Method of fabricating metal printed wiring boards

• US 3,934,334 A
• Filed: 04/15/1974
• Issued: 01/27/1976
• Est. Priority Date: 04/15/1974
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Hanni, Stephen L.
• Primary Examiner(s): Lanham, C. W.
• Assistant Examiner(s): Walkowski, Joseph A.
• Application Number:
  US05/461,072
• Time in Patent Office: 652 Days
• Field of Search: 29/624, 29/625, 174/68.5, 317/101 B, 117/212, 117/213, 117/215, 117/217, 117/218, 117/230, 117/38, 117/45, 117/47, 117/66-67, 117/71 M, 117/75, 117/130 E, 117/132 A, 117/132 B, 117/132 C, 204/15, 204/29, 204/30, 156/3, 156/4, 53/30 S
• US Class Current: 29/846
• CPC Class Codes: H05K 1/056 the metal substrate being covered by an organic insulating layer
• CPC Class Codes: H05K 2203/105 Using an electrical field; Special methods of applying an electric potential
• CPC Class Codes: H05K 2203/1355 Powder coating of insulating material
• CPC Class Codes: H05K 3/0097 Processing two or more printed circuits simultaneously, e.g. made from a common substrate, or temporarily stacked circuit boards H05K3/0052 takes precedence
• CPC Class Codes: H05K 3/184 using masks
• CPC Class Codes: H05K 3/387 for electroless plating H05K3/4661 takes precedence
• CPC Class Codes: H05K 3/426 initial plating of through-holes in substrates without metal
• CPC Class Codes: H05K 3/445 having insulated holes or insulated via connections through the metal core
• CPC Class Codes: H05K 3/4608 comprising an electrically conductive base or core
• CPC Class Codes: Y10T 29/49155 Manufacturing circuit on or in base

Abstract

An additive process for producing printed wiring boards is taught. In the process metal substrates having desired hole patterns are powder coated with a dielectric material electrostatically. The dielectric powder coating is then fused on the metal substrate. Next, a continuous film of pre-catalyzed adhesive is applied to all surfaces; then a plating resist is applied to all areas on which copper is not desired. The exposed catalyzed adhesive is then activated and plated in an electroless copper bath.

Claims

1. A method for fabricating printed wiring boards comprising:

a. forming a metal substrate having a circuit hole pattern;

b. electrostatically powder coating the metal substrate and hole forming walls with a suitable dielectric;

c. fusing the dielectric powder coating to electrically insulate the metal substrate including the apertures thereof from electrical circuitry; and

d. forming electrical circuitry on the dielectric in conjunction with the

2. A method for fabricating printed wiring boards comprising:

a. blanking sheet metal to form a sheet of metal substrates having circuit hole patterns;

b. electrostatically powder coating the metal substrates and hole forming walls with a suitable dielectric;

c. fusing the dielectric powder coating to electrically insulate the metal substrates including the apertures thereof from electrical circuitry;

d. coating the dielectric with a catalyzed adhesive; and

e. forming electrical circuitry on the dielectric in conjunction with the

3. A method for fabricating printed wiring boards comprising:

a. blanking sheet metal for outlining a plurality of metal substrates, forming hole patterns within said plurality of outlined metal substrates, and forming lead frames adjacent horizontally disposed edges of the sheet metal with holes therein for use in advancing the sheet metal and outlines of metal tabs;

b. preparing the sheet metal for coating with a layer of insulating material;

c. electrostatically powder coating surfaces of the metal substrates of the sheet metal with a dielectric;

d. fusing the coating for thermosetting the dielectric for electrically insulating the metal substrates;

e. coating all the dielectric insulating coating with an adhesive coating in preparation for forming conductor patterns and through hole interconnections by metallization;

f. forming conductor patterns on the adhesive coating;

g. partially removing the adhesive coating from the conductor patterns to form metal plating locking micropores;

h. electrolessly plating the conductor patterns with an electrically conducting material;

i. selectively forming soldering patterns;

j. removing any oxide forming on the exposed soldering patterns; and

k. sealing the exposed soldering patterns to prevent oxidation of the soldering pattern whereby a plurality of printed wiring boards are formed

4. A method for fabricating printed wiring boards according to claim 3 further including winding the printed wiring boards into a coil, placing the coil on a pallet, and wrapping the coil and pallet with heat shrink

5. A method for fabricating printed wiring boards according to claim 3 further including feeding the lead frame and plurality of printed wiring boards through a blanking press for removing the lead frame from the plurality of printed wiring boards, separating the printed wiring boards one from another, stacking them on a pallet, and covering the pallet and

6. A method for fabricating printed wiring boards according to claim 3 wherein the sheet metal blanked is ferrous or non-ferrous metals selected from the group consisting of steel, aluminum and copper and alloys

7. A method for fabricating printed wiring boards according to claim 3 wherein the sheet metal is prepared for the coating of insulating material by vapor degreasing both sides of the metal sheet, dipping the metal sheet in an acid solution to remove oxidized metal, rinsing the sheet metal to remove excess acid, dipping the metal sheet in an alkaline solution and rinsing to remove excess alkaline solution, phosphatizing the metal sheet, vapor degreasing until dry, and sand blasting the metal sheet to debur

8. A method for fabricating printed wiring boards according to claim 3 wherein said fused insulating coat is a smooth, substantially free pin hole coat insulating the metal sheet surfaces including the aperture forming walls, corners, and edges, and having a dielectric strength of not less than about 500 V per mil, and a temperature stability continuous between about 120°

C and 130°

C and a temperature stability for about 30 seconds at 260°

C whereby the metal substrate can be

9. A method according to claim 3 wherein the metal tabs outlined in the lead frames are bent to form metal spacers for spacing the loops of the

10. A method according to claim 3 wherein the sealing of the exposed soldering patterns includes coating the epoxy soldering patterns with

11. A method according to claim 3 wherein the fabricating cycle is an automated cycle.