Lead Solder Research Articles

An Evaluation of FIB Cross-Sectioning Using a Cooling Stage for Metals and Alloys with Low Melting Point

Functions of an observation and an analysis in electron microscope, such as scanning electron microscope (SEM) or transmission electron microscope (TEM) are indispensable to evaluate advanced materials. Therefore a specimen preparation technique, that is a front end of the electron microscopy, has become highly important, thus a choice of it affects a result of the evaluation. The authors was combined a cooling stage in FIB and applied it for evaluation of metals with low melting point. The electron microscopic evaluation of Lead solder, Indium, Tin and Bismuth, metals with low melting point, has been always discussed if the results represent the actual physics. Metals with low melting point are heat sensitive materials, so the comparison of cross-sectioning with room and low temperature, it can be said that low temperature cross-sectioning has less effect and keeps the actual physics of the sample. In this paper, some knowledge from comparisons of cross-sectioning with room and low temperature for metals with low melting point are reported.

Thermal Cycle Consideration in Applying Lead-Free TFBGA Simulation to a Design

Three-dimensional (3D) stacked die packaging has become the trend to improve efficiency for transmitting signals, reduce the volume of the package, and help with functions integration. It is more and more applied popularly in telecommunications. Solder joints, interconnections in the packaging structure, are more easily damaged by critical stress from thermal cycle loading when the component is operating, because the coefficient of the thermal expansion of various materials mismatch. People have studied the common single die during the thermal cycle loading for a long time, but the researches for the stacked die BGA are not as complete. In addition, to protect the environment and comply with legislation, the semiconductor industry wants to find a lead-free material to replace the lead solder joints. Therefore, most extant or new types of packaging started using lead-free material to do thermal cycle testing. The critical solder ball location is not the same as in a single die package where at the die corner, due to it is influenced by stacked die with different geometry, the difference in dice length helps to redistribute the die stress. In this paper, we used FEA software, ANSYS, to build up a 3D thin-profile, fine-pitch, ball grid array (TFBGA) model. The modeling investigated the effect on solder joints under thermal cycle and included deformation, von-Mises stress and strain energy density (SED). Then we utilized Darveaux's approach, which is a common methodology used to calculate the fatigue life based on energy and damage accumulation theories, to predict the fatigue life of the critical solder joint and modify our model with the theory. We changed various kinds of SAC solder joints with different ratios of the components and Anand's constants, analyze the divergence and compared them with the lead solder material. We develop a model to forecast the failure phenomenon and fatigue damage on an electronic package. This would help engineers and designers raise the reliability of the package. In addition, we hope to find a lead-free material that can be substituted for the lead solder material. If this is the case, based on simulating results, we hope to improve it and have much a better reliability performance than the original lead solder.

Editorial role of a clinical biochemist in evaluating the impact of lead poisoning.

World Health Organization has declared that one of the toxic heavy metal “Lead” as number one environmental hazard all over the world with over 120 million people is overexposed to lead and 99 percent of the most serious cases are in the developing world. Lead and its various salts have a significant role in environment and has impact on health which is of great concern and is a multidisciplinary topic of great concern. Understanding of the toxic effects of lead over the past 30 years is an outstanding example of how knowledge generated from simple research can impact public health. Efforts by scientific community have made the greatest impact on reducing exposure to lead, are reduction of lead from gasoline by the efforts of The George Foundation Project Lead Free in the year 2000 in India, elimination of lead solder from canned food, removal of lead from paint in 2011, and abatement of lead-based paint as an ongoing effort in most of the developing countries. While Lead toxicity is a grave problem in environmental pathology [1], Biochemists have looked into the effect of lead on various biochemical pathways. With this clinical lead poisoning was understood in greater detail. The most important signs and symptoms of overt lead intoxication were confined to central nervous system, haemopoitic system and the renal system. Children with acute lead poisoning present clinically with ataxia or even with convulsions or even a reduced level of consciousness [2] Adults rarely have such CNS symptoms unless there is massive exposure to lead vapors or organic forms of lead in illicit alcohol drinks [3]. Whether it is the competition of lead with calcium in various biochemical mechanisms or the direct effect of lead on the active sites of enzymes lead seems to have many deleterious effects in a biological system. Orfila in 1817 made a statement which is of great concern even today. The statement is “If we were to judge of the interest excited by any medical subject by the number of writings to which it has given birth we could not but regard the poisoning by lead as the most important to be known of all those that have been treated of, up to the present time.” This information was arrived by going through Parrish, Case of Suicide in a Child. [4]. Biochemists have diagnosed, evaluated, and helped in the treatment of lead poisoning in general population [5], Elevated blood lead levels and cytogenetic markers in painters exposed to lead containing paints indicated another major source of lead [6] With reference to occupational exposure to lead and subsequent elevated blood lead levels, evaluation and treatment of wrist drop in a patient due to lead poisoning was studies by biochemists [7] Another major breakthrough considering paints as the major source of lead author was involved in multi country study in evaluating the impact of lead from lead based paints [8.] Lead and genotoxicity study used blood lead levels and its correlation to other cytogenetic markers (Elevated blood lead levels and cytogenetic markers in buccal epithelial cells of painters in India [6]. India being the major source of ayurvedic medicines had to face major problem when scientific papers did demonstrate the presence of high levels of lead and other toxic heavy metals in the ayurvedic preparations sold on internet in USA [9, 10]. Many similar studies in India did reveal lead poisoning caused by the use of unbranded ayurvedic medicines [11]. Studies undertaken by the team of clinical biochemists in India at the National referral Centre for lead Projects in India (NRCLPI) located at Bangalore since 1996 resulted in getting unleaded gasoline in India in March 2000. Following this abatement of lead in paints were successfully achieved in the year 2011. New governmental policies were emerged at AYUSH to safeguard our traditional medicines. Cost of blood lead level was brought down from 1,800 to mere 500 Rs with better technology and a turnaround time of less than 15 min after drawing blood and the quantity of blood requirement was brought down to 50 μL. When no uniform methodologies were adopted for the blood lead evaluation biochemists made an effort to introduce the DP ASV point of care with lead care system. Sixteen centers across the country have now lead clinics with same uniform technology to evaluate blood lead levels apart from providing the much needed guidance to the treating clinicians. Plans are made to establish 100 lead clinics across the country by the end of 2013. Over 15,000 school teachers and NGO’s are trained in the basics of lead poisoning and its prevention by the team of biochemists in India.

Assessment of the effects of the Japanese shift to lead-free solders and its impact on material substitution and environmental emissions by a dynamic material flow analysis

Lead-free electronics has been extensively studied, whereas their adoption by society and their impact on material substitution and environmental emissions are not well understood. Through a material flow analysis (MFA), this paper explores the life cycle flows for solder-containing metals in Japan, which leads the world in the shift to lead-free solders in electronics. The results indicate that the shift has been progressing rapidly for a decade, and that substitutes for lead in solders, which include silver and copper, are still in the early life cycle stages. The results also show, however, that such substitution slows down during the late life cycle stages owing to long electronic product lifespans. This deceleration of material substitution in the solder life cycle may not only preclude a reduction in lead emissions to air but also accelerate an increase in silver emissions to air and water. As an effective measure against ongoing lead emissions, our scenario analysis suggests an aggressive recycling program for printed circuit boards that utilizes an existing recycling scheme.

Assessing the replacement of lead in solders: effects on resource use and human health

Human health and environmental concerns are not usually considered at the same time. Tin-lead solders are still widely used in several countries, including Brazil, by manufacturers of electronic assemblies. One of the options to reduce or eliminate lead from the manufacturing environment is its replacement with lead-free alloys. This paper applies emergy synthesis and the DALY indicator (Disability Adjusted Life Years) to assess the impact of manufacturing soft solder using tin, lead and other metals on the environment and on human health. The results are presented together with the company's financial results and the results calculated from the Brazilian statistical value of life. The calculation of emergy per unit showed that more resources are used to produce one ton of lead-free solders than to produce one ton of tin-lead solders, with and without the use of consumer waste recovered through a reverse logistics system. The assessment of air emissions during solder production shows that the benefits of the lead-free solution are limited to the stages of manufacturing and assembling. The tin-lead solder appears as the best option in terms of resource use efficiency and with respect to emissions into the atmosphere when the mining stage is included. A discussion on the influence of the system's boundaries on the decision-making process for materials substitution is presented.

무연 솔더 제거를 위한 디지털 디솔더링 시스템 구현

본 논문은 무연 솔더를 제거하기 위한 디지털 디솔더링 시스템에 관하여 다룬다. 땜납의 모재가 유연납에서 무연납으로 변화된 작업환경에 대처하고, 설정온도에 빠르게 수렴하며 연속작업이 가능한 디솔더링 시스템을 제안한다. 제안 시스템은 디솔더링 스테이션과 디솔더링건으로 구성되며, PID 온도제어를 위한 주변회로는 8bit MCU를 중심으로 설계하였다. 제안 시스템의 성능을 확인하기 위하여 동종의 수입품과 성능을 비교한 결과, 제안시스템은 기존 시스템에 비해 작업온도 도달시간은 11초 빠르며, 리플온도의 변화량은 <TEX>$1.5^{\circ}C$</TEX> 적고, 열 회복율은 약 <TEX>$0.14^{\circ}C$</TEX>/초 빠르게 나타남을 확인 하였다. This paper deals with a digital Desoldering system for removing lead-free solder. We proposed a Desoldering system that is to cope with the changed work environment of the solder materials changing from lead solder to lead-free solder, we can be quickly stable to the set temperature, and continuous operation is possible. Proposed system consists of a Desoldering station and a Desoldering gun. For the PID temperature control, we designed the 8bit MCU peripheral circuit. We had a few experiments to confirm the performance of the proposed system, and compared with the specification of same kind of imports. As a result, proposed system than the imported products showed good performance as follows: the time to reach operating temperature is 11 seconds faster, ripple temperature variation is <TEX>$1.5^{\circ}C$</TEX> lower, temperature recovery rate is about <TEX>$0.14^{\circ}C$</TEX>/sec faster.

Current Problems and Possible Solutions in High-Temperature Lead-Free Soldering

The substitution of lead in the electronics industry is one of the key issues in the current drive towards ecological manufacturing. Legislation has already banned the use of lead in solders for mainstream applications (T M ≈ 220 °C), but the use of lead in the solders for high-temperature applications (>85% lead, T M ≈ 250-350 °C) is still exempt in RoHS2. The search for proper substitutes has been ongoing among solder manufacturers only for a decade without finding a viable low cost alternative and is the subject of intensive research. This article tries to map the current situation in the field of high-temperature lead-free soldering, presenting a short review of current legislation, requirements for substitute alloys, and finally it describes some existing solutions both in the field of promising new materials and new technologies. Currently, there is no drop-in replacement for lead-containing solders and therefore both the new materials and the new technologies may be viable solutions for production of reliable lead-free joints for high-temperature applications.

Study of risk-trade-off assessment method of lead solder in Tokyo Bay by Ecological Risk Assessment Model.

Study of risk-trade-off assessment method of lead solder in Tokyo Bay by Ecological Risk Assessment Model.

HIGH RELIABILITY HIGH MELTING LEAD-FREE MIXED BIAGX SOLDER PASTE SYSTEM

In the current work, a mixed solder powder BiAgX solder paste system with the melting temperature above 260°C and the comparable or even better reliability to the high lead solders has been studied. The mixed solder powder paste system is composed of a high melting first alloy solder powder as majority and the additive solder powder as minority. The additive solder is designed to react aggressively with various surface finish materials before or together with the melting of the majority solder to form a controllable IMC layer. The IMC layer of the mixed powder system is controllable by the species and the quantity of the additive solder and it is observed to be insensitive to thermal aging and thermal cycling in current tests while the high lead ones do show a considerable increase in IMC layer thickness. Microstructure investigation shows the fishbone shape IMC layer interlocks the bonding interface between solder and components. Both micron-sized and nano-sized Ag-rich precipitations in the joints have been observed to be well distributed in the joint. The exposed Ag-rich particles and the surrounding stepwise pattern in Bi matrix on the fracture surface indicate that these Ag-rich particles constrain the dislocation movement in Bi matrix thus enhance the strength and the ductility of the joint. Under thermal aging and thermal cycling, both the micron-sized and nano-sized Ag-rich precipitations exhibit only discernible and localized coarsening. The stable interfacial IMC together with the existence of the well dispersed Ag-rich particles are attributed to the promising reliability in BiAgX solder paste system.

A novel polymer technology for underfill

AbstractCapillary type underfill is still the mainstream underfill for mass production flip chip applications. Flip chip packages are migrating to ultra low-k, Pb-free, 3D and fine pitch packages. Underfill selection is becoming more critical. This paper discusses the performance and potential of underfills using a novel organic-inorganic hybrid polymer technology.Compared to eutectic and high lead solder, tin-silver-copper solder has lower C.T.E., higher elasticity and greater brittleness. In light of these properties, it is generally better to select high Tg and lower CTE underfill in order to prevent bump fatigue during reliability testing. Given the brittleness of low-k dielectric layers of flip chips, the destruction of low-k layers by stress inside the flip chip packages has become a major issue. Underfills for low-k packages should have low stress, and the warpage should be small. It is expected that as the low-k trend expands, the underfill is required to provide less stress. Low Tg underfill shows lower warpage. New chemical technologies have been developed to address the needs of underfills for low-k/Pb-free flip chip packages, specifically organic-inorganic hybrid polymer compounds. The organic-inorganic hybrid polymer provides excellent cure properties which enable a balanced combination of low stress and good bump protection. The material properties of the underfill were characterized using Differential Scanning Calorimetry (DSC), Thermo-Mechanical Analysis (TMA), and Dynamic Mechanical Analysis (DMA). A daisy-chained test vehicle was used for reliability testing. A detailed study is presented on the underfill properties, reliability data, as well as finite element modeling results.

An Undergraduate Experiment Using Differential Scanning Calorimetry: A Study of the Thermal Properties of a Binary Eutectic Alloy of Tin and Lead

An alloy is an intimate association of two or more metals, with or without a definite composition, which has metallic properties. Heterogeneous alloys, such as tin–lead (Sn/Pb) solders, consist of a mixture of crystalline phases with different compositions. A homogeneous alloy with a unique composition having the lowest possible melting point is called a eutectic. A binary eutectic alloy is a mixture of two metals with a well-defined composition that melts at the lowest temperature of any composition of the mixture. The purpose of this project was to study the thermal properties of various compositions of Sn/Pb alloys. The conclusions from this work were as follows: (i) the eutectic composition was found to be 62 wt % Sn with a melting temperature of 183 °C; (ii) as the Sn and Pb compositions decreased from 100%, the alloy melting temperature also decreased; and (iii) by measuring the differential scanning calorimetry (DSC) peak melting point of the Sn/Pb alloy, the alloy composition can be obtained from the constructed binary phase diagram. Overall, the DSC provided a method of analysis for the determination of a binary alloy composition of Sn/Pb and the construction of a simple binary phase diagram.

Packaging Approach for Integrating 40/45-nm ELK Devices Into Wire Bond and Flip-Chip Packages

There is a rapid transition in the semiconductor packaging industry of devices moving toward 40/45-nm extreme low k (ELK) from the development phase into mainstream semiconductor assembly manufacturing. The drive to achieve adoption without major changes to process and equipment infrastructure while meeting the superior yield necessary is high. The main goal of this paper is to share learning's and provide solutions for integration and qualifications of 40/45-nm ELK devices into flip-chip (FC) and wire-bond (WB) package technology. The scope of this paper covers the fine-pitch ball grid array for the WB packages and FC chip-scale package for the FC Devices. The main challenge and focus point for WB 45/40-nm interconnects is on the first bond process. This paper will share some detailed analysis on the following. 1) Characterization for 45 nm ELK ultrafine-pitch. 2) Key factors for good Au ball bond integrity. 3) Recommendations for achieving the required levels of reliability for 45-nm Cu ELK. The challenge of FC Technology today has been changing at a faster rate and more and more adoption has been made from the conventional eutectic solder bumps or high lead solder bumps toward the lead free solder bump mainly due to the Green initiatives. This paper will share analysis on the following areas. 1) Thermo-mechanical simulation on key input factors and its correlation to actual evaluations. 2) Integration of Pb Free ELK bumps with 40-nm ELK technology are various critical processes. 3) Moldable underfill technology for Pb Free + ELK devices. In addition, critical process control is also required at the wafer level process of wafer thinning and dicing, including the need of Laser Grooving will also be covered.

Protecting Children From Toxicants

Protecting Children From Toxicants

Thermodynamic Description of the Quaternary Ag-Cu-In-Sn System

Due to new regulations, the classic Sn-37Pb (wt.%) solder must be replaced by lead-free material. There are many alloys that could be used instead of this classic lead solder, including quaternary Ag-Cu-In-Sn alloy. The CALPHAD method was used for thermodynamic description of this quaternary system. Good agreement between calculation and available experimental information was found. Solidification of the promising lead-free solder Sn-1.5Ag-0.7Cu-9.5In (wt.%) was performed using the Scheil approach, and good agreement between this calculation and differential thermal analysis results was found. The obtained set of Gibbs energy functions can be used in the future for expanding the quaternary system to high-order ones.

Development of n-in-p silicon planar pixel sensors and flip-chip modules for very high radiation environments

Abstract In this paper we present RD small diodes were employed to investigate the width from the active diode to the dicing edge and the guard rings. Tests involving the diodes showed that the strong increase of leakage current was attributed to the edge current when the lateral depletion zone reaches the dicing edge and the lateral depletion along the silicon surface was correlated with the ‘field’ width. The onset was observed at a voltage of 1000 V when the width was equal to ∼400 μm. The pixel sensors that were diced at a width of 450 μm could successfully maintain a bias voltage of 1000 V. Hybrid flip-chip pixel modules with dummy and real chips were also fabricated. Lead (PbSn) solder bump bonding proved to be successful. However, lead-free (SnAg) solder bump bonding requires further optimization.

Recycling of lead solder dross, Generated from PCB manufacturing

The main purpose of this work is to analyze lead solder dross, a waste product from manufacturing of printed circuit boards by wave soldering, and to develop an effective and environmentally sound technology for its recycling. A methodology for determination of the content and chemical composition of the metal and oxide phases of the dross is developed. Two methods for recycling of lead solder dross were examined—carbothermal reduction and recycling using boron-containing substances. The influence of various factors on the metal yield was studied and the optimal parameters of the recycling process are defined. The comparison between them under the same parameters-temperature and retention time, showed that recycling of dross with a mixture of borax and boric acid in a 1:2 ratio provides higher metal yield (93%). The recycling of this hazardous waste under developed technology gets glassy slag and solder, which after correction of the chemical composition can be used again for production of PCB.

Acceleration of galvanic lead solder corrosion due to phosphate

Although orthophosphate is often effective in reducing lead corrosion, bench-scale tests revealed cases in which even high doses of orthophosphate (1–3 mg/L P) in potable water increased lead and tin release from simulated soldered copper joints. Phosphate increased the galvanic current between tin and copper plumbing materials, especially in water with less than 10 mg/L SO 4 2 - and when the percentage of the anodic current carried by SO 4 2 - ion was less than 30%. Tin release was increased more than lead release from 50:50 Pb–Sn solder in these circumstances.

Stress Relaxation and Fatigue Characterisation of Eutectic SnPb Solder Alloy

Soldering is the most important joining technology in the semiconductor industry, especially for IC chip packaging. The binary eutectic SnPb alloy had been in used for decades, before regulations and restriction on the usage of lead in solders was imposed. Thus, replacing SnPb solder alloy with Pb-free solders has also been an issue in the electronic industry. The previously used SnPb alloy was in used due to several reasons, namely (a) it has low melting temperature (183oC) and solidified at a single temperature to form eutectoid composition, (b) binary in composition and is readily available commercially and (c) many researches had been undertaken in the previous decades. Creep, stress relaxation and fatigue tests were conducted on eutectic SnPb solder alloy in order to study the alloy mechanical characteristics, and hence a suitable Pb-free solder alloy could be chosen as a replacement alloy. In this study, creep, stress relaxation and fatigue tests were conducted on eutectic SnPb solder alloy at 30oC and 50oC, respectively. The study showed that stress relaxation in the alloy decayed instantaneously to zero-value when cycling was done at R=-1 and that cycling was done at 600 cycle per minute (CPM) which enable fatigue test to be conducted on the bulk solder alloy. A non-zero stress relaxation value will result in the alloy to failed predominantly due to creep and fatigue failure will not be observed.

Chloride‐to‐sulfate mass ratio: Practical studies in galvanic corrosion of lead solder

The effect of the chloride‐to‐sulfate mass ratio (CSMR) on lead leaching from 50:50 lead–tin solder galvanically coupled to copper in stagnant conditions was examined using bench‐scale testing and data from water utilities. The CSMR was significantly altered by coagulant changeover, blending of desalinated seawater, anion exchange, and NaCl brine leaks from onsite hypochlorite generators. Consistent with previous experiences, increasing the CSMR to the range of 0.1 to 1.0 produced dramatic increases in lead leaching from lead–tin solder galvanically coupled to copper. Before implementing any treatment changes that could increase the CSMR, utilities may want to use the protocol described in this article to ascertain the relative effect of the changes on lead corrosion.

High Melting Temperature Lead Free Solder for Die Attach Application

Two lead free solders were developed for die attach application. The bismuth based solder has a melt temperature of 271C and thermal conductivity of 18W/mK. The zinc based solder has a melt temperature of 337C and thermal conductivity of 85W/mK. Both solders have acceptable wetting on bare copper and nickel plated copper substrate, could be processed using modified high lead solder process condition and survived 260C board level reflow simulation. This paper discusses the solder material properties, and presents the die attach process and reliability test results in a manufacturing environment.