Improving solder wettability of microbumps for 3D stacking

Leuven - Master projects/internships
More than two weeks ago

Preventing Cu oxidation and improving solder wetting during 3D stacking will result in good electrical connection and good reliability data for 3D stacked devices. The aim of this project is to look for thin layers which can improve the solder wetting without having negative impact on the performance of devices.

In microelectronics, Si chips are thinned and stacked on top of each other to obtain a 3D-stacked device with better performance (faster, more functionality and memory, etc.). To electrically contact the Si chips inside this stack, Cu pads/bumps at the top and bottom of subsequent chips are interconnected using solder bumps, i.e. micro-bumps. Oxidation of the Cu pads/bumps before or during bonding should be prevented, because it results in a poor electrical connection and IMC (intermetallic compound) formation. In addition, the solder should have an excellent wetting of Cu pad/bump such that good and reliable IMC is formed.

The aim of this master thesis project is to investigate which thin layers can improve the solder wetting without having negative impact on the performance of devices. These layers will be coated on the Cu pads/bumps.   

The student will do first a literature review to select possible metallic and organic layers for this application. Next, wettability study of the deposited layers will be carried out at the materials science facility of the KU Leuven.  3D stacking of chips containing the selected layers will be done by the student in the cleanroom of imec. The resulting devices will electrically be tested, and then SEM cross-section will be performed to study the IMC formation in the joint. This should provide in-depth information on the wetting behavior and applicability for bonding of the selected thin layers. The results will be presented to imec’s industrial partners during a workshop in April.

Type of project: Internship, Thesis, Combination of internship and thesis

Required degree: Master of Engineering Technology, Master of Science, Master of Engineering Science

Required background: Chemistry/Chemical Engineering, Electrotechnics/Electrical Engineering, Materials Engineering, Nanoscience & Nanotechnology, Physics

Supervising scientist(s): For further information or for application, please contact: Jaber Derakhshandeh (

Allowance only for students from a non-Belgian university

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