The electronic assembly of STG-PCBs
A)SMT-The layout of pcb components
a.When the print circuit board into the reflow soldering furnace of conveyorbelt,the axis of the components should be with the device drive direction isvertical, so that we can prevent the occurrence of the components on theboard in the welding process drift or monuments, "vertical" phenomenon.
b.Components are evenly distributed on the PCBA,especially to spread out the high power and avoid local overheating circuit is working on the PCBwhen stress, affect the reliability of solder joints.
c.It should be staggered the install location on both side of bulkydevice.Otherwise in the welding process it can influence welding effectbecause of the local thermal capacity increase.
d.In wave soldering surface it cannot be placed on four-pin devices, such asPLCC/QFP.
e.In the Surface Mount Technology assembly,the SMT components which isinstalled on the wave soldering,its long axis should be paralleled with thesolder wave in the direction of flow.So that we can reduce the solder bridgebetween the electrodes.
f. The big and small SMT components on the surface of the wave solderingcannot be arranged in a straight line.To stagger the position so that it can protect the welding with the solder wave of the "shadow" effect of virtual welding and leakage caused by the welding
B)SMT-the pads on the PCBs
a.SMT components are on the wave soldering,the larger components of the pads (such as transistors, sockets, etc) to be appropriate to increase,SOT23 pads plus long 0.8-1mm, so you can avoid the symbol "shadow effect" in arising from welding.
b.In the PCB fabrication and assembly,the Pad size is to be determined according to the dimensions of the components,the width of the pad should be equal to or slightly larger than the components of the electrodes width,welding work best.
c.Sometimes in the PCB Assembly, there are two components are connecte to each other,to avoid using a single big bonding pad, because pad on the solder would take two components to the middle, the right way is to separate the two components of the welding plate.Between two bonding pad with thinner wire connection, if it require larger conductor current through parallel on a wire, wire can be covered with green oil.
d.Welding SMT components on the plate or in the vicinity cannot have a through hole, otherwise,in the reflow process,after bonding pad on the solder to melt down the hole to drain away, creates a virtual welding, little tin, also could cause short circuit flow to the other side of the plate.