The invention relates to a process for manufacturing a printed circuitboard,
referred to as the main circuit board, comprising one or more sec-
5 ondary printed circuit boards having a different structure from that of the main
circuit board. The one or more secondary printed circuit boards are inserted
into a main printed circuit board during its manufacture.
The invention is for example used in the design and production of
. hybrid RF or microwave/digital printed circuit boards in the context of high-
10 density designs that require different types of through-holes (for example laser
micro-vias in the main circuit board and through- or blind mechanical drill
holes in the 'inserted circuit boards) and heterogeneous dielectrics to be
used.
In the rest of the description, the expression "main printed circuit
15 board" will be understood to mean the circuit board into which one or more
secondary circuit
1
boards having a different structure are to be inserted.
The need to simultaneously provide digital functions and
RF/microwave functions on the same board is difficult or even impossible to
20 meet when the components, because of their digital functions or their high
density, require the use of laser micro-vias, or even the use of dielectrics of
types and thicknesses specific to each of the envisioned circuit functions. For
example, micro-vias imply the use of a thin dielectric between the layers connected
thereby, which thickness will in addition vary between the various
25 zones of the printed circuit board depending on the number and type of vias.
These small thicknesses and these variations are incompatible with the dielectric
requirements of radio-frequency functions, which require a large thickness
and a high Z-axis dimensional stability the entire length of matched signal
paths, the coordinate system being known to those skilled in the art. In
30 addition, the properties of the dielectrics used with micro-vias are unsuitable
or not entirely suitable for RF signals. These contradictory requirements lead
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to different and separate printed circuit boards being designed for the
RF/microwave functions and digital functions. This leads to a significant increase
in the design and manufacturing cost of the assembly, which limits the
potential for increasing the number of components and therefore functions
5 (densification).
A first approach is to produce the digital functions and
RF/microwave functions on different circuit boards, which are then connected
using appropriate processes after the components of each of the circuit
. boards have been put in place. Another approach consists in defining an
10 "average" structure better suited to the RF functions, but this greatly limits the
capacity to integrate digital functions and often the choice of the associated
components. Managing the RF/microwave and digital functions separately
substantially increases cost and limits the scope for integration.
One of the objectives of the present invention is to provide a pro-
15 cess for manufacturing a printed circuit board, especially allowing the technical
problems of the prior art to ?e solved by integrating, during the step of
manufacturing a bare main printed circuit board, inserts or secondary printed
circuit boards of different structure from that of the main printed circuit board,
thereby providing a single flat surface for component connection correspond-
20 ing to one of the external sides of the main circuit board continued by one of
the external faces of the secondary circuit board, and producing interconnecting
metalized holes along the Z-axis of these two circuit boards.
The term "structure" when used with regard to a printed circuit
board for example means that a digital, radio-frequency, microwave, etc.
25 function, is associated therewith.
The invention relates to a process for manufacturing a printed circuit
board comprising a first main circuit board N having a first structure,
characterized in that it comprises a succession of steps suitable for inserting
30 one or more secondary printed circuit boards RF having a different structure
from that of the main printed circuit board, said steps comprising:
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• a step in which one or more cavities suitable for receiving one or more
inserts are defined;
• a step of preparing the one or more inserts comprising, on at least one
side intended to make. contact with a wall of the cavity, etched features
5 and a metallization and one or more vias;
• a step of placing a second resin in the one or more cavities in order to
ensure the cohesion of the assembly formed by the main circuit board
and the one or more secondary circuit boards;
• a step of inserting the one or more inserts into the one or more cavities
10 , of said main circuit board, in which step the second resin diffuses into
the vias then around the periphery of the insert;
• a step of laminating the assembly formed by the one or more inserts
placed in the main circuit board and a step of grinding and polishing the
surface of the printed circuit board in order to form through-holes then
15 drilling the layers forming the printed circuit board in order to form
through-holes, then producing micro-vias befpre metallization of the assembly
by deposition of a deposit, then finkl etching of features and
tracks in external layers.
The implemented steps especially allow electrical continuity to be
20 ensured across the entirety of the external flat surface of the printed circuit
board composed of the main circuit board and its inserts but also between all
the layers of the printed circuit board composed of the main circuit board and
its inserts, including in the zone of the inserts - by way of the final drilling/
metallization.
25 According to one variant embodiment the impregnated circuit
board is composed of a plurality of laminates and a copper layer and one or
more cavities are produced in the laminates of the printed circuit board by
forming an aperture in an external copper layer, in an epoxy layer, in an
epoxy laminate layer and in an epoxy prepreg layer that is composed of a
30 resin that does not flow and that does not diffuse into the orifices in the circuit
board.
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According to one variant embodiment, the first printed circuit board
comprises at least a plurality of laminate layers, each side comprising a copper
layer on each of its sides, a plurality of prepreg layers being placed between
the laminate layers, and the process comprises at least the following
5 steps:
a) for the first printed circuit board, etching the internal copper layers of
the laminate layers with the desired features and tracks;
b) producing at least one aperture in the main circuit board, corresponding
to the size of the one or more inserts;
10 c) preparing the one or more inserts intended to be inserted into the
15
20
25
30
one or more apertures by etching and metallizing a side of the insert
which will make contact with the bottom of the aperture, and by drilling
one or more vias;
d) cutting at least one layer composed of a first resin that does not flow
to a size tailored to the size of the one or more inserts;
e) assembling the layers and the prepregs, a shim being i?serted into
the aperture, then laminating the assembly;
f) drilling the laminated assembly in order to define one or k vias, metallizing
the assembly and etching the features and tracks envisaged
for the printed circuit board, and generating a plurality of micro-vias;
g) removing the one or more shims and assembling the one or more inserts
in the main circuit board by positioning the inserts on a prepreg
that flows; and
h) laminating the assembly before metallization, deposition on and etching
of the external layers.
The process may comprise a step in which two epoxy prepreg layers
and two copper layers are added before the lamination step is carried
out.
The method uses a laser technique to produce the micro-vias.
It is possible to remove the shim by mechanical machining or cuttin
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According to one variant, one or more edges of an insert are metalized.
According to another variant, one or more walls of the cavity are metalized.
According to another variant, the edges and bottom of a cavity are
metalized.
The insert is, for example, an RF insert.
Other features and advantages of the device according to the invention
will become more clearly apparent on reading the following descrip.
tion of one exemplary embodiment given by way of completely non-limiting
illustration and with reference to the appended figures, which show:
• figure 1, a view of a printed circuit board obtained by the manufacturing
process according to the invention;
• figures 2 to 11, various cross-sectional views, corresponding to steps of
the process;
• figures 12a and 12b, a variant in which the insert is metalized on its
edges; and
• figure 13, another variant in which the cavity that receives the insert has
its walls metalized.
In order to ensure the principle implemented by the process according
to the invention is better understood, the following example is given for
the manufacture of a main printed circuit board having a first structure integrating
digital functions, into which one or more RF inserts or secondary circuit
boards having a structure different from the first structure of the main
25 circuit board are inserted. The opposite is also possible without departing
from the scope of the invention, the RF circuit board becoming the main circuit
board and the inserts corresponding to the digital functions.
Is also possible to depart from the RF field and produce printed circuit
boards having a first structure into which one or more printed circuit
30 boards having a second structure different from the first are inserted.
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Figure 1 shows a schematic top view of a printed circuit board obtained
by implementing the process according to the invention. It comprises a
very-high-density digital circuit board, the construction of which is detailed
below. The digital circuit board N is composed of multilayers and multiple
5 ground planes and internal supplies (not shown for the sake of simplicity,
such a layout being well known to those skilled in the art). The dielectric used
is for example a thin epoxy or polyimide dielectric. It comprises small
through-vias and micro-vias. An RF/microwave circuit board of very high RF
. sensitivity is integrated into the printed circuit board. The RF circuit board is a
10 double-sided circuit board in this example. Figure 1 schematically shows a
plurality of tracks P illustrating the electrical continuity across the external
layer between' zones of the digital circuit board N and zones of the RF circuit
board. The materials used to manufacture the insert are RF materials. The
circuit board obtained also comprises through-vias and wide tracks for signal
15 matching.
In the example given in the following figures, the RF/microwave
functions are pre-manufactured then inserted into a digital architecture.
Figure 2 shows a first step of the process, in the case of 3 epoxy
laminates C4-5, C6-7 and C8-9. Each laminate comprises on its bottom side
20 and on its topside, a copper layer, for example C4-5, which is covered with a
top copper layer 4 and a bottom copper layer 5. Identically, 6 and 7 correspond
to the copper layers of the laminate C6-7 and 8 and 9 to the copper
layers of the layer C8-9. Step 1) consists in etching these internal copper
layers with the features and tracks desired for the intended use.
25 In parallel, in step 2 (figure 3), the insert to be inserted will be prepared.
The RF/microwave insert 20 intended to be inserted in the printed circuit
board N in figure 2 is drilled mechanically. The mechanical drilling consists
in producing vias 20i. After the drilling, the process continues with metallization
of these vias and the layers 20a, 20b of the sides of the insert. The
30 layer 20a corresponds to what is referred to as the external layer, which does
not make contact with the internal or external walls of the cavity. After metali
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lization, the internal side 20b of the insert, i.e. the face making contact with
bottom of fhe cavity in which the insert is positioned, is etched with the desired
features. The insert is given a size and shape chosen depending on the
final application.
5 Figure 4 schematically shows step 3 in which an aperture or cavity
40 is produced in the laminates or prepregs of the printed circuit board, corresponding
to the size and location of the insert 20. The aperture is produced
using a technique known to those skilled in the art, in an external copper layer
1, in an epoxy layer C1-2, in the epoxy laminate layer C4, 5 and in an
10 epoxy prepreg layer C5-6, one of the particularities of which is to be composed
of a resin, or first resin, that does not flow and that does not diffuse
into the orifices in the circuit board.
Figure 4 also shows the cutting (step 4) of a prepreg C5-6" or second
resin to the size of the insert 20, which is chosen to have a resin con-
15 tent tailored to allow the resin to flow and to ensure the insert is correctly positioned
along the Z-axis.
Figure 5 shows (step 5) the assembly of the layers C4-5, C6-7, C8-
9 with the prepregs C3-4, C5-6, C7-8, C9-10, a shim 50 being inserted into
the aperture 40 in order to preserve the size and shape of the aperture
20 formed. Next, a copper layer 3, 10 is .deposited on the top layer C3-4 and on
the bottom layer C9-1 0 of the circuit board formed by assembling the layers
and the assembly is laminated.
Figure 6 schematically shows step 6 of mechanically drilling the assembly
laminated in figure 5 in order to define one or more, k, vias 60i, the
25 number and dimensions of which are defined beforehand depending on the
design of the printed circuit board. The following step consists in metallizing
the assembly with a copper deposit deposited in the vias 60i and on the copper
layers 3, 10. The following step consists in etching the features and
tracks envisaged for the printed circuit board in these layers 3 and 10.
30 In figure 7 (step 7) two epoicy prepreg layers C2-3, C10-11 and two
copper layers 2 and 10 have been added on either side of the circuit board in
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figure 6 before carrying out a lamination step. The resin of the epoxy layers
C2-3 and C10-11 will flow into the vias 60i during the pressing cycle.
In the following step, step 8 (figure 8), the external layers C2-3,
C 10-11 of the printed circuit board are drilled by laser drilling in order to cre-
5 ate micro-vias 80i, then a copper deposit is deposited on the layers C2-3 and
C1 0-11. The deposition of the copper deposit especially allows the micro-vias
to be metalized. The following step consists in etching the features and
tracks envisaged for the printed circuit board in the copper layers 2 and 11.
Figure 9 shows step 9, which consists in removing the shim 50, for
10 example by mechanical machining or by cutting. This step makes use of
known techniques employing mechanical detection of the zone to be removed.
Step 10, illustrated in figure 10, comprises a step of assembling the
·insert 20 and the printed circuit board. The layers or prepregs C1-2, C11-12,
15 the copper layers 1, 12 and the prep reg C5-6" of the size of the insert placed
on the bottom 40f of the cavity 40 are assembled using a technique known to
those skilled in the art. Then the insert 20 is positioned before the assembly
is laminated. In step 10, the resin of the prepregs will diffuse into the vias,
then around the periphery 20p of the insert 20. The resin having risen, the
20 process will implement a step of grinding and polishing the surface of the
printed circuit board.
Figure 11 shows (step 11) mechanical drilling of the layers forming
the printed circuit board, in order to form through-holes 11 Oi, then laser drilling
of the layers C1-2, C11-12, in order to produce a plurality of micro-vias
25 111 i. The following step consists in metallizing the assembly by depositing a
copper deposit, thereby especially allowing the through-holes to be metalized,
then in etching features and tracks in the external copper layers. The
through-holes 11 Oi allow connections to be made between the main circuit
board and the insert along the Z-axis.
30 Figures 12a and 12b schematically show a variant embodiment in
which the process comprises a step of metalizing the edges 20C or sides of
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the insert before its insertion into the cavity of the printed circuit board. This
variant especially makes it possible to obtain an electrical continuity and
shielding of signals in the circuit board. Thus, the signals of the digital portion
of the circuit board are separated from the RF signals of the insert and inter-
5 terence is limited.
Figure 13 shows a variant of the process in which the cavity 40 is
metalized using a technique known to those skilled in the art before the first
micro-vias are produced. The edges 40b and bottom 40f of the cavity will for
example be metalized. This allows the digital circuit board to be better isolat-
10 ed from the RF insert.
According to another variant embodiment, it is possible to insert an
insert having metalized edges (figure 12a) into a cavity the edges and bottom
of which have been metalized. This variant provides effective shielding between
the digital signals and the RF/microwave signals. Furthermore, such
15 an embodiment allows effective ground plane management to be implemented.
The examples described above are applicable to any type of printed
circuit board comprising a circuit board having a first architecture and into
which one or more circuit boards having different architectures are inserted.
20 Inserts may be inserted into both sides of a printed circuit board, i.e.
25
into the top and bottom sides.
The inserts may be located anywhere on the surface of the main
circuit board. Placement on one edge of the main circuit board especially allows
delivery of the RF signals to be facilitated.
The process according to the invention by mixing, during the step
of manufacturing the bare printed circuit board, various architectures, especially
allows, when there is a simultaneous need for digital and RF/microwave
architectures, the number of printed circuit boards to be limited. It allows the
structure of electronic subassemblies to be simplified by decreasing the
30 number of boards. It simplifies the interconnect technology required to interconnect
the various functions.
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The process according to the invention especially allows hybrid,
for example digitai/RF or digital/microwave, modules to be densified.
The approach described especially allows digital and/or
RF/microwave supplies and grounds to be treated in an optimal way and in
s addition makes it possible to metalize the edge face of these inserts without
requiring production of the printed circuit board to be rejigged.

CLAIMS
1 - A process for manufacturing a printed circuit board comprising a first
main circuit board (N) having a first structure, characterized in that it comprises
a succession of steps suitable for inserting one or more secondary
printed circuit boards (RF) having a different structure from that of the main
printed circuit board, said steps comprising:
• a step in which one or more cavities (40) suitable for receiving one or
more inserts (20) are defined;
• a step of preparing the one or more inserts (20) comprising, on at least
one side intended to make contact with a wall (40f) of the cavity, etched
features and a metallization, and one or more vias (20i);
• a step of placing a second resin (C5-6") in the one or more cavities (40)
in order to ensure the cohesion of the assembly formed by the main circuit
board and the one or more secondary circuit boards;
• a step pf inserting the one or more inserts (20) into the one or more
cavitie~ (40) in said main circuit board, in which step the second resin
diffuses into the vias (20i) then around the periphery (20p) of the insert
(20);
20 • a step of laminating the assembly formed by the one or more inserts
placed in the main circuit board and a step of grinding and polishing the
surface of the printed circuit board, drilling the layers forming the printed
circuit board in order to form through-holes (11 Oi), then drilling in order
to produce a plurality of micro-vias (111 i) before metallization of the as-
25 sembly by deposition of a deposit, then final etching of features and
tracks in external layers.
2 - The process as claimed in claim 1, characterized in that the impregnated
circuit board is composed of a plurality of laminates and one or more cavities
30 (40) are produced in the laminates of the printed circuit board by forming an
aperture in an external copper layer (1), in an epoxy layer (C1-2), in an epoxy
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laminate layer (C4-5) and in an epoxy prepreg layer (C5-6) that is composed
of a resin that does not flow and that does not diffuse into the orifices in the
circuit board.
s 3 - The process as claimed in one of claims 1 and 2, characterized in that
the first printed circuit board (N) comprises at least a plurality of laminate layers
(C4-5, C6-7, C8-9), each side comprising a copper layer (2, 11) on each
of its sides, a plurality of prepreg layers (C3-4, C5-6, C?-8, C9-10) being
placed between the laminate layers, and the process comprises at least the
1 o following steps:
a) for the first printed circuit board, etching the internal copper layers of
the laminate layers with the desired features and tracks;
b) producing at least one aperture (40) in the main circuit board, corresponding
to the size of the one or more inserts (20);15 c) preparing the one or more inserts intended to be inserted into the
one or more apertu~es (40) by etching and metallizing a side of the
insert which will mak!e contact with the bottom of the aperture, and by
drilling one or more vias (20i);
d) cutting at least one layer composed of a first resin (C5-6) that does
not flow to a size tailored to the size of the one or more inserts;
e) assembling the layers (C4-5, C6-7, C8-9) and the prepregs (C3-4,
C5-6, C?-8, C9-10), a shim (50) being inserted into the aperture (40),
then laminating the assembly;
f) drilling the laminated assembly in order to define one or k vias (60i),
metallizing the assembly and etching the features and tracks envisaged
for the printed circuit board, and generating a plurality of microvras;
g) removing the one or more shims (50) and assembling the one or
more inserts in the main circuit board by positioning the inserts on a
prepreg (C5-6") that flows; and
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h) laminating the assembly before drilling, metallization, deposition on
and etching of the external layers.
4 - The process as claimed in claim 3, characterized in that it comprises a
5 step in which two epoxy prep reg layers (C2-3, C 10-11) and two copper layers
(2, 1 0) are added before the lamination step is carried out.
5 - The process as claimed in one of claims 1 to 4, characterized in that the
prepreg (C5-6"), which has a size corresponding to that of the insert (20), is
10 positioned at the bottom of the aperture and has a resin conten_t tailored to
allow the resin to flow and to ensure the insert (20) is correctly positioned.
6 - The process as claimed in one of the preceding claims, characterized in
that a laser technique is used to produce the micro-vias.
7 - The process as claimed in
one of the prrceding claims, characterized in
that the shim (50) is removed IJy mechanical machining or cutting.
8 - The process as claimed in one of the preceding claims, characterized in
20 that one or more edges (20a, 20b) of an insert (20) are metalized.
9 - The process as claimed in one of the preceding claims, characterized in
that one or more walls of the cavity (40) ·are metalized
25 10 - The process as claimed in one of the preceding claims, characterized in
that the edges (40b) and bottom (40f) of the cavity (40)aremetalized.
11 - The process as claimed in one of claims 1 to 10, characterized in that
the insert is an RF insert.