Establishing fracture properties of EMC-Copper interfaces in the visco-elastic temperature region

Abstract

An ongoing root cause of failure in microelectronic industry is interface delamination. In order to explore the risk of interface damage, FE simulations for the fabrication steps as well as for the testing conditions are generally made in the design stage. In order to be able to judge the risk for interface fracture, the critical fracture properties of the interfaces being applied should be available, for the occurring combinations of temperature and moisture preconditioning. As a consequence there is an urgent need to establish these critical interface fracture parameters. For brittle interfaces such as between epoxy molding compound (EMC) and metal (-oxide) substrates the critical energy release rate (or delamination toughness) can be considered as the suitable material parameter. This material parameter is strongly dependent on the temperature, the moisture content of the materials involved and on the so-called mode-mixity of the stress state near the crack tip. The present study deals with experimental investigation of the delamination toughness of EMC-Copper lead-frame interfaces as can directly be obtained from the production line. The experimental set-up as designed for this purpose was previously reported, together with some measurement results and toughness evaluations for room temperature fracture tests. This study deals with experiment and simulation procedure of establishing the interfacial fracture toughness from fracture test results at high temperatures, especially in the glass transition temperature region of epoxy molding compound (EMC). In order to calculation accurate fracture toughness, the material property of molding compound is characterized as a function of temperature. A detailed discussion of how EMC responses at its glass transition region will be provided. The influence of the material property on interfacial fracture toughness will be given.

Delamination toughness of Cu-EMC interfaces at harsh environment

“…However, using these methods, a sharp initial crack is not always obtained. For the present delamination study the method earlier developed by Xiao [1][2][3] is used. Here a sharp initial crack is obtained through the following processing steps (as indicated in figure 3).…”

“…For the present study we chose a Mixed Mode Bending set up, analog to the MMB set up, as earlier developed for delamination measurements on real production samples by Xiao, e.a. [1][2][3]. Firstly, harsh environment measurements were performed under "pressure cooker" conditions (Temp>100 °C & RH=100%), as these are considered as the most severe conditions for humidity-interface toughness reduction.…”

Fracture toughness of Cu-EMC interfaces under pressure cooker conditions

“…Researches showed that, using these methods, a sharp initial crack is not always obtained. For the present delamination study the method earlier developed by Xiao [1][2][3] is used. Here a sharp initial crack is obtained through the following processing steps (as indicated in figure 1).…”

“…For the present study we chose a Mixed Mode Bending set up, analog to the MMB set up, as earlier developed for delamination measurements on real production samples by Xiao, e.a. [1][2][3]. For the first time, the interface delamination toughness measurement is perfonned in under "pressure cooker" condition (Temp> 1 00 °C & RH=lOO%).…”