed or timeshared co-processing method can be utilized for the rapid throughput of die as they are removed from the wafer for subsequent placement.
The general purpose of the present invention, which will be described subsequently in greater detail, is to provide a new method for accelerating the die removal from a wafer that has many of the advantages of the method for delivering bare die mentioned heretofore and a novel feature that results in a new method for accelerated flip-chip delivery from a wafer which is not anticipated, rendered obvious, suggested, or even implied by any of the prior art method for delivering bare die, either alone or in any combination thereof.
To attain this, the present invention generally comprises a die acquisition station member, containing a nozzle, a die intermediate transfer station, containing a number of nozzles and a conveying method, such as a shuttle, which translates flip-chips placed on noz
Basch Duane C.
Basch & Nickerson LLP
Delaware Capital Formation Inc.
Osele Mark A.
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