CA1038501A - Electrical interconnection for metallized ceramic arrays - Google Patents

Abstract

ELECTRICAL INTERCONNECTION FOR METALLIZED CERAMIC ARRAYS

Abstract of the Disclosure Metal such as gold used for electroplating small metallized ceramic pieces is conserved by providing arrays of such pieces in which electrical interconnections crossing lines of separation of the pieces completely connect all parts to be plated in the array but are severed when the peices are separated.

Description

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This invention relates to a method for conserying the metal such as gold used in electropiating the small ceramic pieces which are adapted for the mounting of electric devices. This inYention further relates to arrays of ceramic substrates which are electrically interconnected Many ceramic substrates and particularl~ package units include many more small surface areas to be gold plated usually in con~unction ~ ~ I
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with at least one area which may be 20 to 100 times as large as the indivi~
dual small sur~ace areas. Usuall~ barrel plating procedures are used for such packsee units so that there is a strong tendency to build up heavy gold 10deposits ~of the order of 0.02 to o.o8 m~. thick) on the larger surface areas ~hile attaining the much thinner gold deposit (of a thickness of about . .
0.001 to 0.002 mm.) on the smaller surface areas. In addition to the wast~
age of the very expensive gold in the heavy deposits which cannot be re-clalmed, there is a considerable amount o~ gold plated onto the shot used . ~ ~, in barrel plating which can be recovered in great part only b~ extra effort. ~ ~
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In short, then, although procedures for making small ceramic substrates are ,:
available, costs are affected by losses of gold in the procedures over what is actually fully adequate for the electrical requirements. This can be a substantial factor in producing large numbers of such articles.
One ob~ect of this invention is to provide economies in the metal used in the electroplating of partially metallizea ceramic substrates.

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It has been found that increased efficiency in r~ e /e ctr ~ /at ~^~
the U~3 ~r ~old is achieved by so constructing an array ~
of metallized ceramic substrates particularly packaging `
units, having a multiplicity of external terminals and lnternal terminals connected thereto, as well as havinginternal mounting pads, that means are provlded for separation of ceramic substrates from one another and from margins and gutter pieces along predetermlned~lines . .
of separation and interconnections are provided between external terminals of ad~acent parts and between pads of ad~acent parts crossing lines of separation and a metal-llzed collector is provided to whlch ¢ontiguoUs external terminals and pads of contiguous parts are connected.
The metallized collector can be in the margins of the array on one or more sides and can surround the ceramic parts and can also be applled to gutter strips~between ;
parts. The gutter strips and margins are discarded when ,. , the pieoes are finally sepàrated. It will be seen that when all separatiQn means are exercised, the ceramic parts will be individually free from short circuits but that until . .
that time, the metallized collector aan be contacted at any point to provide electrical charge at any metallized ;
unit in the array and, inasmuch as resistance over the~
array is not great, electroplating may be applied to all exposed metallized surfaces at one time. It is preferred to provide a single position for connection to the metallized collector and have the remainder masked agalnst plating.

The arrays Or the invention and the process for construction may be accomplished using any desired fired or unfired substrate for ceramic packages or partsO
In particular, the use of alumina of purities of 90%
and more is preferred for such purposes but materials possesslng superior properties in one way or another may be used. Thus, beryllia may be used for superior heat conductivity, titania or titanates for high dielectric -~
strength, black ceramios may be used where no light emission or penetration is desired. Conventional metallizing is used such as tungsten, molybdenum-manganese, palladium, platinum, etc.
It is contemplated that substantially any deeign o~ ceramic package can be formed in arrays a¢cording to ~-the invention from relatively large ones in which no more than four may be handled in the array to small ones of which there may be several hundred in the array. As an e~ample, in an array about 115 by 85 mm. there may be over ~;
300 small packages about 4 mm. square with several thousand interconnected terminals and pads. It is further contem-plated that arrays of the invention may be constructed uslng a single sheet on which all metalllzing is screened and then an ln~ulating layer of the same ceramic composition is screened over those portions which need not be electro-plated or arrays ~ay be constructed using two or moregreen ceramic sheets which are adhered and ~ired to an integral ceramic structure with metalliæing on the lower .
sheet or on several sheets even on all sheets and suitably connected between levels by via holes or edge metallizing as desired. It is thus contemplated that arrays of the invention may be made in many ways.

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The means for separation Or the individual pack-ages or units, including marginal portions of the array, are also sub~ect to several alternative variations. A conven-ient procedure is to provide perforations through at least one layer of the array along the lines of desired seaparation.
It is not necessary ~hat the perforations extend through all layers but they may. The individual parts can then be snapped apart. Another alternative is to proYide dink lines along the predetermined lines of separation. Dink lines are cut into the green ceramic before firing, suitably to about one third the thickness of the material, and after firing provide an excellent line of separation. It is only necessary to avoid cutting the llne so deep as to sever electrical connections. If desired, both perforation and dinking may be employed together. A ~urther alternative is to provide no perforations or dink lines but to cut grooves with a laser beam in the ceramic itself or such grooves may be employed together with perforations.
Because a multilayer package, one composed of several . , : . .
Iayers of green ceramic, is likely to be thinner in the central enclosed area a suitable means for separation parts ls very helpful in reducing wastage cau~ed by `
improper breaking as are also proper procedures for exercising the means. ~
A metallized collector or band is provided, preferably around at least a part of the periphery of the array, as described above to provide a lead to all parts and the electroplating lead is attached to it. This may be on the uppermost layer or buried in the ceramic except for a location for connection o~ the electroplating lead.

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This latter procedure is more conservative of gold in the electroplating operation. Likewise~ leads between layers may be such that onl~ one metallized collector is needed but at least one metallized collector is necessary.
A part of the interconnections between extlernal terminals of ad~acent ceramic parts are more or less diagonal although they may cross lines of separation at right angles and preferably do. In addition, external terminals are connected to the closest terminal of the adJacent ceramic piece, for example, by edge overlap of the perforation as well as to the terminal of the adJacent ceramic piece on the side thereof. In this way, conductive paths proceed more or less diaeonally through the array and directly across it to connect to the metallized collector. Diagonal inter- ; ;
connections may be distlngulshed as o~fset interconnections as opposed to connections between the closest adJacent terminals. Any other pattern of making interconnections may be used which assures that all parts are connect~
ed in the array and none are connected (except as desired) in the separated package units. When individual packages are separated, the offset inter~
connections are visible along the edge usually as a slight gray mark. Although gold plated parts are readily wet by the usual solders, -the gray metallized area9 are not and they thus introduce no danger of electrical short circuits between adJacentterminals.
In accordance with one aspect of this invention there is provlded the process for facilitating uniform electroplating of ceramic substrates having internal and external terminals and internal pads comprising the steps of I. constructing an array of said substrates having an at least partial margin of ceramic from at least one sheet of fired or unfired ceramic having ;~
aesirea patterns of metallization for said substrate thereon, said array com prising; (A~ spaces at least bet~een said substrates and between substrates and margins for separation of said substrates from one anobher and from margins of said array along predetermined lines of separation, said array further ~ - 6 -comprising (B~ at least one metallized collector and (C~ interconnections ~ between external terminals o~ ad~acent su~strates and between pads o~
ad~acent substrates and between external terminals and pads Or substrates -, adjacent said metallized collector and said metal}ized collector, said : :
interconnections crossing lines of separation and II. firing said array ~.
to maturity of the ceramic.
In accordance with another aspect o~ this invention there is 1 ~.
provided a monolithic fired array of ceramic substrates, aaid substrates having internal and external terminals and internal pads in desired patterns of metallization, said array ~urther comprising (l) ceramic margins and at least one metallized collector on said margins outside said substrates,

(2) spaces, at least between said substrates and between said substrates and said margins, for separation of said substrates from one another and from said margins along predetermined lines of separation; and (3) inter-connections crossing said lines of separation between external terminals of ad~acent substrates and between pads of adjacent substrates and between . external terminals and pads of substrates adjacent said at least one ~ ; .`
metallized collector and said at least one metallized collector.
i The invention having now been described in broad general terms, .
:~ 20 it is now more particularly described by reference to the drawings herewith ~ .
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.l wherein: :~
Figure l 1s a flow sheet showing mechanical and i process steps included in constructing an array ::
ij of the invention;

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.1 Flgure 2 i9 a plan vlew Or an array of the lnvention;
Figure 3 is an enlarged cross-section of the array of~Figure 2 taken at line '3-3;
Figure 4 is a cross-section taken at line 4-4 ~, ~
of the array'o~ Figure 2; ~~~

Figure 5, 6 and 7 are sur~ace vie~ws of the green sheets o~ ceramlc planes 1, 2 and 3~and Fig~re 8';is~a:surface vlew of the-back.of;~

. ceramlc p~ane 1.

Referring to the drawings, CPl designates ceramic:
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~: plane 1 and CP2 and-CP3 designates planes 2 and 3 respectively, the metallizing on each plane (and on the edges of perfor- : '~
atlona) iq designated generlcally as MPl, MP2 and'MP3 re-, ~pe¢tively and i8 most easily seen in the cross-sectional ::
figures 3 and 4. 'It will be recognized that as~shown, the metallizing;is~somewhat~sohematic as~lt ls actually very~
: thln~and, when the-several green:sheets or~planes~of~unfired~
~:~:. ceramic are consoliidated~or laminated to give a composlte;, ;~
~:~:20 .'~ the greén:ceramic and metallizing~accomodate one another :~
so tha~t there:ls no;signirioant bulging. It will also be re¢ognized that the.invention is here lllustrated'ln:a pack- .
, age unit in which three cqramic green shee.ts are emp'loyed but that it m~y ~lso be used with only one or tw~ sheets ;~or~with~:four and`up to as many as ten or even mors.~
In ths~present ln~ention, although arrays~could be-made~ o~ relatively~small size<and~ars contemplated of any:slze desired,~it is most convsnient to form~them in a relatlvely largsr size, from~about: 50~x 75 mm. to~ab~ut :: 30 : 125 x:200 mm., and work:with the entire array at one time.
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It is rather surprising that sufficiently good electrical connections can be maintained using many relatively fine interconnections in a network so that unlform electroplating is possible over the entire array. It is an additional advantage of such an array that the platlng operatlon detects any dlscontinulties and unconnected rererence spots can remaLn unplated.
Referring again to the drawings, the green ceramic ~ -sheets shown in Figures 5, 6, 7 and 8 will be seen to be portions of larger sheets. Because of the small slzes of the individual pieces whlch may be of the order of about 4 mm. square or more or less, an array of these pieces may lnclude very many indivldual pieces and would be merely oon-rusing if shown ln totality and accordingly gnly small parts oi an array are shown very much enlarged. In`producing `
the array, it is necessary to exercise proper care for reg-istry between layers or sheets as is known to those in the art. The sheet material for each layer is of the order of 0.2 to 0.3 mm. thick and may be made using any of the u~ual ceramic compositions such as alumina of 90 to 99.9 or higher purity, beryllia, or other suitable composition9 which may include ingredients conferring color or making the ceramic black or opaque as desired. Thicker single sheets are conveniently made by adhering two or more thinner sheets. This invention is not concerned with the particular ceramic, bUt for general utility alumina of about 94% or grea~er purity is preferred.

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It will be noted that ln Figures 3 and 4 the ~;
sectloning shows refractory because there are sections of a fired piece. Because the sheet material of the green ceramic of Figures 5 through 8 partakes of the properties S of the polymeric binder used, sections of those parts would show the sectioning lines for plastics.
Reference ls now made to Figure 1 whlch shows the process of the invention which leads to arrays of the ~ ~;
invention as produced for commerce.
The first step in constructing an array of the invention i9 to provide the desired number of green ceramic sheets and screen each sheet with its partlcular metallizing.
It will be seen that the boxes withln broken line Box 10 represent this step of the invention, Boxes 1, 3 and 5 are respectively marked "Punch CPl", "Punch CP2", and "Punch CP3" indicating cutting out green sheets from à green ceramic~tape as described by Park in U.S. Patent 2,966,719, and making appropriate holes which may include perforations used to provide means for separation of individual pieces.
The sheet for this purpose is desirably rather thin, for example, 0.2 to 0.3 mm. but depending on the structure being made may be less or more. Boxes 2, 4 and 6 are marked "Screen MPl", "Screen MP2" and ~'Screen MP3" re-spectively re~erring to;screen printing with metallized ;~
composltions of the respective patterns. This screeningwill normally provide overflow into holes giving edge overlap as well as filling via holes. It ls also possible in the screening to avoid edge ovexlap when deslred along relativèly long edges. The metallizing compositions may be of any type such as molybdenum-manganese, tungsten, platinum, or other metals compatible with the particular , ceramlc.

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Broken line Box 15 includes the second step of construction in which an array Or green interconnected multllayer devices are constructed by successlve lamination of the several layers in registry. In Box ll the first operation is "Laminate CP2 to CPl" and in Box 12, "Laminate CPl-CP2 with GP3".
The third step, indicated by broken line Box 16 and Box 17 of the flow dlagram of Figure l is to "Dink".

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This step is the cutting of grooves along lines o~ ~epa-ration ln the back of the array while substantially retaining edge-metallizing which has penetrated perforation holes (MPl and ~P2) as well as the electrically connecting network of MPl If desired when other means for separation are pro-vided, such as leaving space for separation using laser scrlbing or cuttlng, this step i8 bypassed as shown by lead 13. As noted above, perforatlons may be provided and these are produced by the punching operations in Boxes l, 3 and 5.
The fourth and followlng steps include firin8 the sheet to maturity as indicated by "fire" in Box l9. This -pr~ides the "fired arrays" indicated in ~ox ? which one may "nickel platè" in Box 21 and "gold plate" in Box 22 to provide "commercial arrays" in Box 23. Alternative plating schedules will be apparent to those skllled in the art. The plated commercial arrays are not shown in the figures as they would only be distinguishable by the plated layers of metal.
The arrays that is, large con~unct groups, are ~ -ready after pl~ating for the manufacturer who (1) mounts an electronic device in each package, (2) wire bonds the device to the leads ln the package and, (3) embeds or encapsulates the device. There is ~ound to be increased convenience in handling such arrays. The package unlts shown in Figure 2-8 are encapsulated by soldering a lid.
At this point, a simple separatlon of the individual packages in the array is effected by snapping apart along the separation lines provided elther by perforations or dink lines or other means.
Figures 5, 6 and 7 show portions only, here rep-resented as corners of the sheets provided for CP3, CP2 and CPl respectively. It would be within the scope o~ the invention to provide only one or two of these green sheets depending on the particular design which is sought. It is also within the scope o~ the invention to employ variations in metallizin~ in any or all planes to comport with the de-sired device. Such varia~ions will be readlly apparent to those o~ skill ln the art. The important aspect of the metalliæing is that an interconnection network is ~rovided.
A package unit as shown in the arrays of Figures 2-8 comprises a ceramic substrate and numerous internal and external terminals. In Figures 2-8, the ceramic substrate is made from three layers deslgnated CPl, CP2 and CP3 and also as (70), (72) and (74). In each layer, it will be seen that perforation hole~ (26) are provided. The metal-lized pattern MPl on sheet (70) is composed o~ a metallized collector (30), pads (32) and interconnection leads (34) on the upper surface and by metallizing on the walls of holes (26) make connection with edge overlap (36) on the ~ -bottom surface.
The ~.etallized pattern~on sheet (72~ in which are square holes (28) is composed o~ internal terminal~ ~40), external terminals including edge overlap (42), interconnections ,. . .

(46) and metallized collector (48). It will be recog-nized that the edge overlap Or connections (36) and metallized connector (30) will make contact with the edge overlap of terminals (42) so that these a~e all connected by interconnections (46). It is the network of inter-connections (46) particularly which is es~ential for the operation of this invention .
The metallized pattern of sheet (74) having square hole (24) is composed Or square pads (50), inter-connections (52) and metallized collector (54). Ifdesir-ed, provision can be made to avoid the use Or metal-lized collector (54) on the top layer by use of suitable vias to leads at a lower level or plating Or the collector can be prevented by maskin~. Contact bo collector (54) i9 by cllpping and to other collectors may be by a wlre insertec~ throu~h a perforation.
The green sheets (70 and 72) are laminated together under slight pressure as shown in Figure 1, followed by sheet (74) and then the dink lines (60) which are only visi-ble in the cross-sectional views Figures 3 and 4 of the fired array. These would not be cut in the green sheet Or Flgures 7 and 8. It will be noted that these~only ~orm one means for separation Or the units and as such are not necessary when perforations (26) are employed. ~ -~ ~ , - 12 - ; ~ ~

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The process for facilitating uniform electroplating of ceramic substrates having internal and external terminals and internal pads com-prising the steps of I. constructing an array of said substrates having an at least partial margin of ceramic from at least one sheet of fired or unfired ceramic having desired patterns of metallization for said substrate thereon, said array comprising;
(A) spaces at least between said substrates and between substrates and margins for separation of said substrates from one another and from margins of said array along predetermined lines of separation, said array further comprising (B) at least one metallized collector and (C) interconnections between external terminals of adjacent substrates and between pads of adjacent substrates and between external terminals and pads of substrates adjacent said metallized collector and said metallized collector, said interconnections crossing lines of separation and II. firing said array to maturity of the ceramic.

2. The process according to Claim 1 wherein the metallized collector is in a margin at least partially surrounding ceramic substrates of the array.

3. The process according to Claim 1 wherein the spaces for separation of ceramic substrates include perforations with at least partial edge overlap metallizing.

4. The process according to Claim 1 wherein the spaces for separation of ceramic substrates include dinking lines.

5. The process according to Claim 1 wherein at least one gutter with metallized collector is provided between adjacent rows of substrates and adjacent substrates are interconnected to said metallized collector from pads and external terminals.

6. The process according to Claim 1 wherein masking is provided to bury portions of exposed metallizing.

7. A monolithic fired array of ceramic substrates, said substrates having internal and external terminals and internal pads in desired patterns of metallization with exposed surfaces gold plated, said array further com-prising (1) ceramic margins and at least one metallized collector on said margins outside said substrates;
(2) spaces, at least between said substrates and between said substrates and said margins, for separation of said substrates from one another and from said margins along predetermined lines of separation; and (3) interconnections crossing said lines of separation between external terminals of adjacent substrates and between pads of adjacent substrates and between external terminals and pads of substrates adjacent said at least one metallized collector and said at least one metallized collector.

8. A monolithic fired array of ceramic substrates, said substrates having internal and external terminals and internal pads in desired patterns of metallization, said array further comprising (1) ceramic margins and at least one metallized collector on said margins outside said substrates;
(2) spaces, at least between said substrates and between said substrates and said margins, for separation of said substrates from one another and from said margins along predetermined lines of separation; and (3) interconnections crossing said lines of separation between external terminals of adjacent substrates and between pads of adjacent substrates and between external terminals and pads of substrates adjacent said at least one metallized collector and said at least one metallized collector.