U.S. patent application number 12/190537 was filed with the patent office on 2008-12-04 for simultaneous and selective partitioning of via structures using plating resist.
This patent application is currently assigned to SANMINA SCI CORPORATION. Invention is credited to George Dudnikov, JR..
Application Number | 20080296057 12/190537 |
Document ID | / |
Family ID | 36941913 |
Filed Date | 2008-12-04 |
United States Patent
Application |
20080296057 |
Kind Code |
A1 |
Dudnikov, JR.; George |
December 4, 2008 |
Simultaneous and selective partitioning of via structures using
plating resist
Abstract
Systems and methods for simultaneously partitioning a plurality
of via structures into electrically isolated portions by using
plating resist within a PCB stackup are disclosed. Such via
structures are made by selectively depositing plating resist in one
or more locations in a sub-composite structure. A plurality of
sub-composite structures with plating resist deposited in varying
locations are laminated to form a PCB stackup of a desired PCB
design. Through-holes are drilled through the PCB stackup through
conductive layers, dielectric layers and through the plating
resist. Thus, the PCB panel has multiple through-holes that can
then be plated simultaneously by placing the PCB panel into a seed
bath, followed by immersion in an electroless copper bath. Such
partitioned vias increase wiring density and limit stub formation
in via structures. Such partitioned vias allow a plurality of
electrical signals to traverse each electrically isolated portion
without interference from each other.
Inventors: |
Dudnikov, JR.; George; (San
Jose, CA) |
Correspondence
Address: |
LAW OFFICE OF ANDREI D POPOVICI, P.C.
4020 MOORPARK AVE., SUITE101
SAN JOSE
CA
95117
US
|
Assignee: |
SANMINA SCI CORPORATION
San Jose
CA
|
Family ID: |
36941913 |
Appl. No.: |
12/190537 |
Filed: |
August 12, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11369448 |
Mar 6, 2006 |
|
|
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12190537 |
|
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|
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60658886 |
Mar 4, 2005 |
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Current U.S.
Class: |
174/266 ;
174/250 |
Current CPC
Class: |
Y10T 29/49155 20150115;
H05K 3/429 20130101; H05K 3/184 20130101; H05K 3/422 20130101; Y10T
29/49124 20150115; Y10T 29/49165 20150115; Y10T 29/49126 20150115;
H05K 2201/0187 20130101; H05K 2201/0738 20130101; H05K 1/0259
20130101; H05K 2201/09645 20130101; H05K 1/116 20130101; H05K
2201/09718 20130101; Y10T 29/49156 20150115; H05K 1/0257 20130101;
H05K 1/167 20130101; H05K 2201/09881 20130101; Y10T 29/49117
20150115; H05K 2201/096 20130101; Y10T 29/49139 20150115 |
Class at
Publication: |
174/266 ;
174/250 |
International
Class: |
H05K 1/11 20060101
H05K001/11; H05K 1/00 20060101 H05K001/00 |
Claims
1. A multilayer PCB, said multilayer PCB comprising: at least one
sub-composite structure having: a dielectric layer sandwiched
between a conductive pad and a conductive layer; and a selective
deposit of plating resist deposited on said conductive pad; a
through-hole drilled through said multilayer PCB and passing
through said layer of plating resist, wherein an interior surface
of said through-hole is plated with conductive material in areas
that are devoid of said plating resist to form a partitioned via
structure through said multilayer PCB.
2. A sub-composite structure for use with a multilayer PCB, said
sub-composite structure comprising: a dielectric layer sandwiched
between a conductive pad and a conductive layer, and a selective
deposit of plating resist deposited on said conductive pad.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/369,448, filed Mar. 6, 2006, which claims the benefit
of Provisional U.S. Patent Application No. 60/658,886, filed Mar.
4, 2005, both of which are incorporated herein by reference in
their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to printed circuit boards
(PCBs), and more particularly, to systems and methods for
simultaneously partitioning a via structure into electrically
isolated portions by using plating resist within a PCB stackup for
allowing a plurality of electrical signals to traverse each
electrically isolated portion without interference from each
other.
BACKGROUND
[0003] Consumers are increasingly demanding both faster and smaller
electronic products. The use of PCBs has grown enormously as new
electronic applications are marketed. A PCB is formed by laminating
a plurality of conducting layers with one or more nonconducting
layers. As the size of a PCB shrinks, the relative complexity of
its electrical interconnections grows.
[0004] A plated via structure is traditionally used to allow
signals to travel between layers of a PCB. The plated via structure
is a plated hole within the PCB that acts as a medium for the
transmission of an electrical signal. For example, an electrical
signal may travel through a trace on one layer of the PCB, through
the plated via structure's conductive material, and then into a
second trace on a different layer of the PCB.
[0005] Unfortunately, due to limitations within the prior art, the
plated via structure may be longer than necessary to perform the
function of electrical connectivity. For example, the plated via
structure may extend completely through the PCB but only connect
two traces on two proximate adjacent layers. As a result, one or
more stubs may be formed. A stub is excessive conductive material
within the plated via structure which is not necessary to transport
the electrical signal.
[0006] When a high speed signal is transmitted through the plated
via structure, a "stub effect" may distort the signal. The stub
effect is a result of the useless excess conductive material
present within the plated via structure. The stub effect occurs
when a portion of the signal is diverted away from the trace
connections and into one or more stubs of the plated via structure.
The portion of the signal may be reflected from the end of the stub
back toward the trace connections after some delay. This delayed
reflection may interfere with signal integrity and increase, for
example, the bit error rate of the signal. The degenerating effect
of the stub effect may increase with the length of the stub. As
much as 50% of signal attenuation at signals running at 10 Gigabits
per second may be due to the stub in the plated via structure. Via
structures with short stubs can be manufactured but require
sequential processing, which increases costs substantially.
[0007] FIG. 1 is an illustration of a PCB 100 with a plated via
structure 110 and a stub 170 in the prior art. The PCB 100 consists
of conducting layers 130 separated by nonconductive dielectric
layers 120. Typically, the plated via structure 110 includes a
barrel (i.e., shaft of the via structure) that is cylindrical in
shape and is plated with a conductive material 180. The plated via
structure 110 allows an electrical signal 160 to transmit from a
trace 140 on a first conducting layer 130 of the PCB 100 to a trace
150 on a second conducting layer 130. The stub 170 of the plated
via structure 110 is the unnecessary portion of the plated via
structure 110, which may create the stub effect.
[0008] FIG. 2 is an illustration of the PCB 100 with the plated via
structure 110 after the stub 170 (shown in FIG. 1) has been removed
by backdrilling in the prior art. Backdrilling the unnecessary
portion of the plated via structure 110 to reduce or remove the
stub 170 is one method to reduce the stub effect. Backdrilling is a
viable alternative to sequential layer processing but has
limitations. Typically, a drill bit backdrills the stub 170 thereby
removing a portion of the unnecessary excess conductive material of
the plated via structure 110. A backdrilled hole 200 is created
once the drill bit removes a portion of the stub 170 from the
plated via structure 110. The drill bit is commonly a carbide drill
bit in a computer numerically controlled (CNC) drill machine. As a
result of backdrilling, the portion of the stub 170 of the plated
via structure 110 is removed, thereby reducing, but not completely
eliminating, parasitic capacitance, parasitic inductance, and time
delay, which may interfere with signal integrity.
[0009] In most cases, design concessions need to be made to allow
for deviations in the accuracy of the drilling equipment. If the
backdrilling is inaccurate (e.g. too deep or off center), then a
functional portion of the plated via structure 110 may be removed
and the PCB 100 may be ruined. As a consequence, a new PCB 100 must
be reconstructed and backdrilled. Thus, yields are reduced and
costs are increased.
[0010] The backdrilling process is also limited in the tolerances
that can be reliably held. Backdrilling is typically only
controllable to a depth tolerance of +/-5 mils. In many cases,
further design concessions need to be made due to limitations in
the strength and consistency of the layers to allow for variations
in the placement, width, and direction of drilling.
[0011] Yet another limitation is that many designs require the
backdrilling of multiple plated via structures 110 where the stubs
170 may be at different depths. This requires specialized
programming of the drill tool files, which takes time and money to
produce.
[0012] Further, backdrilling multiple plated via structures 110
typically is a serial process, so that the time needed to backdrill
the PCB 100 increases with the number of stubs 170. If any one of
the stubs 170 is drilled improperly, the PCB 100 may be ruined.
Therefore, backdrilling a number of stubs 170 increases the
probability of damage to the PCB 100.
[0013] Another limitation is that many designs also require stubs
to be removed from both surfaces of the PCB 100. This requires that
the PCB 100 be reoriented during the backdrilling process, which
further takes time, requires additional programming, and adds
potential error to the accuracy of the backdrilling process.
[0014] Further, drill bits are prone to breakage which reduces
yields and requires rework of the PCB 100. The process of reworking
each individual plated via structure 110 adds cycle time and
increases costs in production. Moreover, drill bits are expensive,
which further drives up costs.
[0015] One consequence of backdrilling is that the volume of the
removed stub barrel is not functional in the context of circuit
routing. No other trace or interconnect on any layer can pass
through the volume of the removed stub. Circuit traces need to be
re-routed around such volumes. In most cases, additional layers
need to be added to effectively route all the traces in a given
design and thus add to complexity and cost.
[0016] PCBs can be split into two or more sections to reduce stub
lengths or increase wiring density using methods known in the art
such as sequential processing techniques. With sequential
processing, two separate PCB subassemblies are individually
manufactured. The two subassemblies are subsequently laminated
together and through-holes or vias are plated to connect the two
individual PCBs into one. Stubs can be controlled in this manner,
but are limited to the layers between the two individual sub
assemblies. Because of the "sequential nature" of such a lamination
process, additional process steps are required and cost and cycle
time to manufacture is significantly increased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is an illustration of a PCB with a plated via
structure and a stub in the prior art.
[0018] FIG. 2 is an illustration of the PCB with the plated via
structure after the stub has been removed by backdrilling in the
prior art.
[0019] FIG. 3 is an illustration depicting a PCB with a plated via
structure formed through a plating resist, according to certain
embodiments.
[0020] FIG. 4 is an illustration depicting a core sub-composite
structure covered with a layer of etch resist that is selectively
exposed to electromagnetic radiation, according to certain
embodiments.
[0021] FIG. 5 is an illustration depicting the conducting layers
and the dielectric layer of sub-composite structure with an area of
altered etch resist, according to certain embodiments of the
invention.
[0022] FIG. 6 is an illustration depicting the conducting layers
and the dielectric layer of a sub-composite structure with the
altered etch resist and a portion of the conducting layer removed
to form a clearance in the conductive layer, according to certain
embodiments.
[0023] FIG. 7 is an illustration depicting the conducting layers
and the dielectric layer of sub-composite structure with the
unaltered etch resist removed, according to certain
embodiments.
[0024] FIG. 8 is an illustration depicting the conducting layers
and the dielectric layer of a sub-composite structure with the
plating resist deposited within the clearance, according to certain
embodiments.
[0025] FIG. 9 is an illustration depicting a PCB stackup with a
partitioned plated via structure formed using a thicker layer of
plating resist, according to certain embodiments.
[0026] FIG. 10 is an illustration depicting a PCB stackup with a
partitioned plated via structure formed by selectively depositing
plating resist in a clearance formed in a conducting layer and an
adjacent dielectric layer of a sub-composite structure, according
to certain embodiments.
[0027] FIG. 11 is an illustration depicting a PCB stackup with a
partitioned plated via structure formed by selectively depositing
plating resist on the surface of a sub-composite structure on an
anti-pad region of the surface that is coplanar with the top
conducting layer of the sub-composite structure, according to
certain embodiments.
[0028] FIG. 12 is an illustration depicting a PCB stackup with a
partitioned plated via structure formed by selectively depositing
plating resist on a conductive region or conductive pad on the
surface of the sub-composite structure, according to certain
embodiments.
DETAILED DESCRIPTION OF THE INVENTION
[0029] A cost effective and efficient system to minimize signal
degradation is to electrically isolate, reduce, or eliminate a stub
by controlling the formation of a conductive material within a
plated via structure of a printed circuit board (PCB). One or more
areas of plating resists within the via structure are used to
resist the formation of conductive material by intentionally
creating one or more voids in the via structure. As a result, the
formation of conductive material within the via structure may be
limited to those areas necessary for the transmission of electrical
signals. According to certain embodiments, the partitioning of the
via structure into electrically isolated segments can dramatically
increase the route capabilities or wiring density of a PCB design.
This is because each electrically isolated segment of the
partitioned via can be used to electrically connect signals on
layers associated that particular segment.
[0030] A multilayer PCB can be a chip substrate, a motherboard, a
backplane, a backpanel, a centerplane, a flex or rigid flex
circuit. The invention is not restricted to use in PCBs. A via
structure can be a plated through-hole used for transmitting
electrical signals from one conducting layer to another. A plated
via structure can also be a component mounting hole for
electrically connecting an electrical component to other electrical
components on the PCB.
[0031] The methods to electrically isolate, reduce, or eliminate a
stub within via structures of PCBs may be faster and more efficient
than backdrilling. Plating resists may be placed within the many
clearances in the conducting and/or dielectric layers of the PCB
simultaneously. In most cases PCBs can have through-holes and vias
in the order of 100,000 plus. At the same time, the multi-layer PCB
can have multiple layers. It would be advantageous to partition
each of the vias and control the stub to variable degrees for each
via. In other words, each via can be partitioned at different
layers and at different locations. To be able to partition all the
vias simultaneous on a single panel, plating resist can be
selectively deposited on a selected layer of each sub-composite
core during the making of the PCB stackup prior to drilling and
subsequent plating of the vias in the panel. For example, all the
clearances within a layer of a PCB may be formed concurrently. In
another example, the conductive material may be formed within all
of the via structures of a PCB at the same time. In contrast, as
discussed previously, backdrilling is generally performed upon one
via structure at a time. Thus, methods incorporating plating
resists to limit stub formation may allow for faster production of
PCBs than backdrilling.
[0032] FIG. 3 is an illustration depicting a PCB 300 with a plated
via structure 330 formed through a plating resist 370, according to
certain embodiments. The PCB 300 includes conducting layers
310a-310e separated by dielectric layers 320a-320e. The plated via
structure 330 is plated with a seed conductive material 390 and a
further coating of conductive material 392. The plated via 330 is
effectively partitioned into a plurality of electrically isolated
portions (330a, and 330b) by selectively depositing plating resist
in a sub-composite structure for making the PCB stackup. A method
of partitioning a plated via such as plated via 330 is described
herein with reference to FIGS. 4 to 8.
[0033] FIG. 3 shows that the plated via allows an electrical signal
360 to transmit from one trace 340 or component mounting pad on a
first conducting layer 310a to another trace 350 on a second
conducting layer 310b of the PCB 300 by traversing the isolated
portion 330a of the via 330. Similarly, the isolated portion 330b
of the via 330 allows another electrical signal 362 to transmit to
trace 380 without interfering with the signal 360.
[0034] Plating resist is a generally nonconductive material
deposited in one or more clearances of conducting and dielectric
layers. For example, in FIG. 3, plating resist is deposited in a
clearance in the conducting layer 310d. When PCB 300 is placed in a
seed or catalyzing bath, the seed will deposit on all areas of the
via wall but will not deposit on the plating resist. Should small
amounts of seed be deposited on the plating resist, a post
processing operation can be utilized to remove these residual
deposits. Subsequently, when the panel is placed into an
electroless copper or electrolytic copper plating bath, copper will
plate where there is seed or conductivity and will not plate or
deposit in the area where there is plating resist. The plating
resist will form a cylindrical void that effectively partitions the
barrel of the via into segments.
[0035] The plating resist 370 prevents the deposition of the
catalyzing material 390 and conductive material 392 within the via
structure 330 at the conducting layer 310d. As a result, via 330 is
partitioned into the electrically isolated portions 330a, and 330b.
Consequently, the electric signal 360 travels from the first
conducting layer 310a to the second conducting layer 310b without
signal integrity being degraded through interference caused by
section 330b. The conductive material 392 of the plated via
structure 330 is the medium through which the electrical signal 360
travels from the first conducting layer 310a of the PCB 300 to the
second conducting layer 310b. Similarly, electric signal 362
traverses plated via 330 conductive layer 310e. The plated via
structure 330 may be of any shape.
[0036] Some examples of the conductive or catalytic material 390
are electroless copper, palladium seed. The catalytic seeding
process can also include electrophoretic plating, or direct
metallization. The plating process wherein the conductive material
392 such as conductive metal, or copper is deposited within the via
structure 330 may comprise electrolytic plating, or an electroless
process.
[0037] The PCB 300 can have any number of conducting layers and
dielectric layers. FIG. 3 only shows five layers of conducting
layers 310a-310e and five layers of dielectric layers 320a-320e for
the sake of simplicity. Each of the conducting layers 310a-310e may
comprise a partial or full layer such as a power or ground layer,
may comprise a layer of circuit traces, or may comprise a layer
with both circuit traces and a partial layer such as a ground
layer. A non-limiting example of the conducting layers 310a-310e is
copper. Some non-limiting examples of dielectric layers 320a-320e
are FR-4, epoxy glass, polyimide glass, ceramic hydrocarbon,
polyimide film, resin impregnated woven glass, film, resin
impregnated matte material, Kevlar, paper, and resin dielectrics
with dispersed nano-powders. According to certain embodiments, the
partitioned via is filled with an insulating or resistive paste to
improve reliability or functionality.
[0038] A method of partitioning a plated via such as plated via 330
is described herein with reference to FIGS. 4 to 8. As described
further herein, a clearance is a hole that is within at least one
conducting layer 310a-310e and/or at least one dielectric layer
320a-320e. For example, a clearance may be formed in the conducting
layer 310e. Each clearance has a radius greater than the plated via
structure 330. The formation of the clearances through an etching
process is described below with reference to FIGS. 4-8.
[0039] FIGS. 4-8 are examples depicting etching a clearance within
the conducting layer 310d, as well as the placement and deposition
of the plating resist 370, according to certain embodiments of the
invention. It is to be noted that the etching as described with
reference to FIGS. 4-8 would apply to both conductive layers of the
sub-composite structure. For purposes of simplicity, the etching is
described with reference to one conductive layer (310d) of FIG.
4-8. Further, for simplicity, FIGS. 4-8 describes the selective
deposition of plating resist on one location in a core
sub-composite structure. However, it is understood that plating
resist can be selectively deposited on multiple locations in the
sub-composite structure depending on the PCB design. Moreover, each
sub-composite structure may have the plating resist selectively
deposited on different layers than that of other sub-composite
structures so as to achieve the desired PCB design by laminating
these various sub-composite structures to form the PCB stackup.
[0040] FIG. 4 is an illustration depicting a core sub-composite
structure covered with a layer of etch resist that is selectively
exposed to electromagnetic radiation, according to certain
embodiments. FIG. 4 shows sub-composite structure 402 (also
referred to herein as a core) that includes a dielectric layer 320d
sandwiched between two conducting layers 310d, and 310e. Conductive
layer 310d is covered with an etch resist 400. Portions of the etch
resist is covered with a mask 410.
[0041] The etch resist 400 is any material that is applied to an
area of the conducting layer 310d to prevent reaction of that area
during an electromagnetic, chemical, or electrochemical etching
process. The etch resist 400 may be processed by a lithographic
process, by selective deposition, or by direct laser imaging. Some
examples of etch resist 400 are photoresist, organic material, dry
film, sheet, paste, polymer thick film, and liquid.
[0042] Mask 410 is a film or plate that selectively covers an area
to prevent reaction of the covered area during the electromagnetic,
chemical, or electrochemical reaction. Some examples of the mask
410 are silver film, glass, or diazo film. Mask 410 may be
positioned over the etch resist 400 with a mask aligner (not
depicted) which is configured to control the placement of the mask
410. The exposed portion of the etch resist 400 is exposed to
electromagnetic radiation 420, or a laser, as non-limiting
examples, and altered to make the exposed etch resist removable
while leaving the covered etch resist undisturbed. In the case of
using a laser, mask 410 is not needed.
[0043] FIG. 5 is an illustration depicting the conducting layers
310d, 310e and the dielectric layer 320d of sub-composite structure
402 with an area of altered etch resist 500, according to certain
embodiments of the invention. The electromagnetic radiation 420
(FIG. 4) has been terminated and the mask 410 (FIG. 4) has been
removed thereby exposing the unaltered etch resist 400.
[0044] FIG. 6 is an illustration depicting the conducting layers
310d, 310e and the dielectric layer 320b of sub-composite structure
402 with the altered etch resist 500 (FIG. 5) and a portion of the
conducting layer 310d removed to form a clearance 600 in the
conducting layer 310d, according to certain embodiments. The
altered etch resist 500 (FIG. 5) has been removed by methods well
known in the art thereby exposing a portion of the conducting layer
310d. The exposed portion of the conducting layer 310d is then
etched to form the clearance 600 and expose the dielectric layer
320d. Clearance 600 can be in a ground or power plane or in
conductive pad or feature on a signal layer.
[0045] FIG. 7 is an illustration depicting the conducting layers
310d, 310e and the dielectric layer 320d of sub-composite structure
402 with the unaltered etch resist 400 removed, according to
certain embodiments. The unaltered etch resist 400 (FIGS. 4-6) may
be removed by methods well known in the art, thereby exposing the
conducting layer 310d.
[0046] FIG. 8 is an illustration depicting the conducting layers
310d, 310e and the dielectric layer 320d of sub-composite structure
402 with the plating resist 870 deposited within the clearance 600,
according to certain embodiments.
[0047] For example, a plating resist can be deposited into a
clearance using printing, stencil printing, needle dispensing, etc.
The plating resist can be a hydrophobic insulating material that is
resistant to the deposition of a catalytic species capable of
catalyzing an electroless metal deposition. The plating resist can
also be a material that resists deposition of other "seed" deposits
such as colloidal graphite.
[0048] The plating resist can be deposited so as to be flush or
higher than the etched clearance layer. The plating resist can be a
paste or viscous liquid. Some non-limiting examples of plating
resists are silicone resins, polyethylene resins, fluorocarbon
resins, polyurethane resins, and acrylic resins. Such insulating
hydrophobic resinous material can be used alone or in a combined
composition with other resinous materials in amounts sufficient to
maintain hydrophobic properties in the combined composition.
[0049] After depositing the plating resist, the plating resist is
cured using appropriate methods. The sub-composite structure 402
with plating resist 870 in place can now be laminated to the rest
of the multilayer PCB stackup using techniques well known in the
art. Multiple sub-composite structures (cores) with selectively
deposited plating resist areas in varying locations can be
laminated to form a PCB stackup. Through-holes are drilled through
the PCB stackup through conductive layers, dielectric layers and
through the plating resist.
[0050] Thus, the PCB panel has multiple through-holes that can then
be plated simultaneously by placing the panel into a seed bath,
followed by immersion in an electroless copper bath. A non-limiting
example of a seed bath is copper palladium colloid. An example for
surface plating can be found in U.S. Pat. No. 4,668,532. The
electroless copper provides the initial conductivity path to allow
for additional electrolytic copper plating of the barrel of each
through-hole in the panel. The seed chemistry (electroless copper)
will deposit on the surface of the through-hole wall, but will not
deposit effectively on areas of the wall with the plating resist. A
small amount of electroless copper may deposit on the plating
resist but such an amount can be removed with a post processing
step known in the art. For example, any small amounts of
electroless copper that may be deposited on the plating resist can
be removed by contacting the affected areas with a chelating agent
in an alkaline solution for a time period sufficient to remove
essentially all of said catalytic species from the hydrophobic
plating resist. The panel will then follow known processes either
for panel plating or pattern plating. For example, electrolytic or
electroless plating can be used. In other words, the interior walls
of the through-holes are contacted with a metal deposition solution
to metallize only the exposed catalytic areas of the walls not
protected by the hydrophobic plating resist.
[0051] Plating of conductive material in the via structure will
build wherever there is seed material. Similarly, no plating of
conductive material will form where there is plating resist. Thus,
the areas that are void of plated conductive material in the via
structure effectively partition the via into electrically isolated
sections. By strategically placing plating resist in certain
locations and on certain layers of a PCB stackup, multiple
electrically isolated portions in via structures can be formed,
simultaneously.
[0052] Thus, the above method can be used to configure the via
structure into multiple electrically isolated segments. Each such
segment provides interconnect paths to appropriate layers within
the PCB. Such partitioned vias can be subsequently filled with an
insulating material like epoxy or other insulating or resistive
polymer for improved reliability or increased functionality.
Therefore, costly, error prone, and time intensive backdrilling may
be avoided. Similarly, referring back to FIG. 3. the use of the
plating resist 370 avoids possible damage to the PCB 300 which may
result by backdrilling. A further advantage is that, whereas
backdrilling is typically controllable to a depth tolerance of +/-5
mils, a controllable depth tolerance of +/-1 mils or better may be
achieved by the systems and methods described herein. As a result,
the consistency between the plating resist 370, the dielectric
layers 320b, and the conducting layer 310c may be held to a tighter
standard deviation as compared to backdrilling.
[0053] According to certain embodiments, a thicker resist deposit
may be preferred. In such a case, the sub-composite structure or
core is mechanically drilled with through-holes corresponding to
areas where partitioned via structures are desired in the resulting
PCB stackup. The thickness of the sub-composite structure can range
from about 1-50 mils. Thus, a thicker deposit of plating resist can
be produced. The through-holes are filled with plating resist using
specialized hole filling equipment, stenciling or screen printing.
Such a process is known as hole-plugging or via-filling. The
plating resist is then cured using an appropriate process. A
planarizing or scrubbing operation may be employed to remove any
excess plating resist from the surface of the sub-composite
structure. The sub-composite structure can be processed using
standard PCB procedures to form circuit images. It is to be noted
that the through-holes can be filled with plating resist before or
after forming circuit images. The sub-composite structure can then
be laminated into a multilayer PCB stackup and the process can
continue as described above for electroless seeding and subsequent
plating of the interior walls of the one or more via structures in
the PCB stackup. According to certain embodiments, the partitioned
via is filled with an electrically insulating material, ohmically
resistive paste or voltage switchable dielectric material to
improve reliability or functionality. In the case of using voltage
switchable dielectric material, programmable circuit routing in
PCBs can be made. Further, the voltage switchable dielectric
material can provide transient protection. The term "transient" as
used herein encompasses not only electrostatic discharge events but
any phenomena, of short duration, that directly or indirectly
induces voltages and currents into a printed circuit board and
where the amplitudes of such voltages and currents are high enough
to cause degradation or failure of the electronic components on the
printed circuit board.
[0054] FIG. 9 is an illustration depicting a PCB stackup with a
partitioned plated via structure formed using a thicker layer of
plating resist, according to certain embodiments. FIG. 9 shows a
PCB 900 that includes conducting layers 910a-910f separated by
dielectric layers 920a-920f. The plated via structure 930 is plated
with a seed conductive material 990 and a further coating of
conductive material 992. The plated via 930 is effectively
partitioned into a plurality of electrically isolated portions
(930a, and 930b) by selectively depositing plating resist in a
sub-composite structure used for making the PCB stackup.
[0055] FIG. 9 shows that the partitioned plated via allows an
electrical signal 960 to transmit from one trace 940 on a first
conducting layer 910a to another trace 950 on a second conducting
layer 910b of the PCB 900 by traversing the isolated portion 930a
of the via 930 without signal integrity being degraded through
interference caused by portion 930b. The conductive material 992 of
the plated via structure 930 is the medium through which the
electrical signal 960 travels from the first conducting layer 910a
of the PCB 900 to the second conducting layer 910b. Similarly, the
isolated portion 930b of the via 930 allows another electrical
signal 962 to transmit to trace 980 without interfering with the
signal 960. The plating resist 970 prevents the deposition of the
conductive material 990 and 992 within the via structure 930 at the
conducting layers 910c and 910d. As a result, via 930 is
effectively partitioned into the electrically isolated portions
930a, and 930b.
[0056] The PCB 900 can have any number of conducting layers and
dielectric layers. FIG. 9 only shows six layers of conducting
layers 910a-910f and six layers of dielectric layers 920a-920f for
the sake of simplicity. Each of the conducting layers 910a-910f may
comprise a partial or full layer such as a power or ground layer,
and may comprise a layer of circuit traces, or may comprise a layer
with both circuit traces and a partial layer such as a ground
layer. A non-limiting example of the conducting layers 910a-910f is
copper and some non-limiting examples of dielectric layers
920a-920f are epoxy glass, polyimide glass, ceramic hydrocarbon,
polyimide film, Teflon film, resin impregnated matte material,
Kevlar, paper, resin dielectrics with dispersed nano-powders.
[0057] According to certain embodiments, plating resist is
selectively deposited in a clearance formed in a conducting layer
and an adjacent dielectric layer of a sub-composite structure. In
such a case, the sub-composite structure can be mechanically or
laser drilled to form a blind hole. The blind hole starts at one
conductive layer of the sub-composite structure, proceeds through
the dielectric layer and terminates on another conductive layer of
the sub-composite structure. However, the depth of the blind hole
can be drilled to any depth short of reaching the conductive layer
of the sub-composite structure. Plating resist is then deposited
into the blind hole using a squeegeeing, stenciling, or screen
printing operation, for example. The resist is then cured. A
planarizing or scrubbing operation may be employed to remove resist
from the open end of the blind hole. The sub-composite structure
can be processed using standard PCB procedures to form circuit
images. It is to be noted that the plating resist can be deposited
before or after forming circuit images. The sub-composite structure
can then be laminated into a multilayer PCB stackup and the process
can continue as described above for electroless seeding and
subsequent plating of the interior walls of the via structure. The
advantage in such a via structure is that the plating resist does
not come out of the blind end of the hole and a connection can be
made to the undrilled conductive layer of the sub-composite
structure (core). According to certain embodiments, the partitioned
via is filled with an electrically insulating material, ohmically
resistive paste or voltage switchable dielectric material to
improve reliability or functionality. In the case of using voltage
switchable dielectric material, programmable circuit routing in
PCBs can be made. Further, the voltage switchable dielectric
material can provide transient protection.
[0058] FIG. 10 is an illustration depicting a PCB stackup with a
partitioned plated via structure formed by selectively depositing
plating resist in a clearance formed in a conducting layer and an
adjacent dielectric layer of a sub-composite structure, according
to certain embodiments. FIG. 10 shows a PCB 1000 that includes
conducting layers 1010a-1010f separated by dielectric layers
1020a-1020f. The plated via structure 1030 is plated with a seed
conductive material 1090 and a further coating of conductive
material 1092. The plated via 1030 is effectively partitioned into
a plurality of electrically isolated portions (1030a, and 1030b) by
selectively depositing plating resist in a sub-composite structure
used for making the PCB stackup.
[0059] FIG. 10 shows that the partitioned plated via allows an
electrical signal 1060 to transmit from one trace 1040 on a first
conducting layer 1010a to another trace 1050 on a different
conducting layer 1010c of the PCB 1000 by traversing the isolated
portion 1030a of the via 1030 without signal integrity being
degraded through interference caused by portion 1030b. The
conductive material 1092 of the plated via structure 1030 is the
medium through which the electrical signal 1060 travels from the
first conducting layer 1010a of the PCB 1000 to the another
conducting layer 1010c. Similarly, the isolated portion 1030b of
the via 1030 allows another electrical signal 1062 to transmit to
trace 1080 without interfering with the signal 1060. The plating
resist 1070 prevents the deposition of the conductive material 1090
and 1092 within the via structure 1030 at the conducting layer
1010d and the dielectric layer 1020c. As a result, via 1030 is
effectively partitioned into the electrically isolated portions
1030a, and 1030b.
[0060] The PCB 1000 can have any number of conducting layers and
dielectric layers. FIG. 10 only shows six layers of conducting
layers 1010a-1010f and six layers of dielectric layers 1020a-1020f
for the sake of simplicity. Each of the conducting layers
1010a-1010f may comprise a partial or full layer such as a power or
ground layer, and may comprise a layer of circuit traces, or may
comprise a layer with both circuit traces and a partial layer such
as a ground layer. A non-limiting example of the conducting layers
1010a-1010f is copper and some non-limiting examples of dielectric
layers 1020a-1020f are epoxy glass, polyimide glass, ceramic
hydrocarbon, polyimide film, Teflon film, resin impregnated matte
material, Kevlar, paper, resin dielectrics with dispersed
nano-powders.
[0061] According to certain embodiments, plating resist is
selectively deposited on the surface of a sub-composite structure
on the exposed dielectric on the surface that is coplanar with the
top conducting layer of the sub-composite structure. In such a
case, the plating resist is deposited onto an etched surface of a
sub-composite core on the exposed dielectric. The plating resist is
deposited onto the dielectric using screen printing, stenciling,
needle depositing or other methods know in the art. The thickness
of the deposit of plating resist can be adjusted to a range up to 5
mils thick. The deposit of plating resist can be any shape but
typically would be round or square in geometry. After deposition,
the resist is cured using appropriate process. The sub-composite
structure can be processed using standard PCB procedures to form
circuit images. It is to be noted that the plating resist can be
deposited before or after forming circuit images. The sub-composite
structure can then be laminated into a multilayer PCB stackup and
the process can continue as described above for electroless seeding
and subsequent plating of the interior walls of the via structure.
According to certain embodiments, the partitioned via is filled
with an electrically insulating material, ohmically resistive paste
or voltage switchable dielectric material to improve reliability or
functionality. In the case of using voltage switchable dielectric
material, programmable circuit routing in PCBs can be made.
Further, the voltage switchable dielectric material can provide
transient protection.
[0062] FIG. 11 is an illustration depicting a PCB stackup with a
partitioned plated via structure formed by selectively depositing
plating resist on the surface of a sub-composite structure on the
exposed dielectric, according to certain embodiments. FIG. 11 shows
a PCB 1100 that includes conducting layers 1110a-1110e separated by
dielectric layers 1120a-1120e. The plated via structure 1130 is
plated with a seed conductive material 1190 and a further coating
of conductive material 1192. The plated via 1130 is effectively
partitioned into a plurality of electrically isolated portions
(1130a, and 1130b) by selectively depositing plating resist in a
sub-composite structure used for making the PCB stackup.
[0063] FIG. 11 shows that the partitioned plated via allows an
electrical signal 1160 to transmit from one trace 1140 on a first
conducting layer 1110a to another trace 1150 on a different
conducting layer 1110c of the PCB 1100 by traversing the isolated
portion 1130a of the via 1130 without signal integrity being
degraded through interference caused by portion 1130b. The
conductive material 1192 of the plated via structure 1130 is the
medium through which the electrical signal 1160 travels from the
first conducting layer 1110a of the PCB 1100 to the another
conducting layer 1110c. Similarly, the isolated portion 1130b of
the via 1130 allows another electrical signal 1162 to transmit to
trace 1180 without interfering with the signal 1160. The plating
resist 1170 prevents the deposition of the conductive material 1190
and 1192 within the via structure 1130 at an area between the
conducting layer 1110c and another conductive layer 1110e. As a
result, via 1130 is effectively partitioned into the electrically
isolated portions 1130a, and 1130b. The plated via structure 1130
may be of any shape.
[0064] The PCB 1100 can have any number of conducting layers and
dielectric layers. FIG. 11 only shows five layers of conducting
layers 1110a-1110e and five layers of dielectric layers 1120a-1120e
for the sake of simplicity. Each of the conducting layers
1110a-1110e may comprise a partial or full layer such as a power or
ground layer, and may comprise a layer of circuit traces, or may
comprise a layer with both circuit traces and a partial layer such
as a ground layer. A non-limiting example of the conducting layers
1110a-1110e is copper and some non-limiting examples of dielectric
layers 1120a-1120e are epoxy glass, polyimide glass, ceramic
hydrocarbon, polyimide film, Teflon film, resin impregnated matte
material, Kevlar, paper, resin dielectrics with dispersed
nano-powders.
[0065] According to certain embodiments, plating resist is
selectively deposited on the surface of a sub-composite structure
on a conductive region or conductive pad on the surface of the
sub-composite structure. The conductive region could be patterned
to be a plane or could be an individual pad or feature. In the case
of a pad or feature, the plating resist may overlap the pad. The
plating resist is deposited onto the conductive region using screen
printing, stenciling, needle depositing or other methods know in
the art. The deposit of plating resist can be any shape but
typically would be round or square in geometry. After deposition,
the resist is cured using appropriate process. The sub-composite
structure can be processed using standard PCB procedures to form
circuit images. It is to be noted that the plating resist can be
deposited before or after forming circuit images. The sub-composite
structure can then be laminated into a multilayer PCB stackup and
the process can continue as described above for electroless seeding
and subsequent plating of the interior walls of the via structure.
According to certain embodiments, the partitioned via is filled
with an electrically insulating material, ohmically resistive paste
or voltage switchable dielectric material to improve reliability or
functionality. In the case of using voltage switchable dielectric
material, programmable circuit routing in PCBs can be made.
Further, the voltage switchable dielectric material can provide
transient protection.
[0066] FIG. 12 is an illustration depicting a PCB stackup with a
partitioned plated via structure formed by selectively depositing
plating resist on a conductive region or conductive pad on the
surface of the sub-composite structure, according to certain
embodiments. FIG. 12 shows a PCB 1200 that includes conducting
layers 1210a-1210e separated by dielectric layers 1220a-1220e. The
plated via structure 1230 is plated with a seed conductive material
1290 and a further coating of conductive material 1292. The plated
via 1230 is effectively partitioned into a plurality of
electrically isolated portions (1230a, and 1230b) by selectively
depositing plating resist in a sub-composite structure used for
making the PCB stackup.
[0067] FIG. 12 shows that the partitioned plated via allows an
electrical signal 1260 to transmit from one trace 1240 on a first
conducting layer 1210a to another trace 1250 on the conducting pad
1210d of the PCB 1200 by traversing the isolated portion 1230a of
the via 1230 without signal integrity being degraded through
interference caused by portion 1230b. The conductive material 1292
of the plated via structure 1230 is the medium through which the
electrical signal 1260 travels from the first conducting layer
1210a of the PCB 1200 to the conducting pad 1210d. Similarly, the
isolated portion 1230b of the via 1230 allows another electrical
signal 1262 to transmit to trace 1280 without interfering with the
signal 1260. The plating resist 1270 prevents the deposition of the
conductive material 1290 and 1292 within the via structure 1230 at
an area between the conducting layer 1210e and the conducting pad
1210d. As a result, via 1230 is effectively partitioned into the
electrically isolated portions 1230a, and 1230b. The plated via
structure 1230 may be of any shape.
[0068] The PCB 1200 can have any number of conducting layers and
dielectric layers. FIG. 12 only shows five layers of conducting
layers 1210a-1210e and five layers of dielectric layers 1120a-1120e
for the sake of simplicity. Each of the conducting layers
1210a-1210e may comprise a partial or full layer such as a power or
ground layer, and may comprise a layer of circuit traces, or may
comprise a layer with both circuit traces and a partial layer such
as a ground layer. A non-limiting example of the conducting layers
1210a-1210f is copper and some non-limiting examples of dielectric
layers 1220a-1220e are epoxy glass, polyimide glass, ceramic
hydrocarbon, polyimide film, Teflon film, resin impregnated matte
material, Kevlar, paper, resin dielectrics with dispersed
nano-powders.
[0069] Due to the selective nature of the plating resist deposition
and simultaneous plating of the vias resulting in partitioned
sections, vias can be subdivided into multiple sections each
capable of carrying signals without disturbing signals in other
sections. To do so effectively, a computer program is advantageous
to use when designing a PCB layout. For example, the computer
program would be patched to an ECAD software such as Cadence
Allegro.TM. or Mentor Expedition.TM. or Supermax.TM.. The computer
program can also run as a stand alone software module, which would
import data from an ECAD system, partition the vias, then output
appropriate files back to the ECAD or Computer Aided Manufacturing
(CAM) system. Such software can also output files to be used for
programming manufacturing equipment to drill appropriate holes in
selected cores and/or generate art work to manufacture stencils for
selective deposition of the plating resist. Thus, by determining
the locations of the plating resist and location of the resulting
partitioned vias, a PCB design can be optimized to increase routing
density and improve integrity. In the case of a pre-existing design
of a PCB layout, the computer program can be used to identify
locations for selective depositions of plating resist in locations
that correlate to locations for backdrilling, for example.
[0070] In the foregoing specification, embodiments of the invention
have been described with reference to numerous specific details
that may vary from implementation to implementation. The
specification and drawings are, accordingly, to be regarded in an
illustrative rather than a restrictive sense. The invention is
intended to be as broad as the appended claims, including all
equivalents thereto.
* * * * *