Size reduction of electronic components is an incessant quest
in the microelectronics industry. For example, the Ball Grid Array (BGA)
electronics packaging technology helps reduce the size of the electronic
components while maintaining or improving their performance. The main components
of the BGA technology are small solder balls, the connection elements between
the chip and the circuit module or between the module and the card. The
Uniform Droplet Spray (UDS) process is an efficient manufacturing process
for the production of uniform solder balls that can be used for BGA packaging.
This work aims at the control of the UDS process for the production of
solder balls for BGA applications. The first approach used was to reduce
the ball size variation by increasing the robustness of the process. At
this stage the ball size variation was reduced from 19% to 12.5% of the
mean ball diameter. Next a closed-loop system for mean ball size prediction
and control was designed, developed and incorporated into the UDS process.
The control system comprises two parts: the droplet size measurement system
and the ball size control system. The droplet size measurement is based
on digital image processing, which was developed according to the characteristics
of the UDS process. The measurement system is a precise and reliable method
to determine the ball size in situ. The development of the ball size control
system involved the definition of a feedback signal, the development of
a control algorithm, modeling, simulation, and the evaluation of the control
system. The control system showed to be effective to maintain the mean
ball size close to the target size. Now the UDS process is capable of accurately
determining and controlling the ball size distribution. Although this work
has focused on the production of large solder balls (700-800 mm), the measurement
and control system can be adapted to any size of balls produced by the
UDS process. However, such factors as image magnification, camera position
and resolution should be considered to assure reliable, accurate ball size
control.