Design for SMD pads
Standard Package Pad Design
SMD Pad design follows relevant standards，such as IPC782 standard; SMD on the reflow surface, the pad of bigger components
(such as transistors, sockets, etc.) should be appropriately increased, such as the SOT23 pads can be lengthened by 0.8-1mm. This
will avoids the missing solder due to the 'shadow effect' of the component.
The pads size is determined according to the size of the component. The width of the pad is equal to or greater than the width of
the component leads, the soldering effect will be the best.
For the through hole components, in order to ensure the best soldering effect, the gap between the pins and the apertures are
advantageous for insertion, and a smaller capillary is required to achieve a good capillary effect, so a balance needs to be struck
The shadow effect
Avoid using a single large pad between two interconnected SMDs, because the solder on the large pad will pull the two
components in the middle. The correct way is to separate the pads of the two components. Connect thinner wires between
the two pads. If the wires are required to pass a strong current, several wires can be connected in parallel.
There should be no through holes on or near the pads of the SMD. Otherwise, during solder reflow, the solder on the pads
will flow away along the vias, which will result in solder joints, less tin, and may flow to the board. The other side will cause a
For IC pads with a large number of pins, it is necessary to expand the copper of the edge pads to increase the attractive force,
so that the components will return to the middle during reflow soldering.
In order to prevent the solder from overflowing from the through hole to the upper plate during reflow soldering, the part is
short-circuited to the ground or short-circuited between the parts. When designing the multi-layer board, attention should be paid
to the components of the metal case, and the case and the printed board are in contact with the printed board. The other side of
the through hole should not be opened on the solder mask layer. Be sure to cover it with solder mask or screen printing oil (for
example, a crystal of two feet and an LED of three feet).