Package Mounting Methods
Mounting density and package spacing
Since the main purpose for surface mounting is to achieve high-density mounting, fine patterns are also desired in
designing the printed circuit board. However, if the package spacing is too tight, incidences of solder bridging will of
course increase. Considering the three factors of the positioning accuracy of the mounting equipment, dimensional
variations in the printed circuit boards, and the external dimensions of the packages, using a minimum spacing dimension
of at least 0.3 mm is safer. (Figure 3)
0.3 mm (Note)
0.3 mm
0.3 mm
0.3 mm
Note: Land dimension spacing is greater than 0.3 mm
Direction of printed circuit board flow
Soldering faults are likely to occur.
Bad example
Figure 3 Minimum spacing dimensions between packages
Solder resist region
One point in soldering semiconductor devices is that the amount of solder on both sides be uniform. If there is excessive
solder on one side, there will be differences in the hardening time, resulting in stress toward the side with more solder. It is
necessary to use solder resist to separate the solder and keep the solder amounts on uniform when attaching semiconductor
devices or when semiconductor devices and lead-equipped components use the same land.
Layout of semiconductor devices
Faults may occur due to how the semiconductor devices are laid out. In SOP type flow soldering, in order to avoid
insufficient solder wetting, it is better to arrange the leads so that they are parallel to the solder flow (Figure 4). When
laying out semiconductor devices near easily bent sections of the printed circuit boards or separation grooves, the devices
should be laid out so that the received stress is uniform for both poles; in other words, the effects of stress are reduced
when the component poles are arranged perpendicular to the separation grooves or bending line.
Component layout A
Good example
Figure 4 Semiconductor device layout
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