Note: Descriptions are shown in the official language in which they were submitted.
~075~25
The inven~ion relates to a circuit board comprising
a substrate having conductive metal e~bedded in at
least one surEace thereof in the form of one or more
circuits, and to the process of making such a board
S wherein the substra-te of the board is molded to its
~inished form including recesses corresponding to the
desired circuit arrangement and holes, if desired,
the land areas between the recesses being covered
with a plating resist and the board then being plated
to deposit the conductive metal in the recasses and
holes, if any, followed by suitable surface treatments.
Traditionally, printed circuit boards have been
manufactured utilizing a metal clad laminate substrate.
In an early form, thin sheets of copper foil (.001"-
.005") were glued to a phenolic base material, a
positive image of the desired circuit was applied to
the surface of the copper to serve as an etching
resist and the exposed copper was etched away. The
resist material was then remove~, holes were drilled
or punched as needed and the product was finished by
cleaning and applying a water dip lacquer for protec-
tion, while retaining solderability. As a natural
development of this process copper circuits were
applied similarly to both sides of a common substrate.
There was subsequently developed the so-called
"plated-through process tl wherein a two sided substrate
was drilled, subjected to elec~roless metallic deposi-
tion (includ:ing plating through the holes), imprinted
with a negative image serving as a plating resist and
then electro:Lytically plated with copper followed by
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tin-leacl or any other finish sul~able as an etch resis-t
or protective coatincJ. The pla-ting resist was removed
and the board etched to remove the metal covered
thereby, while the tin-lead plating acted as an
etching resist, to protect the desired circuit elements.
In a simpli~ied version of this process the substrate
is activate~, a negative image resist is applied and
the circuitry is plated on electrolessly; this being
known as an "additive process", for use when a plated-
through boarcl is required.
One of the difficulties with the plated-through
process is that the apertures in the board must be as
smooth and clean as possible in order to maintain the
integrity of the plating. Attempts to pieree neatly any
~ 15 and/or all of the substrate material currently available
-~ have failed and, while drilling the holes is practical
and economical, many customers require openings other
than perfect circles for assembly purposes.
In those markets which use massive quantities of
plated-through boards, the aforementioned problems
have caused considerable difficulty. In addition, in
boards such as these, the cost of the substrate amounts
to 25% of the cost of the finished product or higher,
and are subject to delamination and cracking.
Other known proeesses for manufaeturing eircuit
boards, particularly those having a substrate of di-
electric material and a eonductive cireuit inlaid in
a surface thereof include forming the circuit pattern
on a temporary support, embedding it in a substrate
and then removlng the support; or plating a moldable
75~5
substrate with metal, embossing the circuit design on the
plated substrate and removing the excess metal, or usiny a
variety of other e~pedients, all of whlch procedures present
one or more disadvantages such as expense, poor adherence,
difficult quality control and the like.
Accordingly, it is an object of the present invention
to provide a process o making circuit boards by steps which
are simple, easy to control with great accuracy, and economy.
It ls a further ob3ect of the invention to provide
an inlaid circuit board wherein the circuit elements are bonded
chemically and mechanically to the substrate.
It is another object of the invention to provide
certain improvements in the form, construction and arrangement
of the several parts and in the steps of the process whereby
the above named and other objects may effectively be attained
The invention accordingly comprises the several
steps and the relation of one or more of such steps with respect
to each of the others, and the article possessing the features,
properties, and the relation of elements, which are exemplified
in the following detailed disclosure, and the scope of the
invention will be indicated in the claims.
In accordance with a further aspect of the present
invention, there is provided the process of making a circuit
board which includes, in this sequence, providing a mold having
on at least one surface thereof a raised pattern corresponding
to the desired circuit pattern and a depressed fla~ land area
defining said raised circuit pattern area, molding a dielectric
material to form a substrate having a surface recessed in a
pattern corresponding to the desired circuit pattern and a
flat land area defining the recessed pattern area, applying a
plating resist to said land area, and depositing conductive
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~0751!~
metal on said recessed pa~tern area to form th~ desired circuit
pattern.
In accordance with a further aspect of the present
invention, there is provided the process of making a circuit
board which includes, providing a mold having on at least one
surface thereof a pattern in relief corresponding to the desired
circuitry, molding a dielectric material by means of said mold
to form a substra-te having a surface recessed in a pattern
corresponding to the desired circuitry and a flat land area
defining the recessed pattern area, applying a plating resist
to said land area, and plating the substrate electrolessly
with conductive metal, whereby said recessed pattern area is
at least partially filled with conductive metal constituting
the desired circuitry,
In accordance with a further aspect of the present
invention, there is provided the process of makin~ a circuit
board which includes, providing a mold having on at least one
surface thereof a pattern in relief corresponding to the
desired circuitry, molding a dielectric material by means of
said mold to form a substrate having a surface recessed in a
pattern corresponding to the desired circuitry and a flat land
area defining the recessed pattern area, roughening the surface
of the substrate, actïvating chemically the surface of the sub-
strate, applying a plating resist to said flat land area, leav-
ing the recessed circuitry exposed, plating the substrate
electrolessly with conductive metal to at least partially fill
the recessed pattern area, applying an epoxy solder resist to
selected areas of the circuitry, and applying a protective
coating to other areas to insure solderability.
A practical embodiment of the invention is shown in
the accompanying drawing, wherein:
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FIG. 1 is a flow charl: illustrating schematically
the steps for producing a circuit board,
FIG. 2 is a detail plan view of a portion of a
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typical circuit board, parts being broken away,
FIG. 3 is a section taken on the line ~ III of
Fig. 2, at one stage in the process,
FIGS. 4 and 5 are similar sections showing conditions
at other stages of the process.
Referring to the drawinq, and particularly the steps
of the method as outlined in the flow chart,
FIG. 1:
A. A mold is made corresponding to -the customer's
mechanical drawing, the circuit areas being in relief and posts
or pins ~eing provided for forming holes of any desired size or
shape.
B. The board substrate is molded, using any appro-
priate non-conductive material such as filled phenolics or
polyphenylene sulfide, for example, having regard for conditions
both of use and of manufacture, producing a substrate with the
circuit areas depressed and holes, as required~
C. The board is sand blasted, for example, with
240 grit aluminum oxide at 40 psi, and/or chemically roughened
(with preferably both) in preparation for plating, the roughness
may suitably be on the order of 25 micro-inches. Chemical
roughening can be accomplished by degreasing the board with a
chlorinated solvent, such as t~ichloroethylene or the like,
soaking in an alka~ine soak cleaner/surfactant, such as
Enthone's* PC453, or the li~e, followed by rinsing in water and
drying, soaking in a solution of dimethylformamide and ethy~ene
glycol, followed by rinsing, soaking in a solution of methyl-
ethyl ketone and trichloroethylene,
* A Tradename of Enthone, Inc., 1900 Frontage Road, West Haven
Conn. 06516
, ':
followed again by rinsing, ancl finally exposiny th~ board to
an aqueous solution of sulfuric acid and chromium trioxide,
with a final water rinse.
D. In preparation for subsequent applications, the
board surface is activated chemically. ~s an exarnple, but not
limitation, the board may be chemically activated ~y the fol-
lowing, or like, steps:
l. soaking in a surfactant, such as MacDermid's*
PA-3, followed by rinsing in water,
2. soaking in a solu-tion of stannous chloride having
a colloidal or non-colloidal suspension of
palladium chloride, such as Shipley1s Cataprep
followed by rinsing in water,
3. soaking in a solution of fluoboric acid with
surfactants, such as Shipley's** Accelerator l9
or MacDermid's 9071, followed by rinsing in water;
and
4. baking at about lOO~C for about 30 minutes.
E. A plating resist, such as photosensitive or W
curable polymers, for example Riston, KPR***, or the like,
is applied to the raised lands of the board, leaving the de-
pressed circuit areas exposed.
F. The board is plated, preferably by electroless
deposition, with a conduc-tive material such as copper (alone
or over nickel) to the desired thickness, e.g., into the recessed
areas and holes. As an example, but not limitation, the board
may be plated by the following, or like, steps:
1. optionally, pre-soaking in a solution of
fluoboric acid with surfactants, such as
* A Tradename of MacDermid Inc., 526 ~Iuntingdon Avenue, Water-
bury, Conn. 06720
** A Tradename of Shipley Inc. 49 Walnut Park, Wellesley, Mass
02181
*** A Trademark of Dupont Corp., Wilmington, Delaware 19898
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Shipley's ~ccelerator 19 or MaeDermids
9071, Eollowed by rinsing in water;
2. immersing in an elec:troless niekel plating
solution, for example, a solution of nickel
phosphate with wetting agents and niekel
chloride, such as MaeDermid's Eleetroless
Niekel 9340, followed by rinsing in water; and
3. immersing in an electroless eopper plating
solution, for example a solution of eopper
sulfate, formaldehyde, stabilizers, and
wetting agent-grain refiners and hydroxide,
such as MacDermid 9042, until the desired
; thickness of copper is obtained.
G. The coating and cleaning steps inelude
applying an epoxy solder resist to eircuit areas where
no solder connection is to be made, eleaning exposed
eopper areas, for example by abrasion with pumiee,
aluminum oxide, n~lon abrasives or the like, and
protecting said areas with a water base laequer, or
diluted malie aeid or non-aetive Rosin flux, to
provide for solderability. The exposed eopper areas
may also be cleaned chemically before applieation of the
proteetive water base laequer or the like by the
following, or like, steps:
1. soaking in hot alkaline solution,
2. rinsing in eold water
3. soaking in a mild ammonia persulfate dip
. rinsing in eold water
5. soaking in 10% sulfurie aeid solution
6. rinsing in eold water, and
7. drying.
107~82~
The board, ~t that pcint, is ready for inspection,
packing and shipment. Identification and~or explanatory
indicia may convenientl~ be for~ed on the mold, to
appear on the finished board as copper plated areas.
Certain significant stages of the process are
illustrated in Fig. 2 to 5.
As shown in Fig. 4, a substrate 11 of thermo-
plastic insulating dielectric material has been molded
into a form having depressed or recessed areas 12
correspondin~ to the paths of the desired circuits and
holes 13, 14 have been formed simultaneously, in any
desired sizes, shapes and locations. One or both
surfaces of the substrate should be recessed in the
- areas adjacent each hole, as indicated at 15 and 16,
to provide for the annular circuit paths shown in
Fig. 2. The non-recessed areas of the surface lie in a
common plane and constitute raised lands 17, 18. The
substrate has substantially the appearance of Fig. 4
through the steps B, C and D described above. After the
- 20 chemical activation of -the surface (step D) a plat ng
resist 20, 21 is applied in any convenient manner, to the
raised land areas 17, 18 and to the back surface 19,
as shown in Fig. 5 (step E), and the substrate is then
plated (step F) to deposit copper in the recessed
circuit areas 12, and in and around the holes 13, 14,
as indicated at 22, 23 and 24, Fig. 3. Recesses
around certain holes on the back of the substrate are
a~so filled with copper, 25, 26, to provide areas for
connecting the circuits to other elements at those
points. The plating resist need not be removedl the
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coatincJ ar.d clealling steps (G) vary in different areas,
as explained above, ancl axe not specifically illustrated.
The mold may be single or multiple cavity and may
be desigllecl to form depxessed circuit paths in both
surEaces of the substrate as well as in one sur~ace.
The holes have a smooth finish, not rough and torn as
with punched holes.
The material or the substrate must be able to
withstand soldering heat as well as meeting all other
requirements; phenolic based plastics are considered
; to be particularly suitable and may be used alone or
laminated with other materials.
The plating resist can be applied (step E) in
various ways including roller coating or curtain
coating. However, in certain cases, a silk screening
method might be advisable.
In a modified method, step E (plating resist) is
omitted and the entire surface of the substrate is
electrolessly plated with metal (step F) ~ollowed by
milling or sanding off enough metal to expose the land
areas while leaving the metal in the depressed circuit
areas and holes, if any. The thickness of the metal
constituting the circuits can be built up, if desired,
by electroless or electrolytic plating.
In either form of construction the metal consti-
tuting the circuit or circuits is securely bonded in
pre-formed recesses or depressions and in the molded
holes, if any. As suggested above, the conductive
circuits may be made with a first electroless nickel
plating followed by electroless copper plating until the
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desired thickness is obtained.
~ hile circuit boards are conventionally ~lat and
rectangular, boards made a.s disclosed herein co~ld, if desired,
be made in other shapes including circular, arcuate, or
cylindrical shapes. Reference to land areas as "fla-t" is in-
tended to include the non-recessed areas of boards having any
desired cross-sectional contour. Mention of a circuit includes
a plurality of circuits.
Example
As an illustrative example of a preferred embodiment
of the present invention, a circuit board substrate made of
General Electric`s Genal*, which is a filled phenolic material,
was molded to correspond to the desired mechanical drawing of
the circuit, so that the circuit areas were depressed and
appropriate holes of the desired shape and size were provided
therein.
The circuit board substrate was then sandblasted with
240 grit aluminum oxide at 40 psi to obtain a structure on
the surface of approximately 25 micro-inches. It was then
degreased with trichloroethylene to remove dust and grease and
allowed to air-dry.
Next, the circuit board substrate was cleaned by
soaking for about 5 minutes in a 15% to 20% solution of Enthone's
PC453, at about 65C. After a one minute rinse in water, it
was dried completely~
The circui board substrate was then soaked for
about 5 minutes in a solution comprising about 61% dimethyl-
formamide and about 39% ethylene glycol at about 35C, followed
by a one minute rinse in water.
* A Trademark of General Electric Corp., 1350 South 2nd Street,
Coshocton, Ohio 43812
_g_
1(3 75825
Next, it was soaked for about 4 minut~s in a solution of about
40% methyl-ethyl-ketone and about 60% trichloroethylene at a
temperature of about 30"C, follo~ed by a one minute rinse in
water.
The circuit board subst:rate was then immersed in a
solution comprised of about S0% sulfuric acid, about 7% chromium
trioxide (1 molar) and about 43% distilled water, at a temp-
erature of acout 75C, followed by a one minute rinse in water
whereafter, it was immersed in an aqueous rinse solution com-
prising sodium carbonate (5 molar) for about 5 minutes at about
35C, followed by a one minute rinse in water.
Next, the circuit board substrate was chemically
activated, as followso
1) five minute immersion in MacDermid's PA-3 at
22 C
2) one minute rinse in water,
3) two minute immersion in Cataprep* at between
43C to 49C,
4) five minute immersion in Cataprep 44 at 43C to
49C,
5) one minute rinse in water,
6) two minute immersion in Shipley's Accelerator
19 at about 22C,
7) one minute rinse in water, and
8) thirty minute bake at about 100C, just prior
to imaging.
The activated circuit board was then imaged by
application of a plating resist, which was applied to the
raised lands of the board, leaving the depressed
* A Trademark of Shipley Inc., 49 Walnut Park, Wellesley, Mass
; 02181
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circuit areas exposecl.
Next, the imaged circuit board was reactivated
by immersion for about 15 minu-tes in MacDermid's
9071 at abou-t 22~C, followed by a one minute rinse
in wa-ter, and subsequent immersion for approximately
15 minu-tes in MacDermid's Electroless Nickel 9340 at
about 32C, followed by one minute rinse in water.
he circuit board was then plated with copper by
immersion in MacDermid's 9042 until the desired
thickness of copper was obtained.
Finally, -the e~posed copper areas were cleaned
by soaking in hot alkaline solution, rinsing in cold
water, soaking in a mild ammonium persulfate dip,
rinsing in water, soaking in 10% sulfuric acid
solution, rinsing in cold water and drying. Thereafter,
; a protective coating of water-dip lacquer was applied.
It will be understood that various changes may
be made in the form, construction and arrangement of
the several parts and in the steps of the method
without departing from the spirit and scope of the
invention, and it is accordingly intended that all
matter contained in the above description or shown
in the accompanying drawing shall be interpreted as
illustrative and not in a limiting sense.
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