Vias should be located within the footprint pads if possible.
Some components may require a fanout as shown in Figure 4-9, when routed on a
grid size different than the package pitch. Fanouts on connector pads should
be avoided where possible since via fanouts may lead to producibility problems
when the overglaze is printed on these areas. These vias tend to cause the
dielectric covering them to crack if the vias have not been staggered on the
Leadless chip carrier footprint patterns on the MIB should
match the pad patterns on the device and should extend at least 0.015 ± 0.005 inch
beyond the maximum carrier size to allow for good solder fillets.
Recommended discrete component footprint pattern dimensions are
shown in Figure 4-10, which also illustrates one way to identify polarized
capacitors on the MIB. Any polarized devices should be identified with
distinguishing marks on the MIB for ease of assembly and inspection. Connector
footprints should also allow for good solder fillets. Figure 4-11 shows
recommended dimensions for a connector footprint pattern on the
For other surface-mounted devices such as flatpacks or leaded
chip carriers, when possible, the minimum width of the footprint land should
be at least the maximum width of the lead plus the tolerance between the leads
plus 0.010 inch. The land length should be such that if the package was placed
off-center on the footprint, the terminal pad would still be under the lead
(see Figure 4-12 ).
To facilitate assembly and inspection, LCC identifiers may be
part of the footprint. These can either be an out-line of the package as shown
in Figure 4-13 or pin #1 indicators on the MIB located outside the LCC
footprint boundaries. There should also be connector pin identifiers located
at least every 10 pins for ease of assembly, inspection, rework, and test.
These could be 0.010-inch extensions of the terminal pads. If there is room,
the board may have component reference designations and pin number identifiers
screened on last using a colored dielectric. This aids in assembly, rework,
inspection, and test.