Amit Patel, Steve Prokopiak, Nicholas Herrick, Bin Mo, Rahul Raut, Ranjit Pandher, Ph.D.
Alpha, an Alent plc Company
South Plainfield, NJ, USA
The LED lighting industry and indeed, the electronics industry, prefers to have "shiny solder joints", indicated by a qualitative visual examination. No metrics exist to quantify "shininess" of the solder joints. This paper presents the concept of reflectivity as a metric to quantify "shininess" of the joint. A novel approach to quantifying "Reflectivity" of solder alloy joints has been developed and implemented.
Reflective properties of assembled solder alloy joints are seldom analyzed. However, in new market applications such as LED lighting, the ability to quantify the reflectivity of alloys can provide greater value. The techniques developed by Alpha are presented in this study allow designers and manufacturers the ability to quantitatively assess aesthetics of the solder joints, impact of flux residue and select materials that provide a performance and cost of ownership advantage.
In this study, differing solder alloys and flux chemistries are examined for their relative reflectivity. Both alloys are assembled under identical conditions to minimize statistical variation. Using a commercially available spectrometer system the alloys are analyzed and compared to a calibrated mirror.
Investigation of solder alloys of dissimilar flux chemistries and alloys reveals a significant reflectivity difference. The methodology of the experiment and results are discussed in this paper.
Reflective values of assembled solder joints are seldom if at all analyzed in the market place. However, in new applications such as LED lighting, the ability to precisely quantify the reflectivity of alloys can provide important added value and implications.
The technique of using a spectrometer system to scatter visible light onto a soldered sample and measure its reflective value against a standard mirror enables objective comparison between different solder alloys and flux chemistries far better than human perception.
In conclusion, based on the results of measuring both dissimilar alloys and flux chemistries the techniques of measuring solder joint reflectivity demonstrate that the influence of the assembly processes and choice of materials can affect the reflective values of a final solder joint assembly.
Initially Published in the SMTA Proceedings