Note: Descriptions are shown in the official language in which they were submitted.
WO 93/13246 ~7~ 1. 2 S ~ è~ PCT/EP92/03017
- ~
METHOD AND COMPOSITION FOR CLEANING ARTICLES
The present invention relates to a method of
cleaning articles, and to a cleaning composition for use
in the method. -
v 5 In the manufacture of printed circuit boards
. (PCBs), it is usual for soldering flux to be applied to
the boards to promote strong bonding of the solder to the
board~ The flux and solder may be applied, for example,
by the wave soldering method or the reflow soldering
:, 10 meth~d. After soldering, flux remains on the boards.
;. .
That residual flux must be removed in order to reduce the
possibility of early circuit failure.
:The fluxes used in the manufacture of electronic
components, for example, PCBs, using a soldering
:~ 15 technique are generally rosin-containing fluxes or
synthetic water-soluble fluxes. Rosin-containing fluxes
include rosin mildly activated (RMA~ and rosin activated
(RA) fluxes, which are obtained by activation of a rosin-
containing flux using, for example, organic acids,
amines, amides or halogen-containing compounds. Many of
the activating materials decompose on soldering thus
giving rise to inorganic substances that can damage the
electronic components. The residue to be removed thus
comprises a combination of rosin molecules and inorganic
substances.
. In many previously used methods for defluxing
ar icles after soldering, the residual flux has been
`removed using halogenated hydrocarbon solvents. It has
: `,-~.
CONFIRMATION COPY
WO 93t13246 PCI`~EP92/03017
212~1J~ t.~
become recognised in recent years, however, that
these solvents have a particularly harmful effect on the
environment. Further, because of their physical
properties, special requirements are required in their
storage, handling and disposal. It is therefore
desirable to avoid the use of halogenated hydrocarbon
solvents, if possible.
European Patent Specification No. 416,763 discloses
compositions for cleaning dirty articles, for example,
, 10 PCBs; comprising terpene hydrocarbons or other non-
halogenated solvents. After the cleaning step, remainingtraces of solvent are said to be removed azeotropically,
by forming an azeotrope between the solvent and an
aqueous medium, the azeotropic mixture being evaporated
from the surface of the article. Optionally, a low
boiling organic solvent, for example a ketone, amine,
ether or alcohol may be included in the cleaning
composition to promote formation of an azeotrope. The
low boiling organic solvent, if presènt, is preferred to
be a C3 to C4 alcohol.
Japanese Patent Specification No. 3-6300 discloses -;
the use of an oleophilic detergent comprising a terpene
hydrocarbon selected from lOC monoterpenes to l5C sesqui-
terpenes, with turpentine oil and a surfactant. The
composition may further contain an alcohol (the only
example given being a C3 alcohol), ether, ketone, ester,
aromatic compound or water.
US Patent Specification No. 4,983,224 discloses a
WO93/13246 ~1~?~ ~ 6 ~ PCT/EP92/030~7
cleaning composition comprising a terpene or terpenol, a
surfactant and an aprotic solvent, for example, DMF or
DMSO.
European Patent Specification No. 120,~19 discloses
a cleaning composition for removing wax from electronic
components, the composition containing halogenated or
non-halogenated hydrocarbon, a fluorinated alcohol having
at least two fluorine atoms and, optionally, a further,
: polar, organic solvent. The hydrocarbon may be, inter
alia, petroleum ether. The further polar organic solvent
.
may be, for example, an alcohol. As alcohols there are
proposed aliphatic, cyclic and aromatic alcohols that in
each cas~`have seven or fewer carbon atoms.
British Patent Specification No. 2,175,004 discloses
a oleaning composition for removing dirt and grease from
metal and plastic surfaces, the composition containing
from 85 to 97 parts by weight of a non-aromatic
hydrocarbon including aliphatic and/or cyclo-aliphatic
compounds, from 3 to 15 parts by weight of alkylated
aromatic substances containing at least one C8 to C18
alkyl group and, in a preferred form, from 0.1 to 1 part
by weight of an additive which renders the composition
more incompatible with water, so facilitating separation
from water after the cleaning step. The additive may be
selected from aliphatic alcohols having from 8 to 20
carbon atoms, ether derivatives of alkylene glycols and
hydroxycarboxylic acids having more than 8 carbon atoms. -
: British Patent Specification No~ 1,524,448 discloses
~' ~
WO93/132~ PCT/EP92/03017
2 1 2 ~
a cold cleaner for removing oily and fatty contaminations
from surfaces. The composition may contain a mineral oil
fraction, which is preferred to be a mostly paraffinic or
naphthenic fraction, and saturated or unsaturated
aliphatic alcohols or alicyclic alcohols with from 6 to
20 carb~n atoms and/or fatty acids, and a sulphosuccinic
acid diester. As alcohols, unsaturated alcohols are said
to be preferred.
International Patent Specification No. W0 87/00209
disckoses a method of cleaning rosin flux or adhesive ~-
tape residue from printed circuit and/or wiring boards,
in which boards are contacted with a composition
containing a terpene, optionally in combination with a ~-
surfactant that is capable of emulsifying the terpene.
European Patent Specification No. 412,475 discloses
a cleaning composition for cleaning,PCBs, the
composition containing a dibasic ester and a hydrocarbon
solvent other than a terpene~ As hydrocarbon solvents
are proposed petroleum derived solvents, for example,
mineral spirits, naphthas and aromatics. The composition
may contain a further component, for example a non-ionic
surfactant, for improving the miscibility of the dibasic `
ester and hydrocarbon solvent.
European Patent Specification No. 104,633 discloses
a method of cleaning PCBs in which the boards are
immersed in an azeotropic liquid solvent. The azeotropic
liquid may contain a low molecular weight alcohol, for
example, a C3 or C4 alcohol, together with a hydrocarbon
WO93/13246 ~1 2 ~ 9 ~ ~ PCT/EP92/03017
of relatively low molecular weight, for example,
cyclohexane or heptane.
European Patent Specification No. 302,313 discloses
a method of cleaning objects in which the objects are
treated in a closed container with an azeotropic mixture
of water and a further solvent, for example, methylene
chloride, trichloroethylene or tetrachloroethane
The present invention provides a process for
cleaning an article comprising contacting the article
10 wi'ch
' (i) a hydrocarbon-containing fluid comprising one or
more hydrocarbons selected from C8 to C15 paraffinic
and naphthenic hydrocarbons and having an aromatics
~ content of not more than 8% by weight, based on the
;: 15 combined aromatics and hydrocarbon content of the
fluid, :
(ii) an alcohol-containing fluid comprising one or more
alcohols selected from C5 to C15 straight-chain or
brànched-chain, saturated aliphatic alcohols, :.
the fluids being substantially free of any halogen-
containing organic compound and component (ii)
representing at least 5% by volume, based on the total -~
hydrocarbon and alcohol content, when the process
comprises contacting the article with a liquid mixture
comprising components (i) and (ii).
Advantageously, the fluid or fluids contain not more
than 5 ppm of halogen.
The article may be contacted sequentially with a
WO93/13246 PCT/EP92/03017
~ 1 2 ~ 6
hydrocarbon-containing fluid and an alcohol-containing
fluid. Preferably, however, the article is contacted
with a liquid mixture of the said fluids the said mixture
comprising from 75 to 95 parts by volume of one or more
hydrocarbons selected from C8 to C15 paraffinic and
naphthenic hydrocarbons, and from 5 to 25 parts,
preferably from 8 to 15 parts, by volume of one or more
alcohols selected from C5 to C15 straight-chain or
branched-chain, saturated aliphatic alcohols. It will be
appreciated that the aromatics content of the liquid
mixture will be not more than 8~ by weight based on the
combined aromatics and hydrocarbon content of the
mixture.
Advantageously, the hydrocarbon-containing fluid is
a distillation fraction obtained in the distillation of -~
.
petroleum. The hydrocarbon-containing fluid preferably
contains from 0.5 to 2 parts by volume of normal and iso-
paraffins per part by volume of naphthenes. Preferably,
the amount of aromatics, if present, does not exceed 2%,
and more preferably does not exceed 1%, by weight, based
on the total weight of hydrocarbons and aromatics. For
example, the hydrocarbon-containing fluid may contain
approximately 55 parts by volume of normal and iso-
paraffins, and approximately 45 parts by volume of
naphthenes, with less than 1% by weight, based on the
total weight of the fluid, of aromatics.
The distillation boiling range of the hydrocarbon-
containing fluid is preferably within the range of from
.~ ~
WO93/13246 2 ~ PCT/EP92/03017
lSO C to 260 c at atmospheric pressure.
The alcohol-containing fluid, which may
advantageously contain alcohols selected from C6 to C8
alcohols, preferably comprises a mixture of aliphatic
primary alcohols which may be linear or branched. The
distillation boiling range of the alcohol-containing
fluid is preferably within the range of from 150-C to
3lO-C at atmospheric pressure.
In the cleaning process, the article may be
;
contacted with the hydrocarbon and alcohol components by
immersion in the liquid components or a liquid mixture
thereof, either without or, more preferably, with
ultrasonic agitation, by spraying, by contacting the
article with vapour under conditions such that
15~ condensation occurs, or by a combination of the said
methods. If the article is contacted sequentially with
~tbe hydrocarbon-containing fluid and the alcohol-
containin~ fluid, the article may be contacted first with
either of the fluids. The fluids or mixture with which
the article is contacted may be at a temperature o~ from
ambient temperature to 90 C, more preferably at a
temperature of 40 to 50 C. The cleaned article may then
be dried in air, preferably in hot air.
Optionally, the article may be contacted with a
detergent solution and rinsed with water to remove the
detergent solution before drying.
The detergent solution may comprise an alkylbenzene
æulphonate and an alkylphenol alkoxylate, for example, an
.
WO93/13246 PCT/EP92/03017
212~9~
alkylphenol ethoxylate. The alkyl groups of the alkyl-
benzene sulphonate and the alkyl phenol alkoxylate may in
each case advantageously be an aliphatic, cyclic or
alicyclic alkyl group having from 8 to 14 carbon atoms.
The detergent solution may, for example, be a mixture of a
dodecylbenzene sulphonate and a dodecylphenol ethoxylste.
After the article has been contacted with detergent
solution, residual detergent may expediently be removed
by rinsing with water, preferably with deionised water.
-The application of deterqent solution and subsequent
. rinsing assist the removal of the potentially harmful
inorganic substances that may be present in the residual
flux.
The article is preferably an electronic component,
more especially a PCB.
While the method of the invention may be used with
particular advantage in the cleaning of articles that
have been soldered with the use of a rosin-containing
flux, the method may also be ~sed in the cleaning of
articles that have been soldered with the assistance of
synthetic water-soluble fluxes.
The invention further provides a composition for
cleaning articles, comprising:
(i) from 75 to 95 parts by volùme of a distillation
fraction obtained by distillation of petroleum, the
said fraction containing not less than 92%, prefer-
ably not less than 99~, by weight, based on the
total weight of the fraetion, of hydrocarbons
WO 93~13246 f.~ PCr/EP92/03017
selected from c8 to c15 paraffinic and naphthenic
hydrocarbons; and
(ii) from 5 to 25 parts by volume of one or more alcohols
selected from C5 to C15 straight-chain or branched-
chain, saturated alcohols,
the composition being substantially free of any halogen-
containing organic compound.
The process of the invention is particularly
advantageous in the removal of flux residue after
soldering. The use of a hydrocarbon-containing fluid and
. .
an alcohol-containing fluid enables excellent removal of
flux residue to be attained without the use of any ~
~halogenated solvent. It is thought that the advantageous -
cleaning effect is obtained because, as a result of using `
a combination of a polar solvent and a non-polar solvent,
both polar and non-polar components of the flux residue
are readily dissolved. By selecting hydrocarbon
components and alcohol components within the respective
carbon number ranges specified, the dissolution of rosin
molecules is enhanced. The use of mixtureæ of
hydrocarbons and/or mixtures of alcohols also promotes
dissolution of the rosin molecules.
The solvents and solvent mixture used in accordance
with the invention enable the use of halogen-substituted
organic compounds, which are known to have ozone
depleting properties, to be avoided, while excellent
cleaning i8 obtainable. Further, the mixture has low
toxicity and a high flash point so that it is relatively
WO93/13246 PCT/EP92/03017
2 1 ~ 1 o
safe to use and complicated handling procedures are
unnecessary. Moreover, it is non-corrosive to materials
generally used in the manufacture of PCBs. `
The following Examples illustrate the invention:
; 5
:; '
Example l
Defence Standard 59-47 combs and circuit boards were
~ :
~ soldered by one of the following three methods:
.:: `: ~ 10
i
(a) Liquid F~uxes
The board or comb was wave soldered at 250 C using
63/37 (tin/lead~) alloy, at a conveyor speed of l.5 meter
per min. The upper side of the board or comb was
5~; ~preheated to~about 9O C prior to soldering. The flux was
applied using a brush. In each case either a RMA, RA, a
water soluble synthetic or a no clean liquid flux was
used. ("No clean" fluxes are fluxes that can, at least
in the case of lower ~rade electronic parts, be used
without any need for subsequent cleaning.)
(b) Solder Creams
The cream used was of AAS powder at 86% metal, with
a 62% tin content. The cream was applied to the board or
comb by manual screen printing and reflowed by heating in
a BTU infrared oven. In each case either an RMA cream
flux or a "no clean" synthetic water-soluble cream flux
was used.
,
W093~13246 PCT/EP92/03017
2 ~. 2 '~
11
(c) Flux Cored Wire
The board or comb was hand soldered with 60/40
(tin/lead), melting point 362 C, 16 SWG 5-core, solder
containing a RA flux, at a bit temperature of 360 C.
~'~
. .:
Eight soldered printed circuit boards and eight
soldered combs were cleaned with a cleaning composition ~.~
containing 10 parts by volume of isomeric cq, C7 and C8 -
~ ~ .
, ~10 alcohols and 90 parts by volume of a hydrocarbon fluid
consisting of Cll to C13 paraffinics and naphthenics.
Certain properties of the mixture were determined and :
: .,
~ we~re as follows:-
~ .
TEST MEASUREMENT RESULT
: : . METMOD
Distillation ASTM D86
~IBP 182 C
: 50% 213-C
FBP 238 C
Flash Point, PMCC ASTM D93 74 C
Density at 15 C ASTM D40520.7924g/cc
Viscosity at 25 C ASTM D4452.21 cSt
IBP and FBP represent the respective temperatures at
which boiling commences and finishes. PMCC means Pensky-
Martens closed cup.
Each soldered board or comb was individually cleaned
.
in 500 ml of the cleaning composition under ultrasonic
:~ agitation at 45-C.
WO93/13246 PCT/EP92/03017
2~ 12
The soldered board or comb was then rinsed by immer-
sion in a detergent solution containing lO% by vo~ume of
a mixture of dodecylbenzene sulphonate and dodecylphenol
e~hoxylate in deionised water. The board or comb was
then rinsed in deionised water and dried in hot air. ~;
Examination for residual ionic contamination was ~
.. : .
performed on the cleaned board or comb individually in a
Kenco Omegameter for 15 minutes using a set volume of
test solvent composed of 75/25 v/v isopropanol/deionized
water; A series of unsoldered boards and combs were also
,
.
tested to provide a baseline for the purpose of com-
parison. The results are shown in Table I, in which the
ionic contamination level is the amount of ionic material
, .
relative to a baseline determined by measuring the
average contamination of a number of unsoldered combs and
boards.
Table I
~ . _ _ ___ ~
FluxIonic oo~ ration LF rel ~Yg NaCl/sq. in)
Uncleaned Cleaned
._ _
1. No clean liquld 4.2 3.2
. .. ~
2. RM~ liquid 6.0 3.2
. _
3. Synthetic liquid ll0.0 7.0
4. No clean synthetic 6.6 3.2
.
5. RA liquid 27.0 5.6
..... .. ~
~ 6. RM~ cream 19.3 S.O
, : ... . ...
n~ 7. No clean synthetic c~m 25.8 6.6
~ _ . ..
~ 8. RA wire 42.5 3.6
WO93/13246 PCT/EP92/03017
2 ~
13
The surface insulation resistance (SIR~ of the
boards and combs was also determined. For the SIR test,
the initial insulation resistance of each board or comb
was measured using a voltage of 500 V DC for l minute
prior to placing each board or comb in a humidity chamber
at 40 C, 90% relative humidity (RH) for 96 hours. The
SIR was then measured again under the humid conditions
(90% relative humidity at 40 C) using 500 V DC. The
results of the SIR test are given in Table II.
-The results demonstrate that effective cleaning of
. residual soldering fluxes is achieved, with ionic
contamination levels well below the MI~ P-28809A
;;~
requirement of 14~g NaCl/sq. inch (2.2 ~g/cm2)
equivalent. The results also indicate that, after the
cleaning step, the resistivity of the boards and combs is
approximately the same as, or lower than, the resistivity
of the uncleaned boards. Thus, the cleaning step has no
detrimental effect on insulation resistance. In many
cases, SIR is improved after cleaning. The cleaned
boards also perform satisfactorily in the SIR test after
being subjected to an atmosphere of RH 90% at 40 C for 96
hours.
WO 93/13246 PCI/EP92/03017
21269~9 14
Table I I
Surfaoe Insulation R~sistar~e
Flux - ~
Initi~l (~DD6) 96 h, 40~C, 90% R~ (cl~)
.. . ~
1. No clean ur~ l~ 2.30 x 1013 1.17 x 1ol2
id c1ean1 7.90 x 1012 1.l6 x 1012
.. _ _
2. RMP. liq~id ~ 1.03 x 1013 1.18 x 101~
cleaned 1.17 x 1013 3.63 x 1012
3. Synthet~c -- 2.20 Y 107 4.ss X 1o6 - ~~-
liqui~ clean~ 1.23 x 1013 1.32 x 1ol2
4~ ~ 1.19 x 1013 1.88 x 10~2
hetic cle~ 9.93 x 1012 1.97 x 1o~2
:
5. ~ id ur~lear~ 1.0? x 1013 1.14 x 1012
cleaned 1.43 x 1013 1.12 x lol2
. _
6. ~ ~c1ear~1 1.80 x 1013 3.67 x 1ol2
clean~d 1.70 x 1013 3.43 x 10
~ : .. _ .
7. ~o c1ean unc1eaned 1.87 x 1013 9.70 x 1011
synthetic c~oclearYYI 1.60 x 1013 1.3Q x lo
. .......... , ................... ... ... _ . -
8. RA wire ~c1eaned 1.37 x 1013 7.70 x lolO ;-
;~ cleaned 1.19 X 1013 3.60 x loll
:, .
. .
: :
.
. . . .
WOg3/13246 2 ~ ?~ j~ PCT/EP92/03017
Example 2
A cleaning mixture containing 5 parts by volume of
isomeric C6 and C7 alcohols and 95 parts by volume of C10
to C13 paraffins and naphthenes was prepared.
Physical data relating to the mixture were deter-
mined as follows:
. _.
TEST MEASUREMENT KESULT
METHOD
DISTILLATION ASTM D86
, IBP- 165.0 C
50% 192.0-C
FBP 212.0 C
FLASH POINT, PMCCASTM D93 60.O C
: . .
DENSITY AT 15 C ASTM D4052 0.7796g/cc
~:
ANILINE POINT ASTM D611 65.5 C
SAYBOLT COLOR ASTM D156 + 30
To evaluate the efficiency of rosin removal from the
~ .
~ circuit boards, six PCBs coated with activated fluxes
were cleansed, each PCB being cleansed individually in
100 ml of cleaning mixture at 45 C, with ultrasonic
agitation, for five minutes.
After cleaning, the specimen was removed, dried and
the residual rosin remaining on the board extracted by
100 ml of isopropyl alcohol (IPA).
The rosin content of the IPA was determined by
spectrophotometry at wavelength 242 nm.
For comparison purpose, a halogenated cleaning fluid
containing 93 parts by volume of CFC-113 and 7 parts by
volume of methanol was prepared and six PCBs coated with
WO93/13246 PCT/EP92/03017
2I2~9~ 16
activated fluxes were cleansed individually by the
condensing vapour (b.p. 48 C) of the halogenated fluid
for five minutes in a closed container. Upon cleansing,
the specimens were treated as in the case of the
hydrocarbons/alcohols cleaning. The results are given in
Table III, which indicates that an average cleaning
efficiency (that is, % rosin removal) of 87% is obtained
using the hydrocarbon/alcohol mixture, compared with only
61% using the halocarbon solvent system.
~: ' 10
Table III
PCB SAMPLES :-
% rosin
1:5 removal l 2 3 4 5 6 ~
::: ~-
Hydrocarbon/ sO.l 86.7 88.8 85.4 85.7 87.1
~alcohol
mixture
: 20~ : ~ _
Halocarbon/ 61.3 61.8 65.7 54.2 63.5 60.9
alcohol
: mixture
~ 25
: ~ :
~-
: ~
