The printed circuit board (PCB)
The printed circuit board (PCB) is the dominant technology used in the assembly of discrete components into operating circuits. Printed circuit boards in electronic devices are used for mounting electronic components and connecting circuits, comprising the electronic components, by means of circuit patterns. Printed circuit boards (PCBs) serve the purpose of an intermediate level of packaging for attachment and electrical inter-connection of discrete devices such as resistors and capacitors and active devices such as logic and memory modules. A flexible printed circuit board is generally used as a printed circuit board for miniaturized electronic devices. PCBs with electrical components are widely used in the electronics industry in a variety of products including computers, servers, televisions and telecommunication devices.
A printed circuit board typically has a wide variety of electrical components mounted to a printed circuit board (“PCB”) to operatively couple the electrical components to desired circuits. A typical circuit board module includes a printed circuit board and a variety of circuit board components soldered to the printed circuit board. The PCB is generally a laminated board with circuit traces on external surfaces of the board or at interlayer levels within the board, and the electrical components are typically light-emitting diodes (LEDs), processors, memory devices, clock generators, resistors, cooling units, capacitors and virtually any other type of electrical components. Printed circuit boards generally comprise a composite of organic and inorganic materials with external and internal metal traces, permitting assembled electronic components to be mechanically supported and electrically connected. A typical printed circuit board includes one or more metal layers, such as routing and/or plane layers, and one or more insulation layers. PCBs are classified into single-sided PCBs, double-sided PCBs and multi-layer PCBs according to the number of wiring circuit surfaces. A multi-layer PCB designates a PCB having three or more conductive patterns including a surface conductive pattern. The conductive patterns are attached to the respective layers of the PCB while being separated from each other by insulation materials between the respective layers.
PCB Assembly in Bay Area
A printed circuit board (PCB) is fabricated by densely mounting a plurality of parts on a plate made of phenol resin or epoxy resin and densely forming curtailed circuits on the surface of the plate to connect the respective parts to each other. The PCB assembly process may involve alternately stacking a plurality of substrates with conductive circuits formed thereon and prepreg sheets, bonding them under heat and pressure, forming through-holes, and plating them with copper or other metallic materials to provide an electrical connection between the surface and inner layers. Electronic components are typically added to a printed circuit board either by manually placing the pans on the printed circuit board (PCB) or by using a machine such as a robot or a high-speed chip placement machine (a chip shooter) to deposit the parts either on the surface of the board or in plated through holes. Printed circuit boards are commonly manufactured in various shapes and sizes dependent upon the environment and the apparatus for which they are intended. A common method of forming printed circuit boards, including multiple layer printed circuit boards, begins with positioning a thin layer of copper on a plate known as a caul. The caul is generally a steel plate that has been finely milled so that it is extremely flat. A via is a hole within a circuit board which is lined with conductive material (e.g., copper, nickel, etc.) to provide an electrical pathway between multiple conductive layers of the circuit board.
PCB Assembly California
A typical circuit board includes many vias in order to achieve layer-to-layer interconnections between various conductive circuit board features. Soft soldering is employed for fixedly mounting electronic components on a PCB. The process for manufacturing a printed circuit board may include a step of forming resin layers, for example, solder resist layers, over electrical interconnections. Another step is forming apertures in the resin layers and a further step is forming external connection terminals, for example, solder balls on the respective electrical interconnections exposed through the apertures. Through the use of thinner substrate materials, adhesiveless metal deposition processes, and metallized through hole processes, double sided printed circuit boards having thicknesses as low as 50 microns or less be constructed. Moreover, through the use of conductive adhesives such as those forming anisotropic adhesive layers, thin multilayer constructions may be fabricated, offering even higher packaging density for a given surface area. The overall performance and packaging density of printed circuit assemblies have been further benefited by advancements in integrated circuit chip mounting techniques, such as direct chip attachment and other surface mount technologies, whereby an unpackaged integrated circuit chip is directly mounted to a supporting substrate. PCBs are typically designed using computer aided design (CAD) workstations or systems. The PCB designer uses the CAD workstation to arrange traces and pads on the PCB so as to minimize electrical interference between components and to maximize the number of components which will fit on the board.
Multilayer circuit boards permit formation of multiple circuits in a minimum volume or space. They typically comprise a stack of layers where layers of conductors are separated from each other by a layer of dielectric material. The electrical conductors are referred to as foil. Dielectric layers are typically situated between conductive layers to electrically separate the layers. The layers are stacked, bonded, and the hole patterns formed and plated-through with electrical conductive materials. Vias or interconnects are used to electrically connect individual circuit layers to each other and to the outer surfaces and typically pass through all or a portion of the stack. The development of very compact and powerful electronic devices has been possible thanks to high-density printed circuit boards (PCB), obtained by sequential build-up (SBU) technology. Basically, a build-up multilayer circuit is a combination of several superimposed layers of different wiring densities, which are separated by dielectric layers and interconnected through micro blind vias. Printed circuit board may have edge connectors for physical attachment and electrical connection of the printed circuit board to a higher level of packaging. Devices are attached to printed circuit boards by a variety of methods. One attachment method is soldering to pads of discrete passive surface mount technology (SMT) components or active device ball grid array (BGA) or land grid array (LGA) modules. Printed circuit board assemblies often carry surface mount technology components referred to as “SMTs” which are mounted and soldered to one or both sides of the board. Surface mount components are soldered directly to the printed circuit board, and component leads and through-holes in the board may therefore be avoided. The same printed circuit board assemblies also may contain plated through hole components (PTH’s) on one or both sides of the PCB. PIH soldering requires printed circuit having plated through holes. The pads and edge connectors are interconnected by wiring traces formed on the top surface of the printed circuit board. Often wiring traces are formed on the bottom surface of the board and within the board itself. Similarly, devices may be mounted on both the top and bottom surfaces of the printed circuit board. Pads for SMT, BGA, LGA, and PIH/LGA solder connections require surface finish layers that provide good solderability and corrosion resistance. In general, most printed circuit board assemblies (PBAs) contain one or two heat generating sources that necessitate heat removal devices. In many cases a PBA is assembled with many low heat generating components such as capacitors, diodes and transistors. Heat is usually extracted from a concentrated heat source by either heat sink or fan or both.
Printed circuit assembly processes and other electronic interconnection technologies are continuously being improved in terms of performance, reliability, packaging density and environmental resistance. To mount a semiconductor device with high density, it is preferable to mount a semiconductor chip as it is without packaging such as bare mounting. Bare chip mounting is ideal in order to enable high density mounting of a semiconductor device. In bare chip mounting, however, it is insufficient to protect a semiconductor chip and hard to handle it. Wafer level chip size package (CSP) is widely spreading as a package of a semiconductor device. CSP techniques, as compared to conventional semiconductor packaging, have produced a reduced package size and weight, high density packaging, and a reduction in manufacturing costs. In the wafer level CSP, a wiring pattern and external terminals (solder ball, for example) are formed on a semiconductor wafer, and a plurality of semiconductor devices are formed by dicing the semiconductor wafer. In the course of PCB assembly, a printed circuit board is loaded with electronic components and then undergoes an inspection process for determining the status of the assembly. Automatic test systems have generally been used in testing printed circuit board assemblies of various types. Such systems are particularly useful when testing large quantities of identical printed circuit board assemblies, such as computer motherboards. The equipment provides semiconductor manufacturers with the ability to functionally test each device at the wafer and packaged-device levels. In an electrical circuitry inspection process, defects in assembly or in the electronic components themselves, and poor (cold) solder joints are inspected by continuity checks of the installed electronic components. The processes for manufacturing printed circuit boards having mounted components interconnected by circuit conductors influences the circuit board test ability following manufacture.