The ferrite memory arrays are made from pre-formed metal conductors for the ferrite arrays. The conductors are made by forming a thin sheet of a metallizing paste of metal alloy powder, drying the paste layer, bisque firing the dried sheet at a first temperature, and then punching the conductors from the fired sheet. During the bisque firing, the conductor sheet shrinks to 58 percent of its pre-fired volume and the alloy particles sinter together. The conductors are embedded in ferrite sheet material and finally fired at a second higher temperature during which firing the conductors shrink approximately the same degree as the ferrite material

Baba, P. D.

Bhiwandker, N. C.

Heckler, C. H.

English

NASA Technical Reports Server

REPLY TO
ATTN OF: GP
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546
1 2 1974
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r^ A\ j> £ X C~o r~f «
Government or : l2.edu>^ ci C\-fw C.f\
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Bonnie L. Woerner
Enclosure
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https://ntrs.nasa.gov/search.jsp?R=19750004960 2020-03-19T20:31:34+00:00Z
United States Patent
• i
Fletcher et al.
[in 3,849,877
[45] Nov. 26, 1974
[54] METHOD FOR MAKING CONDUCTORS
FOR FERRITE MEMORY ARRAYS
[76] Inventors: James C. Fletcher, Administrator of
the National Aeronautics and Space
Administration with respect to an
invention of; Clarence H. Heckler,
Jr., Palo Alto; Paul D. Baba, San
Carlos; Nutan C. Bhiwandker, Mt.
View, all of Calif.
[22] Filed: Aug. 22, 1973
[21] Appl. No.: 390,466
[52] U.S. Cl 29/604, 29/420, 75/200,
340/174 MA
[51] Int. Cl HOlf 7/06
[58] Field of Search 29/604, 420, 625, 624;
" 340/174 MA, 174 JA; 252/514, 512, 513;
75/200
[56] References Cited
UNITED STATES PATENTS
3,040,301 6/1962 Howatt et al 29/604 U X
3,075,280 1/1963 Jack et al 29/625
3,123,748 3/1964 Brownlow 29/604 U X
3,144,330 8/1964 Storchheim : 29/420 U X
3,414,641 12/1968
3,450,918 6/.1969
3,534,471 10/1970
Miller 252/514 X
Burr 29/598 X
Babbitt et al 29/604
Primary Examiner—C. W. Lanham
Assistant Examiner—Carl E. Hall
Attorney, Agent, or Firm—Wallace J. Nelson; Howard
J. Osborn; John R. Manning
[57] ABSTRACT
Method of forming ferrite memory arrays. The ferrite
memory arrays are made from pre-formed metal con-
ductors for the ferrite arrays. The conductors are
made by forming a thin sheet of a metallizing paste of
metal alloy powder, drying the paste layer, bisque fir-'
ing the dried sheet at a first temperature and then
punching the conductors from the fired sheet. During
the bisque firing, the conductor sheet shrinks to 58
percent of its pre-fired volume and the alloy particles
sinter together.
The conductors.formed are embedded in ferrite sheet
material and finally fired at a second higher
temperature during which firing the conductors shrink
approximately the same degree as the ferrite material.
10 Claims, 1 Drawing Figure
aoaaaoaoac
[DDoooaopaaC
loaapoaaaDat
DDDDaaaoot*
PREPARE A LAYER OF POWDERED
CONDUCTIVE METAL WITH AN
ORGANIC BINDER TO FORM A
PASTE
DRV AND BISQUE FIRE PASTE
LAYER 20-60 MINUTES AT
800*-TOO* C TO FORM A
CONDUCTOR SHEET
FORM A PLURALITY OF INDIVIDUAL
CONDUCTORS FROM THE BISQUE
FIRED SHEET
EMBED THE INDIVIDUAL
CONDUCTORS IN A PREFORMED
FERRITE SHEET
FIRE THE EMBEDDED FERRITE
SHEET AT I34O*-IS60* C FOR
1-20 HOURS IN AN OXYGEN
ATMOSPHERE AND COOL IN
NITR06EN
RECOVER A FERRITE MEMORY
ARRAY
PATENTED MY 26 074
1.849,87
I
aaa a QD aaacd
la DP p DP a an a]±
[OD'D b a a a D aot±
[gap D'DD DP oar*"
PREPARE A LAYER OF POWDERED
CONDUCTIVE METAL WITH AN
ORGANIC BINDER TO FORM A
PASTE
DRY AND BISQUE FIRE PASTE
LAYER 20-60 MINUTES AT
800°- 900° C TO FORM A
CONDUCTOR SHEET
FORM A PLURALITY OF INDIVIDUAL
CONDUCTORS FROM THE BISQUE
FIRED SHEET
EMBED THE INDIVIDUAL
CONDUCTORS IN A PREFORMED
FERRITE SHEET
FIRE THE EMBEDDED FERRITE
SHEET AT I340°-I360°C FOR
1-20 HOURS IN AN OXYGEN
ATMOSPHERE AND COOL IN
NITROGEN
RECOVER A FERRITE MEMORY
ARRAY
3,849,877
1 2
METHOD FOR MAKING CONDUCTORS FOR the original thickness of the conductor material paste.
FERRITE MEMORY ARRAYS In general, the thickness of the dried conductor mate-
/-.OI/-MXT /-Mr -T-UC ixn,r-xrr-i/~>H, T^ ty^ formed from the previously described wet
ORIGIN OF THE INVENTION conductor material paste layer will be on the order of
The invention described herein was made in the per- 5 1 to 4 mis. In a preferred embodiment, the dried sheets
formance of work under a NASA contract and is sub- of conductor material will range in thickness from 2.4
ject to the provisions of Section 305 of the National to 3.2 mis. The dried conductor material sheet is then
Aeronautics and. Space Act of 1958, Public Law placed between two spaced alumina setter sheets ap-
85-568 (72 Stat. 435; 42 U.S.C. 2457). proximately 6 to 10 mis. apart, preferably 6 to 7 mis.,
DA/-f/-nr>niur> /-vir -rue iMwcxrri/-»M 10 and bisque fired at about 800° to 900°C., preferablyBACKGROUND OF THE INVENTION
 84Qo to
M
855oC for about 20 to 60 minutes. The tern-
1. Field of the Invention perature range and time of firing depends on the com-
This invention relates to the making of ferrite mem- position of the particular alloy used as the conductor
ory arrays and more particularly to a method of form- material. The firing takes place in an oxidizing atmo-
ing and embedding metal conductors in the ferrite ma- 15 sphere which is usually air or oxygen. Preferably the fir-
terial. The method of the invention results in the con- ing is carried out for 45 minutes in an oxygen atmo-
trolled shrinkage of the conductors eliminating break- sphere.
age of the conductors and ferrite materials during final During the bisque firing, the particles in the conduc-
firing of the ferrite materials by eliminating the strains tor material sheet sinter together to form a metallic
normally built up between the ferrite and the conduc- 20 conductor sheet of about 58 percent of its prefired vol-
tors during the final firing of the ferrite. ume and from 1 to 3 mis. thick, preferably 2 to 2.3 mis.,
2. Prior Art depending upon the particular alloy composition form-
. In the past, ferrite memory arrays in which metal ing the conductor material. Individual conductors are
conductors were embedded in blocks of ferrite were then punched from the thus formed sheet by means of
formulated by embedding a paste of metal particles, 25
 a die set. Conductors formed are by way of example
binder, and a solvent in the ferrite material and firing about 4 inches X 0.0055 inch X 0.0025 inch although
the ferrite material in the form of sheets at tempera- any dimensional range desired may be utilized. Typical
tures on the order of 1,000° to 1,350°C for 2 to 24 examples are from 4.1 to 4.3 inches long, from 5 to 6
hours. During the firing of the ferrite, the solvent of the mis. wide, and from 2 to 2.3 mis. thick. The conductors
conductor paste volatilized along with the binder and 30 are then embedded in pre-formed ferrite sheets and the
the precious metal particles were sintered together. Be- assembly fired at about 1,000° to 1,375°C. depending
cause of the shrinkage due to the volatilization of the upon the particular ferrite material composition. Struc-
binder and solvent, and the sintering, the conductor tures using the preferred embodiments of the invention
normally shrunk considerably more than the ferrite ma- . are usually fired at temperatures in the range of 1,340°
terial in which it was embedded. To match the shrink- 35 to 1,360°C, with 1,350° C. being preferred. Firing time
age the particle size and shape and the material-to- varies from 1 to 20 hours depending upon the ferrite
binder ratio had to be closely controlled. Even so, compositions, with 4 to 5 hours being utilized with the
strains and factional forces between the ferrite and preferred embodiments. It has been found that the
conductor materials developed which very often re- shrinkage of the bisque fired conductor material and
suited in breakage of the conductor material which had 40 ferrite closely approximate each other, the linear
previously not attained any significant strength. Be- shrinkage being generally on the order of 20 percent
cause of these problems, an inordinately high proper- during the final firing step.
tion of the fired ferrite arrays were rendered useless. The metallizing paste used in the formulation of the
SUMMARY OF THE INVENTION 4S conductors generally comprises from about 60 to 95SUMMAKY Uh 1Mb INVhN HUN 45
 percent preferably 75.to 90 percent of metal powder
The present invention substantially reduces the rate and from 5 to 40 percent preferably 10 to 25 percent
of failure in the final firing of ferrite arrays by providing of an organic binder powder with sufficient amount of
a method wherein the conductors for the arrays are an inert organic vehicle to form a spreadable paste. It
pre-formed and bisque fired at temperatures signifi- is generally preferred to use a conductor material com-
cantly lower than the temperature of the final firing of position where platinum comprises the highest propor-
the ferrite array. This causes the metal particles com- tion of metal powder. An example of a suitable metal-
prising the conductor to sinter together to pre-form the lizing composition is one sold by duPont de Nemours
conductor and allow it to obtain .initial structural .Co. under the designation DP8283 comprising 60 per-
strength. The sintering and driving off of the solvent cent by weight of an alloy of platinum, palladium and
and volatilizable organic binder significantly pre- gold in a ratio of 50:25:25, anorganic resin binder and
shrinks the formed conductor material so that during organic solvent, the overall solids content being 80 per-
the final firing of the ferrite material, the shrinkage of cent by weight.
the embedded conductor material will approximate the Generally suitable metallizing conductor materials
shrinkage of the ferrite. ,- are formed of metals selected from the group consisting
According to the present invention a paste contain- of gold, platinum, palladium, rhodium, irridium or
ing the metal particles suspended in a vehicle of or- other metals of good conductivity and low reactivity
ganic binder and a solvent is formed into a layer ap- with ferrites. The conductor material is fabricated so
proximately 5 to 15 mis. thick, preferably 8 to 10 mis., that the alloy has a melting temperature higher than the
by doctor-blading and then drying for approximately
 65 final firing temperature at which sintering takes place,
16 hours at 30° to 40°C. or until the conductor material and a linear shrinkage equal to or no greater than 5 per-
paste is thoroughly dried. The thickness of the dried cent more than the linear shrinkage of the ferrite mate-
sheet of conductor material will, of course, depend on rial in which the conductors are to be embedded.
3,849,877
3
DESCRIPTION OF PREFERRED EMBODIMENTS ' **
A sheet of conductor material is formed by doctor- Each array is placed on an alumina setter sheet cov-
blading a conductor material paste of metal particles ered with a coating of thoria powder to prevent stick-
compresed of an alloy of gold, platinum and palladium 5 ing. A second alumina setter is supported over the top
and supplied by E. I. duPont under the identification of the array by a pair of spacers. The arrays are fired
platinum alloy paste DP8283 as mentioned above. The in a tube furnace at 1 ,350°C. for 4 hours in an oxygen
doctor blade utilized has a height of approximately 10 atmosphere and then cooled in nitrogen.
mis. The sheets are dried for approximately 1 6 hours at During the final firing, the conductors shrink approx-
30° to 40°C and thereafter have a thickness of approxi- I0 imately 20 percent which approximates the shrinkage
mately 3 to 3.2 mis. The conductor sheet is then bisque of the ferrite, thus substantially eliminating any strains
fired for approximately 45 minutes at 840°C. after between the ferrite and the conductor material and
being placed between two flat alumina setter sheets thereby greatly reducing instances of broken conduc-
spaced 6 to 7 mis. apart. During the bisque firing, the tors due to frictional forces between the ferrite and the
organic binder volatilizes and the alloy powder sinters 15 conductor material.
together to form a metallic conductor sheet approxi- While the invention has been explained by a detailed
mately 2.5 mis. thick and having a volume of approxi- description of certain specific embodiments, it is un-
mately 58 percent of its pre-fired volume. Conductors derstood that various modifications and substitutions
are formed from the bisque fired sintered sheet utilizing can be made in any of them within the scope of the ap-
a punch and die set and are approximately 4 inches X perided claims which are intended to also include
0.0055 inch X 0.0025 inch. equivalents of such embodiments.
Ferrite sheets are prepared by milling a ferrite com-. I claim:
position of Mg^ Mn.432 Zn U4 Fe.Tjg O4 with a polyvi- 1. A method of forming a ferrite memory array com-
nyl chloride binder on a calendar mill with 3 inches rol- -, prising forming a layer of a metal conductor material
lers and with roller speed ratios of 1 : 1 and 1.4:1, main- paste composition comprising from 60 to 95 percent by
tained at a temperature of 80°C. for 40 minutes. A weight of a powdered metal having good conductivity
coarsesurfaced sheet resulted. This was transformed and a low reactivity with ferrites, and from 5 to 40 per-
into 7 mil sheets by cutting 1 inch X 3 inches pieces cent by weight of an organic binder together with an
from the calendered sheet and thermopressing the
 3Q organic vehicle, drying said layer, bisque firing said
pieces to the desired thickness on a Carver hydraulic dried layer at a first temperature below the melting
press at a platen.temperature of 1 50°C., using shims to point of said metal, thereby reducing the density of the
limit the closing of the platens. conductor layer to a first degree by sintering said pow-
The ferrite sheets are then embossed with channels dered metal together to form a conductor sheet, form-
for embedding the conductors. The lamina are embed- 35- ing a plurality of individual conductors from the bisque
ded by thermopressing with an embossing mold using fired sheet, embedding said conductors in a ferrite
a pressure of 5,000 Ibs. at 60°C. using a shim type of sheet and then firing said ferrite sheet at a second and
embossing mold. The channels were either 0.003 or higher temperature than said first temperature to fur-
0.006 inch wide. ther shrink the conductor material at a rate compatible
After laminae are embossed, they are coated with a 40 with the ferrite shrinkage.
squeegee medium, L. Reusche and Co. Type 1 63C, 2. A method as claimed in claim 1 wherein said pow-
scraped, and dried. Since this medium is over 90 per- dered metal is selected from the group consisting of
cent pine oil, only a thin layer of resin is deposited in gold, platinum, palladium, rhodium, irridium and mix-
the bottom of the channels when the laminae are dried. tures and alloys thereof.
This is used to cement the conductors in the channels 45 3. A method as claimed in claim 1 wherein said pow-
during assembly. dered metal is selected from the group consisting of
The conductors are embedded in the embossed fer- gold, platinum, palladium and mixtures and alloys
rite lamina and secured in place by thermobonding at thereof.
a temperature of 60°C. under light pressure. The lami- 4. A method as claimed in claim 3 wherein said metal
nae are then .thermopressed between shims to embed 5® comprises about 80 percent by weight of said conduc-
the conductors so that they are flush with the surface tor material paste composition.
of the lamina. 5. A method as claimed in claim 1 wherein said first
The assembly of the laminae to form monolithic ar- temperature ranges from about 800° to about 900°C.
rays was accomplished with the aid of a multisection 6. A method as claimed in claim 5 wherein said sec-
assembly jig and a pair of trimming dies. After the em- 55 ond temperature ranges from approximately 1,000°C
bedding of a full complement of conductors in a word to approximately 1,375°C for 1 to 20 hours.
lamina and in a digit/sense lamina was completed, each 7. A method as claimed in claim 2 wherein said first
lamina was trimmed to a size that would expose 0.050 temperature ranges from about 840° to 855°C, said
inch at each end of the conductors. This was accom- , bisque firing being carried out for 20 to 60 minutes and
plished by making the digit/sense lamina 0.10 inch wherein said second and higher temperature ranges
longer than the word lamina, the word lamina 0. 1 0 inch from 1 ,340° to 1 ,360°C and said firing is from 1 to 20
wider than the digit/sense lamina, and the 0.0008 inch hours.
insulating lamina 0.1 inch less than the maximum 8. A method as claimed in claim 2 wherein said
length and width. The overall array dimensions were
 65 bisque firing is carried.out at a temperature of about
4. 1 59 inches X 1 . 1 60 inches before firing. 840° to 850°C for about 20 to 60 minutes and said fir-
Bonding of the laminae is accomplished by applying ing is carried out at a temperature of about 1 ,340° to
a pressure of 8 pounds per square inch at a temperature 1 ,360°C for 4 to 5 hours.
3,849,877
5 6
9. A method as claimed in claim 3 wherein said 10. A method as claimed in claim 3 wherein said
bisque firing is carried out at a temperature of about
 sheet of metal paste js initially from 5 to 15 mils thick
840° to 850°C for about.20 to 60 minutes and said fir- ^
 f .. ,. . ,
ing is carried out at a temperature of about 1,340° to and from ' to 4 mlls thick after
l,360°Cfor4to5hours. 5 * * *
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Method for making conductors for ferrite memory arrays

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