One of the electronic assembly markets that has
been emerging in recent years is the automation
equipment associated with odd form component
placement and final product assembly. As with
insertion mount and surface mount equipment,the
procurement process of odd form equipment
typically includes having the machine provider
guarantee certain performance levels and provide
evidence from a machine qualification process that
the machine being shipped is actually capable of
performing to specification. Due to both the slower
tact times and higher component prices in many
typical scenarios (relative to most surface mount
and insertion mount applications),the sample sizes
and test hours required to verify odd form
equipment to the high quality levels that the
electronic assembly industry has come to expect -
with defects measurable in parts per million (PPM)
units - can be quite burdensome. Having to insert
tens or hundreds of thousands of parts during
machine qualification can be quite costly and timeconsuming.
For example,a test involving the
insertions of 20,000 parts with only one defect
would yield a performance estimate of 50 PPM.
But a test with this many real odd form parts would
be very costly.
One alternative method to demonstrate odd form
machine accuracy has relied upon placing surface
mount slugs instead of inserting odd form parts.
Slugs (pieces of glass with the image of an SMT
part etched on it,such as those defined in IPC-
9850),are easily placed on a board with sticky tape
and measured with a coordinate measuring
machine (CMM) in order to obtain very precise
variables data. The benefit of such a variables
approach (as opposed to a go/ no go “attribute”
approach,where each insertion or placement is
only characterized as good or bad,rather than being
precisely measured) is that a very small sample size
of parts can be placed in a slug run to gain a PPM
estimate with a high degree of confidence.
The downside to the slug approach is that these
parts are dissimilar from odd form parts in that they
cannot be inserted into holes,and even if they
could,without adhesive they would move around
after insertion,making the variables data for each
part incorrect. So this difference in the nature of
board assembly (between surface mount and odd
form assembly),combined with the fact that odd
form assembly equipment users use a wide range of
odd-shaped parts that are handled quite differently than slugs,has led us to consider alternative
approaches to estimating PPM that could either
replace or supplement the slug approach.
In this paper,a method used internally by Universal
Instruments Corporation to qualify its Polaris
assembly equipment to 50 PPM or better will be
presented. The method is statistics-based,and
involves insertion rather than placement. Yet it still
gives results,PPM estimates,comparable to slug
runs. This method will be shown to be quite
efficient and,since it requires no operator once it is
started,it is even less labor-intensive than a series
of slug runs. And it does not require the use of
CMM,so it could easily be replicated at a
customer’s facility.
