FR2565062A1 - Machine for soldering or desoldering components on an electronic or electrical circuit - Google Patents

Abstract

The invention relates to a machine for soldering or desoldering components, comprising a pot 2 equipped with an internal duct 6, an auxiliary container 3, pipework means connecting the container 3, on the one hand, to the pot 2 by means of a valve 10 and, on the other hand, to the duct 6, and means 14 for pressurising the solder bath contained in the auxiliary container; these means are particularly constituted by a movable plunger and generate a rise of the liquid in the duct by communicating-vessel effect so as to condition (adjust) the formation of a solder bath wave overflowing from the duct 6 towards the pot 2.

Description

MACHINE FOR WELDING OR DESOLDERING COMPONENTS
ON AN ELECTRONIC OR ELECTRICAL CIRCUIT
The invention relates to a machine for soldering or desoldering components on an electronic or electrical circuit, in particular a printed circuit. It is particularly applicable for individually soldering or desoldering of components in order to allow an individual change of these following a touch-up or troubleshooting; however, the invention can also be applied to solder (or unsolder) in a single pass several components of a circuit in a production unit.

Currently, a process known as "wave soldering" is generally used to solder or desolder components, which consists in causing the formation of a wave on the surface of a solder bath: this wave is produced at the interior of a nozzle or chute by means of a turbine or other mechanical propulsion means disposed in the bath. Such
and a ent / the wave has the double function of serving as a source / # rans ert of heat towards the elements to be welded (or desoldering) and of ensuring a contribution of solder towards these elements.

 However, existing machines of the above type have several faults. First, the mechanical components of the turbine are immersed in the solder bath at high temperature (essentially a tin-based bath having a temperature of the order of 230 to 2500 ° C.) and these very rigorous ambient conditions generate severe manufacturing constraints (in particular to avoid deformations of the mechanical members) and considerably reduce the operating reliability of this type of machine; in addition, the slightest irregularity in the operation of the turbine affects the height of the wave, which itself becomes irregular.

 In addition, the qualities of the welds obtained are often poor due to the phenomena of oxidation and crusting which appear on the surface of the bath. To reduce the influence of these phenomena, it is provided in certain devices to protect the bath with an oil film covering the surface thereof; However, in addition to the greater structural complexity which leads to obtaining this film of oil, it conditions other defects linked to the more or less rapid degradation of the oil at bath temperature (cf. for example , Patent FR No. 2,344,641).

 Furthermore, in known devices, the individual desoldering of a component with a view to changing it is carried out by tearing off said component by means of manual pliers when the latter is in contact with the wave of solder bath; it often happens that the operator pulls too early, which entails risks of tearing of the conductors or neighboring components.

The present invention proposes to overcome the aforementioned defects of conventional wave soldering or desoldering machines
The essential objective of the invention is to provide a wave soldering or desoldering machine which does not comprise any mechanical propulsion member immersed in the solder bath or in contact with it
Another objective of the invention is to improve the quality of the welds produced, by eliminating the defects linked to the oxidation of the bath or to the presence of oil on the surface of the latter.

 The invention applies in particular to machines for individually soldering or desoldering components of a printed circuit; in the context of this application, another objective of the invention is to eliminate the risks of accidental tearing to which current machines of this type lead.

The machine covered by the present invention is of the type comprising a crucible adapted to contain a liquid solder bath, a trough arranged in said crucible and having an open upper face and means capable of generating in the trough a wave of solder bath , coming to flow by overflow into the crucible; according to the present invention, the means capable of generating the aforementioned wave comprise
an auxiliary container adapted to contain the solder bath,
channeling means arranged to communicate the auxiliary container and the crucible so as to allow a transfer of solder bath between them,
a valve associated with said channeling means to prevent the bath from flowing through these means in the direction from the auxiliary container to the crucible,
channeling means arranged to put the auxiliary container into communication with the chute so as to allow a transfer of solder bath between them,
and means for pressurizing the bath contained in the auxiliary container, adapted to make it possible to generate, at the heart of the liquid bath, a pressure equivalent to a liquid column exceeding the level of the upper face of the chute, so as to cause , through the corresponding channeling means, a rise of the liquid bath in said chute and an overflow by the upper face thereof.

 The aforementioned pressurizing means can take several forms (hydraulic or pneumatic pressuring, etc.). According to a preferred embodiment leading to a machine which is both simple and very reliable, these means advantageously comprise a mobile plunger arranged to be able to penetrate into the auxiliary container so as to cause a rise in the liquid therein and, by effect of communicating vases, an identical rise in the chute.

 Thus, in the machine according to the invention, the welding wave is generated by penetration of a simple plunger into the welding bath (or other equivalent means of pressurizing the bath of the auxiliary container), excluding any mechanical propulsion unit of the turbine or other type. The operating principle based on the effect of communicating vessels is extremely reliable and does not imply any particular precaution or manufacturing constraint.

The wave formed at the upper face of the chute flows by overflow into the crucible, the presence of the valve prevents the latter from filling directly during the period of formation of said wave. After filling the crucible by overflow, the plunger is raised and the liquid levels in the auxiliary container and in the crucible are equalized
thanks to a flow of the bath from the crucible to the tale
auxiliary neur.

Preferably, the machine includes
drive means located outside the bath, in view
to train the diver in its vertical downward movement
te in the auxiliary and ascent container.

Furthermore, according to another characteristic
tick of the invention, the auxiliary container as well as the
crucible and its chute are contained in closed enclosures
containing a neutral gas, 11 enclosure containing the crucible being equipped with an opening directly above the chute and with a movable member for closing this opening. This opening
is temporarily open each time you use it to bring
through it the component or components concerned at
wave contact. The small quantities of neutral gas which
escape by this one can be replaced by means of a
reserve connected to the enclosure containing the crucible.

Thus, the machine according to the invention ~ considerably reduces the oxidation of the penny bath.
hard, without the use of oils or other additives; the bath
weld remains constantly in a perfect state of clean
tee which leads to good quality welds.

According to another characteristic of the in
vention, which is advantageously provided in the case of a ma
china to solder or unsolder components individually
a printed circuit, the latter is equipped, above and
at the base of its chute, a body for gripping com
posing, of an organ support arranged to allow abais
serve or raise this organ along the vertical axis of the gou
monkfish, downward facing counter-supports to
contact of the printed circuit, and of elastic means requested
gripping /
both the organ upwards with respect to the counter-supports.

In the event that desoldering is necessary
one component, the printed circuit is maintained, with its face
superior to the contact of the counter-support, by means of the member
grip which is hung on the component concerned
as will be better understood later, the detachment of the
component occurs naturally through the action of
elastic means, when the solder points which link said component to the printed circuit have melted, and this, without risk of tearing of the neighboring elements.

Other characteristics, aims and advantages of the invention will emerge from the description which follows with reference to the appended drawings which present by way of nonlimiting example an embodiment; on these drawings which form an integral part of the present description
- Figure 1 is an overall section
AA ′ by an axial vertical plane / of a machine according to the invention,
FIG. 2 is a front view thereof, in elevation,
FIG. 3 is a detail view in section on a larger scale than FIG. 1, the machine being assumed to be in its working position,
FIGS. 4 and 5 are detailed views of one of the assemblies of the machine, respectively in section through a horizontal plane BB and in section through a vertical plane CC8,
FIG. 6 is a detailed perspective view of one of the components of the machine,
- Figures 7a, 7b, 7c, 7d, 7e are diagrams illustrating the operation of the machine.

 The soldering and desoldering machine shown by way of example in the figures is of the discontinuous, jerky type, for the purpose of individually soldering or desoldering components on a printed circuit; this machine is intended to be installed at the end of '' a circuit production line for exchanging faulty or reworkable components.

 This machine comprises a frame 1 provided with conventional means for adjusting its horizontality (not shown). This frame supports, on the one hand, a crucible 2 adapted to receive a liquid solder bath, on the other hand, an auxiliary container 3 placed near the crucible 2 on the frame 1.

In the example, these crucibles and containers have a shape of revolution around a vertical axis, the container being cylindrical.

The crucible 2 and the container 3 are equipped at their periphery with electrical heating resistors 4 and 5 in order to heat and maintain the solder bath at the appropriate temperature (230 to 250 C)
The crucible 2 is provided with a chute 6 extending along its vertical axis. In the example, this neck 6 is removable to allow you to change it according to the circuits to be soldered or desoldered; it is fitted onto a vertical cylindrical chimney 7 which the crucible comprises around its axis.

 The chute 6 has an open upper face 6a situated above the level of the open upper face 2a of the crucible. A partial cover 8 reduces the risk of splashing during the overflow of the bath from the chute 6 towards the crucible 2, and the heat losses.

 The crucible 2 is placed in communication with the auxiliary container 3 by a conduit 9 arranged below the level of these elements and opening out in the lower part thereof. This conduit 9 opens into the crucible through a chamber with a vertical axis lo, formed in said crucible.

This room has an entrance surrounded by an iQa seat which can be closed by a movable member 11, constituted in the example by a ball; this member is made of a material with a density slightly lower than that of the weld pool. The traditional tin-based solder baths having a density of the order of 9, the ball 11 can be made of stainless steel (-density: 7.8).

 The ball 11 is guided in the chamber 10 by an internal part 12 adapted for it to allow it to move between a high shutter position where it is pressed against the seat 10a and closes the entrance to the chamber 10, and a low opening position in which #the bath can flow through passages 12a formed in room 12 as illustrated in FIG. 3.

 The aforementioned members thus form a valve which authorizes a flow of the bath from the crucible 2 to the container 3 and prevents flow in the opposite direction.

 Furthermore, the chute 6 is placed in communication with the auxiliary container 3 by a conduit 13 arranged below the level of these elements and opening out in the lower part thereof.

 The auxiliary container 3 is provided with a movable cylindrical plunger 14, which is arranged coaxially therewith, so that it can be moved vertically. This plunger is guided on its periphery by three pairs of bars such as 15 which are fixed in the container, these pairs being arranged at 1200 relative to each other around the plunger. These bars guide the plunger at their ends and prevent it from turning around its axis thanks to small vertical grooves made in the plunger, in which they engage.

 The plunger 14 is hollow and is closed at its upper face by a cover 14a on which is fixed a nut 16 (internal side). This nut is engaged with a vertical threaded rod 17 which is rotated by an electric motor 18 with two directions of rotation.

 The motor 18 is carried by a chassis 19 fixed above the container 3 by columns. A vertical ball bearing system 20 guides the rod 17.

 In addition, the auxiliary container 3, open at the top, comprises an upper extension 3a of enlarged diameter; the height of the non-enlarged part of the container is provided such that it exceeds, at its upper end 3b, above the level of the upper face 6a of the chute 6. The enlarged extension 3a is intended to eliminate any risk of accidental overflow of the bath.

 The plunger 14 has a penetration section S which is slightly less than the internal section f. of the container. Thus, the section S of the plunger is much greater than the residual peripheral section s of the container s = - S CC S.

 By section S very much greater than s, we mean a section satisfying the relation: 2s # 2 S 4 lOs.

Furthermore, the crucible 2 and the container 3 are enclosed in enclosures 21 and 22 which contain a neutral gas, in particular argon. These enclosures are connected by conduits such as 23 to a gas source
(overpressure to compensate for gas losses and maintain them in egere /
The enclosure 21 containing the crucible 2 comprises a fixed bass-e portion, which is connected to a movable platform above # 24 by a flexible waterproof bellows 25.

 The upper plate 24 is substantially horizontal and closes the enclosure 21 in the upper part; it is provided with a circular opening 24a situated at the base of the chute 6 and associated with a movable closure member 26, an example of which is described below. This plate 24 is integral with a frame 27 guided vertically by two columns such as 28, so that said plate is movable vertically between a high position located above the level of the upper face 6a of the chute 6 (Figure 1 ) and a low position located below this level (Figure 3). A spring 29 biases the frame 27 upwards so as to tend to maintain the plate 24 in its high position.

 Figures 4 and 5 show by way of example an embodiment of the movable shutter member. This comprises at least one movable flap 30 which is associated with an operating system conditioning the closing of the said flap or flaps in the high position of the plate 24 and its or their opening during the descent of said plate.

 In the example, the plate 24 is constituted by two superimposed plates which are pierced in their center to form the opening 24a and delimit, on the one hand, a circular housing in which is arranged an operating ring 31, on the other share, between said plates, a passage for the flaps 30 which are four in number.

 These four flaps 30 have complementary shapes so as to be able to close against one another in the manner of a diaphragm; each flap 30 is articulated on the plate around an axis such as 32 and is caused to pivot about this axis during the rotation of the crown 31, by virtue of two pins 33 which each flap carries and which are housed in a appropriate light from said crown 31.

 Two rods such as 34 are articulated on the crown 31 at diametrically opposite points in order to rotate the latter by a pull in one direction or the other. Each rod 34 is moved by a lever such as 35, provided with a ramp on which a cam 36 presses when the plate 24 descends. Of course, the ramps of the two levers 35 have opposite orientations so as to produce reverse actions on the two rods 34.

Furthermore, the machine comprises a gripping claw 37 located above and directly above the
such e chute 37a 6. This claw is constituted by two blades forming jaws which are located opposite one another, so 37b to be able to grip a component, and by pushers / allowing to separate said blades for the seizure or release of said component.

 The claw 37 is carried by a claw support 38 by means of vertical rods 39 which give it a vertical sliding faculty with respect to this claw support 38. Elastic means, such as springs 43, of low elasticity modulus, urge claw up. An operating lever 44 keeps the claw in the low position for hooking a component.

 The claw support 38 is carried and guided by the columns 28, so that it can be lowered or raised; a spring 40 biases this support upwards, while a displacement system 41, in the cable example, allows an operator to move it downwards. During this downward movement, the support 38 comes to bear against the frame 27 which carries the plate 24 and drives the latter.

 In addition, the support 38 carries, on either side of the claw 37, two counter-supports such as 42 which are called to come, by their lower face, into contact with the printed circuit. In the example, these counter-supports 42 are formed by small elastic blocks (foam or other).

 Thus, when a printed circuit is in place with one of its components hooked by the claw 37, the only force which is exerted on this component is provided by the springs 43, which tend to reassemble the claw with a low effort (greater than the weight of '' a component but much lower than the pulling force of neighboring conductors or components): as long as the connections between the component and the printed circuit have not melted, the claw remains in the low position, attached to the component, without any risk of tearing off when these connections have melted, the component separates automatically from the printed circuit (pressing against the blocks 42) by the effect of lifting the claw (caused by the springs 43).

 Figures 7a to 7e illustrate an operating cycle of the machine, in the case where a component referenced M is to be desoldered and to be detached from a printed circuit referenced P.

At rest (FIG. 7a), the plunger 14 is in the high position slightly above the level of the weld pool contained in the auxiliary container 3. The level of rest
Nr of the bath is the same in the container 3, in the crucible 2 and in the chute 6, by effect of communicating vessels.

 The cable system 41 is at rest and the plate 24, like the claw 37, are in the high positions the flaps 26 are closed.

The operator sets up the printed circuit P, by attaching to the claw 37 its component to be desoldered
M, the circuit being disposed in abutment against the counter-supports 42.

 The motor 18 is started and slowly moves the plunger 14 downward. The liquid bath level rises in the container 3 and in the chute 6; it remains invariable in the crucible 2 due to the blockage produced by the valve 1Q. When the level of the bath reaches the level Ns (corresponding to that of the upper face of the chute 6), the wave is ready to form (FIG. 7b). A volume V1 of the plunger then entered the container below the rest level Nr.

 FIG. 7c represents the plunger in the intermediate position; the wave is formed in the chute 6 and the bath flows by overflow into the crucible 2, the level of which rises slowly.

 The operator activated the cable system 41 which caused the claw support 38 and the plate 24 to be lowered; during this movement, the flaps 26 are retracted, clearing the opening 24a of the plate: the connections of the component M are in contact with the welding wave.

 At the end of its slow downward movement, the diver reaches its low position (Figure 7d).

A volume V of the plunger has entered the container below the rest level Nr. The vclume V2 of liquid bath which has flowed overflow into the crucible is equal to V - V1. The crucible 2 is adapted to be able to contain, above its rest level Nr, a volume at least equal to this volume of overflow V2.

 The arrangement of the plunger and the height of its stroke are provided so that the total volume of penetration V is large relative to the volume of penetration V1 corresponding to the rise of the bath until a simple flush with the upper face of the chute 6 (By volume V large with respect to volume V1, we mean a vclume satisfying the relation: 3 V1 $ V g 10 V1).

 This condition, linked to that already provided for sections S and of the plunger and of the container, makes it possible to reduce the quantity of solder bath necessary for a given duration of appearance of the wave (because the volume of overflow V2 which generates the said wave is large in front of the volume V1 which is displaced during the stage prior to the formation thereof). It should be noted that the motor 18 and its associated drive means 17 are adapted to ensure a very slow speed of descent of the plunger (of the order of 0.5 cm / s).

 In FIG. 7d, the component M has been shown diagrammatically, which has automatically detached from the circuit P when its connections have melted, this by the action of the low-modulus springs 43 urging the claw 38 upwards.

 The plunger is then moved in the opposite direction upwards (FIG. 7e), the levels returning to the rest level Nr, thanks to the opening of the valve 10.

 it should be noted that when the machine is in use, the plunger is preferably placed on standby, between two passes, in the position of FIG. 7b, so as to remain at temperature.

 Of course, the invention is not limited to the terms of the preceding description but includes all its variants, with any necessary addition in particular it is obvious that the parts containing the liquid bath (crucible 2, container 3 and conduits 9 and 13) are insulated to reduce heat loss.

Claims (12)

 1 / - Machine for soldering or desoldering components, of the type comprising a crucible (2) adapted to contain a liquid solder bath, a chute (6) arranged in said crucible and having an open upper face (6a) and suitable means generating in the chute (6) a wave of solder bath flowing by overflow into the crucible (2), said machine being characterized in that the means capable of generating the wave of solder bath comprise  an auxiliary container (3) adapted to contain the solder bath,  channeling means (9) arranged to communicate the auxiliary container (3) and the crucible (2) so as to allow a transfer of solder bath between them,  a valve (10, 11) associated with said channeling means (9) for preventing flow of the # bath through these means in the direction going from the auxiliary container (3) to the crucible (2),  channeling means (13v) arranged to communicate the auxiliary container (3) and the chute (6) so as to allow a transfer of solder bath between them,  and means (14) for pressurizing the bath contained in the auxiliary container, adapted to allow generating, at the heart of the liquid bath, a pressure equivalent to a liquid column exceeding the level of the upper face (6a) of the chute, so as to cause, through the corresponding channeling means (13), a rise of the liquid bath in said chute and an overflow by the upper face thereof.  2 / - Machine according to claim 1, characterized in that the means for pressurizing the bath contained in the auxiliary container comprises a movable plunger (14), arranged to be able to penetrate into the auxiliary container (3) so as to generate a rise of the liquid therein and, by effect of communicating vessels, an identical rise in the chute (6).  3 / - Machine according to claim 2, characterized in that  the plunger (14) is arranged so that it can be moved between, on the one hand, a high position corresponding to a predetermined level of liquid in the auxiliary container and in the crucible, called the rest level (Nr), and, d on the other hand, a low position in which a volume (V) of said plunger has entered the liquid bath of the auxiliary container, below the rest level (Nr),  the plunger (14) has a penetration section (S) much greater than the residual peripheral section (s) of the auxiliary container (3),  the penetration volume (V) of the plunger (14) is large compared to the penetration volume (V1) corresponding to a rise in the liquid bath until the upper face (6a) of the chute is flush,  the crucible (2) has an open upper face (2a) and has a capacity adapted to contain above its rest level (Nr) a volume of liquid at least equal to the volume of overflow (V2 = V - V1),  the upper face (6a) of the chute is located above the level of the upper face (2a) of the crucible,  the auxiliary container (3}, open in the upper part, has a height such that it exceeds above the level of the upper face (6a) of the chute.  4 / - Machine according to one of claims 2 or 3, characterized in that it comprises drive means (16, 17, 18) of the plunger in a vertical movement of descent in the auxiliary container and ascent.  5 / - Machine according to one of claims 2, 3 or 4, characterized in that the auxiliary container (3) comprises an upper extension (3a) of enlarged diameter.  6 / - Machine according to one of claims 1, 2, 3, 4 or 5 characterized in that  the crucible (2) and the auxiliary container (3) are arranged close to each other,  the communication means connecting the container (3) and the crucible (2) comprise a conduit (9) arranged below the level of these elements and opening out at the bottom into them,  the communication means connecting the container (3) and the chute (6) comprise a conduit (13) arranged below the level of these elements and opening out at the bottom into them.  7 / - Machine according to one of claims 1, 2, 3, 4, 5 or 6, wherein the valve (10) associated with the communication means (9) connecting the auxiliary container (3) and the crucible (2) comprises a vertical axis chamber (10) provided at the top with an inlet surrounded by a seat (10a) and a movable member (11) for closing said seat, with a density slightly lower than that of the weld pool.  8 / - Machine according to one of claims 1, 2, 3, 4, 5, 6 or 7, characterized in that the auxiliary container (3) as well as the crucible (2) and its chute (6) are contained in closed enclosures (21, 22) containing a neutral gas, the enclosure (21) containing the crucible (2) being equipped with an opening (24a) perpendicular to the chute (6) and a movable member (26) for closing this opening.  9 / - Machine according to claim 8, characterized in that  the enclosure (21) containing the crucible (2) comprises a substantially horizontal upper plate (24) which closes it in the upper part,  said plate (24) is arranged to be movable vertically between a high position situated above the level of the upper face (6a) of the chute and a low position situated below this level,  the enclosure (21) comprises a lower portion, connected to said plate (24) by a flexible waterproof bellows (25).  10 / - Machine according to claim 9, characterized in that the movable closure member (26) comprises at least one movable flap (30) carried by the plate (24) and associated with an operating system (31, 34 , 35, 36) adapted to condition the closing of said flaps in the high position of the plate (24) and their opening during the descent of said plate.  11 / - Machine according to one of claims 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, suitable for soldering or desoldering components of a printed circuit individually, characterized in that it comprises, above and below the chute (6), a component gripping member (37), a member support (38) arranged to allow the latter to be lowered or raised along the vertical axis of the chute, the counter-supports (42) oriented downwards to come into contact with the printed circuit, and elastic means (43) biased  gripping, citing the organ / upwards in relation to the counter-supports.  12 / - Machine according to claims 9 and 11 taken together, characterized in that it comprises a displacement system (41) adapted to allow the plate (24) to be moved between its high position and its low position and, in parallel, the support of the gripping member (38).