1. **Consider the choice of PCB parts packaging.**
In the entire PCB schematic design phase, it’s crucial to consider the component packaging and pad patterns during the PCB layout stage. Below are several recommendations to keep in mind when selecting components based on their packaging.
2. **Understand package details.**
Remember that the package encompasses both the electrical pad connections and the mechanical dimensions (XY and Z) of the component. This includes the component’s shape and the pins that connect to the PCB. When selecting components, consider any installation or packaging constraints that may exist on both the top and bottom layers of the final PCB. Some components, such as polarized capacitors, may have stringent clearance requirements that must be factored into the selection process.
3. **Start with a basic layout.**
At the outset of the design, you can create a basic outline of the circuit board and then position some of the planned larger or critical components (such as connectors). This approach allows you to quickly visualize the virtual perspective of the circuit board (without wiring), providing a fairly accurate relative positioning and height of both the board and its components. This step will aid in ensuring that after assembly, the components fit properly within the outer casing (such as a plastic chassis frame). Utilize the 3D preview mode from the Tools menu to examine the entire circuit board.
4. **Examine the land pattern.**
The land pattern represents the actual shape of the pads or holes used for soldering on the PCB. The copper pattern also conveys essential shape information. The dimensions of the pad pattern must guarantee proper soldering and maintain the mechanical and thermal integrity of the connected parts. When designing the PCB layout, it’s important to consider how the circuit board will be soldered, whether through manufacturing processes or manual soldering techniques.
Reflow soldering (where solder is melted in a controlled high-temperature furnace) is capable of handling a wide variety of surface mount devices (SMD). Wave soldering is typically employed to solder the underside of the circuit board for securing through-hole devices, but it can also accommodate some surface-mounted components located on the back of the PCB. Generally, when utilizing this technique, the bottom surface-mounted devices must be arranged in a specific orientation, and the pads may need adjustments to suit this soldering method.
(3) Component selection can evolve throughout the entire design process. In the initial stages, deciding which devices will use plated through holes (PTH) versus surface mount technology (SMT) aids in the overall PCB planning. Considerations include cost, availability, area density, and power consumption. From a manufacturing standpoint, surface-mounted devices are often more cost-effective and simpler to work with. For small to medium-sized prototype projects, opting for larger surface-mounted components or through-hole devices is advisable, as this not only facilitates manual soldering but also enhances the connection between pads and signals.
4. If ready-made packages are not available in the database, custom packaging is usually developed within the tool.
2. Employ effective grounding techniques. Ensure the design incorporates adequate side capacitance and a solid ground plane. When using an integrated circuit, it is crucial to position an appropriate decoupling capacitor near the ground and power terminal. The capacitor’s capacity should align with the specific capacitor technology and operational frequency. Properly placing the bypass capacitor between the power and ground pins, close to the relevant IC pin, optimizes the circuit’s electromagnetic compatibility and susceptibility.
Allocate virtual component packages. Generate a bill of materials (BOM) to verify the virtual components. Virtual components lacking associated packaging will not progress to the layout stage. Compile a material list and review all virtual components in the design. The only items that should remain are power and ground signals, as they are considered virtual components and should only be addressed within the schematic context, not in the layout design. Unless for simulation purposes, components shown in the virtual section should be substituted with packaged components.
4. Ensure the bill of materials data is comprehensive. After generating the BOM report, meticulously review all PCB components for any missing supplier or manufacturer details.
Sort 5 according to component labels. To aid in the organization and review of the BOM, ensure that the component labels are consecutively numbered.
Examine extra gate circuits. Typically, all additional gate inputs should be connected to signals to prevent floating inputs. Verify all extra or overlooked gate circuits and ensure all unused inputs are fully connected. In some instances, if an input terminal is left in a suspended state, the entire PCB system may fail to function correctly. Regarding the common practice of double operation in design, if the IC component can be driven in both directions, it is advisable to utilize one transmission only or to ground the unused input terminal. Arrange an appropriate unity gain (or other beneficial) feedback network to ensure the entire component operates correctly.
In certain cases, an IC with suspended pins may not perform effectively. Generally, an IC device or other gates within the same device can only function optimally when in a saturated state. Simulations often do not capture this scenario, as the simulation model typically does not connect multiple IC parts to represent the suspended connection effect.
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