Soldering & Surface Mount Technology

Brady, N.; Ennis, T.J.

1992 Soldering & Surface Mount Technology

doi: 10.1108/eb037772

Tensile pull strength tests were used to study the strength of solder joints of 25 mil gull wing leads on 132 pin quad flat pack components. The authors generated quadratic and linear models which can be used to predict the pull strength of a solder joint given its geometry. The shape parameters studied were standoff height between the lead and substrate, height of heel fillet, radius of curvature of heel fillet, length of heel fillet, height of solder at toe region, and thickness of solder on the lead. The most significant parameters in determining the tensile pull strength of the solder joint are the height and length of the heel fillet. A study was performed to quantify the effect of lead finish on the accuracy of these models. The lead finish was found to have a significant effect on the solder joint strength. The effect of lateral misregistration on the tensile pull strength of solder joints was also investigated. No correlation between the extent of lateral misregistration and joint pull strength has been found.

Dunkerton, S.B.

1992 Soldering & Surface Mount Technology

doi: 10.1108/eb037773

The increasing complexity of microelectronic devices and the advent of surface mount technology has led to interest in alternatives to mass reflow soldering techniques. One method with advantages for rapid automation and minimal heat input, is laser soldering. Various laser methods are available for application to reflow soldering, the prime options being continuous wave CO2, continuous wave NdYAG and pulsed NdYAG. This paper presents the results of work to compare and contrast the three techniques. The paper concentrates on the soldering of leadframes and SMD gull wing and Jlead to plated Al2O3 substrates, but also mentions soldering to FR4 PCBs.

Hongyuan, F.; Yiyu, Q.; Yihong, J.

1992 Soldering & Surface Mount Technology

doi: 10.1108/eb037774

Pulse control, SEM analysis and metallographic examination have been used to record and study the process by which a ball is formed at the tip of an ultrafine copper wire. The process by which the copper ball is formed, and the laws governing this process, are presented.

Engelmaier, W.

1992 Soldering & Surface Mount Technology

doi: 10.1108/eb037775

In early 1989 the original version of the Reliability Figures of Merit FM for the solder attachments of surface mount SM assemblies was published. That version of the FM was specifically tailored for telecommunications environments. Misapplications of FMs to use environments, such as military applications and accelerated tests, pointed to a real need for generally applicable FMs. Adequate reliability of SM solder connections can only be assured with a Design for Reliability based on solder joint behaviour and the underlying fatigue damage mechanisms. Perceived difficulties with a Design for Reliability stem from the very complex and only partially understood nature of the interacting mechanisms underlying thermally induced solder joint fatigue, combined with the highly temperature, time, and stressdependent behaviour of some of the materials involved, especially solder. In this paper generic FMs are presented. These are simple design tools, easily applied by users unfamiliar with the underlying complexities of solder fatigue and the reliability assessment results are in GoNogo format. The oversimplifications contained in Version 1 of the FMs originally thought necessary for simple design tools and limiting their applicability are omitted, making these generic FMs more readily understood.

Nicholson, A.; Bloomfield, D.

1992 Soldering & Surface Mount Technology

doi: 10.1108/eb037776

In view of the increasing interest in low temperature and leadfree 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 tinlead alloys already in widespread use, with new information experimentally derived where none was currently available.

Jacobson, D.M.; Humpston, G.

1992 Soldering & Surface Mount Technology

doi: 10.1108/eb037777

Soldering and diffusion bonding each have benefits and drawbacks. Solders are capable of bridging joints of irregular geometry but the joints tend to have significant void levels if they are of large area. Erosion of joint surfaces and embrittlement through interalloying with parent materials represent additional weaknesses. Diffusion bonding avoids these problems, but it is not as tolerant to rough mating surfaces and joint quality is highly sensitive to the cleanliness of the surfaces. This type of process usually requires the application of high loads. A hybrid of these two methods of joining known as diffusion soldering combines the merits of both. The metallurgical principles and some features of diffusion soldering are outlined, with reference to the silverindium and silvertin systems. The benefits of applying diffusion soldering processes to the fabrication of assemblies in the electronics industry are explained.

Leske, W.; Koch, J.

1992 Soldering & Surface Mount Technology

doi: 10.1108/eb037778

In SMD as well as in hybrid manufacturing processes, considerable quantities of CFC are still being used in 1991 for the cleaning of component groups. The second BlmSchV, as amended, status at 12 December 1990, prohibits the use of R113 for surface treatment plants as of 31 December 1992. Pursuant to developments in solder pastes, some products are already available which render the use of CFCs superfluous. Two methods in particular are emerging, which work either completely without cleaning or use water as a cleaning medium. A critical comparison is made of the properties of the relevant solder pastes in these categories.

Lea, Colin; Willis, Bob

1992 Soldering & Surface Mount Technology

doi: 10.1108/eb037779

The UK is a leader in the implementation of surface mount technology, and SMARTEX '91 sponsored by the SMART Group is one of only a few shows organised worldwide which is dedicated solely to this field. Perhaps it was not surprising then that this year's threeday event proved a great success.

1992 Soldering & Surface Mount Technology

doi: 10.1108/eb037780

The British Association for Brazing and Soldering BABS will be holding its 1992 Autumn Conference The Joining Environment on 1415 October 1992 at the Forte Posthouse Hotel, Coventry.

1992 Soldering & Surface Mount Technology

doi: 10.1108/eb037781

Alpha Metals has announced the appointment of Stan Renals to the position of General Manager, Alpha Singapore.