U.S. patent application number 09/766011 was filed with the patent office on 2001-07-05 for single mask screening process and structure produced thereby.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Blazick, James M., Cropp, Michael E., Humenik, James N., Leino, Gerald H., Nayak, Jawahar P., Ranalli, Frank V., Sylvester, Deborah A., Trumpetto, John A., Utter, James C., Vallabhaneni, Rao V., Weisman, Renne L..
Application Number | 20010006116 09/766011 |
Document ID | / |
Family ID | 22765232 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006116 |
Kind Code |
A1 |
Blazick, James M. ; et
al. |
July 5, 2001 |
Single mask screening process and structure produced thereby
Abstract
A process of forming a multi-layer feature on a ceramic or
organic article in which first and second layers of paste are
sequentially screened through a screening mask wherein the
screening mask has not been moved between screening steps. A
structure produced by this process is also disclosed.
Inventors: |
Blazick, James M.;
(Marlboro, NY) ; Cropp, Michael E.;
(LaGrangeville, NY) ; Humenik, James N.;
(LaGrangeville, NY) ; Leino, Gerald H.; (Walden,
NY) ; Nayak, Jawahar P.; (Wappingers Falls, NY)
; Ranalli, Frank V.; (Rhinebeck, NY) ; Sylvester,
Deborah A.; (Poughkeepsie, NY) ; Trumpetto, John
A.; (Hopewell Junction, NY) ; Utter, James C.;
(Fishkill, NY) ; Vallabhaneni, Rao V.; (Hopewell
Junction, NY) ; Weisman, Renne L.; (Poughkeepsie,
NY) |
Correspondence
Address: |
IRA D. BLECKER
IBM CORPORATION
ROUT 52, BLDG. 300-482
HOPEWELL JUNCTION
NY
12533
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
22765232 |
Appl. No.: |
09/766011 |
Filed: |
January 18, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09766011 |
Jan 18, 2001 |
|
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09206159 |
Dec 7, 1998 |
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6238741 |
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Current U.S.
Class: |
174/255 ;
361/793 |
Current CPC
Class: |
H05K 3/1233 20130101;
H05K 2201/035 20130101; H01L 51/0004 20130101; H05K 2203/0139
20130101; H05K 3/245 20130101 |
Class at
Publication: |
174/255 ;
361/793 |
International
Class: |
H05K 001/16 |
Claims
What is claimed is:
1. A method of forming a multi-layer feature on an electronic
substrate article, the method comprising the steps of: a. placing a
screening mask having at least one aperture over the electronic
substrate article; b. screening a first paste through the at least
one aperture of the screening mask to form a first layer of the
multi-layer feature; c. screening a second paste through the same
at least one aperture of the same screening mask used in the first
screening step and onto the first paste to form a second layer of
the multi-layer feature in alignment with the first layer of the
multi-layer feature, wherein the screening mask has not been moved
between the two screening steps; and d. removing the screening
mask.
2. The method of claim 1 further comprising the step of heating the
multi-layer feature.
3. The method of claim 1 wherein in the first screening step, the
paste only partially fills the at least one aperture of the
screening mask.
4. The method of claim 3 wherein in the second screening step, the
paste fills the remainder of the at least one aperture of the
screening mask.
5. The method of claim 1 wherein the first paste is wet when the
second paste is screened onto it.
6. The method of claim 1 wherein the first and second pastes are
metal-containing pastes.
7. The method of claim 1 wherein the first and second pastes are
insulative pastes.
8. The method of claim 1 wherein one of the first and second pastes
is a metal-containing paste and the other of the first and second
pastes is an insulative paste.
9. The method of claim 1 wherein the electronic substrate article
is an organic article.
10. The method of claim 2 wherein the electronic substrate article
is an organic article, the first and second pastes comprise solder
and the step of heating the multi-layer feature causes reflow of
the solder layers.
11. The method of claim 2 wherein the electronic substrate article
is a ceramic substrate and the step of heating causes sintering of
the multi-layer feature.
12. The method of claim 11 wherein the ceramic substrate is a
ceramic greensheet and the method further comprises, prior to the
step of heating: screening a paste onto at least a second ceramic
greensheet to form a wiring feature; removing the screening mask;
and stacking and laminating the ceramic greensheets.
13. The method of claim 11 wherein the ceramic substrate is a
ceramic greensheet laminate.
14. The method of claim 11 wherein the ceramic substrate is a
sintered ceramic substrate.
15. The method of claim 1 wherein the screening mask is a metal
mask.
16. The method of claim I wherein the screening mask is that used
in silk screen printing.
17. The method of claim 1 wherein the first and second steps of
screening are by extrusion screening.
18. The method of claim 1 wherein the first and second steps of
screening are by silk screen printing.
19. The method of claim 1 wherein the multi-layer feature is a
termination pad.
20. The method of claim 1 wherein the multi-layer feature is a
wiring line.
21. The method of claim 1 wherein the multi-layer feature is part
of a capacitor.
22. A multi-layer feature structure on an electronic substrate
article comprising: an electronic substrate article; and a
multi-layer feature structure comprising: a first portion adjacent
to the electronic substrate article; and a second portion having a
bottom and a periphery wherein the first portion contacts the
bottom, and surrounds the periphery of, the second portion so that
the second portion is captured by the first portion.
23. The multi-layer feature structure of claim 22 wherein the
multi-layer feature is a termination pad.
24. The multi-layer feature structure of claim 22 wherein the
multi-layer feature is a wiring line.
25. The multi-layer feature structure of claim 22 wherein the
multi-layer feature is part of a capacitor.
26. The multi-layer feature structure of claim 22 wherein the
electronic substrate article is an organic substrate.
27. The multi-layer feature structure of claim 22 wherein the
electronic substrate article is a ceramic greensheet.
28. The multi-layer feature structure of claim 22 wherein the
electronic substrate article is a ceramic greensheet laminate.
29. The multi-layer feature structure of claim 22 wherein the
electronic substrate article is a sintered ceramic substrate.
Description
RELATED APPLICATION
[0001] This application is related to Buechele et al. U.S. patent
application Ser. No. ______ entitled "A SCREENING APPARATUS
INCLUDING A DUAL RESERVOIR DISPENSING ASSEMBLY" filed even date
herewith, the disclosure of which is incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0002] This invention relates to electronic substrates, and more
particularly, relates to ceramic and organic substrates having
multilayer features thereon for electronics packaging applications
and a method for forming such multilayer features.
[0003] Glass, ceramic and glass ceramic (hereafter just ceramic)
and organic structures are used in the production of electronic
substrates and devices for electronics packaging applications. Many
different types of structures can be used. For example, a
multilayered ceramic circuit substrate may comprise patterned metal
layers which act as electrical conductors sandwiched between
ceramic layers which act as insulators. Organic substrates, also
coalled printed circuit boards, may be single layer or multilayer
material (such as fiberglass-impregnated epoxy) and contain
electrical conductors. The substrates are designed with termination
pads for attaching semiconductor chips, capacitors, resistors,
connection leads, pins, solder balls, solder columns etc.
Interconnection between buried conductor levels in ceramic
substrates can be achieved through vias formed by metal
paste-filled holes in the individual ceramic layers (called
greensheets) formed prior to lamination, which, upon sintering will
become a sintered dense metal interconnection of metal based
conductor. In the case of organic substrates, interconnection
between conductor levels is by, for example, plated through hole
vias.
[0004] The termination pads are often multi-layered stacks of
metallization and are conventionally produced with multiple
screenings, with the underlying layer being screened and dried
before application of another mask and screening and drying of the
next layer. Greenstein U.S. Pat. No. 4,025,669, Siuta U.S. Pat.
5,202,153, and Knickerbocker et al. U.S. Pat. No. 5,293,504, the
disclosures of which are incorporated by reference herein, are
examples where multiple screenings have been utilized to obtain
either a thicker layer or a multiple layer stack of
metallization.
[0005] While the prior art shows the individual layers of the stack
to be perfectly aligned with every other layer in the stack, the
reality is very far from this ideal case. For example, Natarajan et
al. U.S. Pat. No. 5,639,562, the disclosure of which is
incorporated by reference herein, shows a two layer composite metal
pad with both layers perfectly aligned.
[0006] Gaynes et al. U.S. Pat. No. 5,565,033, the disclosure of
which is incorporated by reference herein, discloses a process for
making thicker layers of solder pastes and conductive adhesives.
Gaynes et al. recognizes the disadvantages of multiple screenings
as contamination between successively screened layers and the time
associated with two passes through screening and drying.
[0007] In practice, the individual layers may be shifted from the
layer above or below it. Mitani et al. U.S. Pat. No. 4,324,815, the
disclosure of which is incorporated by reference herein, recognizes
the positional error that can occur with each printing step. As
disclosed in Mitani et al., the bottom layer could be made larger
than the top layer so that the top layer is "captured" by the
bottom layer.
[0008] However, with the trend to increasing the density of the
termination pads (and reducing the spacing between adjoining
termination pads), it is no longer possible to oversize the bottom
layer to capture the top layer. For example, a typical pin grid
array substrate has a nominal pad diameter of 1.5 mm, an interpad
space of 0.3 mm and a pad tolerance of +0/-0.220 mm. This is to be
compared with a typical column grid array substrate which has a
nominal pad diameter of 0.800 mm, an interpad space of 0.200 mm and
a pad tolerance of +/-0.050 mm.
[0009] Accordingly, it is a purpose of the present invention to
have an improved process for producing multilayer stacks of
metallization on a ceramic article and/or organic article.
[0010] It is another purpose of the present invention to have an
improved process for producing multilayer stacks of metallization
on a ceramic article and/or organic article which eliminates the
positional errors which heretofore have been inherent in multiple
screenings of metallization.
[0011] It is yet another purpose of the present invention to have
an improved process for producing multilayer stacks of
metallization for use as termination pads, lines and other
features.
BRIEF SUMMARY OF THE INVENTION
[0012] One aspect of the invention relates to a method of forming a
multi-layer feature on an electronic substrate article, the method
comprising the steps of:
[0013] a. placing a screening mask having at least one aperture
over the electronic substrate article;
[0014] b. screening a first paste through the at least one aperture
of the screening mask to form a first layer of the multi-layer
feature;
[0015] c. screening a second paste through the same at least one
aperture of the same screening mask used in the first screening
step and onto the first paste to form a second layer of the
multi-layer feature in alignment with the first layer of the
multi-layer feature, wherein the screening mask has not been moved
between the two screening steps; and
[0016] d. removing the screening mask.
[0017] A second aspect of the invention relates to a multi-layer
feature structure on an electronic substrate article
comprising:
[0018] an electronic substrate article; and
[0019] a multi-layer feature structure comprising:
[0020] a first portion adjacent to the electronic substrate
article; and
[0021] a second portion having a bottom and a periphery wherein the
first portion contacts the bottom, and surrounds the periphery of,
the second portion so that the second portion is captured by the
first portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The features of the invention believed to be novel and the
elements characteristic of the invention are set forth with
particularity in the appended claims. The Figures are for
illustration purposes only and are not drawn to scale. The
invention itself, however, both as to organization and method of
operation, may best be understood by reference to the detailed
description which follows taken in conjunction with the
accompanying drawings in which:
[0023] FIG. 1 is a side view of a prior art multilayer pad in which
the top layer is misaligned with respect to the bottom layer.
[0024] FIG. 2 is a side view of a prior art multilayer pad in which
the bottom layer has been made larger to capture the top layer.
[0025] FIG. 3 is a flow chart showing the process flow for the
prior art process of multiple screenings to form a multilayer
pad.
[0026] FIG. 4 is a flow chart showing the process flow for the
process according to the present invention of multiple screenings
to form a multilayer feature.
[0027] FIGS. 5A, 5B and 5C are schematical cross-sectional views
showing the different steps in producing the multilayer feature
according to the present invention.
[0028] FIGS. 6A and 6B are top views of the multilayer feature
produced according to the present invention.
[0029] FIG. 7 is a schematical cross-sectional view of a second
multilayer feature produced according to the present invention.
[0030] FIG. 8 is a schematical cross-sectional view of a third
multilayer feature produced according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] Referring to the drawings in more detail, and particularly
referring to FIG. 1, multilayer pad 12 has been formed on ceramic
substrate 10. Due to positional error resulting from multiple
screenings, top layer 16 is not aligned with bottom layer 14. The
misalignment results in portion 18 of top layer 16 contacting
ceramic substrate 10. The consequences of this structure are that a
termination pad of reduced dimension has been formed and that if
top layer does not bond well with ceramic substrate 10, the
misalignment can cause delamination or spalling of top layer
16.
[0032] In FIG. 2, multilayer pad 12 on ceramic substrate 10 has
been formed with bottom layer 14 larger than top layer 16. In this
way, full contact between top layer 16 and bottom layer 14 is
assured even if there is positional error from the multiple
screenings. A disadvantage of this arrangement is that excess space
has been taken up by the multilayer pad 12, thereby reducing the
possible density of the remaining multilayer pads (not shown) on
the ceramic substrate.
[0033] The prior art process for producing a two-layer multilayer
pad is illustrated in FIG. 3. The first layer is screened 20
through a mask onto a ceramic greensheet. The mask is removed 22
followed by drying 24 and inspection 26 of the screened features.
Thereafter, the second layer is screened 28 through a mask onto the
first layer. The mask is then removed 30 followed by drying 32 and
inspection 34 of the screened features. Finally the greensheet is
stacked with other ceramic greensheets, laminated and sintered.
[0034] It doesn't matter whether the same mask or different masks
are used in the prior art process to screen both of the layers, the
result will be the same, namely, misalignment between the two
layers due to positional error.
[0035] Referring now to FIG. 4, the process according to the
present invention is illustrated. The first layer of the multilayer
feature is screened 36 onto an electronic substrate article with
the mask. Without moving the mask, the second layer is screened 38
through the same mask.
[0036] Referring now to FIG. 5A, mask 48 having feature opening 50
in line with via 47 is situated on electronic substrate article 46.
Mask 48 is preferably a metal mask suitable for extrusion screening
but it is contemplated within the scope of the present invention
that a mesh mask suitable for silk screen printing could also be
used, although it is clearly not preferred because of the inherent
movement of the mesh mask during the silk screen printing process.
Nozzle 52 is poised to provide a quantity of paste for
screening.
[0037] The preferred screening apparatus, including the nozzle, is
described in more detail in Applicants' RELATED APPLICATION. Nozzle
52 should be relatively pliable for reasons which will become
apparent hereafter. Suitable materials for nozzle 52 could be
polyurethane, elastomers, thermoplastics, natural rubber, silicone,
TEFLON (TEFLON, a tetrafluoroethylene (TFE) compound is a trademark
of E.I. duPont de Nemours & Co.) or other similar
materials.
[0038] Nozzle 52 will screen the paste into feature opening 50. Due
to the pliable nature of the nozzle 52, part of the screened paste
is scooped out by the pliable nozzle 52 leaving layer 54 only
partially filling the feature opening 50. Nozzle 52 will also wipe
the mask, removing any paste residue. The resulting unfilled
portion 56 of feature opening 50 will be filled by the second
layer. If unfilled portion 56 were not present, there would be no
place for the second layer to fill in the feature opening 50. As
can be seen in FIG. 5B, the first layer 54 will fill the bottom
portion of feature opening 50 and will also usually fill the top
portion of feature opening 50 along the walls of feature opening
50. The resulting unfilled portion 56 is dish-shaped.
[0039] It is not necessary to dry layer 54 before proceeding to the
next screening step.
[0040] Next, nozzle 58 will screen the second layer 60 of paste
into feature opening 50 to fill it as illustrated in FIG. 5C.
Nozzle 58 is chosen to be made of a hard material such as a
carbide, tool steel or ceramic material. The purpose of nozzle 58
is to fill the remaining portion 56 of feature opening 50. If
nozzle 58 were pliable like nozzle 52, paste would be screened into
feature opening 50 and then scooped out so that the feature opening
would remain unfilled.
[0041] The pastes used are preferably metal-containing (conducting)
pastes although insulative (nonconducting) paste or pastes, or
combinations of metal-containing pastes and insulative pastes,
could be used for a given application.
[0042] Also, the pastes for the different layers will typically
differ from layer to layer so that the most advantageous properties
can be developed for each layer. That is, the first layer 54 may be
formulated for adhesion to the electronic substrate article 46
while the second layer 60 may be formulated for soldering or
brazing.
[0043] The present invention is most suitable for a two-layer
multilayer feature. It is possible, however, by varying the
hardness of the nozzles 52, 58 to build up three or more layers
according to the present invention.
[0044] Referring back to FIG. 4, the mask is removed 40 followed by
drying 42 and inspection 44 of the screened features.
[0045] In a preferred embodiment of the present invention, the
multilayer feature shown in FIGS. 5A, 5B and 5C is a multilayer
termination pad formed on a ceramic greensheet 46. Subsequent to
the step of inspecting, the ceramic greensheet 46 with the
multilayer termination pad would be stacked with other appropriate
greensheets having appropriate wiring features (as is well known to
those skilled in the art), laminated under pressure and then
sintered to form a multilayer ceramic substrate having at least one
multilayer termination pad.
[0046] The resulting multilayer feature is shown in FIG. 6A prior
to laminating and in FIG. 6B after laminating and sintering. As a
result of laminating, the exposed part of first layer 54 becomes
greater. As can be seen, first layer 54 completely captures second
layer 60. Due to the fact that the screening mask is never moved
between screening steps, there is complete alignment between first
layer 54 and second layer 60. This would be true even if first
layer 54 did not rise up along the walls of the feature opening as
shown in FIG. 5B.
[0047] Surprisingly, there is little or no contamination of the
first layer 54 by the second layer 60 even though the paste for the
second layer 60 can be screened on while the paste for the first
layer 54 is still wet. The fact that first nozzle 52 wipes the mask
48 after screening is useful in avoiding intermixing of the first
layer 54 and the second layer 60.
[0048] Instead of forming the multilayer termination pads on
ceramic greensheets, the multilayer termination pads could be
formed on a greensheet laminate, i.e. a stack of laminated
greensheets, a sintered ceramic substrate, or an organic substrate,
in which case the process flow of FIG. 4 would still apply. After
inspection, the greensheet laminate and multilayer termination pads
would be sintered while the sintered ceramic substrate and
multilayer termination pads would be resintered. As to the organic
substrate the preferred multilayer termination pad would comprise
solder paste. After inspection, the organic substrate and
multilayer termination pad would be heated to cause reflow of the
solder.
[0049] Too, instead of forming multilayer termination pads, the
present invention could be utilized to form other multilayer
features. Illustrated in FIG. 7 is another embodiment of the
present invention in which multilayer lines or wiring patterns 62,
one of which contacts via 47, are formed-on ceramic article 46.
Illustrated in FIG. 8 are ceramic articles 46, preferably ceramic
greensheets, wherein one ceramic article 46 contains a multilayer
feature 64 which in conjunction with via 47 forms an in-line
capacitor. In practice, the two ceramic articles 46 in FIG. 8 would
be adhered together, or in the case of ceramic greensheets, would
be laminated and sintered.
[0050] It will be apparent to those skilled in the art having
regard to this disclosure that other modifications of this
invention beyond those embodiments specifically described here may
be made without departing from the spirit of the invention.
Accordingly, such modifications are considered within the scope of
the invention as limited solely by the appended claims.
* * * * *