Apparatus for the continuous hot tinning of printed circuit boards

Apparatus for the continuous hot tinning of printed circuit boards includes conveying rollers for passing the circuit boards through the apparatus, and a trough for accommodating the molten tin, together with nozzles for applying tin from the trough to appropriate locations on the circuit boards. A hollow column is disposed at at least one side and preferably at both sides of the path of conveying movement of the circuit boards through the apparatus, with the open lower end of the or each column dipping into the trough so as to be below the level of the molten tin therein. Tin is pumped from the trough through the columns by pumps at the lower ends thereof, and then to the nozzles arranged above and below the path of conveying movement and directed so as to spray molten tin on to the printed circuit boards. In a process using the apparatus for soldering the connecting pins of components to a circuit board, molten tin from a trough is sprayed against the underside of the board at the appropriate locations.

BACKGROUND OF THE INVENTION 
The invention relates generally to an apparatus for continuous hot tinning 
of printed circuit boards, and a process for soldering the terminals of 
components to the conductor tracks and soldering eyes of a printed circuit 
board. 
The manufacture of printed circuit boards or cards is increasingly changing 
over from using galvanic processes to a hot tinning process. In such a 
process, the copper conductor tracks which are already applied to an 
insulating base material or substrate are coated with a eutectic lead-tin 
layer. 
For the sake of simplicity herein, reference is only made hereinafter to a 
tin layer and a hot tinning operation. 
Hot tinning operations include a cyclic process which operates in a 
vertical mode and a continuous process which operates in a horizontal 
mode. In the cycline process, the printed circuit boards or cards are 
dipped into liquid tin. When the printed circuit boards are taken out of 
the tin, they are then passed between nozzles and hot air is blown 
thereonto, thereby blowing free the holes and bores in the board while 
also blowing away excess tin so as to make the layer of tin applied 
thereto move even and flat. On the other hand, in the horizontal-mode 
continuous process, the board is guided through a standing wave of solder 
or tin material which is produced in front of baffle plates of a nozzle 
out of which the molten tin is discharged. The printed circuit board is 
then passed between two nozzles and blown off using hot air. 
Prior to the tinning operation, the printed circuit board is treated with a 
fluxing agent. However, a part of fluxing agent tends to remain clinging 
to the board and is thus carried into the tin. The fluxing agent burns in 
the hot tin, with the result that in a tin bath which is not stirred or 
agitated in some suitable fashion, the residues of the burnt fluxing agent 
float on the surface of the tin. By virtue of the continuous movement in 
which the bath is involved in the course of operation however, such 
residues are entrained with the tin and thus contaminate the surface of 
the circuit board. Such residues also have a tendency to clog the 
conduits, lines and pumps of the system. Finally, they also put the 
surfaces of the conveyor rollers used in the system under additional 
stress so that the conveyor roller surfaces tend to suffer from a high 
rate of wear. All that means that extensive cleaning and maintenance 
operations are required during each working shift involved in carrying out 
the hot tinning process. 
Furthermore, as already indicated above, after the actual hot tinning 
operation, the printed circuit boards are blown off using hot air, and the 
fact that the air has to be suitably heated involves the consumption of a 
great deal of heat energy and thus increases operating costs. 
To give a more detailed picture of the kind of equipment involved, 
reference may be made to U.S. Pat. No. 2,821,959 diclosing an apparatus 
for soldering components to a printed circuit board or card, comprising a 
printed circuit board heating station, a fluxing station, a hot tinning 
station, a cleaning station and a drying station, and further including 
conveyor rollers which are arranged horizontally above and below the path 
of conveying movement of the printed circuit boards, for engaging the 
printed circuit boards to convey them through the equipment. The apparatus 
further has a trough at the hot tinning station, for accommodating the 
molten tin, at least one nozzle for applying the tin to the copper 
conductor tracks on the printed circuit board, with a conduit between the 
trough and the nozzle, the conduit going upwardly beyond the plane of the 
nozzle. A pump is provided for conveying the tin from the trough through 
the conduit into the nozzle, while the tin in the trough is heated by 
suitable heating means. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an apparatus for the hot 
tinning of printed circuit boards, which is such that the tin to be 
applied to the circuit boards is at least substantially free from 
impurities due to burnt fluxing agent residues. 
Another object of the present invention is to provide a printed circuit 
board hot tinning apparatus which provides for a reduced level of 
expenditure in respect of maintenance and cleaning. 
Still another object of the present invention is to provide a printed 
circuit board hot tinning apparatus which provides for a reduced level of 
energy costs. 
A further object of the present invention is to provide a printed circuit 
board hot tinning apparatus adapted to provide for quick and easy 
application of tinning solder to the appropriate locations on a printed 
circuit board, in a contact-free manner. 
A still further object of the present invention is to provide a process for 
soldering terminal means of components to a printed circuit board in a 
quick and easy operation, with the amount of tinning solder wastage being 
at least substantially reduced. 
Yet a further object of the present invention is to provide a process for 
soldering terminal means of components to a printed circuit board in which 
the solder is applied to the board only at the respective locations 
thereon at which solder is required. 
In accordance with the principles of the present invention, these and other 
objects are achieved by an apparatus for the continuous hot tinning of 
printed circuit boards, comprising a station for heating the printed 
circuit board, a fluxing station, a hot tinning station, a cleaning 
station and a drying station. Conveyor rollers are arranged horizontally 
above and below the path of transportation movement of the circuit boards 
through the apparatus, for engaging the circuit boards to convey same, 
while the hot tinning station includes a suitable container of a generally 
trough-like configuration to accommodate molten tin. The tin in the trough 
is suitably heated by associated heating means. Columns or pillars are 
arranged at both sides of the path of conveying movement of the printed 
circuit boards, in the trough, with the lower ends of the columns or 
pillars being open and dipping to a substantial depth into the trough and 
thus into the tin thereof. The upper ends of the columns or pillars are 
disposed above the path of transportation movement of the circuit boards 
through the apparatus, while nozzles are arranged above and below the path 
of transportation movement on both sides thereof and are directed 
theretowards to apply the tin solder to the circuit boards as they pass 
through the apparatus. The inlets of the nozzles are connected to the 
columns or pillars, in the plane of the path of transportation movement of 
the printed circuit boards. 
In that arrangement, with the molten tin being continuously pumped around 
the system from the trough, through the columns or pillars and then 
through the nozzles, then dropping back into the trough, the tin is 
continuously moved around and thus agitated in the trough. As a result, 
burnt fluxing agent residues and other impurities, due to their low 
specific gravity, rise upwardly in the molten bath and thus collect at the 
surface thereof from where they flow away through an overflow means, 
without external intervention, in the normal course of operation of the 
equipment. In order to provide for further and more secure separation of 
tin material and impurities, the tin is drawn from the trough at a low 
point therein, and thus at a substantial distance below the surface of the 
tin at which the impurities are to be found, and is then pumped upwardly 
beyond the plane of the path of conveying movement of the printed circuit 
boards through the apparatus. From there the tin material flows downwardly 
to the applicator nozzles simple due to static pressure or the force of 
gravity acting thereon. That ensures that the tin material is applied to 
the conductor tracks or paths on the printed circuit board in a very 
uniform manner. A static pressure corresponding to a difference in height 
or pressure head of about 600 mm has been found to be sufficient. 
It will be seen therefore that the columns or pillars are disposed in the 
circuit through which the molten tin passes, with the tin being pumped up 
in the columns or pillars by suitable pump means. At the same time, the 
collars or pillars form support members for carrying other components of 
the apparatus. From the columns, the molten tin flows into the nozzles 
under the above-indicated static pressure and is discharged therefrom in a 
uniform manner. The overflow arrangement which is provided in the upper 
region of the trough containing the molten tin ensures that any burnt 
fluxing agent residues and other impurities and contaminatory material 
which float on the surface of the molten bath can satisfactorily flow away 
and thus do not constitute a major problem by virtue of always being 
present in the bath. Such impurities are thus readily removed from the tin 
circuit of the apparatus and therefore are no longer in a position to clog 
fine passages and nozzles in the system. The amount of wear produced at 
the conveyor rollers for conveying the printed circuit boards through the 
apparatus is also reduced by virtue of the removal of such impurities from 
the tin circuit of the apparatus. The fact that such impurities are 
removed from the apparatus also means that the level of defects which 
occur in the application of the tin to the printed circuit boards, due to 
the presence of contaminatory material, is also reduced. 
In an advantageous feature of the present invention, the nozzles are in the 
form of nozzle bars which extend at least substantially over the entire 
width of the path of conveying movement of the printed circuit boards, 
with the nozzle bars comprising a pipe at a central position and an 
annular space defined therearound, while the columns comprise two pipes 
which are disposed in mutually concentric relationship, the inner pipes 
being open at their lower ends and dipping into the trough containing the 
tin, with the annular spaces defined in the nozzle bars communicating with 
the inner pipes, while the space between the inner and outer pipes of each 
column or pillar is connected at its intake end to a hot oil source, while 
also being connected to the central pipes of the respective nozzle bars. 
That embodiment thus provides, in addition to the tin circuit, a hot oil 
circuit, wherein the hot oil flows through and around the columns or 
pillars and also passes through the nozzle bar. That arrangement therefore 
ensures that the tin is held at the desired temperature thereof throughout 
its circuit through the apparatus and in particular over the entire length 
of the nozzle bars where it is particularly important that the tin should 
remain in a suitably fluid condition. 
Another advantageous embodiment of the apparatus of the invention provides 
that the nozzles have outlet openings for discharging hot air, downstream 
of the outlet openings for the tin, as considered in the direction of 
movement of the circuit boards through the apparatus. The hot air which 
issues from the nozzles is kept at substantially the same temperature as 
the tin. When the jets of hot air issuing from the outlet openings of the 
nozzles impinge on to the layer of tin which has just been applied to the 
respective printed circuit boards, that layer is rendered more uniform and 
even by virtue of the effect of the air. The preferred embodiment of this 
construction provides that the hot air issues from the same nozzle bars as 
the tin. Within the apparatus, the air is delivered in the vicinity of the 
tin and the hot oil circuits, with the air thus being heated to the 
desired temperature thereof. That means that there is not need to provide 
for particular heating of the air, thus further reducing the level of 
energy costs incurred. 
A further embodiment of the apparatus of the invention provides that, in 
the feed conduits leading to the outlet openings for the tin, the nozzles 
each have a slider which is displaceable by the force of a spring means 
into the feed conduit, into a position of closing off that conduit, while 
the slider is displaceable out of the feed conduit into a position of 
opening same, by an electromagnetically operated actuator. That 
construction is thus so designed that in the rest position of the 
respective slider, the outlet openings for discharge of the tin from the 
nozzles are closed. The electromagnetically operated actuator must be 
brought into operation in order to move the respective sliders into the 
open position thereof, thereby to permit the tin to flow through the feed 
conduits and out of the respective nozzles. 
Another embodiment of the invention provides that each of the nozzles 
comprises first and second half shell members which are held together by 
suitable screw members or bolts and which are recessesd on their mutually 
oppositely disposed sides to provide the respective annular spaces 
referred to above in each nozzle. Desirably, the nozzles are so arranged 
as to be displaceable about their respective longitudinal axis or with 
respect to the path of conveying movement of the circuit boards, whereby 
the apparatus can be readily adapted to different operating conditions. 
Still another embodiment of the apparatus of the invention provides that 
the nozzles are subdivided over the length thereof into a plurality of 
nozzle portions. In an advantageous form of that construction, the nozzles 
are subdivided into a middle wide nozzle portion, with two outer narrow 
portions on respective sides thereof, as considered in the direction 
transverse with respect to the path of conveying movement of the printed 
circuit board through the apparatus. The above-mentioned sliders for 
controlling the feed of tin to the nozzles and the control means for 
controlling the discharge of hot air can be actuated separately for each 
of the nozzle portions. The middle wide nozzle portion is recommended to 
be around 300 mm in width while a width of 150 mm is recommended for each 
of the two outer narrower portions on respective sides of the middle 
portion. With that arrangement, printed circuit boards of various standard 
widths may be passed through the apparatus according to the invention 
individually or simultaneously. 
It has already been noted above that the conveyor rollers of the apparatus 
tend to be subjected to a high level of mechanical loading. In addition, 
they are also subjected to a high level of thermal loading by virtue of 
coming into contact with the hot printed circuit boards. Hitherto, 
attempts have been made to deal with those loading on the conveyor rollers 
by virtue of the choice of suitable plastic materials for constituting the 
surface at least of the conveyor rollers. Embodiments of the apparatus of 
this invention provide that the rollers are subjected to a lower level of 
mechanical loading, because, as indicated above, impurities and 
contaminatory material are removed from the tin and thus do not reach the 
surfaces of the conveyor rollers, while in another preferred embodiment of 
the invention, in order to reduce the level of thermal loading on the 
rollers, the rollers for conveying the printed circuit boards through the 
apparatus have hollow shafts and the shafts are part of a coolant circuit. 
Tests have shown that it is desirable for the circuit boards not to be 
passed through the apparatus in a precisely horizontal position. A slight 
angle of inclination or a fall in respect of the circuit boards of from 
example 3.degree. relative to the horizontal in any direction has been 
found to be desirable. With the printed circuit boards inclined in that 
manner, any impurities which have still remained in the molten tin and 
which have been applied therewith to the printed circuit board flow away 
into one corner or an edge of the printed circuit board. A preferred 
embodiment of the invention provides that the inclined position of the 
printed circuit boards as they pass through the apparatus is achieved by 
the assembly comprising the conveyor rollers, nozzles and associated 
components being adjustable in respect of their angle of inclination 
transversely with respect to the path of conveying movement of the boards. 
A preferred embodiment also provides that the conveyor rollers are 
arranged along the path of conveying movement of the boards, at a slight 
angle of inclination. 
Another embodiment of the invention provides that the columns or pillars 
are held in the trough containing the molten tin and the nozzles are held 
between the columns or pillars. Arranged below the nozzles is a plate 
arrangement acting as a catch means to catch molten tin which drops from 
the printed circuit board to which the tin has been applied, the catch 
means having a fall thereacross to provide for the accumulation of molten 
tin at a lowest part of the catch means. A drain pipe extends from the 
lowest part of the catch means and leads into the trough, to return the 
molten tin thereinto. A cover plate is disposed above the path of 
conveying movement to form an upward cover means thereover, while a 
further cover plate is disposed above the trough to provide a cover means 
above the trough. The above-mentioned drain pipe extends through the cover 
means above the trough, in any suitable fashion. The catch means is 
desirably of a funnel-like configuration, with the lowest part thereof 
substantially at its centre. 
In order for the molten tin to be conveyed into the columns or pillars and 
then upwardly therein, and in order to provide that the tin is circulated 
in the tin circuit of the apparatus, another preferred embodiment of the 
invention provides that an electric motor is disposed on each column while 
mounted in each colum is a shaft whose upper end is coupled to the 
respective electric motor while a suitable pump member such as a pump 
wheel or impeller is carried at the lower end portion of each shaft. The 
pump member thus displaces molten tin from the trough and upwardly within 
the respective column or pillar. 
In order to provide compensation for the tin which is removed from the 
circuit of the apparatus by virtue of tin being applied to the printed 
circuit boards, an embodiment of the apparatus of the invention provides 
that a piece of tin material, also as an anode, is suspended above the 
trough in such a way as to be displaceable in respect of height relative 
thereto, with the lower end of the piece of tin dipping into the molten 
tin in the trough. The fact that the piece of tin is in contact with the 
molten tin in the trough means that the piece of tin melts away at its 
lower end and thus provides a make-up feed of tin to the molten tin in the 
bath. The level of the tin bath in the trough is measured by suitable 
sensing means in such a way that, when the level of the tin bath in the 
trough falls below a given reference level, the piece of tin suspended 
above the trough is moved downwardly by a given amount to ensure that the 
trough has a continuous make-up feed of tin thereinto. The piece of tin 
thus again dips into the molten bath, melts away and thus raises the level 
of the bath to the desired value. 
In the above-mentioned apparatus as disclosed in U.S. Pat. No. 2,821,959, 
after the hot tinning operation, compressed air is blown on to the printed 
circuit boards in a cleaning station. The blowing means used in that 
apparatus may be referred to as air blades, in that they cut away excess 
tin material. Thus, the compressed air which is blown on to the printed 
circuit boards is intended in particular to displace from holes and bores 
in the printed circuit board, any tin which has penetrated thereinto, as 
long as the tin is still hot and thus suitably soft and fluid. A preferred 
embodiment of the apparatus of the present invention provides that, in 
order to enhance the cleaning action, in the station for cleaning the 
printed circuit boards, the conveyor rollers are suspended or mounted by 
resilient mounting means, while a shaker means is operatively connected to 
the conveyor rollers. The shaker means is mounted by means springs and the 
conveyor rollers are carried in the shaker means. The shaking action 
imparted to the printed circuit boards by operation of the shaker means 
assists with removing the tin from the bores and holes in the printed 
circuit boards. 
In addition, the operation of applying a fluxing agent to the printed 
circuit baords prior to the hot tining thereof often gives rise to the 
difficulty that the fluxing agent not only wets the walls of the bores and 
holes in the circuit board, but remains clinging therein. That results in 
the fluxing agent being introduced into the tin bath, which is an 
undesirable phenomenon, as already referred to above. In order to prevent 
that from happening, a further embodiment of the invention provides that 
disposed in the fluxing station, downstream of fluxing agent applicator 
means and above and below the path of conveying movement of the circuit 
boards, are nozzles which are directed on to the circuit boards, for 
blowing free the holes and bores which are to be found therein. The 
nozzles may be the same kind as those with which the hot tin is applied to 
the boards. The fluxing agent is thus applied to the boards through one 
outlet of the nozzles, while air is blown on to the boards through the 
other outlet opening thereof, as when the tin is applied thereto. Both the 
fluxing agent and the air may be suitably heated by means of the hot oil 
system. 
It may be found that the nozzles do not cause the tin generally to be 
applied to the circuit boards in such a way as to form a layer of uniform 
thickness thereon. On the contrary, there are raised portions, portions of 
increased thickness and so forth in the layer of tin which is produced in 
that way. Accordingly, it is desirable for the layer of tin on the circuit 
board to be rendered more uniform or levelled off. For that purpose, a 
previous process provides that the circuit boards are passed through a 
wave of hot oil which is discharged under pressure through a nozzle formed 
from baffle plates. That gives rise to oil vapours or mist, in particular 
when there is no circuit board passing through that arrangement. It is not 
really possible to retain the oil mist produced in those circumstances, 
with the result that it penetrates into the environment, with potentially 
harmful consequences. Now, in a preferred embodiment of the invention, for 
the purposes of levelling off the layer of tin applied to the circuit 
board without causing environmental pollution of the kind indicated above, 
while at the same time recycling the oil in the apparatus, disposed 
downstream of the nozzles for applying the tin to the circuit boards, in 
the direction of movement of the latter through the apparatus, and above 
and below the path of their conveying movement, are nozzles for spraying 
hot oil and nozzles for blowing air at a lower temperature, on to the 
circuit boards. The nozzles cause oil to be sprayed on to the circuit 
boards at a temperature in the region of around 220.degree. C., in a 
restricted or limited jet or stream. The pressure involved in such an 
arrangement is substantially higher than in an oil wave, so that the layer 
of tin on the circuit board is satisfactorily levelled while using a 
smaller volume of oil. The levelling action with that arrangement occurs 
uniformly on the top side and the under side of the respective circuit 
boards. The tin on the circuit boards is cooled down and caused to set by 
the air which is then blown on to the circuit boards, at a lower 
temperature. The conveyor rollers which subsequently engage the circuit 
boards to convey them on through the apparatus do not then cause grooves, 
channels and the like to be impressed into the tin as the tin is already 
sufficiently hard to withstand that effect. Instead of the 
lower-temperature air referred to above, it is also possible to blow 
cooler oil on to the circuit boards. 
The nozzles are advantageously disposed in the above-mentioned shaker 
means. In that arrangement, they should be supplied with oil and/or air 
intermittently only when a circuit board is moving therepast. That ensures 
that oil is not unnecessarily discharged from the nozzles, which could 
cause further environmental pollution. Instead of using a respective pair 
of nozzles for the discharge of oil and air respectively, it is also 
possible to provide more than one pair of nozzles for each of the oil and 
air discharge functions. 
It should further be mentioned herein that the fluxing station may use the 
same nozzles or nozzle bars, as are used for applying the layer of tin. 
The nozzles are advantageously heated in order to ensure that the fluxing 
agent is of the correct viscosity. 
Where, as indicated above, the apparatus is also to be used in an operation 
for soldering components to the conductor tracks or paths or soldering 
eyes or pads of printed circuit boards, it is desirable for the nozzles to 
be rotatable about their respective longitudinal axes. For the same 
purpose, another embodiment of the apparatus provides that the nozzles are 
fixed only to one column or pillar, and the latter is pivotable about its 
vertical axis, being operatively connected for that purpose to a pivoting 
mechanism. 
Now one of the last steps involved in the industrial production of printed 
circuit boards lies in electrically connecting the connections or 
terminals of the components involved, to the conductor tracks or paths and 
soldering eyes or pads of the boards. Machine-operated soldering processes 
have been used for that purpose, one form of such a process which is 
frequently employed being a drag soldering process while another form of 
the process is a wave soldering process. In the drag soldering process, 
the circuit board is pulled or dragged over the surface of the liquid 
solder material, the solder thus coming into contact with the members 
which are to be soldered together and also the entire underside of the 
circuit board. In the wave soldering process, the liquid solder is pumped 
into a nozzle by a suitable pump, with the outlet opening of the nozzle 
being disposed above the level of the solder in the trough. The liquid 
solder issues from the nozzle in the form of a wave and flows back into 
the trough. The circuit board is passed with its underside over that wave 
and the members which are to be soldered together pick up solder and are 
thus suitably joined to each other. In addition, the solder contacts the 
entire underside of the circuit board. It will be seen therefore that in 
both those forms of process, the undersides of the circuit boards are in 
contact with the hot solder, over a very substantial area. The result of 
that is that the circuit boards and also the components thereon are heated 
up and subjected to a thermal loading, which can cause major difficulties 
in relation to sensitive components. Another point in common to the two 
forms of the process set forth above is that the trough must provide a 
large free surface area occupied by liquid solder. Hot gases and vapours 
are there formed from fluxing agent residues, impurities and other 
materials. As it is very difficult to catch such hot vapours and gases, 
they can cause serious environmental pollution in the area of the 
apparatus. 
Thus, in another aspect of the invention, there is provided a process for 
soldering terminal or connecting means of components to conductor tracks 
and soldering eyes or pads of a printed circuit board which is provided 
with the components on one or both sides thereof. In that process, the 
solder is contained in a molten state in a container trough, with the 
circuit boards being passed over the trough. Liquid solder is then sprayed 
against the underside of the circuit boards. Desirably, the liquid solder 
is sprayed against the underside of the circuit boards cyclically when a 
location thereon to be soldered moves past the point of liquid solder 
spray. While the hot liquid solder in the above-mentioned wave soldering 
process is in contact with the underside of the circuit board, as 
considered in the direction of conveying movement thereof, over a length 
of about 10 cm, and in the drag soldering process, the underside of the 
circuit baord is in contact with the hot solder over its entire length, 
the above-indicated process of the invention provides that contact between 
the circuit board and the solder is restricted to a length of only about 1 
cm. The solder thus impinges in the form of a jet on to the underside of 
the circuit boards. In the direction of conveying movement of the board, 
the jet is of a length of around 1 or only a few milimeters. After 
impinging on the board, it divides up towards both sides, and flow or 
creeps a few millimeters under the circuit board, whereupon excess solder 
drips off. The amount of contact is thus restricted to an overall length 
of only about 10 millimeters. That accordingly provides that the resulting 
thermal loading on the circuit board and the components thereon is 
comparatively low so that even sensitive components can be soldered to the 
circuit board in that way, by a machine-operated process. In accordance 
with a preferred embodiment of the process, the solder can be sprayed 
against the underside of the circuit board at different angles at 
different locations. In that way it is also possible for surface mounted 
devices (known as SMD) to be soldered to the board by a machine process. 
Such devices are large components which bear with an entire side against 
the circuit boards and whose ends are partially metallised. The process of 
the invention now provides that the solder is directed in the form of a 
jet precisely on to the line of contact between the circuit board or a 
conductor track or path thereon, and the metallisation of the device in 
question. In that way, solder is applied only where it is acutally 
required, thus reducing the level of thermal loading to a negligible 
amount. 
Spraying is an operation which is easy to control from a mechanical point 
of view, in that the amount of solder, the tine, the duration, the 
strength, the angle involved and other such parameters can be accurately 
controlled. There is thus no longer any need for the circuit board to be 
brought into contact with the liquid solder, over the entire surface of 
the board, insofar as soldering is required only at a number of separate 
locations on the board. Thus, in comparison with the above-indicated 
dragsoldering and wave soldering processes, the amount of solder which has 
to be pumped around the system used, and the amount of energy required for 
heating up the solder, and other factors involved in the operation, are 
thus reduced. There is also no need for the hot solder to be in contact 
with air over the entire surface of the trough containing same, and gases, 
vapours and the like which are produced over the large surface area of the 
trough in the above-indicated drag-soldering and wave soldering processes 
are no longer produced to cause atmospheric environmental pollution. As 
mentioned, the thermal loading on the circuit board and the components 
thereon is also reduced. 
In horizontal section, the above-mentioned components are generally square 
or rectangular. Frequently they are applied to the circuit boards in such 
a way that their edges extend at least substantially parallel to the edges 
of the board. A jet of liquid solder which is sprayed in parallel 
relationship to the line of contact which is thus formed between the 
circuit board or a conductor track thereon, and the metallisation on the 
component to be soldered to the circuit board, thus impinges precisely on 
that line of contact, where the metallisation on the component in question 
is then soldered to the conductor track or path. It may however also 
happen that the surface mounted devices are fitted to the circuit board at 
an angle. In that case the jet of solder intersects the line of contact 
between the device and the circuit board, at an acute angle. The 
metallisation of the device is only connected to the conductor track or 
path, by a solder spot, and dead areas are thus formed. 
Accordingly, a preferred embodiment of the process of the invention 
provides that the soldering operation is to be such that, even when the 
lines of contact between the metallisation on the device or component to 
be mounted on the circuit board, and the circuit board itself, extend at 
an acute angle with respect to the direction of movement of the circuit 
board, the metallisation is soldered to a respective conductor track, 
along the entire line of contact between the metallisation and that 
conductor track. In that embodiment of the process therefore the liquid 
solder is sprayed against the underside of the respective circuit board, 
at an angle which periodically alters with respect to the direction of 
movement of the circuit board. In that embodiment, the angle is to alter 
periodically in a range of from about -45.degree. to about +45.degree., 
with the line representing 0.degree. extending at an angle of 90.degree. 
to the direction of movement of the circuit board. The angle 
advantageously alters at a rate of from about 5 to about 20 oscillations 
per minute. With the spray jet of solder producing a reciprocating 
movement in that way about a vertical axis, the jet of solder impinges on 
the underside of a circuit board and thus the line of contact between the 
metallisation on a component or a device and a conductor track or path, 
from a different direction from one moment to the next, on a periodic 
basis. That therefore ensures that even lines of contact which extend at 
an acute angle with respect to the direction of movement of the circuit 
boards are encountered by the spray jet or solder, over their entire 
length, thus giving the desired complete and total soldering connection 
between the metallisation and the respective conductor track or path. 
Further objects, features and advantages of the invention will be apparent 
from the following description of preferred embodiments.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to the drawings, FIG. 1 generally shows a printed circuit 
board or card as indicated at 22. It substantially comprises the base 
material or substrate 24 and copper conductor tracks or paths 26 which are 
provided thereon. The conductor tracks 26 were produced on the substrate 
material 24 by means on any suitable process. The conductor tracks 26 are 
to be hot-tinned by means of the hot tinning apparatus and process 
described hereinafter. 
In general, as shown on an enlarged scale in FIG. 2, the conductor tracks 
26 are disposed on the top side and the underside of the substrate 
material 24. Holes 28 are provided, which extend through the circuit 
board. In the view shown in FIG. 2, it will be seen that the walls of the 
holes 28 also have a copper coating thereon, which can also be hot tinned, 
as will be described hereinafter, thereby providing at the wall of the 
hole 28 the solderable feed-through contacting means as indicated at 34. 
As shown in FIG. 3, a component or device 36 has its connecting or 
terminal pin 38 fitted into the contacting means 34. The application of 
tin in that area facilitates the step of soldering the pin 38 in position 
in a subsequent working operation. 
Referring to FIG. 4, shown in diagrammatic perspective view therein are the 
various stations of the apparatus, through which a printed circuit board 
passes in a hot tinning operation. More particularly, the stations 
involved are a heating station 40, a fluxing station 42, a station 44 for 
hot tinning and levelling of the applied layer of tin, a cleaning station 
46 and a drying station 48 for drying the printed circuit boards. As shown 
in FIG. 4, disposed on respective sides of the station 44 are first and 
second pillars or columns 50, referred to generally hereinafter as columns 
50. Fitted on the columns 50 on the upper ends thereof are resepctive 
electric motors 52. 
Looking now at FIG. 5, it will be seen therefrom that the motore 52 are 
operatively connected to upper end portions of repective shafts 54 for 
driving them in rotation. The shafts 54 are disposed within the columns 50 
and in turn carry pump members as indicated at 56, in the form of pump 
wheels or impellers. The shafts 54 are suitable mounted on bearings 58. 
As can be seen clearly from FIG. 5, the entire hot tinning assembly stands 
in a container in the form of a trough 60. The trough 60 is filled with 
molten tin. For that purpose, tin is put into and held in a molten 
condition by suitable heating means which are not shown in FIG. 5. 
Disposed at the top of the trough 60 is a cover plate 62 which thus closes 
off at least the central part of the trough 60, in an upward direction, to 
prevent impurities and other contaminatory material from passing into the 
trough 60, while also reducing the risk of an accident. At a location at 
which the cover plate 62 is apertured, at the right-hand side of the 
trough 60 in FIG. 5, a piece of tin 64 projects into the trough 60 and 
thus dips into the molten tin material in the tin 60. The piece of tin 64 
is suspended on a cable 66 in such a way as to be displaceable in respect 
of height relative to the surface of the molten tin in the trough 60. 
Thus, the cable 66 passes over a guide roller 68, while a weight 70 is 
connected to the end of the cable 66, to provide compensation for the 
weight of the piece of tin 64. The assembly further includes sensing means 
and control means (not shown) which are operative in such a way that the 
piece of tin 64 is progressively lowered into the trough 60 to ensure that 
the level of the tin material in the trough 60 remains at least 
approximately the same. Thus, the lower end of the piece of tin 64 dips 
into the molten tin in the trough 60 and, as the tin in the trough 60 is 
consumed by being applied to printed circuit boards, as will be described 
in greater detail hereinafter, the piece of tin 64 melts and thus makes up 
the level of the tin in the trough 60. As the tin in the trough 60 is 
consumed, the piece of tin 64 is progressively lowered to maintain the 
lower end portion thereof in the tin in the trough 60. 
In the upper region, the trough 60 also has an overflow pipe as indicated 
at 72 at the left-hand side in FIG. 5. Disposed below the discharge end of 
the overflow pipe 72 is a collecting container 74, for receiving 
impurities and like material which overflows from the surface of the tin 
in the trough 60. 
The columns 50 are open at their lower ends and at that location thus 
provide inlet openings as indicated at 76. As indicated by the arrows in 
FIG. 5, the molten tin is pumped from the trough 60 through the inlet 
openings 76 and into the columns 50 and then upwardly through the columns 
50, by the pump members 56. 
The two columns 50 are connected together by feed pipes 78 and 80 which 
extend generally parallel to each other, as can be seen from the view in 
FIG. 5, and which are disposed in at least approximately superposed 
relationship, when considered in cross-section. The molten tin which is 
pumped up in the columns 50 passes into the respective feed pipes 78 and 
80, in the direction indicated by the broken-line arrows in FIG. 5. Thus, 
tin in the column 50 at the right-hand side of FIG. 5 passes into the 
lower pipe 80 while tin in the left-hand column 50 in FIG. 5 passes into 
the upper pipe 78. 
From the pipes 78 and 80, the tin passes into nozzles in the form of 
respective nozzle bars 82 and 84. As shown in FIG. 5, and also clearly 
visibly in FIG. 6, the nozzle bars 82 and 84 are disposed respectively 
above and below the path of conveying movement of the circuit boards 28 
through the apparatus. As shown in FIG. 6, conveyor rollers 86 are 
likewise disposed respectively above and below the path of conveying 
movement. 
Disposed above the assembly consisting of the pipes 78 and 80, the nozzle 
bars 82 and 84 and the conveyor rollers 86 is an upper cover plate 88 
which thus closes the apparatus in an upward direction. 
Referring still to FIG. 5, disposed beneath the path of conveying movement 
of the circuit boards is a plate arrangement 90 of generally hopper or 
funnel-like configuration, thus forming a catch means for catching tin 
which drips from the printed circuit board 22 being conveyed between the 
nozzle bars 82 and 84. The lowest part of the plate arrangement 90 is 
disposed substantially at the centre thereof, and one or more drain pipes 
of which one is indicated at 92 in FIG. 5 communicated with the 
above-mentioned lowest part of the catch plate arrangement 90. Thus, 
excess tin which has dripped from the printed circuit board 22 flows back 
into the trough 60. 
FIG. 6 also shows a shaker device 94 in the hot tinning station. The shaker 
device 94 is mounted on springs indicated diagrammatically in the form of 
coil springs at 96. The shaker device 94 is caused to oscillate at a 
suitable rate by way of an unbalance means (not shown). The oscillatory 
movement is thus transmitted to the conveying rollers 86 which are carried 
by the shaker device 94 and by means of same to the circuit board 22 which 
is just passing through the shaker device 94. Also disposed at that 
location are suitable means for levelling the layer of tin applied to the 
circuit board, as will be described in greater detail hereinafter. 
Reference will now be made to FIG. 7 showing the structure of the nozzle 
bars, and FIG. 8 showing the connection thereof to the tin circuit and to 
a hot oil circuit. Both of the nozzle bars 82 and 84 each have two outlet 
openings 98 and 100. Tin is discharged through the outlet openings 98 
while hot air is discharged through the outlet openings 100. The outlet 
openings 100 for the hot air are disposed downstream of the outlet 
openings 98 for the tin, in the direction of movement of the circuit board 
22, as indicated by the arrow associated therewith at the right in FIG. 7. 
It will be seen from FIG. 7 that each nozzle bar which extends over at 
least substantially the entire width of the path of conveying movement, as 
can be seen from FIG. 5, includes a pipe 102 at a central position 
therein. Each nozzle bar essentially comprises first and second half shell 
members as indicated at 104 which are recessed with a recess of 
semicircular configuration in cross-section, on their mutually oppositely 
disposed inward sides. At the surfaces of the recesses, the members 104 
have supports 106 for supporting the respective pipe 102 in the recess 
defined by the connected half shell members 104. 
Reference numeral 108 in FIG. 7 denotes screw members or bolts for holding 
the two half shell members 104 together. Reference 110 in FIG. 7 denotes 
an annular space which is defined between the central pipe 102 and the 
surfaces of the recess defined by the half shell members 104 therearound. 
The hot tin is supplied by way of the annular space 110, while the pipes 
102 are disposed in the circuit for a flow of hot oil, as indicated at 
112. The hot tin issues from the annular space 110 into feed conduits 114 
and from there into the outlet openings 98 of the respective nozzles. 
Reference 116 in FIG. 7 denotes sliders which are disposed in the 
respective feed conduits 114. The sliders 116 are movably guided on 
actuating rods 118 which are connected to electromagnetically operated 
actuators (not shown). Springs 120 engage the rods 118 and are so arranged 
as to urge the sliders 116 into a position of closing the respective feed 
conduit 114. Thus, in the event of failure of the electrical system, the 
electromagnetically operated actuators are inoperative and the sliders 116 
are held in position of closing off the feed of tin to the respective 
nozzles and their outlet openings 98. 
Referring now to FIG. 8, it will be seen therefrom that each of the columns 
50 is formed by an inner pipe 122 and an outer pipe 124 which is disposed 
in at least substantially coaxial relationship therewith, thereby defining 
an annular space therebetween. The two pipes 112 and 124 are connected 
together and suitably held in position by supports 126. The inner pipe 122 
forms part of the circuit for the hot tin while the annular space between 
the pipes 122 and 124 is part of the circuit for the hot oil as indicated 
at 112 in FIG. 7. The hot tin issues from the inner pipe 122 into the 
annular space 110 in the respective nozzle bar assembly (see FIG. 7), in 
the direction indicated by the arrows in FIG. 8. From the annular space 
110, the hot tin passes into the feed conduit 114 with the slider 116 
therein. When the slider 116 is in the open position, the tin then issues 
from the nozzle opening. 
The hot oil 112 issues from the annular space between the inner and outer 
pipes 122 and 124 of the respective column 50 and flows into the pipe 102. 
In that way, both the nozzle bars 82 and 84, and therewith also the tin, 
are held at a desired uniform temperature, over the entire width of the 
arrangement. 
Reference will now be made to FIG. 9 showing that the conveyor rollers 86 
are each carried on a respective hollow shaft 128, with the hollow shafts 
128 being part of a coolant circuit, with the flow of coolant through the 
hollow shaft 128 being indicated by the arrows in FIG. 9. 
Reference will now be made again to FIG. 6 in relation to the shaker device 
94 and the above-mentioned means for leveling off the applied layer of tin 
on the circuit board. Such means essentially comprise nozzle 130 and 132 
which are disposed in mutually opposite relationship, above and below the 
path of conveying movement of the circuit boards 22, and directed 
thereonto. The nozzles 130 are disposed upstream of the nozzles 132, in 
the direction of movement of the circuit boards 22. The nozzles 130 are of 
a bent or curved configuration with their outlet openings being directed 
somewhat in the opposite direction to the direction of movement of the 
circuit boards 22, while the nozzles 132 are of such a configuration that 
their outlet openings are directed somewhat in the direction of movement 
of the circuit boards 22. Hot oil is ejected under pressure through the 
nozzles 130, and cooler oil or air is ejected through the nozzles 132. The 
hot oil is at a temperature of around 220.degree. C. and the cooler oil is 
at a temperature of around 150.degree. to 160.degree. C. The applied layer 
of tin which can still be moulded or shaped is levelled off or rendered 
uniform by the action of the hot oil. The tin is cooled down and thus 
caused to set by the cooler oil which is discharged from the nozzles 132 
under pressure, or the air which is similarly discharged from those 
nozzles. That therefore ensures that the conveyor rollers 86 do not form 
depressions or grooves in the surface of the tin, as the tinned circuit 
board passes on through the apparatus. The number of nozzles is not 
limited to the illustrated number of four nozzles, and it is possible to 
use more and, rarely, fewer nozzles. It is also possible to adopt 
constructions in which oil is discharged from more than one pair of 
nozzles and air is discharged from a further pair of nozzles. In all the 
embodiments, the oil should not be supplied on a constant or steady basis, 
but intermittently only when a circuit board is passing through the 
relevant station. For that purpose, the feed conduits leading to the 
nozzles include for example electromagnetically operated valves which are 
controlled by sensors disposed on the path of conveying movement of the 
circuit boards. 
FIG. 4 shows a diagrammatic view of the fluxing station for applying a 
fluxing agent to the circuit board. Referring now to FIG. 10, for that 
purpose the fluxing station 42 has nozzle bars 82 and 84, as were already 
described in relation to the operation of applying the tin to the circuit 
board. The nozzle bars 82 and 84 now have outlet openings 134 for the 
fluxing agent and outlet openings 136 for compressed air. The fluxing 
agent is heated by the hot oil 112 which passes through the pipe 102. The 
slider 116 which is operative in relation to the feed conduit leadinf to 
the outlet opening 134 controls the feed flow of fluxing agent through the 
nozzle. When the slider 116 is in an open condition, the fluxing agent is 
discharged from the respective outlet openings 134 under pressure and 
uniformly wets the circuit boards 22 on the top and undersides thereof. As 
regards the holes 28, not only are they wetted, but the holes are also in 
part completely filled with fluxing agent. FIG. 11 shows the configuration 
of the circuit board 22 with holes 28. That means that an excess amount of 
fluxing agent would be entrained into the station 42 and the tin bath. In 
order to prevent that from happening, the circuit boards 22 are blown off 
by means of compressed air discharged from the outlet openings 136, thus 
cleaning the fluxing agent from the holes 28. 
The individual stations of the apparatus having been described, the 
movement of the circuit boards 22 through the entire apparatus can now be 
described. The circuit boards 22 pass successively through the stations 
shown in FIG. 4, for heating, fluxing, hot tinning, levelling, cleaning 
and drying the circuit boards. The movement of the circuit boards through 
the fluxing station 42 is shown in FIG. 10, where the circuit boards 22 
are wetted with fluxing agent on their top side and their underside 
respectively, by means of suitable nozzles. The fluxing agent which 
initially completely fills the holes 28 in the circuit boards 22 is blown 
away by compressed air from the outlet openings 136, as indicated above. 
The circuit boards then pass through the hot tinning and levelling station 
shown in FIGS. 5, 6, 7 and 8. In that station, as indicated above, the 
molten tin is pumped from the trough 60 up into the columns 50. From the 
columns 50 the tin passes into the annular spaces 110 in the nozzle bars 
(see FIG. 7), under the action of the force of gravity and thus under a 
constant static pressure. The presence of a circuit board 22 passing 
through the station is detected by a sensor. The sliders 116 are then 
drawn into the open position so that the tin issues from the outlet 
openings 98 and is deposited on the copper conductor tracks on both sides 
of the circuit board 22. The compressed air issuing from the outlet 
openings 100 provides for a first operation of levelling the applied tin 
on the circuit board, or making the layer of tin thereon more uniform. The 
hot oil which passes through the pipes 102 (see FIG. 7) holds both the tin 
and the air at the appropriate desired temperature. 
Excess tin on the circuit board runs off to the side and rearwardly, and 
drips down from the circuit board, to be caught by the plate arrangement 
90 in FIG. 5. FIG. 5 also shows that the assembly consisting of the nozzle 
bars 82 and 84 and the conveyor rollers is in an inclined position in the 
view shown in FIG. 5, which thus promotes the draining flow of tin towards 
the side of the respective circuit board. FIG. 7 shows that the circuit 
board 22 moves along a path which is inclined downwardly towards the rear 
of the respective circuit board 22, which thus promotes the flow of excess 
tin towards the rear of the respective board 22. Thus, the path of 
conveying movement of the circuit boards 22 does not extend horizontally 
but somewhat upwardly towards the right in FIG. 7. 
When the tin has dripped on to the funnel-shaped plate arrangment 90 to be 
caught thereon, it flows to the lowest part thereof and then into the 
drain pipe 92 from which it flows back into the trough 60. Fluxing agent 
residues and other impurities in the trough 60 float to the top of the 
molten bath in the trough 60 and then pass into the overflow pipe 72 and 
by way thereof into the container 74. 
The tin-spraying nozzle bars 82 and 84 shown in FIG. 5 are illustrated at 
the left in FIG. 6. After the circuit board 22 has passed through between 
the nozzle bars 82 and 84, it is advanced into the shaker device 94 which, 
as indicated above, is set shaking or oscillating by suitable means (not 
shown). Tin which has penetrated into the holes 28 in the circuit board 22 
is removed therefrom, by virtue of the oscillating movement. The applied 
tin on the circuit board 22 is levelled or rendered uniform by the hot oil 
which issues under pressure from the nozzles 130, thus removing raised 
locations and the like. The tin on the circuit board is then cooled by the 
cooler air issuing from the nozzles 132. As it cools, the tin becomes so 
hard that, as mentioned, the conveyor rollers 86 do not leave any grooves, 
depressions or the like in the tin on the circuit board 22, as the circuit 
board continues to move through the apparatus. 
Instead of two nozzles 130 and 132 respectively, it is also possible to use 
more nozzles, and likewise a pair of nozzles may also be omitted. 
Reference will now be made to FIGS. 12 through 16 to describe the way in 
which the above-described apparatus can be used for soldering devices and 
components to the conductor tracks and soldering eyes of circuit boards. 
In FIGS. 12 and 13, reference numeral 22 again denotes a circuit board 
which, as indicated by the arrows in FIG. 12 and in FIG. 16, is advanced 
through the apparatus by a conveyor arrangement diagrammatically indicated 
at 140. Reference numeral 142 in FIG. 13 denotes a soldering eye or pad, 
through which is passed the terminal or connecting pin 38 of an electronic 
component or device (not shown in FIG. 13 but corresponding to the device 
36 shown in FIG. 3). The component or device is disposed on the top side 
of the circuit board 22 while disposed on the underside thereof is a 
further device 36, as in the form of an SMD (surface mounted device). The 
device 36 has metal caps 144 which represent the electrical connections. 
Two nozzles 82 and 84 are disposed at a spacing from each other beneath 
the path of conveying movement of the circuit boards 22. As indicated by 
the diagrammatic arrows in FIG. 13, the liquid solder issues from the 
nozzles 82 and 84 in the form of a jet which extends over the entire width 
of the circuit boards 22. The jet impinges on the soldering eyes 142 and 
the caps 144, there forming the solder connections as indicated at 146. As 
described above, the jet of solder issues from the nozzles cyclically only 
when a location which needs to be suitably soldered thereby is passing. 
The construction shown in FIG. 14 comprises a trough 60 in which the molten 
solder is contained. Once again, pillars or columns 50 dip into the trough 
60, and carry motors 52 on the upper ends of respective ones of the 
pillars or columns 50. The motors 52 drive pump members 56 shown as pump 
wheels or impellers, by way of respective drive shafts 54. The pump 
members 56 urge the liquid solder upwardly in the columns 50. The trough 
60 is closed upwardly by the cover member 62 while any impurities floating 
on the surface of the molten solder in the trough 60, as indicated by the 
dots thereat, are discharged into the container 74 by way of the overflow 
pipe 72. A piece of tin 64 is again suspended on a cable 66 which is 
passed around a roller 68 and connected to a counterweight 70. The piece 
of tin 64 is moved downwardly as the solder in the trough 60 is consumed, 
and melts away at its lower end where it dips into the molten solder. 
Reference numeral 88 again denotes a cover plate which provides for cover 
over the major operation part of the apparatus. The funnel-shaped plate 
arrangment 90 catches any solder dripping from the circuit board 22, which 
then flows back into the trough 60 by way of a drain pipe 92. 
Referring now to FIG. 15, the two nozzles 82 and 84 have outlet openings 
from which the liquid solder issues in the form of a wide jet or curtain. 
Sliders 116 extend in a closed position into the feed conduits carrying 
solder to the outler openings of the nozzles 82 and 84. The sliders 116 
are carried on operating rods 118 which are urged by springs 120 towards a 
position in which the sliders 116 close off the respective feed conduits 
carrying solder to the outlet openings of the nozzles. The liquid solder 
is supplied by way of an annular space 110 in each of the nozzle bars, the 
annular spaces 110 being in communication with the interior of the columns 
50. Pipes 112 extend in a concentric position in each of the nozzle bars, 
being part of a circuit for a heating agent such as oil. That ensures that 
the liquid solder is held at the appropriate temperature. 
FIG. 15 clearly shows that the hold solder only impinges, in the form of a 
jet, on the line of contact between the underneath surface of the circuit 
board 22 and the ends of the surface mounted device 36 which is disposed 
on that surface of the circuit board. Solder accumulates only the 
above-mentioned line of contact, thereby forming the solder joints as 
indicated at 146 where the metal caps 144 of the device 36 are connected 
to a conductor track (not specifically visible in FIG. 15). That therefore 
eliminates the previous fear of the device being subjected to a high level 
of thermal stress. As indicated by the arrows shown in FIG. 15, the two 
nozzles 82 and 84 may be rotated in both directions about their respective 
longitudinal axes, thereby making it possible to adjust the angle at which 
the jet of solder strikes the circuit board. It is also possible for the 
sliders 116 associated with the two nozzles 82 and 84 to be opened at 
different times. That will be the case when the length of the device 36, 
as considered in the direction of conveying movement of the circuit baord 
22, is in such a relationship to the spacing between the two nozzles 82 
and 84 that, if the two nozzles were actuated simultaneously, the jets of 
the solder would become excessively long or if the angles of impingement 
of the solder on the circuit board are unfavourable. Thus, the situation 
is entirely different if, instead of the large device 36 shown at the 
centre of FIG. 15, the two small devices 36 which are located at 
respective sides thereof are to be soldered to the circuit board 22. 
Reference will now be made to FIG. 16 which again shows a circuit board 22 
which is advanced in the direction of the arrow in FIG. 16, by a conveyor 
arrangement as diagrammatically indicated at 140. In other respects the 
structure shown in FIG. 16 corresponds to that shown in FIG. 12, as 
described above. The two feed pipes 78 and 80 which carry the nozzles 82 
and 84 are fixed to the column 50 by holders 150. The holders 150 are such 
that it is possible for both liquid solder to pass into the nozzles and 
also for a heating agent to be circulated therein. The liquid solder and 
the heating agent are delivered from the column 50. FIG. 16 also shows a 
device 36 whose edges extend at an angle which differs from 90.degree., 
relative to the direction of movement of the circuit board 22 through the 
apparatus. In operation the column 50 and therewith the mounting and guide 
pipes 78 and 80 fixed thereto, with the nozzles, pivot about the vertical 
axis diagrammatically indicated at 148. For that purpose, the column 50 is 
actuated by a mechanical pivoting arrangement. It pivots the column 50 
about its vertical axis 148 up to about a maximum of 45.degree. in any 
direction. That reciprocating or oscillating movement occurs at a 
frequency of from about 5 to about 20 oscillations per minute. In that 
way, the jet of solder impinges on the line of contact between the 
metalliztion on the component 36 and a conductor track, at a constantly 
varying angle. A condition of parallelism occurs at a given moment. That 
means that the line of contact is subjected to the effect of the jet of 
solder, over its entire length, thus providing a complete soldered join 
between the device 36 and the circuit board. Any solder which impinges 
outside the line of contact drips off and/or is shaken off in the course 
of the further movement of the circuit board 22 through the apparatus. 
In other respects the arrangement of the column 50 in FIG. 16 corresponds 
to the arrangement of one of the columns 50 as shown for example FIG. 5. 
It will be appreciated that the above-described constructions and processes 
were set forth solely by way of example of the present invention and that 
various modifications and alternations may be made therein without thereby 
departing from the spirit and scope of the invention.