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board, reducing the size of the PCA by one-third to one-half.
During 1991 and 1992, PCA's rarely had only SMT components
because some components were not available in the surface-mount
format.
The key feature of size for all components, both SMT and
through hole, is "lead pitch". Lead pitch is the center-to-
center distance between the adjacent leads that connect
components to the printed circuit board. For example, the lead
pitch of a through hole component may be 100 mils or one-tenth of
an inch. By comparison, the lead pitch of a comparable SMT
component is about 50 mils.
When lead pitch is reduced to 20 or 25 mils, the component
is a "fine pitch" component. Many Compaq U.S. PCA's had multiple
fine pitch devices on the same board that required significant
process engineering controls, thus increasing the complexity of
the manufacturing process. The manufacturing process was further
complicated when fine pitch devices were scattered throughout the
board, were placed near the edges of the board, or were placed on
the bottom side of the board.
SMT manufacturing is capital intensive and works best with
SMT placement equipment featuring "vision" technology. This
technology has the precise capability to place small SMT
components on the correct electronic connections on each printed
circuit board during the soldering process. Vision technology
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Last modified: May 25, 2011