US3647534A

US3647534A - Preparation of welding surfaces on semiconductors

Info

Publication number: US3647534A
Authority: US
Inventors: Stanley B Rice Jr
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1965-10-29
Filing date: 1969-04-16
Publication date: 1972-03-07
Anticipated expiration: 1989-03-07

Abstract

A method of forming a weldable surface on a ceramic member by: 1. DISPERSING PARTICLES OF CUPROUS OXIDE WHICH WILL REACT WITH THE CERAMIC ONTO THE CERAMIC SURFACE; 2. HEATING THE PARTICLES UNDER TIME AND TEMPERATURE CONDITIONS WHICH CAUSE THE PARTICLES TO REACT WITH THE CERAMIC; AND 3. IMMERSING THE CERAMIC IN A NICKEL SOLUTION FOR DEPOSITING A LAYER OF NICKEL ON THE REACTED AREA.

Description

United States Patent Rice, Jr.

[ 1 Mar. 7, 1972 [54] PREPARATION OF WELDING I SURFACES ON SEMICONDUCTORS [72] inventor: Stanley B. Rice, .lr., Garland, Tex,

[73] Assignee: Texas Instruments Incorporated, Dallas,

Tex.

[22] Filed: Apr. 16, 1969 211 App1.No.: 851,507

Related US. Application Data [62] Division of Ser. No. 505,687, Oct. 29, 1965, Pat. No.

[52] US. Cl. ..117/212, 117/10 [51] lnt.CI ..B44d l/l8 [58] Field oiSearch ..117/212, 10

[56] References Cited UNITED STATES PATENTS 3,424,658 1/1969 Norton ..117/212 3,296,359 111967 Ramsey, Jr., et a1 ..l17l212 3,259,559 7/1966 Schneble, Jr., et 31.. ....1 17/212 2,993,815 7/1961 Treptow ....1 12/212 7] ABSTRACT A method of fonning a weldable surface on a ceramic member by:

1. dispersing particles of cuprous oxide which will react with the ceramic onto the ceramic surface;

2. heating the particles under time and temperature conditions which cause the particles to react with the ceramic; and

3. immersing the ceramic in a nickel solution for depositing a layer of nickel on the reacted area.

2 Claims, 13 Drawing Figures PATENTEDMAR 71912 3,647. 534

SHEET 2 [IF 2 PREPARATION OF WELDING SURFACES ON SEMICONDUCTORS This is'a division of copending application, Ser. No. 505,687 filed Oct. 29, 1965 now US. Pat. No. 3,494,790.

This invention relates to the preparation on welding surfaces of semiconductors, and with regard to certain more specific features to improved means for obtaining welding surfaces on semiconductor bars or the like to provide for connecting conductive leads thereto.

Among the several objects of the invention may be noted the provision of improved means for forming uniform weldable metalsurfaces on portions of semiconductor bars and more particularly on the surfaces of very small or closely spaced marginal grooves or notches therein; the provision of a method of fonning such weldable surfaces permitting the advantageous use of extremely small particles of metal not formerly useable in small or closely spaced notches or grooves; and the provision of a method of the class described which requires less time and smaller quantities of certain materials than were heretofore required for forming the desired weldable surfaces on the ceramic bar material. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the methods, constructions and products hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated:

FIG. 1' is a fragmentary perspective view of a ceramic semiconductor bar having several sidewise notches or grooves in it, one of which is provided with a weldable surface applied according to the invention;

Smaller particles of aluminum were tried but they did not react with the ceramic. This was probably due to the thin film of aluminum oxide, about 30 to 40'angstroms thick, which sur- FIG. 2 is an enlarged fragmentary section through the groove in the FIG. 1 ceramic bar, being viewed on line 2-2 of FIG. I;

' FIGS. 3-6 are sections illustrating diagrammatically various steps employed in carrying out one form of the invention;

FIG. 7 is a fragmentary cross section taken on line 7-7 of FIG. 2, showing a conventional lead welded to a prepared surface of a notch or groove;

FIGS. 8-l2 are sections illustrating diagrammatically various steps employed in carrying out another form of the invention; and

FIG. 13 is a section similar to FIG. 12 showing a conventional lead welded to the prepared surface of a notch or groove.

For clarity of illustration, dimensions are exaggerated and therefore the drawings are not to exact scale.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

weldable surfaces have been provided on ceramics containing magnesium oxide and silicate by placing aluminum particles of l to 2 mil size in small or closely spaced groove therein and then reacting the aluminum with the ceramic at a temperature of about l,000 C. in an atmosphere of helium. After the reaction, excess oxides were scraped from the reacted surface. The reacted surface was then plated with nickel by an electroless plating process. Such nickel plating normally occurs at a rate of about 0.5 mil per hour, and 3 or 4 mils of nickel are required in order to obtain a good weldable surface on the ceramic. Thus several hours were required for plating this process were not successful, for example, in grooves 9 mils wide and only 2 or 3 mils deep. Uniform coverage in the desired metallized areas could not be obtained, probably due to the inability of the grooves of such small size to contain sufficient aluminum powder for intimate contact with the ceramic substrate, or in the case of closely spaced grooves, to prevent overlap of conductive material between grooves.

to remove the oxide film was tried but they were found not to I be controllable. The present invention permits application of a continuous, uniform layer of metal in a very small or closely spaced grooves (orif required, on larger areas) and reduces the time required by prior methods for electroless plating of a satisfactory weldable metal surface on the ceramic bar.

Briefly, one process for metallizing a ceramic according to this invention comprises grinding and mixing together particles of aluminum and another metal (such as tin) having a melting point lower than the melting point of aluminum, then suspending them in a liquid vehicle or carrier and inserting them by means of a hypodermic needle into a groove or other surface of the ceramic. Other application means may be employed. Then the ceramic and metals are heated in a furnace at a temperature to melt tin and aluminum. The metals and ceramic react during heating to form a thin continuous metallic film between the ceramic and a layer of unreacted oxide on the surface. After removal of the oxide, the reacted area is then plated by an electroless nickel-plating process to provide a nickel surface to which leads or the like may be welded.

Another embodiment of this invention overcomes the long electroless plating time required. This embodiment comprises applying powdered cuprous oxide to a ceramic surface, sintering it under conditions which result in reducing the cuprous oxide to cupric oxide. Reaction between the cupric oxide and the ceramic forms a good bond with the silicon in the ceramic throughout a reacted area. Then the ceramic is placed in a reduction furnace for removing the oxygen remaining from the cupric oxide. The result is a layer of copper covering the ceramic in the reacted area. This copper layer is pulled off, leaving a very thin molecular layer of copper on the reacted area. Next the ceramic is placed in an-electroless nickel-plating solution and plated for about 1 hour to deposit about 0.5 mil thickness of nickel on the reacted area. Leads can be welded to the plated area.

Referring now more particularly to FIGS. 1-7 of the drawings, at numeral 1 is illustrated a portion of a rectangular ceramic member preferably formed of a mixture of magnesium and silicate, such as forsterite (2 MgO-SiO or steatite (MgO-SiO2). This member, for example, may constitute a so-called silicon or semiconductor bar on which is a semiconductor network, requiring leads for forming outside connections. Thus the ceramic l constitutes a base or substrate for a so-called integrated circuit package. There are a plurality of small irregularly shaped marginal notches or grooves 3 in ceramic member 1 which are to be prepared so that leads can be welded to the package.

Small particles of aluminum, preferably less than 1.8 mils in size, and small particles of tin, preferably less than 1.2 mils in size, are ground together to smaller sizes. The preferred ratio of tin to aluminum is 1 part tin to 2 parts aluminum by weight. Tin is selected because of its relatively low melting point (about 232 C. Other metals with low melting points can also be used.

The finely powdered metals are then dispersed in a vehicle or carrier which holds the metals in suspension while they are being applied to the ceramic. The vehicle may be one manufactured by the DuPont company of Wilmington, Delaware and designated in the trade as l i-220. Other vehicles which "can be used-include amyl acetate, dextrim, gum arabic, gum

tragacanth, and other organic substances. The DuPont product is preferred since it leaves practically no residue after firing. The vehicleand metal particles suspended by it are applied in the grooves 3 in ceramic 1. ln FIG. 3 the metal particles in groove 3 are designated and the carrier or vehicle is designated 7.

The ceramic 1, carrying the metal particles 5 and carrier 7, is then placed in a tube furnace and heated in a reducing atmosphere at a temperature of about 800 C. for about 1 hour. The atmosphere may be hydrogen. During heating the tin particles melt at about 232 C. They have a fluxing or dissolving action on the aluminum oxide or the aluminum particles, so as to release the oxide as the aluminum melts at about 700 C. Then the tin combines with the aluminum particles to form a liquid tin-aluminum alloy. This alloy reacts intimately with the magnesium and silicate of the ceramic so that there is produced a compound or alloy, referred to as spinel (M- gAl,O,). This spinel is present in a reacted area or zone designated 9. At the same time there occurs a layer or coating 11 of unreacted oxide on the reacted zone. The reacted area or zone 9 is firmly adhered to the ceramic 1, whereas the unreacted oxide layer 11 is loose and is easily removed. FIG. 5 shows the ceramic and reacted zone after the oxide layer 11 has been removed.

It may be noted at this point that the process has been tried employing under the same operating conditions particles of tin or aluminum individually, instead of together. No reaction occurred in either instance. The tin particles coalesced together in globules on the ceramic surface and could be brushed off. The aluminum particles did not react at all, probably, as above mentioned, because the aluminum could not rupture the surrounding film of aluminum oxide to'j'react with the ceramic materials. The oxide flushing or diss lving action of the tin removes this difiiculty.

Next the ceramic and reacted zone or area 9 are placed in a solution containing nickel (or other weldable metal ions) and the reacted zone 9 is plated by electroless plating with a layer 13 of nickel. This plating occurs by a catalytic decomposition of the solution at the surface of zone 9. A typical "electroless plating solution may contain sodium hypophosphite. and nickelous chloride with buffers. The reactions which occur are as follows:

l-l- P0- +H- iO+HPO +l-I+H (ac id or2H) The hydrogen then reduces the nickel at the surface as follows:

This electroless plating is continued until the desired thickness of the nickel layer 13 is provided. Normally layers of 3 to 4 mils of nickel are required to provide a good weldable metal surface. This plating occurs at a rate of about 0.5 mils per hour. Thus 6 to 8 hours are required to obtain a nickel coating 3 to 4 mils thick. After nickel plating, the nickel is annealed in a conventional manner and leads of Kovar are welded to the metallized surface (see FIGS. 1, 2 and 7).

While the drawings illustrate the nickel layer 13 as being depressed in the center portion and with the lead 15 located in this depression, it will be understood that this is only for the purpose of illustration. Also, there may be some small portion of the reacted zone 9 and the nickel layer 13 present on the surface of ceramic 1 adjacent to the groove 3. If this occurs it can be removed by conventional lapping. It will be understood that lowmelting-point metals other than tin may be used for fluxing or dissolving the aluminum oxide from the aluminum particles.

FIGS. 8-13 illustrate an alternative process of forming a weldable area in a marginal notch, groove or other recess 3 in ceramic 1. In this embodiment, small particles 17 of copper in the cuprous form (Cu,0) are mixed with a vehicle or carrier 19 in the manner described in connection with FIGS. l7. Carrier 19 may be any of the organic substances above, described. The copper and vehicle are applied in the groove 3 (FIG. 8). The ceramic, metal and vehicle are then placed in a 'fumace and sintered for about 1 hour in air at a temperature of approximately l,000 C. The vehicle carrying the copper is 4 the cuprousoxideKCu o) to the cupric form (CuO). The ceramic and sintered copper are cooled, at which time there exists a crust 21 above the reacted zone 23.

Next the ceramic 1 with the crust 21 on the reacted zone 23 are placed in a reduction furnace for removing the remaining oxygen. After first flushing the furnace within'ert helium to clear out air for safety, hydrogen is introduced into the furnace at a temperature of about 300 C. This temperature is then raised to about 1,000 C. and held for about 15 minutes. The ceramic is then cooled in the hydrogen atmosphere. After it has cooled and been removed from the hydrogen atmosphere, there occurs a layer 25 of metallic copper covering the reacted zone or area 23 (FIG. 10). This layer of copper 25 Y is only loosely adherent and is easily pulled from the reacted zone or area 23 (FIG( 11). The looseness is apparently due to disruptive stresses caused by differential shrinkage upon cooling. When this loose copper layer is stripped sway there is left on the reacted zone 23 a very thin molecular facing of copper. This is indicated by dots 29 in FIGS. 1113. In view of its extreme thinness, this layer is not disrupted upon cooling and therefore remains tightly on the zone 23. I

The ceramic and the reacted zone 23 on which is the molecular copper layer are next exposed to a solution containing nickel and, by electroless plating, a layer of nickel is plated on the reacted zone 23. This nickel layer is designated 27 in FIG. 12. The electroless plating is continued for approximately l hour and a layer of nickel about 0.5 mils thick is thus obtained on the reacted area 23. This is substantially thinner than the 3 to 4 mils thickness usually required with other processes. If desired, the nickel may be annealed before the leads such as 15 are welded to it.

It may be mentioned that the use of cuprous oxide (Cu,O for particles 17 is of some importance. An attempt has been made to substitute cupric oxide (CuO) for particles 17 but the result upon reduction in hydrogen was the formation of copper globules formed on the substrate surfaces, and these were not sufficiently adhered. I

Ceramic articles produced by either method of the invention may be used in manufacturing integrated semiconductor network packages with leads 15 constituting their outside connections. In manufacturing a package of this type, an appropriate surface of ceramic 1 is coated with a glass frit and 4 fired to form a thin glass glaze. Then circuitry is evaporated on the glaze and connected by internal accessory leads to the metallized groove or notch areas, thereby completing a circuit through the leads 15.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As variouschanges could be made in the above methods, constructions and products without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The method of forming a weldable metallized surface on a ceramic member containing magnesium and a silicate, said ceramic member having a groove on a surface thereof, comprising placing cuprous oxide powder in said groove, sintering the ceramic and cuprous oxide in air at a temperature at about l,000 C. for about 1 hour, cooling the ceramic, cuprous oxide and reactive zone therebetween, heating them in an atmosphere of hydrogen at a temperature of 300 to l,000 C. for about 15 minutes and then cooling them in a hydrogen atmosphere to provide a substantial layer of loosely adherent copper in the groove, removing saidlayer of copper whereby a molecular layer of copper remains on said ceramic, immersing the ceramic in a solution containing nickel and depositing by electroless plating a layer of nickel on the molecular copper layer on the reactive zone.

2. The method of fonning a weldable area on a ceramic member containing magnesium oxide and a silicate comprising dispersing particles of cuprous oxide in a vehicle to form a for about 15 minutes and cooling them in a hydrogen atmosphere to provide a layer of loosely adherent copper and oxide stripping the loosened mass of copper and oxide from the ceramic leaving a molecular layer of copper thereon, and immersing the ceramic in a solution containing nickel for about 1 hour to deposit by electroless plating a layer of nickel on the reacted zone.

0' i t I t in An: In.

Claims

2. The method of forming a weldable area on a ceramic member containing magnesium oxide and a silicate comprising dispersing particles of cuprous oxide in a vehicle to form a dispersion, applying the dispersion on said area of the ceramic member, sintering the area with the applied material at a temperature of about 1,000* C. for 1 hour to dissipate the vehicle and react the cuprous oxide with the silicate and to convert some of the cuprous oxide to cupric oxide, reducing the cupric oxide to copper, cooling the ceramic, cuprous oxide and the reactive zone therebetween and then heating them in an atmosphere of hydrogen at a temperature of 300* to 1,000* C. for about 15 minutes and cooling them in a hydrogen atmosphere to provide a layer of loosely adherent copper and oxide stripping the loosened mass of copper and oxide from the ceramic leaving a molecular layer of copper thereon, and immersing the ceramic in a solution containing nickel for about 1 hour to deposit by electroless plating a layer of nickel on the reacted zone.
3. IMMERSING THE CERAMIC IN A NICKEL SOLUTION FOR DEPOSITING A LAYER OF NICKEL ON THE REACTED AREA.