REMOVABLE COMMONING BAR

Abstract: Method for use in the manufacture of printed circuit boards (1) wherein the conductive circuit (3) placed on a dielectric substrate (2) includes a commoning portion (4) which electrically connects selected portions (5) of the printed circuit (3) which will subsequently be electroplated. The commoning portion (4) of the printed circuit (3) is peeled away from the substrate (2) after the selected portions (5) of the printed circuit are electroplated, leaving the electroplated portions (5) electrically separated, except as they might be otherwise electrically connected through other paths in the printed circuit board (1).

Description: Description Removable Commoning Bar Field of the Invention This invention relates generally to the manufacture of printed circuit boards and more specifically to an improved method for electroplating portions of a conductive circuit on a dielectric substrate. Prior Art Printed circuit boards are well known in the computer industry. Generally, they comprise planar dielectric substrates on which a conductive circuit has been made. The conductive circuit is used to enable electrical communication between components of -a computer. The dielectric substrates may be formed from a wide variety of materials including, for example, resins or resin-impregnated papers or fabric. The conductive circuits may be formed from insulated wiring attached to the surface of the dielectric substrate in a suitable pattern or from conductive material placed on the dielectric substrate in such a pattern. Conductive metal circuits may be placed on the substrate by a variety of already known methods. In "subtractive" methods, the substrate is usually first coated with a layer of conductive metal by, for example, lamination. The metal is exposed to a pattern of light which causes a portion of the photoresist to harden while the remainder may be removed, resulting in a mask. The mask protects portions of the conductive layer while the unprotected portion is removed by, for example, acid or etching. The photoresist mask may then be removed, leaving a printed circuit on the dielectric substrate. In "additive" methods for placing a conductive pattern on a substrate, the substrate is seeded with a catalytic material which enables the electroless deposition of conductive metals, such as copper from a plating bath. After seeding and before electroless plating a photoresist mask is placed on the substrate so that a pattern of conductive metal is deposited, Electroplating may be used to build up the circuit after a thin conductive pattern has been formed by the electroless plating method. In some computer designs, a printed circuit board is connected to the frame of the computer by connectors on the frame which make contact with conductive lands or pads along the edge of .the printed circuit board. Alternatively, connectors- comprising cable assemblies may be connected to such lands or pads for communication between the printed circuit board and more remote compo- nents. In order to make good electrical contact it is often desirable to deposit a thin layer of a noble metal such as gold, silver or palladium on the lands or pads. Electroplating noble metals onto lands or pads around the edges of printed circuit boards is an important part of the manufacture of such boards. Such electroplating is normally done by electrically commoning the lands or pads sought to be plated and then accomplishing the electroplating by dipping in an electroplating bath or by jet plating, which is also an electroplating technique. Commoning of the lands or pads can be done in a variety of ways. Strip electrodes can be used. Electri¬ cal strips which are imbedded in an insulating tape are sometimes used. Good results have been achieved by using a commoning bar which is a part'of the printed circuit board. The "printed" commoning bar electrically connects the lands and pads which are to be electroplated. After the 5 plating procedure the commoning bar is removed so that the lands and pads are no longer electrically connected. Removal of the commoning bar which is part of the printed circuit on the printed circuit board has presented, difficulties to those involved in the 10) manufacture of printed circuit boards. The most successful means of removing the commoning bar in the past has been to cut away the portion of the printed circuit board which includes the commoning bar. This technique is illustrated in Japanese Patent Publication 5 36-18276. Although effective, this method destroys a» portion of the board, uses up valuable printed circuit board area and results in the debris normally encountered • in cutting or sawing. • . • Summary of the Invention 0 It is an object of the present invention to overcome disadvantages of the prior art. It is also an object of this invention to provide an improved method for making printed circuit boards having electroplated portions. 5 It is a further object of this invention to present an improved method for removing an electrical commoning bar form a printed circuit board after electroplating portions of the printed circuit on the board. These and other objects are provided by the present 0 invention which, in one aspect, is a method of making a printed circuit board having a conductive pattern on a dielectric substrate and having selected portions of the conductive pattern electroplated, the method comprising: (a) placing on a dielectric substrate a conductive pattern, which pattern includes a commoning portion electrically connecting the selected portions. (b) electroplating the selected portions using the commoning portion as a commoning electrode, and (c) removing the commoning portion from the substrate. In another aspect the present invention relates to a printed circuit board made by this process. By way of example, the present invention is described, below, with reference to the..drawings which are intended to be illustrative but not to be limiting. Brief Description of the Drawings FIG. 1 shows a schematic view of a pattern of lands or pads along the edge of a printed circuit boa " rd electrically connected by a commoning bar. FIG. 2 shows schematically the commoning bar being removed in accordance with the method of the present invention. Detailed Description It has been discovered that a commoning bar which electrically connects portions of a printed circuit can be removed from the printed circuit board, after electroplating selected portions of the printed circuit board, by peeling, leaving the electroplated portions of the board in place and electrically separated, while avoiding the disadvantages of the prior art. Referring to FIG. 1, there is shown printed circuit board 1 which comprises dielectric substrate 2 and conductive pattern 3. FIG. 1 shows only a portion of substrate 2 and a portion of printed circuit 3. As described above, the printed circuit board may be made from any of the materials which are will known as dielectric substrates and conductive materials. The selection of the materials is not critical to the performance of the invention. Printed circuit 3 includes commoning bar portion 4 and lands or pad portion 5. The lands or pads are designed for contact with connectors which will permit the processing units on board 2 to communicate with other parts of the computer which includes the printed circuit • . board. ζ Commoning bar portion 4 of printed circuit 3 electrically connects portions 5 of the printed circuit board. In the normal construction of a printed circuit board it would be desirable to electroplate.portions 5 of circuit 3 with a noble metal in order to improve electrical contact with connectors, as explained above. After printed circuit 3 is made as shown in FIG. 1 with portions 5 electrically connected by commoning bar portion 4, portions 5 are electroplated. Normally a noble metal is selected for electroplating on portions 5 because of the good ohmic contact which is well known to be achieved by the use of such metals in connectors. The particular metal used and the particular electroplating mechanism used are not critical to the operation of the invention. Any useful metal and electroplating method may be used. Referring to FIG. 2, there is shown printed circuit board 1 in which commoning bar 4 is removed from the sur¬ face of substrate 2 after electroplating. Commoning bar portion 4 is removed by peeling it away from surface 2. Peeling may be done in any of a number of ways. Any useful such way may be employed in the method of the present invention. In FIG. 2 the peeling is being accomplished by means of a pair of tweezers 6 which obtain purchase on portion 4 and pull it away from substrate:- 2. Any useful practical means may be employed to start the peeling of portion 4 from substrate 2. One suitable means is by the use of a knife blade, such as the blade of knife 7. In a preferred embodiment of the method of the present invention, the printed circuit is narrowed o-r "necked down" at the location where it is desired for the printed circuit to separate from the commoning portion. The narrowing facilitates such separation. Such narrowing or "necking down" is shown at location 12 in FIGS. 1 and 2. Good separation during peeling has been accomplish when a copper printed circuit having a thickness of about 0.0022 inch is "necked down" to a width of about 0.006 inch. In an alternative embodiment of the method of the present invention, the blade of knife 7 is used to score printed circuit 3 between commoning portion 4 and selected portion 5 at locations 8 prior to peeling. Lands or pads 9 are electrically isolated from each other after portion 4 has been peeled away, although they remain electrically connected to other portions of the printed circuit board by means of, for example, printed circuit lines 10 and plated thru holes 11. The present invention has been disclosed in the above teachings and in the accompanying drawings with sufficient clarity and conciseness to enable one skilled in the art to make and to use the invention, to know the best mode for carrying out the invention, and to distinguish it from other inventions and from what is old. Many variations and obvious adaptations of the invention will readily come to mind and these are intended to be contained within the scope of the invention as claimed below.

Claims: CLAIMS 1. A method of making a printed circuit board (1) having a conductive pattern (3) on a dielectric substrate (2) and having selected portions (5) of the conductive pattern (3) electroplated, the method comprising: (a) placing on a dielectric substrate (2) a conductive pattern (3) , which pattern includes a commoning portion electrically connecting the selected portions. (b) electroplating the selected portions (5) using the commoning portion (4) as a commoning electrode, and (c) removing the commoning portion (4) from the substrate. 2. The method of Claim 1 wherein the selected portions (5) are connector tabs arranged near the edge of a • printed circuit board (1) . 3. The method of Claim 1 wherein the selected portions (5) are electroplated with a conductive metal. 4. The method of Claim 3 wherein the conductive metal is gold, palladium or alloys thereof. 5. The method of Claim 1 wherein (c) comprises first scoring the printed circuit between the commoning portion (4) and the selected portion (5) in at least one location followed by peeling the commoning portion (4) off the substrate (2) . 6. The method of Claim 1 wherein, in (a) , the commoning portions (4) are connected to the selected portions (5) by a connecting portions (12) which are sufficiently narrow to enable separation of the commoning portion (4) from the selected portion (5) in (c) . 7. A printed circuit board (1) comprising a conductive pattern (3) on a dielectric substrate ( 2) having selected portions of the conductive pattern electro¬ plated, wherein the printed circuit board is made by the process of Claim 1.

Inventors: CIBULSKY MICHAEL J, CIBULSKY, MICHAEL, J.
Applicants: IBM, INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1986
Main classification: C25D5
IPC codes: C25D5, C25D7, H05K1, H05K3