- Through-hole components with polarity or direction requirements should maintain a consistent alignment throughout the layout and should be arranged as neat as possible. For SMD devices, if they cannot be placed in the same direction, they should be consistent in both X and Y directions for example for tantalum capacitors.
- If the component needs to be glued, ensure the component has at least 3mm space.
- For PCBs which need have heatsinks, the location and orientation of the heatsink should be considered. There must be sufficient space to ensure that the heatsink does not touch other components. Ensure that a minimum distance of 0.5mm is maintained.
- The distance between the devices must satisfy the required space for normal operation, for example, a memory card
- Metal parts with different properties or devices with metallic cases must not touch each other. A minimum distance of 1.0mm should be maintained between components.
- It is recommended that fine pitch devices be placed on the same side of the PCB and larger devices (such as inductors) be arranged on the top side.
- Polarized components should be aligned such that all the positive poles are on one side of the board and negative poles on the other where possible. Avoid positioning taller components next to shorter ones, which may hinder inspection. A viewing angle of no less than 45 degrees must be maintained throughout the layout to aid manual solder joint inspection.
- In general, surface array devices should not be placed on the bottom side of the board. In the event there is, other surface array devices should not be placed on the top side, in a region including the outline of the surface array device extending 8.00mm outwards, see Figure 17; In the event there is, the same region on the top layer, with an additional 8mm boarder about this region, must not contain surface array devices.
- All SMD components shall be smaller than 50mm on at least one side.
- It is not recommended for two surface-mount gullwing pin devices to overlap, for example, SOP packages as shown in Figure 18.
- In the event that solder pads are shared between two SMD components, the packages must be the same, see Figure 19.
- Through-hole devices and SMD components are allowed to overlap when it can be confirmed that the SMD pad and the solder paste printed thereon has no effect on the soldering of the through-hole device. See Figure 20.
- The required distance between SMD components is
- For PCBs requiring solder reflow, SMT device spacing varies according to the table 1.
|(Units in mm)||0402 ~ 0805||1206 ~ 1810||STC3528 ~ 7343||SOT / SOP||SOJ / PLCC||QFP||BGA|
|0402 ~ 0805||0.40||0.55||0.70||0.65||0.70||0.45||5.00(3.00)|
|1206 ~ 1810||0.45||0.65||0.50||0.60||0.45||5.00(3.00)|
|STC3528 ~ 7343||0.50||0.55||0.60||0.45||5.00(3.00)|
|SOT / SOP||0.45||0.50||0.45||5.00|
|SOJ / PLCC||0.30||0.45||5.00|
- The distance between fine pitch devices and the board edge must be greater than 10mm so as to not adversely affect printing quality.
|Component Type||Pitch 1.27mm’s Gullwing Pin (e.g. SOP, QFP) and Surface Array Components||0603 Size and Greater SMD Chip Components and Other Footprints|
|Minimum Spacing, D||10mm||5mm|
- For PCB with non-transmission side larger than 300mm, heavier through-hole components should not be placed in the middle of the PCB. This will reduce the board deformation caused by the weight of the components during soldering.
- To facilitate plug-in sockets, the socket should be placed where convenient.
- The distance between through-hole components should be > 10mm.
- The distance between through-hole components and the transmission edge should be ≥ 10mm, and non-transmission edge should be ≥ 5mm.
- Wave soldering is suitable for the following SMD components:
- Chip resistors, capacitors, and inductors that have a package size greater or equal to 0603 and standoff value less than 0.15mm.
- SOP packages with pitch ≥ 1.27mm and Standoff value ≤15mm.
- SOT packages with pitch ≥ 27mm and visible pins.
- The long axis of SOP package components should be perpendicular to the direction of travel of the solder wave in the wave soldering process. SOP components also need extra pads at the end of the solder pad rows to act as ‘solder thieves,’ see Figure 23.
- The orientation of SOT-23 package components should be such that the pins point parallel to the direction of travel.
- General component spacing principles: In order to reduce shadow effect problems caused by wave soldering, certain distances must be maintained between components and individual pads.
- For components of the same type according to Table 3:
|Pad Spacing L (mm/mil)||Component Spacing B (mm/mil)|
|Footprint||Minimum Spacing||Recommended Spacing||Minimum Spacing||Recommended Spacing|
|Tantalum Capacitors 3216 and 3528||1.02/40||1.27/50||1.02/40||1.27/50|
|Tantalum Capacitors 6032 and 7343||1.27/50||1.52/60||2.03/80||2.54/100|
- For different component types, the solder pad edge spacing should be ≥ 1.0mm. Distance requirements are shown in Figure 26 and Table 4.
|Footprint (mm/mil)||0603 – 1810||SOT||SOP||Through-Holes||Vias||ICT Point||Solder Thief Pad Edge|
|0603 – 1810||1.27/50||1.52/60||2.54/100||1.27/50||0.6/24||0.6/24||2.54/100|
|Solder Thief Pad Edge||2.54/100||2.54/100||2.54/100||2.54/100||0.6/24||0.6/24||0.6/24|
- In addition to the special requirements relating to the specific structure of the device, through-hole components must be placed on the top layer.
- The spacing between adjacent components is shown in Figure 27.
- In order to facilitate manual soldering and maintenance/repair the conditions shown in Figure 28 must be satisfied.
- The optimum component pitch is ≥ 2.0mm, the distance between the solder pad edges must be at least 1.00mm as shown in Figure 29. In addition, the component bodies must not interfere with each other.
- For a long row of through hole component holes, the components should be positioned such that the row is parallel to the direction of travel of the solder wave. In special circumstances where the row of pads must be aligned perpendicular to the direction of travel, suitable adjustments should be made, such replacing the standard pads with elliptical pads. When the spacing between adjacent pad edges is 0.6mm-1.0mm, the implementation of oval pads or solder thieves is recommended.
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