pcb design

Designing a proper stack-up is critical to achieve the lowest cost and highest reliability PCB design. This is getting increasingly more difficult as high speed digital design is getting more complex. A stack-up refers to the arrangement of the copper and insulating layers that make up a Printed Circuit Board (PCB). The stack-up must consider several job functions to ensure success. A collaborative effort between the layout, signal integrity, hardware engineer and manufacturing (fabrication/assembly) vendor is key to ensuring that all parameters are met and incorporated into the stack-up . It is critical that the stack-up is generated and agreed upon by all parties early in the design phase. This ensures that each discipline knows what the final layout will entail and prevents any issues during the critical layout phase of a design. It is strongly recommended to follow the associated Platform Design Guide (PDG) whenever possible. A collaborative effort between the layout, signal int...

QFP  —Quad Flat Pack, a fine-pitch SMT package that is rectangular or square with gull-wing shaped leads on all four sides. The lead pitch of a QFP is typically either 0.8mm or 0.65mm, although there are variations on this theme with smaller lead pitches: TQFP   also 0.8mm; PQFP   tooled at either 0.65mm (0.026") or 0.025" and SQFP   at 0.5mm (0.020"). Any of these packages can have a wide variety of lead counts from 44 leads on up to 240 or more. Although these terms are descriptive, there are no industry- wide standards for sizes. Any printed circuit designer will need a spec sheet for the particular manufacturer's part, as a brief descrition like "PQFP-160" is inadequate to define the mechanical size and lead pitch of the part.    Ratsnest  —A bunch of straight lines (unrouted connections) between pins which represents graphically the connectivity of a PCB CAD database. [Derived from the pattern of the lines: as they crisscross the b...

Manhattan length  —The length of the two sides of a right triangle as a distance between two points, as opposed to the hypotenuse.. (Derived from the Manhattan Alogorithm  for determining the length of a taxicab trip following streets and avenues on the island of Manhattan, NY.)  Routing of traces in orthagonal patterns in a PCB design, or in a semiconductor chip, follows the same pattern as streets and avenues in a city.  The minimum distance between two component leads, or two nodes on a chip, when routing on 90 degrees is the  Manhattan length  .  Advanced PCB auto-routers permit specification of maximum length of classes of nets as a percentage of  Manhattan length  . For example, one could specify clocks as 120% and random nets as 160% of  Manhattan length  . (This percentage, expressed as a ratio, becomes the "Manhattan coefficient", ie. a Manhattan coefficient of 1.2 means the routed length is 120% of the  Manhat...