Introduction to Surface-Mount Technology

In chapter 1, the surface-mount technology and reflow soldering technology are overviewed. A brief introduction is presented into the type of electronic components, including through-hole- and surface-mounted ones. Steps of reflow soldering technology are outlined, and details are given regarding the properties of solder material in this technology. The rheological behavior of solder pastes is detailed, and some recent advancements in addressing the thixotropic behavior of this material are summarized. The process of stencil printing is detailed next, which is the most crucial step in reflow soldering technology; since even 60–70% of the soldering failures can be traced back to this process. The topic includes the structures of stencils, discussion of the primary process parameters, and process optimization possibilities by numerical modeling. Process issues of component placement are presented. The critical parameter (process and machines capability), which is used extensively for characterizing the placement process is studied. In connection with the measurement of process capability, the method of Gage R&R (repeatability and reproducibility) is detailed, including the estimation of respective variances. Process of the reflow soldering itself is detailed, including the two main phenomena taking place when the solder is in the molten state, namely: wetting of the liquid solder due to surface tension, and intermetallic compound formation due to diffusion. Solder profile calculation and component movements during the soldering (e.g., self-alignment of passive components) are presented too. Lastly, the pin-in-paste technology (reflow solder of through-hole components) is detailed, including some recent advancements in the optimization of this technology by utilizing machine learning techniques

Analysis of surface mount technology solder joints

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The factors determining the quality of surface mount technology (SMT) solder joints are numerous, and complex. The exploration of these factors, and how they may affect the reliability and quality of the joints can only be achieved through continuous research. In this project, essential areas of SMT joints were selected for study and analysis, with the intention of providing additional design and process guidelines for the production of quality SMT joints. In the infrared reflow process, one of the common defect phenomena is the occurrence of tombstoning; that is after soldering only one end of the component is soldered while the other is lifted up, assuming a position like a tombstone. The initiation of tombstoning during reflow was analysed based on the forces acting on the component. A model was developed to predict the initiation of this phenomenon. The model shows that, under vibration-free conditions, the surface tension of the molten solder is the source of the force causing the initiation of tombstoning. The contact angle, which varies with the length of the printed circuit board solder land, has a significant effect on the value of the surface tension acting as a force pulling upward on the component. The model further shows that tombstoning initiation is due to the combined effects of the surface tension; the weight of the component; the dimensions of the component; the length of the solder underneath the component; and the length of the solder protruding from the end of the component. Selected components were used as examples for predicting the conditions of initiation, and these conditions were further substantiated by a series of experiments. Another area of study was a method which directly pulled the components off printed circuit boards and this was used as a means for testing the bond quality of surface mount technology leadless chip solder joints. Components D7243, CC1206, RC1206, RC121O, and CC1 812 were selected for this study. It was found that the ultimate tensile force which breaks a component off the printed circuit board has the potential to be used as a parameter for measuring the quality of the solder joint. The effect of solder thickness on the strength of a joint has also been investigated. The shape of joints soldered by two methods, wave soldering and infrared reflow, were compared. Joints at the two ends of a component produced by infrared reflow were found more uniform than the ones produced by wave soldering. A recommendation is made here for the wave soldering approach in achieving uniform solder joints. The effects of solder shape on the joint strength were further investigated by finite element analysis. A convex joint was found marginally more robust than a concave joint. Two aspects of the internal structure of SMT solder joints were investigated, void content and copper/tin intermetallic compounds. The voiding conditions of wave-soldered and infrared reflow joints were compared. No voids were found in all specimens that were produced by wave soldering. However, there were always voids inside joints produced by infrared reflow. Microhardness tests indicated that the hardness of compounds at the copper/solder interface of infrared reflowed joints is lower than that in the wave-soldered joints. It is considered that the lower hardness of the interfacial region of the infrared reflowed joints is due to the presence of voids. Scanning electron microscopy was used to study the formation of copper/tin intermetallic compounds for joints produced by infrared reflow. The results show that Cu 6 Sn5 was the only compound with a detectable thickness. Other compounds such as Cu3 Sn, were virtually not found at all. Aging of the joints at 100°C, shows that both the Cu 6Sn5 and the overall interfacial thickness grew with time. One of the important areas which had been overlooked previously and was studied in some details was the effects of solder paste exposure on the quality of solder paste. The characteristic changes of solder paste due to exposure were investigated in three areas, weight loss, tackiness, and rheology. The evaporation of low boiling point solvents was considered as the main contribution to the loss in the weight of the solder paste. The weight loss against exposure time was found to follow an exponential behaviour. A method was designed to evaluate the tackiness changes of solder paste due to exposure. It was found that the decay of tackiness against exposure time can be expressed by a power law. It is recommended that solder paste manufacturers should provide the necessary characteristic constants so as to enable the characteristics to be calculated after a specific exposure. The rheological changes of the solder paste as a result of exposure were also investigated. The implication on the printability of the solder paste due to these changes was studied and discussed

SURFACE MOUNT TECHNOLOGY RJ45 STRETCHABLE PIN AGAINST PULL FORCE

Techniques are provided herein for a stretchable, spring-like structure that is added into the copper pin of Surface Mount Technology (SMT) RJ45. The structure can stretch when the RJ45 is pulled to mitigate the force on the RJ45 pin

Automated inspection of solder joints for surface mount technology

Researchers at NASA/GSFC evaluated various automated inspection systems (AIS) technologies using test boards with known defects in surface mount solder joints. These boards were complex and included almost every type of surface mount device typical of critical assemblies used for space flight applications: X-ray radiography; X-ray laminography; Ultrasonic Imaging; Optical Imaging; Laser Imaging; and Infrared Inspection. Vendors, representative of the different technologies, inspected the test boards with their particular machine. The results of the evaluation showed limitations of AIS. Furthermore, none of the AIS technologies evaluated proved to meet all of the inspection criteria for use in high-reliability applications. It was found that certain inspection systems could supplement but not replace manual inspection for low-volume, high-reliability, surface mount solder joints

Analysis of CyberOptics Corporation

This analysis looks at CyberOptics, a Minnesota based company with segments in metrology, semiconductors, and surface mount technology. The goal of the project is to determine an appropriate valuation given recent financial data, and give an opinion on whether to buy, hold, or sell given a closing stock date

Variability reduction in stencil printing of solder paste for surface mount technology

Competition in stencil printing to produce excellence in the finished product is intense. Faults in the printing process are a major source of board failure. Studies have shown that over 63% of defects identified after reDow originated from the solder paste printing ( A. Lotfi ,1998 ) . However. understanding these failures are a challenging problem as the printing process has a large number of non linearly dependent variables such as factors relating to paste (formulation. viscosity), the environment (temperature, humidity) and machine parameter (alignment, pressure and speed of squeegee, blade hardness etc). The process engineer is challenged to widen the process window so that future modifications to the process, such as the addition of a new component, can be achieved with little. if any, change in materials or process parameters. This thesis reports the effect of temperature and humidity variation from the manufacturing environment on the solder paste consistency and optimization of the essential parameters of squeegee pressure, squeegee speed. separation speed and print gap. The outcome of variation in temperature and humidity to the solder paste viscosity were analyzed and tests were done to determine the characteristic of the solder paste. The tests results indicate that the temperature and humidity has an impact on the solder paste printability. thus some attempts must be taken to control these variables. For parameter optimization. the analysis was carried out using statistical optimization. The main aim was to combine these parameters with three main pitch categories to produce the acceptable print formation. The results showed that. the ideal print result requires optimum statistical combinations of four parameters essentially related to a particular pitch. It is also shown that there is a diversity and contrasts of the combination of the parameters for each category of pitch. Detailed explanations as to the phenomenon are outlined in the thesis

The Design of a Lumped Element Impedance-Matching Network with Reduced Parasitic Effects Obtained From Numerical Modeling

This paper presents an impedance-matching network design with numerical modeling of the parasitic effects. A modeling tool CEMPIE (a Circuit Extraction approach based on a Mixed Potential Integral Equation formulation) is used to model the hoard-level parasitics of surface mount technology (SMT) resistors for impedance-matching networks. A 3-layer design of impedance-matching network with 0402 SMT resistors is implemented according to the modeling results. And its performance is demonstrated

Clustered yield model for SMT boards and MCM's, A

Includes bibliographical references.This paper describes a clustered yield model for complex surface mount technology (SMT) assemblies and multichip modules (MCM's). Based on yield modeling techniques that have been proven in the manufacturing of integrated circuits (IC's), this model uses the negative binomial distribution of defects to calculate board yield after test. Manufacturing data validates that this model accurately predicts the clustering of defects and the yield predictions are significantly better than traditional binomial models

SMT board for acquisition of electrocardiograph signals and GSM transmission

Portable equipments for telemedical applications is one of the most innovative sectors in biomedical engineering. Health departments of governments are interested in tele diagnostic systems to avoid collapses in hospital and urgency services. In this paper, we describe a potable electrocardiograph/holter equipment with telephony and GSM transmission, using a surface mount technology with low voltage battery supply. This project has been developed in collaboration with Teleasistencia Cardiotest, S.L. This prototype is patent pending