Editorial

Citation

Goosey, M. (2009), "Editorial", Soldering & Surface Mount Technology, Vol. 21 No. 4. https://doi.org/10.1108/ssmt.2009.21921daa.001

Editorial

Article Type: Editorial From: Soldering & Surface Mount Technology, Volume 21, Issue 4

In this issue of Soldering & Surface Mount Technology, there are seven papers representing a diverse range of topics from the study of fundamental lead-free solder formulations to the use of conductive adhesives as alternatives to the more conventional solder-based assembly approaches. In the first of two papers on conductive adhesives, Kati Kokko, Hanna Harjunpää, Anna-Maija Haltia, Pekka Heino and Minna Kellomäki present the results of a study into the influence of conformal coatings on anisotropically conductive adhesive joints. Interestingly, this paper approaches the subject from a medical perspective and it shows that the type of conformal coating used to protect delicate electronics from the harsh environments experienced in these types of applications can have a significant impact on the overall reliability of adhesive-based flip-chip joints. Following on directly from this paper, and on a closely related subject, Martin Wickham, Ling Zou and Christopher Hunt present the results of a study into the influence of substrate and component finishes on the reliability of isotropically conductive adhesive joints. The use of these types of adhesives is becoming increasingly important in a range of applications and it is therefore important that the factors impacting their performance and reliability, especially when exposed to harsh environmental conditions, are properly understood.

Moving back to more conventional methods of joint formation using metallic solders, as opposed to conductive adhesives, the five other papers in this issue cover various aspects relating both to the solders themselves and the soldering process. In the third paper, T.K. Yeh, K.L. Lin and B. Salam cover their paper to study the influence of silver concentration on the high-temperature oxidation of Sn-Zn-Ag-Al-Ga solders. Tin-zinc alloys have been of interest during the move to lead-free because they are closer to conventional tin-lead solder in terms of melting point than the tin-copper and tin-silver-copper alloys. However, their widespread use has been limited because they are very easily oxidised. More complex alloys, such as Sn-Zn-Ag-Al-Ga, have also been developed in order to have improved properties and in the paper reported here it was found that increasing the silver levels helped to improve the high-temperature oxidation performance of this type of solder.

The next three papers then cover aspects of soldering and assembly and the influence of processing conditions such as reflow profile on solder joint structure and reliability. In the first of these three papers, D. Di Maio and C.P. Hunt present the results of their paper to assess the factors impacting the dissolution of copper in lead-free solders and the development of a method for assessing soldering parameters. With the move to lead-free assembly the potential for copper dissolution has increased and, particularly with the increasingly fine features on circuit boards, there can be the real possibility of lands and plated through holes losing sufficient copper to compromise functionality and reliability. In this paper, the development of a simple and automated technique for determining the dissolution of copper in lead-free solders is reported. The technique provides repeatable measurements that allow the various experimental parameters to be isolated and factors that greatly influenced the copper dissolution rate taken into account. The copper dissolution rates in seven lead-free and tin-lead alloys were compared at different temperatures and it was generally observed that samples with thicker intermetallic layers exhibited longer dissolution times.

Jianbiao Pan, Tzu-Chien Chou, Jasbir Bath, Dennis Willie and Brian J. Toleno then present the results of a study into the effects of reflow profile and thermal conditioning on the intermetallic compound thickness in tin-silver-copper (SAC305) soldered joints. Their paper reports experimental results of intermetallic compound (IMC) thickness variations for different thermal conditions/combinations, including peak temperature, time above liquidus, alloy composition and thermal shock. The authors reported that the IMC thickness increased with higher peak reflow temperatures and longer times above liquidus.

The final paper in this trio is from Tao Bo, Yin Zhouping, Ding Han and Wu Yiping and covers reflow profile optimisation of micro-ball grid array (μBGA) solder joints. In this paper, a novel reflow profile optimisation method is reported where the combined effect of reflow temperature and time on the mechanical reliability of μBGA joints is determined. By using a vibration fatigue testing approach the authors provide a useful method for achieving reflow profile optimisation and process control for quantitative mechanical reliability estimation of μBGA joints.

The last paper is by Hongbo Xu, Mingyu Li, Yonggao Fu, Ling Wang and Jongmyung Kim and it details a local melt process for solder bumping using induction heating reflow. In this interesting paper, the authors describe a local melt process for solder bumping in electronic packaging applications. The paper investigates the local melt process in solder balls reflowed onto nickel-gold coated copper pads and focuses on the effect of the inductive heat on the thermal distribution during the melting process. The temperature distribution within the solder ball is a key factor in determining the success of the process and the geometry control quality of the final joints.

Finally, over the last year or so, and contrary to the poor economic situation in the electronics industry, I have been pleased to see that there have been an increasing number of papers being submitted to the journal. Interestingly, a growing proportion of these are emanating from researchers in China and other countries in the Far East. This is a welcome development and perhaps, in some small way, an indicator of the overall shift in the centre of gravity for electronics manufacturing and research taking place around the world. As always, I welcome your comments and feedback and can be contacted at: m.goosey@lboro.ac.uk

Martin Goosey