Method for additive de-marking of packaged integrated circuits and resulting packages

A method for additively de-marking a packaged integrated circuit die bearing engraved marking indicia on an exterior surface thereof. The marked surface is covered with an overlayer of material to fill the engraved markings and provide a surface suitable for re-marking. The covering material may be applied in a flowable state by applicator contact or by non-contact dispensing, or may be applied as a preformed segment. The exterior surface to be covered may be pre-treated to enhance bonding of the covering material. The covering material may be bonded to the marked surface in a post-application curing operation. De-marked integrated circuit packages are also disclosed.

BACKGROUND OF THE INVENTION 
The present invention relates generally to removal of markings from 
integrated circuit packages, and more specifically to de-marking 
laser-marked thin packages by covering the marked surface with a material 
suitable for re-marking, as well as to de-marked packages so fabricated. 
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 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 
co-pending U.S. patent applications Ser. Nos. 08/907,962 and 08/909,187, 
each filed Aug. 11, 1997 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 a method for additively de-marking an IC 
package marked on an exterior surface thereof, as well as such de-marked 
IC packages. 
One embodiment of the method includes 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 covering material may be dispensed in a fluid or gelled state onto the 
package surface by direct contact with a dispensing applicator such as a 
rotatable roller, an open-cell sponge element, or a brush. Alternatively, 
the covering material may be dispensed in a fluid 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 is an infra-red lamp. 
A dam may be formed on the marked 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, or may be stenciled or extruded onto 
the IC package. 
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 from a dispensing tape carrying 
multiple segments, and then heated to fluidize the coating material, drive 
off the binder, and cause the covering material to solidify upon cooling 
into a layer bonded to the marked surface. Alternatively, the preformed 
material may comprise a tape segment severed from a tape of covering 
material and adhered to the marked surface. The adherence may be permanent 
upon application, or may be further enhanced by post-application curing. 
Pre-treatment of the package surface to be covered, as by laser or flame 
spray, to enhance bonding of the subsequently-applied covering material 
thereto may also be effected in accordance with the invention.

DETAILED DESCRIPTION 
Referring now to FIGS. 1, 1A and 1B, an exemplary TSOP 10 is depicted in 
the form of a 50-pin Plastic TSOP sold by Micron Technology, Inc. of 
Boise, Id. Package 10 comprises a Dynamic Random Access Memory (DRAM) IC 
die 12 (shown in broken lines) mechanically attached and electrically 
connected to lead frame 14 having lead fingers 16 extending from the 
exterior of a transfer-molded, filled polymer package 20 (generally termed 
a "plastic package" in the art). The total height H of package 10 
including lead fingers 16 is about 0.047 inch maximum, while the actual 
thickness T of the package 20 may range from about 0.039 to 0.045 inch, 
substantially less than 1/20 of an inch. Exterior surface 22 of package 20 
has marking indicia represented by the numbers and letters enclosed by box 
24 engraved thereon as by a laser marker, as known in the art. Such 
indicia may include, in actual practice, numbers, letters, symbols or 
logos, the type of indicia having no effect on the practice of the present 
invention. It will be readily appreciated by those of ordinary skill in 
the art that the thickness of packaging material above die 12 is 
unsuitable for abrasive de-marking, wherein a layer of packaging material 
is removed, as package integrity will almost certainly be compromised, if 
TSOP 10 is not destroyed outright. 
FIG. 2 depicts an exemplary TQFP 50 in the form of a 100-Pin Plastic TQFP 
sold by Micron Technology, Inc. of Boise, Id. For the sake of convenience, 
the same reference numerals have been used in FIG. 2 as in FIG. 1 to 
identify like components. While TQFP 50 employs a package thickness 
slightly exceeding that of TSOP 10, being on the order of about 0.053 to 
0.057 inch, nonetheless, TQFP 50 also is unsuitable for abrasive 
de-marking due to the thin layer of protection afforded by the filled 
polymer package material. 
FIG. 3 depicts an enlarged side sectional view of a portion of surface 22 
of TSOP 10. As can readily be seen, marking indicia 24 comprise recesses 
26 burned in surface 22 in a selected pattern to define letters, numbers, 
symbols or logos, as desired. IC die 12 is illustrated below indicia 24 to 
indicate the close proximity of the active surface 18 of die 12 to the 
bottoms of the recesses 26. FIG. 4 depicts the same portion of surface 22, 
but additively de-marked by the application of a suitable covering 
material 30 thereto. Material 30 preferably comprises a dielectric 
material having sufficiently low viscosity to fill recesses 26 of marking 
indicia 24, wettable to the filled polymer package material so as to 
easily spread over marked exterior surface 22, and exhibiting sufficiently 
low surface tension so as to relax over surface 22 and not form a convex 
meniscus thereover, trapping too great a thickness of covering material 30 
on surface 22. A preferable thickness for covering material 30 is between 
about 0.001 inch and about 0.005 inch. The covering material 30, in one 
embodiment, may be applied in a fluid state, and subsequently cured into a 
permanent solid state bonded to exterior surface 22. Suitable covering 
materials are offered under the HYSOL.RTM. trademark by The Dexter 
Corporation of Windsor, Conn., and more specifically by the Dexter 
Electronic Materials division of Industry, California. Depending upon the 
chosen manner of application, package material and the temperature 
requirements for the covering material in use on the IC package to which 
it is applied, the material may comprise, by way of example and not 
limitation, inter alia: a HYSOL.RTM. two-component heat cure epoxy such as 
an RE2039/EE4183 resin with an HD0242 hardener or an RE2039/EE4183 resin 
with an HD0243 hardener; a HYSOL.RTM. room temperature cure epoxy such as 
an RE2038/EE4143 resin or RE2039/EE4183 resin with an HD3404 hardener, an 
RE2039/EE4183 resin with an HD3561 hardener or a single-component epoxy 
such as ES4212, ES4312 or ES4412, a liquid encapsulant such as HYSOL.RTM. 
FP4510, FP 4511, FP4520, FP4526, or FP4527; a one-component epoxy or 
casting compound such as HYSOL.RTM. EO0104, EO0202, EO1016, EO1060, 
FP4322,FP4323, EO1070, FP4401 or FP4402, or a urethane such as HYSOL.RTM. 
US0028 or US0096. Other manufacturers offer additional suitable covering 
materials. 
It is desirable that the covering material bond well to the marked surface 
to be covered. In that regard, the composition of the package material 
should be carefully considered in relation to the covering material to be 
employed, as silicon or wax residue on the package surface may reduce the 
capacity of some covering materials to bond adequately. It is 
contemplated, however, that laser or flame pre-treatment of the marked 
surface may reduce or effectively eliminate the undesirable effects of the 
wax or silicon presence. 
FIG. 5 depicts a first embodiment 100 of an additive de-marking apparatus 
according to the invention. Apparatus 100 includes a packaged IC handling 
device 102 for presenting an exemplary TSOP IC package 10 or TQFP package 
50 for coating by contact applicator 104, which is provided with a 
covering material 106 from reservoir 108. As shown, handling device 102 
may comprise a multi-cavity turntable as known in the art, or may also 
suitably comprise a multi-aperture platen holding a plurality of packages 
10 or 50 for de-marking, or a track upon which packages 10 or 50 may 
travel past applicator 104. In operation, a package 10 or 50 is contacted 
on marked exterior surface 22 by applicator 104, optionally comprising a 
roller, stamp, open-cell sponge, brush, or other contact applicator 
configuration known in the art. Applicator 104 dispenses covering material 
106 in the required quantity to coat at least a portion of surface 22 and 
especially to obscure the marking indicia (not shown) thereon. Subsequent 
to receiving a quantity of covering material 106, each package 10 or 50 
may be moved while supported by handling device 102 to a curing station 
110 for stabilization of the layer or coating of covering material 106 and 
bonding thereof to marked exterior surface 22. Curing may be effected by, 
for example, application of heat, or application of light or other 
electromagnetic radiation in a selected wavelength range from a source 
112. 
FIG. 6 depicts a second embodiment 200 of an additive de-marking apparatus 
according to the invention. Apparatus 200 includes a handling device 202, 
depicted as a track or belt conveyor, for presenting an exemplary TSOP 
package 10 (or, again, TQFP package 50) for covering of marked exterior 
surface 22 by non-contact applicator 204. Applicator 204 is provided with 
covering material 206 from reservoir 208. The applicator 204 may include a 
dispensing nozzle fed by a controlled, metered volume of covering material 
206 from reservoir 208, such metering being effected by a metering pump or 
a valve, as known in the art. The nozzle may define a circular aperture to 
dispense a pool of covering material 206 on a central area of marked 
exterior surface 22 of package 10, or may define a slot, such as may be 
beneficially employed to cover a marked surface 22 moving at a controlled 
rate therepast in a direction transverse to the slot. A mask 216 having an 
aperture 218 therein may optionally be inserted between package 10 and 
applicator 204 to reduce the potential for excess covering material 206 
falling onto the lead fingers of the package. After marked exterior 
surface 22 is coated, each package 10 may travel to a curing station 210 
for stabilization of the coating and bonding thereof to marked exterior 
surface 22. As noted previously, curing may be effected by a suitable heat 
or electromagnetic radiation source 212. While it is also possible that 
applicator 204 may alternatively comprise an airless or air-driven 
sprayer, such devices present a significant potential for contamination of 
the package leads, may require enclosures or complex venting systems, and 
may also present metering and nozzle clogging problems. 
FIG. 7 depicts a third embodiment 300 of an additive de-marking apparatus 
according to the invention. Apparatus 300 includes a handling device 302, 
depicted as a computer-controlled robotic arm, for presenting an exemplary 
TSOP package 10 or TQFP package 50 for coating of marked exterior surface 
22 by applicator 304, depicted as a contact applicator for applying 
preformed segments of covering material 306. Segments of covering material 
306 may comprise powdered material formed into rectangles with a volatile 
binder and carried on a reel-type reservoir 308 in the form of a carrier 
tape 316, or may comprise segments to be cut from a continuous length of 
covering material 306 formed as a self-supporting tape 318 and fed from 
reservoir 308. If a preformed segment 306 of powdered covering material is 
employed, it may be liquified and the binder driven off in a curing 
station 310 by application of heat from a source 312. If a preformed 
segment of tape-type covering material 306 is employed, it may securely 
bond by mere contact to marked exterior surface 22, or may merely form a 
preliminary "tack" bond with surface 22, such tack bond being subsequently 
made more robust by curing in station 310. Further, if a tape-type 
preformed segment is employed, the covering material 306 may be 
self-adhesive, or may be coated on one side with a separate adhesive which 
may exhibit a tacky adhesiveness to be subsequently strengthened by 
curing. Finally, a separate adhesive may be applied to marked exterior 
surface 22 prior to application of an adhesive-free tape-type segment of 
covering material 306 thereto, if that approach is preferred. 
FIG. 8 depicts a fourth embodiment 400 of an additive de-marking apparatus 
according to the invention. Apparatus 400 includes a packaged IC handling 
device 402, depicted as a track or belt conveyor, for presenting an 
exemplary TSOP package 10 or TQFP package 50 for covering at least a 
portion of marked exterior surface 22. 
Prior to application of a covering material 406, however, a dam applicator 
430 forms a dam structure 432 on or about marked surface 22 for 
containment of subsequently-applied covering material 406. With reference 
to FIGS. 9A-9C, and shown with respect to a schematically-depicted TSOP 
package 10, the dam structure 432 may comprise (see FIG. 9A) a peripheral 
dam element 434 (height exaggerated for clarity) which extends about the 
entire perimeter of a marked surface 22 of the IC package 10. Dam element 
434 may include a skirt portion 436 extending down the side of a package 
and an inwardly-extending shoulder portion 438 resting on the peripheral 
edge of marked surface 22. Alternatively, the dam structure 432 may 
comprise (see FIG. 9B) a peripheral dam element 440 which rests entirely 
on marked surface 22, adhering thereto and encompassing the entire marked 
surface 22 inside of the inner wall of dam element 440. As a further 
alternative, the dam structure may comprise (see FIG. 9C) a smaller dam 
element 442 which is sized to only encompass the marked area of surface 22 
to be covered; this latter alternative may be less preferred due to the 
precision of dam placement required and the absence of alignment features 
such as are provided by the edges of the marked surface 22 for placement 
of other embodiments of the dam structure. 
The dam structure 432 may comprise a preformed plastic frame element 
dispensed from a tape or magazine, or cut from a series of linked frame 
elements, or may comprise a structure stenciled or extruded from a 
thermoplastic or thermosetting material onto marked surface 22. Exemplary 
suitable dam materials may include HYSOL.RTM. FP4450, FP4451 and FP 4460, 
with compatible covering materials including HYSOL.RTM. FP4457 and FP4650. 
After the dam structure 432 is placed on a marked surface 22 of, for 
example, a package 10, package 10 is presented to applicator 404. 
Applicator 404 dispenses a flowable, preferably highly viscous covering 
material 406 from reservoir 408 onto marked surface 22 within the 
perimeter of a dam structure 432 thereon, such as the aforementioned dam 
element 434, 440 or 442. A portion of the layer of covering material 406 
is shown in each of FIGS. 9A-9C. Covering material 406 is dispensed in a 
controlled, metered volume so as to fill engraved markings on surface 22 
and to preferably cover marked surface 22 to a uniform depth, which may be 
substantially the same as the wall height of the dam structure above the 
marked surface 22. The covering material may then be cured at a curing 
station 410 having heat or electromagnetic radiation source 412, as 
previously described, if required or desired to speed solidification of 
the covering material 406 or bonding to the marked surface 22. 
While the invention has been described in terms of certain illustrated 
embodiments, those of ordinary skill in the art will understand and 
appreciate that it is not so limited, and that many additions, deletions 
and modifications to the invention as disclosed herein may be effected 
without departing from the scope of the invention as hereinafter claimed.