Amir Nur Rashid Wagiman

Solder joint fatigue in a surface-mount assembly subjected to mechanical loading

A mechanical approach employing cyclic twisting deformation to a surface mount assembly is examined as an alternative to temperature cycling for evaluating solder joints fatigue performance. This highly accelerated test is aimed at reducing solder joint reliability testing cycle time. In this study, the mechanics of solder joints in a surface mount assembly subjected to cyclic twisting deformation on the PCB is investigated. For this purpose, a test package with 24 by 24 peripheral-array solder joints is modeled using the finite element method. Unified inelastic strain theory defines the strain-rate-dependent plastic stress-strain response of the 60Sn-40Pb solder. Cyclic twisting deformation in the range of plusmn1deg at a rate of 120 seconds per cycle was applied to the PCB assembly sub-model. The calculated stress and strain distributions in the critical solder joint are compared with those predicted for temperature cycling and accelerated temperature cycling tests. Results showed that the accumulated inelastic strain concentrates in a small region of the critical solder joint near the component side for temperature cycling and near the pad side for cyclic twisting cycles. The rate of inelastic strain accumulation per fatigue cycle in the solder joint for both thermal cycling (TC1) and mechanical twisting (MT1) tests are similar. Thus mechanical twisting test imparts similar characteristics in terms of the shear strain range to temperature cycling tests. Low cycle fatigue is dominated by localized shear effect as reflected in the largest shear strain range of the hysteresis loops. The Coffin-Manson strain-based model yielded more conservative prediction of fatigue lives of solder joints when compared to energy-based approach

Effect of Ethanol as Diluent on the Properties of Mineral Silica Filled Epoxy Composites

Epoxy composites with mineral silica containing 0—60 vol% were prepared using a mechanical stirrer. Ethanol at 10wt% was used as the diluent in the epoxy system. The mechanical properties of epoxy composites were studied through flexural and single etch notch tensile mode (SEN-T) fracture toughness tests. Scanning electron microscopy (SEM) was used to assess the flexural fracture surface morphology. The thermal properties were characterized using a dilatometer, dynamic mechanical analyzer (DMA), and thermogravimetric analysis (TGA). In general, it is found that the properties of epoxy composites are governed by the filler loading and the addition of ethanol as the diluent. The addition of the diluent in epoxy permits higher amount of filler content in the epoxy composites system, i.e., 60vol%, compared to that of the non-diluent system at 40vol%. In short, higher filler loading present in a diluent system results in higher stiffness and low coefficient of thermal expansion (CTE) as required in the electronic packaging application.

Underfill flow void solutions through process and materials interaction

Silicon dies were thinned down and bump pitch became smaller to have a lot of input/output in electronic device packages especially in package on package configuration. This presents challenges on underfill (UF) dispense processing. UF voids occurred near the dispense side of bumps in multiple dispense pass technology. In this paper, we will review UF flow behavior on thin die technology, as well as the process and material interaction that cause UF void formation. Process optimization, such as the time between two dispense passes has become a critical parameter to eliminate UF voids without causing UF epoxy roll up that can cause reliability failure.

Development of vapor pressure in FR4-copper composite material during solder reflow process

This paper presents a finite element (FE) methodology for predicting the distribution of vapor pressure in a simple FR4-copper composite material when it is heated up to 215°C. A general purpose finite element software was used to develop a two-dimensional plane strain model of the composite material. FE simulation of transient moisture absorption was performed to predict the distribution of wetness fraction in the material after pre-conditioning at an 85°C/85%RH environment for 15 days. FE simulation of transient moisture desorption was carried out at the peak solder reflow temperature of 215°C to predict new distribution of wetness fraction in the material. The results of the moisture desorption analysis were used to compute the magnitude of vapor pressure in the material and its distribution at 215°C. It was found that the moisture in the material redistributes itself during solder reflow. The moisture concentration in the area close to the FR4-copper interface below the longer copper trace increases during the solder reflow. The magnitude of the vapor pressure in 70% of the FR4 and near the FR4-copper interface below the lower copper trace is closed to the saturation pressure of water vapor at 215°C. The distribution of the vapor pressure in the material is in similar fashion as the new distribution of wetness fraction after the moisture desorption analysis.

Miniaturization innovation evolution of electronics packaging - what's coming next…?

Intels Moores Law focuses on shrinking the transistors in the silicon to be able to pack more and more transistors for a given area. In general, Intel has been able to double the transistor count every 18–24 months and has been doing so while keeping the silicon size at about the same size or even smaller. The key implication to that trend has been the I/O density that needs to be routed through the packaging is also increasing (ie. More I/O count per area).

Assessment of Solder Joint Fatigue Performance Using Cyclic Flexural Loading

The mechanics of solder joints in a surface mount assembly subjected to cyclic flexural load is examined using finite element method. A test assembly with peripheral-array solder joints is supported by eight pins and arranged in a circle on the component side of the printed circuit board (PCB). Cyclic flexural load to the assembly is achieved by prescribed displacement of the central loading pin. Flexural test cases were performed at temperatures 25, 42.5, 100 and 125degC. Results were compared with those of temperature cycling (Reference case), in terms of the rate of inelastic strain accumulation, stress-strain hysteresis loops and the predicted fatigue lives of solder joints.

High Filled Epoxy Composites for Electronic Packaging Application

Increasing demands in the electronic packaging industries have led to the need for high-performance organic substrate material like epoxy composites. This paper investigates the effect of ethanol as diluent in epoxy composites containing 0 to 60 vol% of mineral silica. Flexural properties of epoxy composites were studied at room temperature. Thermal properties were studied using dilatomater, dynamic mechanical analyzer (DMA) and thermogravimetric analysis (TGA). In overall, the properties of the epoxy composites are depend on the filler loading and the addition of ethanol as diluent.