Section 3rd create and set intermediate layers

The middle layer is the layer between the top and bottom layers of the PCB Board. For the structure, see Figure 11-1. You can refer to the annotations in the figure for understanding. How is the middle layer implemented in the production process? Simply put, a multi-layer board is formed by compressing multiple single and double layers. The middle layer is the top or bottom layer of the original single and double layers. In the process of making PCB, first we need to apply copper film on both sides of a base material (generally synthetic resin material, then, the wire connection relationship in the drawing is converted to the sheet of the printed board through optical painting and other techniques (the printed wire, welding pad, and the pass-through film in the drawing are protected, prevent the copper films of these parts from being corroded in the subsequent corrosion process), and then through the chemical corrosion method (with FeCl3 or hydrogen peroxide as the main component of the corrosion liquid) the copper film without film protection corrosion, and finally completed drilling, printing Silk Screen Layer and other post-processing work, such a PCB is basically completed. Similarly, multi-layer PCB is to press multiple layers into a circuit board by pressing the process, and in order to reduce costs and interference through holes, multi-layer PCB is usually no more thick than double or single-layer PCB, which makes the Board layers of multi-layer PCB usually have smaller thickness and lower mechanical strength for ordinary double and single-layer boards, this results in higher processing requirements. Therefore, the cost of multi-layer PCB is much more expensive than that of ordinary double and single layers.

However, due to the existence of the middle layer, multi-board cabling becomes easier, which is also the main purpose of Multi-board selection. However, in practical application, multilayer PCB Board puts forward higher requirements for manual wiring, so that designers need more help from EDA software; at the same time, the existence of the intermediate layer enables the power supply and signal to be transmitted in different board layers, which improves signal isolation and anti-interference performance, in addition, a large area of copper can be used to connect the power source and the local network, which can effectively reduce the line impedance and the potential offset caused by the joint grounding. Therefore, PCB with multi-board structure has better anti-interference performance than ordinary double-board and single-board.

11.3.1 create an intermediate layer

The Protel system provides a dedicated layer stack manager ). This tool can help designers add, modify, and delete work layers, and define and modify layer attributes. Select Design or layer stack manager ...] Command to bring up the layer stack manager attribute Setting Dialog Box shown in 11-2.

Shows a layer-4 PCB stack Manager interface. In addition to the top layer (toplayer) and bottom layer (bottomlayer), there are two internal power layers And Gnd. The positions of these layers are clearly displayed in the diagram. Double-click the layer name or click Properties to bring up the layer property Setting dialog box, as shown in Figure 11-3.

The dialog box contains three options.

(1) Name: Specifies the name of the layer.
(2) copper thickness: Specifies the copper film thickness of the layer. The default value is 1.4mil. The thicker the copper film, the larger the load capacity of the wire with the same width.
(3) Net Name: Specify the network connected to this layer in the drop-down list. This option can only be used to set the inner electrical layer. This option is not available for the signal layer. If the inner electric layer only has one network such as "+ 5 V", you can specify the network name here. However, if the inner electric layer needs to be divided into several different regions, do not specify the network name here.

There is also insulation material between the layers as the carrier of the circuit board or for electrical isolation. The core and prepreg are both insulating materials, but the core and double sides of the plate both have copper films and connections, and The prepreg is only used for interlayer isolation. The attribute Setting dialog box is the same. Double-click core or preg, or select insulation material and click Properties to bring up the insulation property Setting dialog box. As shown in Figure 11-4.

The thickness of the insulation layer is related to factors such as interlayer Withstand Voltage and signal coupling. The layers selection and superposition principles have been described in the previous section. If there are no special requirements, select the default value.

In addition to the core and preg insulation layers, the top and bottom layers of the circuit board usually have insulation layers. Click the selection box before top dielectric (top insulation layer) or bottom dielectric (bottom insulation layer) in the upper left corner of Figure 11-2 to check whether the insulation layer is displayed. click the button next to it to set the properties of the insulation layer.

There is a stack mode selection drop-down list under the options of the top and bottom layers, you can select different stack modes: layer pairs (in pairs), internal layer pairs (in pairs) and build-up (stacked ). As mentioned above, a multi-layer board is actually made up of multiple double or single-layer boards. If different modes are selected, different suppression methods are used in actual production, therefore, the locations of the "core" and "prepreg" shown in 11-5 are also different. For example, the layer pairing mode is that two double-layer panels have one insulation layer (Prepreg), and the inner electrical layer has two single-layer clips and one dual-layer panel. The default layer pairs mode is usually used.

In the layer stack manager attribute Setting Dialog Box shown in Figure 11-2, there is a column-layer operation button on the right. The functions of each button are as follows.

(1) Add layer: add an intermediate signal layer. For example, to add a high-speed signal layer between Gnd and power, select the Gnd layer first, as shown in 11-6. Click the add layer button to add a signal layer under the Gnd layer, as shown in 11-7. Its default name is midlayer1, midlayer2 ,?, And so on. Double-click the layer name or click Properties to set the layer properties.

(2) Add plane: add an inner electrical layer. The method for adding an intermediate signal layer is the same as that for adding an intermediate signal layer. Select the position of the inner electrical layer to be added, and click this button to add the inner electrical layer below the specified layer. The default name is internal plane1, internalplane2 ,?, And so on. Double-click the layer name or click Properties to set the layer properties.

(3) Delete: delete a layer. Except the top and bottom layers, other signal and inner electrical layers can be deleted, but the intermediate signal layer and the split inner electrical layer that have been cabled cannot be deleted. Select the layer to be deleted, and click this button. The dialog box shown in 11-8 is displayed. Click Yes to delete the layer.

(4) Move Up: Move a layer up. Select the layer to be moved up (either the signal layer or the inner electrical layer). Click this button to move the layer to the top layer, but it will not exceed the top layer.

(5) Move Down: move down a layer. Similar to the move up button, if you click this button, the layer moves down a layer but does not exceed the underlying layer.
(6) properties: Properties button. Click this button to bring up the layer attribute Settings dialog box similar to figure 11-3.

11.3.2 intermediate layer settings

After completing the settings of the layer stack manager, click OK to exit the layer stack manager and perform related operations on the PCB editing page. When operating on the middle layer, you must first set whether the middle layer is displayed on the PCB editing interface. Select [design]/[OPTIONS ...] Command, the option Setting Dialog Box shown in 11-9 is displayed. Check the inner electrical layer option under internal planes to display the inner electrical layer.

After completing the settings, you can see the displayed layers at the bottom of the PCB editing environment, as shown in 11-10. Click the Board layer label of the circuit board to switch between different layers for operation. If you are not familiar with the default color of the system, you can select [tools]/[preferences ...] The "Colors" option under the command defines the color of each layer. The related content is described in Chapter 8th for your reference.