U.S. patent application number 11/778155 was filed with the patent office on 2007-12-06 for method of making an electronic package.
Invention is credited to Lisa J. Jimarez, Miguel A. Jimarez, Voya R. Markovich, Cynthia S. Milkovich, Charles H. Perry, Brenda L. Peterson.
Application Number | 20070278654 11/778155 |
Document ID | / |
Family ID | 25061222 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070278654 |
Kind Code |
A1 |
Jimarez; Lisa J. ; et
al. |
December 6, 2007 |
Method of making an electronic package
Abstract
An electronic package and method of making the electronic
package is provided. A layer of dielectric material is positioned
on a first surface of a substrate which includes a plurality of
conductive contacts. At least one through hole is formed in the
layer of dielectric material in alignment with at least one of the
plurality of conductive contacts. A conductive material is
positioned in the at least one through hole substantially filling
the through hole. At least one conductive member is positioned on
the conductive material in the through hole and in electrical
contact with the conductive material. The electronic package
improves field operating life of an assembly which includes a
semiconductor chip attached to a second surface of the substrate
and a printed wiring board attached to the conductive members.
Inventors: |
Jimarez; Lisa J.; (Newark
Valley, NY) ; Jimarez; Miguel A.; (Newark Valley,
NY) ; Markovich; Voya R.; (Endwell, NY) ;
Milkovich; Cynthia S.; (Vestal, NY) ; Perry; Charles
H.; (Poughkeepsie, NY) ; Peterson; Brenda L.;
(Wappingers Falls, NY) |
Correspondence
Address: |
JOHN A. JORDAN, ESQ.
11 HYSPOT ROAD
GREENFIELD CTR.
NY
12833
US
|
Family ID: |
25061222 |
Appl. No.: |
11/778155 |
Filed: |
July 16, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11182167 |
Jul 15, 2005 |
7278207 |
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11778155 |
Jul 16, 2007 |
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10251072 |
Sep 19, 2002 |
6961995 |
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11182167 |
Jul 15, 2005 |
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09761124 |
Jan 16, 2001 |
6486415 |
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10251072 |
Sep 19, 2002 |
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Current U.S.
Class: |
257/690 ;
257/E21.503; 257/E21.508; 257/E23.009; 257/E23.062; 257/E23.069;
257/E23.119; 438/127 |
Current CPC
Class: |
H01L 23/49827 20130101;
H05K 1/0271 20130101; H05K 3/3457 20130101; H05K 3/4688 20130101;
H05K 2201/0133 20130101; H05K 3/3436 20130101; H01L 2924/0002
20130101; H01L 21/486 20130101; H05K 2201/10734 20130101; H01L
21/4857 20130101; H01L 2924/0002 20130101; H05K 3/4605 20130101;
H05K 3/4053 20130101; Y10T 29/49165 20150115; Y10T 29/49128
20150115; H05K 2201/015 20130101; H01L 23/49894 20130101; H05K
1/113 20130101; H01L 23/15 20130101; Y10T 29/4913 20150115; H01L
23/49816 20130101; H05K 2203/061 20130101; H01L 23/49822 20130101;
H05K 2201/09509 20130101; Y10T 29/49147 20150115; H05K 2201/09436
20130101; H05K 3/4644 20130101; Y10T 29/49153 20150115; H05K 1/0306
20130101; H01L 2924/00 20130101; H05K 3/4069 20130101 |
Class at
Publication: |
257/690 ;
438/127; 257/E23.009; 257/E23.119; 257/E21.503; 257/E21.508 |
International
Class: |
H01L 23/29 20060101
H01L023/29; H01L 21/56 20060101 H01L021/56 |
Claims
1. An electronic package comprising: a substrate having a first
surface, said first surface having a plurality of conductive
contacts thereon; a layer of dielectric material having a first and
second surface, said first surface of said dielectric material
positioned substantially on said first surface of said substrate;
at least one through hole positioned in said layer of dielectric
material substantially aligned with at least one of said plurality
of said conductive contacts, said at least one through hole having
a side wall; a conductive material positioned in said at least one
through hole, said conductive material substantially filling said
through hole and being in electrical contact with said at least one
of said plurality of conductive contacts; and at least one
conductive member positioned on said conductive material in said at
least one through hole and in electrical contact with said
conductive material.
2. The electronic package of claim 1 wherein said substrate is
comprised of a ceramic material.
3. The electronic package of claim 2 wherein said ceramic material
includes at least one layer of glass.
4. The electronic package of claim 1 wherein said layer of
dielectric material has an elastic modulus of from about 50,000
psi. to about 300,000 psi.
5. The electronic package of claim 1 wherein said layer of
dielectric material is comprised of a material selected from the
group of organic polymers consisting of fluoropolymers, allyated
polyphenyl ethers, and cyanate ester epoxies.
6. The electronic package of claim 1 wherein said layer of
dielectric material includes a plurality of said through holes
therein.
7. The electronic package of claim 1 wherein said at least one
through hole includes a layer of plated material on said side
wall.
8. The electronic package of claim 7 wherein said layer of plated
material is selected from the group consisting of copper, nickel,
gold, palladium, tin, and lead.
9. The electronic package of claim 1 wherein said conductive
material is selected from the group consisting of eutectic solder,
high melt solder, lead free solders, and conductive inks.
10. The electronic package of claim 1 wherein said conductive
member comprises a solder ball.
11. The electronic package of claim 10 wherein said solder ball
comprises high melt solder and lead free solder.
12. The electronic package of claim 1 further including at least
one conductive pad positioned on said second surface of said
dielectric material, said conductive pad in electrical contact with
both said conductive material and said at least one conductive
member.
13. A method of making an electronic package comprising the steps
of: providing a substrate having a first surface, said first
surface having a plurality of conductive contacts thereon;
positioning a layer of dielectric material having a first and
second surface substantially on said first surface of said
substrate; forming at least one through hole in said layer of
dielectric material in alignment with said at least one of said
plurality of said conductive contacts, said at least one through
hole having a side wall; positioning a conductive material in said
at least one through hole so as to substantially fill said through
hole and to be in electrical contact with said at least one of said
plurality of conductive contacts; and positioning at least one
conductive member on said conductive material in said at least one
through hole and in electrical contact with said conductive
material.
14. The method of making the electronic package of claim 13 wherein
said layer of dielectric material is positioned by laminating a
layer of an organic polymeric material onto a first metal layer,
said first metal layer including at least one clearance hole
therein, and positioning a second layer of metal having a
preselected thickness on one surface of said layer of organic
polymeric material, said second layer of metal and said first metal
layer being separated by said layer of organic polymeric
material.
15. The method of making the electronic package of claim 14 wherein
said at least one clearance hole is formed by etching prior to said
laminating of said layer of organic polymeric material onto said
first metal layer.
16. The method of making the electronic package of claim 14 wherein
said step of positioning said second layer of metal having a
preselected thickness on one of said surfaces of said layer of
organic polymeric material further includes removing a portion of
said second layer of metal to reduce said preselected thickness
after said positioning of said second layer of metal on one of said
surfaces of said layer of organic polymeric material.
17. The method of making the electronic package of claim 16 wherein
the step of removing a portion of said second layer of metal
comprises etching said second layer of metal to a thickness of
about 3 microns.
18. The method of making the electronic package of claim 16 wherein
said step of forming said at least one through hole in said layer
of dielectric material is accomplished by laser drilling.
19. The method of making the electronic package of claim 16 wherein
said step of positioning said conductive material in said at least
one through hole comprises screening.
20. The method of making the electronic package of claim 19 further
including the step of removing said second layer of metal from said
one surface of said organic polymeric material prior to said
screening.
21. The method of making the electronic package of claim 20 further
including the step of plating a layer of copper on said side wall
of said at least one through hole prior to removing said second
layer of metal from said one surface of said organic polymeric
material.
22. The method of making the electronic package of claim 13 wherein
the step of positioning said at least one conductive member on said
conductive material comprises placing a high melt solder ball on
said conductive material.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an electrical
interconnection arrangement for making connection between
electronic substrates and, more particularly, to making electrical
interconnection between a chip carrier and a printed wiring
board.
BACKGROUND OF THE INVENTION
[0002] One of the problems encountered with some chip carrier
substrate interconnections to the next level of packaging is the
high stress on the interconnections caused by coefficient of
thermal expansion (CTE) mismatch between the substrate and the next
level of packaging. The CTE thermal mismatch is particularly large
where a ceramic chip carrier substrate is connected to a printed
wiring board typically made of an epoxy/glass material. When a high
circuit density chip is attached to the chip carrier substrate, the
heat generated by the chip compounds the CTE mismatch problem
between the chip carrier substrate and the printed wiring board
because of large temperature variations between the chip and the
printed wiring board. In addition, certain applications, such as
flip chip applications, have required encapsulation to ensure a
reliable flip chip interconnection in the solder joints between the
chip and the substrate. Such encapsulation typically employs a high
strength epoxy which acts to reinforce the bond between the chip
and the chip carrier substrate. During thermal cycling, this
reinforcing of the chip to chip carrier substrate reduces solder
joint stress between the chip and the chip carrier. When coupled
with the CTE mismatch between a ceramic chip carrier attached by a
solder interconnection to a printed wiring board, this
reinforcement can cause high stress between the ceramic chip
carrier substrate and the printed wiring board to which it is
attached. Repeated thermal cycling can lead to cracking of the
solder interconnection between the ceramic chip carrier and the
printed wiring board, ultimately affecting reliability of the
chip/substrate/printed wiring board package.
[0003] The above described high stresses on the solder
interconnections are generally attributed to the fact that the
bonding of chip to the ceramic chip carrier, including the
encapsulant, forms a composite which acts during thermal cycling to
cause this composite to act like a "bimetallic" element wherein the
composite bends due to the different CTE of the materials. As a
result of the large thermal mismatch between the composite and the
printed wiring board, the thermal cycling induced bending over time
can cause solder interconnection failure. In this regard, the CTE
for a typical chip may be in the order of about 3 parts per million
per degree Centigrade (ppm/degree C.). The CTE for a typical
ceramic chip carrier may be in the order of about 3-5 ppm/degree
C., while a typical printed wiring board CTE may be about 18-22
ppm/degree C.
[0004] In general, others have attempted to address the problems
caused by CTE mismatch of materials in electronic packages by
providing various interposing structures that attempt to reduce the
CTE mismatch. For example, multiple layers of materials with
varying CTEs may be employed to form an interposing layer between
one level of packaging and the next, with the layers having a
gradation of CTEs such that the layer contacting one level of
packaging is selected to have a CTE which more closely matches the
CTE of that level while the layer contacting the next level of
packaging has a CTE more closely matching that level while layers
between may gradually reduce the difference. In addition, efforts
have also been made to use interposing layers which are flexible in
nature such as to reduce the stress on electrical interconnections
during thermal cycling created by thermal mismatch. However, these
various efforts typically are either difficult to assemble or are
not totally effective in their purpose.
[0005] The present invention is directed at overcoming the problems
set forth above. It is desirable to have an electronic package and
method to make the electronic package that significantly absorbs
the stresses that occur between a chip carrier and a printed wiring
board during thermal cycling. Electronic packages produced by this
method will have increased operational field life.
SUMMARY OF THE INVENTION
[0006] Accordingly, it is the object of this invention to enhance
the art of packaging technology.
[0007] It is another object of this invention to provide a novel
method of producing an electronic package that provides an improved
interconnection between a chip carrier substrate and a printed
wiring board.
[0008] It is yet another object of this invention to provide an
electronic package that will be manufactured with relatively lower
costs than many current products.
[0009] Still another object of this invention to provide an
electronic package having a layer of dielectric material between a
chip carrier substrate and printed wiring board that substantially
absorbs stress caused by thermal cycling resulting in a package
having much improved operational field life.
[0010] Still yet another object of this invention is to provide an
electronic package having at least one through hole in a layer of
dielectric material substantially filled with a conductive material
and having a conductive member positioned on the conductive
material.
[0011] According to one aspect of the invention, there is provided
an electronic package comprising a substrate having a first
surface, the first surface having a plurality of conductive
contacts thereon and a layer of dielectric material having a first
and second surface, the first surface of the dielectric material
positioned substantially on the first surface of said substrate. At
least one through hole is positioned in the layer of dielectric
material substantially aligned with at least one of the plurality
of the conductive contacts, the at least one through hole having a
side wall. A conductive material is positioned in the at least one
through hole, the conductive material substantially filling the
through hole and being in electrical contact with the at least one
of the plurality of conductive contacts, and at least one
conductive member positioned on the conductive material in the at
least one through hole and in electrical contact with the
conductive material.
[0012] According to another aspect of the invention, there is
provided a method of making an electronic package comprising the
steps of providing a substrate having a first surface, the first
surface having a plurality of conductive contacts thereon,
positioning a layer of dielectric material having a first and
second surface substantially on the first surface of the substrate,
and forming at least one through hole in the layer of dielectric
material in alignment with the at least one of the plurality of
said conductive contacts, the at least one through hole having a
side wall. The method includes positioning a conductive material in
the at least one through hole so as to substantially fill the
through hole and to be in electrical contact with the at least one
of the plurality of conductive contacts, and positioning at least
one conductive member on the conductive material in the at least
one through hole and in electrical contact with the conductive
material.
[0013] The above objects, advantages, and features of the present
invention will become more readily apparent from the following
detailed description of the presently preferred embodiments as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a sectional view in elevation of one embodiment of
the electronic package of the present invention, illustrating a
substrate assembled to a printed wiring board, the substrate having
a layer of dielectric material thereon, the layer of dielectric
material having through holes filled with conductive material.
Conductive members are positioned on the conductive material.
[0015] FIG. 2 is a sectional view in elevation of another
embodiment of the electronic package of the present invention,
illustrating conductive members in electrical contact with
conductive pads and the conductive material substantially filling
the through holes.
[0016] FIG. 3 is a flow diagram of the steps carried out in making
an electronic package, in accordance with one embodiment of the
present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0017] An electronic package 10 embodying the present invention is
shown in FIG. 1. Electronic package 10 includes a substrate 2 with
a first surface 4. First surface 4 has a plurality of conductive
contacts 6 thereon. Another surface 5 of substrate 2 can include a
plurality of contacts 7 adapted for bonding an electrical element
such as an electrical component (not shown) thereon. One example of
such a component is a semiconductor chip. A layer of dielectric
material 8 having a first surface 12 and a second surface 14 is
positioned substantially on first surface 4 of substrate 2. A
plurality of through holes 16 each with a side wall 18 are
positioned in layer of dielectric material 8. Through holes 16 are
substantially aligned with the plurality of conductive contacts 6.
Conductive material 20 is positioned in through holes 16.
Conductive material 20 substantially fills through holes 16 and is
in electrical contact with plurality of conductive contacts 6.
Conductive members 22 are positioned on conductive material 20 and
make electrical contact with conductive material 20 in through
holes 16. Conductive members 22 are adapted for electrical
connection to a printed wiring board 23, shown in phantom.
##STR1##
[0018] Substrate 2 is preferably comprised of a ceramic material.
Examples of ceramic materials that can be used in this invention
include aluminum silicate and aluminum oxides. The substrate can
include at least one layer 24 of glass, examples of which are
silicon oxides and silicates.
[0019] Layer of dielectric material 8 may be comprised of a
material selected from the group consisting of fluoropolymers,
allyated polyphenyl esters, and cyanate ester epoxys. The
fluoropolymer polytetrafluoroethylene is preferred in this
invention. A suitable polytetrafluoroethylene is available under
the product name RO 2800 from Rogers Corporation (Rogers, Conn.).
The allyated polyphenyl esters employed in this invention are
produced by polymerization of unsaturated allyated polyphenyl ester
compounds to form a cross linked thermosetting resin which is
highly resistant to chemical attack, moisture absorption, and heat.
These resins also exhibit low shrinkage and good electrical
resistivity. The allyl group can be of the form
CH.sub.2.dbd.CH.sub.2 or CH.sub.2.dbd.C--R where R can be any
length of carbon atoms. The cyanate esters that can be employed
pursuant to the present invention have two or more --O--CHN groups
and are curable through the cyclotrimerization reaction. The
cyanate esters can be monomeric or less preferably polymeric,
including oligomers and can be represented by those materials
containing the following group:
[0020] where A represents independently a single bond,
--C(CH.sub.3)(H)--, --SO.sub.2--, --O--, --C(CF.sub.2).sub.2--,
--CH.sub.2OCH.sub.2--, --S--, --C(.dbd.O)--. --O--C(.dbd.O)--O--,
--S(.dbd.O)--, --O--P(.dbd.O)--O--, --O--P(.dbd.O)(.dbd.O)--O--,
divalent alkylene radicals such as --CH.sub.2-- and
--C(CH.sub.3).sub.2--; divalent alkylene radicals interrupted by
heteroatoms in the chain such as O, S, and N.
[0021] Each R is independently selected from the group of hydrogen,
alkyl containing 1 to 9 carbon atoms: each n independently is an
integer of 0 to 4.
[0022] Other cyanates useful in the method and structure of the
invention can be prepared by well known methods, for example, by
reacting the corresponding polyvalent phenol with a halogenated
cyanate, as described in U.S. Pat. Nos. 3,553,244; 3,740,348; and
3,755,402.
[0023] The phenol reactant can be any aromatic compound containing
one or more reactive hydroxyl groups. The phenolic reactant is
preferably a di- or tri-polyhydroxy compound of the formula:
##STR2## in which each a and b is independently 0, 1, 2, or 3, and
at least one a is not 0; n is within the range of 0 to about 8,
preferably 0 to 3; each R is independently selected from
non-interfering alkyl, aryl, alkaryl, heteroatomic, heterocyclic,
carbonyloxy, carboxy, and the like ring substituents, such as
hydrogen, C.sub.1-6 alkyl, C.sub.1-6 alkyl, C.sub.1-6 alkoxy,
halogen, maleimide, propargyl ether, glycidyl ether, and the like;
and A is a polyvalent linking moiety which can be, for example,
aromatic, aliphatic, cycloaliphatic, polycyclic, and heteroatomic.
Examples of linking moiety A include --O--, --SO.sub.2--, --CO--,
--OCOO--, --S--, --C.sub.1-12--, dicyclopentadienyl, aralkyl, aryl,
cycloaliphatic, and a direct bond.
[0024] Specific cyanate esters that can be employed in the present
invention are available and well-known and include those discussed
in the U.S. Pat. Nos. 4,195,132; 3,681,292; 4,740,584; 4,745,215;
4,477,629; and 4,546,131; European patent application EP0147548/82;
and German Offen. 2611796, disclosures of which are incorporated
herein by reference. A preferred polyfunctional cyanate ester is
Bisphenol AD dicyanate (4,4'-ethylidenebisphenoldicyanate)
available from Vantico Corporation under the trade designation
AROCY L-10 hexafluoro bisphenol A dicyanate (Arocy-40S), and
bisphenol M dicyanate (RTX366) commercially available from Vantico
Corporation. The layer of dielectric material 8 is comprised of a
material having an elastic modulus of from about 50,000 pounds per
square inch (psi) to about 300,000 psi. The modulus of elasticity
is sometimes referred to as the Young's modulus. The modulus of
elasticity can be thought of as stiffness of a material or its
resistance to elastic deformation. The greater the elastic modulus,
the stiffer the material or the smaller the elastic strain that
results from the application of a given stress. When layer of
dielectric material 8 is comprised of a material with this modulus
of elasticity, it is relatively compliant and warpage between
substrate 2 and conductive members 22 during operation of the
electronic package is greatly reduced.
[0025] Referring to FIG. 2, plurality of through holes 16 can
include at least one through hole with a layer of plated material
26 on side wall 18. Layer of plated material 26 is selected from
the group consisting of copper, lead, nickel, gold, palladium, and
tin. Conductive material 20 can be positioned on side wall 18 of
plurality of through holes 16 or on layer of plated material 24.
Conductive material 20 is selected from the group consisting of
eutectic solder, high melt solders, lead free solders or conductive
inks. One example of a eutectic solder is one including about 63%
tin and about 37% lead having a melting point of about 183 degrees
C. One example of a high melt solder is solder having a composition
of about 90% to about 97% lead with the balance comprising tin.
Another example of a high melt solder is known as 90/10 solder,
defined as about 90% by weight lead and about 10% by weight tin.
Minimum melting points for high melt solders having these
compositions range from about 268 degrees C. to about 314 degrees
C. Lead free solders can include an element selected from the group
consisting of tin, bismuth, indium, silver, antimony, and copper.
For example, one solder used in this invention is a lead free
solder comprising about 3.8% silver, about 0.7% to about 0.9%
copper, with the remainder tin. Conductive inks include, but are
not limited to particles of silver, gold, graphite polymer, or
copper suspended in an organic liquid carrier. Some examples of
conductive inks that can be employed in this invention are
available from Conductive Compounds, Londonderry, N.H., under the
product names AG-500, EP-600, UV-1009, and C-100.
[0026] Through holes 16 substantially filled with conductive
material 20 form columns of conductive material which tend to
function as stress relieving "springs". When conductive members 22
are connected to printed wiring board 23, the compliant layer of
dielectric material 8 and columns of conductive material 20
together absorb stresses between substrate 2 and printed wiring
board 23 to assure substantial prevention of failure of conductive
members 22 due to the mismatch of CTEs between substrate 2 and
printed wiring board 23 during thermal cycling associated with
field operation.
[0027] Solder member 22 preferably comprises a solder ball. The
solder ball is comprised of a high melt solder of the type
previously described. On second surface 14 of dielectric material 8
conductive pads 28 may be positioned. Conductive pads 28 are in
electrical contact with both conductive material 20 and conductive
members 22.
[0028] FIG. 3 illustrates the various steps involved in making an
electronic package according to one aspect of the present
invention. A substrate is provided, as depicted in Block 10, the
substrate having a first surface with a plurality of conductive
contacts thereon.
[0029] As depicted in Block 20, a layer of dielectric material is
then positioned substantially on the first surface of the
substrate, the layer of dielectric material having a first and
second surface.
[0030] Block 30 describes the step of forming at least one through
hole in the dielectric layer in alignment with the at least one of
the plurality of conductive contacts, the at least one through hole
having a side wall. Alternatively, the dielectric layer can be
formed with a through hole therein and then laminated on the first
surface of the substrate. This is accomplished by first laminating
a layer of organic polymeric material, such as
polytetrafluoroethylene, allyated polyphenyl ester or cyanate ester
resin, onto both sides of a first metal layer, the first metal
layer including a clearance hole formed by etching. A second layer
of metal, having a preselected thickness is then positioned on one
of the surfaces of the layer of organic material. This surface is
defined as the second surface of the layer of dielectric material.
The preselected thickness of the second metal layer being about
0.0003 inches to about 0.0006 inches. A portion of the second layer
of metal is then removed to reduce the preselected thickness to
about 3 microns. At least one through hole having a side wall is
then formed in the layer of dielectric material by the step of
laser drilling at the location of the clearance hole so that the
through hole passes through the clearance hole. The first surface
of the layer of dielectric material is then positioned on the first
surface of the substrate so that the at least one through hole in
the dielectric layer is in alignment with at least one of the
plurality of conductive contacts. The layer of dielectric material
is then laminated to the first surface of the substrate.
[0031] As depicted in Block 40, a conductive material is positioned
in the at least one through hole so as to substantially fill the
through hole and to be in electrical contact with at least one of
the plurality of conductive contacts. The conductive material is
positioned in the through hole by the step of screening. The
reduced thickness second layer of metal functions as a mask, later
removed by flash etching. The side wall of the at least one through
hole can be plated with a layer of plated material prior to
screening of the conductive material. When the side wall of the at
least one through hole includes a layer of plated material, the
reduced thickness layer of metal is removed from the surface of the
organic polymeric material by flash etching prior to screening the
conductive material into the at least one through hole.
[0032] Block 50 describes the step of positioning at least one
conductive member on the conductive material in the at least one
through hole and in electrical contact with the conductive
material. The at least one conductive member is positioned by
placing a high melt solder ball on the screened conductive material
in the through hole. The substrate is then placed in a solder
reflow oven where the screened conductive material is reflowed
forming a solder joint with the high melt solder ball with does not
undergo solder reflow.
[0033] In summary, the defined package structures and methods of
forming same provide an electronic package that is more reliable in
operating field life because the stresses that occur between the
substrate and the printed wiring board during thermal cycling are
absorbed by a combination of a compliant layer of dielectric
material and conductive columns. This is uniquely accomplished by
positioning a layer of compliant dielectric material on a surface
of a substrate, the surface of the substrate having a plurality of
conductive contacts thereon, forming at least one through hole in
the layer of dielectric material in alignment with at least one of
the plurality of the conductive contacts, and positioning a
conductive material in the at least one through hole so as to
substantially fill the through hole. The conductive material forms
conductive columns for a conductive member positioned thereon.
During thermal cycling the compliant dielectric material and
"spring-like" columns serve to absorb stresses caused by the CTE
mismatch between the substrate and a printed wiring board during
thermal cycling. The product made with the unique teachings
described herein will have improved operational field life.
[0034] While there have been shown and described what the present
considered preferred embodiments of the invention, it will be
obvious to those skilled in the art that various changes and
modifications may be made therein without departing from the scope
of the invention as defined by the appended claims.
* * * * *