Thursday, December 13, 2007

Circuit Board Manufacturing

Circuit board manufacturing should be done carefully since it involves sensitive components. There are 9 steps involved in circuit board manufacturing, and these are: patterning or etching, lamination, drilling, plating and coating, solder resisting, screen printing, testing, populating, protection, and packaging. Here is a simple step-by-step guide on how each step is performed.

Patterning is the first step involved in circuit board manufacturing. Also known as “etching”, it is done by sticking a copper layer over a whole substrate and then removing them afterwards by patterning a temporary mask to leave only the important traces of copper. Some PCBs are also made by including traces to a substrate that has a thin copper layer or a bare substrate by multiple electroplating processes. Other copper removal methods for PCB include the following: PCB Milling – This method utilizes 2 to 3 axis mechanical milling systems for removing copper from the substrate. Silk screen printing – This method utilizes etch-resistant-inks. A sequence of etching is done for removing unwanted copper while protecting the copper foil. The ink can be printed on a blank but non-conductive board or on a conductive board. Photoengraving – This method makes use of chemical etching and a photomask for the removal of the copper foil.

Lamination and drilling procedures Multi-layer print circuit boards have trace layers inside them. They are formed by laminating thin boards that are separately etched from one another together. Next, drilling of vias or holes is done with a tungsten carbide drill bit. The drilling is done by automated drilling machines and the placement and positioning of holes is controlled by a drill file or a drill tape. If there is a need for small holes, they can be drilled by lasers for more control.

Plating and coating to prevent solder
Part of circuit board manufacturing is plating or coating areas with polymer solder resist or solder masks. This is done to prevent short circuits that are caused by the solder when it bridges between conductors. A coat is also made to serve as protection from harsh environments.

Screen printing
Screen printing is done by printing text and line art on the external surfaces of PCBs. If there is enough space, the text can depict component designators, test points, switch setting requirements, and other features to aid in assembling, servicing, and testing the circuit board. The process is also called red print for one-sided PCBs and silk screen. Digital printing can also be utilized for this process. It allows barcodes and serial information to be included in the PCB.
Testing and populating
Next, unpopulated boards are subjected to bare-board testing where all circuit connections are verified for “correctiveness.” A fixture, a bed of nails, or rigid needle adapters are also used for mass production. After the completion of the PCB, electronic components are attached to form the assembly. These components are attached by inserting them through holes, mounting them on the surface, and soldering. Afterwards, they are subject to tests again. If the tests fail, the components are going to be replaced.

Protection and packaging
To protect the printed circuit board against harsh environmental conditions, they should have a conformal coat that is applied by spraying or dipping them after attaching the components. The coat aids in preventing leakage currents, corrosion, and shortening. The coat is made of wax or a diluted solution of polyurethane, epoxy, acrylic, or silicone rubber.

Finally, when transporting PCBs, they should be in antistatic bags and the person handling them should be earthed to avoid static electricity from damaging them. Circuit board manufacturing companies like Almatron practice these safety measures to ensure high quality printed circuit boards.

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