Amplitude Modulated Droplet Formation in High Precision Solder Droplet Printing

There are many methods used at present to apply solder to wafers, ceramics, laminate and flex circuit boards, and other substrates. Among these, high-precision solder droplet printing technology, which is noncontact, data driven, flexible and environmentally friendly, is a key enabling technology. This technology selectively deposits solder droplets only where required, and therefore needs no mask or secondary resist removal, uses materials more efficiently and creates less waste than other methods. Currently, continuous droplet formation from capillary streams is mainly achieved by application of the well-known Rayleigh instability in which a sinusoidal disturbance is applied to the stream, resulting in evenly spaced and sized droplets. However, changing droplet configurations for various products or varying the size or depth of solder joints is difficult. Amplitude modulated disturbance is employed in this work to generate arbitrary solder stream configurations. The final configuration is mainly determined by several parameters: (1) the degree of modulation of the waveform; (2) the phase difference between the carrier and modulation signals; (3) the charging voltage; and (4) the frequency ratio between the carrier signal and the modulation signal. Many different patterns can be achieved with the proper combination of frequency ratio, phase difference, degree of modulation, and charging voltage. A simulation code was developed to simulate the merging process and determine the parameters needed to achieve certain droplet configuration