Component changes and challenges
This is a question where the answer could be almost as long as
the original text, but the simplest way is to explain that:
- Before the advent of surface mount components, all components
were through-hole technology
- A through-hole means that you automatically have a ‘keep
out’ area around the hole, which is one of the factors limiting
packing density
- The lead pitch for through-hole components was almost always
0.1 inch or a multiple
- Having pins effectively on a 0.1 inch grid made life easier
both for the CAD programme and the test engineer
- The move to surface mount has meant that many components are
substantially smaller, and there is no commonality of pad design,
as there was in the days of the pin through 0.1 inch spaced hole
- Whilst standards exist for most package designs, based on the
evidence of Table 3 there will be substantial differences between
component outlines, which will make life difficult for the assembler
if not CAD
- Many of the earlier designs had expensive hermetic structures,
whereas more modern components are likely to have polymeric cases.
The component challenges identified relate to the smaller size
of components and the greater diversity. From the CAD vendor point
of view, there are many packages for which dimensional and pad information
need to be built into his/her library.
The increasing diversity of packaging is a topic to which we will
return in Unit 11 of Design for Product Build.
[ back to top ]