Heraeus at CIPS 2018

Visit Heraeus at CIPS 2018 and find out more about our materials and material solutions

March 20-22, 2018
Stuttgart, Germany

Come and meet our experts during the exhibition, and find out how we can assist you in optimizing your process for better results.

Visit our expert presentations at CIPS

Pressure less sintering of large dies by infrared radiation

Wolfgang Schmitt speaks at CIPS 2018
Wolfgang Schmitt

Thursday, March 20, 2018 - 19:00 – 22:00
2nd lecture hall, Reithalle
Wolfgang Schmitt, Project Leader Paste Development at Heraeus Electronics

The total pressureless sintering process is a function of the die size. The necessary sintering process time increases with increasing the die size.

For conventional pressureless sintering in a convection oven, chips with a size of 16 mm² need approximately 4 hours process time. The long process time is one of the reasons that pressureless sintering process is not a favour sintering process.

Sintering with IR radiation is an alternative process that enables pressureless sintering performed in significantly shorter times. The influence of the chip sizes on the process time of IR sintering is considerably less than conventional pressureless sintering.

In this study, we observed that good sintered joint with no voids and drying channels were obtained for dies with a size of 56 mm² by IR sintering with a total process time of less than 2 hours. Die shear strength of above 15 MPa and a die shear failure mode of cohesive break in the sintered layer were obtained.

Authors: Wolfgang Schmitt, Ly May Chew, Robert Miller

Silver sinter paste optimized for pressure sintering under air atmosphere on precious and non-precious metal surfaces with high reliable sintered joints

Ly May Chew
Ly May Chew

Wednesday, 21 March 2018 - 08:50 – 09:10
Ly May Chew, Project Leader Paste Development at Heraeus Electronics

In this study, we observed the average initial die shear strength for Ag metallized substrate is higher than that for Au metallized and bare Cu substrates.

This observation points to the self-diffusion of Ag is faster than the interdiffusion between Ag and Au as well as between Ag and Cu. After 1000 h storage at 250 °C, cohesive break in the Cu layer was observed for Ag metallized and bare Cu substrates. In contrast, cohesive break in the sintered layer was observed for Au metallized substrate indicating that Au metallized layer acts as a barrier to prevent Cu from the substrate from diffusion into silver sintered layer. The die shear strength increased considerable after temperature cycling test and high temperature storage is believed due to the sintering process is not yet completed under the mild sintering process conditions we used in this study and consequently Ag, Au and Cu continued to diffused during temperature cycling test and high temperature storage.

It is likely that the sintering process is completed after a certain time of storage at 250 °C as we observed the average die shear strength remained relatively constant after 250 h storage. With a properly formulated sinter paste we can produce highly reliable sintered joints even on bare Cu surface.

Authors: Ly May Chew, Wolfgang Schmitt, Jens Nachreiner, Stefan Gunst