Technical Library | 2023-01-17 17:27:13.0
Reflow profile has significant impact on solder joint performance because it influences wetting and microstructure of the solder joint. The degree of wetting, the microstructure (in particular the intermetallic layer), and the inherent strength of the solder all factor into the reliability of the solder joint. This paper presents experimental results on the effect of reflow profile on both 63%Sn 37%Pb (SnPb) and 96.5%Sn 3.0%Ag 0.5%Cu (SAC 305) solder joint shear force. Specifically, the effect of the reflow peak temperature and time above solder liquidus temperature are studied. Nine reflow profiles for SAC 305 and nine reflow profiles for SnPb have been developed with three levels of peak temperature (230 o C, 240 o C, and 250 o C for SAC 305; and 195 o C, 205 o C, and 215 o C for SnPb) and three levels of time above solder liquidus temperature (30 sec., 60 sec., and 90 sec.). The shear force data of four different sizes of chip resistors (1206, 0805, 0603, and 0402) are compared across the different profiles. The shear force of the resistors is measured at time 0 (right after assembly). The fracture surfaces have been studied using a scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS)
Technical Library | 2020-11-09 16:59:53.0
A customer contacted ACI Technologies regarding a high failure rate of their assemblies. They provided assemblies to be X-rayed and inspected for the purpose of identifying any process related issues such as (but not limited to) solder and assembly workmanship and evidence of damage due to moisture related problems during reflow (a.k.a. "popcorning"). Moisture damage usually appears as physical damage to the component. The first indication of moisture damage would be externally observable changes to the package in the form of bulging or fractures to the outer surface of the component, an example of which is shown in Figure 1. Internally observable indicators of moisture damage typically include fractures to the die inside the package and lifted or fractured wire bonds. These conditions would be apparent during transmissive X-ray inspection. Another symptom of moisture related damage would be inconsistent solder joint sizes that result from package deformation during the liquidus phase of the reflow process. None of these indicators of moisture related damage were present on the customer samples.
Technical Library | 2020-05-08 18:22:31.0
A customer contacted the Helpline to perform analysis on a lead-free assembly which exhibited intermittent functionality. The lead-free assembly exhibiting intermittent functionality when pressure was applied to the ball grid array (BGA) packages. Industrial adaptation of a Restriction of Hazardous Substances (RoHS) compliant solder standard has created a new host of failure modes observed in lead-free assemblies. Pad cratering occurs when fractures propagate along the epoxy resin layer on the underside of the BGA connecting pads. While originating from process, design, and end use conditions, it is the combination of a rigid lead-free solder with inflexible printed circuit board (PCB) laminates that has advanced the prevalence of this condition. Pad cratering is simply the result of mechanical stress exceeding material limitations.
Technical Library | 2020-10-14 14:18:13.0
Thermally conductive adhesives provide many advantages over traditional mechanical fastening techniques. Specifically, they use less material and space and are more amenable to automation than existing solutions. The thermal and mechanical properties of these materials are well understood but little work has been done to characterize and understand their toughness and fracture behavior. This paper presents the effects of filler loading as well as matrix composition on the fracture toughness of thermally conductive silicone adhesives. It was observed that the fracture toughness of these materials increased significantly with initial filler loading, and that the mechanical properties and fracture toughness depended on the molecular architecture of the matrix used.
Technical Library | 2022-01-26 15:26:56.0
In this work an attempt is made to improve the fracture toughness and electrical conductivity of epoxy/glass fiber based laminates by the inclusion of carbon nanotube (CNT) fillers. The fiber orientation of the epoxy/ glass fiber (GF) fabric laminates was optimized based on estimation of mechanical properties. The carboxylic acid functionalized CNTs were incorporated into epoxy matrix by ultra-sonication method. The nano filled epoxy resin was used to prepare laminates with 30/45 GF fabric orientation. The CNT content was varied and its effect on the tensile properties was determined. The fracture toughness of multiphase composites was estimated using single edge notch bend (SENB) test. The presence of CNTs improved the fracture toughness by a crack bridging mechanism. The volume resistivity of multiphase composites was found to be superior to the conventional epoxy/CNT composite. The presence of glass fabric reduces the number of inter-tube contacts contributing to the reduction in volume resistivity.
Technical Library | 2023-11-27 18:29:45.0
This paper examines the modeling of viscoplastic solder behavior in the vicinity of interfacial cracking for flip chip semiconductor packages. Of particular interest is the relationship between viscoplastic deformation in the solder bumps and any possible interface cracking between the epoxy underfill layer and the silicon die. A 3-D finite element code, developed specifically for the study of interfacial fracture problems, was modified to study how viscoplastic solder material properties would affect fracture parameters such as strain energy release rate and phase angle for nearby interfacial cracks. Simplified two-layer periodic symmetry models were developed to investigate these interactions. Comparison of flip chip results using different solder material models showed that viscoplastic models yielded lower stress and fracture parameters than time independent elastic-plastic simulations. It was also found that adding second level attachment greatly increases the magnitude of the solder strain and fracture parameters. As expected, the viscoplastic and temperature dependent elastic-plastic results exhibited greater similarity to each other than results based solely on linear elastic properties. !DOI: 10.1115/1.1649242"
Technical Library | 2012-09-06 18:19:37.0
First published in the 2012 IPC APEX EXPO technical conference proceedings. Pad Cratering opens circuits. This occurs when the resin crack (fracture) migrates through a copper trace or via. This happens at assembly, in service or during handling. When com
Technical Library | 2020-10-14 14:49:14.0
In this study, the modification of an epoxy matrix with different amounts of cube-like and rod-like CaCO3 nanoparticles was investigated. The effects of variations in the morphology of CaCO3 on the mechanical properties and thermal stability of the CaCO3/epoxy composites were studied. The rod-like CaCO3/epoxy composites (EP-rod) showed a higher degradation temperature (4.5 _C) than neat epoxy. The results showed that the mechanical properties, such as the flexural strength, flexural modulus, and fracture toughness of the epoxy composites with CaCO3 were enhanced by the addition of cube-like and rod-like CaCO3 nanoparticles. Moreover, the mechanical properties of the composites were enhanced by increasing the amount of CaCO3 added but decreased when the filler content reached 2%. The fracture toughness Kic and fracture energy release rate Gic of cube-like and rod-like CaCO3/epoxy composites (0.85/0.74 MPa m1/2 and 318.7/229.5 J m
Technical Library | 2021-02-25 14:19:00.0
This study proposes a new design of lightweight and cost-e#14;cient composite materials for the aeronautic industry utilizing recycled fresh scrap rubber, epoxy resin, and graphene nanoplatelets (GnPs). After manufacturing the composites, their bending strength and fracture characteristics were investigated by three-point bending (3PB) tests. Halpin–Tsai homogenization adapted to composites containing GnPs was used to estimate the moduli of the composites, and satisfactory agreement with the 3PB test results was observed.
Technical Library | 2013-01-09 18:31:54.0
The increased temperatures associated with lead free processes have produced significant challenges for PWB laminates. Newly developed laminates have different curing processes, are commonly filled with ceramic particles or micro-clays and can have higher Tg values. These changes designed to reduce Z-axis expansion and improve the materials resistance to thermal excursions through primary attach and rework operations have also produced harder resin systems with reduced fracture toughness.
