The firmly adherent film of bondable metal, such as silver, is applied to the surface of glass or other substrate by decomposing a layer of solution of a thermally decomposable metallo-organic deposition (MOD) compound such as silver neodecanoate in xylene. The MOD compound thermally decomposes into metal and gaseous by-products. Sealing is accomplished by depositing a layer of bonding metal, such as solder or a brazing alloy, on the metal film and then forming an assembly with another high melting point metal surface such as a layer of Kovar. When the assembly is heated above the temperature of the solder, the solder flows, wets the adjacent surfaces and forms a hermetic seal between the metal film and metal surface when the assembly cools

Gallagher, Brian D.

English

NASA Technical Reports Server

United States Patent [191 
Gallagher 
[54] METHOD FOR FORMING HERMETIC 
[75] Inventor: Brian D. Gallagher, Costa Mesa, 
[73] Assignee: The United States of America as 
SEALS 
Calif. 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 765,978 
[22] Filed: Aug. 15,1985 
[51] Int. c1.4 ........................... BWK 1/20; B05D 3/02 
[52] U.S. (3. .................................... 228/124; 228/209, 
228/208; 421/229 
[58] Field of Search ............ 228/124, 209, 208; 
421/229 
~561 References Cited 
U.S. PATENT DOCUMENTS 
2,984,575 5/1961 Fitch ................................... 228/124 
3,391,447 7/1968 Ard ..................................... 228/124 
3,593,412 7/1971 Foote .................................. 228/122 
4,262,040 4/1981 Russo .................................. 427/229 
4,333,966 6/1982 Deffeyes et al. .......... 427/229 
4,399,090 8/1983 Sprangers et al. .................. 427/229 
3,207,838 9/1965 McCormack ............ 228/209 
4,188,417 2/1980 Lichtenberg ............ 427/229 
pi] Patent Number: 4,650,108 
[45] Date of Patent: Mar. 17, 1987 
4,418,099 11/1983 Cuevos et al. ...................... 427/229 
4,459,264 7/1984 Mizuhara ............................ 427/229 
FOREIGN PATENT DOCUMENTS 
2203617 VI973 Fed. Rep. of Germany ...... 228/122 
Primary Examiner-Nicholas P. Godici 
Assistant Examiner-Samuel M. Heinrich 
Attorney. Agent. or Firm-Paul F. McCaul; John R. 
Manning; Thomas H. Jones 
A firmly adherent film 16 of bondable metal, such as 
silver, is applied to the surface 10 of glass or other sub- 
strate by decomposing a layer 14 of a solution of a ther- 
mally decomposable metallo-organic deposition 
(MOD) compound such as silver neodecanoate in xy- 
lene. The MOD compound thermally decomposes into 
metal and gaseous by-products. Sealing is accomplished 
by depositing a layer 18 of bonding metal, such as solder 
or a brazing alloy, on the metal film and then forming an 
assembly with another high melting point metal surface 
20 such as a layer of Kovar. When the assembly is 
heated above the temperature of the solder, the solder 
flows, wets the adjacent surfaces and forms a hermetic 
seal between the metal film 14 and metal surface 20 
when the assembly cools. 
1571 ABSTRACT 
12 Claims, 14 Drawing Fignres 
SILVER NEODECANOATE 
56\ /- 
60J . 
https://ntrs.nasa.gov/search.jsp?R=19870011901 2020-03-23T15:28:29+00:00Z
U.S. Patent MW. 17,1987 Sheet 1 of 3 4,650,108 
TEMPERATURE pel 
148.1 
N 
0 a 
US. Patent M=. 17,1987 Sheet 2 of 3 4,650,108 
TGA 
os c 
l- 
W 
I 
a 
1 1 1 1 1 1 1 1 1  I I I '  
-METHANOL - 
- 
TEMPERATURE ["C] 
f ig. 3. 
U.S. Patent MW. 17,1987 
14- r10  
12 
Fig 4. 
Fig. 6u. 
39 
34 
Fig. 6c. 
Fig. 6e. 
Sheet 3 of 3 4,650,108 
20 
16 
18 
12 
Fig. 5 
54 
59 
SOLDER PASTE 64 
5 0  
Fig. 7c. 
56\ JSILVER NEODECANOATE 
Fig. 6b. 
42 
Fig. 6d 
METAL FRAME 
I 
Fig. 7a 
/ STD AU PLATED METAL 
66 CAP 
5 0  
Fig. 7d 
4,650,108 
1 
METHOD FOR FORMING HERMETIC SEALS 
ORIGIN OF THE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA contract, and is sub- 
ject to the provisions of Public Law 96-517 (35 USC 
202) in which the Contractor has elected not to retain 
title. 
10 
TECHNICAL FIELD 
The invention relates to forming hermetic seals be- 
tween a high melting metal surface and a second surface 
of glass, ceramic, refractory or semiconductor and, 
more particularly, this invention relates to a method for l5 
depositing a film of bondable metal, such as silver, on 
the second surface. 
It is very difficult to directly bond or seal the glass, 
ceramics, semiconductor or refractory surfaces. Most 
bonding or sealing materials, such as solders or brazes, 20 
will crack, peel or separate from these surfaces unless 
the surface has been pretreated to deposit a thin, adher- 
ent film of a bondable metal such as silver or its mixtures 
with other metals. The present processes utilized for 
depositing the bondable metal, such as electroless plat- 25 
ing or vapor decomposition, requires special apparatus 
and processing or operate at high temperature. The 
vapor decomposition processes cannot be utilized with 
thermally sensitive substrates, such as photovoltaic cells 
or other semiconductors, since the high temperature 30 
required to decompose the compound can cause diffu- 
sion affecting the characteristics of the doped layers, 
electrodes or contacts. 
STATEMENT OF THE INVENTION 35 
An improved method of depositing a film of bondable 
metal on the surface of glass or other substrates is pro- 
vided by the present invention. The method is reliable 
and provides a well-controlled, firmly adherent film of 
metal on the substrate at a low temperature. The film, 40 
once formed, can be subjected to high temperature such 
as during brazing without disruption of the film or re- 
moval from the surface. The method can also be utilized 
to selectively deposit films covering a portion of the 
surface such as a perimeter border pattern which can be 45 
used to selectively form an edge seal. 
The method of the invention utilizes a thermally 
decomposable, metallo-organic deposition (MOD) 
compound dissolved in an organic solvent that vapor- 
izes at low temperature. The amount of solvent can be 50 
varied to provide different viscosities. The solution of 
MOD compound is deposited on the substrate and the 
solvent is evaporated to form a layer of MOD. The 
layer is then heated to at least the decomposition tem- 
perature of the MOD compound. The MOD compound 55 
thermally decomposes into metal and gaseous by-pro- 
ducts. The metal deposits as a firmly adherent film on 
the surface of the substrate. Selective portions of the 
layer can be decomposed to form metal patterns, such 
as a perimeter pattern, by use of masks or by use of a 60 
translatable light or heat source. The remaining layer of 
MOD compound can be removed in a solvent bath. 
Alternatively, the layer can be deposited in a pattern by 
a writing or masking technique. 
bonding metal, such as solder or a brazing alloy, on the 
metal film. A fluxing agent may be present, if desired, to 
prevent oxidation. An assembly of the metal part with 
Sealing is accomplished by depositing a layer of 65 
2 
another high melting surface, such as a metal-coated 
sheet of glass is then formed. The assembly is then 
heated while being biased by clamping or other pressure 
future to fuse the bonding alloy and join the two metal 
surfaces. Sealing, in special cases, could also be accom- 
plished by ultrasonic bonding. 
The MOD compounds utilized in the invention have 
high solubility in organic solvents and high uniform 
metal content providing a high, uniform deposit of 
metal at low concentration. The compounds decompose 
at low temperatures without going through a melting 
stage and completely form gaseous by-products without 
leaving a carbon deposit. The compounds are stable 
under ambient conditions, are non-toxic and produce 
non-toxic decomposition products. 
The method of the invention can be utilized to form 
hermetic seals for solar photovoltaic elements or panels 
or microelectronic devices such as VLSI devices or 
hybrid microelectronics. The method can be utilized in 
any application requiring forming a seal between a 
glass, ceramic, semiconductor or refractory surface and 
a high melting metal surface. 
These and many other features and attendant advan- 
tages of the invention will become apparent as the in- 
vention becomes better understood by reference to the 
following detailed description when considered in con- 
junction with the accompanying drawings. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a phase stability diagram for the Ag-C-0 
system; 
FIG. 2 is a thermogravimetric analysis (TGA) for 
silver neodecanoate dissolved in methanol; 
FIG. 3 is a differential scanning calorimeter DSC for 
the silver neodecanoate composition tested in FIG. 2; 
FIG. 4 is a cross sectional view of an assembly for 
forming a hermetic seal in accordance with the inven- 
tion; 
FIG. 5 is a cross-sectional view of the assembly in 
FIG. 4 after firing; 
FIGS. a(u)-(e) are a series of steps illustrating the 
formation of a hermetically sealed glass-glass sandwich 
according to the invention; and 
FIGS. 7(u)-(d) are a series of steps illustrating form- 
ing a hermetically sealed microelectronic device. 
DETAILED DESCRIPTION OF THE 
INVENTION 
The metallo-organic decomposition (MOD) com- 
pound contains a heteroatom such as 0, S or N bridging 
the metal ion to the organic group. The MOD com- 
pound can be selected from compounds of the formula: 
MXR 
where M is the metal, X is the bridging atom and R is a 
thermally decomposable organic group containing from 
2 to 20 carbon atoms. The bondable metal M preferably 
contains at least 90 percent of an inert, noble metal, such 
as silver. Up to 10 percent, usually 5 percent, of various 
other metals can be present as modifiers, such as Bi 
which acts as a fluxing agent or Pt to improve solder- 
ability. Other suitable alloying metals are Ni, Cr or Co. 
The XR group can be selected from amines, amides, 
mercaptides or mono or dibasic carboxylic acids. Other 
representative MOD compounds are amine, alkoxides, 
and metal-pyridine complexes. The most well-behaved 
4.650,108 I -  
3 
and preferred MOD compounds are metal carboxylate 
salts of the formula: 
R' 
I 
I 
R2 
R3- C-C-0- M 
where R1, Rz and R3 are aliphatic or aromatic hydrocar- 
bon groups such as hydrogen, alkyl, alkoxy, alkyl-thio, 
phenyl, hydroxyalkyl, hydroxyphenyl and the like and 
the carbon content of the sum of R1, R2 and R3 is from 
2 to 14 carbon atoms. Preferably, at least one of R', Rz 
and R3 contains a secondary or tertiary carbon since 
such compounds are more soluble in organic solvent. 
The solubility also increases with increasing chain 
length of the organic radical. However, the metal con- 
tent of the compound will decrease. The most preferred 
carboxylic acids are neodecanoates or 2-ethyl hexano- 
ates. 
The organic solvent may be chosen from a wide 
variety of materials, suitably halogenated hydrocar- 
bons, such as chloroform or carbon tetrachloride; ali- 
phatic materials such as kerosene or heptane; aromatic 
solvents such as benzene, toluene, xylene, or benzyl 
alcohol; alkanols such as methanol, ethanol or butanol; 
ketones such as acetone or MEK; acetones such as ethyl 
or butyl acetate; or esters such as ethyl ether. The MOD 
compound can be present in amounts up to the solubil- 
ity limit, generally from 5 to 30 percent by weight. 
Other thermally decomposable materials, such as rheol- 
ogy adjusters, thickeners or plasticizers such as butyl 
carbitol, may be dissolved in the common solvent in 
amounts up to 10 percent by weight. 
alloys and melt at a temperature from about looo" F. to 
about 2ooo" 
The layer 12 of MOD can be applied by brush, roller, 
Representative MOD compounds utilizable in the 35 screening, printing, spray, dip or spin-on techniques. 
The thermal decomposition can be effected by inserting method of the invention are neodecanoates or 2-ethyl 
hexanoates of Ag, 97.5 Ag 2.5 Pt, 96.5 Ag 1 Bi 2.5 Pt, 99 the coated substrate in a furnace as a resistance 
Ag 1 Bi, 97.5 Ag 2.5 Ni, 97.5 Ag 2.5 Co, 97.5 Ag 2.5 Cr. furnace Or by means O f a  beam Or coherent Or imoher- 
The MOD compounds are prepared from &e free ent light. An edge pattern may be applied by applying a 
carboxylic acid by fipst converting the acid to the am- 40 narrow beam such as a laser along the edges Of Ohe 
monium salt at room temperature in aqueous ammo- surface or by printing a narrow l i e  by  jet printing 
nium hydroxide followed by an mion exchange of the or other technique along the edge of the substrate. 
metal with moium ion ( +). the case of silver The substrate can be any materid not directly bond- 
the silver neodecanoate is recovered as a white solid. able to a ~& melting Point metal. The invention is 
45 readily applicable to substrates such as glass, ceramics 
EXAMPLE 1 or refractories such as quartz, silica, titania or zirconia 
A solution containing 30 percent by weight of and semiconductors such silicon Or germanium Or 
neodecanoate (about 10 percent silver) in xylene was 1II-V ComPoWds Such as gallium arsenide. The high 
prepared. The phase stability diagram of this com- melting Point surface Can be metal Commonly 
pound, as shown in FIG. 1, indicates there is a broad 50 fOrmed by soldering Or brazing Such as iron, silver, 
process window in which no carbon is formed and in gold, Platinum, aluminum Or alloys thereof. 
which the only reaction products are Ag, co and COz. Formation of a hermetically sealed assembly between 
This occurs during reaction in at ambient pressure two pieces of glass is illustrated in FIG. 6. In FIGS. 6a 
and temperatures above the decomposition temperature and 6b. a wide 30 border layer and narrow 32 border 
and below about 900" C. In the TGA shown in FIG. 2, 5s layer are deposited on two sheets M,36 of glass from a 
the initial horizontal portion corresponds to evapoba- 38 percent solution of sfier neodecanoate in xylene by 
tion of the methanol solvent. Decomposition starts at means of an on demand ink jet printer. The coated glass 
about 222.8" C. and is essentially completed at 261' e. sheets are heated in air at 260" C. to evaporate the xy- 
This is confirmed by the DSC. chart shorn in FIG. 3 lene and decompose the silver neodecanoate to deposit 
which shows a very well-behaved reaction at about 60 a thin film 39,M of silver shown in FIG. 6d. The two 
260" C. sheets are assembled as shown in FIG. 6e and heated to 
The composition is applied as a layer on the surface of the melting point of the solder 42 by means of a tungsten 
a substrate in an mount sufficient to form at least a lamp to form an adherent assembly. 
monomolecular film of the metal. The metal film can be Formation of a hermetic seal for an integrated circuit 
built up by electroplating or by successive deposition 65 is described in FIG. 7. As shown in the top view of 
and decomposition of MOD layers. Generally, film FIG. 7u, a perimeter border film 50 of silver is deposited 
thickness of over 10-3 in thickness of metal should not by decomposing a layer of silver neodecanoate on the 
be deposited in a single application of MOD since the surface 52 of a silicon chip 54. The chip 54 contains an 
4 
evolution of gaseous products may disrupt the continu- 
ity of the film. 
Referring now to FIG. 4, the silver MOD composi- 
tion in solvent, for example xylene, is applied to a sur- 
5 face 10 of the substrate 12 and dried to form a layer 14. 
The layer 14 is heated to above 260" C. to decompose 
the MOD and form a silver film 16 shown in FIG. 5. An 
assembly is formed containing a layer 18 of bonding 
alloy such as solder and a further higher melting layer 
10 20 of another metal such as Kovar. When the assembly 
is heated to above the temperature of the bonding layer 
18, the alloy will form a bond firmly adhering the film 
14 to the layer 20. 
The bonding alloy is usually a solder or a brazing 
Is alloy. These materials melt at a lower temperature than 
the adjacent metal surfaces and wet these surfaces. 
When the molten alloy cools, a firm, gas impervious 
bond is formed. Lead-tin solders contain, on an atomic 
basis, from 25-50 percent tin, 49-74 percent lead and 
2o optional minor amounts of 0.05 to 2.5 percent of anti- 
mony, copper and bismuth, usually a maximum of 0.05 
to 2.0 percent antimony; 0.08 percent copper and 0.25 
percent bismuth. Soft solders contain from 25-50 per- 
cent lead, 25-50 percent tin and 25-50 percent bismuth 
25 and melt at temperatures from about 265' F. to 335" F. 
Silver solders contain from 10 to 80 percent silver, 15 
to 52 percent copper, 4 to 38 percent zinc and 3 to 16 
percent of other materials such as Cd, P or Ni. These 
3o solders melt at temperatures from aboat 1200" F. to 
1500" F. Brazing alloys are generally copper-zinc brass 
. 
4,650,108 
5 6 
integrated circuit 56 in the form of a stack of doped 
layers of semiconductor connected by a series of con- 
ductor paths. 
external devices by means of electrodes 58,60 placed on 
the back surfaces 59 of the chip 54, asghown in FIG. 76. 
A layer 64 of solder paste is applied to the film 50 and 
a standard such as a gold plated metal cap 66* is 
placed on the solder layer 64 as shown in FIG. 7d The 10 substrate. 
assembly is heated to fuse and seal the solder to the 
silver film 50 and the cap 66, as shown in FIG. 7d. 
The low temperature metallization sealing process 
can be utilized in any application requiring joining or 
sealing a glass, ceramic or semiconductor to a higher 15 metals are selected from Pt, Cr, CO, Ni or Bi. 
melting metal. The fusing of the solder or braze can be 
energy or by means of a heat gun. 
the invention have been described and that numerous 
substitutions, modifications and alterations are permissi- 
ble without departing from the spirit and scope of the 
invention as defined in the following claims. 
heating the assembly to above the melting point of 
the material and soldering or brazing the second 
surface to the first surface to form a seal. 
ne integrated circuit 56 can be connected to other 2. A method according t0 Claim 1 further including 
5 the step of selectively decomposing the layer of com- 
pound to form a pattern of silver film and removing the 
in which the high 
melting point metal surface is a coating on the surface of 
4. A method according to claim 1 in which the bond- 
able metal comprises silver containing up to 10 atomic 
percent of other metals. 
5. A method according to claim 4 in which the other 
6. A method according to claim 5 in which the com- 
of the solution from the second surface. 
3. A method according to claim 
effected with a directed beam of radiation, by ultrasonic pound selected from carboxylates, amines, alkoxida 
or metal pyridine complexes. 
It is to be realized that only preferred embodiments of 2o pound is a carboxylate of the 7. A method according to claim 3 in which the com- 
R1 0 
I II 
I 
R*-C-C-0-M 
25 R3 I claim: 
1. A method of forming a seal between a first metal 
surface having a high melting Point and a second Sur-  
face selected from glass, ceramic, refractory or semi- 
conductor comprising the steps of: 
where M is silver of an alloy thereof and R1, R2 and R3 
are organic groups containing a total of 2 to 14 carbon 
atoms. 
8. A method according to claim 7 in which R1, R* or 
R3 contain a secondary or tertiary carbon atom. 
9. A method according to claim 8 in which the com- 
pound is selected from neodecanoates or 2-ethyl hex- 
anoates. 
10. A method according to claim 1 in which the 
bonding material is selected from a solder or brazing 
alloy. 
the step of selectively applying said solution to portions 
12. A method according to claim 11 in which the 
Dattern is in the form of a border on the second surface. 
applying a solution of a silver-organic compound in 30 
an organic solvent to the second surface to form a 
thin, uniform layer, said compound including a 
moiety an atom selected from 0, N or s 
bridging a silver atom to an organic group; 
evaporating the solvent from the solution to form a 
layer of said compound; 
of silver adherent to the second surface; 
material on the film; 
35 
decomposing the compound to form a film 11. A method according to claim 1 further including 
depositing a layer of low melting point metal bonding 40 of the second surface to form a paern. 
placing the first surface on the layer of material to 
- fo& an assembly; and 
45 
50 
+ * * * *  
55 
65 


Method for forming hermetic seals

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