The printed circuit board (PCB) or printed wiring board (PWB) is the object that connects and interfaces most electronic components with each other and with other elements in computers, communication devices, consumer electronics, automated manufacturing and inspection equipment.
The procedures of manufacturing these circuit boards and of inserting and connecting multiple components, such as resistors, capacitors and integrated circuits, can be applied in mass production environments, achieving substantial automation, which results in costs reduction, high reliability and high component packaging densities. Backplanes and panels (interconnecting boards, in which printed circuits, panels or integrated circuit packages can be plugged or mounted into or onto) are also manufactured in a similar manner. Modern, highly-dense, populated boards require sophisticated and high resolution manufacturing techniques with precise registration capabilities.
A PCB is produced from a base of insulating material on which a thin copper layer is laminated or plated, known as a bare copper plated board, from which a chemical etching step selectively removes areas of the copper to produce electrically conducting paths. This selective removal is achieved by covering the copper layer with a patterned mask (etch-resist) that protects the copper layer in the following etching step. For simpler PCBs, screen-printing techniques are generally utilized to form the patterned mask, and for more densely populated PCBs having generally complicated multi-layer conducting paths, Liquid Photo Imageable etch and solder resist mask procedures are commonly utilized. The pattern that remains on the board after the etching step is commonly known as the primary image conductor pattern.
The components leads must then be connected to predetermined positions in the conducting paths (called pads) by soldering the leads and the conducting paths utilizing a molten metal alloy, which, after solidifying, achieves a permanent electrically conductive bond. In mass production, wave-soldering methods are commonly utilized, wherein the PCB passes through a molten solder wave that coats the pads and leads and thus forms the required solder joints. A solder resist mask protects the conducting paths from being coated with solder during the soldering step. The solder resist mask leaves uncovered only the pads that need to be covered by the molten solder; otherwise, the conducting paths would also be covered with solder, causing several problems such as short circuits by bridging solder.
Various finishing processes in the manufacturing of PCBs currently use (or will be able to use shortly) state of the art inkjet printers. These printers are used to deposit specific kinds of material on the surface of the PCB according to computer generated graphics.
In one application, an inkjet printer may be used to cover the PCB with a material that acts as a solder mask in the ensuing manufacturing processes and acts as a protective cover layer throughout the life of the finished electronics subsystem. This solder mask may be applied using any conventional method such as “curtain coating” and “silkscreen” methods.
The solder mask coating may also be applied digitally, as described, for example, in U.S. Patent Application Publication No. 2005/0176177 (Zohar et al), the disclosures of which are incorporated herein in their entireties, and which disclose a method and apparatus for applying ink, according to a solder mask pattern, to a printed circuit board having elevated pads defining pad edges. The method includes flooding the printed circuit board with ink such that the ink advances to the pad edges and is stopped thereby and thereat, without climbing onto the elevated pads.
In another application, inkjet printers deposit notation ink to print human or machine readable information such as legend, 1D or 2D Barcode, geometry defining lines, etc. See, for example, U.S. Pat. No. 6,754,551 (Zohar et al.), the disclosure of which is incorporated herein in its entirety, and which describes a jet dispensing print system for dispensing a liquid or viscous substance as a pattern onto the surface of a PCB in an industrial manufacturing PCB production line.
There is a growing need to speed up the manufacturing process of PCBs, to reduce the footprint of PCB manufacturing tools and to reduce the cost associated with the manufacturing of PCSs.