Layout outsourcing design wiring steps in PCB industry

Wiring is an extremely important part of PCB layout design outsourcing, which will directly affect the performance of PCB. In the layout design process, layout engineers have their own understanding of layout, but all layout engineers are consistent in how to improve the efficiency of wiring, which can not only save the development cycle of the project for customers, but also maximize the quality and cost. The following is the general layout outsourcing design process and steps.

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 initial stage. 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 devices must be considered. The number of wiring layers and the stacking up method will directly affect the wiring and impedance of the printed wire. The size of the board is helpful to determine the stacking mode and the width of the printed line to achieve the desired design effect.

2. Pcb design rules and limitations

The auto routing tool itself does not know what to do. To complete the routing task, the routing tool needs to work under the correct rules and restrictions. Different signal lines have different wiring requirements. All signal lines with special requirements should be classified, and different design classifications are also different. Each signal class should have a priority. The higher the priority, the stricter the rules. The rules involve the width of printed wire, the maximum number of vias, parallelism, the interaction between signal wires, and layer restrictions. These rules have a great impact on the performance of wiring tools. Careful consideration of design requirements is an important step for successful cabling.

3. Layout of circuit board components

To optimize the assembly process, design for manufacturability (DFM) rules impose restrictions on 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.

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Layout outsourcing design

4. Fan out design

In the fan out design stage, to enable the automatic wiring tool to connect the component pins, each pin of the surface mount device should have at least one via, so that when more connections are needed, the circuit board can conduct internal connection, online test (ICT) and circuit reprocessing.

In order to maximize the efficiency of the automatic routing tool, it is necessary to use the largest via size and printed wire as much as possible, and it is ideal to set the spacing at 50mil. Use the type of vias that maximize the number of routing diameters. When fan out design is carried out, the problem of circuit online test should be considered. Test fixtures can be expensive and are usually ordered when they are about to go into full production. It is too late to consider adding nodes to achieve 100% testability.

5. Manual wiring and key signal processing

Although this paper mainly discusses the problem of automatic routing, manual routing is an important process of PCB design now and in the future. Manual routing is helpful for automatic routing tools. No matter how many key signals are, these signals can be wired first, either manually or with automatic wiring tools. The key signals usually have to be carefully designed to achieve the desired performance. After wiring, it is much easier for relevant engineers to check these signal wiring. After passing the inspection, fix these lines, and then start to automatically route the rest of the signals.

6. PCB layout design automatic wiring

For the wiring of key signals, it is necessary to consider controlling some electrical parameters during wiring, such as reducing the distributed inductance and EMC, etc. The wiring of other signals is similar. All EDA manufacturers will provide a method to control these parameters. The quality of automatic routing can be guaranteed to a certain extent after knowing what input parameters the automatic routing tool has and the impact of the input parameters on routing.

7. Appearance of circuit board

In the past, the design often paid attention to the visual effect of the circuit board, but now it is different. The circuit board designed automatically is not more beautiful than that designed manually, but it can meet the specified requirements in terms of electronic characteristics, and the complete performance of the design is guaranteed.

For layout engineers, whether the technology is powerful or not should not be judged only from the number of layers and speed. Only when the number of devices, signal speed and other conditions are equal, can the smaller the area, the fewer layers, and the lower the cost of PCB board design be completed, and can ensure good performance and beauty, this is the master.