Search results

Civic engagement means more than formal participation in the political process. Students can experience civic life across campus in ways that may not jump off the page as being relevant on first reading. Whether in the classroom through intentionally designed curricular experiences or through participating in a student organization focused on civic engagement, higher education should be helping develop students as active, participatory citizens. This chapter aims to provide the first look at how students across the United States are organizing on college campuses to participate in the political process.

The increasing incidence of educator stress and burnout is cause for concern. Nonetheless, the findings of this Canadian‐based study indicate that school principals are experiencing less than average levels of Emotional Exhaustion and Depersonalization burnout, and an average level of Personal Accomplishment burnout. Work conditions most likely to contribute to burnout were work stress, work overload, a deteriorating sense of status and recognition, and unsatisfactory interpersonal relationships. The implications of the study are discussed in terms of both individual and organizational factors.

Prominence is given in this issue to the interesting Diamond Jubilee celebration held last month in connection with the Norwich Public Library. It was a courageous but entirely proper thing to hold this celebration in war time, because although it was calculated to raise opposition from short‐sighted people, at the same time it was good policy to affirm that the Public Library is an essential part of national economy even in the greatest of wars. Excellent arguments on behalf of this last proposition were advanced at that meeting in the happy speech made by Mr. L. Stanley Jast, which we hope to see published in even fuller form sooner or later, and equally in the letter from Sir Frederic Kenyon. This gains greatly in force from the fact that Sir Frederic is not only an officer in the Army, but is, we believe, at this moment serving in France. If any of our readers have had doubts about the present seasonableness of their work, and there may conceivably be such, they may wisely ponder the letter and again take heart of grace. As for the celebration as a whole, it was, as we have said, opportune; it was also skilfully engineered and advertised, and was an undoubted success upon which the Norwich Library Committee and Mr. G. A. Stephen have every reason to congratulate themselves.

Substitution of lead‐free solders in electronic assemblies requires changes in the conventional Sn:Pb finishes on substrates and component leads to prevent contamination of the candidate solder. Options for solderability preservative coatings on the printed wiring board include organic (azole or rosin/resin based) films and tin‐based plated metallic coatings. This paper compares the solderability performance of electroless tin coatings versus organic azole films after exposure to a series of humidity and thermal cycling conditions. It is shown that the solderability of immersion tin is directly related to the tin oxide growth on the surface and is not affected by the formation of Sn‐Cu intermetallic phases as long as the intermetallic phase is protected by a surface Sn layer. For a nominal tin thickness of 60 ?inches, the typical thermal excursions associated with assembly were not sufficient to cause the intermetallic phase to consume the entire tin layer. Exposure to elevated temperatures, in the presence of humidity, promoted heavy tin oxide formation which led to solderability loss. In contrast, thin azole films were shown to be more robust to humidity exposure; however, upon heating in the presence of oxygen, they decomposed and led to severe solderability degradation. Evaluations of lead‐free solder pastes for surface mount assembly applications indicated that immersion tin significantly improved the spreading of Sn:Ag and Sn:Bi alloys compared with azole surface finishes.

One concern that has slowed the progress of surface mounted technology, in particular leadless chip carriers, has been the question of the reliability of the surface mount attachment technology. This concern follows from the realisation that the functional reliability of surface mount technology is a very complex issue involving many not very well understood components. What is needed is a relatively simple, useful, predictive model. The model reported here sidesteps the numerous complex underlying issues, which, if considered separately, make a predictive reliability model all but impossible, by taking a purely phenomenological approach and relegating second‐order effects to a lumped empirical figure of merit.

The kinetics of wetting were studied on several different prepared surfaces of copper (Cu) to simulate the microstructure observed in pre‐tinned Cu‐clad printed circuit boards. The results illustrate the effectiveness of pre‐tinning in maintaining the solderability of Cu surfaces. Pre‐tinning with Pb‐rich solder (95Pb‐5Sn) is particularly effective since solderability is preserved even after a relatively long ageing treatment. On the other hand, pre‐tinning with eutectic solder risks the loss of solderability during ageing or baking due to surface exposure of an ε‐phase intermetallic with poor wetting properties. The results also confirm the presence of carbon in pre‐tinned specimens due to the use of flux. The effect of carbon on solderability is not yet known.

A critical analysis of packaging and sealing methods for integrated circuits, hybrid microcircuits and multichip modules has been done. The best hermetic and high yield weld seal is examined along with other conventional seals like solder seal, frit seal and plastic seal with special emphasis on materials and processes involved in each case. An overview of emerging technology is also presented. A comparative analysis is made for selection of the right technology and material for a particular requirement.

In view of the increasing interest in low temperature and lead‐free solder alloys, a review was made of existing information on the physical properties of bismuth alloys suitable for electronic bonding applications, by reflow and wave soldering. A comparison was made, where possible, with existing tin‐lead alloys already in widespread use, with new information experimentally derived where none was currently available.

Since the introduction of surface mounting technology (SMT), interest in solder joints has increased greatly. In this work soldered joints were examined for different kinds of components. Factors which influenced the temperature cycle most strongly were the component size and its placing on the circuit board. These factors led to significant differences in maximum temperature and cooling rate between different solder joints on one and the same circuit board. The microstructure of the solder joints could then be related to their individual cooling rates. The near ternary eutectic Sn‐Pb‐Ag solder presented large variations in microstructure for the interval of cooling rates which was investigated. Strengths of the joints are therefore expected to vary because of the relation between microstructure and strength. Dissolution of elements from metallised coatings can also influence markedly the structures and properties in the solder joints.

The dissolution rates of iron and alloyed steels in molten lead‐free solders were investigated in order to clarify the effect of erosion of iron plating on soldering iron tips. The dissolution rates of iron‐based alloys in lead‐free solders were found to be about three times greater than in conventional Sn‐Pb eutectics, indicating that the iron plating of a soldering iron tip is subjected to heavier damage when used with lead‐free rather than eutectic Sn‐Pb. Several steel alloys showed dissolution rates similar to that of pure iron, suggesting that compositional changes in the iron plating may have little influence on the erosion depth. Decreases in the reaction temperature and time, and a small addition of iron into the solder was found to be effective in suppressing both dissolution of iron wire and erosion of iron plating.