pcb design

When you give a PCB for fabrication, you need to specify details on PCB materials, impedance controls, finish, copper thickness and so on. Most of the details are so common that they are always assumed. However still it is better to know them. Below is a screenshot of quotation submitted by a fabricator for a PCB design  Let us understand each term one by one and things related to them 1) 4 layer specifies NUMBER OF LAYERS - This means the number of conducting layers. The layers may be either routing layer or plane layer. The commonly used no. of layers are 1, 2, 4, 6, 8 and other even numbered layers. Odd number layer boards may be formed but they are not standard boards and doesn’t offer any savings. The PCB materials used for 3 or 4 layers would almost be same. Routing layers contains tracks while plane layer are generally used to connect power or ground. Plane layers have plane of copper from which connections are drawn up or down wherever needed. I...

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...