Multilayer PCB
Information and help on printed circuit boards also known as pcbs which are found in all electronic gadgets including televisions and computers. Take a screwdriver and break open almost any modern, electronic device, be it a mobile phone, a laptop computer or a flat-panel TV set, and you are bound to find a PCB, or Printed Circuit Board. A PCB consists of a panel of non-conductive material, commonly fibre-glass, onto which are etched or “printed” copper circuits which are, in turn, populated with electrical components.
The Development History of the PCB
Single layer PCBs have been around since the late 1930s when the first one was produced by an Austrian engineer working in the U.K. as part of a radio set. Mass production of PCBs began in the United States during the Second World War, again for the manufacturing of radios that the U.S. army could use in the field.
PCBs are initially more time-consuming and complicated to design than the point-to-point or wire –wrapped circuits that preceded them, but were much easier and cheaper to mass produce, which became an important factor during the boom in low-cost electrical consumer products during the 1950s.
As electronic devices became more complex and smaller the multilayer PCB was developed to pack a larger number of circuits and components into a smaller area. Initially this resulted in the development of the “double-sided” PCB, which had interconnected circuits on both sides of the board. It was then a logical next-step to the multilayer PCB. As the name suggests, multilayer PCBs consist of multiple thin boards stacked one top of the other, with interconnections between them through the “vias” (Vertical Interconnect Access holes). This process greatly increases the surface area onto which circuits can be etched so that many more components can be packed into the same space than with a single board PCB.
Multilayer PCBs were developed during the 1970s and by the mid 1980s multilayer boards accounted for the majority of PCBs manufactured in the USA. At first four to eight layers were possible but boards can now be mass-produced with as many as forty-eight layers. At the present time, the advances in wiring techniques and flexibility of connections used in modern PCBs have improved the performance of a range of products, especially automated and complex devices such as computers and cellular phones.
The boards are now so cheap and easy to mass produced that, in the case of failure of any component part, it is more efficient to replace the entire board than resorting to component-level trouble shooting.
How Multilayer PCBs are manufactured
The conducting layers of a PCB are typically made of thin copper foil, a sheet of which is bonded to the board. A mask is then applied, often using a silk screen printing method which protects the copper with etching resistant inks. The unwanted copper is then removed by etching to leave behind the required copper circuits. The etched layers are then laminated together by pressing them with thin sheets of resin coated fiberglass under high pressure and high temperature. The board is coated with a solder mask which gives it the familiar dark green color. Different types of insulating material can be used to provide different insulating values depending on the requirements of the circuit.
Holes are drilled into the boards using computer controlled drills with tungsten carbide bits. For some very high-density boards lasers may be used to produce the holes. For multilayer PCBs the sides of these holes need to be made conductive, in order that the circuits on individual layers may be electrically connected. Problems can arise with multilayer boards with four or more layers. Drilling can produce a smear of the bonding agent in the laminate which must be removed by chemicals before the holes can be plated.
Where Multilayer PCBs are manufactured
Although the home of the mass produced multilayer PCB is the United States most boards are now manufactured in Asia. Countries such as China, Korea and Thailand have invested heavily over the last few years in PCB plants and now produce the majority (86%) of the world’s PCB units. China alone now accounts for 34% of PCB production.
Worldwide production has declined during the recent economic crisis but demand is strong again in 2010 with a prediction of a 12% growth in the market. For the foreseeable future the multilayer PCB will be an essential component for the electrical gadgets and devices we now take so much for granted.
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