Teach you to easily get the PCB component selection in the package

writer: G March 06, 2018

1. Using a good grounding method

Make sure the design has enough bypass capacitance and ground plane. When using integrated circuits, make sure that proper decoupling capacitors are used near the power supply terminals, preferably at ground level. The proper capacitance depends on the application, capacitor technology and operating frequency. When the bypass capacitor is placed between the supply and ground pins and placed near the correct IC pin, the circuit's electromagnetic compatibility and susceptibility can be optimized.

2. The distribution of virtual components package

Print a bom to check the virtual components. Virtual components are not encapsulated and will not be delivered to the layout stage. Create a bill of materials and look at all the virtual components in the design. The only entries should be power and ground signals, since they are considered as virtual components and are handled exclusively in the schematic environment and are not passed on to the layout. Unless used for simulation purposes, the components shown in the virtual section should be replaced with the packaged components.

3. Make sure you have a complete bill of materials data

Check that there is enough complete data in the bill of materials report. After creating the Bill of Materials report, double-check the incomplete device, supplier, or manufacturer information for all component entries.

4. According to the component label to sort

To help sort and view bill of materials, make sure component numbers are consecutively numbered.

5. Checking the extra gate

In general, all redundant gate inputs should have signal connections to prevent the inputs from floating. Make sure you check all the redundant or missing gates, and all the unconnected inputs are fully connected. In some cases, the entire system will not work properly if the input is in a floating state. Take the dual op amps often used in the design. If only one of the op amps is used in a two-op amp IC, it is recommended to either use the other op amp either by grounding the unused op amp input and placing a suitable unity gain (or other gain ) Feedback network to ensure that the entire component is working properly.

In some cases, ICs with floating pins may not work properly within the specifications. Normally this IC will only meet the specifications if the IC or other gates in the same device are not operating in saturation - the input or output is close to or at the component rails. This is often not the case with simulations, as simulation models generally do not connect multiple parts of an IC together to model the effects of a suspended connection.

6. Considering the choice of component package

Throughout the schematic drawing phase, component packaging and pad pattern decisions that need to be made during the layout phase should be considered.

Here are some suggestions to consider when choosing components based on component packages.

● Remember that the package includes the electrical pad connections and mechanical dimensions (x, y, and z) of the component, that is, the outline of the component body and the pins that connect the PCB. 

When selecting components, consider any mounting or packaging restrictions that may exist on the top and bottom layers of the final PCB. Some components (such as polar capacitors) may have a high headroom limit and need to be considered during component selection. When you first start designing, you can draw a basic outline of the circuit board shape and then place a few large or key components (such as connectors) that you plan to use. This allows you to see the (unrouted) virtual view of the board intuitively and quickly and shows the relative positioning and component height of relatively accurate boards and components. This will help to ensure that the PCB can be properly placed in the overpack (plastic, chassis, frame, etc.) after assembly. Call the 3D Preview mode from the Tools menu to browse through the entire board.

● Pad pattern shows the actual pad or via shape of the soldered device on the PCB. 

These copper patterns on the PCB also contain some basic shape information. The size of the pad pattern needs to be correct to ensure proper soldering and to ensure proper mechanical and thermal integrity of the connected components. When designing a PCB layout, consider how the circuit board will be manufactured, or how the pads will be soldered if they are soldered by hand. Reflow soldering (melting of flux in controlled high temperature furnaces) can handle a wide range of surface mount devices (smd). Wave soldering is generally used to solder the back side of the board to hold through-hole devices, but it can also handle some of the surface-mount components placed on the back of the PCB. In general, when using this technique, the underlying surface-mount devices must be arranged in a particular orientation, and the pads may need to be modified to accommodate this type of bonding.

The choice of components can be changed throughout the design process. Early in the design process to determine which devices should be plated through hole (pth), which should use surface-mount technology (smt) will help the overall planning of the PCB. Factors to consider are device cost, availability, device area density, power consumption, and more. From a manufacturing point of view, surface-mount devices are generally cheaper than through-hole devices and are generally more amenable to use. For small and medium-scale prototype projects, the best choice for larger surface mount devices or through-hole devices, not only hand-welding convenience, but also help to debug and debug better connection pads and signals.

● If there is no ready-made package in the database, it is common to create a custom package in the tool.


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