1. Determine the number of layers of PCB

     The size of the circuit board and the number of wiring layers need to be determined in the early stage of the design. If the design requires the use of a high -density grid array (BGA) component, you must consider the minimum number of wiring layers required for the wiring of these devices. The number of wiring layers and the stack-up method directly affect the wiring and impedance of the printing line. The size of the board helps to determine the layers of layers and the width of the lines, and achieve the designed effect.

     Over the years, people have always thought that the less the number of circuit boards, the lower the cost, but there are many other factors that affect the manufacturing cost of the circuit board. In recent years, the cost difference between multi -layer plates has been greatly reduced. When starting design, it is best to use more circuit layers and make copper evenly distributed to avoid discovery that a small number of signals do not meet the defined rules and space requirements at the end of the design, which is forced to add a new layer. Careful planning before designing will reduce a lot of trouble in the wiring.

     2. Design rules and restrictions

     The automatic wiring tool itself does not know what to do. To complete the wiring task, the wiring tool needs to work under the correct rules and restrictions. Different signal cables have different wiring requirements. The signal lines of all special requirements should be classified, and different design classifications are different. Each signal class should have priority, the higher the priority, and the stricter the rules. The rules involve the width of the lines, the maximum number of perforated, parallelism, the interaction between the signal lines, and the restrictions of layers. These rules have a great impact on the performance of the wiring tool. Carefully considering the design requirements is an important step of successful wiring.

     3. The layout of the component

     In order to optimize the assembly process, the manufacturing design (DFM) rules will limit the component layout. If the assembly department allows the component to move, it can be appropriately optimized to the circuit and it is easier to automatically wiring. The defined rules and constraints will affect layout design.

     When layout, we need to consider the Routing Channel and the perforated area. These paths and regions are obvious for designers, but the automatic wiring tools will only consider one signal at a time. By setting the wiring constraint conditions and setting the layer of the signal line, the wiring tool can be as conceived by the designer's imagination. Complete the wiring like that.

     4. Fan out of design

     During the design stage of the fan, the automatic wiring tool should be connected to the component pins. Each pin of the surface installation device should have at least one perforated so that when more connections are needed, the circuit board can perform the inner layer in the inner layer. Connect, online test (ICT) and circuit re -processing.

     In order to make the automatic wiring tool efficiency, it is necessary to use the maximum perforated size and printing line as much as possible. The interval is set to 50mil ideal. The most perforated type of the wiring trail should be adopted. When the fan is carried out, consider the online testing problem of the circuit. The test fixture may be expensive, and it is usually ordered when it is about to be put into full production. It is too late to consider adding a node to achieve 100%testability at this time.

     After careful consideration and prediction, the design of the circuit online test can be carried out in the early stages of the design. It is realized in the later stage of the production process. According to the wiring route and the online test of the circuit, the type of over -pore fan is determined. Essence In order to reduce the sensory resistance generated by the filter capacitor connection cable, the over -hole should be as close to the pins of the surface -on -side installation device as much as possible. If necessary, a manual wiring may be used. Considering which pores are used, you must consider the relationship between excessive holes and pins, and set the priority of excessive hole specifications.