Fumio Kuriyama

Processing, properties, and reliability of electroplated lead-free solder bumps

Eutectic tin-silver (Sn-Ag), tin-copper (Sn-Cu), and tin-silver-copper (Sn-Ag-Cu) solder alloys are potential lead-free materials for low-temperature processing of solder bumps on wafers. But, before they can be adopted to replace the existing lead-free materials, processes have to be developed to provide controls over composition, height and shape uniformity, and defect formation, such as micro-voids, which are detrimental to bump reliability. Over the last six years, we have developed an electroplating technology using a dip-plating machine for processing the three types of eutectic lead-free solder bumps on silicon wafer. Our process is suitable for mass production with well-controlled bump geometry and composition, and uniformity within 10% over the entire wafer. In this paper, we will describe our process and present our results on the bump properties, such as composition, melting point, and microstructure of the bumps.

Process development of electroplate bumping for ULSI flip chip technology

For flip-chip packaging applications, a fine pitch bump process on LSI wafers is required due to increased chip circuit density, operating speed, and performance. Plating process is suitable for making the fine pitch bumps with high-speed deposition and high reliability. At the same time, lead-free processes, for electronic devices and components, are required to address environmental concerns. Also, high-speed bumping processes have to be developed for mass production, low cost, small footprint, and high throughput. Ebara has developed electroplating technologies for eutectic Sn-Pb solder, high lead solder, lead-free solder, and copper stud bumps on silicon wafers with higher deposition rates. The bumps were fabricated as column or mushroom type using resist plating masks, such as negative, positive spin-on, and dry film photo resists. The results show that Ebaras processes are suitable for mass production, with well-controlled bump geometry.

Electroplating copper filling for 3D packaging

Electroplating technology for via filling with copper for three-dimensional packaging is one of the strong candidates. The Cu electroplating technology for perfect via filling is discussed in this paper. A plating solution was prepared, in which plating deposition potential was found to be influential on its solution flow rate. The characteristics of organic additives in the plating solution were electrochemically measured with a rotary electrode so as to evaluate the influence of the solution flow and agitation on the organic additive functions. Optimization of organic additive concentrations and ratios in the plating solution was tried in order to establish the bottom-up growth in electroplating for perfect via filling. The selected plating solutions were applied to a dip-type plating system and evaluated by using the paddle agitation of the plating system. The combination of the plating system and plating solution showed the perfect filling of the high-aspect ratio via on a 300mm wafer.

Composition control for lead-free alloy electroplating on flip chip bumping

In lead-free alloy electroplating for Sn-Ag, Sn-Cu or Sn-Ag-Cu solder bumping, composition control is an important subject since the composition ratio is influential to the alloy structures and properties of the solders. The general assumption is that its very difficult to control the compositions of plated lead-free alloys in plating production lines because the composition ratio of the alloy element Ag or Cu is small and sensitive to the plating conditions in Sn base eutectic alloys. Also, when comparing with Sn-Pb solder, the larger electric potential difference between the components of lead-free alloys will make the composition ratio of plated alloys unstable in electroplating. Good bump height uniformity is not the only requirement for the integration process. It is also important to attain well-controlled compositional uniformity of lead-free solder. Therefore, it is important to control the electric potential distribution, metal ion concentrations, and their concentration ratios in the plating solution near the plating surface. In bump plating production lines, there are also other factors influencing the plated solder compositions including plating rate, plating solution flow, anode, and substrate pattern conditions. This paper describes our study of the factors affecting the control of the compositions in the lead-free alloy plating processes. The composition control of lead-free solder bumping has been primarily experienced on 300mm wafers for flip chip or wafer level packaging. The results of this study show that an advanced electroplating process can be successfully applied to the fabrication of the lead-free solder bumps, and further, that it can be carried out with the present electroplating and reflow tools.