Frequently Asked Questions regarding PCB designs

	^{engineering layers of copper into advanced circuitry}

	Why does component placement take so long? Careful component placement is an essential element affecting the quality of the finished printed circuit board design. After creating a physical outline of the circuit board based on your equipment enclosure or form factor, all dedicated-position components like switches, I/O connectors and indicators with mandatory locations are placed. The remaining components are then placed based on their circuit interconnection to closely emulate the schematic flow. This produces the best possible routing regardless of whether manual or automatic routing methods are to be used. Component heights will be taken into consideration at this stage with regards to air flow and cooling. Also during this stage the PCB designer must insure that the "footprint" or "land pattern" of every component is correct for each individual schematic part. Component orientation and component-to-component spacing is considered for automated pick and place machines ("chip shooters") and for rework equipment limitations. The use of solder-side components and mixed-technologies (surface mount and through-hole components) as well as odd-form components will be weighed as these choices affect assembly costs.
	Why would anyone manually route a board instead of auto-routing it? PCB traces can be routed either manually or with an "auto-router." The auto-router is a programmed algorithm contained within the PCB Designer's CAD software and used by the computer's processor to route copper traces automatically. The best PCB layouts are generally achieved using manual routing because a PCB designer has a conceptual overview of the circuit flow based on an understanding of electronics. Auto-routers tend to be somewhat erratic when placing traces, only solving individual point-to-point sequential trace routes without any regard to bussed-line symmetries and electrical function groupings. For an auto-router to work efficiently at all it must be constraint-driven. To achieve useable end results from an auto-router, the constraints must be manually entered regarding each trace to be routed. Constraints consist of strict rules such as trace widths, maximum net lengths and copper-to-copper spacing limits to name just a few. Frequently a board can be manually routed in the same amount of time or less than it takes to enter all the constraints required for auto-routing a particular design.
	Should Signal Integrity (SI) and EMI be a concern? The constant down-sizing of IC packaging has led to ever increasing speeds in signal edge transitions. These extremely fast signal edge transitions can create problems with a signal's electrical integrity and can create EMI problems. In some instances the schematic designer may include termination components on a high-speed signal, but it is the PCB designer who must manage ground currents while also working to minimize trace stubs that can cause undesired reflected energy (signal bounce.) Adjacent signal cross-talk is another signal integrity issue a PCB designer will minimize during routing. A PCB designer may also utilize copper plane layers to improve signal integrity and reduce EMI.
	What determines the cost of a circuit board? The cost to fabricate a circuit board is dependant on how far your circuit board designer pushes the current fabrication technology. The idea is to get all the functionality, performance and density your design requires from its circuit board without causing a PCB manufacturer to use any more expensive process step or materials than are absolutely required. The result is a higher yield from the PCB manufacturer and is directly reflected in a lower circuit board unit cost to you. A good PCB designer is familiar familiar with the complex processes of manufacturing and assembling printed circuit boards and will make informed decisions regarding your circuit board design so as not to make your circuit board overly difficult and expensive to manufacture. We will design your circuit board for smoother assembly process flow while minimizing its potential for solder defects. A good PCB designer will use factors like the overall thickness of the finished circuit board and its overall area to determine pad sizes and the smallest drill hole size to use. This comes from an understanding of such things as the aspect ratio of plated through-holes, multiple layer registration and many other issues that affect PCB fabrication. A good PCB designer also understands the issues that will affect your assembly costs and board reliability. The planarity of a circuit board will affect the your ability to attach Ball Grid Array packages. The finish applied to prevent copper oxidation may also affect planarity, or may exhibit a short shelf-life which could be problematic depending on your company's assembly cycle. Hot-air reflow, wave soldering and potential rework cycles may call for improved circuit board materials with specific qualities that resist thermal expansion. We will work closely with you to make the correct decisions for your applications. Knowledge of circuit board fabrication and assembly processes are vital to keeping PCB costs down.