U.S. patent application number 09/813376 was filed with the patent office on 2001-12-13 for method of forming conductive line features for enhanced reliability of multi-layer ceramic substrates.
Invention is credited to Brody, Jeffrey A., Cox, Harry D., Garant, John, Liu, Hsichang, McLaughlin, Paul G., Wayson, Tom.
Application Number | 20010051210 09/813376 |
Document ID | / |
Family ID | 23822448 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010051210 |
Kind Code |
A1 |
Brody, Jeffrey A. ; et
al. |
December 13, 2001 |
Method of forming conductive line features for enhanced reliability
of multi-layer ceramic substrates
Abstract
A method for minimizing formation of cracks at junctions between
conductive vias and conductive lines in line-to-via connections on
a substrate. The method comprises providing a transition zone
connected between a base section of the line and a cap, the
transition zone providing a volume of conductive paste during a
conductive paste screen printing operation that is greater than the
volume provided by the base section being directly connected to the
cap. In particular, the transition zone volume is an effective
amount to prevent necking of the conductive line into the via when
the mask is misaligned to the substrate within an expected
alignment tolerance. The transition zone may comprise a jogged end
extending from the base section to the cap at an angle to the line,
or a flared end extending from the base section. Line-to-via
connection structures, patterns on a mask for making such
structures, and masks having such patterns are also disclosed.
Inventors: |
Brody, Jeffrey A.; (Hopewell
Junction, NY) ; Cox, Harry D.; (Rifton, NY) ;
Garant, John; (Hopewell Junction, NY) ; Liu,
Hsichang; (Fishkill, NY) ; McLaughlin, Paul G.;
(Poughkeepsie, NY) ; Wayson, Tom; (Owego,
NY) |
Correspondence
Address: |
Kevin R. Casey
Ratner & Prestia
One Westlakes, Berwyn, Suite 301
P.O. Box 980
Valley Forge
PA
19482-0980
US
|
Family ID: |
23822448 |
Appl. No.: |
09/813376 |
Filed: |
March 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09813376 |
Mar 21, 2001 |
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09458877 |
Dec 10, 1999 |
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6217989 |
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Current U.S.
Class: |
174/253 ;
118/504; 174/262; 257/E23.067; 257/E23.07; 427/282; 427/97.8;
427/98.5 |
Current CPC
Class: |
H05K 2201/09727
20130101; H01L 2924/00 20130101; H05K 1/116 20130101; Y10S 428/901
20130101; Y10T 428/24917 20150115; H01L 23/49827 20130101; H05K
1/0306 20130101; Y10T 428/24926 20150115; H01L 2924/09701 20130101;
H05K 3/4053 20130101; H05K 3/4629 20130101; H05K 3/4611 20130101;
H01L 2924/0002 20130101; H01L 23/49838 20130101; H01L 2924/0002
20130101 |
Class at
Publication: |
427/96 ;
427/282 |
International
Class: |
B05D 001/32; B05D
005/12 |
Claims
What is claimed:
1. A conductive line-to-via connection comprising: a conductive via
having a via diameter; and a conductive line connected to the
conductive via, the conductive line having (a) a base section with
a first width, (b) a cap with a cap diameter greater than the via
diameter and greater than the first width, and (c) a transition
zone between the base section and the cap, the transition zone
having a second width greater than the first width.
2. The line-to-via connection of claim 1 wherein the second width
is less than or equal to the cap diameter.
3. The line-to-via connection of claim 1 wherein the transition
zone comprises a jogged end extending from the base section to the
cap at an angle to the line.
4. The line-to-via connection of claim 3 wherein the angle is
greater than or equal to about 90.degree..
5. The line-to-via connection of claim 3 wherein the angle is one
of about 90.degree. and about 135.degree..
6. The line-to-via connection of claim 3 wherein a ratio of cap
diameter to via diameter is in a range of about 1.1 to about 1.3, a
ratio of second width to first width is about 1.25 to 1.5, and a
ratio of second width to cap diameter is about 0.8 to about
1.0.
7. The line-to-via connection of claim 6 wherein the first width is
about 0.07 mm, the cap diameter is in a range of about 0.11 to
about 0.013 mm, the via diameter is in a range of about 0.09 to
about 0.10 mm, and the second width is about 0.09 to 0.11 mm.
8. The line-to-via connection of claim 1 wherein the transition
zone comprises a flared end extending from the base section to the
cap.
9. The line-to-via connection of claim 8 wherein a ratio of cap
diameter to via diameter is in a range of about 1.1 to about 1.3, a
ratio of second width to first width is about 1.25 to 1.5, and a
ratio of second width to cap diameter is about 0.8 to about
1.0.
10. The line-to-via connection of claim 9 wherein the first width
is about 0.07 mm, the cap diameter is in a range of about 0.11 to
about 0.013 mm, the via diameter is in a range of about 0.09 to
about 0.10 mm, and the second width is about 0.09 to 0.11 mm.
11. The line-to-via connection of claim 1 wherein the conductive
line and the conductive via each comprise a metal.
12. The line-to-via connection of claim 11 wherein the metal
comprises one of copper, lead-tin solder, molybdenum, and
tungsten.
13. A ceramic substrate comprising: a conductive via having a via
diameter; a conductive line connected to the conductive via, the
conductive line having a base section with a first width, a cap
with a cap diameter greater than the via diameter and greater than
the first width, and a transition zone between the base section and
the cap with a second width greater than the first width.
14. The ceramic substrate of claim 13 further comprising more than
one layer.
15. A line pattern in a screen printing mask for forming a
conductive line having a base on a substrate, a cap adapted to be
positioned over a via with a via diameter in the substrate, and a
transition zone connected between the base and the cap, the line
pattern comprising: a cap section having a shape adapted to print
the cap, the cap section shape having a cap diameter greater than
the via diameter; a base section having a shape adapted to print
the base, the base section shape having a first width; and a
transition section having a shape, the transition section connected
between the base section and the cap section and adapted to print
the transition zone connected between the base and the cap, the
transition section shape having a second width greater than the
first width.
16. The line pattern of claim 15 wherein the second width is less
than or equal to the cap diameter.
17. The line pattern of claim 15 wherein the transition section
shape comprises a jogged end extending from the base section shape
to the cap section shape at an angle to the base section shape.
18. The line pattern of claim 17 wherein the angle is greater than
or equal to about 90.degree..
19. The line pattern of claim 17 wherein the angle is one of about
90.degree. or about 135.degree..
20. The line pattern of claim 17 wherein a ratio of cap diameter to
via diameter is in a range of about 1.1 to about 1.3, a ratio of
second width to first width is about 1.25 to 1.5, and a ratio of
second width to cap diameter is about 0.8 to 1.0.
21. The line pattern of claim 20 wherein the first width is about
0.07 mm, the cap diameter is in a range of about 0.11 to about
0.013 mm, the via diameter is in a range of about 0.09 to about
0.10 mm, and the second width is about 0.09 to 0.11 mm.
22. The line pattern of claim 15 wherein the transition section has
a flared end extending from the base section.
23. The line pattern of claim 22 wherein a ratio of cap diameter to
via diameter is in a range of about 1.1 to about 1.3, a ratio of
second width to first width is about 1.25 to about 1.6, and a ratio
of second width to cap diameter is about 0.8 to about 1.0.
24. The line pattern of claim 23 wherein the first width is about
0.07 mm, the cap diameter is in a range of about 0.11 to about
0.013 mm, the via diameter is in a range of about 0.09 to about
0.10 mm, and the second width is about 0.09 to 0.11 mm.
25. A screening mask comprising a line pattern for forming a
conductive line having a base on a substrate, a cap adapted to be
positioned over a via with a via diameter in the substrate, and a
transition zone connected between the base and the cap, the line
pattern comprising: a cap section having a shape adapted to print
the cap, the cap section shape having a cap diameter greater than
the via diameter; a base section having a shape adapted to print
the base, the base section shape having a first width; a transition
section having a shape, the transition section connected between
the base section and the cap section and adapted to print the
transition zone connected between the base and the cap, the
transition section shape having a second width greater than the
first width.
26. A method for minimizing formation of cracks at junctions
between conductive vias and conductive lines in line-to-via
connections on a substrate, each line having a base with a width
and a cap with a cap diameter, each cap positioned in the substrate
over a via with a via diameter less than the cap diameter, the
method comprising: screen printing the conductive lines onto the
substrate with conductive paste using a mask that provides a
transition zone connected between the base and the cap, the
transition zone providing a volume of conductive paste available to
fill the via during printing that is greater than a volume of
available paste provided by the base being directly connected to
the cap, the volume of paste in the transition zone comprising an
effective amount to prevent necking of the conductive lines into
the vias when the mask is misaligned to the substrate within an
expected alignment tolerance.
27. The method of claim 26 comprising providing a transition zone
having a greater width than the base width.
28. The method of claim 27 comprising providing a transition zone
having a width less than or equal to the cap diameter.
29. The method of claim 26 wherein the transition zone is provided
with one of a jogged end extending from the line to the cap at an
angle to the line and a flared end extending from the line to the
cap.
30. A method for minimizing formation of cracks at junctions
between conductive vias and conductive lines in line-to-via
connections on a substrate, each line having a width, each via
having a cap with a cap diameter surrounding a via in the substrate
having a via diameter less than the cap diameter, the method
comprising providing a transition zone connected between the line
and the cap, the transition zone having a greater width than the
line width.
31. The method of claim 30 further comprising providing the
transition zone with a lesser than or equal width to the cap
diameter.
32. The method of claim 30 wherein the step of providing the
transition zone comprises providing one of a jogged end extending
from the line to the cap at an angle to the line, and a flared end
extending from the line to the cap.
Description
BACKGROUND OF THE INVENTION
[0001] Multi-layer ceramic (MLC) substrates, such as are used for
chip carriers, comprise a number of discrete ceramic sheets
laminated and sintered together. Each sheet has conductive lines
printed on its surface with a conductive substance such as a metal,
for example, copper paste. Holes punched through the ceramic sheet
before sintering of the sheet (the unsintered sheet is known in the
art as a "green" sheet) are filled with the conductive paste to
provide conductive connections or "vias" between layers of the
substrate. Thus, for example, a chip mounted on a completed MLC
substrate is electrically connected to an underlying circuit board
through the lines and vias of the MLC. Reliable connections in the
MLC are critical to achieving the expected performance of the chip;
the reliability of the connections is highly dependent upon the
integrity of the line-to-via junctions.
[0002] Typically, the manufacture of such MLC substrates starts
with a glass ceramic powder that is formed into a slurry and cast
into a large sheet similar to how a sheet of paper is made. The
large cast sheet is then dried and cut into smaller blanks. Via
holes are punched into the blanks, and the lines are screen printed
onto the blanks using masks and a conductive paste. Then, the
layers of the MLC are stacked together and laminated in a press,
cut to size, and sintered in an oven to create a homogenous ceramic
substrate. One or more terminal plating steps may then be
performed, including attaching one or more layers of thin film
interconnects on top of the substrate, before joining the chip to
the substrate.
[0003] Referring now to FIG. 1, there is shown a typical mask 10
known in the art and used to print the conductive lines on the
green sheet blanks. Mask 10 comprises line patterns 12 and 13 each
having a rectangular base section 14 with a width w.sub.l connected
a to circular "cap" section 16 with a diameter d.sub.c. Circular
cap section 16 is intended to be aligned with a hole punched in the
blank, such that the paste flows down into the hole, creating a
conductive via. Line pattern 12 has a "jogged" end 15 that is at an
angle, typically 90.degree. or 135.degree., to rectangular base
section 14.
[0004] Referring now to FIG. 2, there is shown a cross section of a
line-to-via connection 20 on a green sheet blank 22 as manufactured
using a mask of the prior art such as mask 10 shown in FIG. 1. One
known problem, which may be encountered in the creation of such MLC
substrates, is that the mask may be misaligned with blank 22 such
that the hole punched in the blank for the via 27 is not perfectly
centered underneath cap section 16 on mask 10 (shown in FIG. 1). In
such case, line-to-via connection 20 between conductive line 24 and
conductive via 27 may comprise a necked region 28 within the cap
29.
[0005] Cap diameter d.sub.c is typically greater than via diameter
d.sub.v and greater than width w.sub.l. For example, line 24 may
have a width (w.sub.l in FIG. 1) of about 0.071 mm (2.8 mils), via
27 may have a diameter d.sub.v of about 0.089 to about 0.1 mm
(about 3.5 to about 4 mils), and cap 29 may have a diameter d.sub.c
of about 0.114 to about 0.0127 mm (about 4.5 to about 5 mils),
whereas the alignment capabilities of the mask to the blank may
only provide alignment of the cap to the via within an accuracy of
about 0.05 mm (2 mils). Necked region 28 comprises an area having a
thickness t.sub.2 that is less than the thickness t.sub.1 of the
remainder of line 24. This thinner area is subject to concentrated
thermal fatigue stresses during normal operation of the chip, and
may be susceptible to cracking, causing a major reliability problem
for the MLC package.
[0006] An object of the present invention is to provide a method to
solve the cracking problem using line-to-via connection structures
and mask pattern structures that minimize necking.
SUMMARY OF THE INVENTION
[0007] To achieve this and other objects, and in view of its
purposes, the present invention provides a method for minimizing
formation of cracks at junctions between conductive vias and
conductive lines in line-to-via connections on a substrate. Each
line has a base section and a cap. Each cap is positioned over a
via in the substrate, the cap diameter being greater than the via
diameter.
[0008] The method comprises screen printing the conductive lines
onto the substrate with conductive paste using a mask that provides
a transition zone connected between the base section and the cap.
The transition zone provides a volume of conductive paste during
printing that is greater than the volume provided by the base
section being directly connected to the cap. In particular, the
transition zone volume is an effective amount to prevent necking of
the conductive lines into the vias when the mask is misaligned to
the substrate within an expected alignment tolerance. In one
embodiment, the method comprises providing the transition zone with
a greater width than the width of the base section.
[0009] The invention thus also comprises an improvement in standard
conductive line-to-via connections. A standard conductive
line-to-via connection comprises a conductive line connected to a
conductive via having a via diameter. The standard conductive line
has a base section with a first width and a cap with a cap diameter
greater than the via diameter and greater than the first width. The
improvement comprises the conductive line having a transition zone
between the base section and the cap, the transition zone having a
second width greater than the first width. The transition zone may
comprise a jogged end extending from the base section to the cap at
an angle to the line, or a flared end extending from the base
section.
[0010] The invention also comprises a line pattern in a screen
printing mask for forming such a conductive line on a substrate.
The line comprises a base section, a cap adapted to be positioned
over a via in the substrate, and a transition zone connected
between the base section and the cap. The line pattern has a cap
shape adapted to print the cap, a base section shape adapted to
print the base section, and a transition shape connected between
the base section and the cap and adapted to print a transition zone
connected between the base section and the cap. The cap shape has a
cap diameter greater than the via diameter. The transition shape
has a width greater than the width of the base section shape. The
present invention also comprises a screening mask having such a
line pattern.
[0011] It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
but are not restrictive, of the invention.
BRIEF DESCRIPTION OF DRAWING
[0012] The invention is best understood from the following detailed
description when read in connection with the accompanying drawing.
It is emphasized that, according to common practice, the various
features of the drawing are not to scale. On the contrary, the
dimensions of the various features are arbitrarily expanded or
reduced for clarity. Included in the drawing are the following
figures:
[0013] FIG. 1 is a plan view of a mask of the prior art, showing
typical patterns used for screen printing lines and vias onto
blanks;
[0014] FIG. 2 is a cross-sectional view of a blank of the prior
art, showing a line-to-via connection created when a mask such as
the mask shown in FIG. 1 is misaligned with the blank during a
screen printing step;
[0015] FIG. 3 is a plan view of a mask having exemplary patterns in
accordance with the present invention; and
[0016] FIG. 4 is a cross-sectional view of an exemplary line-to-via
connection created on a blank in accordance with the present
invention.
DETAILED DESCRIPTION OF INVENTION
[0017] Referring now to the drawing, in which like reference
numbers refer to like elements throughout, FIG. 3 shows a plan view
of an exemplary mask 110 having patterns 32 and 34. FIG. 4 shows a
cross-sectional view of an exemplary blank 112 having a line-to-via
connection 40 printed on the blank 112 using patterns similar to
those shown in FIG. 3. Because patterns 32 and 34 on mask 110 as
shown in FIG. 3 are then transferred to blank 112 as printed lines
that resemble patterns 32 and 34 in plan view, FIG. 3 is used
interchangeably to refer to features of the patterns on the mask as
well as features of the lines printed on the blank using the mask.
Thus, the reference numbers referring to features of the patterns
as shown in FIG. 3 are also used to refer to the actual features of
the lines as printed by the patterns. In addition to comprising a
method for preventing cracks at junctions between lines and vias,
the present invention also comprises line-to-via connection
structures, patterns, and masks including such patterns for
creating the line-to-via connection structures.
[0018] To minimize the formation of cracks at junctions between
conductive vias and conductive lines in line-to-via connections on
a substrate, the present invention comprises screen printing
conductive lines 42 onto the substrate or blank 112 using a mask
110 that provides a transition zone 36 connected between the line
base section 43 and the cap 46. Transition zone 36 has a geometry
sufficient to provide a volume of conductive paste available to
fill the via during printing that is greater than the volume of
available paste that is provided by the line base being directly
connected to the cap, such as is illustrated by base section 14 and
cap section 16 in FIG. 1. The volume of the transition zone 36 is
specifically an effective amount to prevent necking of conductive
line 42 into the via 44 when mask 110 is misaligned to blank 112.
"Misaligned" means that the alignment is offset from perfect
alignment (where cap 46 is perfectly centered directly over via 44)
within the expected tolerances of the alignment process. Thus, when
the mask 110 is misaligned within the expected tolerances,
transition zone 36 provides an effective amount of conductive paste
available to flow into the via 44 to prevent necking.
[0019] As shown in FIG. 3, the invention comprises patterns 32 and
34 in a screen printing mask 110 for forming conductive lines 42 on
a substrate, as shown in FIG. 4. The substrate is typically a green
(unsintered) ceramic blank 112. Each pattern on mask 110 comprises
shapes adapted to print the shapes as features on blank 112 during
a screen printing step using conductive paste. The attributes of
the pattern are expressed in terms of the features created by the
pattern. For each feature, therefore, there is a corresponding
shape in the pattern adapted to print the feature. Each pattern 32
and 34 as shown in FIG. 3 comprises a cap 46 having a diameter
d.sub.c greater than the diameter d.sub.v of via 44 in blank 112
(shown in FIG. 4) over which the cap 46 is substantially aligned
during printing. Each pattern 32 and 34 also comprises a line base
section 43 having a first width w.sub.l. A transition zone 36,
connected between line base section 43 and cap 46, has a width
w.sub.tf or w.sub.tj that is greater than the base section width
w.sub.l.
[0020] Transition zone 36 may comprise a jogged end 38 extending
from the line base section 43 to the cap 46 at an angle .alpha. to
the base section 43 as illustrated by pattern 32. Angle .alpha. may
be any angle suitable to achieve the configuration desired, but is
typically an angle of 90.degree. or larger, in particular an angle
of 90.degree. or 135.degree.. Jogged end 38 has a width w.sub.tj.
For lines not having a jogged end, such as in pattern 34, the
transition shape may comprise a flared end 39 extending from line
base section 43 to cap 46. Flared end 39 has a width w.sub.tf.
[0021] The result of using patterns 32 or 34 as shown in FIG. 3 is
line-to-via connections such as connection 40 shown in
cross-section in FIG. 4. Line-to-via connection 40 comprises
conductive line 42 connected to conductive via 44. Transition zone
36 between base section 43 and cap 46, as shown in FIG. 3, provides
a greater reservoir of conductive paste at the end of the line 42
than without such a transition zone 36. This larger reservoir
provides enough paste to fill via 44 while maintaining a thickness
of at least t.sub.1 at the junction between line 42 and via 44 as
shown in FIG. 4. As shown in FIG. 3, transition zones 36 each have
a width (w.sub.tf or w.sub.tj) greater than width w.sub.l of base
section 43, providing the effectively larger reservoir of
paste.
[0022] Although in the embodiments illustrated and described above,
the transition zone geometry has an intermediate width greater than
the line base section width but less than the cap width, other
geometries may also be acceptable. For example, the transition zone
may include a variable width, such as a width that gradually
increases from the line base section width to the cap width. Rather
than merely being a different width, the transition zone may have a
geometric shape, such as but not limited to a square, rectangle,
diamond, circle, semicircle, or oval, superimposed over the line
base section connected to the cap. The transition zone preferably
has a width less than or equal to the cap width in some portion of
the zone. It is advantageous for the transition zone width to be
less than or equal to the cap width to optimize the conductor
dimensions and prevent oversize conductor features from potentially
causing bridging to or shorting of adjacent conductors.
[0023] Every transition zone shape must supply an available volume
of paste, however, to effectively fill the via without
necking--even when the pattern and via are misaligned within
predetermined alignment tolerances. Those skilled in the art, given
the volumes of the via and the line features as well as the
properties of the conductive paste being used, may calculate an
effective volume based on the parameters of the individual
application, or may derive the effective volume through
experimentation. This effective volume may then be translated to a
transition zone geometry that provides the available volume of
paste to the via.
[0024] Although the lines and vias described above may comprise any
conductive material, typically the conductive material is a metal,
such as copper, lead-tin solder, molybdenum, and tungsten. Also,
although described with respect to line-to-via connections on an
MLC substrate (typically comprising glass ceramic, alumina, or
plastic board), line-to-via connections having the features
described above may be useful in other substrate materials.
Furthermore, although described with respect to a screen printing
process using conductive paste, the method of preventing crack
formation at line-via interfaces may be applied to other printing
processes for providing lines on substrates that fill holes in the
substrate.
EXAMPLES
[0025] The following examples are included to more clearly
demonstrate the overall nature of the invention. These examples are
exemplary, not restrictive, of the invention.
[0026] In a standard line-to-via connection 40 as shown in FIGS. 3
and 4, width w.sub.l may be about 0.071 mm (2.8 mils). Cap diameter
d.sub.c may be in a range of about 0.114 to about 0.0127 mm (about
4.5 to about 5 mils). Via diameter d.sub.v is typically in a range
of about 0.089 to about 0.1 mm (about 3.5 to about 4 mils).
[0027] For a pattern 32 having a jogged end 38 such as shown in
FIG. 3, the width w.sub.tj of transition zone 36 maybe about 0.089
to 0.107 mm (about 3.5 to 4.2 mils). The above dimensions for the
transition zone 36 also translate to a ratio with respect to the
other features. Thus, for d.sub.c/d.sub.v in the range of about 1.1
to about 1.3, w.sub.tj/w.sub.l is about 1.25 to 1.5 and
w.sub.tj/d.sub.c is about 0.8 to about 1.0.
[0028] Given the same standard line width w.sub.l and ranges for
cap diameter d.sub.c and via diameter d.sub.v above, for a pattern
34 having a flared end 39, width w.sub.tf may be about 0.089 to
0.107 mm (about 3.5 to 4.2 mils). Thus, expressed in the form of a
ratio, for d.sub.c/d.sub.v in the range of about 1.1 to about 1.3,
w.sub.tf/w.sub.l is about 1.25 to 1.5 and w.sub.tf/d.sub.c is about
0.8 to about 1.0.
[0029] Although illustrated and described above with reference to
certain specific embodiments, the present invention is nevertheless
not intended to be limited to the details shown. Rather, various
modifications may be made in the details within the scope and range
of equivalents of the claims and without departing from the spirit
of the invention.
* * * * *