Raya Mertens

Optimization of Scan Strategies in Selective Laser Melting of Aluminum Parts With Downfacing Areas

Selective laser melting (SLM) is an additive manufacturing technique in which metalproducts are manufactured in a layer-by-layer manner. One of the main advantages ofSLM is the large geometrical design freedom. Because of the layered build, parts withinner cavities can be produced. However, complex structures, such as downfacing areas,influence the process behavior significantly. The downfacing areas can be either horizon-tal or inclined structures. The first part of this work describes the process parameter opti-mization for noncomplex, upfacing structures to obtain relative densities above 99%.Inthe second part of this research, parameters are optimized for downfacing areas, bothhorizontal and inclined. The experimental results are compared to simulations of a ther-mal model, which calculates the melt pool dimensions based on the material properties(such as thermal conductivity) and process parameters (such as laser power and scanspeed). The simulations show a great similarity between the thermal model and the actualprocess. [DOI: 10.1115/1.4028620]Keywords: SLM, AlSi10Mg, downfacing structures

Investigation of the reliability of Cu and Co UBM layers in thermal-cycling tests

Despite the approaching ban on Pb in electronics, possibilities for replacing small pitch SnPb bumps are still limited. Electroplating, which is the most important process for small pitch bumping, complicates the alloy formation. In this paper, pure Sn bumps are investigated on their reliability behavior during thermal-cycling tests. Both electroplated Cu and Co are tested as UBM material. A Cu-SnPb sample is used as reference. The system lifetime of this reference sample could not be achieved with pure Sn. However, it is believed that by modifying some process conditions, the CoSn lifetime could be improved.

A Modified Electromigration Test Structure for Flip Chip Interconnections

Due to decreasing dimensions, electromigration becomes a major concern for flip chip joint reliability. A novel test structure for in-situ monitoring of electromigration in a flip chip connection is proposed. With this structure, small resistance changes at the cathodic and anodic sides can be mounted separately. This allows studying the asymmetric behavior of solder joints under electromigration conditions. The design of the new test structure is described and compared to the traditional measurement method. As a first test case, a Cu-Sn-Cu flip chip joint, stressed with a current of 6000Amp/cm2 at 150degC, is studied. First tests clearly indicate diverging resistance values when comparing the cathodic and anodic side of the flip chip bumps. Microstructural analysis shows extensive Cu-migration from cathode to anode