Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1999-11-15
2003-06-17
Voeltz, Emanuel Todd (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C438S014000
Reexamination Certificate
active
06580957
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a laser marking technique and, more specifically, to an apparatus and method for efficiently marking the surface of a singulated article such as a packaged semiconductor device using a laser, wherein the laser is substantially continually in use.
2. State of the Art
As the production rates of semiconductor devices (frequently referred to as “chips”), including packaged die, have increased, manufacturers of chips have searched for ways to quickly and efficiently mark their product. Typically, finished semiconductor devices are marked with the company name, a part or serial number, or other information such as lot number. As production rates continue to increase, however, current marking techniques may not efficiently meet the demand.
Typical conventional marking methods utilize a mechanical ink transferring device to stamp each individual semiconductor device or, at best, a pair of devices. Such an ink stamping apparatus is capable of marking approximately 2,500 semiconductor devices per hour or, if paired for marking, 5,000 per hour. These figures, while impressive, still present a significant bottleneck in the production cycle. In addition, ink stamping methods add an inherent lag time to the production cycle before product is shipped because of additional set-up time to achieve a good quality mark and additional cure time associated with ink drying. Moreover, mold release materials (such as carnuba wax or silicon) may cause the ink to not adhere to the plastic or ceramic package.
Manufacturing processes using such an ink stamping method generally include the ink stamping step just after post-encapsulation processing (if the package is to be marked) to allow for an extended (48 hour) drying or cure time without affecting the production rate. Such early marking may result, however, in the marking of chips which are later proven defective in a post-encapsulation burn-in cycle. Even if chips are ink-stamped at the end of the production cycle, curing (even if by UV rather than heat-induced) is necessary as a last step.
Another problem associated with ink stamping methods is that the quality (definition, consistency) of ink stamped marks may vary substantially over time. This variation may be dependent upon the pressure (force) applied by the stamp, the quantity of ink applied, variations in ink pigment and carrier (solvent) content, ambient temperature and humidity, and/or the condition (wear, ink residue) of the surface of the stamp. In any event, the character of a stamped mark may vary widely from chip to chip. Moreover, volatile solvents may present ventilation problems in a cleanroom environment.
As a result of the deficiencies associated with ink stamping, it has become increasingly popular to use a laser beam to mark the surface of a chip package. Unlike ink stamping, laser marking is fast, requires no curing time, and produces a consistently high-quality mark with minimal set-up time. In laser marking apparatuses, the laser beam basically burns a mark into the surface of the article of manufacture to produce a permanent mark, in contrast to inked marks, which may smear, degrade, fade or wear off. In the case of a packaged chip, the laser marking creates a different reflectivity from the rest of the package surface. Thus, by holding the chip at an angle to a light source, the information inscribed on the chip by the laser can easily be read.
Various machines and methods have been developed for marking a chip or other article of manufacture with a laser. As illustrated in U.S. Pat. No. 5,357,077 to Tsuruta, a plurality of semiconductor devices is placed in a tubular holder and transported by a coextensive group of conveyor belts to a laser for marking. Similarly, in U.S. Pat. No. 4,638,144 to Latta, Jr., electronic parts in the form of strips of lead frame supported components are conveyed to a laser marking station in magazines, unloaded, laser marked, and then reloaded into magazines. Likewise in U.S. Pat. No. 4,375,025 to Carlson, a strip of electronic components is conveyed by drive wheels to and from a position where a laser beam inscribes various characters or other information on the component surfaces. None of the above-mentioned references, however, disclose conveying articles of manufacture along multiple, separate paths so that a single laser can be marking articles on one path while articles are moved into marking position along another path. Thus, the lasers in the above-mentioned documents are inactive for substantial periods while awaiting articles of manufacture to be moved into the marking position.
U.S. Pat. No. 4,370,542 to Mills et al. discloses a laser marking apparatus for marking a cable. The apparatus sequentially moves laterally adjacent cables along a marking platen and selectively positions and operates a laterally translatable laser to mark a stationary cable portion while another cable portion is being moved. The device, however, is not capable of marking semiconductor devices or similar singulated articles of manufacture.
Thus, it would be advantageous to provide a marking apparatus and method thereof that efficiently utilizes the speed and accuracy of a laser to precisely and clearly mark singulated semiconductor devices. Moreover, it would be advantageous to develop a method and apparatus for marking the surface of a semiconductor device that can mark in excess of 10,000 chips per hour.
SUMMARY OF THE INVENTION
According to the present invention, a laser marking apparatus and method are disclosed wherein a singulated article such as a packaged semiconductor device (chip) is subjected to a laser beam for marking purposes. While the laser beam is actively marking a chip at one marking location, another chip is moving into position at another, adjacent marking location accessible by the same laser beam source. Once a chip has been marked, the laser source alternates to the adjacent marking location and begins marking another chip while the previously marked chip is being replaced by an unmarked chip. In this manner, the laser is substantially continually marking a chip at one or the other of the marking locations and is not waiting for chips to be positioned at a marking location.
In a particular and preferred aspect of the invention, more than one chip may be present at each marking location. That is, a plurality of chips is positioned (preferably in a row) at each marking location, and all of the chips at one marking location are marked in succession and then replaced by a like plurality of unmarked chips while the laser marks a plurality of chips at another marking location.
In another particular and preferred aspect of the invention, a single lens is positioned over a marking field including two or more locations such that chips positioned at any point within the marking field can be marked by translating the laser beam but without moving the lens. In such an arrangement, the number of marking locations within a marking field is ultimately limited by the size of the lens. This affects the quantity of chips on adjacent paths that can be reached by a laser beam passed through the lens, and the speed of the microprocessor controlling the speed (vectoring) of the laser marking. As the size of the lens increases, the quality of marking resolution may decrease as the size of the impingement point of the laser beam increases unacceptably. As speeds of the galvanometers controlling the laser increase, the speed of marking may ultimately be limited by the speed at which chips can be positioned at and removed from a marking location. Currently, lasers can write approximately 160 characters per second (c.p.s.); however, some newer galvanometers afford operational speeds of over 200 c.p.s.
In yet another particular aspect of the invention, the chips are gravity fed from magazines onto tracks inclined at a particular angle relative to the support surface. The chips freely slide along the track when not retained by various components of the apparatus. For example, m
Gain, Jr. Edward F.
Micro)n Technology, Inc.
Todd Voeltz Emanuel
TraskBritt
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