Patent GB-1020061-A (GB)
Title: Multilayer circuits
IPC: H05K3/46
Filed: 1963-04-16
Abstract: 1,020,061. Printed circuits. RADIO CORPORATION OF AMERICA. April 16, 1963 [April 27, 1962], No. 14970/63. Heading H1R. A circuit comprising a monolithic ceramic body and interconnected conductors disposed in different layers is made by preparing a plurality of dry thin films of finely divided ceramic particles and a volatile binder, forming thin metallic conductors upon selected surfaces of at least two films, stacking the films, volatilizing the binder, and sintering the ceramic particles and metals; before stacking, holes are formed at desired locations in said films and are filled with metallic paste to provide connections between conductors in different layers. As shown, Fig. 4, dielectric wafers 108, 110, 112 are formed from a single sheet of powdered ceramic of composition 1À0 mol. barium carbonate : 5À0 mol. titanium dioxide, mixed with a volatile binder, e.g. a vinyl chloride-acetate copolymer, a solvent, e.g. methyl ethyl ketone, a plasticizer, e.g. butyl benzyl phthlate, and a defloccuant; the mixture is milled and spread on a thin glass support and dried. The conductive areas for the three wafers are formed on the ceramic sheet by screen printing with a paste comprising 58% by weight palladium suspended in a binder of methyl cellulose and a solvent of butyl carbitol acetate, and are oven-dried. The sheet is stripped from the support, holes are punched where required through the metallized areas, the sheet is turned over, and metallic paste is deposited in and around the holes; suction may be used to draw the paste into the holes. The sheet is then cut into wafers 108, 110, 112, each wafer being provided with edge notches 114 which are metallized, and the wafers are stacked and heated to c. 125‹ C. at a pressure of 1000 p.s.i. for 5 minutes, followed by sintering at 1250‹ C. to form a monolithic assembly (Fig. 5, not shown). In a modification, the ceramic composition comprises alumina, ball clay, and talc. The holes may be punched before the screening on of the metallic paste, which may comprise molybdenum and manganese powders. A plurality of one circuit pattern may be formed on each of a plurality of sheets; the sheets are stacked and bonded, and wafer stacks are then cut from the sheet stack, the notches are metallized, and the stacks fired at 1550‹ C. in a reducing atmosphere. The exposed metallized areas may be electroplated, first with nickel, then with copper, and then coated with solder. (Fig. 6, not shown), depicts wafers comprising deposited resistors, such as 128, 146, and capacitor electrodes 138, 170 which co-operate in the finished circuit with a ceramicdielectric. Transistors, diodes &c. can be accommodated in a recess in a wafer stack. Other useful ceramic compositions include: lanthanum oxide and titanium dioxide; reacted barium titanate; combinations of barium titanate, calcium titanate, strontium titanate, calcium zirconate, magnesium zirconate, and cerium dioxide. Powdered devitrifiable glasses may be used. Metal compounds which decompose on heating may replace metals in the metallizing compound, which may be sprayed through a mask or evaporated on to the wafer.