Coating apparatus – With means to apply electrical and/or radiant energy to work...
Reexamination Certificate
1998-02-02
2001-03-13
Edwards, Laura (Department: 1734)
Coating apparatus
With means to apply electrical and/or radiant energy to work...
C118S641000, C118S058000, C118S066000, C118S076000, C118S257000, C118S301000
Reexamination Certificate
active
06200386
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to removal of markings from integrated circuit packages, and more specifically to apparatus for de-marking laser-marked thin packages by covering the marked surface with a material suitable for re-marking.
It is known in the art to apply markings to surfaces of integrated circuits packaged in filled-polymer, transfer-molded packages as well as to other packages such as preformed ceramic packages into which an integrated circuit (IC) die is inserted. Marking techniques known in the art include ink-marking, wherein a package surface is stamped or rolled with a wet ink mark, and laser marking, wherein a package surface receives identification indicia actually engraved therein with a laser beam. Ink marking is relatively slow, requires periodic changing of the applicator to change marking indicia as well as cleaning of the applicator as ink accumulates thereon, and requires drying of the ink after application. Further, ink marks may smudge or subsequently be abraded off of the package surface. As a consequence, use of laser marking is becoming more prevalent due to the speed of marking, the indelibility of the mark once applied, and the ability to readily change the marking indicia to be applied through a re-programming of the computer controlling movement of the laser beam or a mirror or mirrors reflecting same to the package surface. One particularly efficient laser-marking apparatus is disclosed in pending U.S. patent application Ser. No. 08/590,919, filed Jan. 24, 1996 now U.S. Pat. No. 5,937,270 by the present inventor and assigned to the assignee of the present invention.
Sometimes it becomes necessary to remove marks previously applied to an IC package. In the case of ink-marked IC packages, removal is relatively easily effected using solvents or a mild abrasive action which scrubs the package surface without removing package material. However, in the case of a laser-marked IC package, a preferred method of removal is abrasive removal, wherein a layer of package material is removed from the package surface to a depth sufficient to remove the engraved laser mark, and preferably in a manner to provide a reflective surface suitable for re-marking. Such a method and apparatus for effecting same, is disclosed in U.S. patent applications Ser. Nos. 08/907,962 and 08/909,187, each filed Aug. 11, 1997 now U.S. Pat. Nos. 5,938,508 and 5,997,388 by the present inventor and Tony T. Ibarra and assigned to the assignee of the present invention.
There are some widely-employed, thin IC package configurations which are not, however, readily susceptible to abrasive engraved mark removal. In such configurations, the thickness of the package material between the marked package surface and a surface of the IC die within the package is insufficient to permit mark removal by a subtractive technique involving removal of package material to a depth at least equivalent to the bottoms of the engraved markings without compromising package integrity. Wire-bonded IC dice with wire loops extending above the active surface of the IC die and well into the package material present particular challenges to abrasive mark removal. In some extreme cases, the forces involved in abrasive removal will simply destroy the package and enclosed IC.
One such example of a thin plastic package configuration presenting the above-mentioned de-marking problem is a so-called Thin Small Outline Package, or TSOP. Another is a Thin Quad Flat Pack, or TQFP. Such packages are dimensioned with a total package thickness, excluding lead fingers, of less than about one-half the thickness of a plastic Small Outline J-lead package, or SOJ. In terms of actual filled-polymer package dimensions, a TSOP or TQFP plastic package may be less than 0.040 inch in thickness, leaving little or no margin for removal of package material above the active surface of the encased IC die.
Thus, when it is necessary or desirable to de-mark a thin, laser-marked plastic package without damage thereto and in a manner which will facilitate subsequent re-marking, the prior art is devoid of an adequate solution.
BRIEF SUMMARY OF THE INVENTION
The present invention includes apparatus for additively de-marking an IC package marked on an exterior surface thereof.
A broad embodiment of the apparatus includes devices for dispensing an opaque covering material over an IC package surface bearing engraved markings, such as laser markings. The covering material may be, or be alterable as by application of heat to be, of sufficiently low viscosity to enter and fill the indentations in the package surface comprising the markings. The covering material may also be sufficiently wettable in its fluid state to the filled-polymer package material and with sufficiently low surface tension so as to spread evenly over the package surface without forming a meniscus at the peripheral edges of the surface and trapping an undesirable thickness of coating material thereon. The covering material may be indelible, i.e., permanent, under normal operating conditions to be encountered by the package, and bondable to the package surface after application as, by way of example, by thermal bonding or curing. After final bonding, the covering material may present a layer of sufficient thickness to withstand re-marking by laser without damage to the package or encapsulated die, as well as exhibiting an exposed surface of sufficient reflectivity to facilitate such re-marking.
The apparatus of the invention is preferably automated, and includes a packaged IC handling device. The handling device may be a multi-cavity receptacle, such as a platen or turntable for carrying a plurality of packaged IC's, a track or belt-type conveyor, a robotic arm, or other handling device as known in the art. The apparatus of the invention also includes a covering material applicator, which may comprise either a contact or non-contact applicator and vary in structure and operation depending upon the state of the covering material as it is applied. A pre-treatment device such as a laser or flame-sprayer may optionally be employed to treat the exterior surface to be covered prior to application of the covering material. A curing station may be employed to facilitate post-application solidification of the covering material, or bonding of the covering material to the exterior surface of the IC package.
The covering material may be dispensed in a fluid or gelled state onto the package surface by direct contact of a contact-type dispensing applicator such as a rotatable roller, an open-cell sponge element, or a brush. Alternatively, the covering material may be dispensed in a flowable state from a nozzle or other aperture of a non-contact applicator as a drop, stream or spray while the IC package is stationary thereunder, or as it moves past the applicator. A mask with an aperture sized to the marked package surface may also be used to prevent contamination of the package leads. Subsequent to application, the covering material may be cured to a permanent state bonded to the now-covered package surface by thermal curing effected by passage through an oven or under a heat surface such as an infra-red lamp, heretofore referenced generally as a curing station.
A dam may be formed on the marked exterior package surface prior to application of the covering material to the marked IC package surface, and a flowable liquid or gelled covering material dispensed onto the surface area contained within the dam perimeter. The dam may be sized to encompass the length and thickness of the package, or to rest partially or entirely on the marked package surface. If a dam is to be formed, it may be a preformed dam element applied to the IC package by an applicator from a strip or tape of such elements. Alternatively, the dam may be stenciled or extruded onto the IC package by an applicator.
The covering material may also be applied as a preformed segment of material. For example, a powdered material maintained in segment shape by a volatile fluid binder may be applied
Edwards Laura
Micron Electronics Inc.
Trask & Britt
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