WO1993013904A1

WO1993013904A1 - Soldering apparatus with improved configuration of solder streams

Info

Publication number: WO1993013904A1
Application number: PCT/NL1993/000003
Authority: WO
Inventors: Michiel Jeroen Van Schaik
Original assignee: Soltec B.V.
Priority date: 1992-01-14
Filing date: 1993-01-07
Publication date: 1993-07-22
Also published as: US5379931A; NL9200060A; EP0621814A1; DE69317875T2; EP0621814B1; DE69317875D1

Abstract

The invention relates to a soldering device comprising: a vessel (1) opened at the top for filling with solder; at least two solder towers (5, 6) placed in the vessel, each adapted for delivering a flow (8, 12) of solder on their upper side; and a transporting member (3) for carrying along the objects for soldering above the solder towers. In order to prevent, both in the case of soldering machines which operate in a normal atmosphere and those operating in an inert atmosphere, the solder flows falling back into the vessel forming splashes which collide with the underside of the printed circuit boards, the solder towers are adapted for generating jets directed toward each other, wherein the jets intersect before they make contact with the solder level prevalent in the vessel. According to a preferred embodiment the rear tower (6) in the direction of movement forms a jet of solder comprising a movement component counter to the movement of the objects for soldering and enclosing an acute angle with the object for soldering.

Description

SOLDERING APPARATUS WITH IMPROVED CONFIGURATION OF SOLDER STREAMS

The invention relates to a soldering machine com¬ prising: a vessel opened at the top for filling with solder; at least two solder towers placed in the vessel, each adapted for delivering a flow of solder on their upper side; and a transporting member for carrying along the objects for soldering above the solder towers. Such soldering devices are generally known. The problem often arises with such soldering devices that the solder flows falling back into the vessel cause splashes of solder which can spatter so high that they make contact with the underside of the objects for soldering such as the printed circuit boards for solde¬ ring.

This problem occurs particularly, although not exclusively, in soldering machines, wherein the soldering- process takes place inside an atmosphere of inert gas. These splashed solder droplets will make contact with the underside of the plate where they form solder globules. These globules adhere hardly or not at all to the other solder so that there is a danger of them coming loose and causing short-circuit. Although this problem occurs in the case of normal soldering machines placed in a normal atmosphere, the problem arises to a greater extent in soldering machines operating in an atmosphere substantial- ly excluding oxygen. The low-oxygen atmosphere probably results in an increase of the surface tension, whereby the formation of droplets and globules of solder is stimula¬ ted.

The object of the present invention is to avoid the above stated problems.

This object is achieved in that the solder towers are adapted for generating solder jets directed toward eachother, wherein the solder jets intersect before they make contact with the solder level prevailing in the vessel. As a result of these steps the splashes caused by the fall of the combined solder jet on the solder level are shielded by the form of the solder jets so that it is no longer possible for the solder splashes to contact the surface of the objects for soldering.

Similar problems occur when the object for solde¬ ring leaves the final solder jet. In this situation, certainly when the soldering process takes place in a nitrogen atmosphere, the solder also has the tendency to form globules on the object for soldering at the position where the solder wave leaves the object for soldering.

According to a preferred embodiment of the present invention the rear tower in the direction of movement is adapted for generating a jet of solder comprising a movement component counter to the movement of the objects for soldering.

As a result of this step any globules that may have formed are washed away by the solder jet so that the problems of such solder globules are prevented.

The present invention will subsequently be elucida¬ ted with reference to the annexed figures, in which: fig. 1 shows a sectional view of a soldering device according to a first embodiment of the invention; and fig. 2 is a sectional view of an alternative embo¬ diment of the invention.

In the device shown in fig. 1 the soldering device comprises a solder vessel 1 suitable for filling with solder 2. Understood by solder is any form of metal solder suitable for mutually connecting two other metals. Such a metal does not necessarily have to contain tin.

Arranged above vessel 1 is a conveyor belt 3 for transporting the objects for soldering, in the present case printed circuit boards 4. Such a conveyor belt forms the subject of the Netherlands patent application 8901014. Two solder towers 5, 6 are further arranged in the solder vessel 1. The first solder tower is provided with a nozzle 7 which is adapted for generating a solder jet 8 which contacts the printed circuit board for soldering on the underside. Arranged in the solder tower 5 for this purpose is a pump 9 which is connected to the nozzle 7 by means of a channel 10.

The second solder tower 6 is likewise provided with a nozzle 11 with which a second solder jet 12 is genera¬ ted. Arranged in the second solder tower 6 is a pump 13 which is connected to the second nozzle 11 by means of a channel 14.

It should be noted here that both pumps 9, 13 draw the molten solder out of the solder vessel 1.

After contacting the printed circuit board 4 on the underside both solder jets 8, 12 fall back into the solder bath 2.

According to the invention the solder jets 8 and 12 are oriented and have a force such that the generated solder jets make mutual contact before together reaching the level of the solder bath. This step ensures that any splashes resulting from the falling of the solder jets into the bath cannot reach the underside of the printed circuit board. This underside is wholly shielded by the generated solder jets 8, 12 themselves. It is noted herein, which cannot be fully seen in the drawing, that these solder jets have a breadth corres¬ ponding with the breadth of the printed circuit boards 4 for soldering.

Fig. 1 further shows how a shield 15 s fixed to the first nozzle 7. This shield provides a , x>d guiding of the solder falling into the liquid 2.

It is remarked here that both solder jets 8, 12 are so-called unsupported solder jets, which means that they are not supported and have a partially free trajectory. in addition the invention is intended in the first instance for use in soldering devices wherein the solde¬ ring process is performed in a non-oxidizing atmosphere. that is, in an atmosphere of a so-called protective gas. Performing the soldering treatment under the protection of a protective gas generally results in a solder connection of improved quality. As a consequence of the fact that oxidation pro¬ blems occur less in such a situation the problem arises during performing of the soldering process in such an environment that any splashes contacting the underside of the object for soldering are easily soldered fast to the object for soldering, which is undesirable. The present invention is therefore particularly for use in soldering devices which make use of a protective gas. This does not mean however that such soldering devices cannot be used on classical soldering apparatus, wherein soldering takes place in the normal oxygen-containing atmosphere. It can also occur in this situation that the spattering solder splashes adhere to the underside of the object for solde¬ ring, even though the danger thereof is smaller.

Another aspect of the present invention relates to the fact that the angle at which the rear solder jet 12 contacts the underside of the printed circuit board 4 is an acute angle. This angle is designated α in fig. 1. This step also has the objective of preventing the so-called "drawing of fillets" by the solder. This problem arises at the location where the printed circuit board leaves the solder wave. At this position small fillets on the printed circuit board, caused for instance by components placed on the other side of the board which extend with their termi¬ nal leads through the openings arranged in the board, have the tendency to draw fillets when leaving the solder wave. Such fillets are in contact with the solder wave for a slightly longer time so that the supplied solder adheres to the fillet and the fillet becomes still longer. At some stage a maximum length of such a fillet is reached or it breaks off.

By supplying the solder wave at the smallest possi¬ ble acute angle is achieved that such fillets are already washed away as they begin to develop so that they cannot grow any further. Formation of such fillets is thus pre¬ vented.

Fig. 2 shows a similar configuration, with the difference that a combination of two solder towers is applied, wherein the second solder tower delivers a solder flow which is for the greater part supported.

This device also comprises a solder vessel 1, wherein a solder tower 5 is used which corresponds with solder tower 5 in the first embodiment. The second solder tower differs, however, from the solder tower according to the first embodiment. This second solder tower 16 is provided on its front side with an overflow edge 17 so that the solder flow 18 flows away at the front over the overflow edge 17. There it meets the solder jet 8 coming from the first solder tower 5 so that both jets contact the solder level 2 together.

Placed on the other side of the second solder tower 16 is a second run-off edge 19 so that the solder flow 20 flowing away at that position flows downward along the substantially vertical wall 21.

The vertical wall 21 forms part of a plate designa¬ ted in its entirety with 23. This further comprises a horizontal portion 22 and a second, lower vertical portion 24. Plate 23 is fastened for sliding in the height to a profile 25 which is fixed by means of supports 26 to a vertical plate 27. Openings 28 are arranged in the verti¬ cal plate 27. The solder flow 20 flows first along tne vertical portion of plate 21 so that at the position where the solder flow leaves the printed circuit board 4 or other soldered object the direction of the flow extends substantially perpendicularly of the surface of the object for soldering. Should fillets form here when the solder flow disengages from the object for soldering these fil- .lets cannot then cause a short-circuit as quickly as in the case the solder is disengaged at a small angle relati¬ ve to the printed circuit board. Due to the small vertical length of plate 21 a small fall height is obtained so that the creation of splashes is prevented. Splashes could in any case result in globules on the soldered object which could likewise cause short-circuit.

It is remarked here that due to the presence of gas substantially excluding oxygen the formation of fillets and globules is stimulated.

The solder flow then flows along the horizontal plate 22 and subsequently along the vertical portion 24 of plate 23. The solder flow then falls into the solder bath 2. The distance to the soldered board has in the meantime become so reat that any splashes that may occur can no longer reach the object for soldering. The second solder tower 16 is of course also provi¬ ded with a pump, not shown in the drawing, for pumping upward of the solder flow.

The second solder tower moreover does not necessa¬ rily function as final solder tower; it is possible for a third solder tower to be used, the construction of which corresponds with that of the second solder tower 6 in fig. 1.

This embodiment also prevents splashes caused by the falling of the combined solder jet onto the solder level from contacting the objects for soldering.

Claims

1. Soldering device comprising:

- a vessel opened at the top for filling with solder;

- at least two solder towers placed in the vessel, each adapted for delivering a flow of solder on their upper side; and

- a transporting member for carrying along the objects for soldering above the solder towers, characterized in that the solder towers are adapted for generating solder jets directed toward each other, wherein the solder jets intersect before they make contact with the solder level prevalent in the vessel.

2. Solder tower as claimed in claim 1, characte¬ rized in that the solder towers are each adapted for generating a jet of solder which leaves the tower before contacting the object for soldering.

3. Solder tower as claimed in claim 1, characte¬ rized in that the rear solder tower in the flow direction is adapted for generating a jet of solder which leaves the tower before contacting the object for soldering.

4. Soldering device as claimed in claim 3, charac¬ terized in that the rear tower in the direction of movement is adapted for generating a jet of solder compri¬ sing a movement component counter to the movement of the objects for soldering.

5. Soldering device as claimed in claim 4, charac¬ terized in that the final solder tower in the direction of movement of the transporting member is adapted for genera¬ ting a solder jet which encloses an acute angle with the object for soldering.

6. Soldering device as claimed in claim 5, charac¬ terized in that the acute angle is smaller than 45°.

7. Soldering device as claimed in any of the claims 3-6, characterized in that the solder jet generated by the first tower in the direction of movement of the transpor¬ ting member is at least partially supported by the tower.

8. Soldering device as claimed in any of the claims 3, 4 or 5, characterized in that the foremost solder jet has a greater thickness than the rear solder jet.

9. Soldering device as claimed in any of the fore¬ going claims, characterized in that the rear solder tower in flow direction is provided on its rear side with a vertically extending overflow edge formed by a vertical wall, wherein the fall height of the overflow edge is limited.

10. Soldering device as claimed in any of the foregoing claims, characterized in that the vertical wall transposes on its underside into a wall extending partial¬ ly in horizontal direction.

11. Soldering device as claimed in claim 9 or 10, characterized in that the height of the overflow edge is adjustable.