The requirements of SMT processing technology for component layout design
The layout of components should be designed according to the production equipment and process characteristics of smt patch processing. Different processes, such as smt patch reflow soldering and wave soldering, have different component layouts: when double-sided reflow soldering, there are also different requirements for the layout of the main surface and the auxiliary surface, and so on.
(1) The distribution of components on the PCB should be as uniform as possible.
(2) Similar components should be arranged in the same direction as much as possible, and the characteristic directions should be consistent to facilitate mounting, welding and testing.
(3) A certain maintenance gap should be left around the large components, and the size of the heater head of the SMD rework equipment can be operated.
(4) The heating element should be as far away as possible from other components, generally placed in the corners and in a ventilated position in the chassis.
(5) Keep temperature-sensitive components away from heating components.
(6) The layout of components and parts that need to be adjusted or frequently replaced, such as potentiometers, adjustable inductance coils, variable capacitors, micro switches, fuses, buttons, plugs, etc., should be considered for the overall structure requirements , Placed in a position that is easy to adjust and replace.
(7) Fixing holes should be provided near the terminals, plug-in parts, the center of long series of terminals and the parts that are often subjected to force. There should be corresponding space around the fixing holes to prevent deformation due to thermal expansion and warping during wave soldering. From the phenomenon.
(8) For some parts (such as transformers, electrolytic capacitors, piezoresistors, bridge stacks, radiators, etc.) that require secondary processing due to large volume (area) tolerances and low precision, the distance between them and other components is in the original Add a certain amount of affluence on the basis of the setting.
(9) Do not place valuable components on the corners, sides of the PCB, or near connectors, mounting holes, slots, cutting, gaps and corners of the jigsaw. These locations are the high stress areas of the printed board and are easy to Cause cracking or cracking of solder joints and components in SMT chip processing.
(10) The layout of components should meet the process requirements and spacing requirements of smt processing, reflow soldering and wave soldering.
① When single-sided mixed mounting, smt patch mounting and plug-in components should be placed on side A.
② When using double-sided reflow soldering, it is required that the FPCB design should place large components on the main (A) side and small components on the axis (B) side. The design of components placed on the shaft (B) surface should follow the following principles. The positioning hole of the printed board and the position occupied by the fixing bracket should be reserved.
(12) When the PCB area is too large, in order to prevent the PCB from bending when going through the soldering furnace, a 5-10mm wide blank should be left in the middle of the PCB without placing components, which is used to add a layer to prevent the PCB from bending when going through the furnace. Or support.
(13) When the mass of the axial component exceeds 5g and there is a high vibration requirement, or the mass of the component exceeds 15g with general requirements, it should be rounded with a bracket and then welded. There are two fixing methods: one is to firmly clamp on the board with a removable fixing clip; the other is to fix it on the board with adhesive glue. Those components that are large, heavy, and generate a lot of heat should not be mounted on the printed circuit board, but should be mounted on the chassis bottom plate of the complete machine.