Surface Mount Device Assembly Research Articles

Assembly of Surface-Mounted Devices on Flexible Substrates by Isotropic Conductive Adhesive and Solder and Lifetime Characterization.

The assembly of passive components on flexible electronics is essential for the functionalization of circuits. For this purpose, adhesive bonding technology by isotropic conductive adhesive (ICA) is increasingly used in addition to soldering processes. Nevertheless, a comparative study, especially for bending characterization, is not available. In this paper, soldering and conductive adhesive bonding of 0603 and 0402 components on flexible polyimide substrates is compared using the design of experiments methods (DoE), considering failure for shear strength and bending behavior. Various solder pastes and conductive adhesives are used. Process variation also includes curing and soldering profiles, respectively, amount of adhesive, and final surface metallization. Samples created with conductive adhesive H20E, a large amount of adhesive, and a faster curing profile could achieve the highest shear strength. In the bending characterization using adhesive bonding, samples on immersion silver surface finish withstood more cycles to failure than samples on bare copper surface. In comparison, the samples soldered to bare copper surface finish withstood more cycles to failure than the soldered samples on immersion silver surface finish.

Cost-effective, Reliable, and Precise Surface Mount Device (SMD) on PCBs

Automated Pick-and-Place (P&P) machines offer a new prospective for the assembly of Surface Mount Devices (SMDs) on Printed Circuit Boards (PCBs), owing to their advantages of time-effectiveness and precision. SMDs are widely used to improve production efficiency and reduce common defects. However, these machines are quite expensive and not easily available for the local market. This study is based on the design of a P&P machine model that incorporates principles of machine learning theory. The model has been developed in such a way that it can be introduced to the local market in a more cost-effective manner without compromising on its precision and accuracy.

Evaluation of Epoxy Flux for Use in Hearing Aid SMD Assemblies

Miniaturization of everyday products has been driving sales for some time and continues to fuel the consumer market. Everyone expects size reduction with each new product generation [1], [2]. Almost everything has electronics inside that must get smaller. There is no market demanding smaller devices that are faster, more capable, more feature-rich than that of the hearing aid industry. While radios, Bluetooth wireless systems and other accessories are added to hearing instruments feature lists, the consumer nonetheless continues to wish for them to be even smaller. Advancements in circuit fabrication, component shrinkage and die consolidation have aided the industry in satisfying this need. However, as this demand continues and even intensifies, current surface mount device assembly materials are becoming inadequate and the limiting factor for overall circuit size reduction; specifically, the die attachment, protection and reinforcement process is limiting how small hearing aid circuits can be. For hearing aids, the addition of more features and connection to more accessories each require a number of integrated circuits and associated passives attached to a flexible circuit. These circuits are invariably bent and twisted during assembly, up to 180°, requiring the integrated circuit solder joints to be reinforced by underfilling to prevent detachment. Unfortunately, the underfilling process is time-consuming and the capillary action necessary for its success is finicky. Even more unfavorably, a designated “keep out” area for other components must surround the die to be underfilled to allow for the dispensing equipment to access the die, reducing the useable board space and limiting the overall possibility of circuit size reduction. Additionally, the underfill material must stay away from circuit board edges and areas to be bent during final assembly. In an attempt to increase useable circuit board space, decrease overall circuit board size, and reduce assembly steps, the application of two epoxy flux materials for die attach fluxing and underfilling of hearing aids was evaluated. Epoxy flux is a relatively new material, which combines the functionality of flux and underfill into a single step. Epoxy flux's application, while eliminating steps, would more significantly eliminate the necessary “keep out” areas around die and allow for more densely placed surface mount components. The epoxy flux materials were applied by both printing and dipping, and then evaluated using x-ray imaging, scanning acoustic microscope imaging, die peel testing, multiple reflow integrity testing and die shear testing.

Empirical Modeling of the Time-Dependent Structural Build-up of Lead-Free Solder Pastes Used in the Electronics Assembly Applications

Abstract Solder paste is the primary bonding material used in the assembly of surface mount devices in electronics industries. It generally has a flocculated structure, which may break-down on shearing and slowly rebuild at rest. The proper characterization of the time-dependent rheological behaviors of solder pastes is crucial for establishing the relationships between the pastes’ structure and flow behavior and for correlating the physical parameters with paste printing performance. In this paper, we present a novel method that has been developed for characterizing the time-dependent and non-Newtonian rheological behavior of solder pastes and flux mediums as a function of shear rates. The objective of the study reported in this paper was to investigate the thixotropic build-up behavior of solder paste and flux mediums. The stretched exponential model has been used to model the structural changes during the build-up process and to correlate model parameters with the paste printing process. As expected, for solder paste samples, the rate of structural recovery was found dependent on the applied shear rate. The model parameters, such as equilibrium viscosity and characteristic time, have been correlated with the shear-thinning and slumping behaviors of solder paste during the stencil printing process.

Modeling the Structural Breakdown of Solder Paste Using the Structural Kinetic Model

Solder paste is the most important strategic bonding material used in the assembly of surface mount devices in electronic industries. It is known to exhibit a thixotropic behavior, which is recognized by the decrease in apparent viscosity of paste material with time when subjected to a constant shear rate. The proper characterization of this time-dependent rheological behavior of solder pastes is crucial for establishing the relationships between the pastes’ structure and flow behavior; and for correlating the physical parameters with paste printing performance. In this article, we present a novel method which has been developed for characterizing the time-dependent and non-Newtonian rheological behavior of solder pastes and flux mediums as a function of shear rates. We also present results of the study of the rheology of the solder pastes and flux mediums using the structural kinetic modeling approach, which postulates that the network structure of solder pastes breaks down irreversibly under shear, leading to time and shear-dependent changes in the flow properties. Our results show that for the solder pastes used in the study, the rate and extent of thixotropy was generally found to increase with increasing shear rate. The technique demonstrated in this study has wide utility for RD and for qualifying new flip-chip assembly lines.

An Automated Feature Selection Method for Visual Inspection Systems

Automated visual inspection (AVI) systems these days are considered essential in the assembly of surface-mounted devices (SMDs) in the electronics industry. This industry has faced the problem of rapid introduction and retirement of SMD-based products with the consequent obsolescence of the inspection systems already in the assembly lines. The constant introduction of new products has caused AVI systems to become rapidly obsolete. The general goal of this research centers on developing self-training AVI systems for the inspection of SMD components. The premise is that these systems would be less prone to obsolescence. In this paper, the authors describe the methodology being used for automatically selecting the features to inspect new components. In particular, this paper explores the use of multivariate stepwise discriminant analysis techniques, such as Wilks' Lambda, in order to automate the feature selection process. All of these techniques are applied to a case study of the inspection of SMD components. Note to Practitioners-In this paper, we present a methodology that would allow the automation of the tedious task of exploring and selecting features to develop algorithms for automated visual inspection systems. In particular, the proposed method selects a subset of features among all of the known features. The chosen subset seeks to minimize inspection errors while keeping the algorithmic development time to a minimum. This is particularly useful for adapting pre-existing systems to inspect new components, especially when the characteristics of the new components are similar to those of components already inspected by the inspection system. We applied this methodology to a case of study of the inspection of surface-mounted devices

Optimal Cross-Coupled Synchronizing Control of Dual-Drive Gantry System for a SMD Assembly Machine

The present paper deals with the development of synchronizing controller for dual-drive servo system that is often used for SMD (Surface Mount Device) assembly machine. Instead of coordinating the commands to the individual feed drives and implementing closed position loop control for each axis, this work is achieved by the evaluation of an optimal cross-coupled compensator aimed specifically at improving synchronous accuracy in dual feed drives. The optimal control formulation explicitly includes the synchronous error in the performance index to be minimized. In this paper, surface chip mounter is used for experiment. It demands to synchronize the positions of its two primary driving axes. The system is modeled as the first order approximation and cross-coupled optimal synchronizing controller is designed. The synchronizing control is simulated and experimented with actual system for various velocity profiles. The results show that the proposed controller reduces the synchronous error considerably, compared to the conventional uncoupled control for the dual-drive system.

Knowledge-based control of adhesive dispensing for surface mount device assembly

Knowledge-based control of adhesive dispensing for surface mount device assembly