Mastering Printed Circuit Board Assembly Today, engineers do not really have to concern themselves with printed circuit board assembly. The ability for clients to supply schematics and design specifications and to leave the board layout to the in-house specialists is found in the design services made available from many PCB manufacturers. For a fabless design firm or a company that designs limited-volume products, this is an excellent solution. However, a firm that manufactures high-volume units will frequently want to control each part of the manufacturing process in order to minimize per-unit costs. To help optimize each process through design, engineers in such a firm can benefit from a thorough comprehension of the stages of PCB assembly. Board Fab The production of the board itself is the first process. Single or double-sided boards start off as substrate material clad with a ½ or 1 ounce layer of copper. The substrate material and thickness are selected to offer mechanical reliability for basic circuits. Common choices are 31 or 62 mils. Trace width is dependent upon the material used for high-frequency boards and therefore must be chosen a lot more carefully. Mechanical stiffness may become much more of an issue due to the fact that this material is oftentimes softer. Photolithography is used by fab houses to make the traces. To keep the finished lines crisp, the trace design should meet minimum requirements for width and separation. Component pads should also meet width and separation design specs to maintain solderability. When two double-sided boards are laminated together, a four-layer board is generated. When it comes to providing dedicated power planes and to minimizing board area, the use of four-layer boards is an excellent way; that said a non-trivial increase in cost and process time at the fab house is added. Manual Part Placement The very first component assembly step is manual part placement. This is the point when assemblers solder leaded components. In order to minimize the cost of this relatively expensive stage, the number of leaded parts in a design should be minimized. Placement of Surface Mount Parts For PCBs designed with surface mount components, the first component assembly step is surface mount part placement. This is a totally automated process, and so is far less expensive than manual part placement. As bare boards travel a conveyer belt on the assembly line, the process commences. Robots on the line are loaded with long strips of components much like a machine gun with bullets, and place each part on the PCB. In the very last step, the parts are soldered in place at once by a wave of solder. This process is fast and efficient. Any leaded parts need to be soldered manually after the wave-soldering stage. There are several parts which do not have surface mount versions, including custom components and connectors, on many boards. XPtronics Inc.
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Mastering Printed Circuit Board Assembly
Testing that is Automated In order to validate each PCB assembly, an automated test could also be used. Automated testing is usually top of mind when engineers are designing boards; this is evident in the special test point pads provided and the allowance of room for a test jig. Designers can supply the fab house with a test harness and the proper equipment, and integrate the test into the assembly process. The test can be as simple as a power-on check or as complex as a full use case validation. The flexibility to balance the time / cost of testing the printed circuit board assembly with the degree of reliability of the manufactured product is provided to designers. Today, engineers do not really have to concern themselves with printed circuit board assembly. The ability for clients t...
Document Tags: prototype pcb assembly, printed circuit board assembly http://www.xptronicsinc.com/
XPtronics Inc.
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