DE2138547A1 - Method and device for cleaning objects, in particular for Entfer NEN of fluxes and similar filing ments of electrical construction and circuit parts - Google Patents

Description

K α ί i A. [.-Rose

DBr / Fo Munich-Pullach, August 2, 1971

14 607

IMPERIAL SMELTING CORPORATION (N.S.C.) LIMITED, Austral House, Basinghall Avenue, E.G. 2 London, England

Method and device for cleaning objects, in particular for removal of fluxes and similar deposits from electrical components and circuit parts

The invention relates to a method and a device for Cleaning of objects and in particular for removing fluxes and similar residues from electrical construction and Circuit parts. In particular, the invention relates to the removal of such materials from printed circuits, after the components are soldered onto it.

In the manufacture of printed circuits for electrical systems, special techniques are used to make a soldered Connection between a printed circuit and the small components such as resistors, capacitors and the like and to achieve the circuit itself, which is printed on a surface of a chip made of insulating material. Egg. A typical technique has the following steps:

1. A number of holes are punched through the insulating support board to accommodate the connections of the various electrical

209813/1708 *

localize tronic components that affect the circuit should be soldered on.

2. The desired circuit is created on the appropriate side of the panel using a variety of techniques.

3. The necessary components, which have short stiff lines, are moved through the board from the side remote from the printed circuit board to the appropriate ones Places where the board had been punched in the first step.

4. Using an overflow technique, a coating of liquid is created Flux applied to the protruding ends and appropriate parts of the circuit. The flux is designed so that it does not wet the unprinted areas of the insulation backing board, so that the solder does not adhere to these areas.

5. Using a similar dipping technique, solder is applied simultaneously applied to all lines protruding from the side of the circuit board, so that these lines are connected to the Circuit are soldered in one process step.

6. The remnants of the flux after-which they are through Contact with the solder that has been heated must be removed from the board, in part for normal purposes Cleanliness in a number of use cases and in part because if the circuit gets hot at any later stage the flux will melt, will trickle down and pose a very serious detriment to the electronic performance of the circuit can. Furthermore, these flux residues show the

209813/1708

2139547

Tendency to have a corrosive effect and are therefore not desirable.

Various methods are known by which to effectively remove residual flux from printed circuit boards can be carried out. Azeotropic solvent mixtures were found in the same way as single solvents are used in processes with two separate solvent systems Found use, wherein in the first of the systems using a solvent, the flux residue with optional Use of mechanical or ultrasonic cleaning aids is removed and in which in the second system the circuit boards are cleaned by means of a solvent or a steam bath is rinsed.

The present invention generally deals with cleaning of articles is particularly concerned with the removal of flux residues from such electrical devices directed and uses non-azeotropic solvent mixtures. One of the components of the previously used Solvent mixtures consisted of chlorofluoro carbon. It is well known, however, that substances of this class cannot be used as solvents for the ionic form / constituents are effective, as they often occur in flux remnants. As a result, the solvent mixtures including polar solvents such as the lower ones were formed aliphatic alcohols and ketones. However, since such solvent mixtures can give off flammable or explosive vapors, was the use of such chlorofluorocarbon / aliphatic Alcohol or ketone mixtures have heretofore been restricted to azeotropic proportions, as for example in U.S. Patent 2,999,815 and is cited in British Patent 1,026,003 which describes certain aseotropic mixtures which are not give off dangerous flammable vapors.

209813/1708

The object of the invention is to provide a method for removing flux residues from electrical devices using a non-azeotropic solvent mixture that has a flammable component contains, wherein the vapor above the solvent mixture is of controlled non-combustible composition.

The invention provides a method of uniting an object created, which is characterized in that the object initially with a body of liquid from not azeotropic solvent is brought into contact, the object is removed from contact with the liquid, the article then contacted with a supply of uncontaminated liquid non-azeotropic solvent which comes from the evaporation of the body of liquid and the subsequent condensation of the vapor and allowing the condensed liquid solvent to drain off the article.

The article is preferably a piece of an electrical one Circuit, such as a printed circuit board, to be cleaned of solder flux residue.

The solvent can consist of two components or many components exist but need not be azeotropic. A non-azeotropic solvent gives a vapor of various kinds Compositions when it boils and the term "non-azeotropic" as used herein includes mixtures of solvents one which (i) have an azeotrope for a given composition different from that used in the present invention Composition or which (ii) do not contain such an azeotrope. For example, a non-azeotropic Mixture of a chlorofluorocarbon and a low

209813/1708

their aliphatic alcohol or ketone may be such a solvent. A particular mixture consists of 1,1,2-trichloro-1,2,2-trifluroethane and isopropyl alcohol, for example in a volume ratio of 55 ' 4-5 to 80:20 and preferably of about 65 * 35 »a weight ratio of about 4: 1.

The solvent vapor can either condense on the wetted object itself or can be condensed separately and be noticed on the object, or any combination of the two can be used Find.

In a practical procedure, the object (or a continuous series of objects) is moved on a path which leads it under the surface of the body of liquid and then up through a steamy space, where it is brought into contact with the supply of liquid produced by condensation of the vapor.

The vapor is conveniently released by evaporating part of the liquid in conjunction with any part of the Liquid body, which is brought into contact with the object, achieved, this part generally thermal is isolated from any part of the body of liquid.

It is a particular feature of the invention that the vapor composition is preferably controlled so that it does not is flammable; this can be done by dividing the body of liquid into three compartments, a first compartment to be touched the object to be cleaned, a second thermally insulated but otherwise completely connected to the first compartment standing compartment for boiling the liquid of the same composition as that in the first compartment and a second

209813/1708 '

Compartment for boiling liquid, which is only passed through an overflow or the like in a sighting Flow is supplied from the second compartment and which is consequently enriched with ingredients which have a high Have boiling point.

If the ingredients are chosen so that the higher boiling point ingredients are a better solvent for represent the material to be cleaned from the object, this material inevitably collects in the third compartment and can be removed periodically. If at the same time the component with the lower boiling point is less flammable is than the component with the higher boiling point, the use of the second compartment ensures the one steam made with a relatively high content of the low boiling point ingredient (and which is the first to boil in the beginning), that the vapor is non-flammable and is also not a source of evaporation loss. If the special combination from chlorofluorocarbon with low boiling point / alcohol with a high boiling point is used, this means that higher proportions of alcohol can be safely used with consequently less need to use additional and possibly damaging supersonic cleaning.

To compensate for the evaporation losses, the solvent can be replaced in a manner controlled by the depth of solvent in the body of liquid »preferably an optional filling of the individual components is carried out depending on the density of the liquid.

In another aspect, the invention consists in one Device for cleaning objects caused by the following Ingredients labeled: A container for not

209813/1708

azeotropic liquid in an article washing compartment and at least one solvent evaporation compartment is divided, which has heating devices $ and a vapor space, which communicates with the solvent evaporation compartment and is open at the top and bottom to allow removal of items from the item washing compartment, and which is positioned above the article washing compartment to allow condensed vapor back into the article washing compartment can drain.

For the liquid in the article washing compartment and / or in The steam space for condensing the steam can have cooling devices be provided. A heat insulating partition is usually between the article washing compartment and the solvent arranged in the evaporator compartment.

Conveniently continuous conveyor systems are used, to guide the object into the liquid and out of the liquid up through the vapor space *

In a preferred embodiment of the device according to the invention, two solvent / evaporator compartments are provided, one of which can be separated from the object washing compartment by a first partition, preferably thermally insulated, and equipped with devices or designed in such a way that a liquid flow in both directions is guaranteed and of which the other such compartment is separated from the first-mentioned solvent evaporator compartment by a second partition ₂ which is equipped with devices or designed such that a liquid flow is ensured in only one direction from the first-mentioned compartment. The first partition wall can consist of a weir provided with an opening which ends at or near the liquid level, the second Tt

209813/1708

can be a diaphragm-like weir provided with an opening which extends above the liquid level so as to allow boiling liquid to be splashed into each of the To prevent solvent evaporator compartments.

Liquid level control means for at least one of the solvent evaporator compartments and / or dependent on the faces fluid supply control means for selectively W Viederauffüllen the liquid components may be provided. It is an aspect of the invention to provide a liquid density control device for immersion in a liquid which has a housing which allows liquid to pass therethrough and has an upper inlet conduit for relatively lower density liquid and a lower inlet conduit for relatively high density liquid; the housing having valve means at each of the inlets and a working float for opening and closing the valve means depending on the liquid density. Devices are preferably provided in order to control the total supply of liquid as a function of the depth of the liquid.

In the following the invention will be explained with reference to the drawings explained in more detail. It shows:

1 shows a sketchy section through the device according to the invention;

Fig. 2 shows a detail of a liquid supply device for use with the Device according to Figure 1;

3 shows a further detail of a device for compensating the evaporation evaporation in the device according to FIG.

209813 / $ 170

The device according to FIG. 1 consists of a vessel 1, which in the area of one end has a pair of weirs 2 and 3 arranged close to one another, which are each provided with openings in the area of the upper edge at 2a and in the area of the lower edge at 3a, the weir 2 defining the compartment A together with one end of the vessel. A third thermally insulated weir 4, which is provided with an opening in the region of the lower edge at 4a, is also arranged in the vessel in order to form compartments B and C, as illustrated in the drawing. The weir 4 extends approximately to the same level as the opening 2a. An upwardly extending well 5 forms a vapor space D above compartment C, while a vapor trap 6 covers as is practical a portion of the remaining surface of the liquid in that compartment.

Thermostatically controlled heaters 7 and 8 are below of the liquid level in the compartments A and B and are by a thermostat 9 in the vapor space D actuated. Cooling coils 10 are also provided in the steam space below the thermostat.

The compartment 0 has cooling coils 11, which are arranged in an upper part thereof, but below the liquid level and it is a fluid tightness indicated generally at 12 Control device is provided, the construction and mode of operation of which will be described later in connection with that generally designated by 13 Liquid level control is described in more detail. A circulation pump 14 ensures the constant mixing of the liquid; speed in compartment C along with the filtration of solids existing impurities.

A conveyor system for printed circuit boards or similar electrical Circuits is indicated generally at 15 and is from

209813/1708

- ίο -

the usual design to pass the panels down below the steam and up through the shaft 5.

In operation, a non-azeotropic liquid solvent mixture is used typically a 4: 1 mixture in a volume ratio of trichlorotrifluorethane and isopropyl alcohol in the compartment C passed in a sufficient amount that the thermally insulated weir 4 just above the surface in the compartments B and C protrudes and the liquid level in compartment A is slightly lower. The heating devices 2 and 5 are switched on until the liquid in compartments A and B boils.

The effect of boiling on the non-azeotropic liquid is that the lower boiling point ingredients in. Steam pass while the ingredients with higher boiling point remain. The liquid in compartment B, however can boil over the weir 4 and be replaced by the opening 4a; this way it will always have the same composition as the liquid in compartment C. The liquid in compartment B can neither pass through the higher weir 3 boiled over, still passed through the screened opening 2a, so that the liquid in the compartment A is effective in components is enriched with a higher boiling point.

The vapor generated is condensed on coils 10 and falls as a liquid into compartment C; this therefore contains liquid of roughly the same composition as the steam.

As a result, there is a total circulation of the liquid from compartment C to compartment B to compartment A and backwards by means of evaporation (as distinct from the circulation caused by the pump in compartment C) and, since the flux on the circuits to be cleaned in the components

209813/1708

is more soluble with a higher boiling point, it will tend to collect in compartment A and compartment C to be left at a relatively low level of dissolved flux.

Any printed circuit board or the like will run into the relatively unpolluted solvent in compartment C and any Adhering flux residues are dissolved. Furthermore, when the table is out of the relatively cold liquid in the compartment C exits, the vapor in the vapor space D condenses on it to form a pure solvent of the same composition to create, which drains into the compartment C and thus rinses the board and removes any liquid carried over from the compartment C.

The liquid in compartment A can be discarded if the impurities that have accumulated in it reach a level have built up unacceptable levels. The advantages of this method of operation are that this solvent represents only part of the total amount used and in any case a relatively low level of contains the more expensive, low boiling point solvents.

In any practical system there are small evaporation losses. These can be compensated for by the details illustrated in FIGS.

The liquid level control 13 consists of a vertical one Tube 16 with an air inlet 17 and an outlet 18 at the desired one Fluid level. It communicates with compartment A through a line 19 below the liquid level.

The outlet 18 is in communication with! -Connector 20, which to the air spaces 21 and 22 in sealed vessels

209813/1708

and 24 leads which have liquid outlets 25 and 26, respectively. The vessel 23 contains a solvent, for example low density, e.g. a mixture of fluorocarbon and aliphatic alcohol and the vessel 24 contains a solvent high density e.g. fluorocarbon alone. the Downpipes 27 and 28 are provided for refilling and are otherwise sealed at the top.

When the liquid level in A drops, outlet 18 becomes exposed and air can flow into the T-connector 20 thus allowing solvent to flow out of the outlets 25 and 26 flows into compartment C. The mix, however, is not azeotropic and hence the evaporation loss is not necessarily of the same composition as the solvent is in compartment C, it is not desirable either to supply the same amount of each solvent. Hence the outlets to the density (and consequently composition) Control device 12 connected, the outlet 25 for the lower density solvent to the upper Inlet 29 and outlet 26 for the higher density solvent are connected to the lower inlet 30.

The Bichte control device 12 consists of a housing 31, with an upper (for low density liquid) inlet 29 and the lower (for high density liquid) inlet 30 such as previously mentioned that perforated for free movement and possibly some filtering action of the solvent are. The housing also contains a hollow polythene body 52 with a central BaUastrosr 33, which is attached to a Threaded stop 34 and a seal 35 liquid tightly sealed ist rad © inea BleibäEL & st 56 contains »The swimmer know © also lower AmOTdnungaetangen 37 or -38 which P.S. 7. S. Blebttelle 39 bsw. 4Ö carry that on shoulders 41 or 42 and seal them.

209S13 / 1708

if the solvent density is too low, the float sinks and seals the inlet 29 for the solvent less Dense off. If the visibility is too high, the float rises and seals the inlet 30 for the solvent higher Dense off.

Various changes can be made without being dated Deviate basic ideas of the invention.

All technical details that can be recognized in the description and shown in the drawings are essential for the invention significant.

209813/1708

Claims (1)

PATENT CLAIMS Method for legging an object, characterized in that that the object is first in contact with a body of liquid of a non-azeotropic solvent is brought, the object is removed from contact with the liquid, the object then with a Supply of uncontaminated liquid, non-azeotropic solvent from the evaporation of the liquid body and the condensation of the vapor is brought into contact, and then the condensed liquid solvent from the object is allowed to expire. 2. The method according to claim 1, characterized in that the article is a printed circuit board. 3. The method according to claim 1, characterized in that a Solvent is used, which is formed by a mixture consisting of two components. 4. The method according to claim 1, characterized in that as Solvent a mixture of a chlorofluorocarbon and a lower aliphatic alcohol or ketone use finds. 5. The method according to claim 4, characterized in that as Solvent a mixture of 1,1,2-trichToro-1,2,2, -trifluoro Ethane and isopropyl alcohol is used. 6. The method according to claim 4 or 5 »characterized in that the corresponding volume ratios of the mixture between 55:45 and 80:20 lie. 209813/1708 7. The method according to any one of the preceding claims, characterized in that the solvent vapor on the wetted Object itself is condensed. 8. The method according to any one of the preceding claims, characterized characterized in that the solvent vapor condenses in an area above the object and onto the object is dropped. 9 * Method according to one of the preceding claims, characterized characterized in that the object or a continuous series of objects is moved in a path which takes it below the surface of the body of liquid and then up through a steam-laden seam, where it comes into contact is brought with the supply of liquid, which is generated by condensation of the vapor. 10. The method according to any one of the preceding claims, characterized characterized in that the vapor is generated by vaporizing part of the liquid, which in connection with However im isolated
generally thermally / from any part of the body of liquid which is brought into contact with the object. 11. The method according to claim 10, characterized in that the body of liquid is divided into three parts, a first part for touching the object to be cleaned one second thermally insulated, but fully connected to the first part for boiling liquid of the same Composition like that in the first part and a third part for boiling liquid that is simply overflowed or a similar stream is fed with only one sifting from the second part and which consequently has no components is enriched with a high boiling point. 209813/1708 12. The method according to any one of the preceding claims, characterized characterized in that evaporation losses from the body of liquid as a function of the depth of the body of liquid be replaced. 13. Method according to one of the preceding claims, characterized in that evaporation losses from the body of liquid by optionally filling the individual components in | Be replaced depending on the density of the liquid. Device for cleaning objects according to the method according to one or more of the preceding claims 1 - 13, characterized by the following components: a container (1) for a non-azeotropic liquid which is divided into an article washing compartment (C) and at least one solvent evaporator compartment (A, B) with heating devices (7, 8)} and a with the solvent evaporator compartment (A, B) in communication steam space (S), which is open at the top and bottom to allow the removal of objects from the object washing compartment (C), and the above Article washing compartment (C) is arranged to allow condensed steam to enter the article washing compartment (C) can run back. 15 · Device according to claim 14, characterized in that Cooling facilities (10, 11) in the article washing compartment (C) and / or are provided in the steam space (D) for condensing the steam. 16. The device according to claim 15, characterized in that a heat-insulated partition (4) is arranged between the article-Waechabteil (C) and the solvent evaporator compartments (A, B). 209813/1708 17 · Device according to claim 15 or 16, characterized in that g @ k®ass @ ieh net that continuous conveyors (15) ^ to guide of objects in the liquid and outwards u & d above are provided through the steam space (B). 18. Device according to one of the preceding claims 15, 17, characterized in that two solvents! Evaporator compartments (A, B) are provided, separated from deaen eia. @ A / voa the article washing compartment (C) by a first partition (4) is, which is equipped with means (4 &) or is designed in such a way to flow a liquid in both Directions to ensure and from which the other © (A) from the first mentioned solvent evaporator compartment (B) by a second partition (2, 3) is separated, which is equipped with devices (2a, 3a) or designed in such a way, that a liquid flow from the first-mentioned compartment (B) can only take place in one direction. 19. Device according to claim 18, characterized in that the first partition (4) consists of a partition provided with an opening (4a) Weir exists, the upper edge of which is arranged on or in the area of the liquid level. 20. Apparatus according to claim 18 or 19, characterized in that the second partition (2, 3) consists of one with blendähnlicben Orifices (2a, 3a) provided weir (2, 3), which extends above the liquid level, so as to allow the spraying of boiling liquid in each of the liquid evaporator compartments (A or B). 21. Device according to one of the preceding claims 15 to 20, characterized in that control devices (13) for Controlling the liquid level in at least one of the liquid evaporator compartments (A, B) are provided. 209813/1708 22. Device according to one of the preceding. Claims 15 to 21, characterized in that density-dependent liquid supply control devices (12) are provided for optional replenishment of the liquid components. 23 · Liquid-tight gating device for immersion in a liquid, characterized in that a housing (31) for the passage of a liquid having an upper inlet conduit (29) for relatively low density liquid and a lower inlet conduit (30) for relatively high density liquid is provided, the housing (31) having valve means (37 to 42) on each of the inlets (29, 30) and an actuating float (32 to 36) to the valve devices (37 to 42) as a function of the liquid density close and open. 24. The device according to claim 22, characterized in that the density-dependent liquid supply control device (12) the apparatus of claim (23) is provided. 209813/1708