1. The middle layer is the layer between the top and bottom layers of the PCB. How is the middle layer realized in the production process?
2. Essentially, multi-layer boards are created by pressing together multiple single-layer and double-layer boards, where the middle layer corresponds to the original top or bottom layers of these individual boards.
3. In the PCB production process, a copper film is first applied to both sides of a base material (usually a synthetic resin). The wire connections are then transferred to the board through processes such as photolithography (where wires, pads, and vias are coated to prevent corrosion during subsequent etching).
4. Chemical etching (using solutions like FeCl3 or H2O2) removes unprotected copper film, and the board undergoes further processes such as drilling and silk screen printing to complete the PCB.
5. Similarly, multi-layer PCBs are assembled by pressing together multiple completed layers. To minimize costs and via interference, multi-layer PCBs are often not much thicker than double-layer or single-layer boards.
6. This results in multi-layer PCBs having layers that are generally thinner and less mechanically strong than their double-layer or single-layer counterparts, leading to higher processing demands and, consequently, increased production costs.
1. However, due to the presence of the intermediate layer, wiring in multilayer boards becomes easier, which is the primary reason for choosing them. In practical applications, multilayer PCBs demand more meticulous manual wiring, requiring greater support from EDA software. Additionally, the intermediate layer enables power and signals to traverse different board layers, enhancing signal isolation and interference resistance. This also allows large-area copper connections for power and ground networks, effectively reducing line impedance and minimizing ground potential deviation from a common ground. Therefore, PCBs with a multilayer structure generally offer better anti-interference performance compared to standard double-layer or single-layer boards.
2. Creation of the Middle Layer
3. The Protel system provides a specialized tool for layer setting and management: the Layer Stack Manager. This tool assists designers in adding, modifying, and deleting working layers, as well as defining and adjusting layer attributes. To access this, select [Design]/[Layer Stack Manager…] to open the Layer Stack Manager property setting dialog box.
4. In this dialog box, you can set the following three options:
5. (1) Name: Defines the layer’s name.
6. (2) Copper Thickness: Sets the copper film thickness for this layer, with a default of 1.4 mil. Thicker copper films increase the current-carrying capacity of wires of the same width.
7. (3) Net Name: Specifies the network connected to this layer from the drop-down list. This option applies only to internal electrical layers; signal layers do not have this option. If an internal electrical layer has a single network, such as “+5V”, the network name can be specified here. If the layer requires multiple network areas, do not assign a network name.
8. Insulating materials between layers provide circuit board support or electrical isolation. Core and Prepreg are both insulating materials; however, Core includes copper films and wires on both sides, whereas Prepreg is solely used for interlayer isolation. Their property setting dialogs are identical. Double-click Core or Prepreg, or select the insulation material and click the Properties button to open the insulation layer property setting dialog box.
9. The thickness of the insulating layer affects interlayer withstand voltage and signal coupling, as discussed previously. The default value is generally used unless specific requirements dictate otherwise.
10. Besides “Core” and “Prepreg,” insulating layers are typically present on the top and bottom layers of the circuit board.
11. In the top and bottom insulation layer settings, there is a stacking mode selection drop-down list offering different modes: Layer Pairs, Internal Layer Pairs, and Build-up. As mentioned, multilayer boards are created by pressing multiple double-layer or single-layer boards. Different modes reflect different pressing methods, altering the placement of “Core” and “Prepreg.” For example, the Layer Pairs mode involves two double-layer boards sandwiching an insulating layer (Prepreg), while the Internal Layer Pairs mode has two single-layer boards sandwiching a double-layer board. The default Layer Pairs mode is commonly used.
12. On the right side of the Layer Stack Manager property setting dialog box, there are buttons for layer operations. Their functions are as follows:
13. (1) Add Layer: Adds an intermediate signal layer. For instance, to add a high-speed signal layer between GND and Power, select the GND layer first, then click the Add Layer button. A signal layer will be added beneath the GND layer, named MidLayer1, MidLayer2, and so on. Double-click the layer name or click the Properties button to configure layer properties.
14. (2) Add Plane: Adds an internal electrical layer. The process is similar to adding an intermediate signal layer: select the location for the new internal electrical layer and click the button to add it below the specified layer. Default names are Internal Plane1, Internal Plane2, etc. Double-click the layer name or click Properties to set layer properties.
15. (3) Delete: Removes a layer. While the top and bottom layers cannot be deleted, other signal layers and internal electric layers can be removed, except for routed middle signal layers and subdivided internal electric layers. Select the layer to delete, click the button, and confirm by clicking Yes in the dialog box.
16. (4) Move Up: Moves the selected layer up by one position. The layer will move up without surpassing the top layer.
17. (5) Move Down: Moves the selected layer down by one position. Similarly, the layer will move down without going below the bottom layer.
18. (6) Properties: Opens the layer attribute setting dialog box for the selected layer.
19. After configuring the Layer Stack Manager, click OK to exit and proceed with PCB editing. To display the middle layer in the PCB editing interface, set its visibility by selecting [Design]/[Options…] and checking the internal electrical layer option under Internal planes.
20. Once settings are complete, the layers will be visible in the PCB editing environment. Use the mouse to click on layer labels to switch between different layers for operation. If the default colors are not preferred, customize them by selecting the Colors option under [Tools]/[Preferences…]. Further details on this are covered in Chapter 8 for reference.
2. Essentially, multi-layer boards are created by pressing together multiple single-layer and double-layer boards, where the middle layer corresponds to the original top or bottom layers of these individual boards.
3. In the PCB production process, a copper film is first applied to both sides of a base material (usually a synthetic resin). The wire connections are then transferred to the board through processes such as photolithography (where wires, pads, and vias are coated to prevent corrosion during subsequent etching).
4. Chemical etching (using solutions like FeCl3 or H2O2) removes unprotected copper film, and the board undergoes further processes such as drilling and silk screen printing to complete the PCB.
5. Similarly, multi-layer PCBs are assembled by pressing together multiple completed layers. To minimize costs and via interference, multi-layer PCBs are often not much thicker than double-layer or single-layer boards.
6. This results in multi-layer PCBs having layers that are generally thinner and less mechanically strong than their double-layer or single-layer counterparts, leading to higher processing demands and, consequently, increased production costs.
1. However, due to the presence of the intermediate layer, wiring in multilayer boards becomes easier, which is the primary reason for choosing them. In practical applications, multilayer PCBs demand more meticulous manual wiring, requiring greater support from EDA software. Additionally, the intermediate layer enables power and signals to traverse different board layers, enhancing signal isolation and interference resistance. This also allows large-area copper connections for power and ground networks, effectively reducing line impedance and minimizing ground potential deviation from a common ground. Therefore, PCBs with a multilayer structure generally offer better anti-interference performance compared to standard double-layer or single-layer boards.
2. Creation of the Middle Layer
3. The Protel system provides a specialized tool for layer setting and management: the Layer Stack Manager. This tool assists designers in adding, modifying, and deleting working layers, as well as defining and adjusting layer attributes. To access this, select [Design]/[Layer Stack Manager…] to open the Layer Stack Manager property setting dialog box.
4. In this dialog box, you can set the following three options:
5. (1) Name: Defines the layer’s name.
6. (2) Copper Thickness: Sets the copper film thickness for this layer, with a default of 1.4 mil. Thicker copper films increase the current-carrying capacity of wires of the same width.
7. (3) Net Name: Specifies the network connected to this layer from the drop-down list. This option applies only to internal electrical layers; signal layers do not have this option. If an internal electrical layer has a single network, such as “+5V”, the network name can be specified here. If the layer requires multiple network areas, do not assign a network name.
8. Insulating materials between layers provide circuit board support or electrical isolation. Core and Prepreg are both insulating materials; however, Core includes copper films and wires on both sides, whereas Prepreg is solely used for interlayer isolation. Their property setting dialogs are identical. Double-click Core or Prepreg, or select the insulation material and click the Properties button to open the insulation layer property setting dialog box.
9. The thickness of the insulating layer affects interlayer withstand voltage and signal coupling, as discussed previously. The default value is generally used unless specific requirements dictate otherwise.
10. Besides “Core” and “Prepreg,” insulating layers are typically present on the top and bottom layers of the circuit board.
11. In the top and bottom insulation layer settings, there is a stacking mode selection drop-down list offering different modes: Layer Pairs, Internal Layer Pairs, and Build-up. As mentioned, multilayer boards are created by pressing multiple double-layer or single-layer boards. Different modes reflect different pressing methods, altering the placement of “Core” and “Prepreg.” For example, the Layer Pairs mode involves two double-layer boards sandwiching an insulating layer (Prepreg), while the Internal Layer Pairs mode has two single-layer boards sandwiching a double-layer board. The default Layer Pairs mode is commonly used.
12. On the right side of the Layer Stack Manager property setting dialog box, there are buttons for layer operations. Their functions are as follows:
13. (1) Add Layer: Adds an intermediate signal layer. For instance, to add a high-speed signal layer between GND and Power, select the GND layer first, then click the Add Layer button. A signal layer will be added beneath the GND layer, named MidLayer1, MidLayer2, and so on. Double-click the layer name or click the Properties button to configure layer properties.
14. (2) Add Plane: Adds an internal electrical layer. The process is similar to adding an intermediate signal layer: select the location for the new internal electrical layer and click the button to add it below the specified layer. Default names are Internal Plane1, Internal Plane2, etc. Double-click the layer name or click Properties to set layer properties.
15. (3) Delete: Removes a layer. While the top and bottom layers cannot be deleted, other signal layers and internal electric layers can be removed, except for routed middle signal layers and subdivided internal electric layers. Select the layer to delete, click the button, and confirm by clicking Yes in the dialog box.
16. (4) Move Up: Moves the selected layer up by one position. The layer will move up without surpassing the top layer.
17. (5) Move Down: Moves the selected layer down by one position. Similarly, the layer will move down without going below the bottom layer.
18. (6) Properties: Opens the layer attribute setting dialog box for the selected layer.
19. After configuring the Layer Stack Manager, click OK to exit and proceed with PCB editing. To display the middle layer in the PCB editing interface, set its visibility by selecting [Design]/[Options…] and checking the internal electrical layer option under Internal planes.
20. Once settings are complete, the layers will be visible in the PCB editing environment. Use the mouse to click on layer labels to switch between different layers for operation. If the default colors are not preferred, customize them by selecting the Colors option under [Tools]/[Preferences…]. Further details on this are covered in Chapter 8 for reference.
