Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
The present invention relates to a new and improved
construction of apparatus Eor applying solder to different
circuit boards, generally referred to herein broadly as simply
printed-circuit boards.
In its more particular aspects, the apparatus for
the application of a solder layer or covering to the metalized
surfaces of a horizontally advanced printed-circuit board,
utilizes a supply container or receptacle con-taining molten
solder and a substantially chimney-like solder applicator
structure or solder applicator device which protrudes out of
such supply container. The solder is upwardly pumped out of
the supply container through the solder applicator device in
such a manner that a wave of liquid solder is formed over an
outlet or discharge opening of the solder applicator device
which is directed into contact with the printed-circuit board.
At the upper edge of both of the side walls of the solder
applicator or applying device, and which side walls extend
transversely with respect to the feed or advance direction of
the printed-circuit boards, there are arranged guide elements
formed of metal plating or sheet metal. These guide elements
can be adjusted as to their angle of inclination with respect
to the feed plane of the printed-circuit boards which extends
at a certain spacing above the discharge opening of the solder
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applicator device, the solder of the solder wave flowing back
by means of these guide elements i.nto the suppl~ container.
A solderiny apparatus of the aforemen~ioned type is
disclosed in United States Patent No. 2,993,272~ granted July
25, 1961, and serves for soldering electrical components to
printed-circuit boards. The circuit boards which contain the
~lectrical components are continuously horizontally guided over
the solder wave and -the bottom face or underside of such
circuit boards along with the terminals of the electrical
components are coated with solder. During the fabrication of
circuit boards for printed-circuits it is advantageous to
provide, prior to the mounting of the electrical components, a
protective solderable coa~ing at the metallic surfaces
appeariny at both the top and bottom faces of the circuit
boards and also at the bore or drill holes, and thus, to
improve the shelf life propérties thereof and to also prepare
the circuit boards such that their soldering properties are
enhanced.
In European Patent No. 1~0013359, granted August
12, 1981, there is disclosed an apparatus which renders
possible, during horizontal passage of the circuit boards, the
application of a solder layer into the bore or drill holes and
also to both faces of a clrcuit board which is not yet
equipped with the electrical components, in contrast to the
heretofore known
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technique of vertically immersing the circuit boards into a
molten solder bath. This equipment consists of a firs-t
container from which liquid solder is pumped into a second
container in such a quantity that there is formed in the second
container a solder bath level which continuously lies above
horizontally extending slot-shaped openings. These slot-shaped
openings are provided at oppositely situated walls of the
second container and are located in the feed or advance plane
of the printed-circuit boards. The printed-circuit boards
which are to be equipped with the electrical components are
displaced by means of -the slot-shaped openings through a static
column of liquid solder and thus coated with solder.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to
provide a new and improved construction of apparatus for
applying solder to printed-circuit boards or the like in a
manner such that it can be incorporated intc an automated
production of manufacturing line working with essentially
horizontal passage or travel of the printed-circuit boards and
allows for faultless application of the solder layer, in a
manner complying with present day quality requirements, to both
faces of the printed-circuit boards which do not yet contain
the electrical components and also ensures for as uniform as
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possible coating of the through-metalized bore or drill holes
of the prin-ted-circuit boards.
Still a further significant object of the present
invention is directed to a new and improved construction of
apparatus for the application of solder to circuit boards,
which apparatus is relatively simple in construction and
design, quite economical to manufacture, extremely reliable in
operation, not readily subject to breakdown or malfunction,
requires a minimum of maintenance and servicing, and allows for
high-quality deposition of the solder upon the circuit boards.
Now in order to implement these and still further
objects of the invention, which will become more readily
apparent as the description proceeds, the solder applying
apparatus of the present development is manifested by the
features that the solder wave possesses a height which exceeds
the feed or travel plane of the printed-circuit boards. Both
of the metallic guide elements extend at least partially
approximately parallel to the mentioned feed plane. ~t the
inlet side and at the outlet side of the apparatus, that is at
the side where the printed-circuit boards or the like entex and
exit, respectively, from the solder applying apparatus, and
specifically at the reyion of the ends of the guide elements
there are arranged directly over the feed plane elements which
extend txansversely to the direction o~ feed or advance of the
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printed-circuit boards. These elements, during passage of the
printed-circuit boards, bear against the latter and, on the one
hand, define a boundary or confinement for the solder blanket
at the inlet side and at the outlet side, respectively, which
tends to spread out upon the upper surface or face of the
printed-circuit board duxing through-passage thereof, and, on
the other hand, act as scraper or stripper means at -the surface
of the printed-circuit boards.
One of the more notable advantages of the present
development resides in the fact that, through the use of
relatively simple means and with correspondingly modest
equipment expenditure there can be usefully employed the known
principle of solder wave soldering for the present day
requirements as concerns coating of printed-circuit boards at
both sides or faces thereof as well as coating of the metalized
inner walls of the bore or drill holes with solder. By virtue
of the intensive flushing of the bore or drill holes with
solder in both directions, which is continuo~lsly positively
brought about during the entire through~pass of the
printed-circuit boards, there is attained an outstanding
coating of the drill holes or bores both internally thereof and
at their marginal zones at both faces or sides of the circui-t
boards. The continuously produced friction effect by vir-tue of
the completely effective solder wave, which prevails between
the liquid solder and the metallic surfaces additionally causes
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an optimum wetting or imbuing of the sur~aces. By specially
constructing the elements which contact the through-passing
printed-circuit boards and which act both as solder scrapers or
strippers and also as limiting means for the solder, there is
extensively prevented any retention of flux agent residues at
the surfaces of the circuit boards.
BRIEF ~ESCRIPTION OF THE DR~WINGS
The invention will be better understood and objects
other than those set forth above, will become apparent when
consideration is given to the following detai~ed description
thereof. Such description ma]ces reference to the annexed
drawings wherein:
Figure 1 schematically illustrates a solder
applying apparatus constructed according to the invention and
specifi.cally depicts the more essential. components thereof in
sectional view;
Figure 2a illustrates a :Eirst possible construction
of an element used in the solder applying apparatus of Figure 1
and serving for limi-ting and scrapin~ of solder upon the
printed-circuit boards;
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Figure 2b illustrates a second construction of such
solder limiting and scrapex element, likewise usable in the
arrangement of Figure 1;
Figure 3a schematically illustrates in longitudinal
sectional view a portion of the solder applying apparatus shown
in Figure 1 and ser~ing to explain the function thereof; and
Figure 3b is a cross-sectional view of the
arrangement of Figure 3a, taken substantially along the line
A - A thereof.
10 DETAILED ~ESCRIPTION OF THE PREFERRED EMBODIMENTS
Describing now the drawings, it is to be understood
that only enough of the construction of the solder applying
apparatus has been shown therein as will enable those skilled
in the art to readily understand the underlyiny principles and
concepts of the present development, while simplifying the
illustration of such drawings. Turning attention now
specifically to the arrangement of solder applyiny apparatus as
depicted in Figure 1, it will be seen that such comprises a
supply container or xeceptacle 3 which contains molten solder
which is maintained by any suitable and therefore not
particularly shown heating device at the required temperature
as is well known in this technology. Within the solder
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~ontainer 3 ~here is arranged an upwardly open, substantially
chimney-like configured solder applicator device or structure 2
which protrudes out of the solder bath, ~enerally indicated by
reference character 30. This solder applying or applicator
device 2 has at its upper end a discharge or outlet opening 2c
through which there effluxes the solder in the direction of the
printed-circuit boards 1 passing thereabove. soth the solder
applicator device 2 and also the supply container 3 have only
been partially shown in Figure 1. The feed or travel plane,
generally indicated by reference character 32, of the
printed-circuit boards 1 which are to be coated at both sides
or faces with a respective solder layer or coating, is located
at a predetermined distance above this discharge or outlet
opening 2c of the solder applicator device 2. The
printed-circuit boards 1 which have previously been imbued at
both faces wi-th a suitable flux agent or the like and
pre-heated are transported from the inlet or entry side E at a
p.redetermined velocity in the direction of the outlet or exit
side A of the arrangement, i.eO ~rom the side E where the
printed-circuit boards 1 enter the operative region of the
solder applying apparatus to the oppositely situated outlet
side A where the printed-circuit boards, following application
of the solder thereto, depart from the op~rative region of such
solder applying apparatus.
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The feed or travel movement imparted to the
printed-circuit boards 1 can be accomplished by any suitable
known conveying or transport facilities which, in the
illustrated exemplary embodiment, are cons~ituted for instance
by means oE pairs of feed rolls 8, 9 located, respectively, at
the region of the inlet side E and the outlet side A, and
preferably a respective roll of each roll pair 8, 9 are
synchronously driven. These feed rolls 8; 9 can extend over
the entire width of the printed-circuit boards 1 or, however,
can only engage discrete portions oE the printed-circuit boards
1, for instance can engage the marginal or edge regions
thereof. The number of pairs of such feed or transport rolls
8, 9 arranged at the respective inlet side E and outlet side A
is dependent upon the maximum length of the printed-circuit
boards 1 which are to be processed, and specifically; is to be
chosen such that each of the printed-circuit boards 1 remains
within the feed or travel plane 32 throughout the entire time
of passage of the printed-circuit boards 1 through the
effecti~e region of the solder applying apparatus. For the
purpose of accommodating the e~uipment to different thi.cknesses
of the printed-circuit boards 1 at least one~of both rolls of
each of the roll pairs 8, 9 can be appropriately displaceably
arranged in a direction essentially perpendicular to the feed
or travel plane 32.
At the upper edge of those side walls 2a and 2b of
the solder applicator device 2 which extend transversely with
respect to the feed or advance direction of the printed-circui-t
~oards 1 there is pivotably or rotatably mounted a respective
guide element 4 and 5, formed of sheet metal or metal platiny.
The width of such guide elements 4 and 5 approximately
corresponds to the width of the related side walls 2a and 2b.
The discharge or outlet opening 2c of the chimney-like
applicator device or structure 2, viewed in the transverse
direction, is at least as long as, and in the exemplary
embodiment under discussion~ preferably longer than the maximum
width of the printed-circuit boards 1 which are to be
processed. The plane containing at least the straight portions
4a and 5a of the guide elements 4 and 5 extends approximately
parallel to the feed or advance plane 32 of the printed-circuit
boards 1. The ends or end portions 4c and 5c of the sheet
metal guide elements or guides 4 and 5 are preferably
downwardly bent or flexed, i.e. are bent so as to extend
towards the interior of the supply container or receptacle 3,
in order to ensure for a clean return flow of the solder back
into the confines of the supply container or receptacle 3.
The straight or linear portion 5a of the metallic
guide element 5 which confronts the inlet or entry side E of
the arrangement and which extends approximately parallel -to the
feed or advance plane 32 of the printed circuit boards 1, in
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the eY~emplary embodiment under discussion, is shorter than the
corresponding straight or linear portion 4a o~ the other
metallic guide element ~ which confronts the outlet or delivery
side A, something which however is not crucial as far as the
teachings of the invention is concerned. Equally, as will be
apparent from Figure 1 the height of the side walls 2a ancl 2b
differs from one another, again a feature which, however, is
not crucial for the faultless functioning of the equipment.
The angle of inclination of the guide elements 4 and 5 with
respect to the feed or travel plane 32 of the printed-circuit
boards 1 can be selectively adjusted by means of any sui-table
adjustment and arresting devices 10 which can be displaced
upwardly and downwardly along the side walls 2a and 2b. Of
course, any other appropriate adjustment means for varying the
inclination of the guide elements or plates 4 and 5 can be
utilized. In this way there can be selectively altered r as
desired, the size of the intermediate spaces 34 between the
guide elements 4 and 5 and the printed-circuit boards 1.
Additionally, the supply container 3 together with the solder
applicator device 2 can be displaced in substantially vertical
direction relative to the feed or transport plane 32 by any
suitable displacement or adjustment facility, as generally
indicated by the displacement or adjustment mechanism 36 shown
in Figure 1. For instance, this displacement or adjustment
mechanism 36 can constitute a suitable hoisting device or can
be representa-tive of an elevationally displaceable table or
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platform upon which the supply container 3 and its related
parts are supported. The arrangement shown in Figure 1
containing the metallic guide elements 4 and 5 of different
length and which slightly ascend with respect to the feed or
travel plane 32 in the direction from the inlet side E to the
outlet or delivery side A, has been found to be extremely
advantageous in practice.
Directly above the feed or travel plane 32 of the
printed-circuit boards 1 there are arranged above or at least
at the neighborhood of the bending or flexure locations 4b and
5b of the metallic guide elements 4 and 5, respectively,
substantially cylindrical-shaped elements or members 6a and 6b
which extend transversely, for instance perpendicular to the
feed or travel direction of the printed-circuit boards 1. The
cylindrical element 6b which is arranged above the solder wave
at the region of the inlet or entry location E of the
printed-circuit boards 1, serves for limiting the solder
blanket or the like Eormed upon the top surface of the
printed-circuit boards 1 during through-passage of each such
printed-circuit board, whereas the other cylindrical element
t~ ~ , apart from ].imiting or confining the solder blanket at the
outlet side or location ~, additionally serves for stripping or
scraping the solder and a portion of the flux agent residues
from the printed-circuit board 1 emerging from the solder
applying apparatus.
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~ 5 to the details of these elements 6a and 6b
reference now will be made to Figures 2a and 2b, wherein these
elements in each case have been here merely yenerally
designated by reference character 6. As shown in Figure 2a the
element 6 can consist of a core 21 and a jacket or outer shell
22. The cross~section of the core 21, as bes-t seen by
referring to Figure 2a, possesses the shape, for instance, of a
circular segment, whereas the jacket or outer shell 22 has the
shape, for instance, of a circular or ring-shaped cross-section
configuration. The jacket 22 is mounted upon the core 21 in
such a fashion that it can freely rotate thereupon. This core
21 preferably consists of metal, for instance steel. The
jacket or outer shell 2~ preferably consists of a permanently
elastic, heat-resistant material, preferably is formed of a
suitable plastics material.
By virtue of the different cross-sectional shapes
of the jacket 22 and core 21 there is formed therehetween a
hollow space or compartment 24 which is efEective as an air
cushion. ~he core 21 of the element 6 is rigidly connected in
the solder applying apparatus, and specifically in such a
manner that the hollow space or compartment 2~ confronts the
feed or travel plane 32 of the printed-circuit boards 1, iOe.
the planar or flat surface 21a of the core 21 is located
substantially parallel to the feed plane 32 of the
printed-circuit boards 1 and this core 21 can expand at least
32
in one direction along its lengthwise axis when subjected to
thermal effects. The jacket or outer surface 22, in turn, can
freely expand ln all directions. Of course, it is possible to
form the hollow space or compartment 2~ by using a multiplicity
of different cross-sectional shapes of the core 21 and the
jacket 22.
A further possible construction of the element 6
has been depicted in Figure 2b, wherein the core 21 possesses
an elliptical-like cross-sec-tional configuration, and the
jacket or outer shell 22 is constructed such tha-t between such
jacket 22 and the core 21 there is formed the hollow space or
compartment 2~.
During operation of the solder applying apparatus
depicted in Figure 1 there is automatically turned-on a
suitable schematically indicated pump 26 (Figure 1) as soon as
a printed-circuit board 1 or the li]~e arrives at the region of
the inlet location or en-try side E of the arranyement.
Consequently, liquid solder is upwardly conveyed or pumped
within the solder applicator device or structure 2. This pump
26 is again automatically turned-off as soon as the
printed-circuit board 1 has departed from the region of the
outlet or delivery location A. The upwardly emerging solder
forms over the discharge opening 2a of the solder applicator
device 2 a solder wave or splash which exceeds or extends
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beyond the circuit board-feed or travel plane 32, and the
propagation of which in the direction of the inlet side E and
the outlet side A above the feed plane 32 is limited by the
confining or limiting elements 6b and 6a, this solder wave then
flowing-off by means of the metallic guide elements 4 and 5.
As soon as the printed-circuit board 1, after entry at the
inlet location E, has reached the operable zone or region of
the element 6b and that of the metallic guide element 5, this
circuit board is initially brought into contact at its
underside or face with the hot solder wave, then penetrates
through the solder wave which is da~ned-up by the element 6b
and is continuously heated during the progressive feed or
advance movement of such circuit board 1. With optimum
geometric arrangement of the metallic guide elements 4 and 5 in
relation to the feed or travel plane 32 of the printed-circuit
boards 1 there is achieved the beneficial result that the
inserted printed-circuit board l is exposed to the action oE a
non-symmetrical solder wave or the like. The arrangement can
be optimized by carrying out three measures, namely:
0 1) By adjusting the inclination angle oE the metallic yuide
elements 4 and 5 with respect to the feed plane 32;
2) By selecting an appropriate height of the side walls 2a
and 2b, and thus, the spacing of the rotational axes of
the sheet metal guides 4 and 5 from the feed plane 32; and
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3) By vertically displacing the supply container 3 along with
the solder applicator device 2 relative to the feed or
travel plane 32.
It is possible to determine and optimize the
quantity of solder which comes into contact with the underside
or bottom face of the prlnted-circuit board 1 by means of, on
the one hand, the pump output or delivery capacity and, on the
other hand, the spacing of the upper end of each of the side
walls 2a and 2b with respect to the feed or travel plane 32.
Additionally, the flow velocity of the solder, especially at
the bottom face of the printed-circuit boards 1, can be
influenced by altering the angle of inclination of the metallic
guide elements 4 and 5. In this way there also can be
influenced the outflow velocity of the solder blanket which
forms at the upper surface or Eace of the printed-circuit
boards 1. By optimi~ing such influencing parameters there is
produced the aforementioned non-symmetrical solder wave,
wherein th~ quantity of the solder flowing towards the inlet
location E is greater than the quantity of ~older flowing
towards the outlet location A. Hence, each inserted
printed-circuit board 1, already at the incipient phase of its
travel through the solder applying apparatus is exposed, on the
one hand, to the greatest possible friction between the liquid
solder and, on the other hand, there is inputted thereto a
sufficiently great amount of thermal energy in order to ensure
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for the best possible imbuing of th~ metalized surfaces with
solder. The liquid solder, during the further advance movement
of the pri.nted-circuit board 1, additionally passes both
laterally and also through the bores 28 (Figures 3a and 3b) of
the printed-circuit board 1 in such a quantity onto the upper
surface of such printed-circuit board that there is formed at
that location a coherent solder blanket or covering, the
expanse of which is limited by both of the elements 6a and 6b.
In Figures 3a and 3b there have been more
specifically depicted the flow conditions of the solder. From
the sectional view of Figure 3b there is particularly evident
the lateral flow of the solder onto and from the top face or
upper surface of the printed-circuit board 1. The lateral
limiting of the solder wave is accomplished at both sides by
means of the side walls 7. The flushing of the bores or drill
holes 28 in vertical direction, both from above and from below;
ensures for thei.r faultless coating with solder in the event
that these bores or drill holes 28 are through-metalized. The
solder which flows-off over the metallic guide elements 4 and 5
produces a suction action which enhances the flushing-through
of the bores or drill holes 28 with the solder. The continuous
flushing action ensures for a complete expulsion of the air out
of these drill holes or bores 28, something ha~ing an
advantageous effect upon the coating of the inner walls of
these drill holes 28. In this way there is formed a
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so-to-speak "dynamic" solder blanket or cover, so that all oE
the free metalized surfaces are continuously exposed at both
sides or faces to a frictional action by virtue of the applied
solder, enhancing the optimum coating of the printed-circuit
boards 1. The metallic guide element 4 located at the exit or
outlet side A ensures for retention of the thermal energy which
is inputted to the printed-circuit board by the solder which
f].ows away over the metallic guide element ~, which augments
the good wetting of the metalized surfaces with solder.
The length of the guide section 4a extending
approximately parallel to the feed or advance plane 32
therefore is essentially dependent upon the expanse of the
solder blanket in the direction of the outlet or exit side A
which is governed by the arrangement of -the element 6a. It is
basically possible Eor both of the metall.ic guide elements 4
and 5 to possess a random length which is accommodated to the
momentarily encountered conditions.
As explained, the element 6a, apart from delimiting
the solder blanket, additionally assumes the function of
stripping-ofE the solder from the printed-circuit board 1. By
virtue of the air cushion 24 the elements 6a and 6b optimumly
accommodate themselves over their entlre length to the surface
of the printed-circuit board and prevent the outflo~ of the
solder blanket over the predet~rmined boundaries at the
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printed-circuit board l~ In order to initiate a stripping or
scraping away of the solder also at the bottom face of the
printed-circuit board 1, there can be provided an additional
cylindrical-shaped scraper or stripper element 16 beneath the
feed or travel plane ~2 of the printed-circuit board 1. This
arrangement is earried out advantageously directly beneath the
element 6a, as shown, and both of the elements 6a and 16
contact the through-passing printed-circuit boards 1. In the
event that there are processed circuit boards of different
thickness, then it is advantageous if a-t least one of both
elements 6a and 16 is arranged so as to be appropriately
automatically displaceable or else is fixedly adjustable in a
direction perpendicular to the feed or travel plane 32, and
which ad~ustment strueture or facilities have been generally
indieated by referenee character 40 at the right-hand portion
of Figure 1. It is here particularly pointed out that any
suitable ad-justment device, such as spindle adjustments,
power-operated adjustment elements and so forth can be used.
During forward advance of the printed-circuit boards l,
depending upon the thickness of these printed circuit boards l,
these elements 6a and 16 can be appropriately spaced Erom one
another, and thus, contact the lower and upper faces o~ the
printed-eircuit boards 1 without however losing their
delimiting or constraining effect for the solder blanket. The
feed or advance force for the transport of the printed-circuit
boards 1 can be reduced if the elements 6a, 6b and 16 are not
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arranged exactly in a direction perpendicular to the feed
direction, rather are oriented in a direction enclosing a small
angle with respect to the vertical direction.
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