PCB High Pass Rate And Shorten The Design Time

                 PCB high pass rate and shorten the design time

     Although the current EDA tools are very powerful, as the PCB size requirements are getting smaller and the device density is getting higher and higher, the difficulty of PCB design is not small. How to achieve a high PCB layout rate and shorten the design time? This article introduces the design skills and key points of PCB planning, layout and wiring. Now PCB design time is getting shorter and shorter, smaller and smaller circuit board space, higher and higher device density, extremely demanding layout rules and large-size components make the designer's work more difficult. To In order to solve the design difficulties and speed up the launch of products, many manufacturers now tend to use dedicated EDA tools to realize PCB design. However, dedicated EDA tools cannot produce ideal results, nor can they achieve a 100% deployment rate, and are very messy. It usually takes a lot of time to complete the remaining work. To There are many popular EDA tool software on the market, but they are all the same except the terms used and the positions of the function keys. How to use these tools to better realize the PCB design?

     1. Determine the number of layers of PCB
The size of the circuit board and the number of wiring layers need to be determined at the beginning of the design. If the design requires the use of high-density ball-grid array (BGA) components, the minimum number of wiring layers required for the wiring of these components must be considered. The number of wiring layers and the stack-up mode directly affect the wiring and impedance of the printed wire. The size of the plate helps determine the layering pattern and the width of the printed line to achieve the desired design effect.
For years, it was assumed that a circuit board with fewer layers would cost less, but there are many other factors that affect the cost of making a circuit board. In recent years, cost differentials between laminates have decreased considerably. At the beginning of the design, it is better to use more circuit layers and distribute the applied copper evenly, so as to avoid the discovery of a small number of signals near the end of the design that do not conform to the defined rules and space requirements, thus forcing the addition of new layers. Careful planning prior to design will save a lot of trouble in wiring.

      2. Design rules and limitations
The cabling tool itself does not know what to do. In order to perform the wiring task, the wiring tool needs to operate under the correct rules and limitations. Different signal lines have different wiring requirements, to all special requirements of the signal line classification, different design classification is not the same. Each signal class should have a priority, and the higher the priority, the stricter the rules. Rules related to print wire widths, maximum number of holes to pass, parallelism, signal line interactions, and layer limitations can have a significant impact on the performance of the wiring tool. Careful consideration of design requirements is an important step in successful cabling.

      3. Layout of components
To optimize the assembly process, manufacturability design (DFM) rules impose constraints on the component layout. If the assembly department allows the components to move, the circuit can be properly optimized to facilitate automatic wiring. The rules and constraints defined affect the layout design.
Routing channels and through-hole areas should be considered in layout. These paths and areas are obvious to the designer, but the automatic routing tool considers only one signal at a time. By setting the wiring constraints and setting the layers of the signalable wires, the routing tool can perform the routing as the designer intended.

      4. The fan out design
During the fanning out design phase, to enable the automatic wiring tool to connect the component pins, the surface-mount device should have at least one through hole for each pin to allow for inline connections, in-line testing (ICT), and circuit reprocessing on the board if additional connections are required.
To maximize the efficiency of the automatic wiring tool, be sure to use the largest hole size and print line possible, ideally with an interval of 50mil. Use the hole type that maximizes the number of wiring paths. The on-line test of the circuit should be considered when the fan out design is carried out. Test fixtures can be expensive and are usually ordered near full production, when it is too late to consider adding nodes to achieve 100% testability.

      5. After careful consideration and prediction, the design of on-line circuit test can be carried out at the beginning of the design and realized at the end of the production process. According to the wiring path and on-line circuit test, the type of through-hole fan-out can be determined. Power supply and grounding also affect the design of wiring and fan-out. To reduce the filter capacitor impedance of cable, via should as far as possible near the surface-mount device pins, manual wiring can be used when necessary, it may affect the originally envisaged wiring path, even may cause you to reconsider using what kind of a hole, must therefore be considered the relationship between impedance and hole and pin set via the specifications of the priority.