Solder leveling device having means for vertically guiding printed circuit boards

A printed circuit board solder leveling device comprising guides distributed across the width of the soldering bath container. Each guide comprises opposed guide rods spaced apart a distance greater than the thickness of a printed circuit board so that there is loose contact only of the guides with opposite sides of the board.

BACKGROUND OF THE INVENTION 
The present invention relates to a device for the application of solder on 
printed circuit boards. 
In the case of a known system of this type, a guiding system consists of 
two vertical guiding rails each of which has a U-shaped guiding channel 
(German Disclosure Publication No. 24 11 854). The printed circuit boards 
are guided in these guiding channels and also are held on two narrow sides 
located opposite each other. The guiding rails extend from the soldering 
bath upward past blast nozzles from which emerges hot air jets which are 
directed against the surfaces of the printed circuit boards pulled out of 
the soldering bath. By means of these air jets, excessive solder is 
removed from the printed circuit board which passes by and, additionally, 
the solder is removed from passage holes in the printed circuit boards. In 
order to be able to properly hold and guide the printed circuit boards, 
particularly when they are exposed to the hot air jets, the width of the 
guiding channels is selected in such a manner that it corresponds 
approximately with the thickness of the printed circuit boards. 
This requires a very exacting and, therefore, complex positioning of the 
printing circuit boards for their introduction into the guiding channels. 
Furthermore, printed circuit boards which are slightly curved can only be 
introduced with difficulty or not at all. Furthermore, an adjustment or 
exchange of the guiding rails becomes necessary for the processing of 
printed circuit boards of different widths or thicknesses. Since the 
printed circuit boards are softened in the hot solder bath, there is 
additionally the danger of damaging the printed circuit boards, which are 
not yet resistant to mechanical wear when leaving the soldering bath, 
owing to the heavy lateral guide. 
SUMMARY OF THE INVENTION 
It is the purpose of the present invention to avoid the aforementioned 
disadvantages and thus to provide a device of the type mentioned above 
with which printed circuit boards of different widths and thicknesses and 
also printed circuit boards which are not exactly plane can be introduced 
into a soldering bath without the necessity of very exact positioning and 
thus with a high operating speed, whereby the printed circuit boards 
nevertheless are properly guided and held during their movement and are 
not exposed to the danger of being damaged. 
This task is accomplished according to the invention by the provision that 
the printed circuit boards are not guided along two edges by two rows of 
guiding elements, but rather are guided across their entire width on both 
sides. A proper guiding is guaranteed by the thus resulting multitude of 
guiding points without necessitating a constant mechanical contact between 
the printed circuit boards and the guiding elements. Moreover, the 
necessity of a very exact positioning of the printed circuit boards, as is 
required for the introduction into guiding rails, is estimated. Even 
slightly curved printed circuit boards can be introduced and guided 
without any difficulty. The danger of damaging the printed circuit boards 
is thus largely avoided. Furthermore, the necessity of adjusting the 
guiding elements to different board widths or thicknesses is eliminated. 
According to the invention, the placement of printed circuit boards in or 
for their removal from the device is characterized by the fact that the 
respective, vertically aligned printed circuit board is necessarily 
centered vetially with respect to its plane relative to the guiding system 
in th soldering bath container during the placement or removal process. In 
this manner, a quick and exact placement or removal, of each printed 
circuit board into or from the device is guaranteed without requiring a 
complex manipulation. 
The centering of the printed circuit boards is appropriately effected by 
means of guiding elements which are preferably arranged between the 
opening in the casing cover and the blast nozzles. 
It is particularly essential according to the invention that the printed 
circuit board is guided and/or positioned without constant mechanical 
contact. In this fashion, on the one hand, exact guiding and positioning 
of the respective printed circuit boards is guaranteed in the soldering 
bath and, on the other hand, the danger or damaging the printed circuit 
plates which are especially sensitive after coating is avoided. 
Advantageously, the guiding and/or positioning of the printed circuit board 
is effected without constant mechanical contact by means of a guiding 
system which has several guiding elements running essentially vertically 
which are arranged in two rows opposite each other and in rows at a 
distance from each other distributed across the entire width of the 
printed circuit boards introduced into the soldering bath. 
The device according to the invention solves the especially critical phase 
of the removal of the respective printed circuit board from the soldering 
bath container in a technically advantageous manner. This phase is a 
critical one for two reasons. First of all, the carrier material of the 
printed circuit plates is softened owing to the relatively high 
temperature of the soldering bath so that the printed circuit plates are 
particularly sensitive to being damaged when pulled out of the device, for 
example, by being bent or such. Secondly, the hot air jets, acting on both 
wide sides of the printed circuit board when it is pulled out, can cause 
vibrations of the printed circuit board by means of which the printed 
circuit board can abut against components of the device and damage to the 
printed circuit board can thus be caused. The respective printed circuit 
board can be subjected to vibrations by the hot air jets because the blast 
nozzles are arranged staggered with respect to each other in the vertical 
direction on opposite sides of the transport path of the printed circuit 
boards. This staggering is necessary since, if the blast nozzles were 
arranged directly opposite each other, they would essentially neutralize 
each other when blowing through the passage holes in the respective 
printed circuit board and, thus, the excessive solder would not be 
sufficiently removed from the passage holes in the printed circuit boards. 
The device according to the invention makes sure that, with the removal of 
the respective printed circuit plate, the latter is stabilized relative to 
the air jets acting upon the two wide sides of the printed circuit board 
in a vertically staggered fashion. This stabilization is achieved by means 
of a number of elements which are arranged in two rows opposite each other 
and in rows at a distance from each other distributed across the entire 
width of the printed circuit board introduced into the soldering bath and 
which extend from below as far as possible into the space between the two 
blast nozzles. In this context, it is particularly expedient that the 
elements are designed vertically in an elastic way relative to the 
respective wide sides of the printed circuit board. 
In the preferred embodiment of the invention, these elements are formed by 
the upper final sections of the guiding elements.

DETAILED DESCRIPTION OF THE INVENTION 
The structure and the mode of operation of the tin-plating device for 
printed circuit boards now will be described on the basis of the drawings. 
As employed below, the term "tin-plating" refers not only to a lead-tin 
alloy, but also to any suitable solder of a different type. The 
tin-plating device has a casing indicated by 1 which is closed on the top 
by a cover 2. In this cover 2, there is a slot-like opening 3 for the 
printed circuit boards. 
A solder bath container 4 is arranged in a lower part 1a of the casing 1 
and is open towards the opening 3 and is closed off at the bottom by a 
perforated bottom 5. The interior of the solder bath container 4 is in 
connection, through perforated bottom 5 with a distribution chamber 6 
which is provided on the bottom of the lower part 1a of the casing. The 
actual solder bath 7 is in the solder bath container 4. A collecting 
chamber 8 is formed for the solder between the walls 4a of the solder bath 
container 4 and the walls 1b of the lower part 1a of the casing. The 
solder is transported from the distribution chamber 6 upward through the 
solder bath container 4 by means of a pump which is not shown. The solder 
flows subsequently into the collecting chamber 8 over the upper edges of 
the container walls 4a from where it enters again the distribution chamber 
6. The heating system required for the heating of the solder which is of 
an actually known design is not shown. While the pump is not operating, 
the level S of the solder bath is below the upper edge of the walls 4a of 
the solder bath container 4, as is shown in the drawings. 
Guides 9 are arranged in the interior of the solder bath container 4 at a 
distance from each other and distributed across the width of the solder 
bath container 4, as can be seen from FIG. 2 in which a portion of the 
casing is not shown at the bottom and on the right side. Each of these 
guides 9 is formed by two rod-like guide elements 10 and 11 which are 
spaced opposite each other at a certain distance from each other and which 
are connected to each other at their lower ends, as can be particularly 
seen from FIG. 1. The thus clamp-like designed guides 9 extend into the 
area of the perforated bottom 5 of the solder bath container 4 and project 
above the solder bath level S. At the end of their upper final section 10a 
or 11a, respectively, the rod-like guide elements 10, 11 are provided with 
deflections 12 and 13, respectively. As is shown in FIG. 1, the deflection 
12, 13 of each guide element 10, 11 projects toward the opposite guide 
element 10 or 11, respectively, so that there is produced a narrowing 14 
of the space 15 between the two guide elements 10, 11 by means of 
deflections 12, 13 of the guide elements 10, 11. 
The upper final sections 10a, 11a of the guide elements 10 and 11, 
respectively, projecting upward out of the solder bath 7 can be 
spring-elastically spread apart and are, for this purpose, supported by 
stationary support springs 16 and 17, respectively. In the area of the 
solder bath level S, mounting supports 18 and 19, respectively, are 
attached to the inner sides of the walls 4a opposite each other of the 
solder bath container 4 in which the guides 9, i.e. the guide elements 10 
and 11, are held. Instead of a single mounting support 18 or 19, 
respectively, for the guide elements 10 or 11, respectively, also a 
separate mounting support can be provided for each guide element 10 or 11 
which is fastened to the container walls 4a. The mounting supports 18, 19 
are attached at such a level on the walls 4a that they slightly project 
above the solder level S when the pump is out of operation so that the 
seat of the guides 9 in mounting supports 18, 19 can be inspected at any 
time. Two blast nozzles 20 and 21 are arranged above the guides 9 and 
extend across the entire width of the solder bath container 4 and form 
between themselves an interspace 22 which is aligned with the narrowing 
14. These blast nozzles 20, 21 are connected to a hot air source, such as 
is described in greater detail, for example, in the German Disclosure 
Publication No. 24 11 854. Two semi-circular tubs or thoughs 32, 33 which 
extend preferably across the entire width of the solder bath container 4 
and in which the excessive solder, as removed by the hot air jets, is 
caught, are arranged in parallel to the two blast nozzles 20, 21. A worm 
gear, not shown, is arranged in each of the tubs 32, 33, by means of which 
the excess solder is discharged laterally from the system before 
solidifying, preferably in a continuous manner. There are two guide 
elements 23 and 24 extending in parallel to each other above the two blast 
nozzles 20, 21 and also extending across the width of the solder bath 
container 4 parallel to the blast nozzles 20, 21. Each of these guide 
elements 23, 24 has a carrier rod 25 or 26, respectively, on which guide 
disks 27 or 28, respectively, are positioned at a distance from each other 
(see especially FIG. 2). The guide disks 27, 28 can be made so that they 
are spring-elastically deflectable. The guide elements 23, 24 form between 
them an opening 29 which is aligned with the opening 3 in the casing cover 
2 and the space 22 between the blast nozzles 20, 21. 
A printed circuit board 30 is shown by dot-dash lines and is held by a 
schematically indicated gripping device 31. 
The operating method of the described tin-plating device is as follows. The 
printed circuit board 30, which is seized in a known manner by the 
gripping device 31, is introduced into the device through the opening 3 in 
the casing cover 2 and passes between the two guide elements or members 23 
and 24. These guide elements 23, 24 have the task of guiding curved 
printed circuit boards 30, without damaging them, past and between the 
blast nozzles 20, 21 to the guides 9. Subsequently, the printed circuit 
board 30 passes through the narrowing 14 between the guide elements 10, 
11, arranged opposite each other, into the space 15 between guide elements 
10, 11. The width of narrowing 14 is somewhat larger than the thickness of 
the printed circuit board 30 so that the latter, if it is entirely planar, 
can be passed, without contact, between the deflections 12, 13 of the 
guide elements 10 and 11. The upper final sections 10a, 11a of the guide 
elements 10 and 11 are pushed apart by the gripping device 31 and spring 
back again into their original position owing to their own elasticity 
and/or under the effect of the support springs 16, 17. When curved boards 
are introduced, the final sections 10a, 11a can also be spread apart, 
which permits the introduction even of curved boards without damaging 
these boards by the guide elements 10, 11. 
After having passed the narrowing 14, the printed circuit board 30 enters 
the space 15 between the guide elements 10, 11 which is considerably 
larger than the thickness of the printed circuit board 30. The solder is 
then applied on the printed circuit board 30 in the solder bath 7 in the 
known manner. Since, as already mentioned, the guides 9 extend into the 
area of the perforated bottom 5, even curved boards are held by guides 9 
essentially in the center of the solder bath container 4. Guides 9 thus 
prevent the printed circuit boards 30 from coming into contact with the 
walls 4a of the solder bath container 4. As is shown in FIG. 1, the guide 
elements 10 and 11 converge together towards the bottom whereby the space 
15 between these guide elements 10, 11 becomes correspondingly narrower. 
This measure contributes additionally to a proper positioning even of 
curved printed circuit boards 30 in the center of the solder bath 
container 4. 
After the tin-plating process is terminated, the printed circuit board 30 
is pulled out again from the solder bath 7 in the known manner. By doing 
so, it is moved through the narrowing 14 and between the blast nozzles 20 
and 21. During this movement, hot air jets leaving the blast nozzles 20 
and 21 act on both sides of the printed circuit board 30. Excess solder is 
removed by means of these hot air jets and solder in the passage holes in 
the printed circuit board 30 is removed, as described in detail, for 
example, in German Disclosure Publication No. 24 11 854. After the excess 
solder has been removed, the printed circuit board 30 is led out of the 
device through the opening 29 and the casing opening 3. 
Owing to the guide elements 10, 11 on both sides of the printed circuit 
board 30 being formed in rows, being arranged at a certain distance from 
each other and being distributed across the width of the printed circuit 
board 30, several guide points are formed which guarantee sufficient 
guiding and positioning without a constant mechanical contact between the 
printed circuit board 30 and the guide elements 10, 11. As has already 
been mentioned, the width of the narrowing 14 is somewhat larger than the 
thickness of the printed circuit board 30 so that, as a rule, the guide 
elements 10, 11, i.e. their deflections 12, 13, do not rest on the printed 
circuit board 30. Since the upper final sections 10a, 11a of the guide 
elements 10, 11 can be bent out in a spring-elastic manner, these final 
sections 10a, 11a can elastically turn away if the printed circuit board 
30 abuts against deflections 12, 13. The printed circuit board 30 is 
exactly guided, on the one hand, and damage thereto by the guides 9 is 
avoided, on the other hand, since these guides 9 do not represent a solid 
mechanical resistance to the printed circuit board 30. 
The distance between the guide elements 10, 11, arranged opposite each 
other, becomes larger below the narrowing 14. This means that no contact 
normally takes place below this narrowing 14 between the printed circuit 
board 30 and the guide elements 10, 11. The printed circuit board 30 thus 
is freely accessible on all sides in the solder bath 7 and is not covered 
anywhere by the guides 9. 
When pulling out the printed circuit board from the solder bath container 
4, the upper final sections 10a, 11a of the guide elements 10, 11 act in a 
particularly advantageous manner as stabilizing elements which prevent 
vibration of the printed circuit board by the hot air jets from the blast 
nozzles 20 and 21, arranged as shown in FIG. 1 to be vertically staggered 
with respect to each other which would otherwise cause the printed circuit 
board, being particularly sensitive in this position, to abut against 
components of the device and thus would lead to damage to the printed 
circuit board. For the purpose of the desired stabilization of the 
respective printed circuit board when it is removed from the device, the 
upper final sections 10a, 11a of the guide elements 10, 11 project as far 
as possible into the space 22 between the two blast nozzles 20 and 21 
which are somewhat staggered with respect to each other in the vertical 
direction. Additionally, the upper final sections 10a, 11a of the guide 
elements 10, 11 are designed to be spring-elastic in directions transverse 
to the wide sides of the passing printed circuit boards so that the 
respective printed circuit board is stabilized by these means and damage 
to the printed circuit board, by abutting against the upper final sections 
10a, 11a of the guide elements 10, 11, is avoided. Finally, the width of 
the gap 14, between the upper final sections 10a, 11a of the guide 
elements 10, 11 or of the deflections 12, 13 is determined or adjusted for 
the desired stabilization of the printed circuit board to be removed from 
the solder bath. 
Since the guides 9 act on the front and rear sides of the printed circuit 
board 30 and the printed circuit board 30 need not, therefore, be guided 
at its edges, the necessity of an exact lateral positioning is eliminated 
and printed circuit boards 30 of different widths can be processed without 
requiring an adjustment of the guides 9. 
It goes without saying that the described tin-plating device can be 
designed differently from what has been shown with regard to various 
parts. Only a few of the possible variations are mentioned below. The 
width of the gap between the deflections 12, 13, i.e. the width of the 
narrowing 14, can be changed by modifying the force which is exerted on 
the upper final sections 10a, 11a by the support springs 16, 17. This can, 
for example, be achieved by using support springs 16, 17 with different 
spring characteristics. If the upper final sections 10a, 11a of the guide 
elements 10, 11 have the necessary spring-elastic properties, the support 
springs 16, 17 may be eliminated under certain circumstances. 
Owing to the fact that the guide elements 10, 11 are positioned opposite 
each other in pairs and are connected with each other, a particularly 
advantageous design is obtained from the point of view of production, 
effect and maintenance. However, it is also possible not to connect the 
lower ends of the pairs of guide elements 10, 11 arranged opposite each 
other. Furthermore, the guide elements 10 can be laterally staggered 
vis-a-vis the guide elements 11 so that guide elements 10, 11 are no 
longer directly opposite each other relative to the printed circuit board 
30.