GB2282749A

GB2282749A - Cleaning printed circuit boards etc

Info

Publication number: GB2282749A
Application number: GB9420574A
Authority: GB
Inventors: Sidney Treacher
Original assignee: CROFTSHAW Ltd
Current assignee: CROFTSHAW Ltd
Priority date: 1993-10-13
Filing date: 1994-10-12
Publication date: 1995-04-19
Anticipated expiration: 2014-10-12
Also published as: WO1995010343A1; GB2282749A8; AU7819394A; GB2282749B; FI961633A; FI961633A0; GB9420574D0; EP0723472A1; GB9321067D0

Abstract

Apparatus for cleaning electronic components and the like comprising a cell (1) for a water-miscible solvent, at least one cell (2, 3) for rinse water, an active filter (6) holding an absorptive medium for impurities precipitated in the rinse water, a water pump (11) to circulate aqueous effluent from the rinse cells through the active filter to the solvent cell and a concentrator (9) to separate the solvent and rinse water from the aqueous effluent emerging from the active filter; whereby, in use, the component to be cleaned is exposed to the solvent in the solvent cell and then rinsed in water in the or each rinse cell, the aqueous effluent being pumped from the rinse cell through the absorptive medium in the active filter so as to remove any suspended impurities or precipitates therefrom and back to the solvent cell; with the concentrator to separate the solvent from the rinse water and return recovered solvent to the solvent cell. Preferably, the concentrator is connected between the active filter and the solvent cell so that recovered solvent can continuously be returned to the solvent cell. <IMAGE>

Description

2282749 1 1 CLEANING APEARATUS This invention relates to apparatus for

cleaning electronic components using a solvent system in a manner to minimise emission of solvents and particulate materials into the environment.

It is well known to use various solvents and solvent blends as a cleaning agent for the removal of oil and other contaminants from substrates such as drill cuttings etc. Most of these solvents cannot be used for the removal of inorganic/organic fluxes or other contaminants encountered on electronic components and printed circuit boards. Removal of flux from such circuit boards is not only necessary for cosmetic reasons but also to prevent corrosion by such fluxes on the boards and to allow automatic testing of such boards. Whilst conventional solvents used for this purpose have included chlorofluorocarbons, the so-called "CFC's", EP- A0523892 claims and describes a process for using oxygenated solvents for this purpose thereby rendering such solvents environmentally more acceptarle.

In use, however, such solvents can be rendered more efficient and more environmentally friendly if these solvents could be recovered and re-used. The difficulty with this has been that such solvents are invariably rinsed off the surfaces of the cleaned components with water and the water discharged. Also, due to the efficiency of the solvent, there is a rapid build up of contamination in rinse tanks, especially due to the carry over of the contaminants from one tank to the next. If the cleaning solvent is changed out when the final rinse reaches an unacceptable level (typically 1000 ppm flux) then the process would be uneconomic. An extension of all such cleaning baths can be achieved in two ways: (a) by increasing the number of tanks (effectively increasing the degree of dilution of the contamination thereby adding significantly to 2 the size and -cost of the equipment, or, (b) by removal of contamination from the final rinse thereby increasing the running cos--s. The latter method, whilst preferred by the electronics industry is not so simple. For instance, the solvents are usually mixed with substantial amounts of rinse water and the solvent/rinse water mixture is difficult to separate not only from each other but also from other suspended impurities since use of absorbents to achieve this have invariably resulted in said absorbent removing the solvent at the same time as the other suspended impurities thereby resulting in loss of valuable solvents. Moreover, some of the conventional absorbents such as the commercial water purification carbons have little capacity for flux residues.

It is an object of the present invention to provide apparatus designed to clean and rinse the soiled electronic component, and to recover and recycle the solvent and, possibly the water used.

According to the present invention, apparatus for cleaning electronic components and the like comprises:- i) a solvent cell capable of containing a water- miscible solvent; at least one rinse cell capable of containing water; an active filter capable of holding an absorptive medium for suspended impurities in the rinse water; a water pump capable of circulating aqueous effluent from the or each rinse cell through the active filter to the solvent cell; and, a concentrator capable of separating the solvent and water from an aqueous effluent emerging from the active filter; whereby, in use, the component to be cleaned is exposed to the solvent in the solvent cell and then rinsed in water in the or each rinse cell, the aqueous effluent being pumped from the rinse cell through the absorptive medium in the gctive filter ii) iii) iv) v) 3 so as to remove any suspended impurities or precipitates therefrom and back to the solvent cell; with the concentrator to separate the solvent from the rinse water.

The expression "electronic components" as used herein and throughout the specification is meant to include inter alia electronic circuit boards, printed circuit boards, precision engineered components and the like which have been exposed to solders, f luxes and/or oil treatments during the production thereof.

By the expression "aqueous effluent" is meant here and throughout the specification the effluent comprising the water-miscible cleansing solvent and water whether generated during cleaning or rinsing cycles which may or may not include suspended impurities, whether they be particulate, colloids or emulsions, and dissolved impurities including soluble cationic and anionic impurities.

By the expression "suspended impurities" is meant here and throughout the specification, impurities which may be in particulate, colloidal or emulsion form but does not include dissolved impurities.

Examples of the water-miscible solvents that may be used in the apparatus of the present invention are suitably oxygenated solvents which are suitably high boiling and preferably have a boiling point above that of water. It is furthermore desirable that such solvents are non-flammable and are of low bio-toxicity. Examples of such solvents include inter alia alcohols, glycol ethers, glycol ether esters and natural terpenoids. More specifically these include one or more of ethoxy propanol, butyldiglycol ether, ethyldiglycol ether, ethoxypropoxy propanol, ethoxy propyl acetate and butyldiglycol acetate. Formulations containing these types of compounds are commercially available as PROZONE (trade mark) and HYKLEEN (trade mark) (both ex BP Chemicals Ltd).

4 Examples of absorptive media for use in apparatus according to the present invention include certain f orms of carbon such as eg those derived f rom coal, coconut shells or wood; clays such as eg Attapulgite, Montmorillonite and Fullers Earth; polymeric fibres such as polypropylene fibres; or a combination of these.

These absorptive media can be made in the f orm of permeable and replaceable f ilter cartridges with or without a mixed bed of deionising resin admixed therewith.

Since the aqueous effluent may also contain dissolved impurities which may be cationic or anionic, it is preferable that the aqueous effluent is treated with a de-ionising resin either before, during or after passing the effluent through the adsorptive media. The de-ionising resin used may be either a cationic resin or an anionic resin or a mixture of both, depending upon the nature of the dissolved impurities in the effluent. This treatment with the de-ionising resin may be carried out either before or after passing the effluent through the absorptive medium.

According to an embodiment of the present invention, the active filter comprises a mixed bed of de-ionising resin and 4-he absorptive medium. Preferably, the two components are mixed in the correct proportions so that the de-ionising resin is exhausted by saturation before the absorptive medium is saturated, thereby allowing measurement of the increase in water resistivity as a warning that the mixed bed is about to allow organic contaminants into the flow of rinse water.

According to an embodiment of the present invention the concentrator is connected between the active filter and the solvent cell; whereby, in use, recovered solvent can continuously be returned to the solvent cell.

J According to a further embodiment of the present invention the concentrator comprises a heated surf ace in a tank and means to deliver aqueous effluent across the surface; whereby, in use, water will be evaporated from the effluent and solvent will remain in the tank for return to the solvent cell.

Preferably apparatus in accordance with the present invention includes a dryer to clean dried and rinsed electronic components.

According to another embodiment of the present invention, the apparatus further comprises a particulate filter in the water circulation system comprising the rinse cell, the absorptive filter and the water pump.

The apparatus is suitably in a single unit. All the cells and other associated parts in the apparatus are suitably made in stainless steel and the whole apparatus is suitably constructed as an integrated package capable of cleaning electronic components and recycling the cleaning and/or rinsing liquids used in the process. Ultrasonic generators can be attached to the solvent cell to aid the cleaning step by agitation and help remove particles from the surface thereof.

Each of the cells may be provided with heating means in order to heat the solvent or rinse water in the respective cells to a higher than ambient temperature. Thermostatic temperature controllers may also be provided in each cell.

Thus each cell may be provided with tubular recesses capable of receiving sealed cartridge heaters and sensors fitted at the interface with the temperature controller.

The above and other features of the present invention is 6 illustrated more specifically with reference to the drawing, which is a schematic f low diagram representing the cleaning apparatus according to the invention.

The cleaning apparatus is a single unit consisting of a solvent cell 1, with two rinsing cells 2 and 3, and a dryer 4. Each of cells 1, 2 and 3 is in the form of an open I-ank. Rinse cell 3 is fitted with liquid level control weir 5. Rinse cell 2 is also provided with a liquid level control and interceptor tank 12. Solvent cell 1 is fitted with heating means (not shown) and a sensor (not shown) to control the temperature in the cell. The rinsing cells 2 and 3 are arranged to cascade from cell 3 to cell 2 over the weir 5 and rinse water (which can be de-ionised) overflows from cell 2 into a level control interceptor tank 12. Cell 1 and tank 12 each has a circulating pump 10 and 11 respectively associated therewith. Each of these pumps is capable of separately pumping solvent or rinse water into the respective cells 1 and 3. Pump 11 is connected and is capable of re-circulating the used rinse water/solvent mixture from tank 12 through an absorptive medium located in active filter 6. The water/solvent mixture emergent from filter 6 free of all suspended impurities is connected to and is capable of passing through a further particulate filter 8. Filter 8 removes any particles generated by attrizion of the absorptive media in the active filter 6. The cleane--4 water/solvent mixture emerging from particulate filter 8 can either be fed directly to the rinse cell 3 or to a concentrator tank 9 which is connected and is capable of (a) removing the excess water from the solvent/water mixture and (b) recirculating the concentrated solvent back to the solvent cell 1. Cell 1 is also connected to a particulate filter 7 via pump 10 through which used solvent can be pumped, cleaned and recycled to Cell 1; preferably through immersed sprays using offset or parallel manifolds or other agitation.

A dryer 4 is located adjacent to rinse cell 3 in order to 7 dry the cleaned electronic components.

The solvent cell 1 is fitted with stainless steel heating tubes, to accept sealed cartridge heaters, and a sensor (none shown) is fitted to interface with a temperature controller. Ultrasonic generators (not shown) can be attached to the solvent cell.

In use, baskets of soiled electronic components, for example printed circuit boards, are immersed in a suitable flux solvent such as 11PROZONE11 (trade mark) contained in solvent cell 1 where heated jets of solvent dissolve residue flux on the boards and clean the board surfaces and components mounted on the board. At the end of a cleaning cycle, typically immersion at 40'C to 60'C for four to six minutes, the baskets are removed from the solvent cell and, having drained, are then transferred to the first rinse cell 2 which contains rinsing water (which may be de-ionised).

The rinsing water in cell 2 is continually being replenished by the water recirculated into cell 3 via the active filter 6 and through the particulate filter 8. The water in cell 3 cascades into cell 2 over the weir 5. The level of water in cell 2 is controlled by the interceptor tank 12.

Any residual solvent on the boards is dissolved in the rinse water. Residue flux, previously dissolved in the solvent, is not soluble in the rinse water and is precipitated as a colloid. Ionic contamination present in the flux, which would include quite heavy metals, such as tin, copper, lead from solder and board surfaces together with activators (typically containing water soluble chloride radicals) are also dissolved by the rinse water. Typically, the basket of printed circuit boards is immersed in the first rinse water cell 24 at 350 to 60' centigrade for two to four minutes.

8 The basket of printed circuit boards is then transferred to the second rinse cell 3 and immersed at 350 C for two to three minutes. Final traces of ionics are removed in the second rinse cell; baskets from the rinse processes are drained before transfer to the dryer 28, wherein a circulator fan and heaters dry the basket of boards. Final traces of ionics are removed in the second rinse cell; baskets from the rinse process are drained before transfer to the dryer.

The suspended impurities in the solvents withdrawn f rom cell 1 by pump 10 are removed by passing the used solvent through a particulate filter 7 and the cleaned solvent recycled to cell 1. Any remaining suspended impurities or dissolved impurities carried over to or generated by the rinse water in cell 2 is removed by passing the used rinse water from cell 2 collected in tank 12 through the absorptive medium in active filter 6. The cleaned mixture of water and solvent emergent therefrom is then passed through another particulate filter 6 before it is either recycled to cell 3 or sent to the concentrator tank 9. In this manner, almost all of the solvent is recovered and none of the water, if any discharged, contains any contaminants.

As the solvent is soluble in the rinse water it is not removed by the filters and accordingly its concentration will increase. A concentration of up to 10% does not af f ect rinsing or drying.

The concentrator 9 takes the form of a container for the contents of the rinse cells and can operate either on a batch process or on a continuous trickle system. The concentrator preferably forms an integral part of the unit.

On a batch system, used rinse water, being the entire contents of rinse cells 2 and 3, the interceptor tank 12, the active filter 6 and the rinse water particulate filter 8, is pumped to the concentrator; using rinse water pump 11. The 9 used rinse water in the concentrator contains solvent in solution and is heated, by heaters to 80' centigrade and a fan draws air across the surf ace of the heated solution to speed evaporation of water. Water vapour can either escape to atmosphere or can be condensed by a condenser for recycling.

All the water is allowed to evaporate, specific gravity sensors or timers being used to control the concentrator heaters. The solvent remaining in the concentrator is permitted to cool before returning it to the solvent cell 1.

In an alternative, continuous-action, concentrator, used rinse water, containing solvent in solution, f lows slowly across a corrugated heated surf ace - in a tank - to return solvent directly to the solvent cell.

In alternative, un-illustrated apparatus solvent may be applied by sprays in air or immersion where parts are cleaned individually or in baskets on a continuously moving conveyor belt or chain; i.e. the cleaning process operates continuously through the same cycle instead of a batch operation. In a modification the conveyor belt or chain is indexed through the process f or a predetermined time. Such apparatus still needs components to contain solvent and rinse water, an active f ilter, a pump to circulate rinse water through the active f ilter and a concentrator to extract solvent from used rinse water and to return it to the solvent container.

iii) iv) v)

Claims

CLAIMS:

1. Apparatus for cleaning electronic components and the like comprising:i) a solvent cell capable of containing a water-miscible solvent; ii) at least one rinse cell capable of containing water; an active filter capable of holding an absorptive medium for impurities precipitated in the rinse water; a water pump capable of circulating aqueous effluent from the or each rinse cell through the active filter to the solvent cell; and, a concentrator capable of separating the solvent and water =om an aqueous effluent emerging from the active filter; whereby, in use, the component to be cleaned is exposed to the solvent in the solvent cell and then rinsed in water in the or each rinse cell, the aqueous effluent being pumped from the rinse cell through the absorptive medium in the active filter so as to remove any suspended impurities or precipitates therefrom and back to the solvent cell; with the concentrator to separate the solvent from the rinse water.

Apparatus as claimed in claim 1; wherein the concentrator is connected between the active filter and the solvent cell; whereby, in use, recovered solvent can continuously be returned to the solvent cell.

3. Apparatus as claimed in claim 2; wherein the concentrator comprises a heated surface in a tank and means to deliver aqueous effluent across the surface; whereby, in use, water will be evaporated 11 from the effluent and solvent will remain in the tank for return to the solvent cell.

4. Apparatus as claimed in any of claims 1 to 3 and further comprising a particulate filter in the water circulation system comprising the rinse cell, the absorptive filter and the water pump.

5. Apparatus as claimed in any of claims 1 to 4 and including a dryer to clean dried and rinsed electronic components.

Apparatus as claimed in any of claims 1 to 5, wherein the active filter includes a deionising resin bed; whereby, in use, ionic contaminants can be removed from the aqueous effluent.

Apparatus as claimed in claim 6 and including means to measure the resistivitity of aqueous effluent from the active filter; whereby, in use, the level of active filter contamination can be measured.

Apparatus as claimed in any of claims 1 to 7 and including two or more rinse cells provided in series connected so that, in use, water can flow serially from rinse cell to rinse cell, to be pumped through the active filter and back to the rinse cells.

9. Apparatus as claimed in any of claims 1 to 8, wherein an ultrasonic generator is operatively connected to the solvent cell; whereby, in use, the cleaning of electronic components is assisted by agitating the solvent and helping to remove particles from surfaces of the component.

10. Apparatus as claimed in any of claims 1 to 9, wherein heating means are provided for one or more 12 of the cells; whereby, in use, the solvent and/or the rinse water can be heated.

11. Apparatus as claimed in any of the preceding claims and contained in the one unit.

12. Apparatus for cleaning electronic components and the like and substantially as described with reference to or as shown by the Drawing.

13. Apparatus for cleaning electronic components and the like comprising a solvent container capable of containing a water-miscible solvent, at least one rinse container capable of containing water, an active filter capable of holding an absorptive medium for impurities precipitated in the rinse water, a water pump capable of circulating aqueous effluent from the or each rinse cell through the active filter to the solvent cell, a concentrator capable of separating the solvent and water from an aqueous effluent emerging from the active filter and means to apply solvent and rinse water to components to be cleaned.

14. Apparatus as claimed in claim 13, wherein the solvent container and the or each rinse container is an open topped cell; whereby, in use, components can be lowered for immersion in solvent or rinse water.

Apparatus as claimed in claim 13 and further comprising a conveyor for components; whereby, in use, components to e cleaned can be conveyed to and immersed in the solvent container and the or each rinse container.

16.

Apparatus as claimed in claim 13 and further comprising means to spray solvent and rinse water 13 onto components to be cleaned.

17. Apparatus as claimed in claim 16 and further comprising a conveyor for components; whereby, in use, components to be cleaned can be sprayed with solvent and rinse water as they are conveyed through the apparatus.

14- Amendments to the claims have been filed as follows 1 fAMMENDED} Apparatus for cleaningelectronic components and the like comprising:

i) a solvent cell to contain a water-miscible ii) iii) v) solvent; at least one rinse cell, fluidically isolated from the solvent cell and to contain rinse water; an active filter to contain an absorptive medium for impurities precipitated in the rinse water; a water pump connected in a water circulation system comprising the or each rinse cell and the active filter; and, a concentrator connectable between the active filter and the solvent cell and capable of separating the solvent and rinse water from the permeate emerging from the active filter; whereby, in use, the component to be cleaned is exposed to the solvent in the solvent cell and then to the rinse water in the or each rinse cell, the aqueous effluent being pumped from the rinse cell through the absorptive medium in the active filter, so as to remove any suspended impurities or precipitates therefrom, and back to the rinse cell; with the concentrator to separate the solvent from the rinse water and return it to the solvent cell.

2. {AMMENDED} Apparatus as claimed in claim 1; wherein the concentrator is permanently connected between the active filter and the solvent cell; whereby, in use, recovered solvent can continuously be returned to the solvent cell.

3.

Apparatus as claimed in claim 2; wherein the q : 1. ', is concentrator comprises a heated surface in a tank and means to deliver aqueous effluent across the surface; whereby, in use, water will be evaporated from the effluent and solvent will remain in the tank for return to the solvent cell.

Apparatus as claimed in any of claims 1 to 3 and further comprising a particulate filter in the water circulation system comprising the rinse cell, the absorptive filter and the water pump.

5. Apparatus as claimed in any of claims 1 to 4 and including a dryer to clean dried and rinsed electronic components.

Apparatus as claimed in any of claims 1 to 5, wherein the active filter includes a deionising resin bed; whereby, in use, ionic contaminants can be removed from the aqueous effluent.

7. Apparatus as claimed in claim 6 and including means to measure the resistivitity of aqueous effluent from the active filter; whereby, in use, the level of active filter contamination can be measured.

8. Apparatus as claimed in any of claims 1 to 7 and including two or more rinse cells provided in series connected so that, in use, water can flow serially from rinse cell to rinse cell, to be pumped through the active filter and back to the rinse cells.

9.

Apparatus as claimed in any of claims 1 to 8, wherein an ultrasonic generator is operatively connected to the solvent cell; whereby, in use, the cleaning of electronic components is assisted by agitating the solvent and helping to remove particles from surfaces of the component.

1 (0 10. Apparatus as claimed in any of claims 1 to 9, wherein heating means are provided for one or more of the cells; whereby, in use, the solvent and/or the rinse water can be heated.

11. Apparatus as claimed in any of the preceding claims and contained in the one unit.

12. Apparatus for cleaning electronic components and the like and substantially as described with reference to or as shown by the Drawing.

13. {DELETED} 14. {AMENDED} Apparatus as claimed in any of claims 1 to 12, wherein the solvent cell and the or each rinse cell is open topped; whereby, in use, components can be lowered for immersion in solvent or rinse water.

15. (AMENDED} Apparatus as claimed in any of claims 1 to 12 and further comprising a conveyor for components; whereby, in use, components to be cleaned can be conveyed to and immersed in the solvent cell and the or each rinse cell.

16. {AMENDED} Apparatus as claimed in any of claims 1 to 12 and further comprising means to spray solvent and rinse water onto components to be cleaned.

17. Apparatus as claimed in claim 16 and further comprising a conveyor for components; whereby, in use, components to be cleaned can be sprayed with solvent and rinse water as they are conveyed through the apparatus.

1 It -1