Note: Descriptions are shown in the official language in which they were submitted.
83 11317~6
1 This invention relates to circuit boards and more par-
ticularly to the connection and soldering of components to such
boards a~d to the method and article produced thereby.
: Circuit boards for mounting and interconnecting elec-
S trical and elec~ronic components have been produced and used for
a long time. One type of such circuit boards is manufactured
from a board of insulating material, for example, a board of
molded phenolic or epoxy resin, to which is laminated on one
side of the board a copper foil. To the copper foil laminated
side of such board is applied a printed mask of m~terial resis-
tant to copper etching reagents. The printed mask corresponds to
the required conductive pattern. The CQpper in the areas left
free by the printed mask is etched away and subsequently ~he
printed mask layer is removed. The conductive copper pattern
remaining when the mask layer is removed as well as the under-
laying insulating material is provided with perforations for
receiving the connector wires of the components at points in the
pattern where soldering eyes or lands have been provided in said
pattern. Subsequently, the components are mounted on the circuit
boards by inserting the connector wires from the conductor-free
; side, through such perforations, and soldering the extruding
leads to the respective conductors or conductor lands.
Another type of circuit board is manufactured by
scribing and bonding pre-formed conductors, such as wires, along
paths between pairs of terminal points or soldering eyes on an
- insulating base, such as a moulded board of phenolic or epoxy
resin. Perforations for receiving component connector wires are
provided in such wire scribed board either before the wire is
scribed thereon o, thereafter. Subsequent to wire scribing and
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1 1~31746
1 perforation of the wire scribed board, the components are mounted
thereon by inserting the connector wires through the perforations
much in the same manner as in the printed circuit board.
In order ~o produce a soldered connection between the
connector wires of the component and the soldering eye in the
appropriate conductive path on the printed circuit and wire
scribed circuit boards, it is necessary to carry out the mounting
of the components in such a way that the connector wires are
introduced into the respectively associated perforation holes
., 10 from the side of the board free of conductive paths. The con-
: nector wires are then connected electrically and mechanically to
the conductive paths or, respectively, their soldering eyes,e.g.,i
: a bulk soldering process by bringing the side of the board bear-
ing the conductive paths into contact with a tin solder bath,
for example, by means of a drag-soldering bath device or a solder
wave devlce.
'~ In such soldering process not only is the soldering eye
coated with tin solder but also the whole of the pattern of
' conductive paths. This causes not only a functionally useless 20 excessive use of tin solder but often leads to the formation of
solder bridges between adjacent conductive paths. The miniatu-
rization of co~ponents has increased the densi~y of the conducti~ e
paths and, hence, has reduced the distances between conductive
paths and between conductor paths and the soldering eyes. With
unprotected conductive paths, the danger of the formation of
solder bridges and short-circuits is increased. To a~oid bridge~
and s rt-circuits it has become necessary to cover over the
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1 conductive paths for drag or wave soldering by imprinting a
solder-resistant protective layer or mask over the conductor
paths while leaving the soldering eyes or lands free of such
soldering resistant mask. Soldering masks are applied either by
screen printing or, in the case of so-called fine-conductor
boards having greatly reduced distances between the conductive
paths, by photographic printing. Such masks fulfill their
purpose but lead to increasing of the price and complication of
the production of the printed circuit boards and increase manu-
facturing rejections.
A further disadvantage of the mounted printed circuitboards described above is the relatively frequent occurrence of
unreliable so-called "cold" soldering points. Here a costly
checking and finishing of the mounted printed circuit boards
becomes necessary after the soldering process. It has been
found that, in spite of careful testing, the occurrence of
defective soldering points in later service cannot,with certainty
be avoided. In addition, such printed circuit boards tend,
during the mounting process, to become damaged at the soldering
eyes.
It has, heretofore, been proposed to improve the qua-
lity of the soldering points by utilizing printed circuit boards
having a pattern of conductive paths applied to one side of the
board and to provide the walls of the perforations for receiving
the connector wires of the components with a metal coating con-
nected electrically and mechanically to the respectively asso-
ciated conductive paths. If one starts out from molded laminate,
laminated on one side with copper or provided on one side with
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1746
1 scribed wire, the walls of the holes are, for example, in accord-
ance with known methods, provided with a metal coating by means
of currentless metallization, alone or in combination with
galvanic deposition of metal. This considerably improves the
soldering point quality because, in the soldering process, not
only is a connection produced between the soldering eye and the
connector wire from the component but, at the same time, the
interstice between the connector wire and the metal coating on
the wall of the hole is filled with the solder. Thus, the length
of the electrical connection is increased and, at the same time,
a mechanical connection is formed.
Circuit boards having metal coated perforation walls,
however, have a considerably increased tendency to solder bridge
formation. Thus, the application of a soldering mask, with its
additional costs and disadvantages in method technique is neces-
sary. The need for exact orientation of the applied soldering
mask layer with the pattern of the conductive paths and holes
imposes severe demands upon the process of applying the soldering
mask. The soldering mask m~st be applied in registration with
the conductor pattern to insure, on the one hand, that all of
the soldering eyes and walls of the holes remain completely free
of mask material while, on the other hand, all of the conductive
paths are completely and reliably covered over. If this is not
achieved, a worsening of the soldered connections occurs, leading
to unusability, and/or conductor bridge formation.
In order to avoid this waste-charged and relatively
costly process it has heretofore been proposed to completely coat
B the pattern of conductive paths with a soldering mask layerf t~h
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By so completely coating the pattern, the difficulty of the
exact registration of the mask image with the pattern of the
conductive paths is indeed avoided. However, because the mask
is applied before the production of the perforations, a costly
process of metallization of the walls of the holes is necessary
in order to insure that the thickness of the mask layer is
reliably bridged over and mechanically and electrically secure
contact is produced with the conductive path associated in each
case, with the metallization of the hole wall, which contact
must also be fully preserved under temperature and mechanical
loadings. To improve the behavior of the soldering and to
compensate for the fact that connector wire of the component,
because of the omission of a soldering eyP or land, is only
connected to the end face of the conductive path forming part
of the hole wall and the metalliæation of the hole walls,
special metallization processes become necessary which, in the
course of the metallization process, form substitute soldering
eyes on the surface of the soldering mask layer. Apart from
the fact that such a method and the associated baths are
difficult to control, circuit boards of that kind can neither
before nor after mounting be tested for their operational
soundness in a way suited to practical operàtion.
With the rapid advance of small or miniaturized
components and, hence, the necessity of higher conductor
density on circuit boards, circuit boards which have conductive
paths on both board sides and have perforations provided with
a metal coating, have become more desirable. In such circuit
boards, however, the board side coming into contact with the
solder must
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1 again be provided with a soldering mask in order to avoid the
formation of solder bridges. Mounted circuit boards of ~hat kind
exhibit an outstanding solder joint quali~y but are elaborate in
production and, hence, costly.
The high density of conductive paths which can be
accommodated on one side of a circuit board by wire scribing
technique, or employing printed circuits fine line conductor
technology does in many cases, for example, in the broadcasting
and television equipment, allow the accommodation of all the
conductor paths on only one side of the circuit board. However,
such boards, provided on one side with a pattern of conductive
paths or bare scribed wires and, by necessity, relatively small
clearances between conductive paths and between conductor paths
and soldering lands or joints when bulk-soldered, such as by
drag or wave soldering, show a rather pronounced tendency to
form solder bridges combined with inadequate soldering at the
soldering points. The latter may, in known manner, be avoided
by the employment of perforations or holes wi~h metallized walls,
which, however, leads to a further increased tendency to solder
bridge formation and, hence, make the application of solder masks
practically unavoidable. Their production in the case of fine-
conductor boards, having regard to accuracy of the registration
on the one hand and the necessary resolution on the other, is
costly and difficult and, for numerous fields of application, is
excluded for economic grounds.
\ An object of the present invention is to provide a
simple and economical circuit board having components mounted
thereon and connected thereto in which the circuit board is free
~ 746
1 of the formation of solder bridges or other undesirable connec-
tions, and having solder joints of excellent quality.
In the instant invention, circuit boards provided on
one side with conductive paths of the conductive pattern and
have perforations or holes with metallized walls for receiving
the connector parts, for example, component leads, are employed.
The components are fitted to the side provided with the pattern
of conductive paths and the component leads are connected, elec-
trically and mechanically, by means of a soldering process per-
formed from the side of the board free of conductor paths. Thesolder fills the interstice between the metallization of the
wall of the hole and the component leads or pins and, preferably,
reaches to the circuit board surface carrying the conductor paths
to cover over or fill ~he region of the soldering land or eye or
a corresponding restricted region of the conductive path.
Advantageously, the metalli~ation of the walls of the
hole does not substantially reach beyond a circle approximating
the hole diameter and/or the edge of the hole on the side of the
board free of conductor paths. It is thereby ensured that,
even in the case of conductor paths and the component holes asso-
ciated with them being arranged extraordinarily closely, no
short-circuits can occur by bent over ends of component leads
with conductor paths or metal coatings reaching onto the surface.
The printed circuit board or wire scribed circuit
board, in the practice of the instant invention, with the conduc-
tor or circuit pattern on one side of the board and the other
side of the board free of conductor or circuit patterns, is
provided with perforations through the board at the ends or
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1 points in the conductor or circuit pattern at which component
connections are to be made. Such perforations may be provided
through the board before the circuit pattern is formed or scribed
or may be formed, such as by drilling of the board, after the
S conductors or circuit pattern has been completed. The walls of
the perforations are next, either electrolessly or in combination
with a galvanic plating process, coated with metal. Preferably,
the metal coating of the perforation walls extends along the wall
of component holes, up to the surface of the circuit board free
of conductors or circuit patterns, without substantially e~tendin~
onto said surface, along such perforation wall to the side of
the board bearing such conductors or circuit patterns and,
preferably, reaches to the surface of the associated conductor to
at least cover a region of the said conductor around the perfora-
tion opening on the conductor or circuit pattern side.
Advantageously, the metallization of the walls of thehole does not reach beyond the edge of the hole on the side of th~
board not provided with conductive paths. It is thereby ensured
that even in the case of conductive paths and the perforations
associated with them being arranged extraordinarily closely, no
short-circuits can occur by bent over ends of connector wires
from the components with metal coatings reaching on to the surface
With the conductor or circuit pattern on one side of
the circuit board, the board perforated at the points where the
components are to be connected and the walls of such perforations
metal coated, the components are mounted on the circuit board
from the side of the circuit board bearing the conductors or
circuit pattern. This may be accomplished with automatic assem-
31~46
1 bling equipment or by hand and is carried out by inserting the
component leads, connector wires or pins through the component
mounting holes where the connections are to be made.
The wire connector on the components utilized in the
practice of the instant inven~ion are smaller, in diameter, than
the inside diameter of the opening in the metal coated wall
perforations and are longer than required to pass through the
circuit board with the component in place. Thus, when the compo-
nents are in place on the side of the circuit board bearing the
conductor or circuit pattern, the component wires fit loosely in
the perforation holes and project outwardly from the opposite
side of the circuit board which side is free of circuit pattern
conductors.
With the component wires extending loosely through the
perforations and projecting from the circuit pattern free side
of the board, the projecting ends of the component wires are
lowered into a pan containing hot, mol~en solder. This is
accomplished by positioning the circuit board, with the component~ ;
thereon, over the molten solder containing pan, with the conduc-
tor and circuit pattern free side of the board facing the molten
solder and then lowering the board toward the solder so that the
projecting ends of the component wires are immersed in the hot,
molten solder and the circuit pattern free board surface touches
the solder surface.
The hot, molten solder heats the ends of the component
wires and, as this is being accomplished, the molten solder is
drawn upward, along the component wires and between such wires
and the metal coated walls of the perforation holes, by capillary
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1 action. Thus, the space between the metal coated perforation
wall and the component wire or lead at each of the component con-
nections is filled with solder which forms a mechanical and an
electrical connection between such wire and such metal coated
hole. The molten solder flows upward through the perforation
hole and, to a certain degree, outward at the top of the hole
over a pad-area of the respec~ive conductor around the perfora-
tion opening at the component side of the circuit board.
~fter the molten solder has been drawn upward into ~he
space between the component wires or leads and the metal coated
hole walls and has filled such space, the ends of the conductor
wires are lifted out of the molten solder by lifting the board
and the solder cools and solidifies forming a permanent mechani-
cal and electrical connection between the component wires or
leads or pins and the circuit board.
The instant invention will be more fully understood
from the following description and Examples of preferred embodi-
ments taken with the appended drawings in which
~ igure 1 is a perspective view, partly in section,
showing a printed circuit board to which components are to be
applied in accordance with the instant invention;
Figure 2 is a perspective view similar to Figure 1 but
showing another embodiment of the conductor pattern;
Figure 3 is an enlarged side view, in section, showing
a portion of the circuit board, a metal coated circuit board
perforation, a component and a component wire, lead or connector
in such perforation above the hot, molten solder bath before the
immersion of the component wire end in the molten bath per the
process of the instant invention;
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Figure 4 is an enlarged view, similar to Figure 3 but
showing the e~d of the component wire immersed and the process
of the invention underway;
Figure 5 is an enlarged side view, in section, showing
the component mounted thereon in accordance with the instant
invention.
Figure 6 shows a perspective partial illustration of a
printed circuit board having a plurality of different electrical
and/or electronic components mounted.
lo Re~erring now to the drawings, printed circuit board,
generally designated 1, of a suitable carrier material, is pro-
vided only on one side, namely, on the mounted side 8, with
conductor paths 2 in a predetermined conductor pattern. The con-
nection or mounting points of the conductor pattern are charac-
terized by mounting holes 9 which are through-metallized or
coated with a metal layer 3. The side 7 of the printed circuit
board 1 opposite the conductor path pattern is provided with no
kind of electrically-conductive tracks at all and the ~etal layer
3 of the walls of the holes ends here is substantially flush with
the surface 7 without the formation of any sort of collar. Con-
ductor paths 2 may be formed by the printing circuit process and
the perforations 9 may then be metallized or conductor paths 2
m~y be scribed wires followed by metallizing of the walls of
perforations 9.
Referring to Figure 3, component lead 5 of an electri-
cal or electronic component 6 is mounted on circuit board 1 so
that the end of wire S stands out freely at the side 7 of the
printed circuit board 1 which side 7 is free of conductor paths.
As best shown in Figures 4 and 5, when the end of wire S is
immersed in hot molten solder 4, molten solder 4 flows up around
wire 5 ~ith perforation 9 between wire 5 and metal wall 3 and,
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l at 4a, fills the interstice between the metal wall 3 of the
perforation and the connector wire 5 as well as the region of
the soldering eye on the mounting side 8, Figure 5. Thus, the
soldering process is performed from the side 7, in which case
the freely projecting end of the connector wire 5 is acted upon
by heat and the solder rises from the bottom upwards in the ..
interstice by a kind of capillary action, fills up the hole in
this way in the manner illustrated, but project beyond the region
having the metal collar~ Thus, solder 4a is nearly flush with
the end of metal wall 3 at the side 7 and projects beyond metal
wall 3, over the metal collar at.mounting side 8. Excess tin
solder remains exclusively on the freely projecting end of the
component lead 5 and does not overlap the cross-sectional area
of the perforation on the side from which the soldering process
is effected. On the opposite circuit board side 8, carrying
conductor paths 2, the maximum solder cover is substantially over
only the metal collar round the wall of the hole because the
solder is drawn upwards from the underlying side 7 and flows onto
the mounting side 8 radially from inside to outside. The surface
tension of the solder prevents solder 4a from flowing over the
edge of the collar or land areas at circuit board side 8.
Figure 6 shows a perspective partial illustration of a
printed circuit board having a plurality of different electrical
~ and/or electronic components mounted... It is essential here too
; 25 that a start is made from a circuit board l which bears conduc-
tor paths 2 only on one side, and that on the side 8 bearing the
conductor paths 2, all of the components 6 lie while the side 7
is k t free o~ conductor patbs and components. The surface 7 is
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1 merely characterized in that the free ends of the connector wires
5 from the components 6 project from it more or less in order to
guarantee ~he heat contact necessary in the soldering process.
The side 7 of the board, not bearing the conductor
paths of the conductor path pattern or components, is advanta-
geously provided with printed information, for example, with
characterizing and test data useful to the mounting and operation .
an image of the conductor path pattern and the like. In this
case, it is of particular advantage that side 7 of the board,
apart from the mounting holes, is-completely free and available
for printing of this kind.
The production of the mounted printed circuit boards
provided with components and in accordance with the invention is
to be described below by way of example.
EX~MPLE 1
In a preferred embodiment, a base material, for example ,
a phenolic paper press laminate is used, one side of which is
provided with an adhesion-promoting layer. After the production
of the perforations intended as mounting holès for component
leads, the board is prepared in known manner for electroless
metal deposition and sensitized catalytically, for exa~ple, with
a solution of a tin-palladium-chloride-complex and exposed to a
metallization bath working without e~ternal current supply, to
provide the adhesion-promoting layers, as well as the walls of
the holes, with a thin, preferably 1 to 6 microns thick metal
layer, preferably a ductile copper layer. Deposits of metal
which may be present on, and loosely adhering to the side of the
board not provided with the adhesion-promoting layer are removed
by brushing or other suitable way.
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1 Then the negative of the required pattern of conductor
paths is applied, in mask form, by means of screen or photographi .
printing or some other method in order subsequently to build up
the conductor paths simultaneously with the metallization of the
walls of the holes by galvanic deposition of metal to the desired
thickness. To this end, a copper layer of preferably 2~ to 40
microns is deposited. Instead of galvanic deposition of metal,
the build up of the conductor paths, as well as the metallization
of the walls of the holes, may be achieved in the same way by
1~ means of electroless deposition of metal, preferably depositing
a ductile copper layer of appropriate thickness.
The masking layer is next removed and ~he thus exposed
thin electrolessly deposited metal layer between the conductor
paths is removed in known manner. This is achieved, for example,
in a simple form by the action of an etching agent for a period
of time adequate for removing the thin metal layer without
residue and without, at the same time, reducing the thickness of
the conductor paths to a substantial degree.
The board, finished in a known manner by blanking and
other manufacturing processes, is then provided with the compo-
ments mounted from the side of the board bearing the conductor
paths of the conductor pattern, e.g., by means of automatic com-
ponent lead insertion machinery, or by hand, so that the wires
from the components reach at least slightly beyond the plane of
the edges of the holes on the side of the board free of conductor
paths. The board thus prepared is preferably subjected to a bulk
soldering process, for example, a drag soldering device.
The end of the connector wires from the components,
reaching into the bath of hot, solder metal, bring about contact
1` 1131746
1 with the hot solder at sufficient depth to satisfactorily heat
the wire, so that the solder rises up between the component wire
and the metal coating of the wall of the holes, fills the inter-
stice between the two and preferably forms a coating of solder
on the associated surface of the conductor path on the opposite
side of the board in regions of small extent similar to soldering
pads or lands. The soldered connections thus produced are of
extraordinary reliability. The outlay upon inspection and check-
ing of solder joints and respectively touch-up of imperfect solde .
joints is superfluous or at least largely reduced and at the
same time the quantities of rejects are drastically reduced. The
high mechanical strength of the soldered connections thus achieve
brings about great reliability in service of the mounted printed
circuit boards in accordance with the invention even under
unfavorable service conditions such, for example, as under
vibration.
According to a preferred embodiment of the method
according to Example 1, boards provided with printed mask are
subjected, in pairs, to the galvanic or electroless deposition of
metal for the build up of the conductor paths and the metalliza-
tion of the walls of the holes. With the sides of the boards
which are not to be provided with conductor paths brought into
the metallizing bath solution facing one another.
EXAMPLE 2
As the starting material,a base material is used which
- as well as the adhesion-promoting layer is applied to one side
- contains a substance which is catalytic to the electroless
deposition of metal so that in the case of process of Example 1
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1 the step of catalyzation is unnecessary. Thus, a further simpli-
fication of the production process is achieved.
EXAMPLE 3
As the starting material, a solid epoxy resin board
blank is employed having applied to one side an adhesion-promotin
layer containing a substance which acts catalytically upon the
electroless deposition of metal applied. Af~er providing ~he
board blank with the holes of the component mounting hole pattern
a negative pattern mask of the conductor paths is applied, for
example, by the method of photographic printing. After appro-
priate treatment of the adhesion-promoting layer in an oxidizing
medium for the production of a microporous surface, the board is
brought into a bath for electrolessly depositing ductile copper
and left there for a period of time adequate to building up the
conductor paths and metallize the walls of the holes to the
desired thickness. Depending upon the choice of the mask mate-
rial, after completion of the metal deposition the mask layer is
either removed or preferably, however, left on the board, The
back is then provided with the required printed information.
Subsequently, the components are mounted on the board from the
side bearing the conductor paths and, the soldered connections
between component leads and conductor circuitry are formed in
accordance with the instant invention employing one of the known
bulk soldering methods with the conductor-free board side facing
the solder pot.
EXAMPLE 4
A molded epoxy resin laminated paper board provided
on one side with copper foil, is first provided with the pattern
of component mounting holes. The board is exposed to a tin-
~ 11317~6
l palladium-chloride-complex solution, thus being catalyzed for
electroless deposition of copper and a thin copper layer is
subsequently formed by electroless deposition. Then the surface
is provided with a galvanic plating bath resistant masking layer
for~ing a negative of the required conductive pattern. A copper
layer of the desired thickness is then deposited in the areas not
covered by said masking layer including the hole walls and the
masking layer subsequently removed.Finally, the thus exposed
thin copper film between the conductor paths is removed, e.g.,
by spray etching. After known final fabrication steps, the
printed circuit board is provided with the components by insertin
the component leads from the side bearing the conductor paths of
the conductor pattern, with said lead wires projecting at least
slightly beyond the edges of the holes on the opposite side of
the board free of conductor paths. Subsequently, as previously
described, the soldered connections are produced by dip or drag
soldering from the side free of conductor paths and ~omponents
and in accordance with the invention.
In the practice of the instant invention, even in the
case of very narrow clearances between conductor paths, soldering
masks are not required. At the same time, high quality of
solder joints is achieved simply and economically.
The mounted printed circuit boards in accordance with
the instant invention are distinguished by low reject rates and
high reliability in service. Through the metal layer on the
walls of the holes, together with the arrangement of the compo-
nents on the side bearing the conductor paths, great electrical
and mechanical reliability of the soldered connection is achieved
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3l746
1 The absence of conductor paths on the soldering side of the board
prevents the formation of solder bridges as well as the danger of
short-circuit formation by bent-over component lead wires in a
reliable and inexpensive manner. The large area available for
printed information allows to provide detailed measuring and
operating data and instructions as well as components specifica-
tions employed and the pattern of the conductor paths.
The terms and expressions which have been employed are
used as terms of description and not of limitation, and there is
no intention, in the use of such terms and expressions, of
excluding any equivalents of the feature shown and described or
portions thereof, but it is recognized that various modifications
are possible within the scope of the invention claimed.
