Fusible powdered metal paste

There is provided an inorganic salt-free, anhydrous, noncorrosive powdered solder metal paste and vehicle therefor which vehicle is characterized by the presence therein of a flux and a nonaqueous organic liquid having a surface tension or surface energy of from 43 to 65 dynes/cm. and higher at 20.degree. C. When powdered solder metal or powdered solder metal alloy is distributed in such a vehicle in an amount sufficient to form a paste, a deposit will not undergo hot slump at elevated temperatures. The pastes and vehicles are free of inorganic metal salts.

This invention relates to a paste vehicle and a heat-fusible metal powder. 
The vehicle is especially useful for making noncorrosive metalliferous 
pastes for joining by soft soldering. 
BACKGROUND OF THE INVENTION AND PRIOR ART 
The joining or coating, using a fusible soft solder metal powder-containing 
paste can be done efficiently, provided, however, that upon heating and 
before fusion of the metal, the soft solder metal powder containing paste 
exhibits controlled hot slump; in other words, the metal powder stays 
substantially where and as the paste was deposited on the substrate. This 
primary property has been difficult to obtain with conventional metal 
powder-containing pastes. The instant vehicles and pastes provide such 
property. 
Restriction of flow of any resulting fused metal (that is a lack of general 
spreading), except into intended joints or to form intended joints as in 
the joining of electronic components to printed circuit boards or hybrid 
circuit board to avoid bridging in surface mounted device attachments, are 
other properties desired. The inventive products here can also provide 
desired restriction of metal flow on remelting. For most electronic 
soldering purposes at this time, the composition must be free of corrosive 
agents such as inorganic salts. 
Soft solder pastes, for example, (melting below 400.degree. C., preferably 
below 330.degree. C.) usually contain tin and lead; a little silver often 
is alloyed with the tin, particularly for electronic work, e.g., for 
making microelectronic connections. Soft solder pastes now are 
experiencing wider acceptance in industry, primarily because pastes are 
more readily adapted to automated manufacture and screen-printing on a 
substrate than are the more conventional and manually effected solder bar, 
separate flux and iron, or solder wire (e.g., one containing the flux in a 
core within the wire) and an iron. The make-up of prior powder 
metal-containing paste compositions has been largely influenced by the 
prior practices particularly in respect of fluxing or surface preparing 
agents. These have comprised substantial portions of organic acids, e.g., 
rosin acid, inorganic salt materials, e.g., zinc chloride, ammonium 
chloride, borax and the like, and rosin-based fluxes. 
These soft solder compositions have not been entirely satisfactory in a 
number of respects. First, because of the presence of inorganic salt 
fluxes they have tended to be corrosive to the base metal or to introduce 
water as water of hydration leading to spattering. This problem was 
alleviated to a great extent with rosin-based flux vehicles. However the 
rosin-based fluxes or vehicles permit excessive movement of the solder 
particles away from the deposition site on heating; they also often give 
rise to sputtering and "dewetting" which leaves a residue as a halo around 
the solder joint. Their solder pastes have been prone to excessive solder 
balling, i.e., the formation of discrete minute balls of soft solder. This 
is highly undesirable and leads to electrical bridging across what should 
be electrically isolated connections especially on printed circuit boards. 
In the preferred embodiment of a soft solder composition an alkali 
solubilized in a polyhydric alcohol, e.g., glycerine, acts as a fluxing 
agent and improves solderability. For best results herein, in a soft 
solder metal powder, a slump control system and an inorganic salt-free 
fluxing system are present. The compositions hereof are practically 
noncorrosive and easy to formulate and handle. They are readily adaptable 
to screen printing. Disadvantages attendant prior compositions, such as 
spattering due to evolution of water vapor, solder balling and bridging, 
corrosivity, dewetting, tenacious residue, failure of the solder to melt 
due to excessive oxidation, etc., are not observed in the metal-bearing 
pastes here. "Inorganic metal salts" are metal or ammonium salts of 
inorganic acids Lange's "Handbook of Chemistry", 10th Edition, pp. 
209-333. 
To better understand the applications of solder pastes, reference may be 
had to "Technology of Electronic Grade Solder Pastes" Taylor et al, Solid 
State Technology, September 1981, pages 127-135. 
One prior paste composition is disclosed by Knoth U.S. Pat. No. 1,772,952. 
This paste comprises a solder metal powder, an amine and a binder or 
vehicle such as vaseline. These compositions do not, however, possess 
antislump properties which are currently in demand in the electronics 
industry. U.S. Pat. No. 2,493,372 to Williams dated Jan. 3, 1950 discloses 
a paste composition including a metal powder, e.g., tin-lead, a salt flux, 
and a C, H and O compound. Reference may also be had to U.S. Pat. No. 
3,954,494 dated May 4, 1976 which discloses a wax-flux composition. U.S. 
Pat. No. 804,664 also shows a tin-lead metal powder paste in a 
vaseline--glycerine--inorganic salt flux system. 
Another solder paste composition comprising powdered solder, a resin, a 
salt of an amino acid ester and a solvent is discussed by Melchiors et al 
in U.S. Pat. No. 3,065,538 dated Nov. 27, 1962. 
Another aqueous base solder composition is shown by Johnson in U.S. Pat. 
No: 3,073,270 dated Jan. 15, 1963. 
Also exemplary of prior solder paste compositions is the patent to Petersen 
et al U.S. Pat. No. 3,925,112 dated Dec. 9, 1975. According this 
invention, there are provided emulsified self-cleaning soldering fluxes 
having an aqueous phase including from 2 to 3 pbw (parts by weight) of a 
water soluble hydrazine salt and an oil phase including from 5 to 50 parts 
of a mixture of petrolatum and wax. Also provided are water solutions of 2 
to 30 pbw of the water soluble hydrazine salt, up to 5 parts of a 
vegetable gum thickener, a wetting agent and the balance water. 
Another prior paste composition is disclosed by Mastrangelo in U.S. Pat. 
No. 4,273,593 dated June 16, 1981. This paste comprises a solder metal 
powder and a vehicle, the latter being a hydroxypropyl cellulose blended 
with glycerine and/or water and further blended with a mixture of 
polyalkoxyalkanols. 
It has now been found that an improved vehicle for the instant powdered 
metal solder pastes is provided as an essentially inorganic salt free 
nonaqueous vehicle medium comprising a normally liquid nonaqueous organic 
liquid as an antislump agent, usually and preferably a polyhydric alcohol 
system, characterized in that the liquid has a minimum surface tension of 
43 dynes/cm (20.degree. C.), and generally from 43 to 65 or higher 
dynes/cm. Such system provides a slump control property to the metal 
bearing paste such that when it is heated toward the melting point of the 
soft solder metal powder, e.g., 118.degree. C. to 325.degree. C., the 
shape of the deposit is substantially maintained until the metal fuses. 
Although as will be seen from Table I below, and nonaqueous liquid having 
a surface tension above 43 dynes/cm. may be used in the vehicles hereof, 
polyols are the most practical antislump materials and the invention will 
be described with reference to polyols for convenience. 
These vehicles also desirably include a low surface energy material such as 
a hydrocarbon. The hydrocarbon, which is preferably solid or semi-solid 
(e.g., grease-like) melts, of course, and wets the substrate around the 
deposit, but carries no significant amount of the metal particles with it. 
Although hydrocarbons having melting points above 15.degree. C. are 
preferred, in certain embodiments normally liquid hydrocarbons such as 
hexane, cyclohexane, toluene or mixtures thereof, e.g., mineral spirits, 
may be used. The high surface energy material serves as a binder under 
heat conditions to hold the particles in position. Also the hydrocarbon is 
easily cleaned, along with any residue that may be left, away from the 
joint or surrounding area. The hydrocarbon by itself is incapable of 
imparting slump control properties to a powdered metal contained therein. 
In the preferred powdered metal compositions especially adapted for screen 
printing, no dewetting is observed. Surprisingly, even after melting, the 
fusible metal resists running from the site of application. Of course, in 
soft solder compositions there is also need for a fluxing agent. Such 
agent serves to clean the surfaces of the substrate or joining metal as 
well as the solder particles, and to inhibit the formation of oxide 
coating on the solder particles as the temperature is elevated toward 
melting. 
The desirable properties of antislump, anticorrosion and freedom from 
spattering in the metal-bearing pastes here are not observed in prior 
compositions known to me. Other additives may desirably be present as will 
be pointed out below. The instant pastes have no water in them other than 
insignificant amounts possibly present as an adventitious impurity that 
might be associated with good quality technical grade ingredients. No 
water is added deliberately as such or as a hydrate; so it can be said 
that the instant pastes and vehicles are "nonaqueous" as a practical 
matter. Also, it has been found that the high surface tension liquid, 
e.g., a polyol, can be a single component vehicle or a part of a 
multicomponent vehicle, i.e., including also a hydrocarbon. The substrate 
on which the paste is deposited has no significant effect on the hot slump 
resistance. 
BRIEF STATEMENT OF THE INVENTION 
Briefly stated, the present invention is a nonaqueous or anhydrous 
inorganic salt-free, powdered solder metal paste composition comprising a 
major amount of a soft solder metal powder and a minor amount of a paste 
vehicle containing a noncorrosive anhydrous fluxing agent, and an 
antislump composition including a nonaqueous liquid having a surface 
tension above 43 dynes/cm. at 20.degree. C. and preferably a polyol 
containing from 2 to 6 hydroxyl groups and having a surface energy of from 
43 to 65 or higher dynes/cm. (20.degree. C.). Preferably these pastes also 
include a paste forming vehicle ingredient which is a hydrocarbon. 
To further extend the utility of the soft solder alloys, there may be added 
other ingredients, such as, one or more surfactants, one or more condensed 
or fused ring aliphatic acids, e.g., cholic acid or abietic acid or rosin 
acids, and one or more plasticizers such as di-n-butyl phthalate. The 
pastes including a powdered soft solder alloy form a shiny and coherent 
(i.e. coalesced) solder pool in a controlled area of application. 
DETAILED DESCRIPTION OF THE INVENTION 
It has been found that slumping of a paste composition containing a major 
amount of a powdered soft solder metal or soft solder metal alloy can be 
effectively controlled by a unique composition composed of a hydrocarbon 
or a mixture of hydrocarbons, e.g., petrolatum, and a polyhydric material, 
e.g., glycerine and sodium hydroxide. The combination of a hydrocarbon 
having a melting point of at least 15.degree. C. and less than the melting 
point of the metal, and a polyhydric alcohol, such as di- or 
triethanolamine, or glycerine, or pentaerythritol, or the like, is 
however, effective in maintaining quite substantially the profile of the 
paste as it was initially deposited on the surface or substrate. A solder 
paste requires, however, a flux. At the fusion point, the metal in the 
present compositions has not run or spattered or balled up into small 
discrete balls of molten metal prior to the fusion of the entire mass. A 
polyhydric alcohol or polyol alone also is capable of conferring this 
property upon a paste composition containing a major amount of a metal or 
a metal alloy. However, the composition is unsatisfactory as a soft solder 
composition, requiring also a suitable hydrocarbon diluent and a 
noncorrosive flux. 
To form a solder paste, the vehicle portion hereof are blended with a 
powdered solder alloy to the extent of from 75% to about 93% metal by 
weight of the paste, and desirably from 80% to 90%, and preferably about 
85% powdered metal. The particle size of the powdered metal is desirably 
such that it will not settle out of the vehicle which is quite viscous 
(20,000 to 200,000 cps., Brookfield No. 7 spindle at 20 rpm) on standing. 
In general, the particle size is less than 100 mesh (U.S. Standard Sieve 
Size), desirably--200+400 mesh. A mixture of various sizes and/or shapes 
of metal powders often is advantageous for achieving desired rheology and 
other paste properties in these applications. Solder powder particles are 
available in two forms, i.e., those having irregular shape and those 
having spherical shape. Either shape, or a mixture thereof may be used, 
although the spherical shape is desired. Example 131 below is the best 
mode presently known to me of practicing my invention. Where normally 
liquid hydrocarbon diluents are used, e.g., toluene, the particle size of 
the solder powder should be less than about 10 microns in order to 
minimize settling. 
Preparation of the vehicle and paste is achieved with conventional stirring 
or blending means. Warming can be done, if necessary or desired, to 
facilitate by dissolving or melting ingredients together for putting them 
into very intimately dispersed condition and/or otherwise making a 
multiphase dispersion with the ingredients in a very fine state of 
subdivision preparatory to blending with the metalliferous powder to form 
a mass of paste consistency. Preferred compositions include additional 
fluxing agents, optionally a surfactant, optionally an organic carboxylic 
acid, and optionally a diluent; i.e., a plasticizer and/or solvent. Each 
of these ingredients will be discussed below. Thereafter, the solder 
alloys will be discussed followed by general processing techniques, and 
specific examples. 
THE HYDROCARBON INGREDIENT 
Hydrocarbons are preferred ingredients for the metal paste compositions 
thereof. Fluorinated hydrocarbons or chlorofluorinated hydrocarbons may be 
used to replace part or all of the hydrocarbon. The useful materials range 
in melting point from below about room temperature to normally solid 
materials, e.g., petroleum hydrocarbon waxes containing from 18 to 60 or 
more carbons and melting in the range of 28.degree. C. to 100.degree. C. 
The useful hydrocarbons also have a very low ash or solid residue content 
and either melt and flow, sublime and/or thermally decompose at a 
temperature below the melting point of the solder (i.e., below 330.degree. 
C.). The amount of ash or solid residue from the hydrocarbon remaining of 
the melt temperature should be less than 0.5% and preferably less than 
0.1%. The useful hydrocarbons may be paraffinic, aromatic, or mixed 
aromatic paraffinic or mixtures of compounds of such characteristics, and 
include various mixtures of hydrocarbons, e.g., octadecane, mineral 
spirits, paraffin wax, and petrolatum, e.g., Vaseline. Synthetic 
hydrocarbons normally solid or semi-solid include commercially available 
polyethylenes, polypropylenes, poly(ethylene-propylene), polybutenes, 
poly(ethylenestryene), hydrogenated nonpolar polymeric hydrocarbons having 
Ring and Ball softening points of from 15.degree. C. to 130.degree. C., 
such polymers having a molecular weight less than about 1500 and 
preferably less than 1000, hydrogenated polyterpenes, etc. The best 
material known to me for use herein is petrolatum. Halogen substituted 
hydrocarbons, e.g., fluorocarbons and chlorofluoro carbons may also be 
used, they also being relatively inert at the temperatures encountered. 
"Petrolatum" is a well known colloidal system of nonstraight-chain solid 
paraffinic hydrocarbons and high boiling liquid paraffinic hydrocarbons, 
in which most of the liquid hydrocarbons are held inside the micelles. A 
detailed historical account including the chemistry of petrolatum and 
modern manufacturing methods is found in Drug and Cosmetic Industry, Vol. 
89, 36-37, 76, 78-80, and 82, July 1961. "Petrolatum for Drugs and 
Cosmetics" Schindler. Petrolatum is typically a yellowish to amber or 
white semisolid, unctuous mass, practically odorless and tasteless. It has 
a density at 25.degree. C. of from 0.820 to 0.865, a melting point of 
38.degree. to 54.degree. C., and a refractive index .eta.60/0 of 
1.460-1.474. It is readily commercially available under the well known 
proprietary marks Vaseline, Cosmoline, Stanolene, Penreco brand petroleum 
jelly as well as other convenient trade designations. Petrolatum may be 
used in its commercially available form or it may be modified by the 
addition of petroleum wax or paraffin wax in particulate form, e.g., 
microcrystalline wax. 
The hydrocarbon ingredient is utilized in an amount which ranges from 10 to 
90 pbw of the vehicle system, or 0.7% to 22.5% of the solder paste. A 
nonaqueous organic liquid having a surface energy in the range of 43 to 65 
or higher dynes/cm appears to be essential for the slump control 
characteristics of the present powdered metal pastes. Although water has a 
high surface energy as does sulfuric acid, these materials are not 
satisfactory because of spattering or reactivity at elevated temperatures. 
SLUMP CONTROL SYSTEM 
As indicated above, the ability of a soft solder paste to resist hot slump, 
or running during softening and melting is essential in modern 
microelectronic processing and particularly silk and stencil screening of 
soft solder pastes. It has been found that a combination of a hydrocarbon 
as above defined and particularly petrolatum, and a nonaqueous organic 
liquid having a surface tension at 20.degree. C. greater than 43 
dynes/cm., and preferably one or more polyhydric alcohols containing 2 to 
6 OH groups and having a surface tension or energy of from 43 to 65 or 
higher dynes/cm at 20.degree. C., is effective in providing a good paste 
and in preventing slumping of the metal particles. The hydrocarbon alone 
with powdered soft solder composition appears incapable of conferring this 
property to any degree. Nonaqueous organic liquid alone gives sufficient 
antislump properties but sometimes insufficient soldering properties. Soft 
solder pastes also require a flux and to obtain the noncorrosiveness 
required in modern electronic applications the flux should not be an 
inorganic salt, e.g., ZnCl.sub.2, NH.sub.4 Cl, or borax, this latter being 
highly hydrated and thus given to spattering. 
The antislump agents hereof are generally polar compounds. 
Table I below gives specific examples of liquids of various kinds useful in 
inhibiting slump. The polyols useful herein are aliphatic and normally 
liquid or of relatively low melting point, i.e., below about 170.degree. 
C. and include ethylene glycol, diethylene glycol, propylene glycol, 
dipropylene glycol, sorbitol, mannitol, trimethylolethane, 
trimethylolpropane, diethanolamine, triethanolamine, pentaerythritol, and 
erythritol. These polyols coact with a hydrocarbon, especially petrolatum 
in the absence of water and in the presence of a finely divided metal 
powder to control slumping on heating and to provide a satisfactory paste 
medium. A fluxing agent either as a separate ingredient, e.g., sodium 
hydroxide, or as a moiety of the polyol (e.g., triethanolamine or 
diethanolamine) must be present. The secondary or tertiary amine group 
appears to be suitable for fluxing. The polyol is generally insoluble in 
the hydrocarbon. The amount of liquid polyol constitutes from about 0.5% 
to 10.0% by weight of the vehicle and powdered solder metal composition. 
A comparative study of various agents in 88.9% powdered metal compositions 
demonstrates the significance of the limitation respecting surface energy 
or surface tension. 
TABLE I 
______________________________________ 
Slump/Resistance Study 
(For 60% Sn; 40% Pb Powdered Metal)* 
Surface Slump 
Tension Antislump Resis- 
(Dyne/Cm) 
Agent tance Remarks 
______________________________________ 
63.4 7% NaOH/93% Yes Fluxing occurred 
Glycerine 
63.4 Glycerine Yes No fluxing 
58.2 Formamide Yes Little fluxing 
occurred 
55.1 Conc H.sub.2 SO.sub.4 
Yes Oxidizing occurred 
50.8 Methylene Iodide 
Yes P/M turned green 
48.4 Triethanolamine 
Yes Fluxing occurred 
48.5 Diethanolamine Yes Fluxing occurred 
48.3 Monoethanolamine 
Yes 
47.7 Ethylene Glycol 
Yes Little fluxing 
occurred 
45.2 Triethylene Glycol 
Yes Little fluxing 
occurred 
44.0 Tetraethylene Glycol 
Yes Little fluxing 
occurred 
44.5 Polyethylene Glycol 
Yes Little fluxing 
200 occurred 
44.5 Polyethylene Glycol 
Yes Little fluxing 
600 occurred 
42.9 Aniline No 
40.9 Phenol No Solid Chemical 
38.0 Pyridine No 
36.8 Nitromethane No 
32.7 Acetic anhydride 
No Oxidizing occurred 
32.5 Oleic acid No 
32.3 Carbon Disulfide 
No 
27.8 Acetic acid No Oxidizing occurred 
27.5 n-Octyl alcohol 
No 
25.5 Cyclohexane No 
24.2 Ethyl bromide No 
23.0 i-Butyl alcohol 
No 
20.7 t-Butyl alcohol 
No 
-- Vaseline No 
______________________________________ 
*NOTE: 
1. Formula used for slump resistance studies: 88.9% (97.5% Pb; 1.0% Sn; 
1.5% Ag) + 7.8% Vaseline + 3.3% Antislump agent. 
Paste was examined on Cu coupon at designated temperature. 
Table II below shows the hot slump effect on a solder composition using the 
"antislump agent" as the sole vehicle. 
TABLE II 
______________________________________ 
Slump/Resistance Study 
(60% Sn; 40% Pb/Single Phase Vehicle System) 
Surface Tension 
Antislump Slump 
(Dyne/Cm) Agent Resistance Remarks 
______________________________________ 
63.4 7% NaOH/93% Yes Excellent 
Glycerine Soldering 
63.4 Glycerine Yes Oxidizing 
55.1 Conc H.sub.2 SO.sub.4 
Yes Occurred 
50.8 CH.sub.2 I.sub.2 
Yes Solid 
48.9 Triethanolamine 
Yes Chemical 
47.7 Ethylene Glycol 
Yes 
40.9 Phenol No 
38.0 Pyridine -- P/M ppt'd 
quickly 
27.5 n-Octyl alcohol 
-- P/M ppt'd 
quickly 
-- Vaseline No 
______________________________________ 
Note: 
1. Paste was examined on Cu coupon at 235.degree. C. 
2. The vehicle NaOH/glycerine also provided good slump resistance for 
Nordox Red Cuprous. (Cu.sub.2 O). 
Table III below shows the effect of temperature on hot slump resistance 
with selected polyols and other additives. 
TABLE III 
______________________________________ 
Slump/Resistance Study 
(Temp. Effect) 
Surface Tension 
Antislump Temp. (.degree.C.) 
Slump 
(Dyne/Cm) Agent at Test Resistance 
______________________________________ 
48.9 Triethanolamine 
150 Yes 
235 Yes 
325 Yes 
44.5 Polyethylene 150 Yes 
Glycol 200 235 Yes 
325 Yes 
42.9 Aniline 150 No 
235 No 
325 No 
38.0 Pyridine 150 No 
235 No 
325 No 
______________________________________ 
Note: 
1. Formula used for slump resistance studies: 88.9% (97.5% Pb; 1.0% Sn; 
1.5% Ag) + 7.8% Vaseline + 3.3% Antislump agent. 
Paste was examined on Cu coupon at designated temperature. 
2. When the paste was examined on substrate which has been surface treate 
with FC723* (surface tension 11 dyne/cm), the slump resistance behavior 
was still about the same as that on the Cu coupon. 
*Fluorad FC723 is an oleophilic, hydrophilic fluorocarbon in an inert 
vehicle having a specific gravity of 1.78 produced by 3M. 
FLUXING SYSTEM 
As indicated above, there must be present a noncorrosive anhydrous fluxing 
system in a solder paste composition hereof. The fluxing system may be a 
single chemical specie dissolved or dispersed in the hydrocarbon/polyol 
system. Alternatively, the fluxing system may comprise a plurality of 
fluxing agents dissolved or dispersed in the hydrocarbon/polyol system. 
Best results have been secured with alkali or basic reacting fluxing 
agents, and particularly alkali metal hydroxides. These can be used as 
solutions in the polyol or as alcoholates of a monohydric or polyhydric 
alcohol, e.g., methyl, ethyl or isopropyl alcohol, dissolved in the 
polyol, or the alkali metal salt of the polyol, e.g., sodium glycerate. 
The alkali metal hydroxide in such component is a preferred noncorrosive 
fluxing agent and is effective in a proportion of about 0.1-5% by weight 
of the vehicle, and, advantageously, 0.25-3.5%. The liquid polyol can 
constitute from about 0.5 to 75.0% by weight of the vehicle, and, 
advantageously, about 40%. On the basis of the entire solder paste, the 
amount of polyol ranges from about 0.3 to 18.8%. The alkali metal 
hydroxides useful herein include in descending order of preference sodium 
hydroxide, potassium hydroxide, lithium hydroxide and cesium hydroxide. 
Such alkali metal hydroxides have a limited solubility in polyhydric 
alcohols or mixtures of same that are liquid and are conveniently used in 
concentrations at or near the limit of solubility, i.e., less than about 
10% by weight of the polyol. As indicated, they can be present as an 
alkali metal alcoholate, e.g., sodium ethylate, dissolved or well 
dispersed in the polyol, the alcoholate being equivalent to the hydroxide. 
The polyhydric alcohols include glycerine (which is preferred), ethylene 
glycol, diethylene glycol, propylene glycol, sorbitol, mannitol, 
pentaerythritol, erythritol, etc., containing from 2 to 6 OH groups. A 
sodium hydroxide/glyerine solution is particularly effective and may be 
used as the sole fluxing agent, or it may be used in combination with an 
alkanolamine, e.g., triethanolamine or diethanolamine to provide effective 
fluxing systems for the instant pastes. 
A useful fluxing ingredient is also provided as an amine component of the 
vehicle. Such component is effective in a broad proportion, e.g., about 
2-40% by weight of the vehicle and, advantageously 3-10%. The essential 
functional group of this component is an 
##STR1## 
wherein R, R.sub.1, and R.sub.2 are independently selected from hydrogen, 
alkyl, alkylene, cycloalkyl, cycloalkylene, carboxyalkylene, 
aminoalkylene, hydroxyalkylene, carbonylalkyl, etc., no more than two of 
R, R.sub.1 and R.sub.2 being hydrogen. The alkyl and cycloalkyl groups may 
contain from 1 to 30 carbon atoms. The amine component may contain one to 
three amino groups. A particularly useful group of amine compounds is the 
water soluble alkanolamine group including mono-, di, and 
trimethanolamines, mono-, di-, and triethanolamines; mono-, di-, and 
tripropanolamines, and mixtures of the mono-, di-, and trialkanolamines. 
Alkyl and cycloalkyl amines, particularly the C.sub.2 -C.sub.18 mono and 
polyamines, e.g., triethylamine, tri-isopropylamine, diethylamine, 
mono-n-butyl amine, propylene diamine cyclohexylamine, cyclopropyl 
methylamine, tetramethylene diamine, rosin amine, cyclohexylamine 
hydrochloride, cyclohexylene amine, diaminoethylamine, diaminopropylamine, 
etc. Thus, the kind and configuration of the amino compounds useful herein 
are very broad and results among the examples are reasonably equivalent 
for fluxing. Amidino and guanidino fluxing agents, advantageously 
aliphatic ones, can be considered as useful amines for the instant 
purpose. Aromatic amines, while functional, often impart toxicity and 
therefore are not favored. Similarly, pyridine-type materials, such as, 
pyridine or a lutedine give off intensely objectionable odors and are not 
favored, but could be considered functioning like amines here. The 
preferred amines are the alkanolamines. Also useful to supplement the base 
system are the amino acids, particularly the water soluble amino-acids, 
e.g., aminoacetic acid, beta-aminopropionic acid, 
(beta-alanine)aminobutyric acids, epsilon-aminocaproic acid, N-methyl 
glycine, betaine, alpha-delta-diaminovaleric aliphatic carboxylic acids. 
Thus, urea, propionamide, butanamide, 2,2-dimethylpropionamide, 
N-methylpropionamide, N,N-beta-trimethylbutyramide, steroylamide, etc., 
can be such base system supplements. 
OTHER FLUXING AND/OR SOLDERABILITY INGREDIENTS 
Organic carboxylic acids are useful as fluxing and/or solderability 
ingredients, particularly in a supplemental role in combination with the 
other ingredients described above. Any high boiling (above 300.degree. C.) 
aliphatic carboxylic acid may be used. I prefer, however, to use condensed 
ring acids such as abietic acid, cholic acid, rosin acids, polymerized 
rosin acids, hydrogenated rosin acids rosin esters disproportionated rosin 
ester gum, wood rosin, gum rosin, tall oil rosin, or fatty acids such as 
stearic acid, oleic acid, etc. Fatty amine and fatty acid compounds are 
also useful in this capacity. Examples include 
N-tallow-1,3-diaminopropane, 3-diaminopropane dioleate, etc. The acids are 
used in small amounts of from 0.5 to 10% by weight of the vehicle 
composition, or on the basis of the fully formulated solder paste, from 
about 0.03% to about 2.5%. 
It has also been found that a surfactant may be advantageously included in 
the vehicles hereof. Although such surfactant or wetting agent may be 
anionic, cationic, amphoteric, or nonionic, nonionic agents are preferred. 
Many surfactant materials are known. They are used in the present vehicles 
to help to control the rheological properties, shelf-life stability, air 
voids, etc. The amount used is determined by cut and try and is that 
amount which is sufficient to impart the desired control. These agents 
assist in the dispersion of the powdered metal and in carrying the fluxing 
agent to the surfaces being joined or coated. Generally less than 10% by 
weight each of other ingredients is used and usually from 0.01% to 5% by 
weight of the vehicle or 0.001% to about 4.5% of the solder paste. 
Specific surfactants include the alkylarylpolyether alcohols, ammonium 
perfluorinated carboxylates, fluorinated alkyl esters of fatty acids, 
acetylenic glycols (which as sometimes can act as a defoamer), 
polyoxyethylene sorbitan monostearate, etc. Surfactants commonly used in 
solder pastes may be used herein. 
Solvents and/or diluents may also be present in the vehicle compositions 
hereof. For example, when a paste containing powdered solder metal is to 
be used in a screen printing process, solvents are conveniently used to 
adjust the viscosity to a satisfactory level. Solvent materials are 
desirably volatile, at least at the melting point of the solder alloy. Any 
solvent including low molecular weight alcohols, e.g., ethyl or propyl, 
isopropyl, butyl, amyl, cyclohexyl, terpene alcohols, etc.; ketones, e.g., 
methyl ethyl ketone, methyl isobutyl ketone; 2-butoxyethanol-1, ethylene 
glycol dimethyl sulfoxide, hydrocarbons, e.g., kerosene, terpene 
hydrocarbons, hexane, cyclohexane, heptane, octane, naphthas such as 
mineral spirits, ethyl acetate, amyl acetate, etc. The solvent ingredients 
may also include higher boiling materials commonly regarded as 
plasticizers such as dibutyl phthalate, tricresyl phosphate, etc. 
The selection of the solvent and/or diluent is controlled by the end use, 
cost, environmental factors, desired plasticity, etc. The solvent or 
diluent may be water soluble or substantially water insoluble. The solvent 
or diluent leaves the system after application to a substrate as in screen 
printing, the residue being the solder paste composition hereof. 
Minor amounts of known odorants, bactericides, fungicides, etc., may also 
be included in the vehicles hereof if desired. Amounts of such ingredients 
usually range from about 0.1 to 2% by weight of the vehicle. 
PREATION OF THE VEHICLES 
The simplest preparation of the vehicles hereof involves only effective 
mechanical mixing of the ingredients into the petroleum hydrocarbon 
ingredient, e.g., petrolatum. 
The hydrocarbon can, if desired or necessary, be heated to melt it and 
facilitate the blending operation, and warming of some of the other 
ingredients also can be of help. It is not necessary that the mixture be a 
solution. The paste-like vehicle can be cloudy and contain one or more 
phases with the disperse phase fine enough so that it will not separate 
substantially on standing. 
The materials discussed in detail above are considered to be ingredients of 
the vehicles hereof. 
THE METAL POWDER 
Solder compositions useful herein as the metal powder for blending with the 
above described vehicles to form a paste, or for extrusion of a hollow 
wire for making a cored solder wire, are well known. A number of 
representative compositions useful herein are given in the Taylor et al 
article, supra. In general the solder compositions have a melting point in 
the range of from about 118.degree. C. to about 330.degree. C. and 
comprise tin together with lead and/or silver. Other metals such as zinc, 
aluminum, bismuth, cadmium, nickel, indium and cadmium may also be used in 
the solder compositions. 
For making a solder paste, the metal powder is comminuted so that it is 
easily and stably dispersed in the vehicle by grinding, ball milling, 
paddle blending, ribbon blender, etc. The entire powder should pass 
through a 50 mesh screen (U.S. Sieve Series) (297 microns). Typically, the 
powder is finer than 100 mesh (149 microns) because larger particles are 
difficult to disperse and maintain in suspension in the paste. A particle 
size in the range of -200+400 mesh (U.S. Sieve Series) is preferred. Even 
smaller particle sizes, i.e., 10 microns or less are desired where 
normally liquid hydrocarbons are used in the vehicle as in silk screening 
paste compositions. For most purposes, from 3 to 20 parts by weight of 
solder metal powder is blended with 1 part by weight of vehicle. The paste 
compositions hereof generally will have a viscosity in the range of 20,000 
cps to 200,000 cps. The preferred apparent viscosity will depend on the 
method of dispensing or application of the solder paste to the materials 
to be joined. Hand trowelling pastes are more satisfactory at the higher 
apparent viscosities than pastes intended for automatic dispensing such as 
extruding, flowing or spraying onto a substrate or those which are most 
suited for application to a substrate, e.g., a printed circuit, by a 
screen printed process. Viscosity can be controlled easily by the amount 
of solvent or solvent mixture and/or plasticizer employed in the vehicle, 
or by the vehicle to powder ratio. Pastes often are degassed at reduced 
pressure. 
In fabricating cored solder wire, conventional procedures are used 
substituting a vehicle of the present invention for a conventional core 
composition such as a rosin based paste. 
Effective control of hot slump in solder pastes is demonstrated by the 
following specific examples. These examples are intended to enable those 
skilled in the art to apply the principles of this invention in practical 
embodiments, but are not intended to limit the scope of the invention. In 
this specification all temperatures are in degrees Celsius unless 
otherwise stated, all parts, percentages, and ratios are by weight unless 
otherwise expressly stated, and sieve sizes are for the U.S. Standard 
Sieve series. 
Testing for resistance to hot slump of a solder paste was done by applying 
a deposit of the paste (about 5 mm diameter by 4-5 mm high) by spatula to 
a copper coupon, then gradually and automatically warming the coupon with 
a Browne Corporation reflow instrument (in effect an automated travelling 
hot plate) from room temperature to 330.degree. in about a half-minute to 
a minute. The thus-heated deposit was observed visually for collapse of 
the metal prior to its fusing as the vehicle disappeared therefrom. 
Significant collapse of particulate metal of the deposit prior to its 
fusion would indicate hot slump. None of the exemplary pastes given below 
showed significant hot slump. In the case of solder paste the spreading of 
molten metal from the deposit area was also observed in the same test. 
None of the exemplary tin-containing solder pastes given below showed 
significant spreading over the coupon; all had desirably restricted flow. 
Great spreading away from the locus of application is undesirable for many 
applications such as soldering in the manufacture of electronic devices. 
In the examples the petrolatum indicated as Petrolatum A was Vaseline brand 
petroleum jelly, Vaseline being the trademark of Chesebrough Manufacturing 
Co., Inc. for USP petrolatum sold at retail for household use. The other 
petrolatums used were Penreco USP petrolatums, Penreco being the trademark 
of Pennzoil Co.; Petrolatum B was their Regent grade white petrolatum 
(Melting Point 118.degree.-130.degree. F.); Petrolatum C was their Royal 
grade (Melting pont 118.degree.-130.degree. F.); and Petrolatum D was 
their Amber grade (Melting Point 122.degree.-135.degree. F.).