Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~3~9
IMPROVED FUSIBLE Powdered METAL PASTE
This invention relates to a paste vehicle and a heat-
fusible or sinterable metal powder. The vehicle is especially
useful for making metalliferous pastes for joining by soft soldering,
infiltrating, lacing metal I or for a moldmg purpose.
BACKGROUND OF IRE INVENTION AND Prior PUT
the joining, infiltrating, or coating, or the manufacturing
ox many kinds of molded metal parts using a fusible metal powder-
containing paste can be done efficiently, (often with automation)
provided, however, that upon heating and before fusion of the
metal, the 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
pcwder-containlng 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 pores,
or to form intended joints as in the joining of copper-~ased or iron
based metal parts, or in the infiltration of porous metal compacts
such as steel compacts, or the adhering of electronic cc~onents to
printed circuit boards or hybrid circuit board to avoid bridging in
surface mounted devise attachments, are other properties desired
'lye inventive products here can also provide desired restriction of
metal flow on remelting. For most electronic soldering purposes at
this tin, the composition must be free of corrosive agents such as
inorgam c salts.
Brazing can be done with a paste of powdery powdered
copper-based ahoy or elemental ocpper-bearing, or with a cupreous
so-called "silver solder. Facing applications, erg., to coat,
build-up or hard-faoe metal surface s, can be done with pastes
containing various metal or alloy Pharisee, e.g., copper, copper-
based, cobalt-based or nickel-based alloys, stainless steel, hard facing
~2~35~
--2
alloys, etc. In hard facing, the metal Fodder usually is heated to
a wish state Weller liquid phase sistering of the metal occurs.
wherefore hard-facing Fx7wders can be considered here as essentially
s:~lter~le. Sometimes -essay pastes can contain particulate refractory
neutrals such as alumina or silicon carbide for wear F~lrposes.
Infiltration of porous metal compacts, typically, steel compacts,
call for fusion that will fill the pores of the compact with metal.
Such Fetes usually are copper-rich and contain a little iron, erg.,
.01 to I by weight. Often a bit of refrac*ory-providing material
lo is used in them; the refractory material remains as a removable
surface residue when the job is done. Molding applications, such as
injection molding to make metal parts, can use a variety of metal
powers in a paste vehicle. Most molded pastes here are formed of
paste, then are heated to leave a sistered object. For efficiency and
economy -the vehicle weight proportion ordinarily is minor relative to
that of the weight of fusible metal powder.
Soft solder pastes, for example, (melting below 400C.,
preferably below 330C~ usually contain tin and lead; a little
silver often is alloyed with the tin, particularly for electronic
2C work, e.g., for making microelectronic connections. Soft solder
pastes new 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
I (e.g., one containing the flux in a core within the wire) and an
iron. I make-up of prior powder metal-containing paste compositions
has been largely influenced by the prior practice s particularly in
respect of fluxing or surface preparing agents. These haze coursed
substantial portions of organic acids, ego, rosin acid, inorganic
salt materials, e.g., zinc chloride, ammonium chloride, borax and
the like, and recensed fluxes.
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 ads alleviated to a great extent with recensed flux
I
vehicles. However the recensed fluxes or vehicles permit excessive
r~vement of the solder particles away from the deposition site on
heating; they also often give rise to sputtering and "dotting"
which leaves a residue as a halo around the solder joint. Their
5 solder pastes have been prone to exoe suave solder balling, i.e., the
font ion of discrete minute kills of soft solder. this is highly
undesirable and leads to electrical bridging across what should be
electrically isolated connections especially on printed circuit
~xoarcls.
Lo In a preferred embodiment of a soft solder composition an
alkali solu~ilized in a polyhydric alcohol, e.g., glycerine, act as
a fluxing agent and improves solder ability. 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 by formulate and handle. They are
readily adaptable to screen printing. Disadvantages attendant prior
compositions such as spattering clue to evolution of water vapor,
solder balling and bridging, corrosivity, dotting, 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 a onlum salts Lange's
book of Chemistry, Thea Edition, pp. 209-333.
To better understand the applications of solder pastes,
reference nay be had to technology of Electronic Grade Solder Pastes"
Tailor et at, Solid State Technology September 1981, pages 127-135.
One prior paste composition is
disclosed by Knot U.S. Patent 1,772,952.
Lois paste comprises a solder metal powder, an amine and a binder or
vehicle such as Vaseline m eye compositions do not, however,
possess anti slump properties which are currently in demand in the
electronics industry. U. S. Patent 2,493,372 to William dated 3
January 1950 discloses a paste composition including a metal powder,
eye., tunneled, a salt flu, and a C, H and O compound. Referent ox
may also ye had to Us S. Patent 3,954,494 dated 4 May 1976 which
discloses a wax-flux composition. U. S. Patent 80~,664 also shows a
tin-lead metal powder paste in a Vaseline - glycerine - inorganic
salt flux system.
I
Another solder paste composition comprising powdered
solder, a resin, a salt of an amino acid ester and a solvent is
discussed by Melchiors et at in Patent 3,065,538 dated 27 November
1962.
Another aqueous base solder composition is shown by Johnson
in Patent No.: 3,073,270 dated 15 January 1963.
Aye exemplary of prior solder paste compositions is the
t~lt~nt to Petersen et at 3,925,112 dated 9 December 1975. according
thus invention, where are provided emulsified self-cleaning soldering
LIT fluxes having an aqueous phase including from 2 to 30 pow Imparts by
weight) of a water soluble hydrazine salt and an oil phase mcluding
from 5 to 50 parts of a mixture of petrolatum and wax. Also provided
are water solutions ox 2 to 30 pow of the water soluble hydrazine
salt, up to 5 parts of a vegetable gum thickener, a wetting agent
cud the balance water.
Another prior paste composition is disclosed by Mastrangelo
in U. S. Patent 4,273,593 dated 16 June 1981. This paste comprises
a solder m tat powder and a vehicle, the latter being 2 hydroxypropyl
cellulose blended with glycerine and/or water and further blended
with a mixture of poly~lkoxyalkanols.
It has now been found that an improved vehicle for the
instant powdered metal pastes is provided as an essentially non aqueous
vehicle medium comprising a normally liquid non aqueous organic
liquid as an anti slump agent, usually and preferably a polyhydric
I alcohol system, characterized in that the liquid has a mimmum
surface tension of 43 dynes/cm (20C.), 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, ego 118C. to
I 325C., -the shape of the deposit is substantially maintained until
-the metal fuses. Al-though as will be seen from Table I below, and
norlaqueous liquid having a surface tension above 43 dynes/om. may
be used in the vehicles hereof, polyols are the most practical
ankisl~p materials and the invention will be described with reference
35 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 courser and wets
the substrate around the deposit, but carries no significant amount
of the metal particles with it. Apparently, the anti slump system
remains Burr and provides a cohesive force for the powdered metal.
Althc~1gh hydrocarbons having melting points above 15C. are preferred,
in retain embodiments normally likelihood hydrocarbons such as hexane,
cyclohexane, Tulane or mixtures thereof, e.g., mineral spirits, may
be used. I've high surface energy material ryes 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 dotting 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 chide coating on the
solder particles as the temperature is elevated toward melting.
The desirable properties of anti slump, anti corrosion and
freedc~n Fran spattering in the metal-bearing pastes here are no-t
observed in prior compositions known to me. Other additives may
desirably be present as will be pointed out below. The instant
pasts have no water in them other than insignificant amounts possibly
present as an adventitious impurity that might be associated with
good Colette technical grade ingredients, No water is added deliberately
as such or as a hydrate; so it can be said that the instant pastes
end vehicles are nuances as a practical matter. also, it has
been found that the high surface tension liquid, i.e., -the polyol,
con be a single go onent vehicle or a part of a multi component
vehicle, i.e., including also a hydrocarbon. Ire substrate on which
the paste its deposited has no significant effect on the hot stump
resistance.
- -
GRIEF STATEMENT OF TIE; INVASION
refly stated, the present invention is a non aqueous or
an hydrous inorganic salt-free, powdered metal paste composition
comprising a major amount of a metal powder and a minor amount of a
paste vehicle containing an anti slump composition including a non aqueous
liquid having a surface tension above 43 dynes/cm. at 20C. and
preferably a polyol containing from 2 to 8 carbon atoms and having a
surface energy of from 43 to 65 or higher dynes/cm. (20C.). Preferably
these pastes also include a paste forming vehicle ingredient which
is a hydrocarbon For soft solder compositions a fluxing ingredient
is present.
To further extend the utility of the metal or metal alloys,
there may key added other ingredients, such as, one or more surfactants,
one or more condensed or fused ring aliphatic acids, e.g., colic
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 ally o'er a shiny and coherent it coalesced) solder pool
in a controlled area of application.
DETAILED DESCRIPTION OF THE INVASION
20 It has been found that slumping of a paste composition
containing a major amount of a powdered metal or 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. me combination of
a hydrocarbon having a melting point of at least 15C~ and loss than
the melting point of the metal, and a polyhydric alcohol, such as a
dip or triethanolamine, or glycerine, or pentaerythritol, ox the
like, is however, effective in maintaining quite substantially the
profile of the paste as it was initially deposited on the surface or
I substrate A solder paste requires, however, a flux. it the fusion
point, the metal in the present compositions has not run or spattered
or balled up into small discrete byway of molten metal prior to the
fusion of the entire mass. A polyhydric alcohol or polyol alone
I
--7--
also is capable of conferring this property upon a paste composition
containing a major amount of a metal or a metal alloy Hoover
such a composition while useful with high melting powdered metals,
is unsatisfactory as a soft solder position requiring also a
Sybil hydrocarbon delineate and a noncorrosive flux.
To form a solder paste, the vehicle portions hereof are
blended with a powdered metal to the extent of from 75% to about 93
metal by weight of the paste, and desirably from 80~ to 90%, and
rehirable about 85% powdered metal. me particle size of the
10 powdered metal is desirably such that it will not settle out of the
vehicle which is quite viscous 120,000 to 200,000 cups., Brook field
No. 7 spindle at 20 rum) on standing. In general, for soft solder
ccn~ositions the particle size is less than lo mesh (U. SO Standard
Sieve Size), desirably 200 400 mesh. A mixture of various sizes
15 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., whose
having irregular shape and those having spherical shape. Either
shape, or a mixture thereof may be used, although the spherical
20 shape is desired. Where normally liquid
hydrocarbon delineates are used, erg., Tulane, the particle size of
the solder powder should key less than about lo microns in order to
mum mite titling Typically a brazing (or "silver soldering)
Foist will contain about 65-75 pow metal powder of -l50 mesh size,
an infiltration paste 80-90 pow metal powder of -lo mesh size, a
facing paste 60-90 pow metal powder of -lo to -200 mesh size, and a
molding paste (as for injection mowing) 85-9Q pow of metal powder
of -400 mush size. In each case the balance of lo pow is made up
with the vehicles hereof. A mixture of various sizes and/or shapes
owe the particles in the metal powders often is advantageous for
achieving desired rheology and other paste properties in these
Appalachians.
Preparation of the vehicle and paste is achieved with
conventional stirring or blending means. Warming can be done, if
35 necessary or desired, to facilitate by dissolving or melting ingredients
~V~3~
together for putting them into very intimately dispersed condition
and/or otherwise making a multi phase dispersion with the ingredients
in a very fine state of subdivision preparatory to blending with the
metalliferous powder to Norm a mass of paste consistency. Preferred
c~r~ositions for soft solders include additional fluxing agents,
optionally a surfactant, optionally an organic carbcxylic acid, and
optionally a delineate; i.e., a plasticizer and/or solvent. Each of
eke ~nyredients will be discussed below. Thereafter, the metals
or real alloys will be discussed followed by general processing
techniques, and specific examples.
THE HYDROCARBON ingredient
Hydrocarbons are preferred ingredients for the metal paste
compositions hereof. Fluorinated hydrocarbons or chlorofluorinated
hydrocarbons may ye used to replate part or all of the hydrocarbon.
me 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 cartons and melting in the
range of 28~C. to 100C. The useful hydrocarbons also have a very
low ash ox solid residue content and either melt and flow, sublime
and/or thermally decompose at a temperature below the melt my point
of the solder (i.e., below 330C.). me amount of ash or solid
residue from the hydrocarbon remaining at the melt temperature
should be less than 0.5% and preferably less than Oily. The useful
hydrocarbons may be paraffL~ic, aromatic, or mixed aromatic paraffinic
or ~uxtlres of ccmpo~mds of such characteristics, and in use various
mixtures of hydrccarbons7 e.g., octadecane, mineral spirits, paraffin
wry and petrolatum, e.g., Vaseline. Synthetic hydrocarbons normally
solid or semi-solid include commercially available polyethylenest
polypropylene, polyethylene propylene polybutenes, polyethylene-
styrenes), hydrogenated nonpolar polymeric hydrocarbons having Ring and Ball softening points of from 15C. to 130C., such polymers
having a molecular weight less than about 1500 and preferably less
than Lowe, hydrogenated polyterpenes, etc. the best material known
to me for use grin is petrolatum. Halogen substituted hydrocarbons,
eye, fluorocarbons and chlorofluoro carbons may also be used, they
also being relatively inert at the temperatures enco~mtered.
d
"Petrolatum'` is a well known colloidal system of non straight-
chain solid paraffinic hydrocarbons and high boiling Lockwood paraffinic
hydrocarbons, in which most of the liquid hydrocarbons are held
inside the Melissa. A detailed historical account including the
S chemistry of pe-trolatum and modern manufacturing methods is found in
Roy and Cosmetic Industry, Vol. 89, 36-37, 76, 78-80, and 82, July
1961. "Petrolatum for Drugs and Cosmetics" Chandler. Petrolatum
is typically a yellc~ish to amber or white ser~solid, unctuous mass,
practically odorless and tasteless. It has a density at 25C. of
LO from 0.820 to 0.865, a melting point of 38 to 54C., and a refractive
irks 60t0 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. Petrolat~n may be used in its commercially
available form or it may be modified by the addition of petroleum
ax or paraffin wax in particulate form, e.g., microcrystalline wax
me hydrocarbon mgredient is utilized in an amount which
ranges from 10 to 90 pow of the vehicle system, or 0.7% to 22.5% of
the solder paste. A nonequals 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 powdered metal paste
to resist hot slump, or running during softening and melting is
essential in various applications such as molding, casting, infiltrations,
cxkatincJ and in modern microelectronic processing and particularly
silk and stencil screening of soft solder pastes. It has been found
that a combination of hydrocarbon as above defined and particularly
pe-trolatum, and a non aqueous organic liquid having a surface tension
at 20C. greater than 43 dynes/cm., and preferably one or more
--10--
polyhydric alcohols containing 2 to 6 OH groups and having a surface
tension ox energy of prom 43 to 65 or higher dynes~om at 20C., is
effective in providing a good paste and in preventing slumping of
the metal particles. The hydrocarbon alone with powdered metal
composition appears incapable of conferring this property to any
degree. Non aqueous organic liquid alone gives sufficient anti slump
properties but in the case of soft solders, insufficient soldering
properties. Soft solder pastes also require a flux and to obtain
ale noncorrosiveness required in modern electronic applications the
LO flux should not be an inorganic salt, e.g., ZnC12, NH4Cl, or borax,
the latter being highly hydrated and thus given to spattering.
the anti lump agents hereof are generally polo cc~Es~lds.
A detailed mechanism of the anti slump properties of this
combination is obscure at present.
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 ox relatively low melting pollinate it below about 170C~
and mclude ethylene glycol, diethylene glycol, propylene glycol,
20 dipropyle~ glycol, sorbitol, minutely, trimethylolethane, in-
methylolpropane, diethanolamine, triethanolamine, pentaerythritol,
awl erythritol. These polyols cocci with a hydrocarbon, especially
petrolatum in the a Noah of water and in the presence of a finely
~-Lvided metal powder to control slumping on heating and to provide a
satisfactory paste medium A fluxing agent either as a separate
ingredient, ego, sodium hydroxide, or as a moiety of the polyol
(e.g., triethanol~nine or diethanolamine) must be present. me
secondary or tertiary amine group appears to be suitable for fluxing.
Thy polyol ivy generally soluble in the hydrocarbon The amount of
Lydia 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 38.9% powdered
metal compositions demonstrates the significance of the limitation
respecting surface energy or surface tension.
~11-
TABLE I
Slump/Resistance Study
(For 60% Sun; 40% Pub Powdered Metal)*
Surface
Tension Anti slump Slump
m) Resistance Remarks
63.4 7% Noah% Glycerine Yes Fluxing occurred
63.4 Glycerine Yes No fluxing
58/2 Formamide Yes Little fluxing
occurred
55.1 Cone H2S04 Yes Oxidizing occurred
50.8 Ethylene Iodide Yes P/M binned 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 i'
44.0 Tetraethylene Glycol Yes "
44.5 Polyethylene Glycol 200 Yes if
44.5 Polyethylene Glycol 600 Yes "
42.9 Aniline No
40,9 Phenol No Solid Chemical
38.0 Pardon JO
36.8 Nitromethane No
32~7 septic Andre 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
2505 Cyclohexane No
24.2 ethyl bromide No
23,0 i-Butyl alcohol no
20~7 t-Butyl alcohol No
- -I Vaseline No
NOTE: 1. Formula used for slump resistance studies:
88.9% (97.5~ Pub; 1.0% Sun; 1.5% Ago -I 7.8%
Vaseline -I 3.3% Antislw~p agent.
Paste was examined on Cut coupon at designated
temperature.
-12-
Treble If below shows the hot slump effect on a solder
composition using the "anti slump agent" as -the sole vehicle.
liable II
Slu~p/Resistance Study
(60~ Sun; 40~, Pb/Sin~le Phase Vehicle System)
Surface Tension Antislwmp Slump
(UX~n~/~n) Pent Resistant Remarks
63~4 7% Noah Yes Excellent
Glycerine Soldering
63.4 Glycerine Yes
55.1 Cone H2SO4 Yes Oxidizing
Occurred
50.8 OH I Yes
48.9 rye ~anolamLne Yes
47~7 Ethylene Glycol Yes
40.9 Phenol No Solid
Chemical
38.0 Pardon P/M ppt'd
quickly
27.5 n-Octyl alcohol ---- PAM Fpt'd
quickly
Vaseline No
__ . __ . . _ _ _ .
Note: 1. Paste was examined on Cut coupon at 235C.
2. Ire Rockwell NaOH/glycerine also provided Good
slop resistance for Nordox Ted Cuprcus. (Queue).
Table III below shows the effect of ten~era-ture on hot
slwnp resistance with selected polyols and other additives.
Lo 3
13-
TABLE III
Sl~un?/Resistance Stun
(Temp. Effect)
Surface Tension Anti slump Temp. C) Slump
(Oyr~/Cm) Agent at Test Resistance
48~9 Trieth~nolamine 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 E~rridine 150 No
235 No
325 No
ote: 1. Formula used for slump resistance studies:
88.9~ (97.5~ Pub; 1.0% Sun; 1.5% Pug) 7,8%
Vaseline 3.3% Anti slump agent.
Paste was exam mod on Cut coupon a designated
t~mperabure.
. When the paste was examined on substrate which
has been surface streaked with FC-723* (surface
tension 11 dyne/am), the slump resistance behavior
was still about the same as that on the Cut coupon.
*Flurried FC-723 is an oleophilic, hydrophobic fluorocarbon
in an inert vehicle having a specific gravity of 1.78
produced by EM.
FLUXING SYSTEM
As indicated above, -there must be present a noncorrosive
an hydrous fluxing system in a soft solder paste composition hereof.
Ire fluxing system may be a single chemical specie dissolved or
diapered 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
keen sucker with alkali or basic reacting fluxing agents, and
particularly alkali metal hydroxides. muse can be used as solutions
in the polyol or as alcoholates of a mandrake or polyhydric alcohol,
e.g., methyl, ethyl or isopropyl alcohol, dissolved in the polyol,
or the alkali metal salt of the polyol, ego, sodium guy overate.
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%.
Lowe 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 anoint of polyol ranges from about .3 to
18.8%. me alkali metal hydroxides useful herein include in descending
20 order of preference sodium hydroxide, potassium hydroxide, lithium
hydroxide and sesame hydroxide. Such alkali metal hydroxides have a
limited volubility in polyhydric alcohols or mixtures of same that
are liquid and are conveniently used in concentrations at or near
the limit of volubility, i.e., less than about 10% by weight of the
25 polyol. As indicated, they can be present as an alkali metal alcohol ate,
e.g., sodium ethyl ate, dissolved or well dispersed in the polyol,
the alcohol ate being equivalent to the hydroxide. The polyhydric
alcohols include glycerine (which is preferred), ethylene glycol,
diethylene glycol, propylene glycol, sorbitol, minutely, pentaerythritol,
30 erythrltol, etc., containing Fran 2 to 6 OH groups. A sodium hydra
~dde/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., triethanola~QLne or diethanolamine to provide
I
-15~
effective fluxing systems for the instant pastes.
A useful fluxing ingredient is also prc~rided as an amine
component of the vehicle. Such component is effective in a broad
proportion, e.g., about 2-~0~ by weight of the chicle and, advantageously
3~10~. rL'he essential functior~l group of this cc~ponent is an
N- _ Al
wherein R, Al, and R2 are independently selected from hydrogen,
alkyd, alkaline, eyeloalkyl, cyeloalkylene, earboxyalkylene, amino-
alkaline, hydroxyalkylene, earbonylalkyl, eta, no more than two of
R, Al and R2 being hydrogen. me alkyd and cycloalkyl groups may
contain from 1 to 30 earn atoms. me amine component may contain
one to three amino groups. A particularly useful group of amine
compounds is the water voluble alkanolamine group including one-,
dip and trimethanolamines, moo-, do-, and triethanolamines; moo-,
I-, and tripropanolamines, and mixtures of the moo-, do-, and
trialkanolamines. Alkyd and eyeloalkyl amine, particularly the C2-
C18 moo and polyamides, e.g., triethylamine, tri-isopropylarmne,
diethylamine, mono-n-butyl amine, propylene Damon eyclohexylamine,
eyelopropyl methyl amine, tetramethylene Damon, rosin amine, Swahili-
h~ylarnine hyc~oehloride, eyeldlexylene anise, diaminoethylarnine,cli~inopropylc~nine, etc. Thus, the Sunday and configuration of the
amino ec~pouncls useful herein are very broad and results among the
examples are reasonably equivalent for fluxing. Houdini art guanidino
fluxing agents, advantageously aliphatie ones, elm ye considered as
I useful amine for the instant purpose. Aromatic amine, while
~unetionall often impart twixt and therefore are not favored.
Similarly, pyric~ne-type materials, such as, pardon or a letdown
--16~
give off intensely objectionable odors and are not favored, but
could be considered functioning like amine here The preferred
anuses are the alkanolamines. Also useful to supplement the base
system are the amino acids, particularly the water soluble amino,
acids, e.g., arninoacetic acid, beta- arninopropionic acid, (beta-
Allen) amirlobutyric acids, epsilon- aminocaproic acid Methyl
Gleason, button, alpha-del-ta-diaminovaleric alipnatic carboxylic
acids. Issue, urea, propionamide, ~ltanamide, 2,2 dimethylpropion-
I to, ~-meth~lpropionamide, N,N-be-ta-trimethylbutyramide, stroll-
lo Aryan, etc., can be such base system supplements.
OTHER VEHICLE ING~EDIENIS
Organic carboxylic acids are useful as fluxing and/orsolderability ingredients, particularly in a supplemental role in
oombinatiorl with the other ingredients described cibove. Any nigh
boiling (above 300C.) aliphatic carboxylic acid may be used. I
prefer, however, to use condensed ring acids such as abietic acid,
colic acid, rosin acids, polymerized rosin acids, hydrcger~ted
rosin acids rosin esters disproportionate rosin ester gum, wood
rosin, gum rosin, tall oil rosin, or fatty acids such as Starkey
acid, oleic acid, etc. Fatty amine cud fatty acid compounds are
also useful in -this capacity. Examples include N-tallow~1,3-diarnino-
propane, 3-diaminoproF~ane dwelt, etch The acids are used in
small amounts of Fran 0.5 to 10% by weight of the vehicle composition,
or on the basis of the fully forn~lated solder paste, from about
.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
event may be amonic, cat ionic, ar~photeric, or non ionic, non ionic
events are preferred. Many surEactant materials are known my
are used in the present vehicles to help to corrtrol the theological
properties, shelf-life stability, air voids, etc. me amount used
I
17-
is determined by cut and try and is that amount which is sufficient
to impart the desired control. 'muse agents assist in the dispersion
of the powdered metal and in carrying the fluxing agent to the
surf owes being joined or coated. Generally less than 10'~ by weight
each of other ingredients is used and usually Fran .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,
~r~r~ni~n per fluorinated carboxylates, fluorinated alkali esters of
fatty acids, acetylenic glycols (which sometimes can act as a
ill d~fo~ner), polyoxye~hylene sorbitan menstruate, etc. Surfactants
commonly used in solder pastes may be used herein.
Solvents and/or delineates may also be present in the
vehicle compositions hereof For example, when a paste containing
powdered solder metal is to he 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 propel, isopropyl, bottle, Amy,
cyclohexyl, terrapin alcohols, etch; kittens, e.g., methyl ethyl
kitten, methyl is~butyl kitten; 2-butoxyethanol~l~ ethylene luckily
dim ethyl sulfoxide, hydrocarbons, ego, kerosene, terrapin hydrocarbons,
hexane, cyclohexane, Hutton, octane, naphthas such as mineral
spirits, ethyl acetate, Amy acetate, etch The solvent ingredients
may also include higher boiling materials commonly regarded as
plasticizers such as dibutyl phthalate/ tricresyl phosphate, etc.
eye selection of the solvent and/or delineate is controlled
by the end use, cost, environmental factors, desired plasticity,
etc. 'Ire solvent or delineate may be water soluble or substantially
water soluble. The solvent or delineate leaves the system after
application to a substrate as in screen printing, the residue being
the solder paste composition hereof.
Minor omits of known odor ants, bactericide, fungicides,
etc., may also be included in the vehicles hereof if desired
Amounts of such ingredients usually range from about 0.1 to 2g by
weight of the vehicle
-18-
From -lime to -tinner it is desirable -to include in the
compositions of the present invention, particularly in the case of
silver solder brazing pastes an inorganic fluxing agent such as a
metallic halide, for example, zinc chloride, tin chloride, aluminum
chloride, or arnrnonium chloride. Such an agent may be present in an
amount ranging from about .5 to 5% by weight of -the vehicle and is
u~cful in cleaning the surface to be treated of the metal or metal
ally. Such oxidation, unless reproved destroys the integrity of
the coating or juncture between the metals involved.
I it the metal fusion temperatures encountered herein all
organic ingredients are removed from the system either by volatile-
ration or decomposition
PREPARATION OF TIE VEX EN
The simplest preparation of the vehicles hereof involves
only effective mechanical rnLxing 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. me paste e vehicle can be
claldy and contain one or more phases with the disperse phase fine
enough so that i-t will no-t separate substantially on standing.
I've materials discussed in de-tail above are considered to
be ingredients of the vehicles hereof.
lo
--19--
THE kettle POWDER
For raking a paste, the metal powder is commented so that
it is easily and stably dispersed in the vehicle key grinding, ball
milling, paddle blending, ribbon blender, etc. The powder should
past through a 20 mesh screen (U. S. Sieve Series) (841 microns).
icily the powder is fmer than 100 mesh (149 microns) beau æ
larger particles are difficult to disperse and maintain in suspension
in -the paste. For most applications, a particle size in the range
of -150 + 400 mesh (U. S. Sieve Series) is preferred. For rust
purposes, from 3 to 20 parts by weight of metal powder is blended
with 1 p rut by weight of vehicle. I prefer to use spherically
shaped particles, although irregular particles or flakes may be
used. The paste compositions hereof generally will have a viscosity
in the range of 20,000 cups. to 200,000 cups., Brook field No. 7 spindle
at 20 rip The preferred apparent viscosity will depend on the
method of dispensing or application of the paste to the materials to
be joined. Hand troweling pastes are more satisfactory at the
higher apparent viscosities than pastes intended for automatic
dispensing such as extruding, flowing or spraying or those which
are most suited for application by a screen printing 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 power ratio. Pastes often are degassed at reduced
pressure.
Solder compositions useful herein as thy metal powder for
blending with the above described vehicles to form a paste, or or
extrusion ox a hollow wire for making a cored solder wire, are well
Icnown. A number of representative compositions useful herein cure
given in the Taylor et at article, swooper. In general the solder
compositions have a melting point in the range of from akcut 118C.
to about 330C. 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.
-20-
For making a solder paste, the metal powder is commented
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 cud
r~intain 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
I Lydia hydrocarbons are used in the vehicle as in silk screening
paste compositions. For most E~lrposes, from 3 to 20 parts by weight
of solder metal powder is blended with 1 part by weight of vehicle.
me paste compositions hereof generally will have a viscosity in the
range of 20,0~0 cups to 200,000 cups. The preferred apparent viscosity
will depend on the method of dispensing or application of the solder
paste to the materials to be joined. Hand troweling 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, my a screen printed process.
Viscosity can be controlled easily by the amount of solvent or
solvent mixture andtor plasticizer employed in the vehicle, or by
the vehicle to powder ratio. Pastes often are degassed at reduced
pressure.
In fcibricating cored solder wire, conventional procedures
are used substituting a vehicle of the pro ant invention for a
conventional core composition such as a rosin based paste.
Effective control of hot slump in powdered metal pastes is
menstruated by the following specific examples. These examples are
-Untended 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,
an ratios are by weight unless otherwise expressly stated, and
sieve sizes are for the U. S. Standard Sieve series.
I
-21-
Testing for resistance to hot slump of a metal-containing
paste was doze by applying a deposit of the paste layout 5 mm diameter
by 4-5 mm high) by spatula to a copper coupon, then gradually and
automatically warming the coupon with a Browse Corporation reflow
instrument (in effect an automated traveling hot plate from room
temperature to fusion in about a half-minute to a minute. The
thus - heated deposit way 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 skewed significant hot slump. In -the case of solder
paste the spreading ox molten metal from the deposit area was also
observed in the same test. None of the exemplary tin-contaLning
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 toe petrolatum indicated as Petrolatum A
was Vase me brawl petroleum jelly, Vaseline being the trademark of
Chesebrough Manufacturing Co., Inc. for US petrolatum sold at
retail for household use The other petrolatums used were Yenreco
US petrolatums, Penreco being the trademark of Pencil Co.; Petrol-
tug B was their Regent grade white petrolatum (Meltmg Point 118-
130F.); Petrolatum C was their Royal grade (Melting Point 118-
130F.); and Petrolatum D was their Amber grade (Melting Point 122-
135F.).
I
-22-
In the following examples the following designations have
the following identities:
Briton N-60 = alpha-(nonylphenyl)-omega-hydrQ~y-
poly(oxy-1,2-ethanediyl), (Aegis-
to Jo.: 9016-45-9).
*me trademark of Room & Hays Company
.. .. _ . _ . . _ _
Armenia* = bis(hydrogenated tallow alkyl)amine,
Amen* ARC = Basque C16 hydrocarbon alkyl)amine,
Dune en T = N-tallow trim ethylene Damon, and
Damon* 'DO = N-tallow trim ethylene Damon
dwelt, respectively.
*'rho trademarks of Akzona, Inc.
. .
PEG* 6000 DO = alpha-(l-oxooctadecyl)-omega-[(l-Qxo-
octadecyl)oxy] poly(oxy-1,2-ethanediyl3,
(Reg. No : 9005-08-07),
PEG* 6000 = alpha-hydro-omega-hydroxy-poly(oxy-lt2-
ethanediyl), Reg. No.: 25322-68-3,
Carbowax* 3350 = a polyoxyethylenic wax,
n-llexyl Car-
bottle* = diethylene glycol moo n-hexyl ether, and
twill Car-
bottle* = diethylene glycol monobutyl ether,
respectively.
*Lowe trademarks o-f Union Carbide Corp.
.. . .. , __ ___
-23-
Flurried*
FC~340 = a liquid fluorocarbon.
*The trademark of EM Company
,
5Surfynol*
EYE = 5-decyne-4,7-diol,2,4,7,9-tetramethyl,
Reg. No : 126-86-3.
*the traderr~rk of Alp Products
and Shekels, Inc.
Donnelly* DO = 2-(2-methoxyethoxy)ethanol,
(Reg. No. 111-77-3), art
Donnelly* DE = 2-(2-ethoxyethoxy)ethanol, (Reg. No.
111-90-0), respectively.
*me trademarks of Dow Chemical Cc~any
. . _ _ " . _ _ . _ . _ _ .
Pastes tabulated below were rude by blending the nicker
size flying ingredients, metal powder and other solder ability
ingredients with petroleum hydrocarbon in a molten condition, then
blending in the other vehicle ingredients when the mass cooled to
32. The specification for -the solder powders was 5% mix ~200
mush, rnax. -325 mesh. me formulations were evaluated according
to standards established for electronic grade solder pastes. Act
cordir~ly, although some of -the exemplified pastes may not hove met
elf -thy electronic grade criteria, -they were operative for other
utilization such as for raking a joint using a trowel to apply -the
paste. Of the exemplified solder pastes, those preferred for micro-
electronics irk slicked no solder balling.
In -the solder tests no spattering was observed dying
heating to effect melting, and no significant hot stump or solder
it
spreading was observed that is, they had good restriction of flow.
E~rrtherrnore, there was no dotting in evidence on the copter
substrate, and cleaning of joint easily could be had with a
suitable organic solvent, erg., a petroleum naphtha, alcohol, etc.
En Jay of contrast 20 parts of a prior art fluxing comic-
session (specifically that of Example 1 of U. S. Patent 3,925,112,
itch patent discloses some petrolatum as one of the ingredients in
the oily phase of an aqueous soldering flux emulsion) was compounded
with 80 parts ox solder alloy powder herein exemplified in the same
Lo runner as the pastes herein exerr~lified; resistance to hot slump was
not demonstrated nor was restricted flaw (spreading) of melted
solder, and there was considerable spattering.
-25- I
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-45-
EXAMPLE 132
-
Petrolatum A, 95 parts, was blended thoroughly with 5
parts of triethanolamine to make a v2hlcle for a brazing paste.
30 parts of such vehicle was thoroughly blended with 70 parts of
elemental copper powder, the opera powder being -150 mesh, to
make a soft paste. No significant hot slump was observed upon
testing on a copper coupon with the Reflow instnwnent.
A T-bar of an upright piece of steel temporarily wired
to rest on and project from a horizontal flat piece of steel was
made key applying the brazing paste deposit near one end of the
interface between the pieces and heating the resulting assembly in
a belt furnace. The assembly was maintained at 1121C. for 10-20
minutes. The result was a good brazed joint between the pieces,
with the brazing metal flowing into the joint by couplet and
exhibiting no appreciable spreading away from the joint.
EXAMPLE 133
Petrolatum A, 95 parts, was blended thoroughly with 5
parts of a clear solution of 7 parts of sodium hydroxide in 93
parts of glycerine to mike a vehicle or a brazing paste. 30
parts of such vehicle was thoroughly blended with 70 parts of
elemental copper powder like that of Example 132 to make a soft
paste. lye paste was tested for hot slump and brazing effectiveness
like the paste of Example 132. No significant hot slump was
observed. The resulting brazed joint was a good one, generally
resenting that of Example 132.
I
EXAMPLE 134
The vehicle of Example 132 us used for Managua an inflator-
lion paste. 20 parts of such vehicle was blended thoroughly with
80 parts of a powdered rnetalliferous infiltration composition to
rake a grainy paste.
To do this testing a coherent porous "green" (unsintered)
compact of steel powder was coated approx~unately 6 run thick all
over with the post The rnetalliferous infiltration composition
of the paste was a blend of elemental copper powder, a powdered
copper-base alloy containing iron, a high green strength copper
power (SCM Corporation's HUGS grade), silicon powder, and manganese
powder; the infiltration c~nposition had the following approximate
nut composition: OWE copper; 1.81% iron; I silicon; 0.32
zinc; and 1.00~ manganese.
No hot slump of the deposit was observed upon testing
with the Reflow instrument. me paste-coated compact was heated
for three hours at 1232C. to give a very efficient infiltration
of the pores; 99~ of the infiltration composition went into the
c~npact, and only I residue was left; this easily brushed off
from the surface of the resulting infiltrated and sistered compact
EX~MPI,E 135
The vehicle of Example 133 was used for matins an infiltration
past. 20 parts of such vehicle was blended thoroughly with 80
parts of the powdered metalliferous infiltration compositions of
Example 134 to make a grainy paste. The paste was tested for hot
slump and infiltration effectiveness like -the paste of Example
134. No significant hot slump was observed. the infiltration of
the compact was quite good, but did not reach the dramatically
high efficiency obtained in Example 134.
-47-
E.~PLE 136
. . _
A soft paste was made by blending thoroughly 20 parts of
vehicle with 80 pats of -80 mush 316 L stainless steel powder.
I vehicle was 90 parts of Petrolatum A blended with 10 parts of
a solution of 7 ports of sodium hydroxide dissolved in 93 parts of
glycerine. me asset was extruded into a fused silica boat as a
squat cylindrical shape with a small pointy peak rising about 5
mm. from a position ox ntral to the top (somewhat resembling -the
shape of the familiar milk chocolate Casey The boat then was
placed into the 600F. zone of a small electrically heated tube
fume ox through which hydrogen gas was flowing. The boat then was
moved about 2.5 cm -towards the top temperature zone of the furnace
at 4-minute intervals until about 20 cm was traversed, then was
moved the remaining approximately 5 cm into the top temperature
zone (about 1121C.~ and held there for 8 minutes. me brat was
removed to a hydrogen-protected tooling zone of the tube for 12
minutes to cool the resulting coherent sistered porous metal part
to room t~perature~ The main body of the part retained the
original shape of the exudate with no significant hot slump.
Only the pointy peak of the Kiss had blunted a bit and had
drooped somewhat.
EXAMPLE 137
A vehicle for a powdered metal paste was made by thoroughly
blending 75 parts by weight of pe-trolaturn with 5 parts by weight
of a cluck solution of 7 parts Noah in 93 parts of glycerine 10
parts I weight of bottle carbitol were coded -to make the vehicle
portion.
30 parts by weigh-t of -the foregoing vehicle was blended
thoroughly with 70 parts of 316L - stainless steel powder -100
-48-
mesh size with 35-50~ ~325 mesh to form a soft paste.
The paste was tested for hot slump by application to a
copper coupon and heating on a Browse Corporation reflow instrument
at 330C. No significant hot slump was ox æ rued,
EXPEL l38
A vehicle for powdered copper metal was made consisting
of 82'~ petrolatum and 18% of a I aye- glycerol solution.
90 parts by weight copper shot (-20 80 mesh) was hank
blended with 10 parts my weight of -the vehicle. 'the resulting
paste was applied to a vertical an a 30 angled surface (steel)
in a 1" circular and a l" square preform shape. These panels were
heated in a furnace.
The best furnace was run at foe for 30 minutes with
300 cubic meet per hour of dissociated ammonia gas.
Both forms sistered. The leading edges into the belt
furnace oxidized and did not Sinatra Both samples held their
respective shapes. me leading edges and leading corners of the
preforms set at a 30 angle slumped presumably when the vehicle
vaporized.
Thus, the vehicle successfully held the shot together up
to sistering temperature Any slumping that occurred is attributed
to the cxidized/unsintered leading loose shot edge.
-49-
EXAMPLE 139
The present example illustrates -the present invention
with a hard surfacing paste
queue vehicle was formed in the manner indicated above (as
for example in Example 137) by blending -the following ingredients
in the amounts indicated.
Petrolatum 65.0 parts
Triethanolamine25.0 parts
Colic acid 2.0 parts
Dibutylphthalate8.0 parts
The powdered hard metal nickel alloy had the following
elemental analysis:
Carbon 0.64%
Silicon 4.24%
Chromium 14.27
Cobalt 6.01~
Iron ~.65%
Boron OWE%
Nickel Balance
The sieve analysis was:
~115 mesh owe%
~150 mesh Trace
~200 mesh 21.8
-~325 mesh 56~3
-325 mesh 21.9
-50-
Ten parts by weigh-t of -the vehicle were thoroughly
blended with 90 parts by weight of the hard metal powder. The
resulting paste was applied to a steel bar:
a on a vertical face,
S b) on a flat angled surface (30-45) as
it a circle 0.74" X 0.125" thick
ii) a square 1" X 1" X 0.312" thick
c) on a flat horizontal steel surface in the
forms indicated in IBM above.
The preforms were then heated in a traveling belt furnace
under the -following conditions.
Belt speed - minute (I- 30 miss. in ho-t zone
Preheat - 600F.
Hot Zone - (a) Run 1 - 1800F.
(by Run 2 - 1900F.
(c) Run 3 - 2000F.
Atmosphere - Dissociated ammonia.
Results:
. . . _
Run 1: No melting, no apparent powder oxidation. All
forms held their original shape and approximate
dimensions. Some cracks developed.
Run 2: Melting started on the vertical sample. No melting
on all other samples which held their original
shape and dimensions. Cracks developed where
powder fell apart when the vehicle vapored.
-51-
Run 3; Vertical sample melted and the cmgled sample began to
melt, but held shape with some shrinkage. Vertical
sample began to run downwards and brazed to steel bars
together.
Conclusion:
I've vehicle restrained slumping and allowed the paste to
retain its shape up to melting -temperature of the alloy. Not all
complies melted, possibly because of the large -thermal mass of the
steel bars.
EXPEL 140
This example is to test stinter a bronze part for application
to the Anatoli Michelson hollow core mold process using a thinner
porous core mold using a bronze paste.
me paste was made in the manner illustrated in the preceding
examples according to the following formulation:
Copper Powder 77 wow
Tin Powder 8~5 w/%
No slump Vehicle
(Example Al) 14.5 wow
The paste WAS hand applied to refractory shapes in a thickness ranging
from 0.125 -to 0.?.5". One refractory shape was a graphite triangle and
the other an etched alumina rod.
The samples were placed on a thin alumina substrate on a
belt Ursa under -the following conditions.
I
~52-
Belt Spree Mooney.
Preheat 600F. (nvlO miss.)
Hot %one1540F. (I 15 wins.)
Atmosphere Dissociated ammonia
The parts were sistered. Wren the graphite triangle (spacer)
was cut in half, the bronze separated and showed good surface integrity.
Slight slumping was observed
It was indicated in this example that the sistering time my
temperature were not optimal, kit the concept worked.
The instant vehicles also are useful for swilled "functional"
or "thick film" pastes for mieroeleetronie circuit predation. These
pastes often contain very finely-divided noble or non-noble elemental
metals and alloys and metal chides such as those of ruthenium, lead,
etc., to modify resistivity; glass forming or oeramie-for~ing powder
is a fundamental component of such pastes. They usually are screen-
printed and fired on a substrate to obtain effective adhesion of the
powdered components one to another and to a substrate.
The fired products are used as dielectrics, conductors,
resistors, and capacitors. Muir paths for conducting electricity
need good line definition. mere fore, lack of significant hot slump
and accompanying shape change and thickness change Fran the original
paste deposit(s) is essential], and the inventive vehicles can provide
that control.
Their firing profile (time and temperature) often is delicate
and different for various oempositions and substrates. Typically
wiring peacock temperature, for example, with a platinun~silver alloy ox
~llaclL~gold alloy powder-containing paste on an alumina slibs-trate
to mice a conductor will be 850-950C.; for soda lime glass substrate
such puke is 550-660C.; for porcelain-enameled steel substrates such
puke is 625-675C.
-53-
he petal or alloy powder in those special pastes usually is
smaller -than 10 microns in effective diameter, often being as fine as
2 microns or of sub micron size. Normally such powder is spherical;
sometimes it is in the form of flake. The powder components useful
here can include pure gold, silver, copper, etc., as well as an alloy
containing same, or can be all glass~Eormers or ceramic-forming go
positions without elemental metal content. The vehicle for such paste
is in minor proportion relative to that of -the powdered components to
be adhered together by the firing. Gold, plating and palladium
Lo containing pastes usually cure fired in air, while copper-bearing ones
are wired in a protective atmosphere such as nitrogen.
Without the necessary anti slump systems of this inversion,
the hydrocarbon itself imparts no significant anti-ho-t slump or molten
metal flow restriction effects to pastes containing subject metal
powders. However, ale presence of a relatively small proportion of an
alkali particularly with a polyol and within the broad ranges herein-
before described exerts substantially enhanced anti-hot slump effect
and molten metal flow restriction effect than is exerted by the same
anti slump system without the alkali and used in a larger proportion
within said broad ranges.
Accordingly, it should be evident that one skilled in the
art of formulating metal powder-bearing pastes now has a way for:
controlling hot slump to a user's desired specification by formulating
for diminishing such slump modestly or even clear down to practically
zero; and for imparting, where necessary or desired, restriction of
wow of the molten metal anywhere from a modest desired proportion
down to insig~Lficance. The combination -in the instant vehicle of
hydrocarbon/antislump agent-flux system as defined herein provides
such control.
