In Terms Of PCB Assembly, There Are Size And Cost Design Challenges Perhaps the two most critical design issues for PCB assembly, following schedule and performance, are size and price. In many cases, the PCB footprint is determined at the start of the project, as is the per unit assembly cost. In some cases, only rough targets are given and lucky designers are told to attempt to "minimize" size and expense. In any case, the design issues are identical. When determining how to approach the design, here are some ideas. External Connections Should Be the First Step The size of the connections in relation to other boards or to the housing will determine the size of the boards on most occasions. There are limitations on connector positioning or orientation many times. The periphery of the board will not be smaller than the total of the connector widths even in the best cases. This is the time to carefully challenge connector choices, if at all possible. For instance, can an USB mini be utilized in place of a USB-B? Or can a SMA be utilized to replace a BNC? Designers can massage an initial connector replacement when these choices are made. Keeping the power connectors away from the sensitive signal inputs is often the overriding concern. This strategy helps segregate the associated sensitive components at the same time. Continue With Component Selection The choice of components is the next biggest contributor to both size and expense. Typically, leaded discretes requiring through-hole assembly are the largest components. These parts make the boards easiest to debug and so are excellent choices for the early part of a product lifecycle. In terms of assembly, they are relatively costly since they require hand placement. Surface Mount Components Engineers can choose surface mount components to make the most of the savings of automated placement and wave soldering during assembly. The size of a PCB is also decreased dramatically. The boards are still fairly easy to debug and to replace components manually, if necessary, as long as components are not chosen too small (for instance, a 0805 resistor/capacitor package). Designers can also make use of mixed-mode designs when some components do not have a surface mount version. In this case, all of the surface mount components are added first, followed by a manual assembly step for the leaded components. The inner layers are frequently reserved for power planes, leaving the bottom portion allocated solely to surface mount components, in four-layer board design. Components that are High Density To obtain further size reductions, engineers can select high-density components. The choice of integrated circuits is one example of this strategy. The use of leaded DIP packages for ICs is granted with through-hole design. A surface mount version that can shrink sizes by over 50% is included in a lot of modern ICs. One high-density version of an integrated circuit is a ball-grid array
XPtronics Inc.
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In Terms Of PCB Assembly, There Are Size And Cost Design Challenges (BGA). The connections come from under the part instead of the side in this case. ICs with many pins can achieve a size reduction to 10% of the DIP package or more. The ability to smolder these parts manually is not possible and they are not easy to debug. When a design is proven and mature, these are suitable choices. The most compact footprint is afforded with high-density components. However, if the designer is unable to manage the increase in the number of traces, quite often a design loses the efficiency of small components. Minimizing Cost and Size In general, designers can minimize cost and size of PCB assembly by employing an iterative design, starting with the connectors and completing with the component choice and trace placement. For high-volume products, an excellent strategy is to evolve the design philosophy through the entire product lifetime, starting with leaded components, and then optimizing with surface mount and high-density parts. Perhaps the two most critical design issues for PCB assembly, following schedule and performance, are size and price. In...
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XPtronics Inc.
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