Suitable thicknesses of base metal and interlayer, and evolution of phases for Ag/Sn/Ag transient liquid-phase joints used for power die attachment

Both real Si insulated gate bipolar transistors (IGBT) with conventional Ni\Ag metallization and a dummy Si die with thickened Ni\Ag metallization have been bonded on Ag foils electroplated with 2.7 m and 6.8 m thick Sn as an interlayer at 250ºC for 0 min, 40 min and 640 min. From microstructure characterization of the resulting joints, suitable thicknesses are suggested for the Ag base metal and the Sn interlayer for Ag/Sn/Ag transient liquid phase (TLP) joints used in power die attachment, and the diffusivities of Ag and Sn in the Ag phase are extracted. In combination with the kinetic constants of Ag3Sn growth and diffusivities of Ag and Sn in Ag reported in the literature, the extracted diffusivities of Ag and Sn in Ag phase are also used to simulate and predict the diffusion-controlled growth and evolution of phases in the Ag/Sn/Ag TLP joints during an extended bonding process and in service

Additive manufacturing using 3D screen printing

Additive manufacturing is an interesting technique for the manufacture of intricate parts. This paper gives an introduction the 3D screen printing which might be well suited to make small scale metal antenna parts on a mass production basis

Direct typing - a new method for the production of cellular P/M parts

The screen printing process can be modified in order to yield 3-dimensional green parts of complex shape. To this end, a powder is mixed with suitable additives and printed layer-on-layer. This process, called "Direct Typing Process" (DTP), was developed and patented by the company Bauer-RaD and sucessfully demonstrated for silicon carbide and other ceramics. The new approach seems to be especiall y promising for making complex cellular P/M structures, i.e. micro fluidic devices or catalyst carriers, as well as mechanically optimised structural parts. In a joint effort with Fraunhofer IFAM Dresden, the suitability for the manufacture of metallic P/M parts was examined for stainless steel 316L

Mechanical properties of cellular solids produced from hollow stainless steel spheres

Mechanical properties of cellular hollow sphere structures are studied in this work. The material was fabricated by coating the metallic powder slurry on expanded polystyrol (EPS) spheres, drying, forming under compression, debinding, and final sintering of the spheres to each other. Longitudinal elastic wave velocities were measured using ultrasound phase spectroscopy while compression tests were carried out up to a homologous temperature of 0.6. Dependence of the relative Young's modulus on the relative density is similar to conventional open-cell foams. Compression stress-strain plots show the three stages of elastic deformation, plateau, and densification. With increasing temperature the overall level of the compressive stress-strain plots shifts to lower stresses. The hollow sphere solids show slightly better high temperature strength in comparison to the base metal. However, due to the considerable scatter in the experimental data points, this improvement seems to be insignificant. Structural observations on samples deformed to within the plateau region clearly show the heterogeneous progress of deformation

New opportunities in centrifugal powder compaction

Centrifugal sedimentation processes such as the high speed centrifugal compaction process (HCP) are known to produce green bodies with high packing density and very few defects resulting in high quality components. However the producible geometries as well as the freedom of possible gradient designs are limited. At Fraunhofer IFAM Dresden a new sedimentation process route was developed that uses a continuous suspension feed to overcome the limitations of a batchwise sedimentation. The process allows to produce homogenous sediments in terms of porosity as well as mean particle size over the height of the sediment. The green parts are strengthened by a binder infiltration step and can be machined in green state in order to achieve desired shapes with structure's dimensions down to 200 µm. Having a high green density of 68% and low organic content of <1 wt.% the sediments show good sintering properties and sinter without warpage or cracks

Bremsscheibe

The disk has an inner friction ring (2), an outer friction ring (3), and a wire structure element (1) arranged between the inner and outer rings. The structure element is connected with one of the rings in a firmly-bonded and/or form-fit manner. The element is designed as an open-cell three-dimensional wire structure, where porosity of the element is maintained between 70 and 95 percent. The element comprises metallic wires, where diameter of the wires lies in the range between 0.1 mm and 3 mm. Connection elements designed as rods or fins are formed in an inner side of the element. The wire structure element is formed as knitted fabric, woven fabric or meshwork

Slurry based additive manufacturing of aluminium alloys

Additive Manufacturing of metal parts based on binder-containing slurries allow for a great materials variety. With this approach it is basically possible to process all sinterable materials like copper or even use powder mixtures. Nevertheless, there are still a few restrictions in materials selection due to the used binder and the requirements of the sintering step. Aluminium alloys especially are difficult to process since the binder is usually removed thermally which can lead to unwanted contaminations, i. e. a high oxygen content. At Fraunhofer IFAM Dresden the debinding step was optimized to reach low oxygen contents for an AlSi1 alloy. The developed process step show an almost complete debinding with final oxygen levels down to 0.18 wt.% in the sintered material. The new binder-powder system is suitable for processing via 3D screen printing which opens up a pathway for the manufacturing of intricate parts for thermal management applications