Statistical analysis of the impact of refinishing process on leaded components

Refinishing process such as Hot Solder Dip (HSD) process can be used to prevent tin whisker growth in microelectronics components by replacing the lead-free finishes with conventional tin–lead coatings. In some applications, it is also used to ensure reliable solder joints by replacing contaminated finishes and lead-free alloys with tin–lead to result in a homogeneous solder joint with tin–lead paste. In this paper, the impact of a HSD refinishing process on leaded components was statistically studied by comparing the electrical test data of refinished samples with those not-refinished. The likely damage from the component refinishing was thought to be the degradation of package integrity through thermo-mechanical stressing. This might be detectable as a microscopic leakage current if moisture could be encouraged into any open areas. Ten types of leaded components were selected and samples for each type of the component were allocated into 2 lots, one for refinishing and one used as a control. 150 cycles −65/150 °C thermal cycling followed by 500 h 85%RH/85 °C humidity test was applied to all the samples (both refinished and not-refinished) to amplify any incipient failure points and accelerate moisture ingress into the package. Electrical test was then carried out to measure any small changes in current under zero and reverse bias conditions. In the end, a data reduction process in conjunction with a statistical hypothesis test was used to analyze the electrical test data. The results showed that there was no significant difference between the measured currents of refinished and not-refinished post-aged samples. Therefore it was concluded that the refinishing process did not have a significant impact on the tested components. This conclusion was further strengthened by other experimental test results such as CSAM images

Modelling the impact of refinishing processes on COTS components for use in aerospace applications

Commercial off the shelf components (COTS) are being adopted by electronic equipment manufacturers for use in aerospace applications. To ensure that these components meet the quality and reliability standards, refinishing processes, such as hot solder dip and laser deballing/reballing, are used to replace component lead-free solder terminations with tin–lead solder. These processes provide a risk mitigation strategy against tin whiskers induced short circuit failures. Being an additional step to the subsequent PCB assembly process it is important that this additional process does not impose significant thermo-mechanical stress which can impact subsequent reliability. As part of a major study in collaboration with industry partners, process models have been developed to predict the thermo-mechanical behaviour of components when subjected to the refinishing process. This paper details the techniques used to provide model input data (e.g., process parameters and package geometric/materials data) as well as the development and application of these modelling techniques to the refinishing process

Similarity approach for reducing qualification tests of electronic components

Qualification analysis and reliability testing of electronic components represent a major activity in the process of development of electronic equipment. Electronics manufacturers have to adopt often costly test programmes to ensure qualification standards and reliability requirements are met. This paper details a novel similarity-based qualification approach for assessing expected reliability of electronic components, and in general electronic prod- ucts, as an alternative to conventional physical testing. The originality of this work is in the proposed approach which introduces a new way of qualifying electronic components based on similarity with previously assessed and qualified components. This novel approach has the potential to transform in a major way the current oper- ational practices in the industry, demanding at present substantial physical testing, by offering a complementary, “virtual qualification” route for addressing the cost and time challenges associated with qualification tests. A major achievement is the comprehensive and detailed demonstration of the proposed reliability qualification approach. Case studies on qualifying electronic components to the thermal loads induced by a particular post- manufacturing process widely adopted by high-reliability electronics sectors – the robotic hot solder dip (refinishing) process, and associated risks of thermo-mechanical damage are presented and discussed

Experimental and modelling study on delamination risks for refinished electronic packages under hot solder dip loads

For electronic packaging engineers in the high reliability sectors such as aerospace, defense, oil & gas, etc., the use of commercial off-the-shelf components offer significant advantages due to their high availability, fast delivery time, and low cost. However, these components pose significant reliability challenges due to the risks associated with tin whisker formation and uncertainty on the long-term reliability of lead-free solders. To address these risks, the hot solder dip process is used to refinish the package by replacing lead-free solder finishes with lead-based finishes to meet the stringent packaging and assembly requirements for these sectors which are exempt from RoHS legislation. But the hot solder dip process is an extra process that exposes the package to an additional thermal load which will result in thermo-mechanical stresses that need to be properly understood and controlled. To address this challenge, a multi-disciplinary methodology combining thermo-mechanical models with “dip-to-destroy” experiments and Scanning Acoustic Microscopy has been developed to identify the risk of package material delamination for a number of package designs. Results show that the developed models can predict delamination risks for a range of imposed thermal gradients. Electronic package designs with a direct heat path from dipped terminations to internals of the package show a higher risk of overstress-induced delamination, and this failure is generally driven by the high temperature excursion above the glass transition point of the molding compound. The novelty and significance of these findings is that the derived methodology can be used by electronic packaging designers to optimize the thermal parameters of the hot-solder-dip process so that subsequent refinished packages can meet the stringent high reliability requirements for these sectors

Fundamental Studies of Tin Whiskering in Microelectronics Finishes

Fundamental Studies of Tin Whiskering in Microelectronics Finishes Abstract Common electronics materials, such as tin, copper, steel, and brass, are ambient reactive under common use conditions, and as such are prone to corrosion. During the early 1940s, reports of failures due to electrical shorting of components caused by `whisker' (i.e., filamentary surface protrusion) growth on many surface types - including the aforementioned metals - began to emerge. Lead alloying of tin (3-10% by weight, typically in the eutectic proportion) eliminated whiskering risk for decades, until the July 2006 adoption of the Restriction of Hazardous Substances (RoHS) directive was issued by the European Union. This directive, which has since been adopted by California and parts of China, severely restricted the use of lead (<1000 ppm) in all electrical and electronics equipment being placed on the EU market, imposing the need for developing reliable new "lead-free" alternatives to SnPb. In spite of the abundance of modern-day anecdotes chronicling whisker-related failures in satellites, nuclear power stations, missiles, pacemakers, and spacecraft navigation equipment, pure tin finishes are still increasingly being employed today, and the root cause(s) of tin whiskering remains elusive. This work describes a series of structured experiments exploring the fundamental relationships between the incidence of tin whiskering (as dependent variable) and numerous independent variables. These variables included deposition method (electroplating, electroless plating, template-based electrochemical synthesis, and various physical vapor deposition techniques, including resistive evaporation, electron beam evaporation, and sputtering), the inclusion of microparticles and organic contamination, the effects of sample geometry, and nanostructuring. Key findings pertain to correlations between sample geometry and whisker propensity, and also to the stress evolution across a series of 4"-diameter silicon wafers of varying thicknesses with respect to the degree of post-metallization whiskering. Regarding sample geometry, it was found that smaller, thinner substrates displayed a more rapid onset of whiskering immediately following metallization. Changes in wafer-level stress were not found to correlate with whiskering morphology (number, density, length) after 6 weeks of aging. This result points either to the irrelevance of macrostress in the substrate/film composite, or to a difference in whiskering mechanism for rigid substrates (whose stress gradient over time is significant) when compared with thinner, flexible susbtrates (whose stress is less variable with time). Organic contamination was found to have no appreciable effect when explicitly introduced. Furthermore, electron-beam evaporated films whiskered more readily than films deposited via electroplating from baths containing organic "brighteners." Beyond such findings, novel in themselves, our work is also unique in that we emphasize the "clean" deposition of tin (with chromium adhesion layers and copper underlayers) by vacuum-based physical vapor deposition, to circumvent the question of contamination entirely. By employing silicon substrates exclusively, we have distinguished ourselves from other works (which, for example, use copper coupons fabricated from rolled shim stock) because we have better sample-to-sample consistency in terms of material properties, machinability, and orientation

ACCLPP

The Department of Health and Human Services (HHS) and the Centers for Disease Control and Prevention (CDC) convened a meeting of the Advisory Committee on Childhood Lead Poisoning Prevention (ACCLPP). The proceedings were held on October 19-20, 2004 at the Doubletree Hotel-Buckhead in Atlanta, Georgia.200

Identifying and reducing lead exposure associated with the use of cultural practices in southern Nevada Hispanic communities

Despite large amounts of national data on lead and childhood lead poisoning, the status of childhood lead exposure in Nevada as a result of the use of cultural practices in the Hispanic population is unknown. The influx of immigrant Hispanic populations to Nevada, their low education level, the high number of them who are living in poverty present an increased risk for children to be exposed to lead through the use of imported consumables, home remedies and alternative medicine (i.e., healers/ sobadores). A 61-question survey collected data from Hispanics over 18 years of age who have or take care of children six years or under. Results from the study demonstrated a significant relationship exists in the proportion of children who had reported to suffer from empacho and from a stomach illness, χ2 (1, N = 189) = 29.024, p \u3c .001). Children who had empacho were more than 2.1 times as likely to also suffer from a stomach illness. A total 8.5% of respondents whose children suffered from empacho also used Azarcón, a folk remedy containing a high percentage of lead, LR (1, N = 190) =12.044, p = .001). A significant relationship exists between suffering from empacho and using a curandera/sobadora, χ2 (1, N = 192) = 26.91, p \u3c .001). Individuals who reported their iv children as suffering from empacho were 11.6 times more likely to use a curandera/sobadora than those who did not report having empacho. Foreign born Hispanics were more knowledgeable and 2.8 times more likely to believe their child had a high chance of getting elevated blood lead levels as compared to U.S. born respondents, χ2 (1, N = 212) = 3.814, p = .051. These results were inconclusive but should be explored further. On the other hand, they had less knowledge than their counterparts regarding the cost for getting child tested for lead, χ2 (1, N = 212) = 7.7, p = .006 and the time needed for treatment of elevated blood lead levels, χ2 (1, N = 212) = 3.4, p = .066. Foreign born Hispanics were almost 2.6 times as likely to believe treatment for elevated BLLs would take too much spare time and 4 times more likely to believe the lead test would be too expensive. There was a significant relationship between country of origin and language, with 96.6% of foreign born Hispanics and 35.4% U.S. born respondents choosing Spanish as their preferred language for prevention messages, LR (1, N = 208) = 62.8, p \u3c .001. Language is an indicator of the degree individuals have acculturated to American society (i.e., the process whereby one group contributes more to the flow of cultural elements than the other, much weaker one). Language may also influence how these individuals respond to health promotion and behavior change campaigns and the type of media they choose. A lead prevention campaign to be developed will incorporate language, folk traditions and the importance of the nuclear and expanded family to be thoroughly involved in preventing their children from being exposed to lead through folk remedies, folk healers and other items identified in this study

Preventing lead poisoning in young children

A STATEMENT BY THE CENTERS FOR DISEASE CONTROL AND PREVENTION -- OCTOBER 1991This is the fourth revision of the statement on Preventing Lead Poisoning in Young Children by the Centers for Disease Control (CDC). The recommendations continued herein are based mainly on the scientific data showing adverse effects of lead in young children at increasingly lower blood lead levels. They are tempered, however, by practical considerations, for example, of the numbers of children echo would require followup and the resources required to prevent this disease. It is possible that further scientific data and development of infrastructure and technology will result in a lowering of the blood lead level at which interventions are recommended at a future time.This statement is a departure from previous ones in several ways. Perhaps most important is the emphasis on primary prevention and the need for coordination between pediatric health-care providers and public agencies. This statement reflects the vision expressed in the Department of Health and Human Services' Strategic Plan for the Elimination of Childhood Lead Poisoning, which calls for a concerted, coordinated societywide effort to eliminate this disease.1991https://semspub.epa.gov/work/10/500007444.pdf871

The Nature and extent of lead poisoning in children in the United States: a report to Congress

This national study on lead poisoning in children is organized in three parts. Part 1 provides an executive summary. Part2 presents background information, an overview, findings, and conclusions. Part 3, which constitut.as the bulk of the report, discusses terms, issues, and findings concerning lead metabolism, its relationship to lead exposure and adverse effects of lead, and adverse health effects of lead in relationship to public health risk and societal well-being. Also discussed are the number of children exposed to lead in the United States; numbers of children exposed to lead according to lead source; numbers of women of child bearing age and pregnant women exposed to lead; low-level lead sources and children's aggregate exposure to lead; methods and alternatives for reducing environmental exposure to lead for young children and related risk groups; environmental releases of lead as evaluated under the Superfund Amendments and Reauthorization Act of 1966; and exposure to lead and toxicity in children and other related groups. Information gaps, research needs, and recommendations are discussed. Appendices provide numerous tables of data, a draft report on lead-contaminated soil cleanup, the final and proposed national priorities list of waste sites with lead as a contaminant, and methodological details of blood-lead prevalence projections from the National Health and Nutrition Examination Survey II data. References number 255."July 1988."Includes bibliographical references