Abrading – Precision device or process - or with condition responsive... – By optical sensor
Reexamination Certificate
2001-07-19
2002-07-16
Rachuba, M. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
By optical sensor
C451S008000, C451S049000, C451S068000, C451S388000, C029S840000, C029S843000, C029SDIG004
Reexamination Certificate
active
06419550
ABSTRACT:
TECHNICAL FIELD
The present invention relates to apparatus and methods for substantial planarization of solder bumps for use in, for example, testing and fabrication of chip scale packages, bumped die, and other similar devices.
BACKGROUND OF THE INVENTION
The demand for smaller packaging of electronic components continues to drive the development of smaller chip scale packages (CSP's), bumped die, and other similar devices having solder bumps, ball grid arrays (BGA's), or the like. As a result, spacing (or “pitch”) between adjacent solder balls on bumped devices has steadily decreased. Typical requirements for ball pitch have decreased from 1.27 mm to 0.5 mm or less, and the trend continues.
FIG. 1
is a side elevational view of a typical bumped device
10
(CSP, bumped die, etc.) mounted on, for example, a printed circuit board
20
. The bumped device
10
includes a plurality of solder balls
12
attached to a plurality of ball pads (not shown) which are formed on a die
14
. Each solder ball
12
has an outer edge
16
that aligns with a corresponding contact pad
18
on the printed circuit board
20
. A conductive lead
22
is attached to each contact pad
18
. Ideally, the outer edge
16
of each solder ball
12
contacts the corresponding contact pad
18
during assembly of the bumped device
10
with the printed circuit board
20
, completing the electrical circuit between the conductive leads
22
and the die
14
.
The height and width of the solder bumps
12
on the bumped device
10
are not precisely uniform. Variation of the solder bump height and width depends on several factors, including variation in size of the original unattached solder balls, variation in the sizes of the ball pads, and differences in the attachment process.
As the demand for smaller packaging continues, however, CSP reliability concerns arise. For example, using typical manufacturing methods and solders, the nominal variation between the tallest and shortest balls (shown as the distance d on
FIG. 1
) is presently about 60 microns (&mgr;m). Therefore, when the device
10
is placed on a flat surface resting on the solder balls, the three tallest balls or bumps define the seating plane of the device, and the smaller balls do not touch the corresponding contact pads of the printed circuit board or test interposer.
During assembly, and in some cases during testing, a moderate compression force may be applied to the bumped device
10
to drive the outer surfaces
16
of the solder balls
12
into contact with the contact pads
18
of the printed circuit board or test interposer
20
. Typically, the compression force needed to bring the solder bumps into contact with the contact pads varies between 30 grams and 2000 grams depending upon the manufacturing or test process involved. The applied compression force should be kept to a minimum, however, because larger forces may damage the circuitry of the die
14
, the CSP solder balls, or the test interposer.
One approach to the problem is to mount the contact pads
18
of the test interposer
20
on micro-springs. As the tallest solder bumps engage the micro-spring mounted contact pads, the micro-springs are compressed, allowing the shorter solder balls to engage the corresponding contact pads. Numerous micro-spring contact pad models are available as shown and described in Robert Crowley's article in
Chip Scale Review
published May 1998, p. 37, incorporated herein by reference. Although desirable results may be achieved with such devices, micro-spring mounted contact pads
18
are very expensive, relatively difficult to maintain, and may excessively damage the solder ball itself.
During assembly of the bumped device
10
with the printed circuit board
20
, some of the shorter solder balls may not solder to their associated contact pads during the reflow process. In the past, to increase the numbers of solder balls making contact with the contact pads during reflow, the volume of the solder balls was increased. As packaging sizes and pitch requirements continue to decrease, however, the volume of the solder balls must be reduced accordingly, and thus, the percentage of balls that will not attach to the contact pads during reflow increases. Again, if considerable force is applied during assembly, the CSP or the printed circuit board
20
may be damaged.
SUMMARY OF THE INVENTION
The present invention is directed toward apparatus and methods for substantial planarization of solder bumps for use in, for example, testing and fabrication of chip scale packages, bumped die, and other similar devices. In one embodiment, an apparatus in accordance with the invention includes a planarization member engageable with at least some of the plurality of outer surfaces, and a securing element engageable with the bumped device to securely position the bumped device during engagement with the planarization member. During engagement with the at least some outer surfaces, the planarization member applies a planarization action on one or more of the outer surfaces to substantially planarize the plurality of outer surfaces. In one embodiment, the planarization member includes a cutting tool and the planarization action comprises a milling action. In another embodiment, the planarization member includes a heated platen and the planarization action comprises a thermo-mechanical deformation action. In yet another embodiment, the planarization member includes an abrasive surface and the planarization action comprising a grinding action. Alternately, the planarization member includes a chemical solution and the planarization action comprises a chemical reaction. In yet another embodiment, the planarization member includes a solder deposition device and the planarization action comprises a solder deposition.
Alternately, an apparatus may include a planarization gauge that measures a planarization condition of the outer surfaces. The planarization gauge may measure the planarization condition before or after the planarization member is engaged with the outer surfaces.
In a further embodiment, an apparatus includes a load device engageable with at least one of the bumped device or the planarization member to urge the at least some outer surfaces of the bumped device into engagement with the planarization member. The planarization member applies a planarization action on one or more of the plurality of outer surfaces to substantially planarize the plurality of outer surfaces.
In one embodiment, the planarization member includes a substantially flat surface and the load device includes a mass having a weight that urges the at least some outer surfaces into engagement with the flat surface to mechanically flatten the surfaces. In another embodiment, the load device includes a fixed surface and a pressurizable vessel, a pressure in the pressurizable vessel urging the bumped device away from the fixed surface and into engagement with the planarization member. In yet another embodiment, the load device includes a press engageable with the bumped device. In still another embodiment, the load device includes a centrifuge engageable with the planarization member.
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Using Silicon Contacts to Test and Burn-In FLASH Memory, Microprocessors, and FPGA's, International Conference on Multichip
Dorsey & Whitney LLP
Rachuba M.
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