WO1998048954A1

WO1998048954A1 - Method and machine for treating parts by immersion in a cleaning liquid

Info

Publication number: WO1998048954A1
Application number: PCT/FR1998/000852
Authority: WO
Inventors: Jean-Paul Garidel
Original assignee: Garidel Jean Paul
Priority date: 1997-04-28
Filing date: 1998-04-28
Publication date: 1998-11-05
Also published as: FR2762532A1; FR2762532B1

Abstract

The invention concerns a method for treating a part (2) formed by a support (3) whereon components are fixed, by melting a filler material, consisting in: placing the part (2) at a predetermined cleaning temperature higher than the boiling point of the part cleaning liquid; when the part (2) reaches the cleaning temperature, immersing it into a cleaning liquid. The invention is characterised in that the method consists in: placing the part (2) at a cleaning temperature less than the melting point of the filler material; and immersing the part (2) in the cleaning liquid the temperature of which is not less than its boiling point.

Description

METHOD AND MACHINE FOR TREATING PARTS BY IMMERSION IN A CLEANING LIQUID

TECHNICAL AREA

The present invention relates to the technical field of treatment using a parts cleaning liquid in the general sense, and it relates more specifically to the treatment of parts formed from a support on which components of the electronic type, for example, are mounted. , electrical, electromechanical or mechanical, using a filler material deposited punctually in relation to the fixing lugs of the components.

The invention finds a particularly advantageous application in the technique relating to the assembly of components by polymerization in which the filler material is formed by a polymer or in the technique of reflow or soldering of components for which the filler material consists of an alloy.

PRIOR ART

In the preferred technical field of the invention, various types of machine are known which make it possible to secure the components on a support by melting the filler material. It is thus known to use a soldering machine, for example, of the wave, infrared, forced convection or vapor phase type. The brazing machine aims to quickly and uniformly raise the temperature of the support and the components up to a temperature slightly higher than the melting point of the filler material, making it possible to obtain soldering or polymerization of the filler material. .

In a conventional manner, the parts leaving the brazing machine are subjected to cooling and then undergo a cleaning operation making it possible in particular to eliminate weld fluxes, ionic residues or greases from manufacture and handling. Such a cleaning machine comprises one or more baths in which the parts are immersed in order to ensure the cleaning operation.

To carry out this cleaning operation, it must be considered that the time of immersion of the parts in the cleaning bath is relatively long, in order to ensure effective cleaning while not damaging the support and / or the components. Given the relatively long duration of the cleaning operation, it turns out in practice to be very difficult to integrate the cleaning machine into a continuous production line for parts. In addition, a cleaning bath is generally equipped with an ultrasonic transducer, in order to ensure the creation of microbubbles ensuring mechanical cleaning of the part. However, it should be considered that certain components are sensitive to ultrasonic waves and that certain applications do not accept the use of ultrasound, so that the absence of an ultrasonic transducer in the cleaning bath reduces the effectiveness of the treatment. The object of the invention is to remedy the drawbacks set out above by proposing a treatment method for parts formed of a support on which components are fixed by melting a filler material, this method being suitable to ensure effective cleaning of parts while having a limited cleaning time.

STATEMENT OF THE INVENTION

To achieve such an objective, the method according to the invention consists:

- to bring the part to a determined cleaning temperature whose value is higher than the boiling point of a part cleaning liquid,

- and when the part is at cleaning temperature, immerse it in a cleaning liquid.

According to the invention, the method consists:

- to bring the part to a cleaning temperature whose value is lower than the melting point of the filler material,

- and immerse the part in the cleaning liquid, the temperature is at least equal to its boiling point. The method according to the invention thus makes it possible to ensure cleaning of hot parts in a cleaning liquid in order to obtain their rapid and effective cleaning. The object of the invention also aims to propose an installation for treating a part formed of a support on which components are fixed by melting a filler material, the installation comprising:

- a unit for assembling the components on the support, by melting the filler material, - and a unit for cleaning the part comprising at least one tank containing a cleaning liquid.

According to the invention, the installation comprises means for placing the part at a cleaning temperature above the boiling point of the cleaning liquid and below the melting point of the filler material, to allow the part to be immersed. in the cleaning fluid, at its cleaning temperature.

The object of the invention can advantageously be implemented in the field of assembly in the vapor phase, of the components on a support. This technique, known for example from patent FR 2 656 913, describes a vapor phase treatment machine comprising a tank containing a liquid of the fluorocarbon type intended to be brought to boiling point by heating means so as to produce, in a zone of 'assembly or welding, a saturated and inert primary vapor whose temperature is slightly higher than the melting point of the filler material. The assembly or welding zone is surmounted, in the case of a so-called double phase machine, by a preheating or cooling zone in which a secondary vapor reigns, originating from the vaporization of a secondary liquid.

When using a single vapor phase machine, i.e. one without secondary steam, it appears necessary to rinse the support after the brazing operation, in order to avoid contamination of the cleaning tank . In addition, the cleaning operation requires the use of a parts rinsing liquid. The object of the invention also aims to provide a method and an installation designed, in the case of the use of a vapor phase brazing machine, to ensure effective rinsing of the parts after the brazing and cleaning operations while limiting the number of liquids used. The object of the invention is to propose a treatment installation comprising a vapor phase assembly unit, called a double phase, using a secondary vapor placed above the primary fluid to ensure a rinsing and confinement function. primary liquid, but also above the bath of cleaning liquid to ensure its containment and the rinsing of the part.

Various other characteristics will emerge from the description given below with reference to the appended drawings which show, by way of nonlimiting examples, embodiments and implementation of the subject of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic view of a complete treatment installation according to the invention.

Fig. 2 is a cross-sectional view of an embodiment of part of a treatment installation according to the invention.

Fig. 3 is another alternative embodiment of part of a treatment installation according to the invention.

Fig.4 is a sectional elevation view of another embodiment of a treatment installation according to the invention. Fig. 5 is a cross-sectional view taken substantially along the lines V-V of FIG. 4.

BEST WAY TO IMPLEMENT THE INVENTION

Fig. 1 illustrates an embodiment of an installation 1 in accordance with the invention making it possible to process a part 2 in the general sense, by its immersion in a cleaning liquid. In the preferred embodiment described below, the part 2 is formed of a support 3 equipped with components of all types in combination or not, such as electronic, electrical, mechanical or electromechanical organized in an appropriate manner to assume specific functions in relation to their intended application. In the example illustrated, the installation 1 comprises a unit Pa ensuring the assembly of the components on the support 3 by melting a filler material deposited punctually in relation to the fixing lugs of the components. Conventionally, the filler material is formed by a polymer, or by an alloy. For example, the support 3 constitutes a printed circuit which, equipped with its various components, constitutes a card or part 2.

The assembly unit P _a can be formed by any machine ensuring the mounting of components on a support, by melting a filler material. For example, the assembly unit P _a can be an infrared oven, a forced convection oven, a so-called wave assembly machine, a vapor reflow machine, single or double phase.

The treatment installation 1 according to the invention also comprises a cleaning unit P _n ensuring cleaning of the part 2 following the assembly operation. As shown more precisely in FIG. 2, the cleaning unit P _n comprises at least one tank 5 containing a cleaning liquid 6 heated by heating resistors 7 leading to the formation of a secondary vapor 8 between the level of the liquid and a coil 9 for condensing the cleaning fluid vapor. Conventionally, the cleaning tank 5 has a cover 10 allowing a part 2 brought by transfer means P _an , to be taken care of by a handling means 11 shown diagrammatically. The handling means 11 allows the vertical movement of the part 2 inside the tank 5 while ensuring at the end of the cleaning cycle, the output of the part and its handling by a transfer means P _nr . Of course, the cleaning unit P _n can include several baths, such as a cleaning bath followed by a rinsing bath. By way of example, the cleaning liquid is a composition based on hydrofluoroether.

According to the invention, the installation 1 includes means M adapted to place the parts 2 at a cleaning temperature T _e higher than the boiling point of the cleaning liquid 6 so as to create, during the immersion of the parts at this temperature, bubbles ensuring, by mechanical effect, the removal dirt or residue. The cleaning temperature T _e is lower than the lowest point of thermal degradation of the part to avoid its damage. In other words, each part to be cleaned, is composed of one or more components or elements for which, it is known the respective point of thermal degradation. The cleaning temperature is chosen to be lower than the lowest value of the thermal degradation points presented for the components or constituent elements of the part 2. Of course, the cleaning temperature T _e is lower than the point of flammability of the liquid of cleaning. It should be noted that the cleaning liquid 6 is placed and maintained during the cleaning cycle, at a value at least equal to its boiling temperature. The heating bath is kept in boiling point and kept in boiling by heating resistors 7 in the example illustrated.

Furthermore, it should be considered that the cleaning temperature T _e of the parts is lower than the melting point of the filler material. It must be considered that the part 2 which leaves the assembly machine P _a does not undergo, unlike conventional techniques, a cooling operation. It should be considered that the object of the invention is to use the temperature taken by the part 2 during its assembly operation, so that the part has the desired cleaning temperature T _e during its immersion in the bath. of cleaning liquid 6 placed in boiling. It thus appears that the method of the invention can advantageously be implemented on existing installations by deactivating the cooling means generally fitted to assembly machines P _a and by directing the parts to the cleaning unit.

The means M for placing the parts 2 at a cleaning temperature T _e are advantageously provided by means P _an of direct transfer or handling of the parts 2, from the assembly machine P _a to the cleaning machine P _n . The transfer means are thus adapted to allow the movement of the parts 2 of the assembly machine P _a to the machine for cleaning P „, so that when the parts are immersed in the cleaning bath, the parts 2 have the desired cleaning temperature T _e . Of course, if the temperature conditions presented by the part 2 at the end of the assembly operation, combined with the transfer means P _an , do not allow the part to naturally reach its cleaning temperature T _e , it can be provided to raise its temperature by any appropriate means, so that it has its cleaning temperature T _e during its immersion in the bath.

Advantageously, the cleaning temperature T _e is greater than the boiling point of the cleaning liquid 6 preferably by at least 20 ° C. This difference makes it possible to obtain, during the immersion of the part 2 in the bath cleaning system placed at a temperature at least equal to its boiling point, the formation of bubbles ensuring mechanical cleaning of the part. This boiling is all the more marked as the difference between the room temperature and the boiling temperature of the liquid is important. According to another preferred embodiment characteristic, the cleaning temperature T _e of the part has a value lower than the melting point of the filler material, with a sufficient distance to guarantee the solidification of the filler material. To guarantee the polymerization or the weld produced, it is possible to envisage a cleaning temperature T _e having a value, preferably, of 5 to 10 ° C. lower than the melting point of the filler material. In other words, a cleaning temperature must be sought as close as possible to the melting point of the filler material while guaranteeing the solidity of the weld or of the polymerization, so as to ensure effective hot cleaning of the part. The hot cleaning of the part combined with the mechanical effect of the nucleated boiling makes it possible to obtain an effective and practically instantaneous cleaning of the part. By way of comparison, the time for holding the part inside the liquid bath is of the order of 10 seconds by implementing the method according to the invention with respect to a duration of 10 minutes with respect to a conventional cleaning, all values being equal.

For example, for a filler material of Sn Pb Ag type, its melting point is 179 ° C. The cleaning liquid 6 used has a boiling point at 75 ° C. Under these conditions, the cleaning temperature T _e of the part 2 will be chosen closest, at a lower value, to 179 ° C to optimize the efficiency of the cleaning operation. To guarantee the solidity of the solder produced, a cleaning temperature T _e of the order of 174 to 169 ° C. is chosen. It should be noted that this temperature is very much higher than the boiling point of the liquid, so that the mechanical action of cleaning bubbles is important.

Fig. 2 illustrates a first embodiment of a treatment installation according to the invention comprising a cleaning unit P „combined upstream, with a unit P _a of assembly in vapor phase. This assembly unit P _a comprises, conventionally, a tank 12 containing a primary liquid 13 in which are immersed heating means 14, such as electrical resistances. The heating means 14 are intended to bring the primary liquid 13 to a boil, so that an inert saturated primary vapor 15 can be produced, the temperature of which is slightly higher than the melting point of the filler material previously deposited on the support 2 in relation to the fixing lugs of the components. The primary steam 15 is intended to reign in a zone of use, assembly or welding, delimited substantially by the level of the liquid and by means of cooling or confinement 16. The assembly unit P _a also comprises conventionally, a cover 17 allowing a part 2 brought by a transfer means P _^ , to be supported using a handling means 18 shown schematically. The means 18 allows the vertical displacement of the part 2 inside the treatment tank 12, while ensuring at the end of the brazing cycle, the output of the part and its taking up by the transfer means P _^ .

Fig. 3 shows a preferred embodiment of a treatment unit combining the use of a cleaning unit P _n and an assembly unit P _a of double phase vapor reflow. The assembly unit P _a can be of the type described in document PCT / FR 94/01 388. Compared to the assembly unit P _a described in FIG. 2, the double phase assembly unit P _further comprises, at the upper part of the tank 12, means 20 for confining the primary steam. These confinement means 20 consist of secondary vapor created by the heating of a secondary liquid 21. According to one of the characteristics of the invention, the tank 12 of the assembly unit P _a communicates through its upper part, with the upper part of the tank 5 of the cleaning unit P _n . The same secondary vapor 20 therefore thus prevails on the one hand, above the primary vapor 15 of the assembly unit to ensure its confinement and, on the other hand, above the vapor 8 of the cleaning liquid to also ensure its containment. In addition, the secondary steam 20 makes it possible to rinse the part 2 at the outlet of the assembly unit P _a , thus avoiding subsequent contamination of the cleaning bath. Furthermore, the secondary steam 20 prevailing in the cleaning tank 5 makes it possible to clean the part 2 at the outlet of the cleaning bath. The common secondary steam 20 which, on the one hand, confines the primary steam 15 and the steam 8 of the cleaning liquid and, on the other hand, rinses the parts leaving the assembly and cleaning units, makes it possible to '' use a single secondary liquid to ensure all these operations.

Preferably, the cleaning tank 5 has, at its upper part, an injection nozzle 23 for secondary steam 20 making it possible to accelerate the drying and rinsing time of the parts 2.

In the foregoing description, the installation 1 according to the invention comprises an assembly unit P _a and a cleaning unit P _n between which direct transfer means P _an handle the parts between the two machines. According to a preferred embodiment, the processing unit 1 comprises, upstream of the assembly unit P _a , a preheating unit P _c , for example of the infrared or forced conduction type. The preheating unit P _c is suitable for raising the temperature of the parts 2 before the assembly operation or the polymerization of the filler material. At the outlet of the preheating unit P _c , the parts 2 are moved by the transfer means P _^ to the assembly unit P _a .

More preferably, the installation 1 comprises, upstream of the preheating unit P _c , a unit P _s for storing or accumulating the parts 2, so as to obtain a continuous line of parts having a given length. At the outlet of this storage unit P _s , the parts are conveyed by transfer means P _sc , to the preheating unit P _c . The storage unit P _s is powered in parts 2 coming from an upstream station not shown, for placing the components on the supports 3

More preferably, the treatment installation 1 comprises a cooling unit P _r placed downstream of the cleaning unit P _n . The parts brought by the transfer means P _nr are cooled by this unit P _r to then be transferred to a subsequent station, for example a test station.

In its full version, the treatment installation 1 thus comprises five stations or units each ensuring a specific function. These five units P _s , P _c , P _a , P _n , P _r are interconnected by transfer means P _9C , P _Cfl , P _an , P _nr making it possible to constitute a continuous production line for the parts 2. Advantageously, the transfer means are designed so as to authorize the obtaining of treatment cycles including all or part of the five operations performed by the corresponding units. The transfer means are thus adapted to selectively pass from one determined unit to another, without the use of the other unit or units. Thus, it can be envisaged that the installation includes treatment cycles requiring, for example:

- cleaning and cooling operations by the units P _n , P _r ,

- preheating, assembly and cleaning operations by the respective units P _c , P _a , P _n , - assembly, cleaning and cooling operations by the respective units P _a , P _n , P _r .

The transfer means P _sc , P _^ , P _an , P _nr between the different units are constituted by any conventional means known to those skilled in the art.

In the preferred example described above, the object of the invention is implemented to ensure the cleaning of parts previously subjected to an assembly operation by brazing. It should be noted that the object of the invention can be applied to any part which has to be cleaned and which does not previously comprise an assembly operation by brazing. As explained above, the cleaning of such parts is carried out hot by bringing the part to a cleaning temperature T _e higher than the boiling point of the liquid but lower than the lowest point of thermal degradation, presented by the or the components of the part to be cleaned. Fig. 4 illustrates another embodiment of a cleaning unit P _n associated with an assembly unit P _a of all types known per se. According to this exemplary embodiment, the cleaning unit P _n comprises an envelope 30 formed of an internal structure 31, called hot, preferably equipped with a thermal insulation coating 32. The internal structure 31 internally delimits a hermetic enclosure 33 accessible by at least one and, as illustrated in the exemplary embodiment, by two doors 34 and 35, respectively of entry and exit.

In the illustrated embodiment, the internal structure 31 comprises a sole 36 from which rise two vertical side walls 37 leading to a ceiling 38. The internal structure 31 is completed, in the illustrated example, by walls front 40 and rear 41 belonging respectively to the entry doors 34 and exit 35 which are equipped with automatic opening and closing means known per se not shown. This internal structure 31 constituted by the sole 36, the side walls 37, the ceiling 38 and the front 40 and rear 41 walls internally delimit an airtight or sealed enclosure when the doors are closed. The various constituent elements of the internal structure 5 are made of a material having good conduction or thermal transfer capacity.

The envelope 30 is equipped with heating means 43 for the internal structure 31, so as to place the latter at a determined temperature. For example, the heating means 43 consist of electrical resistors mounted on the external faces of at least some and, preferably, of all the constituent parts of the internal structure 31. Of course, it can be envisaged to produce the heating means 43 in other forms, such as for example, from a circulation circuit of a heat transfer fluid. The heating means 43 are adapted to put and maintain the cleaning liquid 6 at a value at least equal to its boiling point.

The installation P _n also includes means 45 for introducing the cleaning liquid inside the internal structure 31 up to a given level to allow the immersion in said liquid, of the parts 2 carried by an internal means of support and travel con 47. For example, the introduction means 45 may be constituted by a pipe opening at the upper part of the internal structure and connected to a storage tank.

The installation P _n also comprises means 50 for extracting the cleaning liquid 6 contained inside the internal structure 31. For example, the extraction means 50 are constituted by a source of compressed air opening out to the inside the internal structure 31 for expelling the cleaning liquid which is sent to its storage tank from a return pipe 51.

After the installation of parts 2 inside the envelope 30, the cleaning liquid is transferred inside the hermetic internal structure to ensure the immersion of the parts in the bath. The cleaning liquid is then removed to ensure the extraction of the parts 2 thus cleaned. It should be noted that the parts 2 to be treated remain during the treatment, in the same plane which is contiguous to the conveying planes downstream and upstream of the installation.

Claims

CLAIMS:

1 - Process for treating a part (2) formed of a support (3) on which components are fixed, by melting a filler material, the process consisting of:

- bringing the part (2) to a determined cleaning temperature (T _e ) whose value is greater than the boiling point of a part cleaning liquid,

- And when the part (2) is at the cleaning temperature, immerse it in a cleaning liquid (6), characterized in that it consists:

- putting the part (2) at a cleaning temperature (T _e ) whose value is lower than the melting point of the filler material,

- And immerse the part (2) in the cleaning liquid (6) whose temperature is at least equal to its boiling point.

2 - Method according to claim 1, characterized in that it consists in bringing the part (2) to a cleaning temperature (T _e ) whose value is less than 5 to 10 ° C at the melting point of the material. bring.

3 - Method according to claim 1 or 2, characterized in that it consists in putting the part (2) at a cleaning temperature (TJ whose value is at least 20 ° C higher than the boiling point cleaning fluid.

4 - Process according to claim 1, characterized in that it consists in using the rise in temperature of the part during the assembly operation so that the part (2) reaches its cleaning temperature.

5 - Method according to one of claims 1 to 4, characterized in that it consists in ensuring the emission of a condensation vapor (20) coming from the vaporization of a secondary liquid (21), above cleaning liquid (6), but also above a primary vapor (15) coming from a primary fluid (13) and ensuring the fusion of the filler material.

6 - Installation for treating a part (2) formed of a support (3) on which components are fixed by melting a filler material, the installation comprising:

- an assembly unit (PJ of the components on the support, by fusion of the material ("contribution,

- and a cleaning unit (P _n ) of the part comprising at least one tank (5) containing a cleaning liquid (6), characterized in that it comprises means suitable for placing the part (2) at a cleaning temperature (T _e ) higher than the boiling point of the cleaning liquid ( 6) and below the melting point of the filler material, to allow the part (2) to be immersed at its cleaning temperature (TJ, in the cleaning liquid (6) whose temperature is at least equal to its boiling point.

7 - Installation according to claim 6, characterized in that the means for placing the part (2) at the cleaning temperature, are constituted by direct transfer means (P _a of the part between the assembly unit (P _a ) and the cleaning unit (P _n ).

8 - Installation according to claim 7, characterized in that the transfer means (P _year ) are interposed between the cleaning unit (P and the assembly unit (P of the type with double vapor phases comprising a treatment tank (12) containing, on the one hand, a liquid (13) intended to be brought to boiling point by heating means (14), so as to produce, in an assembly zone, a primary vapor (15) the temperature is slightly higher than the melting point of the filler material and, on the other hand, a secondary vapor (20) of condensation of the primary vapor, coming from a secondary fluid (21) 9. Installation according to claim 8 , characterized in that the cleaning tank (5) and the assembly tank (12) communicate with each other at their upper part so that they have above the cleaning liquid (6) and above the primary vapor (15), secondary vapor (20) of condensation from the vaporis secondary liquid. 10 - Installation according to claim 6, characterized in that it comprises, as cleaning unit (P _n ) of the part:

an envelope (30) whose internal structure (31) delimits an airtight enclosure (33) accessible by at least two doors,

- means (45) for introducing a cleaning liquid inside the internal structure, up to a given level to allow the parts to be immersed in said liquid, - heating means (43) of the internal structure to a temperature suitable for bringing the cleaning liquid to a value at least equal to its boiling point,

- And means (51) for extracting the cleaning liquid from the interior of the internal structure.

11 - Installation according to claim 8, 9 or 10, characterized in that the cleaning unit (PJ is equipped with transfer means (P _nr ) of the part to a cooling unit (P _r ).

12 - Installation according to claim 6, 10 or 11, characterized in that the transfer means (P _year , P _nr ) respectively between the assembly unit (PJ and the cleaning unit (PJ and between the unit cleaning (PJ and the cooling unit (P _r ), are part of a travel line.

13 - Installation according to claim 12, characterized in that the conveyor line comprises, upstream of the assembly unit (PJ, a preheating unit (PJ.

14 - Installation according to claim 13, characterized in that the conveyor line comprises, upstream of the preheating unit (PJ, a parts accumulation unit (PJ.