Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-12-15
2001-12-25
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C257S726000, C257S727000
Reexamination Certificate
active
06332946
ABSTRACT:
TECHNICAL FIELD
This invention relates to a fixture and related method for assembly of multi-layered ceramic packages, specifically a fixture and related method capable of assembling a plurality of multi-layered ceramic packages having precise tolerances in a high-volume, high-yield assembly process.
BACKGROUND OF THE INVENTION
Multi-layered ceramic (MLC) packages, specifically single chip modules (SCM) and multi-chip modules (MCM), are used in a number of applications. Such modules generally consist of a substrate and a cap that must be bonded together to a specified dimensional tolerance, usually using adhesives that are heat-cured. Industry competitiveness demands low-cost, high-volume, high-yield assembly of such modules.
Stamped fixtures, typically of stainless steel, such as “Auer Boats” manufactured by AUER Precision Company, Inc. of Mesa, Ariz., are prevalent in the industry as fixtures used for such assembly. Such fixtures incur high initial tooling costs, however, for even minor variations in MLC package design, and are not compatible with conveyor equipment designed to work with a tool set complying with the Joint Electronic Device Engineering Council (JEDEC) Standards. Use of typical stamped fixtures requires additional handling which is labor intensive and also results in yield loss due to handling defects. In addition, loose cap-to-substrate alignment tolerances decrease the usable substrate area.
The configuration of a typical stamped stainless steel fixture of the prior art for assembly of an MLC package is shown in
FIG. 1. A
typical MLC package consists of a substrate
100
and cap
102
, the substrate having mounted upon it an integrated circuit chip
104
and having pins
106
extending from the bottom of the substrate.
To assemble the MLC package, the substrate containing the chip is set in a base
110
aligned by guides
111
. An alignment plate
112
is aligned on the substrate using alignment pins
114
attached to the alignment plate, each pin comprising a spacer portion
116
and a pin portion
118
adapted to fit in hole
119
in base
110
. Substrate
100
and chip
104
are typically prepared with chip underfill applied around and wicking under chip
104
, thermally conductive paste applied on top of chip
104
, and seal adhesive placed on the surface of substrate
100
where cap
102
will contact the substrate. The underfill protects the chip-substrate interface and prevents oxidation of the solder used to attach the chip pins to the substrate. The thermally conductive paste creates a conductive pathway from the top of the chip to the cap, so that heat may be dissipated away from the chip through the cap. Finally, the seal adhesive bonds around the perimeter of the cap to seal the area inside the cap to protect it from oxidation. Cap
102
is then placed on top of the substrate so prepared.
Pressure is then applied to press the substrate against the cap, using clip
120
. Clip
120
consists of a bridge
122
having tabs
124
punched therethrough, and prongs
126
attached at either end of bridge
122
. Each prong
126
has an upper stop tab
128
, a lower stop tab
130
, and an angled end
132
. Tabs
124
are spaced to hold the ends of leaf spring
134
therebetween. The compression force, usually 2 to 10 pounds, imparted by the spring serves to “squish” the paste layer on top of the chip to conform it to the space between the chip and the cap, thus assuring a good conductive connection and cap seal.
The clip
120
is inserted manually by squeezing the prongs
126
slightly toward one another and inserting them through alignment plate holes
136
and baseplate holes
138
thus compressing spring
134
. Once the prongs
126
have completely penetrated holes
138
, the prongs are allowed to spring back away from one another, and the lower tabs
130
hold the prongs into place to prevent the force of compressed spring
134
from retracting the clip. Upper tabs
128
prevent the prongs from being inserted too far into holes
138
such that too much compressive force would be imparted on cap
102
. The MLC package so assembled is then put into an oven to heat cure the seal adhesive. Cured modules then must be removed manually from the fixture.
A typical stamped stainless steel fixture of the prior art might accommodate anywhere from one to ten such MLC packages, but typically no more than five on a single base with a single corresponding alignment plate. One clip for each MLC package on the base must be inserted and removed manually, however, for each MLC package. Manual removal of the clip requires compressing prongs
126
toward each other a sufficient amount to clear tabs
128
and
130
through holes
138
and
136
. This operation usually requires handling the clip at ends
132
, sometimes causing finger damage to pins
106
if mishandled.
Another difficulty associated with the stamped fixtures of the prior art is that they cannot be stacked on top of one another. Because the oven curing step may often take three to four hours, the ability to maximize the number of fixtures in a single oven can dramatically increase throughput without requiring investment in additional ovens.
In addition, because the fixtures of the prior art are manufactured by a stamped metal process having inherently loose tolerances, the alignment between the base and the substrate may not meet the tight tolerances of customer specifications. As the industry strives to ever increase the amount of performance per size of unit, more of the substrate closer to the edges is typically used for functional design, and thus close tolerances of cap-to-substrate alignment have become more critical.
Finally, such fixtures must be re-tooled to accommodate even minor variations in MLC package width, length, or height, a serious drawback considering the common height variation in MLC packaging. In addition, a fixture is needed that uses industry standard JEDEC trays.
It is an object of the present invention, therefore, to provide a fixture flexible enough to handle the variations in package dimensions from product line to product line, capable of high-volume production with high yield conforming to precise dimensional tolerances, and strong enough to withstand constant manufacturing use.
SUMMARY OF THE INVENTION
To achieve this and other objects, and in view of its purposes, the present invention provides a fixture for the assembly of a plurality of multi-layered ceramic packages, or modules, each package comprising a substrate and a cap. An alternate embodiment of the fixture of the present invention may be used to assemble only a single package.
The fixture comprises a baseplate, a removable tray located on the baseplate and having a plurality of cavities each adapted to accept a substrate, a package alignment plate removably located on top of the tray, a compression plate pivotably attached to the baseplate, and a plurality of compression devices. The alignment plate has a plurality of openings each adapted to fit a cap. The compression plate pivots in relation to the baseplate between an open position and a closed, pressure-applying position. The compression devices each comprise at least one spring interposed between the compression plate and at least one of the plurality of package caps. Each of the compression devices is designed to uniformly distribute compressive force on at least one of the plurality of package caps when the compression plate is in the closed position.
In an alternate embodiment, the alignment plate further comprises a plurality of fingers extending in the direction of the tray and designed to hold the cap in precise alignment with the substrate. Also, in another embodiment, the removable tray is a “JEDEC Tray” conforming to the JEDEC Tray Standard. In yet another embodiment, each of the compression devices further comprises a pressure plate sized to uniformly distribute compressive force from at least one spring onto one or more of the plurality of package caps.
In accordance with the present invention, a method is also provided for simultaneously assemblin
Emmett Michael
Hering Ronald L.
Hultmark Eric B.
Hutchinson Howard D.
Ball Michael W.
International Business Machines - Corporation
Musser Barbara J.
Ratner & Prestia
Townsend, Esq. Tiffany L.
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