Soldering flux

A soldering flux comprising a bis (2-oxazoline) compound, a dithiol compound, an organic carboxylic acid compound and an activator which does not require post-soldering cleaning and, yet, does not cause corrosion of the base metal or deterioration of electrical characteristics and helps to clear the statutory regulations on the use of chlorofluorohydrocarbons. A soldering flux comprising, in addition to the above components, an organic solvent, a thermoplastic resin or/and an epoxy group-containing compound.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a soldering flux. 
2. Description of the Related Art 
The great majority of soldering fluxes heretofore available comprise a 
rosin or rosin-modified resin supplemented with an activator consisting of 
an organic acid and a hydrohalic acid salt. 
However, these fluxes leave residues on the substrate surface after 
completion of the soldering operation and may cause cracks on cyclic 
heating and cooling and tends to give false "rejects" in the incircuit 
test because of the failure of the contactor pin to penetrate down to the 
printed circuit of the board. Furthermore, on moisture absorption and 
temperature gain, these residues tend to cause corrosion of the base metal 
and deterioration of the electrical characteristics of printed circuit 
boards. 
Therefore, it is common practice to perform cleaning with a 
chlorofluorohydrocarbon to remove residues of the flux after the soldering 
operation. 
However, since the cleaning agent chlorofluorohydrocarbons are under 
rigorous environmental control today, cleaning with them is now a 
virtually forbidden procedure. 
OBJECTS OF THE INVENTION 
The object of this invention is to provide a soldering flux free of the 
above-mentioned problems, that is to say a flux not requiring 
post-soldering cleaning and yet withstanding cyclic heating and cooling, 
being compatible with the in-circuit test, with minimum risks of base 
metal corrosion due to elevation of temperature and humidity and of the 
aging of electrical characteristics and conforming to the statutory 
regulations over the use of chlorofluorohydrocarbons through omission of 
the cleaning operation. 
SUMMARY OF THE INVENTION 
This invention relates to a soldering flux comprising a bis(2-oxazoline) 
compound, a dithiol compound, an organic carboxylic acid compound and an 
activator. 
DETAILED DESCRIPTION OF THE INVENTION 
The bis(2-oxazoline) compound for use in this invention can be represented 
by the general formula 
##STR1## 
wherein R.sub.0 represents a carbon-to-carbon bond or a divalent 
hydrocarbon residue; each R.sub.1, R.sub.2, R.sub.3 and R.sub.4 
individually and independently represent a hydrogen atom, an alkyl group 
or an aryl group. Where R.sub.0 is a hydrocarbon residue, it may be an 
alkylene group, a cycloalkylene group or an arylene group. Where R.sub.0 
represents a carbon-to-carbon bond, the bis(2-oxazoline) compound may for 
example be 2,2'-bis(2-oxazoline), 2,2'-bis(4-methyl-2-oxazoline), 
2,2'-bis(5-methyl-2-oxazoline), 2,2'-bis(5,5'-dimethyl-2oxazoline), 
2,2'-bis(4,4,4', 4'-tetramethyl-2-oxazoline) or the like. Where R.sub.0 
represents an alkylene group, the bis(2-oxazoline) compound includes 
1,2-bis(2-oxazolin-2-yl)ethane, 1,4-bis(2-oxazolin-2-yl)butane, 
1,6-bis(2-oxazolin-2-yl)hexane and 1,8-bis(2-oxazolin- 2-yl)octane, among 
others. Where R.sub.0 is a cycloalkylene group, there can be mentioned 
1,4-bis(2-oxazolin-2-yl)cyclohexane, among others. Where R is an arylene 
group, the bis(2-oxazoline) compound includes 
1,2-bis(2-oxazolin-2-yl)benzene, 1,3-bis(2-oxazolin-2-yl)benzene 
(hereinafter referred to briefly as 1,3-PBO), 
1,4-bis(2-oxazolin-2-yl)benzene, 1,2-bis(5-methyl-2-oxazolin-2-yl)benzene, 
1,3-bis(5-methyl-2 -oxazolin-2-yl)benzene, 
1,4-bis(5-methyl-2-oxazolin-2-yl)benzene, 
1,4-bis(4,4'-dimethyl-2-oxazolin-2-yl)benzene and so on. The most 
preferred of them all is 1,3-PBO. These bis(2-oxazoline) compounds can be 
used independently or in combination. 
The dithiol compound for use in this invention may for example be an 
aliphatic dithiol compound or an aromatic dithiol compound. 
The aromatic dithiol compound may for example be an aromatic dithiol 
compound or a heteroaromatic dithiol compound. 
The dithiol compound is represented by the general formula 
EQU HS-R.sub.5 -SH 
wherein R.sub.5 represents an aliphatic hydrocarbon residue, an aromatic 
hydrocarbon residue or a heteroaromatic residue. The aliphatic dithiol 
compound includes ethylene glycol bisthioglycolate and butylene glycol 
bisthioglycolate, among others. The aromatic dithiol compound includes 
those of 6-14 carbon atoms such as 4,4'-thiobisbenzenethiol, (hereinafter 
referred to briefly as MPS) bis(4-mercaptophenyl)ether and 
3,4-dimercaptotoluene, among others. The heteroaromatic dithiol compound 
includes those of 3-12 carbon atoms such as 
6-dibutylamino-l,3,5-triazine-2,4-dithiol, 
6-aminophenyl-1,3,5-triazine-2,4-dithiol, thiadizole and so on. Preferred 
are MPS and 6-dibutylamino-l,3,5-triazine-2,4-dithiol. In lieu of such 
dithiol compounds, aromatic mercaptocarboxylic acids such as 
thiosalicyclic acid can likewise be employed. These compounds can be used 
independently or in combination. 
The organic carboxylic acid compound for use in this invention includes 
organic mono-, di- and polycarboxylic acids. The organic carboxylic acid 
may contain hydroxyl groups or double bonds. These compounds serve as the 
activator as well. 
The organic monocarboxylic acid includes aliphatic monocarboxylic acids of 
6-21 carbon atoms, such as caproic acid, enanthic acid, capric acid, 
pelargonic acid, lauric acid, myristic acid, palmitic acid, stearic acid, 
arachic acid, behenic acid, etc. and aromatic monocarboxylic acids of 7-11 
carbon atoms, such as benzoic acid, salicylic acid, anisic acid, 
anthranilic acid, p-toluenesulfonic acid, 5-sulfosalicylic acid, 
4-sulfophthalic acid, sulfanylic acid, naphthalenecarboxylic acid and so 
on. 
The aliphatic dicarboxylic acid includes those of 2-34 carbon atoms, such 
as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, 
pimellic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic 
acid, dimer acid, eicosanedioic acid and so on. The aromatic dicarboxylic 
acid includes those of 6-13 carbon atoms, such as phthalic acid, 
isophthalic acid, naphthalenedicarboxylic acid, 
diphenylsulfonedicarboxylic acid and diphenylmethanedicarboxylic acid, 
among others. These species can be used independently or in combination. 
The organic polycarboxylic acid includes those of 4-8 carbon atoms, such 
as trimellitic acid, trimesic acid, pyromellitic acid, 
butane-1,2,3,4-tetracarboxylic acid and so on. 
The hydroxyl-containing organic carboxylic acid includes hydroxycarboxylic 
acids of 3-18 carbon atoms, such as lactic acid, citric acid, tartaric 
acid, levulinic acid, 12-hydroxystearic acid, etc. The double 
bond-containing organic acid includes those of 3-36 carbon atoms such as 
acrylic acid, methacrylic acid, fumaric acid, maleic acid, and so on. 
These carboxylic acids can be used independently or in combination. Among 
these organic carboxylic acid compounds, dicarboxylic acid compounds are 
particularly advantageous in that tough residual films can be obtained. 
As an activator for use in this invention, hydrohalic acid salts of various 
amine compounds can be mentioned. Among such amine compounds are aliphatic 
primary amines, aliphatic secondary amines, aliphatic tertiary amines, 
aliphatic diamines, triamines and polyamines, alicyclic amines, aromatic 
amines, heterocyclic amines, amino alcohols and hydrazine compounds. The 
aliphatic primary amine includes those of 1-8 carbon atoms, such as 
methylamine, ethylamine, n-propylamine, n-butylamine, isobutylamine, 
sec-butylamine, t-butylamine, n-amylamine, sec-amylamine, 
2-ethylbutylamine, n-heptylamine, 2-ethylhexylamine, n-octylamine, 
t-octylamine and so on. The aliphatic secondary amine includes those of 
2-16 carbon atoms, such as dimethylamine, diethylamine, di-n-propylamine, 
isopropylamine, diisopropylamine, di-n-butylamine, diisobutylamine, 
diamylamine, dioctylamine and so on. The aliphatic tertiary amine includes 
those of 3-24 carbon atoms, such as trimethylamine, triethylamine, 
tri-n-propylamine, tri-n-butylamine, triisobutylamine, tri-n-amylamine, 
tri-n-octylamine and so on. 
The aliphatic diamine, triamine and polyamine include compounds of 2-8 
carbon atoms, such as ethylenediamine, 1,2-propylenediamine, 
1,3-diaminopropane, diethylenetriamine, methylaminopropylamine, 
dimethylaminopropylamine, triethylenetetramine, 1,6-hexamethylenediamine, 
3-diethylaminopropylamine, N-2-hydroxyethylenediamine, 
tetraethylenepentamine and so on. 
The alicyclic amine includes compounds of 6-12 carbon atoms, such as 
cyclohexylamine and dicyclohexylamine, among others. 
The aromatic amine includes compounds of 6-14 carbon atoms, such as 
aniline, methylaniline, dimethylaniline, diethylaniline, butylaniline, 
N,N-di-butylaniline, amylaniline, t-amylaniline, N,N-diamylaniline, 
N,N-di-t-amylaniline, o-toluidine, diethylbenzylamine, benzylamine, 
o-chloroaniline and so on. 
The heterocyclic amine includes compounds of 5-9 carbon atoms, such as 
pyridine, .beta.-picoline, 2,6-lutidine, isoquinoline, quinoline, 
pyrrazole, .alpha.-picoline, .gamma.-picoline, 2,4-lutidine and so on. 
The amino alcohol includes compounds of 2-6 carbon atoms, such as 
monoethanolamine, diethanolamine, triethanolamine, monoethylethanolamine, 
mono-n-butylethanolamine, dimethylethanolamine, diethylethanolamine, 
ethyldiethanolamine, n-butyldiethanolamine, di-n-butylethanolamine, 
triisopropanolamine and so on. 
The hydrazine compound include compounds of 0-7 carbon atoms, such as 
hydrazine, phenylhydrazine, .beta.-acetylphenylhydrazine, 
2-hydroxyethylhydrazine and 1,1-dimethylhydrazine, among others. 
The hydrohalic acid salt includes hydrofluorides, hydrochlorides, 
hydrobromides, etc. Preferred are diethylamine hydrochloride, diethyl 
amine hydrobromide, ethylamine hydrochloride, ethylamine hydrobromide, 
2-ethylhexylamine hydrochloride and 2-ethylhexyl amine hydrobromide. 
Regarding the proportions of the respective components for use in this 
invention, the mol ratio of the dithiol compound and organic carboxylic 
acid, taken together, to the bis(2-oxazoline) compound is 0.5-1.5 and 
preferably 0.95-1.05. The amount of the organic carboxylic acid compound 
relative to the dithiol compound is 5-95 mol % and preferably 10-50 mol %. 
The proportion of the activator based on the solid matter of the flux is 
0.05-50 weight % and preferably 5-30 weight %. The hydrohalic acid salt 
component of the activator is not more than 10 weight % and preferably 
0.5-5 weight %, based on the total solid matter of the flux. 
Where the flux is to be used in a liquid form, an organic solvent can be 
added. The solvent includes ketones such as acetone, methyl ethyl ketone, 
etc., alcohols such as methanol, ethanol, isopropyl alcohol, 
methylcellosolve, ethylcellosolve, butylcellosolve, 1-methoxy-2-propanol, 
carbitol, butylcarbitol, etc. and aromatic solvents such as toluene, 
xylene and so on. These solvents can be used independently or in 
combination. 
The organic solvent is used generally in the range of 20-99.5 weight %. If 
the proportion of the solvent is less than 20 weight %, the viscosity of 
the flux will become so high as to affect the coatability. If the 
proportion exceeds 99.5 weight %, the flux will be deficient in the active 
fraction so that solderability may be adversely affected even in an 
oxygen-free atmosphere. 
The flux of this invention may further contain a thermoplastic resin. 
The thermoplastic resin which can be used in this invention includes rosin, 
modified rosin, rosin-modified resin and synthetic resin, for instance. 
As the rosin and rosin-modified resins, there can be mentioned wood rosin, 
gum rosin, tall rosin, disproportionated rosin, hydrogenated rosin, 
polymerized rosin and other modified rosin, among others. The synthetic 
resin includes carboxyl-containing resins such as polyester resins, 
acrylic resins and styrenemaleic resins, epoxy resins, and resol or 
novolac phenolic resins, among others. These thermoplastic resins can be 
used independently or in combination. 
The proportion of such thermoplastic resin based on the solid content of 
the flux is 5-95 weight % and preferably 10-50 weight %. 
The flux of this invention may further contain an epoxy group-containing 
compound. 
The epoxy group-containing compound which can be used in this invention 
includes phenol glycidyl ether compounds, glycidyl ester compounds and 
glycidyl ether ester compounds. 
The phenol glycidyl ether compound includes bisphenol A diglycidyl ether, 
tetrabromobisphenol A diglycidyl ether, bisphenol F diglycidyl ether, 
bisphenol S diglycidyl ether and so on. The glycidyl ester compound 
includes diglycidyl phthalate, diglycidyl terephthaldte, diglycidyl 
tetrahydrophthalate, dimer acid glycidyl ester, 
8,11-dimethyl-7,11-octadecadiene-l,18-diglycidyl ester, n-ethyloctadecane 
diglycidyl ester and so on. The glycidyl ether ester compound includes 
p-oxybenzoic acid diglycidyl ester and so on. These compounds can be used 
independently or in combination. 
For accelerating the reaction between the organic carboxylic acid compound 
and epoxy group-containing compound in this invention, a catalyst may be 
employed. The catalyst includes quaternary ammonium salts such as 
triethylbenzylammonium chloride, trimethylbenzylammonium chloride, 
tetramethylammonium chloride, etc., tertiary amines such as 
benzyldimethylamine, tributylamine, tris-(dimethylamino)methylphenol, etc. 
and imidazole compounds such as 2-methyl-4-ethylimidazole, 
2-methylimidazole, etc., among others. The proportion of the catalyst 
based on the solid matter of the flux is 0.2-2 weight %. 
The mol ratio of the bis(2-oxazoline) compound and epoxy group-containing 
compound, taken together, to the dithiol compound and organic carboxylic 
acid compound, taken together, is 0.8-1.2 and preferably 0.95-1.05. The 
ratio of the bis(2-oxazoline) compound and expoxy group-containing 
compound to the dithiol compound and dicarboxylic acid is 5-95 mol %. 
In order to reduce the eye fatigue of inspectors and preclude the 
inspection error of the optical testing system in post-soldering 
inspections, a matted flux for a dull solder is demanded. With the flux of 
this invention, this object can be accomplished by using a rosin or 
rosin-modified resin for part or the whole of said thermoplastic resin 
and, in combination therewith, a higher saturated or unsaturated aliphatic 
monocarboxylic acid. The proportions of such rosin or rosin-modified resin 
and aliphatic monocarboxylic acid based on the solid content of the flux 
are 5-95 weight % and 2-30 weight %, respectively. The higher saturated or 
unsaturated monocarboxylic acid which can be used for reducing the solder 
gloss includes compounds of 8-21 carbon atoms, such as caprylic acid, 
lauric acid, myristic acid, palmitic acid, stearic acid, arachic acid, 
behenic acid, oleic acid, linoleic acid, linolenic acid and so on. The 
hydrohalic acid salt for use in the activator partly gives stable 
conjugated compounds as the result of reaction with the oxazoline compound 
and epoxy compound. In order to immobilize more of the hydrogen halide by 
such reaction, a double bond-containing compound may be added. The double 
bond-containing compound includes higher unsaturated monocarboxylic acids 
such as oleic acid, linoleic acid, linolenic acid, etc., and equimolar 
reaction products between hydroxyethyl acrylate or hydroxyethyl 
methacrylate and an acid anhydride such as succinic anhydride, maleic 
anhydride, itaconic anhydride, phthalic anhydride, tetrahydrophthalic 
anhydride, hexahydrophthalic anhydride, trimellitic anhydride, etc. The 
proportion of such compound is 1-50 weight % based on the solid content of 
the flux. 
The flux of this invention is a mixture of compounds, each of which is 
highly reactive, and undergoes reaction under the heat of soldering to 
give a heat-and moisture- resistant, tough polymer. Therefore, the 
polymeric film of flux residues after soldering does not undergo cracking 
even under the thermal shock due to cyclic heating and cooling and, in the 
in-circuit test using the contact pin, the pin reaches the circuit easily 
at low pressure. Moreover, the organic carboxylic acid which would 
otherwise cause corrosion and insulation failure is built into the polymer 
and the hydrogen halide liberated from the hydrohalic acid salt on heating 
reacts mostly with the bis(2-oxazoline) compound, with the unreacted 
residue being trapped and fixed within the polymer. Therefore, even if 
residues of the flux are not removed by cleaning, there occurs no 
corrosion or aging of electric characteristics, thus insuring an improved 
reliability of soldered joints. 
Incorporating said thermoplastic resin in a relatively large amount in the 
flux of this invention results in increased water resistance in unreacted 
state, improved wetting under the heat of soldering, and improvements in 
water resistance, toughness and heat resistance of the joints. 
Incorporating the epoxy group-containing compound in the flux of this 
invention results in a marked improvement in the water resistance in 
unreacted state and in the pot life of the flux after addition of an 
organic solvent. Moreover, the epoxy group-containing compound reacts with 
the hydrogen halide liberated from the hydrohalic acid salt on heating, 
sharing the role of capturing the hydrogen halide with the 
bis(2-oxazoline) compound. 
Incorporating said higher saturated or unsaturated monocarboxylic acid 
results in matting, that is to say dulling the gloss of the solder. 
Incorporating said double bond-containing carboxylic acid compound 
contributes further to the conversion of the activator hydrogen halide to 
stable compounds against soldering heat. 
Where the dithiol compound represented by the general formula 
EQU HS-R.sub.5 -SH 
wherein R.sub.5 represents an aliphatic hydrocarbon residue, an aromatic 
hydrocarbon residue or a heteroaromatic residue is to be used and the 
dicarboxylic acid represented by the general formula 
##STR2## 
wherein R.sub.6 represents an aliphatic hydrocarbon residue or an aromatic 
hydrocarbon residue is to be used as the organic carboxylic acid compound, 
there can be obtained a linear copolymer comprising a partial structure of 
the general formula 
##STR3## 
wherein R.sub.0, R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 represent 
the same meanings defined above and a partial structure of the general 
formula 
##STR4## 
wherein R.sub.0, R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.6 represent 
the same meanings defined above. 
The linear copolymer has a weight average molecular weight of 5000-100000. 
Where the diepoxy represented by the general formula 
##STR5## 
wherein X represents an ether bond or an ester bond and R.sub.7 represents 
an aliphatic hydrocarbon residue, a bisphenolic residue, a phthalic acid 
residue or an oxybenzoic acid residue and n is o or an integer of 1 to 100 
is to be used and the said dithiol compound represented by the general 
formula 
HS--Rs--SH 
wherein R.sub.5 represents the same meaning defined above is to be used and 
said dicarboxylic acid represented by the general formula 
##STR6## 
wherein R.sub.6 represents the same meaning mentioned above is to be used 
as the organic carboxylic acid compound, there can be obtained a linear 
copolymer comprising a partial structure of the general formula 
##STR7## 
wherein R.sub.0, R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 represent 
the same meanings defined above, a partial structure of the general 
formula 
##STR8## 
wherein R.sub.0, R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.6 represent 
the same meanings defined above, a partial structure of the general 
formula 
##STR9## 
wherein X, R.sub.5, R.sub.7 and n represent the same meanings defined 
above and a partial structure of the general formula 
##STR10## 
wherein X, R.sub.0, R.sub.7, and n represent the same meanings defined 
above. The linear copolymer has an intrinsic viscosity of 0.05-1.0. 
The flux of this invention undergoes addition polymerization reaction under 
the heat of soldering to give a heat-resistant, low-hygroscopic and 
flexible residual film. Therefore, neither cyclic heating and cooling nor 
external stresses may cause cracks or fractures and, in addition, no 
defective contact occurs in the in-circuit test because the film is easily 
pierced by the contact pin. Furthermore, the thermal polymerization 
reaction converts the organic carboxylic acid and hydrohalic acid salt 
which would otherwise detract from electrical characteristics to stable 
compounds or immobilizes them in a stable condition against the ambient 
atmosphere, with the result that the post-soldering cleaning operation can 
be omitted. This omission of a production step not only contributes to 
production cost reduction but helps to clear the statutory regulations on 
chlorofluorohydrocarbons. The flux of this invention, through the 
combination of rosin and a higher fatty acid, assumes a dull, matted 
appearance. This reduces the eye fatigue of inspectors and precludes the 
assessment error of an optical inspection system. 
Furthermore, since the reactivity between the bis(2-oxazoline) compound and 
dithiol compound is greater than that between the bis(2-oxazoline) 
compound and dicarboxylic acid compound and the reactivity of the epoxy 
group-containing compound and dithiol compound is greater than the 
reactivity between the epoxy group-containing compound and dicarboxylic 
acid compound, the overall reactivity can be controlled by altering the 
proportions of these four different reactants. 
For example, when the reaction must be consummated in a brief time of the 
order of seconds as it is the case with the dip soldering of printed 
circuit boards using a liquid flux and a solder bath or when the reaction 
is completed in a time of the order of several minutes as it is the case 
with the reflow soldering of surface-mounted boards using a mixture of 
flux and solder powders and a reflow furnace, the flux can be tailored to 
the respective process requirements, thus offering broadened versatility 
in use.

EXAMPLES 
The effectiveness of the soldering flux of this invention is now described 
in further detail by way of examples and comparison examples. It should be 
understood that the following abbreviations are used in the examples and 
comparison examples. 
______________________________________ 
.smallcircle. 
1,3-bis(2-Oxazolin-2-yl)benzene 
1,3-PBO 
.smallcircle. 
6-Dibutylamino-1,3,5-triazine- 
DB 
2,4-dithiol (Zisnet (trademark) DB, 
Sankyo Kasei) 
.smallcircle. 
Adipic acid AA 
.smallcircle. 
Succinic acid SA 
.smallcircle. 
Bisphenol A glycidyl ether type 
EP-828 
epoxy compound [Epikote (trademark 828, 
Yuka Shell Epoxy Co.] 
.smallcircle. 
Glycidyl ester type epoxy compound 
SB-20G 
(OS-Resin SB-20G, Okamura Seiyu Co.) 
.smallcircle. 
Diethylamine hydrochloride 
DEA .multidot. HCl 
.smallcircle. 
1-Methoxy-2-propanol MIPA 
.smallcircle. 
Isopropyl alcohol IPA 
.smallcircle. 
Acrylic resin A: A high acid number acrylic resin; 
acid number 110, molecular weight 9000, Tg 50.degree. C. 
.smallcircle. 
Acrylic resin B: A high acid number acrylic resin; 
acid number 140, molecular weight 10000, Tg 80.degree. C. 
.smallcircle. 
Hydrogenated rosin: Acid number 165-175, softening 
point 
80-87.degree. C., colorless and clear 
.smallcircle. 
TMBAC: Trimethylbenzylammonium chloride 
.smallcircle. 
Acrylcarboxylic acid: An equimolar reaction product 
of hydroxyethyl acrylate and hydrophthalic anhydride 
______________________________________ 
Example 1 
First, 0.507 g of 1,3-PBO, 0.384 g of DB, 0.110 g of SA and 0.046 g of 
DEA.multidot.HCl were respectively weighed and, then, 9.22 g of MIPA was 
added. The mixture was stirred well to prepare a homogeneous flux 
solution. This flux was subjected to the tests shown below. 
Examples 2-7 
According to the formulations shown in Tables 1, 2 and 3, fluxes were 
prepared and subjected to various tests as in Example 1. The results are 
shown in Tables 1, 2 and 3. 
Comparison Examples 1 and 2 
According to the formulations shown in Table 3, fluxes were prepared and 
subjected to various tests as in Example 1. The results are shown in Table 
3. 
Example 8 
First, 2.4 g of acrylic resin B, 1.6 g of hydrogenated rosin, 0.4 g of AA, 
2.4 g of DB, 1.78 g of 1,3-PBO, 1.57 g of SB-20G, 0.5 g of 
DEA.multidot.HCl and 0.05 g of TMBAC were weighed out and, then, 90 g of 
MIPA was added. The mixture was stirred well to prepare a homogeneous flux 
solution. The flux thus prepared was subjected to various tests. 
__________________________________________________________________________ 
Insulation resistance 
After 
moistri- 
Corro- 
Soldera- 
Exfoli- 
Dryness 
Spread 
Initial zation sivity 
bility 
ation 
__________________________________________________________________________ 
Pass 82% 1.7 .times. 10.sup.14 (.OMEGA.) 
1.4 .times. 10.sup.13 (.OMEGA.) 
None 
1.49 sec. 
None 
__________________________________________________________________________ 
Using a soldering equipment, the above flux was applied to a 
printed-circuit board of glass - epoxy resin and dried (100.degree. 
C..times.35 sec.) and soldering (3 sec.) was performed. Because of its low 
viscosity and good flowability, the flux spread thin and uniform. 
Moreover, it dried efficiently and caused virtually no bridging, icicling 
or ball formation in soldering. This flux, as well as a commercial rosin 
flux was heat-treated at 180.degree. C. for 30 minutes. In each case, the 
residue was allowed to stand at 50.degree. C..times.95% RH for 1 week and 
the weight gain was determined. The amount of water absorption of this 
flux, with that of the commercial rosin flux being taken as 100, was 76. 
Thus, this flux was less hygroscopic. 
Example 9 
First, 2.0 g of acrylic resin B, 1.34 g of hydrogenated rosin, 0.19 g of 
AA, 1.47 g of DB, 2.45 g of 1,3-PBO, 0.96 g of SB-20G, 0.35 g of 
DEA.multidot.HCl, 0.05 g of TMBAC, 0.5 g of stearic acid and 0.5 g of 
linolic acid were weighed out and, then, 90 g of MIPA was added to give a 
homogeneous flux solution. This flux was applied to a printed circuit 
board of glass-epoxy resin and dried and soldering was carried out by 
dipping it in a solder bath at 245.degree. C. for 3 seconds. The solder 
wettability was very satisfactory and the solder fillet showed a dull 
gloss or matted appearance. 
Example 10 
First, 3.77 g of 1,3-PBO, 4.29 g of SB-20G, 4.42 g of DB, 1.27 g of AA, 
0.51 g of DEA.multidot.HCl, 0.46 g of acrylic A, 0.46 g of acrylic resin B 
and 0.05 g of TMBAC were respectively weighed and, then, 84.73 g of MIPA 
was added to prepare a homogeneous flux. This flux was subjected to 
various tests. 
__________________________________________________________________________ 
Insulation resistance 
After 
moistri- 
Corro- 
Soldera- 
Exfoli- 
Dryness 
Spread 
Initial zation sivity 
bility 
ation 
__________________________________________________________________________ 
Pass 81% 8.5 .times. 10.sup.12 (.OMEGA.) 
6.4 .times. 10.sup.12 (.OMEGA.) 
None 
0.9 sec. 
None 
__________________________________________________________________________ 
This flux was applied to a paper-phenolic resin board and a glass-epoxy 
resin board, each measuring about 10 cm.times.15 cm, and soldering was 
carried out with the flux residues unremoved, each board was subjected to 
200 thermal shock cycles each of 30 minutes' cooling at -40.degree. C. and 
30 minutes' heating at 80.degree. C. As a result, neither board showed 
cracks or fractures, nor was found an exfoliation of flux residues. 
In the in-circuit test comprising contacting the soldered printed circuit, 
the contact pin readily pierced through the residue film at a contact 
force not exceeding 150 g, and as a result, no false test was encountered 
at all in the in-circuit test. Therefore, these boards could be handled 
without cleaning in the same way as the board from which the flux residues 
had been removed by cleaning. 
Example 11 
__________________________________________________________________________ 
Hydro- Acryl- 
Acrylic 
genated 1,3- DEA .multidot. 
Linolic 
carboxylic 
resin B 
rosin 
AA DB PBO 
SB-20G 
HCl TMBAC 
acid 
acid 
__________________________________________________________________________ 
a. 
2.4 1.6 0.6 
1.87 
1.78 
1.57 0.40 
0.05 2.0 -- 
b. 
" " " " " " " " -- " 
__________________________________________________________________________ 
The component materials were respectively taken and 90 g of MIPA was added 
to prepare a homogeneous liquid flux. The solderability of these fluxes 
were 4.06 seconds for flux a and 2.08 seconds for flux b. This flux was 
applied to a printed circuit board of glass-epoxy resin measuring 10 
cm.times.15 cm and heated at 100.degree. C. for 1 minute to evaporate the 
solvent. The fluxed board was then dipped in a solder bath at 
240.about.245.degree. C. for 3 seconds for soldering. The solderred 
printed circuit board was allowed to stand in acetone for one day to 
dissolve the film residues. The acetone solution was then dried by heating 
under reduced pressure. 
The amounts of solid residues were 0.244 g for flux a and 0.191 g for flux 
b. To each residue was added 50 ml of water and the mixture was boiled on 
reflux for 3 hours. The boiled mixture was cooled and filtered. The 
chloride content of the filtrate thus obtained was then determined by ion 
chromatography. From the value found, the residual amount of the chloride 
ions contained in the initial flux was calculated. The results were 59% 
for flux a and 58% for flux b. 
The calculated value represents the percentage of chloride ions relative to 
the solid matter of the flux. 
Thus, the amount of chloride ions favoring the corrosion of base metal and 
aging of electrical characteristics was drastically reduced. 
TABLE 1 
__________________________________________________________________________ 
Insulation resistance 
Solder- 
Composi- Test Spread After moisturi- 
Corrosi- 
ability 
Exfolia- 
tion (g) parameter 
Dryness 
(%) Initial (.OMEGA.) 
zation (.OMEGA.) 
vity (seconds) 
tion 
__________________________________________________________________________ 
Example 1 
1,3-PBO 
0.507 Pass 83 2.3 .times. 10.sup.14 
3.5 .times. 10.sup.13 
No corro- 
0.5 None 
DB 0.384 sion 
SA 0.110 
DEA-HCl 
0.046 
MIPA 9.22 
Example 2 
1,3-PBO 
0.368 Pass 81 3.2 .times. 10.sup.14 
1.2 .times. 10.sup.14 
No corro- 
0.3 None 
DB 0.400 sion 
AA 0. 092 
EP-828 
0.158 
DEA-HCl 
0.046 
MIPA 9.22 
Example 3 
1,3-PBO 
0.368 Pass 81 2.2 .times. 10.sup.14 
6.5 .times. 10.sup.13 
No corro- 
0.95 None 
DB 0.348 sion 
AA 0.124 
sion 
EP-828 
0.158 
DEA-HCl 
0.046 
MIPA 9.22 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Insulation resistance 
Solder- 
Composi- Test Spread After moisturi- 
Corrosi- 
ability 
Exfolia- 
tion (g) parameter 
Dryness 
(%) Initial (.OMEGA.) 
zation (.OMEGA.) 
vity (seconds) 
tion 
__________________________________________________________________________ 
Example 4 
1,3-PBO 
0.216 Pass 82 1.7 .times. 10.sup.14 
4.3 .times. 10.sup.13 
No corro- 
0.65 None 
DB 0.272 sion 
AA 0.146 
EP-828 
0.370 
DEA-HCl 
0.046 
MIPA 9.22 
Example 5 
1,3-PBO 
0.216 Pass 80 1.4 .times. 10.sup.14 
3.0 .times. 10.sup.13 
No corro- 
0.5 Sparse 
DB 0.272 sion 
AA 0.146 
EP-828 
0.370 
DEA-HCl 
0.046 
MIPA 9.22 
Alkyl- 
0.200 
phenol 
resin 
Example 6 
1,3-PBO 
0.231 Pass 83 4.3 .times. 10.sup.13 
1.2 .times. 10.sup.13 
No corro- 
0.7 Sparse 
DB 0.242 sion 
AA 0.130 
EP-828 
0.395 
DEA-HCl 
0.046 
MIPA 9.22 
Rosin 0.010 
__________________________________________________________________________ 
TABLE 3 
__________________________________________________________________________ 
Insulation resistance 
Solder- 
Composi- Test Spread After moisturi- 
Corrosi- 
ability 
Exfolia- 
tion (g) parameter 
Dryness 
(%) Initial (.OMEGA.) 
zation (.OMEGA.) 
vity (seconds) 
tion 
__________________________________________________________________________ 
Example 7 
1,3-PBO 
0.450 Pass 81 5.7 .times. 10.sup.13 
1.5 .times. 10.sup.13 
No corro- 
0.6 None 
DB 0.529 sion 
AA 0.121 
SB-20G 
0.398 
DEA-HCl 
0.046 
MIPA 9.22 
Compari- 
Rosin 1.000 Pass 91 2.2 .times. 10.sup.13 
1.4 .times. 10.sup.11 
Discolora- 
0.75 Yes 
son AA 0.130 sion 
Example 1 
DEA-HCl 
0.046 
IPA 7.86 
Compari- 
Alkyl- 
1.000 Pass 89 3.3 .times. 10.sup.13 
9.1 .times. 10.sup.11 
Discolora- 
1.0 None 
son phenol tion 
Example 2 
resin 
AA 0.130 
DEA-HCl 
0.046 
IPA 7.86 
__________________________________________________________________________ 
______________________________________ 
Test methods 
______________________________________ 
Dryness One drop of the flux is dripped on a copper 
sheet and heated on a hot plate at 230.degree. C. 
for 5 seconds. After cooling, the sample 
is evaluated for tackiness with a 
fingertip. 
Spreadability 
The test is performed in accordance 
with JIS-Z-3197 6.10 
Insulation 
The test is performed in 
resistance 
accordance with JIS-Z-3197 
6.8 [Test board: Type 2 comb 
electrode] 
Corrosivity 
The test is performed in accordance with 
JIS-Z-3197 6.6.1 
Solderability 
A test copper sheet (7 mm wide .times. 0.3 
mm thick) oxidized at 150.degree. C. for 1 
hour is dip-coated with the flux and, 
then, dipped in a solder bath (Solder 
H63A) controlled at 245 .+-. 2.degree. C. The 
time in which the solder surface 
regains horizontality is determined 
(meniscograph method). 
Exfoliation 
The resistance to exfoliation of flux 
residues on flexure of a testpiece. 
______________________________________ 
Example 12 
A cylindrical reactor maintained at 230.degree. C. was charged with 21.6 g 
(0.1 mol) of 1,3-PBO, 13.6 g (0.05 mol) of DB and 7.3 g (0.05 mol) of AA 
and the charge was stirred for about 15 minutes to provide a copolymer. 
This copolymer was clear, hard and soluble in dimethylformamide, dimethyl 
sulfoxide and N-methylpyrrolidone. 
The decomposition temperature (10% weight loss) as determined by 
differential thermal analysis was 330.degree. C. Nuclear magnetic 
resonance spectrometry (.sup.1 H-NMR, 400 MHz, d.sub.6 -DMSO) revealed 
chemical shifts assignable to 
##STR11## 
all of which were formed as the result of reaction, indicating that it was 
a thioether-ester-amide copolymer. Its average molecular weight as 
determined by GPC/LALLS was 41600. 
Example 13 
A cylindrical reactor maintained at 225.degree. C. was charged with 21.6 g 
(0.1 mol) of 1,3-PBO, 12.5 g (0.05 mol) of MPS and 7.5 g (0.05 mol) of AA 
and the charge was stirred for about 2 minutes to provide a copolymer. 
This copolymer was clear, hard and soluble in dimethylformamide, dimethyl 
sulfoxide and N-methylpyrrolidone. 
The decomposition temperature (10% weight loss) as determined by 
differential thermal analysis was 350.degree. C. Nuclear magnetic 
resonance spectrometry (.sup.1 H-NMR, 400 MHz, d.sub.6 -DMSO) revealed 
chemical shifts assignable to 
##STR12## 
all of which were formed as the result of reaction, indicating that it was 
a thioether- ester-amide copolymer. Its average molecular weight as 
determined by GPC/LALLS was 52200. 
Example 14 
A cylindrical reactor maintained at 225.degree. C. was charged with 9.1 g 
(0.0042 mol) of 1,3-PBO, 15 g (0.006 mol) of MPS and 6.7 g (0.0018 mol) of 
Epikote 828 (trademark, Yuka Shell Epoxy Co.) and the charge was stirred 
for about 1.5 minutes to provide a copolymer. This copolymer was clear, 
hard and soluble in dimethylformamide, dimethyl sulfoxide and 
N-methylpyrrolidone. 
The decomposition temperature (10% weight loss) as determined by 
differential thermal analysis was 360.degree. C. Nuclear magnetic 
resonance spectrometry (.sup.1 H-NMR, 400 MHz, d.sub.6 -DMSO) revealed 
chemical shifts assignable to 
##STR13## 
all of which were formed as the result of reaction, indicating that it was 
a thioether-amide copolymer. Its average molecular weight as determined by 
GPC/LALLS was 54900. 
Example 15 
A cylindrical reactor maintained 227.degree. C. was charged with 8.2g 
(0.038 mol) of 1, 3-PBO, 9.62g (0.035 mol) of DB, 9.35g (0.016 mol) of 
SB-20G and 2.76g (0.019 mol) of AA and the charge was stirred for about 5 
minutes to provide a copolymer. This copolymer was clear, hard and soluble 
in dimethylformamide, dimethyl sulfoxide and N-methyl pyrrolidone. The 
decomposition temperature (10% weight loss) as determained by differential 
thermal analysis was 305.degree. C. Nuclear magnetic resonance 
spectrometry (.sup.1 H-NMR, 400 MHz, d.sub.6 DMSO) revealed chemical 
shifts assignable to 
##STR14## 
all of which were formed as the result of reaction, indicating that it was 
a thioether-ester - amide copolymer. The intrinsic viscosity was 0.18 (0.3 
wt % in dimethylformamide at 25.degree. C.). 
Example 16 
A cylindrical reactor maintained 228.degree. C. was charged with 6.48g 
(0.03 mol) of 1,3-PBO, 9.62g (0.035 mol) of DB, 7.4g (0.02 mol) of Epokote 
828 (trademark, Yuka Shell Epoxy Co.) and 2.19g (0.015 mol) of AA and the 
charge was stirred for about 5 minutes to provide a copolymer. This 
copolymer was clear, hard and soluble in tetrahydrofuran, 
dimethylformamide, dimethyl sulfoxide and N-methyl pyrrolidone. The 
decomposition temperature (10% weight loss) as determined by differential 
thermal analysis was 310.degree. C. Nuclear magnetic resonance 
spectrometry (.sup.1 H-NMR, 400 MHz, d.sub.6 DMSO) revealed chemical 
shifts assignable to 
##STR15## 
all of which were formed as the result of reaction, indicating that it was 
a thioether-ester-amide copolymer. The intrinsic viscosity was 0.127 (0.3 
wt % in dimethybformamide at 25.degree. C.). 
Example 17 
A cylindrical reactor maintained 225.degree. C. was charged with 7.56g 
(0.035 mol) of 1,3-PBO, 5.55g (0.015 mol) of Epikote 828 (trademark, Yuka 
Shell Epoxy Co.), 8.16 g (0.03 mol) of DB, 1.25 g (0.005 mol) of MPS and 
2.19 g (0.015 mol) of AA and the charge was stirred for about 4 minutes to 
provide a copolymer. This copolymer was clear, hard and soluble in 
tetrahydrofuran, dimethylformamide, dimethyl sulfoxide and N-methyl 
pyrrolidone. The decomposition temperature (10% weight loss) as determined 
by differential thermal analysis was 305.degree. C. Nuclear magnetic 
resonance spectrometry (.sup.1 H-NMR, 400 MHz, d.sub.6 DMSO) revealed 
chemical shifts assignable to 
##STR16## 
all of which were formed as the result of reaction, indicating that it was 
a thioether-ester-amide copolymer. The intrinsic viscosity was 0.106 (0.3 
wt % in dimethybformamide at 25.degree. C.).