Analysis of the development of damage in copper vias in printed circuit boards by variation of the quality of the quality of the drill hole quality

• Applicant: Professor Dr.-Ing. Martin Schneider-Ramelow
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins ; Synthesis and Properties of Functional Materials
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 510901535

In microelectronic systems, polymer-based substrates reinforced with glass are used as wiring carriers for electronic components. Provided with copper plated-through holes (DuKo) between the Cu layers from the top to the bottom of the PCB, the circuit boards must reliably retain their functionality over long periods of time under ever higher thermomechanical alternating loads. To manufacture the DuKos in printed circuit boards, holes are drilled after curing of the base material. It has been shown that the wear and and the limited service life of the drills significantly influence the drill hole geometries and the roughness of the hole wall in the base material. If the yield limit of the electrochemically deposited Cu is exceeded in the DuKo, plastic deformations occur and microcracks can arise and grow (fatigue), which ultimately lead to electrical failure of the printed structure. The formation and growth of the cracks is decisively influenced by the drill hole geometries and hole wall roughness. The aim of this project is to clarify and quantify these influences. For this purpose, a test plan consisting of experiments and numerical simulation was conceived: Using nano-CT, the wall thickness and roughness distributions are correlated over the entire DuKo length to material characteristics that are decisive for the service life. This influence leads to a local increase in the plastic strain in the copper, which is examined by accompanying FEM analyzes. For early detection of the cracks, IR thermography and the new Intermodulation Distortion method (IMD) are used. The IMD method used here identifies early stages of crack development and, in combination with imaging methods (nano-CT, cross sectioning), creates a new and clearer picture of the early phases of crack formation and propagation. Geometric influence factors are recorded and the lifetime experiments are accompanied by adapted FE models. This will provide information on the origins and influence factors of the crack initiation, so that an improved understanding of the damage mechanism can be developed within the DuKo and thus a more detailed quantification of the process influences on the service life is made possible.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Wolfgang H. Müller