Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
1999-12-07
2002-04-02
Potter, Roy (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S779000
Reexamination Certificate
active
06365973
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to solder materials used in microelectronic device packaging. In particular, the present invention relates to altering the coefficient of thermal expansion of solder used in mechanical, thermal, and/or electrical contacts in microelectronic device packages.
2. State of the Art
A variety of materials are used in the microelectronics industry for a forming components and attaching components together. One highly versatile material is solder, primarily alloys of lead and tin. Solder may be used for mechanical, electrical, and/or thermal attachment of components.
FIG. 4
illustrates an exemplary flip-chip attachment of a microelectronic device
202
to a substrate
204
, such as an FR-4 substrate. The microelectronic device
202
is mechanically and electrically attached to the substrate
204
through a plurality of solder balls
206
which extend between discrete contact pads
208
on an active surface
212
of the microelectronic device
202
and contact pads
214
on the substrate
204
. A heat dissipation device (shown as a heat slug
216
is mechanically attached to a back surface
218
of the microelectronic device
202
with a layer of solder
222
. The solder layer
222
allows thermal conduction of heat from the microelectronic device
202
to the heat slug
216
. The heat from the microelectronic device
202
is dissipated from the heat slug
216
to the ambient environment. Thus, solder is used for both the mechanical and electrical attachment of the microelectronic device
202
to the substrate
204
and the mechanical and thermal attachment of the heat slug
216
to the microelectronic device
202
.
One problem which must be addressed in the connection of various different types of materials (i.e., microelectronic devices, substrates, heat slugs, etc.) is the coefficient of thermal expansion (CTE) for each material. The CTE is a measurement of the expansion and contraction of each material during heating and cooling cycles, respectively. These heating and cooling cycles occur during the operation of the microelectronic device
202
and during power up and power down of the microelectronic device
202
.
The attachment of a heat dissipation device to a microelectronic device is particularly problematical. The material of the heat dissipation device (e.g., heat slug
216
) generally comprises a metal, while the material of the microelectric device
202
generally comprises a silicon material. The CTE difference between a metal and a silicon material is considerable. The CTE difference between the heat slug
216
and the microelectronic device
202
results in stresses that may degrade the performance of the microelectronic device
202
through warpage and may result in premature device failure, such as by the cracking of the microelectronic device
202
.
The microelectronics industry has addressed the CTE mismatch problem with a variety of solutions, such as altering the CTE of the materials used. For example, in heat dissipation devices may be made from aluminum filled with silicon carbide ceramic particles. The silicon carbide ceramic filled aluminum has high heat transfer and has a lessened CTE compared to pure aluminum. Such silicon carbide carbide ceramic filled aluminum products are available from Lanxide Electronic Components, Inc., Newark, Del., USA.
Although the CTE mismatch problem has been or is being continuously addressed, another CTE problem has arisen as a result of industry's continuous generation of smaller and smaller microelectronic devices. The smaller microelectronic devices result in the CTE of the attachment materials, such as solder, having an effect on the microelectronic package.
Unfortunately, the solders presently used generally have a higher CTE than the materials they join (i.e., they expand and contract at a faster rate than the surrounding material when heated and cooled, respectively). For example, in the attachment of the heat slug
216
to the microelectronic device
202
, the CTE mismatch of solder may result in the solder layer
222
becoming detached from the either the heat slug
216
or the microelectronic device
202
. This detachment may reduce the efficiency of the thermal contact between the heat slug
216
and the microelectronic device
202
, which can result in the premature failing of the microelectronic device
202
due to thermal degradation. With regard to the solder balls
206
, the CTE mismatch of the solder in the solder balls
206
may result in one or more of the solder balls
206
becoming detached from the substrate contact pad
214
or the microelectronic device contact pad
208
, either of which may result in a failure of the microelectronic device
202
.
Therefore, it would be advantageous to develop a solder which has a CTE comparable to the components to which the solder is in electrical, mechanical, and/or thermal contact.
SUMMARY OF THE INVENTION
The present invention relates to altering the coefficient of thermal expansion of solder used in thermal and/or electrical contacts in microelectronic packages. Specifically, the present invention relates to a filled solder material comprising a solder material having a plurality of coated filler particles disposed therein.
REFERENCES:
patent: 5520752 (1996-05-01), Lucey, Jr. et al.
patent: 5721455 (1998-02-01), Takashita
patent: 6008543 (1999-12-01), Iwabuchi
Smay, Gary L., “Surface-Energy Determinations of Tin Oxide-Coated Soda-Lime-Silica Glass,” J. Am. Ceram. Soc., 71[4], Apr. 1988, C-217-C-219.
The micrograph set entitled “K7 Package—Solder Column” illustrates an analysis of a commercially available K7 chip assembly produced by Advanced Micro Devices, Inc. the analysis appears to illustrate carbon-containing particulates within a solder joint proximate the “cermic package side” of the assembly, and silicon-containing particulates within a solder joint proximate the “PCB (printed circuit board) side” of the assembly.
Intel Corporation
Potter Roy
Winkle Robert G.
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