GB2243842A

GB2243842A - Circuit board cleaning

Info

Publication number: GB2243842A
Application number: GB9107753A
Authority: GB
Inventors: Ian Russell Cox
Original assignee: Electrolube Ltd
Current assignee: Electrolube Ltd
Priority date: 1990-04-12
Filing date: 1991-04-12
Publication date: 1991-11-13
Anticipated expiration: 2011-04-12
Also published as: GB9107753D0; GB2243842B

Abstract

A method for removing soldering flux and/or adhesive tape residues from a substrate, comprising the steps of: (a) applying to the substrate a solvent comprising at least one component selected from ether-containing terpenoid compounds; (b) rinsing the solvent and dissolved residues from the substrate; and (c) drying the rinsed substrate. The solvent may be 1,4-cineole, 1,8-cineole or eucalyptol. The solvent may additionally contain surfactant, saponifying agent, complexing agent or water. The surfactant may be an alcohol ethoxylate; the saponifying agent morpholine, amoethanolamine or triethanolamine; and the complexing agent EDTA.

Description

QC(J1T BOARD (IENN The invention relates to a method for the removal of soldering flux or adhesive tape residues fram a substrate, and to compositions for this and other cleaning purposes.

During the manufacture of printed circuit and wiring boards, soldering fluxes are initially applied to the board material to ensure firm, uniform bonding of the solder. Also, it is sometimes necessary to temporarily protect certain portions of the board from processing steps such as creating corrosion resistant gold connecting tabs at the board edges. This temporary protection is achieved by applying adhesive tape to susceptible areas. However when the tape is removed tape residues invariably remain. Non-removal of excess flux deposits and adhesive tape residues from the board will affect the efficiency of the electronic equipment and possibly cause circuit failure.

Although water soluble fluxes can be removed by spraying with an aqueous based cleaner at high pressure, water soluble flux is not the material of choice because it contains acids which attack the soldered joints, tracks and component leads.

It is found that the best solder pastes are formulated with rosin (water-insoluble) fluxes. These have traditionally been removed by using halogenated hydrocarbon solvents such as trichlorotrifluoroethane (CFC-113) and 1,1, 1-trichloroethane, but these solvents are ecologically and environmentally undesireable and dangerous. Recently, a solvent system has been used based on hydrocarbon terpenoid compounds such as a and -pinene, 6-terpinene, delta-3-carene, limonene and dipentene.

However these compounds and the resulting solubilized residues are difficult to remove from the substrate necessitating use of specialised and expensive equipment to give satisfactory results.

According to the invention there is provided a method for removing soldering flux and/or adhesive tape residues from a substrate, camprising the steps of (a) applying to the substrate a solvent comprising at least one component selected from ether containing terpenoid compounds ; (b) rinsing the solvent and dissolved residues from the substrate; and (c) drying the rinsed substrate.

The substrate to be cleaned is suitably exposed to said solvent (usually an aqueous solution containing up to 99 wt.

water) at temperatures from zero to 800C for sufficient time to solubilize the residues; treatment times of 1 minute or only a few mintues usualy suffice; treatment temperature may often be as low as 2O0C. Treatment may for example be by spraying, or by dipping, or imnersion in a static, forced circulation or ultrasonic agitation bath.

The solvent and solubilized residues can then be rinsed off (e.g. by dipping or forced flow), usually employing just water - preferably demineralized or deionized. The rinsed substrate can then be air and/or heat dried.

The preferred solvents comprise ether containing terpenoid compounds - the not preferred of which are the cyclic ether-containing terpanoids; of the latter, 1,4-cineole is a suitable example although 1,8-cineole is particularly preferred. The preferred solvents also comprise between 50 and 90% of water.

The preferred solvents used according to the invention are water- soluble. This facilitates rinsing and makes the cleaning process quick and efficient. The solvents used according to the invention are effective at removing tape and flux residues from substrates and have additional advantages in that they have a low inhalation toxicity. They also have major advantages over oammercially available terpenoid cleansing fluids based on limonene and orange oils in being much less flammable and in that the preferred solvents and the residues solubilized thereby are efficiently and simply rinsed from the treated substrate for example with water without the special and expensive equipment needed for use with previously proposed terpenoids.Conformal coating is usually possible inmediately after the drying step.

The solvent used according to the invention may also include one or more additives selected from surfactants, saponifying agents, oomplexing agents, and water.

Suitable surfactants include linear alkyl benzene sulphonates, or ethoxylates, linear or branched alcohol ethyoxylates or ethoxy sulphates, polysorbate esters and alkyl or dialkyl sulphono succinate compounds. Preferred surfactants are the alcohol ethoxylates. These particular compounds are biodegradable. The use of surfactants is beneficial to solubilize the ether-containing terpene in water; to reduce surface tension enabling easy penetration of the solvent under the components attached to the substrate; to aid the cleaning process by emulsification and to exert a rinse aid action by causing the rinsing water to sheet off. The latter effect also promotes drying.

Preferred saponifying agents include amino alcohols and ethers. Particularly preferred examples of these are monoethano lamine, triethano lamine and morpholine. The preferred agents are sufficiently volatile and/or soluble in the solvent camposition to be easily removed from the substrate. The preferred agents react with both natural and synthetic flux resins to assist in the solubilization of the flux resins by forming amine salts and soaps.

Camplexing agents may be chosen from any known oamplexing agents but preferable examples include MEDIA, NTA and other organic nitrogen polycarboxylates and benztriazole and its derivatives. The use of completing agents is beneficial for removing "white residue" which forms during flux removal and consists of aqueous insoluble salts of lead, tin and calcium, and for reducing corrosion of metals on prolonged immersion, or immersion at elevated temperatures.

The preferred solvent used in the invention comprises ethercontaining terpene and at least one other solvent component selected from 0 to 40% weight of surfactant; 0 to 20% by weight of saponifier, 0 to 5% by weight of cowplexing agent and 3 to 99% (preferably 5 to 99%) by weight of water.

A further preferred solvent used in the invention comprises ether-containing terpene and at least one other solvent component selected from 5 to 20% weight of surfactant, 0 to 20% by weight saponifier, 0 to 1% by weight of flexing agent, and 50 to 90% of water.

A particularly preferred solvent composition used according to the invention comprises about 8% by weight cyclic ether-containing terpenoid compound, about 1% by weight LAS 30, about 10% by weight IPA, about 8% by weight CD916, about 10% by weight itonoetbanolamine and about 63% by weight of demineralised water.

A further preferred solvent composition used according to the invention comprises about 4% by weight cyclic ether-containing terpenoid compound, about 2% by weight LAS 30, about 5% by weight IPA, about 7% by weight CD916, about 9% by weight mono- ethanolamine, and about 77% by weight of demineralised water.

The solvent according to the invention may be supplied commercially as a "concentrate" which can be diluted with water by the user.

The "concentrate" solvent preferably comprises about 17% by weight cyclic ether-containing terpenoid compound, about 9% by weight LAS30, about 22% by weight IPA, about 30% by weight CD916 and about 22% by weight ethanolamine. The preferred solvent oamposition is obtained by diluting one part of concentrate with three parts of deionised water.

The present invention also provides for the application of the solvent, (which comprises ether-containing terpenoid campound) to the substrate as a foam by aerosol. A method of the present invention using the solvent as a foam by aerosol comprises the steps of: a) applying said solvent to the substrate as a foam by aerosol, the solvent composition and propellant being chosen to be compatible and to generate a rapidly expanding aqueous foam; b) allowing the foam to contact with the substrate surface (e.g. for 2-5 minutes at room temperature) so that the flux and/or tape and/or solder paste residues react, dissolve and are lifted off; c) rinsing the substrate (e.g. with deionised water or aqueous alcohol blends - which can be applied as bulk, pump spray, trigger spray, aerosol or by bulk spraying); and d) drying the substrate (e.g. by air [static or airknife] or heat).

The nature of the foam is preferably such that it adheres to vertical surfaces, prolonging contact time to allow chemical reaction and dissolution of the residues to be removed.

The preferred propellants for use in the invention are preferably ozone-friendly hydrocarbon propellants such as butanes, propanes and mixtures thereof or alternative chemically compatible propellants (e.g. DME, F12).

propellants are not ozone friendly, and propellant 22 is preferably not used for reasons of chemical incompatibility.

The foamable cleaning ccmposition which may be used in the method of the invention comprises a compatible mixture of propellant, water, and at least one component selected from ether-containing terpenoid compounds, preferably with at least one material selected from surfactants, saponifying agents and cQmplexing agents.

The invention also provides a cleaning composition comprising water and at least one ether-containing terpenoid compound, and at least one material selected from surfactants, saponifying agents and completing agents. The invention further provides a cleaning ccmposition comprising water, at least one compound selected from ether-containing terpenoid compounds, and at least one material selected from surfactants saponifying agents and complexing agents. The preferred said component(s) and preferred said material ( s) in such cleaning compositions according to the invention, and their preferred proportions, are as set out above for the solvent used in accordance with the method of the invention.Cleaning compositions according to the invention are useful for a wide range of cleaning purposes, for example for cleaning the read/write heads of magnetic information storage devices and for cleaning hard surfaces in general.

A preferred solvent cooPosition for use as a read/write head cleaner comprises 0.1 - 1% by weight of ether-containing terpenoid compound, 0 - 5% by weight of surfactant, and 80 98% by weight of water.

Cleaning oompositions according to the invention are advantageous in that they can be used in the above-described simple 3-stage procedure (dip/spray, rinse, dry); in that they are either fully water miscible or form stable emulsions so that concentration of active ingredients is readily and infinitely variable; in that their low viscosity enhances their ease and speed of use; in that they may be employed at low temperatures, e.g. in that they are biodegradable and easily treated by conventional waste water treatment processes; and in that rinsing and drying are simple low cost and low energy operations.The compo6itions have great flexibility in that they can be employed satisfactorily on both synthetic and natural fluxes and for hard surface cleaning in general, the water present facilitating solution of ionic and water-soluble flux; and in that they can be applied in a wide variety of simple ways - spray or dip (open or closed, static or with agitation). They are efficient e.g. cleaning to MIL spec Nit P28809, and allow conformal coating immediately after rinsing and drying.They can be formulated to provide metal/component compatiblity, and show the important safety properties of being "ozone friendly" (in relation to stratospheric ozone depletion), biodegradable with high bioacceptability in waste water, and of low flammability (bulk and spray) and of having low inhalation toxicity.

Exmrrples The invention is further illustrated by the following Examples and with reference to Tables 1-6.

Table 1 shows solvent Formulations A-C expressed in % by weight; Table 2 shows the results obtained using method A to evaluate the removal of flux as determined by visual inspection under normal and UV light; Table 3 shows the results obtained using method B to evaluate the removal of flux using Formulation C of Table 1 in concentrated and diluted form; Table 4 shows the results obtained by using Method C to evaluate the removal of flux using Formulation B of Table 1; Table 5 shows aerosol Formulations E, F and G according to the invention; and Table 6 shows the results obtained using Method D to evaluate the removal of flux as determined by assessment of ionic residues with a Protonique Micro containator.

SSBIE 1 - Solvent Cbmpositions Printed circuit or wiring board cleaning Formulations A - C were prepared. Formulations A, B and C are according to the present invention. Formulations P and Q are ccmmercially available as solder and tape residue cleaners and are not according to the invention.

Formulations A to C give stable, homDgeneous clear solutions.

The use of or pinene or limonene in place of eucalyptol however did not give homogeneous mixtures. In Table 1 LAS 30 is 30% alkyl benzene sulphonate; CD916 is a nonionic surfactant and IPA is isopropylalcohol. Triethanolamine may be substituted for monoethanolamine, being equivalent in effect and even less toxic.

An evaluation of the ability of Formulations A to C from Table 1 and P and Q, (commercial products, blilticore Xersin 2085 and PC85 respectively) to remove flux was carried out using Method A.

MGllgX) A Step (i) - glass microscope slides were dipped into flux solution (Electrolube bulk flux) containing 0.01% Uvitex OB (to increase the sensitivity of the test) and hung to dry at roam temperature.

Further slides were coated (horizontal) with the flux solution as above and were then baked for 1 hour at 1500C.

Step (ii) - The flux coated microscope slides were immersed in 5% solutions of the said formulations at 500C or 200C for 1 minute. The slides were then rinsed with demineralized water and dried. Once dry each slide was examined for flux removal under normal and W light. The results are given in Table 2.

TABLE 1 Material A B C Eucalyptol 8.0 4.0 8.0 LAS 30 1.0 2.0 1.0 IPA 10.0 5.0 10.0 CD916 8.0 7.0 8.0 Monoethanolamine 10.0 5.0 Morpholine - - 10.0 - 0.02 Demin. water 63.0 76.98 63.0 IABLE 2 Immersion Temp. Immersion Tempo.

200C 500C 200C 500C A +++ +++ - (++) - (++) B +++ +++ (++) - (++) C +++ I I I - - (+44) +++ (+++) P + + + (+) - (+) Q tut +++ - (+++) +++ (+++) +++ Total removal ++ Partial removal/removable with mechanical wipe + Part removable with mechanical wipe - Not affected In the "baked flux" column of Table 2, the results in parentheses are those obtained by immersion in the solvent composition for 3 minutes.

Method B is a direct method for measuring the presence of conductive residues which may remain after a substrate has been cleaned. The results given in Table 3 relate to the cleaning ability of formulation C, in concentrated and diluted (5% aqueous) form.

METHOD B This method measures directly conductive residues left on the model PCB. The model boards were prepared as per UL 746C with a 75 um gap between the points or lines.

UL boards (cleaned in 113 trichloroethane and their resistance measured) were dip coated with flux and dried for 1 hr at 1500C. Resistance was measured and the flux coated boards were then subjected to the following cleaning method, no special equipment being required: (a) immersion at 200C for 2 minutes in an ultrasonic tank containing a concentrated solution of Formulation C for one of the boards, an aqueous dilution 5% of Formulation C for an other board, and 113 trichloroethane for another.

(b) rinsing with deionized water, (c) air drying (20 minutes) then heat drying (900C for 15 minutes).

The resistance was again measured for each of the cleaned boards.

The results are given in Table 3.

vaRrs 3 Cleaner 113 C (cony) C (5% aqueous) Trichloroethane Resistance (megohms x 10-2) Clean board 1200 800 4400 Flux Coated 1.6 4.0 0.16 Cleaned/air dried 27.2 96.0 1.6 Dried at 900C 1200 800 4400 The results show that C both in concentrated and dilute form returns boards to the initial state of cleanliness so long as a reasonable drying cycle is applied; C matches current product CFC 113 in performance.

METHOD c This method measures the cleaning effectiveness by measuring the conducivity of aqueous isopropyl alcohol contacted with "cleaned" printed circuit boards populated with surface mount devices (SMD). In addition, the maintenance of the effectiveness of the cleaning composition is demonstrated with increasing levels of flux contamination (to simulate build up of flux in the cleaning solvent as successive boards are cleaned).

a) SMD populated boards were pre-cleaned in 111 trichloroethane (2 mins sonication).

b) These were dip coated in a 10% solution of Frys R8-20 RMA in IPA and then air dried for 5 mins at 2000C.

c) The following cleaning protocol was used - 2 mins sonication (10-150C) in composition 'B' containing various flux concentrations - deionised water pressure rinse (20 secs) each side.

d) Cleanliness evaluation - equipment - Protonique contaminometer.

- 3 boards used for each level TABLE 4 Examples of results obtained - contamination in g NaCl equivalent per cm of board Solutions used Flux contamination Board Number level weight % (i) (ii) (iii) 1) o 0.39 0.25 0.36 2) 5.35 0.93 1.04 0.74 3) 3.40 0.58 0.38 0.50 4) 2.68 0.83 0.69 0.53 5) 1.34 0.64 0.50 0.55 All boards showed contamination level < 1.5 11 g Nacl/cm2 meeting MIL P28809.

MEEB) D This method comprises the following steps: 1) small printed circuit boards (about 8.7cm2 in area) populated with Surface Mount Devices were dipped in flux solution (rosin type). After air drying the flux was baked on for 5 munutes at 2000C; 2) The boards were cleaned by different aerosol sprays by spraying both sides until they were visually clean; 3) The cleaned boards were sprayed with a standard rinse solution of 30% isopropanol/70% water delivered as an aerosol; 4) The ionic contamination was determined conductimetrically using a Protonique Microcontarninmeter.

TABLE 5 Aerosol Compositions wt.

Material/Formula E F G Eucalyptol 4.00 4.00 4.00 LAS 30 0.50 0.50 0.50 Isopropanol 5.00 5.00 5.00 CD916 4.00 4.00 4.00 Monoethanolamine 5.00 5.00 5.00 EDTA 0.05 0.05 Demineralised water 77.45 75.45 73.45 SHAP40 4.00 6.00 8.00 Notes LAS 30 is a 30% alkyl benzene sulphonate CD 916 is a non-ionic surfactant IPA is isopropyl alcohol Triethanolamine or morpholine may be substituted for monoethanolamine SH P40 is a trade mark (SHELL) used on an aerosol propellant mixture of propane/butane with a pressure of 3.2 bar.

The amount of butane used should be ininbtsed to that just giving a good foam so as to minimise potential flammability problems when SHAP40 is lost from the foam. In this work a minimum of 3.0% butane was found necessary.

Best foaming is achieved by using appropriate aerosol hardware (valve, actuator).

In Table 6 the performance of aerosol formulation E is compared with that of standard aerosol sprays (using the same hardward delivery system) containing known cleaning agents (i) 113; (ii) 111/n-propanol; and (iii) iso-propanol.

TABLE 6 Cleaning Efficiency (measured by Protonique Microcontaminometer) Standard MIL P 28809A - 1.45-1.65 Pg equivalents of sodium chloride per an2.

Product Spray Time Amount of Product Cleanliness (visually clean) sprayed s g g NaCl/cm 113 Trichloroethane 600 660 > 11.00 111 Trichloroethane n-propanol 150 146 1.75 Isopropanol 200 190 1.71 E 2 2 0.73

Claims

CLAIMS: 1. A method for removing soldering flux and/or adhesive tape residues and/or solder paste residues from a substrate, comprising the steps of (a) applying to the substrate a solvent comprising at least one ocmponent selected from ether-containing terpenoid compounds; (b) rinsing the solvent and dissolved residues from the substrate; and (c) drying the rinsed substrate.
2. A method according to claim 1 wherein the solvent comprises cyclic ether-containing terpenoid compound.
3. A method according to claim 2 wherein the solvent comprises 1,4-cineole.
4. A method according to claim 2 or 3 wherein the solvent comprises 1,8-cineole.
5. A method according to any preceding claim wherein the solvent includes one or more additives selected from surfactants, saponifying agents, cQmplexing agents, and water.
6. A method according to claim 5 wherein the solvent contains 5-20% by weight of surfactant; 0-20% by weight of saponifier; 0-1% by weight of completing agent; and 50-90% by weight of water.
7. A method according to claim 5 or 6 wherein the solvent contains alcohol ethoxylate surfactant.
8. A method according to claim 5, 6 or 7 wherein the solvent contains saponifying agent selected from monoethanolamine, triethanolamine and morpholine.
9. A method according to any of claims 5 to 8 wherein the solvent contains coanplexing agent selected from EDTA, NTA and other organic nitrogen polycarboxylates.
10. A method according to any of claims 5 to 9 wherein the solvent is substantially as hereinbefore described under Formulation A, B, C, E, F or G.
11. A cleaning oomposition comprising water, at least one component selected from ether-containing terpenoid compounds and at least one material selected from surfactants, saponifying agents, and complexing agents.
12. A cleaning composition according to claim 10 or 11 which contains cyclic ether terpenoid.
13. A cleaning composition according to claim 12 which contains 1,4-cineole and/or 1,8-cineole.
14. A cleaning composition according to claim 11, 12 or 13 which contains alcohol ethoxylate surfactant.
15. A cleaning composition according to any claims 11 to 14 which contains saponifying agent selected fram mono- ethanolamine, triethanolamine and morpholine.
16. A cleaning composition according to any of claims 11 to 15 containing ccmplexing agent selected from MICA, NTA, any other organic nitrogen polycarboxylates, and benztriazole and its derivatives..
17. A cleaning composition according to any of claims 11 to 16 containing 50 to 90 wt.% water, up to 30% ether-containing terpene, up to 40 wt.% surfactant, up to 20 wt.% saponifier and optionally up to 1 wt.% complexing agent.
18. A cleaning composition according to any of claims 11 to 17 which comprises a propellant which is compatible with the cleaning composition.
19. A cleaning composition according to claim 18 containing 3 to 99 wt.% water, up to 40 wt.% surfactant, up to 20 wt.% saponifier and optionally up to 5 wt.% completing agent.
20. A cleaning composition substantially as hereinbefore described under Formulation A, B, C, E, F, or G.