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CHIP PACKAGE
Planar parts such as electronic packages can be inspected with the Model 50C
in the vertical tilt position
(see Figure 1, Tilt Positions, Model 50C - Operation ).
In this orientation, a shorter focal length
lens can be used in the Optimet sensor. In the figure below, a 25 mm
lens was used instead of the usual 75 mm lens. Although the depth of
field is only a few millimeters, a planar part mounted horizontally on
the turntable fits within this narrow depth of field.
The part is a portion of an electronic package that connects a silicon chip
to a PC board without stressing the chip's connections by differential expansion
when the chip gets hot. A critical part of the package is an array of small
bumps called "nubbins" that keep the chip the proper distance from the PC
board. Shown below is a topology map of a 3 x 3 nubbin array. Note that
the vertical scale has been exaggerated to emphasize the nubbin shape; a nubbin
is only 0.1 mm (4 thou) high, but is .625 mm (25 thou) between centers.
Figure 1. Nubbin Array
The inspection task was to have the same machine find the height for each
nubbin in a large 8 x 8 array, but also have "detail" capability to check
the shape of a single nubbin. Below is a topology map of a single nubbin,
again with the vertical scale exaggerated. Points on the map are
accurate to a few microns at the higher resolution of the 25 mm lens.
Figure 2. Single Nubbin
COPLANARITY
Another planar part is the chip carrier package shown in the figure below. The
carrier has 360 leads around its periphery deployed in 120 "lead sets", each having
3 rows of leads. The figure shows one of four sides of the package having
30 lead sets. The inspection task is to check the leads for coplanarity:
do the tips of the leads lie in the same plane.
Figure 3. One side of Chip Package
Two lead sets that were sliced out of the figure above are shown magnified in
the image below. The Model 50C is in the vertical tilt position to
measure the lead sets from above. The thin red lines below show how each
lead of the set bends 90 degrees, penetrates the package rim and ends in the
interior of the package. The lead tips to be inspected are circled in
blue.
Figure 4. Datacloud of Two Lead Sets
The tips of several lead sets are shown in the topology map below.
As before each lead set consists of 3 adjacent leads. The color coding
on the vertical scale covers a range of just 0.1 mm (4 thou). Although
each tip is just 0.2 mm (8 thou) wide by 0.3 mm (12 thou) long, the topology of
each one can be clearly seen.
Figure 5. Lead Coplanarity
TUBULAR PARTS
When the Model 50C is changed to its horizontal tilt position (see Model
50C - Operation), it can accurately measure tubular parts. The Allen
head bit measuring 6.25 mm (.25") across flats was fixtured vertically and
rotated to scan each side of the part. Notice how much more crisp
the confocal optics datacloud is than one using laser triangulation on a part
of approximately the same length
(see Figure 2, Data Cloud, Example ).
Crisper dataclouds mean better dimensional resolution.
Figure 6. Allen Head Bit
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