A NEW METHOD OF PRODUCING SOLDER SPHERES FOR CHIP SCALE PACKAGES AND WAFER BUMPING UTILIZING METAL JET TECHNOLOGY
Author: Richard Godin Company: MPM Corporation Date Published: 4/28/1997
Surface Mount International
Abstract: There are many methods used today to apply solder to wafers, ceramics, laminate and flex circuit boards and other substrates. Some of these methods include sputtering, evaporation and plating. All of these methods have concerns: the vacuum processes are slow and require expensive equipment, plating requires the handling and disposal of hazardous chemicals. This article describes a new method of depositing very fine droplets of solder at speeds equal to or faster than plating. The new method is called Metal Jet Technology. There are several different technologies available in a broad category generally referred to as solder jetting. This paper will introduce two types: the Continuous Stream Metal Jet and the Drop-On- Demand Metal Jet. The Continuous Stream Metal Jet system works by applying a back pressure to a reservoir of molten solder creating a constant stream. The stream is perturbed with a low energy, constant acoustic vibration, breaking the stream into uniform drops at high rates. The drops are selectively charged and deflected to the substrate at high rates of speed. The Drop-On-Demand Metal Jet system applies a low frequency, high-energy mechanical pulse to an annular PZT, which surrounds a capillary tube and squeezes out a drop. This technology is being initially directed to bumping silicon wafers for flip chip applications, Advantages of either method is that they are CAD data driven systems which do not require hard tooling such as masks or stencils and the associated cost to purchase, cost to store, time to acquire and time to change those tools. Metal Jet Technology will provide the industry with a technique to address, in a cost-effective manner, the continuing pressures for miniaturization and higher performance. This technology will enable new packaging designs and is suitable for a variety of applications including direct chip attach site preparation, 3-D substrates, fine line interconnect, substrate via fill, optoelectronics and many others.