PCB layout design for manufacturability
It meets the requirements of manufacturability, assembly and maintainability, facilitates inspection and repair during debugging, and can easily disassemble the device:
1) There should be no more than 2 directions of polar components. It is best to have unified directions and other requirements, as shown in Figure 1-1;
Figure 1-1 Polar components are placed in the same direction
2) The elbow/male and elbow/female crimp connectors must be on the same surface as the crimping part. No tall devices (larger than 3mm) shall be placed within 3mm around the crimping part. No welding parts shall be placed within 1.5mm around the crimping part. On the back, no components should be placed within 2.5mm from the pins of the crimping part, as shown in Figure 1-2.
Figure 1-2 No-go areas for bend/male and bend/female crimp connection device layout
3) No components should be placed 1mm around the crimping device of straight/male and straight/female crimping connectors. When a sheath needs to be installed on the back, no components should be placed 1mm around the crimping component. When no sheath is installed, there should be no components No components should be placed within 2.5mm of the pin, as shown in Figure 1-3.
Figure 1-3 Straight/male and straight/female crimp connector layout forbidden areas
1) For conventional post-soldered components (connectors), when laying out the components on the same layer, the spacing between the components and the connector must be 1.5mm or above. When the components are laid out on the back, the spacing between the components and the connector must be at least 3mm or above. Try not to place SMD devices within 3mm around plug-in components or board edge connectors to prevent stress from damaging the components when the connectors are plugged in or out, as shown in Figure 1-4.
Figure 1-4 Layout of unplugging and plugging components
5) BGA devices: The same-plane devices can be laid out 5mm away from the BGA device. When the space is crowded, the same-plane devices can also be laid out 3mm away, as shown in Figure 1-5.
6) The layout of the back of the power filter capacitor of the BGA device should be as close as possible to the corresponding power pin layout, and placed on the symmetrical center of the two adjacent pads of the BGA. (Some customers require: Do not cover the BGA pads to avoid making X The BGA pad cannot be illuminated during radiographic inspection). As shown in Figure 1-6.
Figure 1-5 BGA peripheral layout range, Figure 1-6 BGA back capacitor layout
7) Double-sided layout of BGA devices. Generally, BGA devices are not allowed to be placed on the back. When there are BGA devices on the back, the BGA devices cannot be placed within the 8mm projection range around the front BGA devices, as shown in Figure 1-7.
8) Double-sided layout devices, unless there are special requirements, place large devices and chips on the TOP layer, and place 0805, 0603, and 0402 resistor capacitor devices on the back, as shown in Figure 1-8.
Figure 1-7 BGA back area layout, Figure 1-8 top and bottom device layout
9) Small components (resistors, capacitors and chip devices) cannot be surrounded by tall components. There must be enough space (at least 3mm on the left and right) to facilitate disassembly. As shown in Figure 1-9 and Figure 1-10, the layout principles of high and short components , tall devices are placed behind low devices and in the direction of least wind resistance to prevent air ducts from being blocked.
Figure 1-9 Device layout requirements
Figure 1-10 Layout of CHIP devices surrounded by tall devices
10) Metal shell devices, metal parts with different properties (such as heat sinks, shields) or metal shell devices cannot collide. Make sure they do not collide with other devices and ensure that the minimum distance of 1mm meets the installation space requirements, as shown in Figure 1 -11 shown.
11) The recommended device layout directions are 0 degrees and 90 degrees. Unless there are special circumstances, please do not place them at 45 degrees, as shown in Figure 1-12.
Figure 1-11 The distance between the device and the shielding cover is 1mm, Figure 1-12 The device placement angle
12) There should be operable space between devices (such as memory sticks inserted at an angle) to facilitate operations such as plugging and unplugging, as shown in Figure 1-13.
13) Layout of PCB with windows For PCBs with window requirements, ensure that there is at least 2mm distance between the components and the window during layout, as shown in Figure 1-14.
Figure 1-13 Spacing operation space reservation between devices and devices, Figure 1-14 Layout spacing requirements between devices and window openings
14) If there are no SMT components within 5mm of the board edge, you do not need to add a 5mm transmission edge to save board materials. However, if there is, it is directly recommended that the customer add a process auxiliary edge; generally the long edge is used as the transmission edge, and when the ratio of the short side to the long side is greater than 80% , the short side can also be used as the transmission side. When the device layout cannot meet the transmission edge width requirements (the board edge is 5mm prohibited), the method of adding auxiliary edges should be used. General requirements for adding the width of the auxiliary edge: the width of the auxiliary edge of the PCB without paneling is 5mm, and the minimum width of the auxiliary edge of the PCB that is panelized is 8mm. If you use the stamp hole imposition method, please pay attention to the stamp hole parameter settings.
15) When delivering, be sure to check the layout of the Mark points, whether the quantity is sufficient, and whether the distance from the edge of the board is more than 5mm, as shown in Figure 1-15.
Figure 1-15 Parameter settings for stamp hole imposition
The above is the sharing of technical articles on PCB design skills "PCB Layout Compliant with Manufacturability" compiled by Fanyi Circuit in this issue.
Review Editor: Tang Zihong
#PCB #layout #design #manufacturability
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